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Title: Effect of starch source in pelleted concentrates on fecal bacteria in pre- and post-partum mares

item PYLES, M - University Of Kentucky
item FOWLER, A - University Of Kentucky
item BILL, V - University Of Kentucky
item CRUM, A - University Of Kentucky
item HAYES, S - University Of Kentucky
item Harlow, Brittany
item Flythe, Michael
item LAWRENCE, L - University Of Kentucky

Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2017
Publication Date: 10/21/2018
Citation: Pyles, M.B., Fowler, A.L., Bill, V.T., Crum, A.D., Hayes, S.H., Harlow, B.E., Flythe, M.D., Lawrence, L.M. 2018. Effect of starch source in pelleted concentrates on fecal bacteria in pre- and post-partum mares. Journal of Equine Veterinary Science. 72:31-36.

Interpretive Summary: When horses consume feed, some components of the diet are absorbed in the small intestine, and some pass through to the large intestine (hindgut) where they are fermented by bacteria and other microorganisms. Starch can be digested and absorbed, but some starch can also reach the hindgut. When starch reaches the hindgut it can disrupt the bacteria found there. It is not well understood how starch-utilization is impacted by botanical source of the starch, processing (e.g. heating, milling) and other factors. It is also well known that the diet and physiology of a mare changes during pregnancy and birth. However, little is known about how foaling disrupts the hindgut bacteria. The purpose of this experiment was to monitor the numbers of particular groups of bacteria in mares on two different diets during and after the foaling process. The starch in the diets came from either oats or from corn and wheat, and it was given in the form of a processed pellet. The diets were otherwise alike. In these forms and in these quantities, the botanical source of the starch made no difference in terms of the number of bacteria. Two groups of bacteria that are generally considered beneficial decreased on the day after the foals were born, but had recovered in 2 weeks. This disturbance in the hindgut bacteria could be due the physiological changes associated with giving birth or simply due to changes in feed intake during foaling. It is important to understand the normal changes in microbiology during foaling before we can evaluate the underlying causes of problems like colic and foal heat diarrhea.

Technical Abstract: Dietary starch source has been shown to affect fecal bacterial communities of horses fed cereal grains with little to no processing. However, processing, such as pelleting, might increase foregut starch digestibility, and mitigate effects of starch source on bacterial communities. The aims of this study were to: 1) determine the effect of starch source in pelleted concentrates on Lactobacillus spp., amylolytic bacteria, and cellulolytic bacteria in mares, and 2) evaluate pre-and postpartum changes in fecal bacterial communities from 324 d of gestation to 28 d postpartum. Thoroughbred mares (n = 18) were paired by last breeding date then randomly assigned to either an oat-based (OB) or a corn and wheat middlings-based (CWB) pelleted concentrate in addition to forage. Beginning at 310 d of gestation, mares were fed 3.2 kg/d (DM) of concentrate. After parturition, concentrate intake gradually increased to 4.8 kg/d (DM). The concentrates contained 38.0%, 36.2% starch, 6.6%, 8.8% WSC, and 5.4%, 7.5% ESC for OB and CWB, respectively. Fecal samples were collected at 324 d of gestation, before parturition, 1 d, 14 d, and 28 d postpartum. Fecal samples were collected immediately after defecation and enumerated by serial dilution and inoculation into selective, enriching media. Data were log transformed then analyzed using mixed model ANOVA with repeated measures to test the main effects of treatment (OB or CWB), time of sample, and treatment by time interaction. Results were considered significant when P < 0.05. There was no effect of starch source on enumerated bacterial communities (P > 0.05), in contrast to previous work. These results suggest that pelleting concentrates may alter some of the effects of starch sources. There was no effect of time on amylolytics (P > 0.05), however lactobacilli and cellulolytic bacteria decreased 1 d postpartum (P < 0.05). Therefore, major physiological events, such as parturition, appear to alter the hindgut microbiota.