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Beynen AC, 2018. Diet and dog farts

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Creature Companion 2018; January: 38, 40.
Anton C. Beynen
Diet and dog farts
Expelling gas through the anus (flatus), is normal in dogs. Excessively noisy and/or stinky farts can
be a source of humor or annoyance. Twenty nine out of 314 owners of apparently healthy dogs
perceived their pets’ flatus at least daily (1). In another questionnaire-based study, one third of 47
owners of flatulent dogs found the smell objectionable and would change the dog’s diet if it would
solve the problem (2).
Flatus largely consists of odorless gases. Malodor is caused by quantitatively minor, volatile sulfur
compounds. Above human’s odor perception threshold, increasing concentrations of hydrogen
sulfide in dog flatus are matched by worsening aroma. The hydrogen sulfide is formed in the large
intestine by bacteria that process sulfate, (sulfur-containing) protein fragments and
carbohydrates. Formation of hydrogen sulfide is reduced by feeding dogs on a highly digestible,
protein-restricted food so that little residue reaches the hindgut, thereby starving and slowing
down the stink-producing bacteria.
Compared with soybean meal in the diet, poultry meal may diminish the volume of gas production
and make the smell less offensive. The latter was shown in dogs fitted with vests containing a
monitoring pump that sampled air near the anus and determined hydrogen sulfide concentrations.
Further reduction of hydrogen sulfide in dog flatus may be achieved by fortifying the diet with a
preparation of the Yucca schidigera plant.
For an individual gassy dog, a series of dietary tests can be successful in finding a suitable food.
Inspecting the ingredient and analysis panels of different foods may lead to identification of
potentially beneficial products that are complete, soybean-free, low-protein (less than 20% crude
protein in a dry food), low-fiber (less than 2% crude fiber) and, possibly, supplemented with a
yucca substance.
Hydrogen sulfide
Part of the gas excreted per rectum is derived from bacterial fermentation in the colon. Hydrogen
sulfide (H2S), a very small constituent, appears to cause malodorous flatus. The culprit is formed by
sulfate-reducing bacteria (3).
In healthy, instrumented dogs fed a commercial dry food, hydrogen sulfide was measured in air
around the anus (4). The dogs moved freely in an enclosed room, together with an odor judge. The
odor ratings on a 1-5 scale correlated highly with flatus H2S concentrations. The sensory detection
limit was 1 ppm. H2S concentrations varied markedly within dogs over time and between dogs on
each day (4). Aging had no effect (5).
Bacterial fermentation
Higher quantities of odorless gases could either dilute or enhance hydrogen sulfide in flatus.
Perhaps, extra gas provides a vehicle that diverts the repellant from tissue metabolism. Feeding
poorly digestible proteins and carbohydrates, high-fiber ingredients and indigestible, fermentable
carbohydrates all promote flatus through increasing substrate availability for bacterial fermentation.
Colonic hydrogen sulfide production is further stimulated by supply of sulfate (6) and/or sulfur-
containing amino acids.
Clinical signs of digestive impairment may include flatus. Dogs with exocrine pancreatic insufficiency
typically present with frequent flatulence, obtaining a severity score of 2 as opposed to 1
(sometimes flatulence) or 0 (no). Dietary digestive enzyme supplementation lowered the rating to
1.2, whereas healthy controls scored 0.5 (7).
Flatus volume
Flatus activity in fecal matter mirrors the state of colonic fermentation. Gas production in feces
incubated at 37 oC was much greater when the donor dogs were fed a soy-grit diet rather than an
all-meat diet (8). Based on conversion by dog feces (9-11), cellulose is nonflatulant, whereas soy
fiber, wheat bran, beet pulp and wheat middlings are flatulent. Cellulose is indigestible in the small
intestine; the other substrates are poorly digestible.
Homogenates were inserted into the ligated colon of anesthetized dogs. Inside the gut segment, gas
production was negligible after introduction of cellulose, but was powerful for navy beans (12). The
intestinal gas area in dogs was quantified noninvasively by radiography. Dietary probiotics had no
effect (13), but mixing 30% soybean meal into an extruded corn-poultry diet (14) or replacing 16%
corn by soya hulls (15) markedly increased intestinal gas volume.
Malodorous flatus
Soybean versus poultry meal in dry food led to higher, smellable levels of hydrogen sulfide in dogs’
rectal gas (16). Dogs (n= 129) were switched from their habitual diet to a high-protein, low-
carbohydrate dry food (36% crude protein, 24% nitrogen-free extract) with “poultry and pork
dehydrated proteins” as first ingredient (17). After 14 days, the owners classified flatulence as
absent in 73% of the dogs, less in 8% and more in 19%.
In a crossover study (18), dogs fed a commercial dry food received placebo and test treats (1 treat/5
kg body weight). Test treats contained three carminatives: activated charcoal (320 mg/treat), Yucca
schidigera (2.5 mg) and zinc acetate dihydrate (57 mg). The test treat reduced the number of
bad/unbearable farts from two to zero during 3 to 8 hours after feeding (Note 1). Addition of 0.5%
ginger root powder to a canine dry food reduced flatus frequency and H2S content (19).
Fecal odor
Offensiveness of flatus and feces may go hand in hand. Higher protein intake was associated with
deteriorated canine fecal aroma (20). In 7 dog studies, yucca ingestion (280 mg preparation/kg diet)
lowered overall offensiveness scores for feces by 31% (21, 22, Notes 2, 3). Incubation of dog feces
with yucca lowered hydrogen sulfide formation (18), but the mechanism of action remains open.
Note 1.
Dogs were fed their daily ration at 8:30 am, and treats were offered 30 minutes later. Hydrogen
sulfide in rectal gas was measured continuously at 20-second intervals between 10:30 am and 3:30
pm on each of the five days of the two treatment periods of the crossover study (18). The number of
flatulence episodes (NOE), i.e. the number of hydrogen sulfide readings > 1 ppm during the sampling
period, was 12 for the control treat and 8 for the test treat. The ppm readings were converted into
odor scores using an earlier derived power function (4). The outcomes were categorized as 1 (no
odor), 2 (slightly noticeable odor), 3 (mildly unpleasant odor, 4 (bad odor), and 5 (unbearable odor).
The article (18) presents the percentage distribution of the scores. Score 1, representing no odor,
accounts for about 40% of the total scores. Because all sulfide readings were above the lower limit
of sensory human detection (> 1 ppm), score 1 falls under smellable flatulence episodes. The
distribution indicates that the control scores 4 and 5 each represented 8% of the total episodes.
These values were 2 and 0% for the test treat. Thus, when consuming the control treat, the dogs had
one flatulence episode each with bad (score 4) and unbearable odor (score 5). In contrast, such
episodes were essentially zero when the test treat was administered.
Flatus score distributions for the two treats
Control treat
Test treat
Score
%
NOE
%
NOE
1
37
43
2
34
48
3
13
7
4
8
2
5
8
0
0
Sum
100
12
100
8
Note 2.
Impact of dietary yucca preparations on canine fecal odor offensiveness
Authors
Yucca dose^
Effect
#
Diet type
Lowe and Kershaw, 1997*
250
54
dry
Lowe, 1991*
200
42
dry
Maia et al., 2010*
250
8
dry
Dos Reis and Saad, 2011*
+
500
0
dry
McFarlane and DPI Global, 8801D*
248
56
dry
McFarlane and DPI Global, 8802D*
248
20
dry, wet
Ravikumar and Swamy, 2009 (22)
250
40
wet
*Summarized and cited by Beynen and Saris (21). ^ mg/kg diet.
# Percentage decrease in degree of maldor. + Same study as reference 20.
Note 3.
In the treat study (18), the test treats contained three carminatives: activated charcoal (320
mg/treat), Yucca schidigera (2.5 mg) and zinc acetate dihydrate (57 mg). The administration of yucca
was equivalent to 33 mg/kg dry food. This dosage is much lower than that (280 mg/kg diet) in the
fecal-odor studies (21, 22). In the treat study, activated charcoal and zinc acetate probably had
contributed to the observed decrease in flatus hydrogen sulfide concentration. The two carminatives
are assumed to bind colonic and fecal sulfur-containing gases (18).
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Beynen AC, 2021. Molybdenum in petfood
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Full-text available
  • Jan 2021
Molybdenum in petfood Molybdenum is a silver-white metal. It occurs in various soil and rock minerals, but is mined as molybdenite, or molybdenum sulfide that co-exists with other metals. Molybdenite-containing rocks are crushed and powdered. Subsequently, molybdenite is isolated from the ground ore and roasted so that industrial molybdenum trioxide is formed, which is mainly used in the steel industry. Other applications are as corrosion inhibitor in the chemical industry and as wires in electronics. By way of natural processes and human activities, molybdenum enters the soil and water and then, via plants and livestock, gets into the food chain. Normally, pure molybdenum is not added to petfood, but the regular ingredients bring along the element. Experiments in rats have shown that molybdenum is an essential nutrient, whereas excessive intakes are toxic. Those features of molybdenum most likely extend to dogs and cats. In 532 samples of commercially available dry and wet foods for dogs and cats, the molybdenum levels have been measured. The outcomes ranged between 0.1 and 2.8 mg molybdenum per kg dietary dry matter (or per kg of the food's residue after removal of its moisture). On the basis of controlled rat studies and experiential knowledge, that range can be considered both adequate and safe for dogs and cats. There is no evidence that deficiency or excess of molybdenum is responsible for any disease in dogs and cats. Thus, commercial petfoods appear to provide sufficient, but not excessive molybdenum. Nevertheless, there may be an optimum range of molybdenum contents for dog and cat foods, but thus far there are no data about this subject. Dietary molybdenum For 532 samples of dog and cat foods, which were analysed in 8 studies (1-8, Note 1), the overall average amount of molybdenum was 0.6 mg Mo/kg dietary dry matter (ddm). The means for two studies were set at zero; their outcomes were described as below the limit of quantification (3) or detection (8). For the 6 other studies, the lowest amount reported was 0.1 mg Mo/kg ddm, which could be seen as lower limit for commercial petfoods. The highest value found (1) was 2.8 mg Mo/kg ddm. The analysed molybdenum concentrations in industrially-produced petfoods may be put into perspective by a rough calculation of molybdenum levels in simplified ingredient mixtures. For corn (9) and poultry byproduct meal (10) molybdenum contents of 1.8 and 0.3 mg/kg dm have been reported. Thus, dog food comprising (on a dry matter basis) 30% poultry meal, 50% corn and 20% molybdenum-free ingredients, would contain 1.0 mg Mo/kg ddm.
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Owner assessment of pruritus and gastrointestinal signs in apparently healthy dogs with no history of cutaneous or noncutaneous disease
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Fermentation Characteristics of Several Carbohydrate Sources for Dog Diets Using the In Vitro Gas Production Technique
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Effect of soya hulls on diet digestibility, palatability, and intestinal gas production in dogs
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  • Jan 2017
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Assessment Through a Pet Owner Survey of the Gastrointestinal Tolerance of a New High Protein-Low Carbohydrate Diet Range in Growing Dogs
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The effect of soy oligosaccharide extraction on diet digestibility, faecal characteristics, and intestinal gas production in dogs
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This study aimed at evaluating the coefficients of total tract apparent digestibility (CTTAD) and metabolisable energy (ME) content of dog foods containing different soybean protein products, as well as the faecal characteristics and intestinal gas production of dogs consuming these diets. The following soybean products were added at 300 g/kg of diet: soybean meal (SBM), soy protein concentrate (SPC) with 600g crude protein (CP)/kg (SPC600), SPC with 700 g CP/kg (SPC700), hydrolysed SPC700 (HSPC), and soy protein isolate (SPI). The CTTAD and faecal characteristics were determined in six dogs according to a 6 x 6 Latin square design. Intestinal gas production was evaluated by radiography of 16 dogs fed the reference diet and diets containing 300 g SBM, SPC700, or SPI/kg. Crude protein digestibility of SBM, SPC600, SPC700, HSPC, and SPI was 0.898, 0.839, 0.852, 0.906, and 0.988, respectively. Soy protein isolate presented the highest ME content (21.26 MJ/kg, P<0.001) and SPC600, the lowest ME (14.15 MJ/kg, P<0.001). Dogs fed the reference and the SPI diets presented harder faeces and higher faecal pH (P<0.001). Soybean meal produced the highest intestinal gas volume (P<0.05), while there was no difference among the other treatments (P>0.05). The removal of soybean oligosaccharides reduces intestinal gas production in dogs. However, soybean ethanol-insoluble fibres must be removed to increase protein digestibility and ME content, as well as to improve the faecal texture of dogs. (C) 2013 Published by Elsevier B.V.
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Oligosaccharides of Food Legumes: Alpha-Galactosidase Activity and the Flatus Problem
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  • Jun 1975
The raffinose family of oligosaccharides--including stachyose and verbascose--occurs in seeds of food legumes at levels that cause flatulence in man and animals. These carbohydrates escape digestion because there is no α-galactosidase activity in mammalian intestinal mucosa and because they are not absorbed into the blood. Consequently, bacteria in the lower intestinal tract metabolize them to form large amounts of carbon dioxide and hydrogen and to lower the pH. The amount and pattern of expelled gases reflect differences in type, location, and abundance of intestinal microorganisms possessing α-galactosidase activity in a favorable nutrient environment. Water and aqueous alcohol extraction, as well as enzymatic hydrolysis, can be used to process food legumes into products having low flatus activity. According to in vitro and in vivo studies, antibiotics and naturally occurring substances can inhibit bacterial activity in the intestinal tract; however, it is unlikely such additives would be approved for human consumption. Breeding soybeans low in oligosaccharide content holds little promise.
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In vitro fermentation characteristics of different carbohydrate sources in two dog breeds (German shepherd and Neapolitan mastiff)
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  • J ANIM PHYSIOL AN N
Few studies have been published on the normal intestinal biota of canines unlike the wealth of information regarding livestock animal species. The in vitro gas production technique (IVGPT) including measurements of accumulating gas during fermentation and end-product determinations allows obtaining a complete picture of microbial activity kinetics. The aim of this study was to study the in vitro fermentation characteristics of different carbohydrate sources using inocula from two dog breeds (German Shepherd and Neapolitan mastiff). Faeces sampled from rectum of two GS and NM adult dogs, fed the same dry food, were used as inocula. The samples, diluted and filtered, were incubated at 39 degrees C under anaerobic condition with nine substrates different for carbohydrate composition (rice, corn, potato, spelt, pure cellulose, beet pulp, wheat bran, inulin and fructo-oligosaccharide). Gas production was recorded 17 times using a manual pressure transducer. After 48 h, the fermentation was stopped and fermenting liquor was analysed for pH and volatile fatty acids (VFA). Organic matter digestibility (OMD) was calculated as difference after burning the residuals. OMD, gas production and end-products were significantly correlated with chemical composition of substrates, in particular carbohydrate fractions (total dietary fibre and starch), confirming the effectiveness of the IVGPT in evaluating dog feeds. Concerning the comparison between breeds significant differences (p < 0.01) were found for OMD, gas production, fermentation kinetic parameters and end-products, suggesting a different pathway of fermentation and consequently, a different anaerobic population.
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Production and Inhibition of Gas in Various Regions in the Intestine of the Dog.
Article
  • Jul 1966
The relationship between the small intestinal and colonic flora and the gas volumes and composition resulting from the introduction of navy bean homogenates into surgically prepared intestinal segments of normal and antibiotically pretreated dogs was investigated. Intestinal gas production was effectively inhibited or greatly reduced in animals pretreated with Neomycin Sulfate and Sulfathalidine, Mexaform, and Vioform, following the administration of navy bean homogenates. Mexaform and Vioform effectively destroyed the anaerobic bacteria of the intestinal tract while the normal aerobic and coliform bacteria increased in total numbers, indicating that the increased gas production from a navy bean homogenate was due to the anaerobic intestinal flora. Contrary to some current belief, it has been shown that bacterial action in the duodenum, jejunum, and ileum of the dog may add significantly to the total intestinal gas volume of animals fed navy bean homogenates.
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Production and elimination of sulfur-containing gases in the rat colon
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  • Apr 1998
  • Am J Physiol
Highly toxic sulfur-containing gases have been pathogenetically implicated in ulcerative colitis. Utilizing a rat model, we studied the production and elimination of sulfur-containing gases within the unperturbed colon. The major sulfur-containing gases were hydrogen sulfide (H2S), methanethiol, and dimethyl sulfide with cecal accumulation rates of 2.6, 0.096, and 0.046 microliter/min, respectively. The dependence of H2S production on dietary components was demonstrated via a sixfold reduction with fasting and a fivefold increase with carrageenan (a nonabsorbable, sulfur compound) feeding. Zinc acetate reduced cecal H2S by fivefold, indicating the importance of H2S binding by divalent cations. During passage from the cecum to the rectum, > 90% of the sulfur gases were absorbed or metabolized. An H2 35S turnover of 97%/min was observed in the isolated cecum. Thus mucosal exposure is > 10 times the measured accumulation rate. Cecal mucosal tissue very rapidly metabolized H2S and methanethiol via a nonmethylating reaction.
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