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Tropical and Subtropical Agroecosystems, 14 (2011): 1 - 13
1
REVIEW [REVISIÓN]
TRACE ELEMENTS IN SHEEP AND GOATS REPRODUCTION: A
REVIEW
[ELEMENTOS TRAZA EN LA REPRODUCCIÓN OVINA Y CAPRINA:
UNA REVISIÓN]
J. F. Vázquez-Armijo1, R. Rojo1,*, A.Z.M. Salem1, D. López1, J. L. Tinoco1, A.
González2, N. Pescador3 and I. A. Domínguez-Vara3
1Centro Universitario UAEM Temascaltepec, Universidad Autónoma del Estado
de México, Km. 67.5 Carr. Fed. Toluca-Tejupilco, 51300, Temascaltepec, México,
México. Email: dr_rojo70@yahoo.com.mx
2Unidad Académica Multidisciplinaria Agronomía y Ciencias, Universidad
Autónoma de Tamaulipas, Centro Universitario Victoria, 87149, Ciudad Victoria,
Tamaulipas, México.
3Universidad Autónoma del Estado de México, Facultad de Medicina Veterinaria
y Zootecnia, El Cerrillo Piedras Blancas, 50090, Toluca, México, México.
*Corresponding author
SUMMARY
The reproduction of small ruminants like goats and
sheep managed under extensive range grazing
conditions can be affected by nutrients availability and
especially by the mineral content of the forages
resources on the rangeland. It has been particularly
demonstrated that trace elements can have equally,
beneficial or detrimental effects, depending on its
balance, on reproductive functions in small ruminants.
Trace elements as copper, molybdenum, selenium and
zinc play key role on the metabolism of carbohydrates,
proteins and lipids; however, the mode of action by
which these elements affect reproduction in sheep and
goats are not completely understood, due to the
complexity in the mode of action of the
metallobiomolecules and the neuro-hormonal
relationship. In this way, their absence or presence of
these minerals in several organs, fluids, or tissues of
the reproductive tract have allowed obtaining
information on the metabolism and the role of these
elements on reproduction in sheep and goats. On this
regard, the objective of this document is to review the
relationships and effects of some trace elements, on
reproductive events in sheep and goats.
Keywords: Minerals; female reproduction; male
reproduction; small ruminants.
RESUMEN
La reproducción de pequeños rumiantes, como cabras
y ovejas, manejados bajo condiciones extensivas de
pastoreo puede verse afectada por la disponibilidad de
nutrientes y sobre todo por el contenido mineral de los
recursos forrajeros presentes en el agostadero.
Particularmente se ha demostrado que los elementos
traza pueden tener tanto efectos beneficiosos o
perjudiciales, dependiendo de su equilibrio, sobre las
funciones reproductivas en pequeños rumiantes. Los
elementos traza como el cobre, molibdeno, selenio y
zinc juegan un papel clave en el metabolismo de los
carbohidratos, proteínas y lípidos, sin embargo, el
modo de acción por el cuál estos elementos afectan la
reproducción en ovinos y caprinos aún no son
entendidos completamente, debido a la complejidad en
el modo de acción de las metalobiomoléculas y la
relación neuro-hormonal. De esta manera, la ausencia
o presencia de estos minerales en varios órganos,
fluidos o tejidos del aparato reproductor han permitido
la obtención de información sobre el metabolismo y la
función de estos elementos sobre la reproducción en
ovinos y caprinos. En este sentido, el objetivo de este
documento fue revisar las relaciones y los efectos de
algunos elementos traza sobre los eventos
reproductivos en el ganado ovino y caprino.
Palabras clave: Minerales, reproducción en la
hembra, reproducción en el macho, pequeños
rumiantes.
Vázquez-Armijo et al., 2011
2
INTRODUCTION
Sheep and goats are considered as prolific species,
despite the fact that most breeds of both species show
annual reproductive cycles (Jainudeen et al., 2000).
During each annual reproductive cycle, there is a
season of low or absent (anestrous season) and a
season of high (breeding season) reproductive activity;
several factors are responsible to regulate these cyclic
activities (Thiéry et al., 2002). In high or medium
latitudes: >30° (Lincoln, 1992), >35° (Malpaux et al.,
1996) or >40° (Chemineau et al., 1992), the
photoperiod and the annual environmental temperature
cycle, are the main modulators of seasonal
reproduction; whereas, in tropical regions, the annual
reproductive cycle in sheep and goats is more likely
regulated by annual rainfall and food availability
(Figure 1) (Galina et al., 1995; Gündoğan et al., 2003;
Porras et al., 2003).
However, reproductive functions in these species are
also regulated by other extrinsic factors, such as, social
and sexual interactions and nutritional status (Figure 2)
(Álvarez and Zarco, 2001; Gündoğan et al., 2003;
Bearden et al., 2004; Zarazaga et al., 2005).
Reproductive functions are highly demanding, in both,
nutrients quality and quantity; in this way, nutritional
status is a very important modulator of reproduction in
sheep and goats (Blache et al., 2008).
Several studies have demonstrated interaction between
nutrition and reproduction in sheep and goats. For
example, flushing or minerals improves has been
shown to improve production and reproduction
parameters (Madibela et al., 2002; Fernández et al.,
2004; Almeida et al., 2007; Griffiths et al., 2007).
Many studies have also confirmed the lack of a clear
nutrition-reproduction interaction (i.e. lack of effect of
supplementary feeding or flushing on ovulation rate,
on oestrus manifestation, on fertility or prolificacy)
(Ahola et al., 2004; Zarazaga et al., 2005; Rosales et
al., 2006). Minerals such as phosphorous (P), calcium
(Ca), magnesium (Mg), iodine (I), manganese (Mn),
copper (Cu), selenium (Se), and zinc (Zn) are all
involved in governing successful reproductive
processes (Wilde, 2006). Although most sheep and
goat production systems based on grazing do not
provide mineral supplementation programs, the use of
commercial pre-mixtures or mineral blocks is a
practice that is usually performed; however, trace
elements inclusion is rarely taken into account in the
formulation of the supplements mentioned, so that
their contribution is low or null, coupled with the
deficiency of elements such as Cu and Se in some
regions where the animals are grazed (McDowell,
1994). Researches on mineral concentration and
interrelationship in soil, forage and blood serum of
sheep and goats in Mexico have shown results that
there are imbalances of minerals, with excesses of P
and iron (Fe) in the sheep, with Cu deficiency
associated to deficiencies of Cu and excesses of Fe in
the soil and in forages (Domínguez-Vara and Huerta-
Bravo, 2008). Mineral concentrations of tree leaves
and grasses consumed by goats in the southern Mexico
State showed that poor levels of minerals were
reported for Cu and Zn, while the concentration of Ca
and Mg was found in the normal range reported by
NRC (2007), however, in serum of goats showed a
marginal deficiency of Cu and Zn (Ramírez, 2009).
Some trace elements, such as Cu, Zn, Se and Mo are
involved in cellular respiration, cellular utilization of
oxygen, DNA and RNA replication, maintenance of
cell membrane integrity, and sequestration of free
radicals (Chan et al., 1998). In destruction of free
radicals are involved Cu, Zn, and Se through
cascading enzyme systems (Chan et al., 1998).
Superoxide radicals are reduced to hydrogen peroxide
by superoxide dismutases in the presence of Cu and Zn
cofactors. Hydrogen peroxide is then reduced to water
by the Se-glutathione peroxidase couple (Chan et al.,
1998). Efficient removal of these superoxide free
radicals maintains the integrity of membranes. On the
other hand, excess intake of these trace elements leads
to disease and toxicity; therefore, a fine balance is
essential for healthy, productive, and reproductive
processes (Chan et al., 1998). On this regard, the
objective of this document is to review the
relationships and effects of some trace elements, on
reproductive events in sheep and goats.
Tropical and Subtropical Agroecosystems, 14 (2011): 1 - 13
3
Figure 1. Model of annual reproductive cycle in sheep and goats, indicating the relationships between annual
photoperiod and rainfall cycle in subtropical areas. Adapted from Arroyo et al. (2006).
Figure 2. Relationships between external factors and nutrients in the control of the reproductive axis (hypothalamus,
pituitary gland, gonads) in sheep and goats. Adapted from Wade and Jones (2004) and Blache et al. (2008).
Vázquez-Armijo et al., 2011
4
MINERAL NUTRITION AND REPRODUCTION
IN SHEEP AND GOATS
Diets and feedstuffs deficient in trace minerals
requirements, can have deleterious effects on
reproduction functions, in both males and females of
both species (Table 1), thus, for feeding purposes, the
mineral status of the animal should be considered in
preparation of the final diets (Smith and Akinbamijo,
2000).
Moreover, cattle and goats are less susceptible to Cu
toxicity than sheep, and young ruminants are more
susceptible than adults because of higher absorption
(NRC, 2005). Although Cu poisoning has been
recorded in sheep grazing pastures fertilized with
chicken litter, the inclusion of poultry litter in sheep
rations is recommended by some researchers as an
alternative source of protein and energy, but attention
should be taken to avoid copper toxicity
(Christodoulopoulos and Roubies, 2007).
In areas from southeast of the State of Tlaxcala and the
mountain area of the State of Puebla, the mortality of
the lambs from birth to 60 d of age was 62 percent; the
lambs had symptoms of nutritional myopathy and the
main finding at necropsy was nutritional muscular
dystrophy, due to Se deficiency (Ramírez-Bribiesca et
al., 2004). It is worth mentioning that Se is the most
toxic essential trace element; so its supplementation
should be cautious, especially in non-selenium
deficient areas (Underwood and Suttle, 2003).
Table 1. Roles of some minerals on physiological functions reproductive failures and toxicity in sheep and goats.
Mineral
element
Physiological functions
Deficiency
Toxicity
Calcium and
Phosphorus
Intracellular messenger for
transmission of nerve
impulses. Release
ATP/ADP and nucleic
acids
Lowered milk production, milk
fever by hypocalcemia in
lactating ewes and does, estrus
suppression and poor
conception rates
Hypercalcemia and soft tissue
calcification, Urinary calculi
formation and skeletal softening
Magnesium
Synthesis of nucleic acids
and glutathione
Tetany
Urolithiasis, lethargy, disturbance
in locomotion, diarrhea, and lower
feed intake
Copper and
Molybdenum
Enzyme component and
catalyst involved in
steroidogenesis and
prostaglandin synthesis
Delayed and depressed estrus,
abortion, death fetuses,
infertility, congenital ataxia
Haemolytic crises,
haemoglobinuria,
haemoglobinaemia, and jaundice;
Severe diarrhea, weight loss,
anorexia, and reproductive failure
Selenium
Component of
selenoproteins, antioxidant
function
Lamb mortality, reduced
sperm motility and uterine
contraction, cystic ovaries, low
fertility rate, retained fetal
membranes
Poor growth, abnormal gait,
vomiting, dispnea, titanic spasms,
labored respiration, and death
Zinc
Component of numerous
metalloenzymes,
influences transcription
and cell replication
Impaired spermatogenesis and
development of secondary sex
organs in males, reduced
fertility
Reduced weight gain and feed
efficiency, depressed feed intake,
and eventually pica
Adapted from Minatel and Carfagnini (2000), Smith and Akinbamijo (2000), Underwood and Suttle (2003),
McDowell (2003), NRC (2005), NRC (2007), Blache et al. (2008), Hefnawy and Tórtora-Pérez (2010).
Mineral concentrations in liver are the best indicator of
the endogenous mineral status of the animal (Humann-
Ziehank et al., 2008). Nonetheless, blood analysis is
more frequently used, because blood samples are
easily taken and is also considered a non invasive
procedure (Kincaid, 2000). Trace elements
deficiencies are expressed in the animal by diverse
forms, since these elements form molecule complexes
of the metabolism of proteins, lipids and
carbohydrates, where they play key roles as
components and enzyme cofactors (Cu) or
transcription factors (Zn) (McArdle and Ashworth,
1999; McDowell, 2003; Underwood and Suttle, 2003).
Based on the before mentioned information, the
mineral status of the animal has effects on every phase
of the reproductive cycle (Bedwal and Bahuguna,
1994; Smith and Akinbamijo, 2000; Robinson et al.,
2006). For instance, during gestation, both, the mother
and fetus are very susceptible imbalances in
micronutrients in the diet, during the time of rapid
Tropical and Subtropical Agroecosystems, 14 (2011): 1 - 13
5
growth and cell differentiation (McArdle and
Ashworth, 1999; Gürdoğan et al., 2006; Ghany-
Hefnawy et al., 2007). Additionally, kilograms of
offspring weaned per female exposed may be affected
by both trace mineral supplementation and source
(Ahola et al., 2004). However, the mechanisms of
action by which these micronutrients affect
reproduction in sheep and goats are not completely
understood, mainly due to the complexity in the mode
of action of the metallobiomolecules and the neuro-
hormonal relationship (Bedwal and Bahuguna, 1994;
Smith and Akinbamijo, 2000; Wilkins and Wilkins,
2002; Zatta and Frank, 2007).
COPPER (Cu) AND MOLYBDENUM (Mo)
Copper is a mineral element that activates several
enzyme systems, and though in less numbers than Zn,
it is considered an essential nutrient (Minatel and
Carfagnini, 2007). However, sheep and goats are not
tolerant to high Cu levels in their diets, and it is thus
considered a toxic element (Minson, 1990; McDowell,
2003; NRC, 2005). The physiological role of Cu in the
organism is related to several functions, which include
cellular respiration, bone formation, connective tissue
development, and essential catalytic cofactor of some
metallo-enzymes, among other (McDowell, 2003;
Underwood and Suttle, 2003). In addition, and
contrary to a Zn deficiency, a Cu deficiency is not
related to programmed cell death (Ashworth and
Antipatis, 2001). Cu requirements for goats have been
reported to vary between 8 to 10 mg per Kg of DM
intake (Meschy, 2000). Whereas, Cu requirements for
sheep have been established between 7 to 11 mg per
kg of DM intake (NRC, 1985). Sheep are highly
sensitive to Cu intoxication, in comparison; goats are
more tolerant to such toxicity (Meschy, 2000).
Nonetheless, goats are very sensitive to Cu deficiency
(Draksler et al., 2002).
Mo is an essential trace element, but its role in
metabolism is not well understood (McDowell, 2003),
its role is mostly on the oxidase enzyme system (NRC,
2007). Excessive Mo intake by the animals, affects the
health and the well being of the animal (McDowell,
2003). Although Mo requirements for sheep and goats
have not been established, values of 0.5 and 0.1 mg/kg
DM in the diet have been recommended, for use in
sheep and goats, respectively (NRC, 2007).
The relationship occurring between Cu and Mo in the
animal metabolism, forces researchers to approach
description of its functions, in an integrated fashion
(NRC, 1981; Miller et al., 1993). The interaction
between these elements can result in a poor use of Cu,
Mo since it interferes with the metabolism of Cu at the
molecular level, forming chelates in the rumen which
reduces its absorption, highly linked to the presence of
sulfur (S) (Suttle, 1991; Aragón et al., 2001). In the
rumen are formed, by reactions between Mo and S,
thiomolybdates which ones, depending on the
proportions present can be identified as follows:
monothiomolybdate (MoO3S) dithiomolybdate
(MoO2S2) trithiomolyibdate (MoOS3) and
tetrathiomolybdate (MoS4) (Whitehead, 2000; Quiroz-
Rocha and Bouda, 2001). The thiomolybdates react
with free Cu atoms, to form insoluble Cu complexes,
thus, forming Cu-Mo-S complexes, this is a complex
that affects Cu utilization, which causes Cu deficiency
(Suttle, 1991; Quiroz-Rocha and Bouda, 2001).
Quiroz-Rocha and Bouda (2001), recommended a
Cu:Mo ratio to be between 3:1 to 6:1, in the rations for
ruminants; values outside these ranges, predispose the
animals to alter their Cu metabolism and status. Under
practical feeding conditions, grazing ruminants are
more susceptible to show Cu toxicity and/or Mo
excess (Kincaid, 2000; McDowell, 2003).
In addition, low Cu content in sheep rations, causes
embryo loss, inhibits embryo implantation and fetal
death (Hidiroglou, 1979). Naziroğlu et al. (1998),
reported information from 148 aborting ewes, found
that the most common cause of abortion, had been low
levels of micronutrients, and among them, was low Cu
concentration. Likewise, Anke (1973; cited by
McDowell et al., 1997 and Hidiroglou, 1979) fed goats
with Cu deficient diets and observed low conception
rates, resides, 50% of the gestating goats with Cu
deficiencies aborted, mummified fetuses and
hemorrhagic placentas and necrotic lesions were also
found. In sheep, postnatal lordosis, detected as muscle
weakness and ataxia, is also caused by Cu deficiency
during gestation (McArdle and Ashworth, 1999;
Ashworth and Antipatis, 2001). It thus appears that,
during sheep and goat gestation, normal growth and
development is affected by radical changes in Cu
availability and metabolism (Hidiroglou and Knipfel,
1981; Hostetler et al., 2003). Du Plessis et al., (1999),
induced a secondary Cu deficiency in ewes, by means
of Mo and S supplementation, this procedure
suppressed estrous behavior, however, the females
continued ovulating, based on this, the results
suggested that by elevating Mo and S, production and
/or expression of hormones, such as estrogens and
luteinizing hormone (LH) and follicle-stimulating
hormone (FSH) were altered. In addition, when goats
are exposed to prolonged periods of Cu deficiencies,
they present nymphomaniac reproductive behavior,
thus suggesting that Cu deficiency affects both,
reproductive behavior and performance (Hidiroglou,
1979). Despite the above, blood Cu levels are not
directly related with reproductive behavior, since, Cu
concentration in rams and gestating ewes did not affect
reproductive behavior and prolificacy, respectively
(Hidiroglou, 1979).
Vázquez-Armijo et al., 2011
6
In general, low fertility associated with delayed or
suppressed estrus, prolonged postpartum periods,
infertility associated to anoestrus, abortions and fetal
losses, are reproductive disorders commonly found in
Cu deficient animals, as well as in animals with excess
of Mo and/or S (Smith and Akinbamijo, 2000;
Underwood and Suttle, 2003).
SELENIUM (Se) AND VITAMIN E
Se poisoning occurs when grazing animals may suffer
from subacute or chronic Se toxicosis in seleniferous
areas (NRC, 2005). Generally, the Se-intoxicated
animals show low growth performance, elevated Se
concentrations in tissues, or death, in critical cases
(NRC, 1983). Nonetheless, several studies supported
the beneficial role of Se in human and animal nutrition
(Watts, 1994; Hefnawy and Tórtora-Pérez, 2010). Se
plays keyroles in several functions, mainly in those of
the selenocysteine (SeCys), which is a key component
of the selenoproteins (Burk, 1991; Holben and Smith,
1999) and their functions are shown in Table 2.
The glutathione peroxidase system (GPX’s) prevents
free radical formation and reduces the risk by
oxidation damage to the tissues (NRC, 1983; Holben
and Smith, 1999). In a similar fashion to the GPX’s,
the P and W selenoproteins have antioxidant effects; in
addition, the W selenoprotein is essential for skeletal
muscle functions (Beckett and Arthur, 2005; Silva et
al., 2000). Another important selenoprotein is the
sperm mitochondrial capsule (Seleno) protein, which
is important for the male fertility and exerts its effects
at the mitochondrial level (Silva et al., 2000; Holben
and Smith, 1999). It could be resumed that, Se is a
vital element in the animal organism, due to the
several metabolic functions, where it plays key roles
(Silva et al., 2000).
As mentioned before, Se and vitamin E play a
biological role as cell antioxidant, by preventing
damage by oxygen peroxide and other peroxides
formed from fatty acids (Smith and Akinbamijo,
2000), both components for a very hard bond, which is
involved in a wide variety of metabolic processes
(Minson, 1990; Church et al., 2002). Even though,
both clinical effects and metabolic effects of Se and
vitamin E are similar, the functions on protecting
tissue cell membranes, by the oxidative processes, are
in independent way (Minson, 1990). Whereas, Se is
required for the formation of GSH-Px, which destroys
potentially toxic peroxides, and vitamin E, is
presumably used to eliminate peroxides that escaped
the destruction by Se (NRC, 1983; Minson, 1990).
Some antioxidant enzymes activity has been shown to
occur in the sheep corpus luteum (CL), these enzymes
are susceptible to major changes in activity, during
early gestation, which suggests that the sheep CL may
be rescued from luteolysis, by increasing the
antioxidant enzyme activity, thus inhibiting the
apoptotic processes (Al-Gubory et al., 2004).
It has been shown in certain areas of Mexico, that Se is
low in goats, due to low Se in the soils and the
pastures (Ramírez-Bribiesca et al., 2001). In a study,
rams were treated with a 33 g Zn, Co and Se soluble
glass bolus (15.2% w/w Zn, 0.5% w/w Co and 0.15%
w/w Se), and they showed improved sperm motility
and viability (Kendall et al., 2000). Gestating sheep
treated orally with Se, at monthly intervals, had greater
lambing rates, than non treated ewes, this effect was
attributed to embryo loss, before 30 days of gestation
(McDowell et al., 1997). Grazing sheep in pastures
with low Se and high estrogen levels, and treated with
Se, increased the conception rate, from 49 to 76%
(McDowell et al., 1997). Overall, several studies have
shown that Se supplementation improves reproductive
performance in sheep (Table 3). However, when goats
are superovulated, they do not respond to Se treatment
(control group: 15.5±5.1 corpora lutea, supplemented
group: 15.9±7.2 corpora lutea) (Peña et al., 2005).
Table 2. Selenoproteins and their possible functions in animal metabolism
Selenoprotein (Name)
Function
GPX1 (Cytosolic glutathione peroxidase)
Se store, antioxidant in cytosol
GPX2 (Gastrointestinal glutathione peroxidase)
Antioxidant protection in gastrointestinal tract
GPX3 (Plasma or extracellular glutathione peroxidase)
Extracellular and plasma antioxidant
GPX4 (Phospholipid-hydroperoxide glutathione peroxidase)
Intracellular antioxidant
GPX5 (Sperm mitochondrial capsule selenoprotein)
Antioxidant in development of spermatic cells
D1 (Type I deiodinase)
Regulation and production {T4 → T3}
D2 (Type II deiodinase)
Activating thyroid hormone
D3 (Type III deiodinase)
Converts T4 to bioinactive rT3
TRs (Thioredoxin Reductase)
DNA synthesis, redox regulator
Sel P (Selenoprotein P)
Antioxidant, Se transport, detoxificant
Sel W (Selenoprotein W)
Muscle metabolism, antioxidant
Silva et al. (2000), Underwood and Suttle (2003), Beckett and Arthur (2005), Köhrle et al. (2005).
Tropical and Subtropical Agroecosystems, 14 (2011): 1 - 13
7
Table 3. Effect of Se supplementation on reproductive performance in sheep
Reproductive parameter, %
Control
Se supplement
Estrus response
84a, 76b, 87c
88a, 100b*, 100c*
Pregnancy
96c
97c
Lambing
72a, 68b, 96c
84a, 100a**, 97c
Prolificacy
122a, 100b, 115c
105a, 112b, 131c**
* Indicate significant differences between means with same superscripts in the same row: P<0.05.
** Indicate significant differences between means with same superscripts in the same row: P<0.01.
a Adapted from Gabryszuk and Klewiec (2002) in 2-year-old ewes (Treated group: sodium selenate (0.1%) injection
– Control group: no injection).
b Adapted from Gabryszuk and Klewiec (2002) in 3-year-old ewes (Treated group: sodium selenate (0.1%) injection
– Control group: no injection).
c Adapted from Koyuncu and Yerlikaya (2007) (Treated group: sodium selenate (0.1%) injection – Control group: no
injection).
On the other hand, McArdle and Ashworth (1999)
reported that Se absorption from the diet is high
(approximately 70%), although, this value is low for
placental tissue, consequently, fetal growth and
development, would depend on the diet and mother Se
treasury. Likewise, Ghany-Hefnawy et al. (2007)
concluded that due to the strong bond between the
mother and the fetus relative to Se metabolism, in
sheep and goats, the Se level in the fetus, is in direct
relationship to the mother´s Se status.
As mentioned earlier, Se and vitamin E share a very
close relationship, as they affect several metabolic
functions, in addition, both components protect the cell
membranes against oxidative degeneration (Hurley
and Doane, 1989; McDowell et al., 1996); and they
could well be involved in the prostaglandin synthesis
(Hurley and Doane, 1989). The parenteral or
intraruminal Se administration has shown increments
in parturition rates in sheep, as it has also been
increments shown in fertility, uterine contractions and
greater numbers of spermatozoa adhered to the
pellucid zone, this latter effect, perhaps, due to greater
sperm motility (Segerson and Ganapathy, 1980;
Hemingway, 2003). It has been shown that Se and
vitamin E increase the percentage of ewes in estrus
and prolificacy, in Karacabey Merino sheep, whereas,
gestation and lambing rates did not change (Koyuncu
and Yerlikaya, 2007). Other studies have shown that
treatment of sheep with Se and vitamin E do not
improve the reproductive parameters mentioned earlier
(Gabryszuk and Klewiec, 2002). As shown, in the
previous study, ewes fed with purified diets and
supplemented parenterally with Se and vitamin E, did
not show improvements in reproductive performance
(Whanger et al., 1977). As sheep, goats do not always
respond to Se and vitamin E treatment; in pregnant
goats, the intramuscular injection of 0.31 mg Se + 4.2
IU vitamin E / kg BW increases the concentration of
Se in blood, however reproductive responses to
treatment, was only by increasing survivability in the
kids at weaning and providing protection against white
muscle disease (Ramírez-Bribiesca et al., 2005). The
information available about the role of selenium and
the effects of supplementation on reproductive activity
and productivity describes that the response to Se
supplementation is affected by Se source used and the
severity of the deficiencies found. It should be
remembered that selenium should be added in the diet
carefully to avoid poisoning in livestock.
ZINC (Zn)
The need for Zn by most animals is based on its
influence on enzymes and proteins and their activities,
that are linked to vitamin A synthesis, carbon dioxide
(CO2) transport, collagen fiber degradation, free
radical destruction, membrane stability of red blood
cells, metabolism of essential fatty acids, carbohydrate
metabolism, protein synthesis, metabolism of nucleic
acids, among others (Powell, 2000; McCall et al.,
2000; Stefanidou et al., 2006; Rubio et al., 2007,).
Thus, the presence of Zn at the cellular level is
essential, for instance, in the gonads, where cell
growth and division, occurs continuously (MacDonald,
2000). Consequently, a Zn deficiency could seriously
affect reproductive events in most species. For
instance, in males, it could affect the espermatogenic
process, as well, as primary and secondary sex organs
development, and in females, it could affect them in
any phase of the reproductive processes (estrus,
gestation or lactation) (Smith and Akinbamijo, 2000).
Zn also plays a key role in maintaining the integrity of
the epithelia of the reproductive organs, which is
necessary for embryo implantation (Hostetler et al.,
2003; Robinson et al., 2006), besides, adequate
concentrations of Zn in the serum and in the diets, are
vital for uterine involution, tissue repair, after
parturition, and particularly, the return to estrus
(Apgar, 1985). In addition, Zn indirectly affects the
reproductive process, since the deficiency of both
elements, in synergism with others; favor the
Vázquez-Armijo et al., 2011
8
appearance of foot rot, in breeding animals (Enjalbert
et al., 2006; Kiliç et al., 2007). Some studies in sheep,
have proposed that Zn requirements are less than those
for bovines, suggesting the sheep require less than 8
parts per million (ppm), than that required for calves,
for normal growth (Haenlein, 1980). Consumption in
goats fed rations with 6-7 ppm, do not show clinical
signs of deficiencies, under this feeding regime,
clinical signs of Zn deficiency are observed during the
lactation, affecting only, Zn concentration in milk by
50%, but not affecting milk production. In male goats,
clinical signs of Zn deficiencies appear when they are
fed rations containing 4 ppm of Zn (Haenlein, 1980).
Plasma Zn levels in goats vary according to the
physiological status, highest concentrations are found
after parturition and during lactation (Kadzere et al.,
1996; Ahmed et al., 2001). In contrast, Gürdoğan et al.
(2006) did not find serum Zn concentration
differences, in sheep with single or twin pregnancies,
nor during parturition or lactation. Likewise, sheep
that aborted did not show Zn plasma differences, in
relation to those that carried gestation to term
(Naziroğlu et al., 1998). Even though, results do not
allow definite conclusions, since, results from others
have found that sheep are highly susceptible to Zn
deficiencies, during lactation (Apgar and Travis,
1979).
Sheep in Southern Australia, grazing on Zn deficient
pastures, were supplemented with 140 mg of Zn
weekly, increased lamb production, in relation, to the
ewes that were not treated (Minson, 1990; McDowell
et al., 1997). In Zn deficient sheep, implantation does
not take place, will be this factor responsible for the
low reproductive success (McDowell et al., 1997;
Hostetler et al., 2003). Likewise, in goats consumption
of low Zn diets, leads to low conception rates and
prolificacy (McDowell et al., 1997). In other studies,
Zn supplementation has increased prolificacy, by 14%
(Minson, 1990). In rams that were fed rations with 2.4
ppm of Zn, atrophy of the seminiferous tubules and
complete inhibition of spermatogenesis were observed
(Minson, 1990; McDowell et al., 1997). However,
when lambs were fed rations with 17.4 mg/kg DM,
testicular development and other reproductive
functions were similar to lambs fed a ration with 32.4
mg/kg DM (Minson, 1990). In male goats, a Zn
deficiency causes testicular atrophy and reductions in
libido and sperm production (Neathery et al., 1971;
McDowell et al., 1997). Likewise, Zn, cobalt (Co) and
Se treatment has resulted in increased sperm motility
and viability (Kendall et al., 2000). Age of sire and
season of year influence semen characteristics, in
Damasco male goats, best semen quality was found
during days of long photoperiod, during spring and
season (Al-Ghalban et al., 2004). However,
spermatogenesis requires extensive cell division and
this requires large quantities of Zn, once the Zn is
involved extensively in nucleic acid metabolism and
protein and therefore is essential for differentiation and
cell replication (Hidiroglou and Knipfel, 1984). In
general, Zn affect the reproductive events in sheep and
goats, directly on events as the manifestation of estrus,
embryo implantation, and reduced spermatogenesis, or
indirectly affecting the health of livestock. Usually
little Zn is available to the body except from ingested
in the diet. As the Zn must be continually
supplemented.
CONCLUSIONS
Cu, Se, and Zn directly affect reproductive events on
sheep and goats, they directly influence events such as,
expression of estrus, embryo implantation and
reduction in spermatogenesis; indirectly, they affect
overall animal health. The scientific evidence so far
obtained on mineral nutrition and its effects on some
reproductive traits in sheep and goats can be
controversial and inconclusive; however attention
should be focused on the presence of these elements
on the diets, since its importance on reproductive
performance of these animals.
ACKNOWLEDGEMENTS
This revision was sponsored by funds from the
Universidad Autónoma del Estado de México (Project
UAEM 2534/ 2007) and by the Secretaría de
Educación Pública-Programa de Mejoramiento del
Profesorado (Project PROMEP /103.5 /07 /257219).
We would like to thank Consejo Nacional de Ciencia y
Tecnología (CONACYT) for the grant received by
José Fernando Vázquez Armijo.
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Submitted April 15, 2010 – Accepted June 11, 2010
Revised received August 11, 2010
