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Factors Affecting Forage Intake and Utilization by Horses
Department of Animal and Food Sciences
Kentucky foals marketed as weanlings and yearlings at public auction annually produce revenue in excess of $300 million. Most of these horses will be raised in forage-based nutritional programs. While forage is an important nutrient source it can not provide all of the nutrients needed by broodmares and growing horses. The amount of supplementation needed will depend upon the nutrient composition of the forage and the amount of forage consumed by the horses.
It is a simple matter to assess nutrient composition of forage but there are few validated methods of predicting the amount of forage any particular horse will consume in a day. Factors that have been examined in other species (such as cattle and sheep) include chemical composition of the forage and stage of maturity of the forage. Because horses and cattle have different types of digestive systems, the information that has been gathered in cattle can not be applied to horses.
The purpose of this project is to investigate the factors that alter (increase or decrease) the amount of forage consumed by horses. Once these factors are understood, equations for predicting the amount of forage consumed by grazing horses can be developed. These experiments will enhance our ability to design effective and efficient nutritional programs for broodmares and growing horses.
2009 Project Description
Data from two experiments conducted in 2008 were analyzed and two additional experiments were conducted. Fecal samples collected from mares and foals were analyzed using real-time PCR and denaturing grade gel electrophoresis to evaluate similarity in fecal microbial populations.
In the second experiment from 2008 samples were analyzed to compare rate of passage and digestibility of a diet fed to mature horses and 6 month old colts. An experiment was conducted to compare dry matter digestibility and rate of passage between mature horses and yearling colts. Ytterbium labeled fiber was administered as a bolus dose at the beginning of a 3-day total fecal collection period to measure rate of passage of particulates. Chromium EDTA was administered at the same time to measure rate of fluid passage. All feces were collected during the 3-day collection period, subsampled and frozen for analysis of dry matter, neutral detergent fiber and acid detergent fiber were used in the calculation of total tract digestibilities. Data were analyzed to characterize heart rate and body weight changes in pregnant mares.
An experiment was conducted to evaluate factors affecting feed intake in pregnant mares. Activities were shared at a field day, at a lay symposium and at a scientific meeting.
The data analyzed in 2009 demonstrated that by 6 and 12 months of age, growing horses have the same capacity to digest fiber as mature horses. This finding suggests that many high fiber byproduct feeds (for example, soy hulls) can be effectively included in diets for growing horses. The inclusion of byproduct feeds may reduce feed costs.
The development of the RT-PCR denaturing grade gel electrophoresis method to evaluate changes in fecal microbial populations will allow us to characterize the normal establishment of hindgut microbial populations in foals. Neonatal foal diarrhea is a significant source of economic loss to the Kentucky horse industry. This method may be useful in subsequent experiments to investigate factors that result in neonatal foal diarrhea, and thus allow us to control the incidence of this problem.
Three graduate students and three undergraduate students received training in various analytical methods and gained experience in conducting and analyzing scientific experiments.
Cassill, B., Jackson, S., and Lawrence, L. 2009. Body weight changes in pregnant mares. J. Equine Vet. Sci 29:400-401
Hayes, S.H., Smith, S.R., Olson, G.L and Lawrence, L. 2009. Relationship of plant grazing tolerance to equine grazing preferences. J. Equine Vet. Sci 29:429-430
Parks, A.G., Hayes, S., Brummer, M., Ringler, J.E., Harvey, K.M., McCown, S., Cassill, B.D., and Lawrence, L.M. 2009. The effects of endophyte infected tall fescue consumption on exercising horses. J. Equine Vet. Sci. 29:299-300
Parks, A.G., S. Hayes and Lawrence, L.M. 2009. Stage of gestation affects resting heart rate. J. Equine Vet Sci 29:432-433.
McCown, S., Ringler, J., Watson, K., Cassill, B., Stine, J. and Lawrence, L. 2009. Sampling factors affecting carbohydrate measurements in pasture grasses. J. Equine Vet. Sci. 29:410-411.
Ringler, J. E. and Lawrence, L.M. 2009. Development of a method to label forages used in passage rate studies in the horse. J. Equine Vet Sci. 29:389-390.
Ringler, J.E., Hayes S., Brummer, M., McCown,S., Parks, A.G. and Lawrence L.M. 2009 Comparison of In Vivo digestibility estimates obtained from weanling and mature horses receiving the same diet. J. Equine Vet. Sci. 29:347.