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Nutrients such as nitrogen, which go unutilized during the digestive process, are then excreted into the environment via urine, gas or fecal matter. Excess nitrogen released in this manner may contribute to a reduction of the quality of air and groundwater sources. Many states have introduced or developed legislation mandating nutrient management plans on livestock operations to reduce environmental nitrogen losses. Strategies for reducing the environmental impacts of nitrogen on equine operations are two fold, including a reduction in nitrogen inputs and better management of nitrogen outputs. The practice of precision feeding, or feeding to accurately meet, but not exceed the nutrients requirements of an animal is a plausible method for reducing nitrogen inputs. This approach is not widely implemented, as feeding protein in excess of requirements is a common practice in the equine industry. Also, precision feeding is predicated on a body of data containing the nutrient availability and digestibility in different feed sources; data which are not fully elucidated in the horse. Management of nitrogen outputs on equine operations is largely based on data extrapolated from other livestock operations as well as a few preliminary efforts on horse farms. The potential impact of equine operations on nitrogen losses is explored in this review, shedding light on areas where further research and management strategies are needed.
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Review Article
Environmental Implications of Nitrogen Output
on Horse Operations: A Review
Rebecca C. Bott
a
,
*
, Elizabeth A. Greene
b
, Nathalie L. Trottier
c
, Carey A. Williams
d
,
Michael L. Westendorf
d
, Ann M. Swinker
e
, Sara L. Mastellar
a
, Krishona L. Martinson
f
a
Department of Animal Science, South Dakota State University, Brookings, SD
b
School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson, AZ
c
Department of Animal Science, Michigan State University, East Lansing, MI
d
Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ
e
Department of Animal Science, Pennsylvania State University, University Park, State College, PA
f
Department of Animal Science, University of Minnesota, St. Paul, MN
article info
Article history:
Received 26 June 2015
Received in revised form 20 August 2015
Accepted 26 August 2015
Available online 31 August 2015
Keywords:
Horse
Protein
Nitrogen
Lysine
Digestibility
Environment
abstract
Nutrients such as nitrogen (N), which go unused during the digestive process, are then
excreted into the environment via urine, gas, or fecal matter. Excess N released in this
manner may contribute to a reduction of the quality of air and groundwater sources. Many
states have introduced or developed legislation mandating nutrient management plans on
livestock operations to reduce environmental N losses. Strategies for reducing the envi-
ronmental impacts of N on equine operations are twofold, including a reduction in N in-
puts and better management of N outputs. The practice of precision feeding, or feeding to
accurately meet, but not exceed the nutrients requirements of an animal is a plausible
method for reducing N inputs. This approach is not widely implemented, as feeding
protein in excess of requirements is a common practice in the equine industry. Also,
precision feeding is predicated on a body of data containing the nutrient availability and
digestibility in different feed sources; data which are not fully elucidated in the horse.
Management of N outputs on equine operations is largely based on data extrapolated from
other livestock operations as well as a few preliminary efforts on horse farms. The po-
tential impact of equine operations on N losses is explored in this review, shedding light on
areas where further research and management strategies are needed.
Published by Elsevier Inc.
1. Introduction
Feeding practices with the goal of precisely meeting the
dietary requirement of the rst limiting amino acids (AA)
have been implemented in many livestock systems to
optimize performance and, recently, to minimize nitrogen
(N) excretion into the environment, for example, the swine
industry [1]. Paradoxically, feeding protein in excess of
requirement has been a common practice in the horse
industry [2]. Fecal and urinary N from livestock contributes
to ground water contamination and decreased environ-
mental air quality [3]. With increasing public awareness
and emerging regulations to limit N losses to the environ-
ment, nutrient management plans may be mandated in the
future to ensure sustainability of equine facilities, espe-
cially in increasingly urbanized areas. Strategies to mitigate
the impact of equine-feeding practices on the environment
are contingent on knowledge of factors that impact protein
utilization of common feeds for equids. Because of the
complexity of the equine digestive tract and the vast dif-
ference in feed types, including forages and cereal grains,
prediction of feed protein digestibility and N output
*Corresponding author at: Rebecca C. Bott, Department of Animal
Science, South Dakota State University, Brookings, SD 57007.
E-mail address: Rebecca.Bott@sdstate.edu (R.C. Bott).
Contents lists available at ScienceDirect
Journal of Equine Veterinary Science
journal homepage: www.j-evs.com
0737-0806/$ see front matter Published by Elsevier Inc.
http://dx.doi.org/10.1016/j.jevs.2015.08.019
Journal of Equine Veterinary Science 45 (2016) 98106
remains a challenge [4]. The goals of this review are to
provide an overview of the current knowledge on N utili-
zation in equids in relation to the environment and to
identify knowledge gaps that preclude the progress in
designing prediction models of N excretion in equids. The
specic objective of this review is to assess the potential
impact of N excretion from equids on the environment.
2. Environmental Implications of Excreted N
Nitrogen in the feces and urine must be managed to
prevent consequences to the environment, such as water
contamination and decreased air quality [5]. Excess N in the
air and water will eventually reach larger bodies of water,
where it can contribute to the deterioration of sheries and
sh habitats through harmful nutrient loading [6]. Manure
nutrients (N, phosphorus, and organic matter) can be major
pollutants in lakes and estuaries as well as rivers. Nitrogen
attached to eroded soil particles may reach waterways
through surface runoff or wind deposition. These waters,
rich in N and other manure nutrients, promote a prolifer-
ation of plant life, especially algae. This process is called
eutrophication [7]. Algae growth and the decomposition of
organic matter in water bodies reduces the dissolved oxy-
gen content of the water, which may lead to sh kills, odors,
and other negative impacts on the aquatic ecosystem [8].
Although the larger environmental concern for N is surface
runoff, N volatilization as ammonia presents other prob-
lems including nonpoint source pollution through rain, and
the effects of volatilized ammonia on human health [9].
Nitrogen in manure can be converted to ammonia
through bacterial degradation, primarily the conversion of
urinary urea to ammonia. Urease, an enzyme produced by
microorganisms in feces, reacts with urinary urea to form
ammonia. Urease activity in feces is high; therefore, urea is
rapidly converted to ammonia after excretion. It is the
physical process of combining urine and feces after depo-
sition on a oor surface, which results in ammonia vola-
tilization in the barn. Ammonia emissions (kg/LU, livestock
unit 500-kg live weight) are predicted to be lower in horses
than in cattle, pigs, poultry, or sheep [10]; however,
ammonia emitted by horses is no less able to impact the
environment on a unit-by-unit basis.
Other factors can inuence ammonia volatilization in
livestock housing. They include temperature, air velocity,
pH, surface area, manure moisture content, and storage
time. For example, high pH and temperature favor
increased ammonia emissions. Horse manure pH typically
ranges from 7.7 to 8.2 when calculated from soiled stall
waste, depending on the bedding source [11]. The pH of
horse manure samples collected between 2007 and 2014
and analyzed at the Pennsylvania State University Ag
Analytical Services Laboratory ranged from 6.9 to 8.2 with
an average of 7.8, which allows for fairly rapid emission of
ammonia into the atmosphere [12]. Only a few studies have
been conducted to calculate the amount of N and/or
ammonia concentration of horse stall waste; however, the
amount will depend on a myriad of factors including
location, time of exposure, and bedding type. Horse stables
are noted to have higher ammonia concentrations than
pastures. This correlated with higher equine exhaled breath
condensate pH in stables compared to pastures [13]. One
study looked at four different bedding types for the pur-
pose of calculating composting rate [11]. The study found
that when long straw is used for bedding, it has a higher
percentage of total N before composting than a pelletized
straw and pelletized wood product. However, the amount
for long straw was not statistically different than when
wood shavings were used for a bedding source. This study
also found that ammonia did not decrease after composting
and therefore indicating that it was not completely con-
verted to nitrate (NO
3
) or that the organic matter was not
completely degraded by the composting. Table 1 indicates
N and phosphorus content of feces and different bedding
sources from soiled stalls in different studies.
The Environmental Protection Agency considers
ammonia a threat to air quality because of contribution to
surface water eutrophication, NO
3
contamination of
Table 1
Concentrations of ammonia gas (NH
3
gas), ammonium (NH
4
), total nitrogen (N), nitrate, and pH collected from various studies.
Study Reference Experimental Conditions Bedding or Treatment Types NH
3
Gas
(ppm)
NH
4
(ppm) Total N % Nitrate
(ppm)
pH
Komar et al, 2011
(mean SE)
Soiled bedding collected from
stalls for 30 d
Pelletized straw d10.1 2.65 0.71 0.04 0 7.8 0.1
Long straw d14.6 2.65 0.94 0.04 0 8.2 0.1
Pelletized wood d13.5 2.65 0.63 0.04 0 7.7 0.1
Wood shavings d17.1 2.65 0.78 0.04 0 7.9 0.1
Williams et al, 2011
(mean SE)
Feces only collected for 5 d from
horses on a low or high
protein diet
Feces only low protein diet 25.4 3.4 300 80 0.24 0.01 dd
Feces only high protein diet 37.8 3.4 700 80 0.28 0.01 dd
Fleming et al, 2008
(mean SD)
Feces and urine added to
containers under
standardized conditions with
bedding for 14 d
Wheat straw 237 118 530 168 d10 17 d
Wood shavings 207 116 805 235 d0d
Hemp 193 114 842 81 d162 58 d
Linen 178 88 783 47 d0d
Straw pellets 80 51 377 68 d0d
Paper cuttings 217 120 843 54 d0d
Garlipp et al, 2011
(mean SE)
Feces and urea added to
containers with bedding
under standardized
conditions for 19 d
Wheat straw 5.75 0.8 d1.07 0.07 d6.9 0.11
Rye straw 4.07 0.8 d1.14 0.07 d6.8 0.11
Wood shavings 2.31 0.8 d0.61 0.07 d6.4 0.11
Abbreviations: SD, standard deviation; SE, standard error.
Cells with empty (d) values were not tested in a given study.
R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106 99
ground water, and the associated impaired air quality [14].
Ammonia contamination has the potential for at least
short-term adverse effects on agricultural workers involved
in animal care [15,16]. Subjects in a study performed to
simulate residing in close proximity to a swine operation
exhibited headaches, eye irritation, and nausea [16].In
studies of workers at swine concentrated animal-feeding
operations (CAFOs), 25% of the workers reported at least
one of the following respiratory symptoms: asthma, bron-
chitis, acute respiratory distress syndrome, and organic
dust toxicity syndrome [15]. However, as far as the authors
know, there has never been a study evaluating the health of
equine farm workers who are exposed to high levels of
ammonia.
In a study conducted in horses fed at approximately
165% of the recommended protein amount [17], authors
showed that elevating protein levels in a horses diet in-
creases the ammonia and N levels excreted in manure, the
ammonia in the atmosphere, and the urea N in the animals
blood. More specically, fecal N and ammonia were higher
(approximately 35 and 50% higher, respectively) in the high
protein fed horses than in the control fed horses. Nitrogen
and ammonia for control horses were 0.242 0.01 and
0.034 0.008, respectively, whereas N and ammonia were
0.278 0.01% and 0.068 0.008%, respectively, for horses
fed high protein diets (P¼.015). When atmospheric
ammonia was tested by an 8-hour accumulation via Dräger
tube, there was a signicantly higher level of ammonia in
the air in the stalls of horses fed the high protein diet. The
high protein horses averaged 37.8 3.4 ppm, whereas the
control horses averaged 25.4 3.4 ppm (P¼.029) [17]. This
could also lead to the question of horse health because
these Dräger tubes were placed on the noseband of the
horseshalters over the course of an 8-hour period while
stalled. These levels could potentially be a problem for the
horseshealth if left exposed for an extended period of
time. A study in Japan found that a horse inhaling only 2
17 ppm of ammonia (range of ammonia in an enclosed
trailer) over the course of 40 hours created excessive nasal
discharge and slight swelling of the nasal cilia [18]. This
same study found that another horse inhaling 40130 ppm
(maximum exposure for humans) had a much more severe
nasal discharge, swelling and irregular distribution of
tracheal epithelium and edema of the submucosa, loss of
nasal cilia, and more severe swelling than the horse
exposed to 217 ppm. This study indicates that inhalation
of these concentrations of ammonia is detrimental to the
respiratory health of horses. Future research should further
investigate the possible negative consequence for long-
term exposure to ammonia using larger sample sizes.
Another study compared sawdust-bedded stalls to
paper bedding (recycled phone books) to investigate the
ammonia differences and horse health over a 14-day period
[19]. Ammonia samples were taken from an air pump
placed at horse nose height for a period of 30 seconds and
found the ammonia levels were higher with the sawdust
bedding (1.422.54 ppm) compared the paper bedding
(0.210.88 ppm). However, horse health variables (e.g.,
endoscopic examination of the nasal passage and trachea,
tracheal wash cytology, tracheal inammation, and general
health observations) did not differ between bedding types.
Pratt et al [20] found that when using straw bedding
instead of rubber mats, ammonia concentrations rose to a
peak of 14 ppm after 14 days in the same stalls; stalls were
cleaned each day. This study did not nd any respiratory or
health complications with horses exposed to this level of
ammonia. However, it is possible that diet may effect
nutrient excretion in the context of environmental
contamination, air quality, and horse health. More research
is needed to evaluate the effect of different feeding stra-
tegies on nutrient excretion in the context of environ-
mental contamination and air quality.
3. Dening a Need for Managing N Input and Output
on Horse Operations
Animals acquire N from protein in the feedstuffs they
eat. A substantial amount of organic N is excreted in urine
or feces, as it has been estimated that less than 45% of
consumed protein is used and made into animal protein
[21,22]. It has been shown that horse owners commonly
over feed protein, up to 150% of the recommended re-
quirements [2]. In a survey conducted by Harper [23], horse
owners fed their horses 161% of National Research Council
[24] crude protein (CP) requirements on average. Mainte-
nance horses were associated with greater overfeeding
than working horses. Maintenance horses require fewer
nutrients than working horses [24]; however, they often
received the same type of concentrate as their working
counterparts on any given farm, just in smaller amounts.
Those concentrates often have higher concentrations of
nutrients than required for maintenance, which leads to
excessive nutrient supplementation and therefore nutrient
excretion. Usually, maintenance horses can be sustained on
forage only diets [25]. Excess protein in the horse diet is
then excreted in sweat, feces, and urine (Fig. 1).
There are several situations when excessive protein or
an imbalance can occur. A forage ration consisting pri-
marily of excellent quality hay typically has excessive levels
of protein and soluble protein. Formulating feed rations
with higher than required protein levels, to ensure all
essential AA requirements, have been met often com-
pounds the problem. It is possible to meet minimum re-
quirements for CP while being decient in single AAs [24].
When this occurs, whole body protein synthesis might be
limited [26]. Depending on the actual performance level of
the horses, this can result in excessive levels of N being fed
and excreted. Furthermore, in many operations, a single
diet is fed to all horses without consideration of activity
levels or physiological states of individual animals. This
practice could lead to oversupplementation or under-
supplementation of individual animals and poor overall N
management.
A few studies have looked at reducing the CP concen-
tration of horse rations through supplementation of
puried limiting AAs. Lysine added to linseed meal and
brewer-dried grain diets with hay has increased foal weight
gain and feed conversion efciency [27,28]. Staniar et al
[29] reduced the CP level of a supplement to 9% while
fortifying with lysine and threonine to growing Thor-
oughbreds on pasture. For the overall observational period,
no differences in physical growth measurements were
R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106100
observed in the crystalline AA supplemented group (9% CP)
compared to the control (14% CP).
Feeding excess dietary N not only is of consequence to
the environment, but also to the animal and cost of the diet.
There is a metabolic energy cost associated with excreting
excess N in the urine, making diets with excess protein
inefcient and not cost effective. Additionally, higher pro-
tein diets can affect acidbase balance [30], heat produc-
tion [31], and water requirements [30]. All these factors are
of particular concern to the athletic horse.
4. Nitrogen Content of Common Equine Feedstuffs
Digestibility of a protein and absorption of its AA con-
stituents are the main determinants of protein quality and
the predictor of utilization for maintenance or productive
functions by the animal as compared. Domesticated equids
are fed a wide variety of feeds ranging from herbage to
seeds. The composition of proteins and their availability for
digestion varies extensively across feeds, thus rendering
prediction of N excretion difcult.
Nitrogen in equine diets comes from forages, grains, and
oil seed meals. Legume forages generally have higher CP
concentration than grasses, w20% versus 11%13% CP dry
matter (DM) basis [32]. Within grasses, cool season grasses
generally have higher CP concentration (average of 15% CP
on a DM basis) than warm season (11% CP DM basis) [32].
Although the CP concentration of grains does not vary as
greatly as that of forages, it can differ between cultivars.
Wheat cultivars can range from 13%15% CP [33]. Oilseed
meals have greater CP concentration than grains. Soybean
meal, cottonseed meal, and linseed meal are about 51%,
44%, and 36% CP on a DM basis, respectively [32].
Several factors inuence the protein content of plants.
Plant maturity plays a role with immature forage plants
having greater protein content than more mature plants as
reviewed by Pagan [34]. For instance, CP content of alfalfa
decreased from 15% to 9% after 20 additional days of growth
[35]. Fertilization and management practices additionally
inuence the N content of forage with greater amounts in
grasses receiving fertilizer and regular clipping [36].
Fertilization can also increase the CP concentration of
grains [37,38]. Crude protein and NO
3
concentration of
common horse feeds are outlined in Table 2.
Sources of N in feedstuffs include protein N and
nonprotein nitrogen (NPN) compounds. Stage of maturity
may affect the AA prole of alfalfa [39], but red clover and
grass AA proles may not be as inuenced by maturity [40].
Some grain cultivars have altered AA characteristics.
Breeding for specic characteristics can change the relative
proportions of proteins present in the plant resulting in an
altered AA prole. One such example is a high fat oat
cultivar [41]. There are also high lysine corn cultivars that
have been specically developed to improve feed value
[42,43].
One of the most common forms of NPN in plants is NO
3
,
and much of the N absorbed from the environment and
therefore used by plants is in the form of NO
3
. Factors
affecting NO
3
accumulation in plants including level of N
fertilization, forage species, maturity, herbicides, and light
intensity have been reviewed by Crawford et al [44] and by
Wright and Davison [45]. Some forms of NPN are
commonly added to ruminant diets as reviewed by Hun-
tington [46]. Urea is a type of NPN that is minimally used by
equids [4749]. Unlike ruminants, NPN compounds are not
added to practical equine diets; because most microbial
Fig. 1. Nitrogen utilization by the horse as adapted from Tanner (2014). The dotted arrow line indicates that the importance and proportion of AA uptake in the
hindgut after the digesta has interacted with the largest portion of the microbial population remains largely unknown. AA, amino acid.
R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106 101
population and bacterial protein synthesis is distal to the
small intestine, horses are not as efcient at using these
forms of N [50].
Selecting feedstuffs containing appropriate protein and
N proles to meet the horses dietary needs may help to
reduce N outputs through strategic selection of inputs.
5. Nitrogen Balance
A Whole Farm Nutrient Balance [14] assessment is a tool
that can be used to determine generation of excess nutri-
ents on farm and can be useful in developing plans to
manage nutrient buildups. This idea may be helpful for
reducing N losses in equine production. The challenge is to
manage the animals, crops, and other farm components to
efciently use available manure N and reduce potential
losses to the environment [51]. Nutrient accumulation oc-
curs when nutrient inputs exceed nutrient outputs [52].
Whole farm balances of inputs and outputs can be used to
assess the risk of nonpoint source pollution and identify
pollution reduction strategies [53]. Nutrient balances can
be calculated on several levels including regional, whole
farm, and eld scales [54].
Whole farm or farm gatenutrient balances compare
the nutrients of concern, which come in and go out of the
farm gate [55]. Products typically going onto a farm
through the gate include purchased hay and grain or con-
centrates, mineral fertilizer, manure, bedding, and live an-
imals [55]. Products typically leaving a farm through the
gate include crops, eggs, milk, meat, ber, live animals, and
manure [55].
A Pennsylvania State University study [23] which fol-
lowed 14 Mid-Atlantic horse farms for an entire year found
that whole farm balances on Mid-Atlantic horse farms
averaged 73% for N, which is similar to ndings in other
species. Kohn et al [56] reported that whole farm N balance
averaged 66% on high efciency dairy farms. Percentage is
an indicator [57] of the proportion of N inputs (feed,
fertilizer, animals, and legume N) not accounted for in the
outputs (crops, animal products, and manure). As a point of
reference, a lower percent would mean a higher or poorer
balance for the farm. On horse farms, there may be a wider
range of N balance values due to the amount of manure
horse farms export. In the Pennsylvania State University
study [23], horse farms exporting all their manure averaged
39% balance for N; and they reported that all farms im-
ported some feed. The mean farm balance for those that did
not export any manure was 100%, indicating that all N
imported onto the farm remains on the farm. Determining
N balance will always be more of a challenge on horse
farms because there are a variety of types of operations,
including breeding, boarding, performance and pleasure,
and so forth [58] often having a high turnover rate of
horses; a Rutgers University study [59] found that an
average of only ve of 13 horses remained on 20 farms
sampled after 1 year (most left the farm, some were
removed due to age, disease, physical defect, and so forth).
Manure that remains on pasture when horses are grazed
can be substantial and will also inuence balance calcula-
tions and is complicated if rotational pastures are poorly
maintained. Finally, the amount of manure exported can
either help or hinder a farms balance depending on the
amount exported.
Whole farm nutrient balance is critical for managing N
losses in the environment. As this issue has gained public
awareness, several states have developed legislation to
manage balance on farms. Depending on the individual
statesdenitions of farming,many equine operations are
not factored into the nutrient balance equation. Many
hobby or small farms, which may have high nonpoint
source pollution potential, may not be accounted for if they
do not hit the threshold of farmingdenitions. In New
Jersey, any facility with less than eight horses is encour-
aged, but not required to establish and follow an animal
waste management plan [60], while Vermonts new small
farm regulations accounts for larger farms, not regulating
Table 2
Concentration range (average) of crude protein (CP), nitrates (NO
3
), and nitrate-nitrogen (NO
3
-N) in common equine feedstuffs
a
.
Feedstuff % of CP % of NO
3
ppm NO
3
-N % of Nitrate
b
Dry forage
Legume hay 18.623.9 (21.3) 0.0050.35 10.56788.2 00.19
Grass hay 7.014.6 (10.8) 00.69 01,563 00.24
Bermudagrass hay 8.213.6 (10.9) 00.25 0567.8 00.16
Straw 2.87.6 (5.2) 01.48 03,341 00.04
Wheat hay 6.814.3 (10.5) 00.53 01,202 00.17
Fresh forage
Mixed mostly grass pasture 10.925.1 (18.0) 00.23 (0.038) 0511 (85.7) 00.57 (0.193)
Grass pasture 7.922.8 (15.4) 00.15 (0.052) 0341 (116.4) 00.44 (0.153)
Grains
Barley 9.614.1 (11.9) 0.010.01 (0.01) 22.1722.17 (22.17) 0.0030.003 (0.003)
Beet pulp 7.511.1 (9.3) 00.05 (0.022) 0116.9 (48.94) 0.0040.02 (0.012)
Corn 7.510.6 (9.0) 0 0 0.0080.008 (0.008)
Oats 10.514.6 (12.5) 0 0 0.020.02 (0.02)
Rice bran 10.618.7 (14.6) 0 0 0
Soybean Meal 46.456.0 (51.2) 00.17 (0.004) 036.9 (9.63) 0.0040.004 (0.004)
Soybeans 34.944.8 (39.9) 0 0 0
Wheat 11.016.1 (13.6) 00.01 (0.003) 028.5 (6.60) 0
a
Data obtained from Equi-Analytical Laboratories, Ithaca, New York, Common Feed Proles. http://equi-analytical.com/interactive-common-feed-prole/.
Accumulated crop years of 20002014.
b
Old Equi-Analytical method of analyzing NO
3
.
R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106102
any farm using less than 10 acres, and/or those where
farming is not considered a business [61]. It is important to
realize that current legislation may help to mitigate some N
losses on targeted operations, although livestock farms
including horse farms of any size can have an impact on the
environment. Farms with compacted soil, bare patches of
pasture, or with manure storage located near ground water
sources should be managed to mitigate potential environ-
mental impacts [62].
The Netherlands was the rst country to research and
develop methods to reduce environmental impact of live-
stock operations. Their programs focused on three solu-
tions (1) reduce nutrient inputs in when fed in excess of
requirements, (2) apply practical management solutions to
reduce nutrient usage of outputs on farm, and (3) increase
manure that is exported off farm [5]. These are all programs
that have been previously tested and implemented on
many concentrated animal-feeding operations in the
United States [51] and have plausible implications on horse
farms. Hauling manure off the property can improve farm
balance although neighboring crop farms have to be willing
to work with the producer [57]. However, equine research
and implementation is much slower to follow. It has been
reported that most horse farms in the Chesapeake Bay area
export nearly 50% of their manure [58,63] found that 58% of
New Jersey horse farms disposed of some or all manure off-
site, whereas 54% of survey farms spread some manure on
their farms.
6. Challenges to Precision-Feeding N in the Horse
Industry
In a Pennsylvania SARE Project Report [64], farm man-
agers reported it was very difcult for horse owners to
balance horse rations. Most farms used a commercial
mixed feed concentrate that could not be adjusted. How-
ever, one farm with 70 horses reported that all horses were
on individual diets. Most farms reported feeding hay from
different weekly truckloads and did not produce hay on
farm. In most cases, farm managers are unable to make
major feed ration adjustments due to these reasons. Con-
centrates often include more CP than is required to ensure
that individual AA and CP requirements have been met
when the concentrate is fed with a variety of forages with
different CP and AA contents. However, caretakers of ani-
mal species should be able to incorporate best manage-
ment practices (BMPs) that help to reduce N excretion. A
major deterrent in reaching a nearly perfect balance is feed
cost and prot[51]. However, in the horse industry, the
deterrent appears to be management traditions, conve-
nience, and a lack of independence. In the equine industry,
feed and supplement cost is less of an issue, especially on
noncommercial or pleasure horse operations. This is an
important consideration because most horse farms fall in
this category. For example, the average size of horse farms
in Minnesota participating in a pasture management pro-
gram was 10 acres with ve horses [65].
When attempting to procure a valid gure on equine N
excretion in light of multiple quantities and types of feed-
stuffs provided at any given equine operation, the most
logical places to evaluate or attempt to calculate prediction
equations are going to be based on either feed consumed or
in fecal N levels excreted. Zeyner and Kienzle [66] used data
from over 250 digestion trials to establish a predictive
formula to estimate digestible nutrients in equine feed ra-
tions. They were able to conrm a strong uniformity of CP,
demonstrated through linear regression of digestible CP by
total consumed CP. Using this information and resulting
formula calculation (digestible crude protein ¼2.27 þ
0.917 CP) allows equine nutritionists to calculate a
reasonable N excretion value based on feed intake of horses
on farms. Mesochina et al [67] evaluated in vivo di-
gestibility data from horses fed 27 different forage diets to
create prediction equations for CP and other dietary pa-
rameters for horses grazing on pasture or rangeland. They
reported that fecal CP and dietary ber were the best pre-
dictors of diet digestibility. However, the most accurate
estimates of diet digestibility were determined when di-
etary variables such as dietary CP and ber were included
in the calculations. Readers should be cautioned that these
approaches may not be reliable predictors in horses that
are fed low protein or excessively high protein diets.
7. Programs and Regulations
In addition to the myriad of intrinsic reasons for man-
aging horses to minimize nitrogenous impacts on the
environment, horse owners, especially in populated areas
near watersheds, recognize regulations imposed by gov-
ernment. Although all horse farms fall under the jurisdic-
tion of the Federal Animal Feeding Operation, which is
administered and regulated by the Environmental Protec-
tion Agency, many states have begun developing and
passing laws which require higher standards than the
federal requirements. Most of these recommendations and/
or regulations pertain to limiting nonpoint source pollution
of state waters and fall under the jurisdiction of the state
level agricultural agencies. Whether they use terms such as
Animal Waste Management, BMPs, and Accepted Agricul-
tural Practices, most contain requirements and limit for
direct animal access to waterways, manure storage and/or
application, and grazing near wells, neighboring property,
and state waters. Recently, Vermont passed legislation [61]
which extends requirements to small farms. In the past,
Vermont required permitting for medium (150499 hors-
es) and large (500 or more horses) farm operations. This
water quality bill includes a certication for small farm
operations, which are currently dened as farms on which
10 or more acres are used for farming,and have no more
than 149 horses and the lower limit has yet to be deter-
mined by the Secretary of Agriculture, Food, and Markets.
Although farms falling under these guidelines are required
to submit annual certication of compliance, the law ex-
tends to any farm, which potentially provides a threat to
water quality through potential threat of discharge or
contamination of groundwater. In addition, there are sec-
tions which will allow for compliance inspection at any
time and require water quality training for 8 hours over
each 5-year period on topics including prevention of dis-
charges, mitigation and management of storm water
runoff, land application of manure or nutrients, nutrient
R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106 103
management planning, and other farm compliance rules
and regulations.
Horse farms may pose an environmental risk of
nonpoint source pollution because they often have higher
stocking rates than can be accommodated by natural
methods of nutrient absorption. In 2011, the Pennsylvania
Department of Environmental Protection [68] mandated
that farms with as few as one animal tting the livestock
classication (e.g., horse, goat, and sheep) must document
the adherence to guidelines and submit a farm manure
management plan. Maryland has incorporated horse op-
erations, which bring in $2500 in gross annual income and/
or have eight or more horses under the Water Quality
Improvement Act of 1998 [69]. New Jersey has tiered re-
quirements for developing animal waste management
plans, with larger farms (>300 animal units) requiring a
Comprehensive Nutrient Management Plan, medium farms
(8299 animal units) completing a self-certied plan, and
smaller farms being encouraged, but not required to com-
plete one [60]. Pending regulations for all horse farms
across the United States is a signicant issue; Land Grant
University Extension services should be prepared to pro-
actively address through educational programs for horse
owners. This could be a major undertaking because the last
American Horse Council report indicated there were 9.2
million horses and 1.96 million horse owners in the United
States [70].
The United States Department of Agriculture Natural
Resources Conservation Service is offering an Environ-
mental Quality Incentives Program [71] to help farms in the
Chesapeake Bay area improve feed management. By help-
ing farmers formulate their rations more accurately to meet
their herds production requirements, these partners
(agencies and universities) are helping farmers decrease
the nutrients that are excreted while maintaining or
improving livestock production and health. These feeding
adjustments can help farmers reduce N excretions by 30%
50%. The Environmental Quality Incentives Program in-
centives include payments and provided assistance and
cost share help to farms for ration balancing. Both Penn-
sylvania and New Jersey have begun incentivizing equine
operations/managers in these programs.
8. Conclusions
There are a myriad of factors at play in N utilization in
horses and the impact on the environment. Management of
horses and the associated N inputs and outputs is critical to
prevent negative environmental consequences such as
decreased air quality and water contamination. Precision-
feeding and waste management are strategies that can
minimize N excretion and environmental contamination.
Feed choices and combinations affect N availability and
absorption in the horse. Selection of feeds that are more
efciently used by horses, and feeding to meet, but not
exceed the dietary protein and N requirements of a horse is
paramount. This will require an understanding of feed
choices and equine digestion, in addition to behavioral
modications in terms of resisting the tendency to feed
more than is necessary.
In addition to feeding behavior changes, it is important
to develop some sort of integrated decision support sys-
tems (DSSs) that are more applicable to the needs of horse
operations. Karmakar et al [72] reviewed many types of DSS
programs and procedures available from academic in-
stitutions and industry, yet most of these were intended for
or aimed at more traditional livestock operations. Several
key decisions revolve around returning the nutrients to the
land to maintain N balance, yet many horse operations have
neither adequate land nor machinery to manage the
manure in this manner. An effective DSS guidance tool for
equine operators would take into consideration the com-
plexities involved in a livestock business, which often in-
cludes managing many animals on an individual basis
belonging to individual owners. Additional considerations
including potentially high stocking rates, contracted bin
removal for manure disposal, and equine business type
would need to be incorporated. Finally, calculations and
methodology are needed for creating and locating adequate
storage, covers or roong for manure piles, drainage, and
gutter installation to divert runoff or groundwater around,
rather than through, the manure in elds and storage sites.
Because of transportation, storage, and application los-
ses, diet management is an important component of whole
farm N management in keeping water and atmospheric
losses at a minimum [51]. Reducing dietary N has been
shown to reduce both ammonia runoff and volatilized N.
Precision feeding can achieve those results without
affecting production. Further investigation into CP, lysine,
and other AA requirements of horses is also an essential
component of moving toward more efcient feeding.
Studies detailing the actual requirements of horses at
maintenance and various physiological states will enable a
movement away from exceeding requirements due to
feeding based on predictive regressions. Current legislation
in several states incentivizes or requires horse owners to
develop more precise feeding strategies or to manage their
farms to reduce potential negative consequences of N on
the environment. Although related legislation has not yet
been enacted in all states, the evidence of the potential
environmental implications of horse and other livestock
operations should provide horse owners with incentive for
incorporating BMPs in feeding and manure management
on their farms.
Acknowledgments
This project was supported in part by the US Depart-
ment of Agriculture, Multi-State project NE-1041 and
renewal NE-1441, Environmental Impacts of Equine Oper-
ations [73]. The authors thank Rozanne McGrath for
editorial assistance.
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R.C. Bott et al. / Journal of Equine Veterinary Science 45 (2016) 98106106
... Excess dietary phosphorus increases the excretion of phosphorus in faeces, compared with horses fed a low phosphorus diet [38]. Bott et al. [77] review literature and databases to assess potential environmental impact from horses and mention higher ammonia levels in stables with horses fed high protein diets. The review also mentions grasses having different crude protein concentration depending on season and maturity in forages plants; cold season grasses have higher levels of protein and immature forage plants have higher content than mature plants. ...
... Soil fertilisation is not always a part of horse keeping, e.g. due to horse keepers' lack of land and machinery [77], but it is included here as it is part of current manure management system (Fig. 2). Application to fields is one of the most common outlets for horse manure in Sweden [9]. ...
... Matching the need for and quality of protein in feed for exercised horses is important to reduce nitrogen excretion according to Lawrence et al. [85] as less quality protein demands increased amount of crude protein in feed, followed by increased excretion. This is in accordance with Bott et al. [77] concluding that precision feeding, waste management, feed choices, and feed combinations contribute to reduction of excretion of nitrogen and reduced environmental impact from horse operations. ...
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Keeping horses causes environmental impacts through the whole chain from feed production to manure. According to national statistics, the number of horses in Sweden is currently 360,000 and is continuing to increase. This result in increasing amounts of horse manure that has to be managed and treated, which is currently done using practices that cause local, regional, and global environmental impacts. However, horse manure and its content of nutrients and organic material could be a useful fertiliser for arable land and a substrate for renewable energy production as biogas. The aim of the paper is to identify and describe potentially critical factors in horse keeping determining the amount (total mass) and characteristics (nutrient content and biodegradability) of horse manure, and thus the potential for anaerobic digestion. A ‘systematic combining’ approach is used as a structural framework for reviewed relevant literature. All factors identified are expressed as discrete choices available to the horse keeper. In all, 12 different factors were identified: type and amount of feed, type and amount of bedding, mucking out regime, residence time outdoors, storage type and residence time of manure in storage, spreading and soil conditions, and transport distance and type of vehicle fuel used. Managing horses in terms of these factors is of vital importance in reducing the direct environmental impacts from horse keeping and in making horse manure attractive as a substrate for anaerobic digestion. The results are also relevant to environmental systems analysis, where numerical calculations are employed and different biogas system set-ups are compared to current and other treatments. In such assessments, the relevance and importance of the critical factors identified here and corresponding conditions can be examined and the most promising system set-up can be devised.
... It is common in the horse industry to feed proteins in excess of requirement [1]. The potential impact of feeding excessive proteins to equids on nitrogen (N) excretion and contamination of ground water is of particular concern and relevance in areas close to water ways [1]. ...
... It is common in the horse industry to feed proteins in excess of requirement [1]. The potential impact of feeding excessive proteins to equids on nitrogen (N) excretion and contamination of ground water is of particular concern and relevance in areas close to water ways [1]. Designing and implementing plans to mitigate the impact of equine feeding practices on the environment (reviewed in [1]) entails accurate predictions of dietary N utilization and excretion. ...
... The potential impact of feeding excessive proteins to equids on nitrogen (N) excretion and contamination of ground water is of particular concern and relevance in areas close to water ways [1]. Designing and implementing plans to mitigate the impact of equine feeding practices on the environment (reviewed in [1]) entails accurate predictions of dietary N utilization and excretion. In livestock, successful predictions of N utilization and excretion are primarily based on knowledge of feed protein quality and understanding of the digestive processes. ...
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Equids evolved grazing forage of low protein and high fiber content. However present day horse feeding management typically consists of higher protein and less fiber, often exceeding protein requirements. Feeding excessive proteins to equids on nitrogen (N) excretion and contamination of ground water is of particular concern and relevance in areas close to water ways. A review was prepared as part of an initiative by the USDA Multi-State project NE-1041 committee on “Environmental Impacts of Equine Operations” to build programs aimed at mitigating N excretion from equine feeding operations. This review presents information on dietary protein utilization in equids and identify knowledge gaps for potential key future research areas to build upon. The review addresses the gastrointestinal anatomy of equids with an emphasis of the evolutionary dietary and anatomical adaptation. Challenges in assessment of protein quality of feeds are emphasized in particular in regards to the significance of pre and post-cecal protein digestibility and the contribution from hindgut N and AA metabolism and absorption. The need for greater understanding of GIT protein digestion processes, anatomical site of N and AA absorption, and systemic access to protein and AA digestibility estimates of equine feeds to refine current CP and generate AA requirement estimates is discussed.
... On the other hand, quite high intakes are required by athletic horses, growing horses and lactating mares, but their requirements are not met [1]. Recent studies show that it is common in practice to feed horses an excess of nutrient requirements, including protein (e.g., [6,7]). Forage-only diets covering energy requirements in trained horses usually contain excess protein compared to needs [8,9]. ...
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Full-text available
Six Finnhorse mares were used in a digestibility trial, in which six typical horse diets were compared. The diets were: (A) haylage 100%; (B) hay 100%; (C) hay 70% and oats 30%; (D) hay 70% and soybean meal + oats 30%; (E) hay 70%, rapeseed meal + oats 30% and (F) hay 70 %, linseed meal + oats 30%. The trial was conducted according to an unbalanced 6 × 4 Latin square design with four 3-week experimental periods. The experimental period consisted of 17-day preliminary feeding which was followed by a 4-day total faecal and urine collection periods to evaluate N excretion. The digestibilities of DM (p < 0.001) and OM (p < 0.001) in the haylage-only diet were lower compared to the other diets. The supplemental protein feeds improved the diet digestibility of CP (p = 0.002) compared to a hay + oats diet. Furthermore, the DM (p = 0.019), OM (p = 0.006), and CP (p = 0.016) digestibilities of the soya-supplemented diet were better than those of the rapeseed- and linseed-supplemented diets. Faecal excretion was greater for haylage (19.3 kg fresh faeces and 3.6 kg DM/day) and hay (18.7 kg fresh faeces and 3.6 kg DM/day) diets (p < 0.001) compared with the other diets. Urine excretion was also greater for forage-only diets compared with diets including protein supplements. Horses excreted 14.0 L urine/day on haylage-only diet (p = 0.026) and 14.3 L/day on a hay-only diet (p = 0.003). Horses excreted more nitrogen in their urine than in dung. N excretion differed between the diets. Horses on a haylage-only diet excreted 51.6 g N in faeces /day and on hay-only diet 51.4 g N/day. On the other hand, when protein content in forages increased, N excretion via urine increased (haylage vs. dried hay). Horses excreted less N in urine with hay-only diet than with haylage-only or protein-supplemented diets (p < 0.001). When N excreted in faeces and urine was counted together, horses excreted less N with a hay-only diet (p < 0.001) than with a supplemented one (oats and/or protein feeds). The results showed that feed choices affected the amount of nitrogen excreted. Feeding recommendations should consider not only the horse category and work level, but also the protein source. When good quality protein is fed, smaller N intakes can be applied to reduce the N excretion via urine and dung. At the farm level, improved understanding of feed quality, as well as feeding planning and practices, is a way to decrease the risk of N leaching and evaporation.
... Total nitrogen excretion paralleled nitrogen intake, with greater (P < 0.0001) excretion observed in horses fed ALF and lesser in horses fed BG. The excess of nitrogen excreted may contribute to environmental impacts such as nitrate leaching to groundwater sources and decreased air quality (Bott et al., 2016). The sources of nitrogen excretion (urine vs. feces) differ in their potential of nitrogen pollution of the environment, where urinary nitrogen is more susceptible to losses than fecal nitrogen (Bussink and Oenema, 1998;Weir et al., 2017). ...
Article
Rhizoma peanut hay has the potential to meet horses’ crude protein requirements with reduced nitrogen excretion. This study aimed to evaluate nutrient intake, apparent digestibility, and nitrogen balance of rhizoma peanut (RP, Arachis glabrata cv Florigraze) hay compared with alfalfa (ALF, Medicago sativa L. cv Legendary XHD) and bermudagrass (CB, Cynodon dactylon L. cv Coastal) hays when fed to maintenance horses at 2% BW/d on a dry-matter (DM) basis. Six mature Quarter Horse geldings (593 ± 40 kg; mean ± SD) were randomly assigned to one of the hays in a replicated 3 × 3 Latin square with 21-d periods. A 14-d adaptation phase was followed by a 3-d total fecal and urine collection. Intake of nutrients is reported on a DM basis. Both legumes (ALF = 1.99% BW and RP = 1.97% BW) provided DM intake greater (P < 0.05) than CB (1.82% BW) but were not different from one another. Digestible energy (DE) intake of ALF (29.9 Mcal/d) and RP (29.4 Mcal/d) were greater (P < 0.05) than CB (20.8 Mcal/d). Crude protein (CP) intake was greater (P < 0.05) for ALF (2,542 g/d), followed by RP (1,859 g/d), and then CB (1,477 g/d). Alfalfa provided the highest (P < 0.05) calcium to phosphorus ratio of 6.3:1, while RP provided 4.4:1, and CB provided the lowest (1.7:1). Intake of all hays exceeded maintenance DE, CP, Ca, and P requirements. Apparent DM (P < 0.05) and CP (P < 0.05) digestibility were greater for ALF (69%, 84%), followed by RP (61%, 72%), and lowest for CB (46%, 64%). Neutral detergent fiber apparent digestibility did not differ (P = 0.2228) among the 3 hays, while acid detergent fiber digestibility (P = 0.0054) was lower for RP and similar for ALF and CB. Apparent digestibility of non-structural carbohydrate (P < 0.05) was greater for ALF, followed by RP, and lowest for CB, while starch (P < 0.05) digestibility was similar between the legumes and lowest for CB. Water intake for ALF was greater (P < 0.05) than RP and CB. Greater urinary excretion (P < 0.05) was observed for alfalfa, while water excreted through feces was greater (P < 0.05) for CB, followed by RP, and lower for ALF. Urinary nitrogen (N) excretion was greater (P < 0.05) for ALF, followed by RP, and lower for CB whereas fecal N excretion for both RP and CB were greater (P < 0.05) than for ALF. Total N excreted was greater (P < 0.05) for ALF (278 g/d), followed by RP (211 g/d), and lower for CB (179 g/d). Nitrogen retention was greater (P < 0.05) for ALF when represented as g/d, but similar to RP when presented as percent of N intake. Results indicate that rhizoma peanut hay is a suitable legume for horses by meeting DE and CP requirements with significantly less N excretion than alfalfa.
... As reviewed elsewhere, overfeeding protein results in increased nitrogenous waste excretion, which has both environmental and horse health implications because this nitrogen is volatized to ammonia. 81 Urinary nitrogen is excreted in the form of urea, which is energy requiring and heat producing and increases water output. 82,83 High protein intakes also resulted in increased plasma lactate concentrations both at rest 84 and following sprint exercise, 85 but did not result in a more rapid onset of fatigue in sprint exercise tests. ...
Article
Skeletal muscle comprises 40% to 55% of mature body weight in horses, and its mass is determined largely by rates of muscle protein synthesis. In order to support exercise, appropriate energy sources are essential: glucose can support both anaerobic and aerobic exercise, whereas fat can only be metabolized aerobically. Following exercise, ingestion of nonfiber carbohydrates and protein can aid muscle growth and recovery. Muscle glycogen replenishment is slow in horses, regardless of dietary interventions. Several heritable muscle disorders, including type 1 and 2 polysaccharide storage myopathy and recurrent exertional rhabdomyolysis, can be managed in part by restricting dietary nonstructural carbohydrate intake.
... Recent work showed similar results in horses, where a large protein meal resulted in hyperinsulinemia in horses with equine metabolic syndrome, indicating that elevated dietary protein intake could exacerbate insulin dysregulation (Loos et al., 2019). Considering protein is commonly overfed in the equine diet (Bott et al., 2016), it is warranted to further investigate the mechanisms underlying MPS in horses and how these respond to the levels of dietary protein. ...
Article
Activation of the mechanistic target of rapamycin (mTOR)-controlled anabolic signaling pathways in skeletal muscle of rodents and humans are responsive to level of dietary protein supply, with maximal activation and rates of protein synthesis achieved with 0.2-0.4 g protein/kg body weight (BW). In horses, few data are available on required level of dietary protein to maximize protein synthesis for maintenance and growth of skeletal muscle. To evaluate the effect of dietary protein level on muscle mTOR pathway activation, five mares received different amounts of a protein supplement that provided 0, 0.06, 0.125, 0.25 or 0.5 g of CP/kg BW per meal in a 5 x 5 Latin square design. On each sample day, horses were fasted overnight and were fed only their protein meal the following morning. A pre- (0 min) and postprandial (90 min) blood sample was collected and a gluteus medius muscle sample was obtained 90 min after feeding the protein meal. Blood samples were analyzed for glucose, insulin and amino acid concentrations. Activation of mTOR pathway components (mTOR and S6-ribosomal protein, rpS6) in the muscle samples was measured by western immunoblot analysis. Postprandial plasma glucose (P = 0.007) and insulin (P =0.09) showed a quadratic increase, while total essential amino acid (P < 0.0001) concentrations increased linearly with graded intake of the protein supplement. Activation of mTOR (P = 0.02) and its downstream target, rpS6 (P = 0.0008), increased quadratically and linearly in relation to level of protein intake, respectively. Comparisons of individual doses showed no differences (P > 0.05) between the 0.25 and 0.5 g of protein intake for either mTOR or rpS6 activation, indicating that protein synthesis may have reached near maximal capacity around 0.25 g CP/kg BW. This is the first study to show that the activation of muscle protein synthetic pathways in horses is dose-dependent on the level of protein intake. Consumption of a moderate dose of high-quality protein resulted in near maximal muscle mTOR pathway activation in mature, sedentary horses.
... Sottraendo al quantitativo di azoto applicato al campo (53,25 kg/ha, provenienti da utilizzo di stallatico equino con una quantità media di azoto pari al 0,7% (Bott et al., 2016)) il quantitativo di azoto assorbito (43,20 kg/ha (Tesi e Lenzi, 2015)), si ottiene il Surplus (10,05 kg/ha), ovvero la quantità di N rimasto sul suolo che potrebbe subire fenomeni di lisciviazione e/o ruscellamento. Al fine di poter confrontare i risultati ottenuti con quelli degli studi reperiti in letteratura, i quali utilizzano cmax=10 mg/L, misurati come N (come suggerito dall'US EPA (2013)), la componente grigia della WF è stata calcolata utilizzando la stessa concentrazione massima. ...
Conference Paper
Full-text available
L’agricoltura nei prossimi decenni continuerà ad essere il maggiore utilizzatore della risorsa acqua, richiedendo lo sviluppo di adeguate politiche di gestione e tutela. In tale contesto assume rilievo la discussione sulla valutazione dell’impronta idrica (Water Footprint-WF) e sul confronto fra i diversi metodi mediante la realizzazione di casi applicativi. In questo lavoro si presenta uno studio di WF, effettuato secondo il metodo del WF Network, sul processo di coltivazione del Pomodorino del Piennolo del Vesuvio DOP. Il confronto con analoghi studi di letteratura mostra come il metodo applicato possa fornire informazioni al coltivatore per una riduzione sia dell’uso della risorsa acqua, che degli impatti sulle acque del proprio sistema produttivo. Inoltre, il fattore resa rischia di portare a un valore di WF più elevato per colture tradizionali di qualità rispetto a colture intensive.
... Identifying amino acid requirements for various physiological states (NRC, 2012) has helped the pig industry to minimize nitrogenous waste (Panetta et al., 2006) without compromising pig growth (Tuitoek et al., 1997). The environmental impacts of excess nitrogen output from equine operations have been reviewed by Bott et al. (2015). Other consequences of overfeeding protein to horses could be compromised respiratory health from increased ammonia output (Whittaker et al., 2009), disrupted acid-base balance (Graham-Thiers and Kronfeld, 2005b) and decreased bone mineralization from increased calcium excretion through urine (Glade et al., 1985). ...
Article
Lysine has been reported as the first limiting amino acid in typical equine diets. Indicator amino acid oxidation (IAAO) has become the standard method for determining amino acid requirements in other species, but prior to this study has not been used to determine equine requirements. The aim of this study was to evaluate whole body protein synthesis and plasma and muscle amino acid concentrations in response to graded levels of lysine intake in yearling horses. Six Thoroughbred colts (358 ± 5 kg) were fed each of six treatment lysine intakes ranging from 76 to 136 mg/kg body weight/day. Blood samples were taken before and 90 min after the morning concentrate meal. Gluteal muscle biopsies were taken ~100 min after the morning concentrate meal. The next day, whole body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [13C] sodium bicarbonate followed by a 6 h primed, constant infusion of [1-13C] phenylalanine. Plasma lysine concentrations increased linearly (P < 0. 05) at both the 0 and 90 min time points with increasing lysine intakes. Free muscle asparagine, aspartate, arginine, glutamine, lysine, taurine and tryptophan concentrations responded quadratically to lysine intake (P < 0.05). Phenylalanine kinetics did not differ between treatment intakes (P > 0.10). A broken line analysis of lysine intake and phenylalanine oxidation failed to yield a breakpoint from which to determine a lysine requirement. These diets may have been limiting in an amino acid other than lysine, underscoring the lack of data concerning amino acid requirements and bioavailability data in the horse. http://www.sciencedirect.com/science/article/pii/S1090023316301046
Evaluating amino acid requirements, specifically threonine requirements, in horses will enable better feed formulation and result in economic production, improved animal health, and reduced environmental pollution. However, the current knowledge of protein and amino acid requirements in horses is still limited. Because horses have a unique digestive system and consume a variety of feed ingredients, their protein digestibility may be affected than other species by different feed composition, and thus amino acid requirements are susceptible to vary between situations. Therefore, a careful evaluation of amino acid requirements with a proper method is needed for various conditions. This review will also provide comprehensive information that needs to be considered when designing an amino acid requirement study in horses.
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The equine population represents an important sector of animal agriculture and, thus, contributes to environmental contamination. The horse industry lags behind other livestock industries in developing prediction models to estimate N and amino acid (AA) requirements aimed at precision feeding and management to optimise animal health and performance while mitigating nutrient excretion. Effective predictions of N utilisation and excretion are based on knowledge of ingredient protein quality and the determinants of N and AA requirements. Protein quality is evaluated on the basis of N and AA digestibility and AA composition. Amino acid composition of grains, pulses and oil seeds is extensive, but there is large deficit on that of forages. Several studies have reported on pre- and post-caecal N digestibility in horses, demonstrating that a large proportion of N from forages is metabolised post-caecally. Few have reported on AA digestibility. It is proposed that whole-tract (i.e. faecal) N and AA digestibility be used in evaluating feed-ingredient protein quality in equids to begin designing predictive models of N and AA requirements. Nitrogen gain and AA composition in deposited tissues and their corresponding efficiency of utilisation are the key determinants for a prediction model. We estimated that N utilisation for maintenance is 0.74. Maintenance requirements for N and AA were derived from faecal N and AA losses in horses and expressed as a function of dry-matter intake and from integument losses in swine. Relative to our factorial model, the NRC (2007) requirement for lysine and N is overestimated when based on a segmented curve and a breakpoint. When based on N equilibrium, lysine NRC (2007) requirement estimate agrees with our factorial model estimate, while N requirement is underestimated. The pool of AA profile used to express requirements of other essential AA has a large impact on requirement, as shown, in particular, for threonine. Threonine requirement based on faecal endogenous AA profile is higher than is lysine requirement for maintenance and lactation.
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A comparative experiment was carried out with five Bulgarian and five foreign durum wheat cultivars. The aim of the experiment was to determine the chemical content and grain technological quality of some Bulgarian and foreign durum wheat cultivars grown under the agriecological conditions of Southern Bulgaria. The Vazhod cultivar proved to give the highest durum wheat grain yield, followed by Beloslava cultivar. Out of the foreign durum wheat cultivars the Durumko was notable for its higher productivity. The crude protein content in the grain was highest in Zagorka, Yavor and Yukon. The highest yield of gluten was reported in Beloslava, Vazhod and Zagorka.
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The effects of nitrogen fertilization on protein content, N uptake and N use efficiency of grain for six spring wheat cultivars were evaluated over a N application range of 0–200 kg ha⁻¹, under two moisture supply levels, on Black Chernozemic soils in Manitoba. Moisture supply influenced protein content, protein yield, and grain N use efficiency (NUE) of applied fertilizer. Increased moisture supply lowered protein content and increased protein yield and NUE. Increasing N level increased protein, N uptake and decreased NUE, but effects depended on moisture supply. Cultivar differences occurred, especially at the higher moisture level.Key words: Protein, Triticum aestivum L., nitrogen uptake, nitrogen use efficiency, moisture
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Recently, a new genotype of oat has been developed specifically for feed purposes by the Crop Development Centre called CDC SO-I ("SuperOat") containing a low-lignin hull and a high-fat groat. However, no quantitative evaluation of protein supply from CDC SO-I to dairy cow has been in done terms of potential protein degradation balance (PDB) and total metabolizable protein (MP) supply. These data are crucial in order to develop more efficient, competitive and optimal feeding the new genotype of oat (CDC SO-I) for livestock. Unlike DVE/OEB, PBI, ARC and NKJ-NJF models, NRC-2001 is a total digestible nutrient (TDN-) based model which is more popular in North America. The objectives of this study were to use the NRC model with inputs based on laboratory and in situ techniques to predict the potential nutrient supply to dairy cows from CDC SO-I in comparison with two conventional oat varieties, CDC Dancer and Derby, in western Canada. The quantitative predictions were made in terms of: (1) Rumen-synthesized microbial protein truly absorbed in the small intestine (AMCP); (2) Rumen undegraded feed protein truly absorbed the small intestine (ARUP); (3) Endogenous protein in the digestive tract (AECP); (4) Total metabolizable protein supply in the small intestine (MP), and (5) Protein degraded balance (PDB). The results show that using the NRC model, the predicted PDB and total MP supplies to dairy cattle were significantly increased from the newly developed genotype of oat (CDC SO-I). Compared with the normal oat, CDC Dancer, CDC SO-I significantly increased (P <0.05) ARUP, by 24%, and total MP supply by 9%, but did not change (P >0.05) AMCP, AECP and PDB, with averages of 55.7, 4.5 and -11.96 g kg-1 dry matter (DM), respectively. Compared with the normal variety, Derby, CDC SO-I significantly increased (P <0.05) AMCP, by 19%, total MP supply by 13% and increased PDB by 114%, but did not change (P >0.05) ARUP and AECP values with averages of 19.2 and 4.5 g kg-1 DM, respectively. In conclusion, CDC SO-I oat increased total absorbed metabolizable protein supply to dairy cattle by 9-13% in comparison with the two conventional oat varieties used in western Canada. However, although CDC SO-I improved protein degraded balance, it still had a negative value (-10.6 g kg-1 DM), indicating the potential imbalance between microbial protein synthesis from available rumen-degradable crude protein (CP) and potential energy from fermentation in the rumen.
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Chapter
This chapter discusses the problem of nitrate accumulation in plants and the consequences of feeding nitrate or nitrite to animals. Most of the chemically combined nitrogen absorbed by plants is in the form of nitrate. The presence of nitrate within the tissues of certain species of plants is normal. In some crops, the nitrate content has been shown to be positively associated with ultimate yield and tissue testing of these crops has been advocated as a guide to optimum fertilization. The internal factors governing the accumulation of nitrate by plants include age, localization, and trait variations. Both stages of development and a number of environmental factors are known to influence nitrate content. The external factors governing the accumulation of nitrate by plants include nutrient supply, moisture content, intensity of light, and herbicides. In case of animals, both nitrate and nitrite, being highly water soluble, freely traverse the gastrointestinal wall into the bloodstream. Nitrite, but not nitrate, oxidizes the ferrous iron of the red blood pigment called hemoglobin to ferric iron, producing a modified brown-colored pigment called methemoglobin, which is incapable of transporting or releasing oxygen to the body tissues; animals so affected are said to be suffering from methemoglobinemia.
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The U.S. Department of Agriculture supports agricultural research by encouraging the formation of multidisciplinary and multi-institutional teams. Project teams focus on agricultural issues related to profitability and economic and environmental sustainability. Recently, a U.S. Department of Agriculture project to study the impact of equine management and feeding practices on the environment was approved. The project, “NE-1041: Environmental Impacts of Equine Operations,” is a Northeast regional project but includes research and extension faculty from across the country. The project team includes representatives from Alabama, Connecticut, Kentucky, Louisiana, Maryland, Michigan, Minnesota, New Jersey, North Carolina, Pennsylvania, South Dakota, and Vermont. The goal of this project is to incorporate the best available data on horse management and feeding practices, manure storage and disposal, pasture and cropping management, soil and environmental quality, erosion control, and farm management practices to minimize negative impacts of equine operations on the environment. The specific objectives of the project are to assess existing data on environmental impacts of equine operations, identify gaps in current knowledge, conduct research when data are lacking or nonexistent, and incorporate existing and newly generated data into a systematic description of nutrient flow in soil, water, and air occurring on horse farms. Estimates will be made of pathogen transports and nitrogen (N)-, phosphorus (P)-, potassium (K)-, and energy (carbon)-loss potentials. In addition to identifying system-wide losses on equine farms, another goal of the project is to assist farmers and agricultural professionals in determining the value of equine management practices and other accepted best management practices.