Introduction
All herbivorous animals are dependant upon the fermentative attack of ingested plant material by the resident and symbiotic bacteria of the gut, in order to fully utilize it as a nutrient source. In ruminants such as sheep and cattle, the intestinal tract evolved a series of "compartments" located anterior to the gastric stomach in which these bacteria reside. Thus, fermentation occurs prior to true gastric digestion. In the horse, whose digestive tract more closely resembles that of a cow rather than that of a pig, the primary site of fermentation is the large bowel. Adaptations for hind gut fermentation include a very limited gut capacity and a resulting rapid rate of ingesta passage. To make this system physiologically feasible, the horse is obligated to consume many small meals over a 24 hour period.
In most situations, nutritional management of the horse ignores their evolutionary development. Horses are usually forced to consume one or two large meals daily, due primarily to confinement housing and the associated intensity of time management. When ingested in this fashion, material reaches the large bowel in quantities which preclude efficient utilization by the resident bacteria and can result in a number of serious negative consequences, including enterotoxemia, colic, and the production of amines.
A similar situation occurs in intensively managed ruminants such as dairy and feedlot cattle. Research has shown that by manipulating ruminal bacterial populations, digestive efficiency can be significantly enhanced, and digestive disorders, such as acidosis, reduced. In vitro experiments done at West Virginia University by Hoover et.al. and others, demonstrated that when ruminal bacteria were provided with a blend of peptides, amino acids and soluble nitrogen matrixed into a controlled release form, (Fermenten™, Biovance Technologies, Omaha, NE) and fed in conjunction with adequate fermentable carbohydrate sources, ruminal microbial yield (gm of microbial protein produced per kg of organic matter fermented) and efficiency were increased by an average of 19 percent. A number of controlled and field experiments with growing and mature dairy and beef cattle were conducted to verify the in vitro results. Significant improvements in performance as measured by fluid milk and milk component yield, feed efficiency, lean tissue accretion and overall reduction in incidence of certain metabolic diseases, were reported.
Bacterial fermentation in the large bowel is key to normal equine nutrient utilization and metabolism. Current management practices can have a serious and negative impact on hind gut function. Poor hind gut function is associated with increased incidences of certain colics, enterolithe formation and/or chronic horse diarrhea. It also can have a negative impact on the growth rate in young horses, recovery of body condition in compromised horses, and an indirect negative influence on a number of other physiologic parameters. Based upon the positive outcomes reported in the ruminant experiments, a series of studies were designed and conducted to test a similar working hypothesis for the horse. I.E., could stimulation of colonic bacterial fermentation be achieved and, if so, could it positively impact animal performance?
EXPERIMENT 1Materials and MethodsSixteen mature horses with an average body weight of 500 kg were divided into two groups of eight animals each. Both groups were fed an isocaloric, isonitrogenous diet consisting of a grain mix, (soybean meal, wheat middlings, ground corn, oats blend) fed at a rate of 2.8 kg/head/day split into two feedings of 1.4 kg each, and approximately 6.8 kg of an 18% CP alfalfa hay also split into two equal feedings. After a five-day adaptation period, a complexed nitrogen source similar to that used in the ruminant experiments (ReStore™, Biovance Technologies, Omaha NE) was introduced into the diet of group one. Over the next five days, the ReStore™ supplementation was gradually increased until the target dose rate of 340 grams was achieved and accepted by all horses in the treatment group. For the next thirty days both groups were fed their respective diets. Approximately 8 hours after their last meal, samples were taken of their intestinal contents, which were segregated by location,
and tested immediately for pH. Samples of contents were then retained and fixed for future analysis to determine apparent fiber digestibility and volatile fatty acid (VFA) content.
Statistical analysis was done by a PROC GLM of SAS. Results were expressed as least squares means. The significant threshold was P<.05 and the tendency threshold at P<0.10.
ResultsSignificant differences (P<.05) were noted between treatment and control groups in cecal and colonic pH values. Average cecal pH in control animals was 6.81, as compared to 6.56 in the treatment group. Average colonic pH for controls was 6.78, while in the treatment group it was 6.47 (Figure 1). The significantly lower cecal and colonic pH measurements were reflective of
significantly higher total VFA concentrations. Total cecal VFA concentration for the treatment animals averaged 81.5 mmol/L as compared to 63 mmol/L for the controls (P<.05). This difference was also reflected in colonic VFA concentrations where treatment animals averaged 84.6 mmol/L and controls averaged 66 mmol (P<.07) (Figure 2). However, no significant differences between treatment and control groups were noted in either pH or VFA content of the duodenum, illuem or jejunum. Apparent fiber digestibly for treatments vs. controls tended to be higher in the treatment animals, with pooled colonic and cecal samples of treatment animals averaging 44.8% disappearance, as compared to 38% in the controls (Figure 3).
DiscussionVFA production, pH reduction and fiber digestibility are all measures of bacterial fermentation activity. In this study, significant differences favoring the treatment group for all parameters tested indicate that when the ReStore™ product was supplemented in the diet, bacterial fermentation was enhanced. These data strongly reflect both the
historical in vitro and in vivo ruminant work. In ruminant systems, ruminally degradable nitrogen is key to fermentation efficiency. As the bacterial populations and fermentation dynamics of hindgut fermenters, such as the horse, are reflective of what occurs in the ruminant, it would be expected that similar interventions would illicit similar results.
The conclusion reached in this study was that when ReStore™ was added to the diet, large bowel fermentation efficiency, as measured by pH, VFA production, and fiber digestibility, is positively and significantly impacted.
EXPERIMENT 2Materials and MethodsThis study was conducted over two reproductive cycles. In year one, 240 multiparous mares with an average age of 12 years and an average body weight of 420 kg, were divided into two groups of 120 each. Mares were housed at 15 different sites, with the largest group being 26 mares at one location, and the smallest being eight (8). Treatment and control groups were maintained at all sites. All mares received a basal diet consisting of a soybean meal, whole oat, ground corn based concentrate fed at an average rate of 3.0 kg/head/day and free choice mixed grass and alfalfa hay. As all mares had access to pasture, hay consumption varied with the individual mare and carrying capacity of the pasture.
Beginning 21 days prior to foaling, treatment mares were supplemented with a peptide source (ReStore™, Biovance Technologies, Omaha, NE) at a feeding rate of 227 grams/head/day. Supplementation continued through to 90 days postpartum. Incidence of postpartum intestinal disturbance, as indicated by colic bouts, inappetance and horse diarrhea not associated with other conditions, were recorded for both groups. In regards to colic incidence, differential diagnosis as to etiology and success of treatment were recorded; but for analytical purposes, initial bouts of treatable colic alone were the basis for statistical treatment. A representative number of treatments and controls (25%) were weighed prior to foaling, again at 5 days postpartum and thereafter at 30-day intervals until 90 days. Beginning in year two, treatment and control groups were reversed. All procedures and observational methods described in year one, remained unchanged however.
Weight loss and incidence of digestive disturbance was analyzed using PROC GLM of SAS; mare, period, treatment, and residual effects were factors of variation. Results were expressed as least squares means, with standard error of the means because of missing data for some mares during the second period due to exit from the study. The significant threshold was set at P <.05 and the tendency threshold at P< 0.10.
ResultsSignificant differences (P<.05) were noted in total reported incidents of treatable colics when treatment animals were compared to controls. Over the course of the two years, in the treatment group, seven mares were treated nine times for colic. In the controls, seventeen mares were treated a total of twenty-three times for the same period. The average colic incidence across the two periods for treatment animals was 7.5%, as compared to 19.2% for the controls (Figure 4). No differences were noted between groups in terms of incidence of horse diarrhea, or inappetance. Weight loss for the period starting at 5 days postpartum until 90 days averaged 34.1 kg for the two years in control animals, and 18.2 kg in treatment animals (P<.05) (Figure 5).
DiscussionThe population of animals chosen for this study represent a population where post parturient digestive disturbance is most likely to occur, i.e. the older, multiparous mare. However, literature is unclear as to magnitude of the epidemiology of this problem. As a consequence, it is somewhat speculative to conclude that colic incidence reported in the control populations reflect the norm. However, considering the replication of sites and the number of observations made over the course of the two years, there is adequate basis for considering the 19.2% colic incidence to be average for this population. Thus, reducing incidence to 7.5% is not only statistically significant but most likely biologically significant as well.
Although this study demonstrated no differences between groups in terms of horse diarrhea incidence and feed intake, reduction and/or elimination of chronic horse diarrhea, especially in older horses, is a common observation reported by veterinarians who have been involved in other field studies with the product. This may be attributable to the fact that even though horse diarrhea and impedance were listed as study parameters, incidence of either is often subjective. Furthermore, based upon the fact that, these horses were managed largely on pasture, whether or not an individual was off feed or suffered from a chronic recurring, nonpathogenic horse diarrhea would be harder to assess than in the field situations where this was reported.
The differences in body condition between control and treatment groups, favoring the treatment animals, strongly support the results of Experiment 1, in which significantly greater production of total volatile fatty acids was reported. VFAs are a key source of energy in the equine. By maximizing microbial colonic yield and efficiency, VFA production would be enhanced. This would provide treatment animals with a greater opportunity to maintain a more positive energy balance than they would be able to achieve otherwise. Also, the hypothetical contribution made by amino acids and peptides of microbial origin to overall equine nitrogen balance (a hypothesis strongly supported by the evolutionary record, but not currently supported in the literature) would also contribute to the differences observed. Older mares, especially lactating older mares, will metabolize muscle mass to meet lactational nitrogen needs. The anecdotal reports of the body condition of the treatment mares throughout the study, suggest that this was not the case in these animals.
The conclusions of this study were that ReStore™, when supplemented in the diets of gestating and lactating mares, positively impacted nutrient utilization as evidenced by a reduction in postpartum weight loss. It also appears to be an effective aid in the control and prevention of certain dietary disturbances common in this population of horses.
