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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.
2011 Project Description
The effect of forage type (alfalfa and timothy hay) and stage of gestation on basal glucose and insulin concentrations in mares was determined to examine whether mares become insulin resistant in late gestation.
Fecal samples were obtained from 9 neonatal foals and their dams to investigate the establishment of the microbial colony of the foal's gastrointestinal tract. These samples will be analyzed in 2012 and will extend our previous findings in this area. In addition, the effect of tall fescue as well as the effect of pasture conditions on growing horses were studied.
An in vitro method to evaluate the value of different forages for horses was developed. The method uses in vitro gas production as an indicator of substrate fermentability. A commercially available system that utilizes rumen fluid as the inoculum was adapted for use in horses by substituting equine feces for the rumen fluid. Several preliminary experiments were conducted to adjust assay conditions including incubation time, fecal dilution rates and buffer combinations. This assay and an assay developed previously will be used to evaluate a variety of forages used for horses and to assess the relationship of forage composition to digestibility and fermentability.
Mares receiving high forage diets did not have altered basal glucose or insulin concentrations in late gestation. In mares at risk for insulin resistance, high forage diets may be more desirable than high concentrate diets. Growth rate and feed intake of weanlings were not affected by consumption of endophyte infected tall fescue.
These observations suggest that low levels of tall fescue in equine pastures will not impact growth of weanlings. Other observations suggest that pasture availability can affect growth rate in nursing foals at 3 and 4 months of age, although it was not determined whether effects were due to pasture consumption by the foals or through effects on milk production in their dams.
These data can be used by horse owners to make decisions regarding the best supplementation programs for their horses. Information on the acceptability and digestibility of forages by horses can be used by horse owners to develop efficient feeding programs. In addition, hay producers can use the results to produce the most desirable product for horses.
Five graduate students and one undergraduate student received training during this period.
Davis, B.E. and L.M. Lawrence, 2011. The effect of endophyte infected tall fescue on weanlings. J. Equine Vet. Sci. 31:290-291.
McCown, S., M. Brummer, S. Hayes, J. Earing and L. Lawrence. 2011. Basal insulin and glucose concentration in gestating and lactating mares. J. Equine Vet. Sci. 31:247-248.
McCown, S., M. Brummer, S. Hayes, J. Earing and L. Lawrence. 2011. Nutrient and dry matter intakes of broodmares fed high forage diets. J. Equine Vet. Sci. 31:264-265.
Strasinger, L. and L. Lawrence. 2011. Growth rates in 3 and 4 month old foals during the summer in Kentucky. J. Equine Vet. Sci. 31:286-287.
Lawrence, L.M. and M. Flythe. 2011. Microbial Colonization of the Foals Gastrointestinal Tract. Equine Disease Quarterly, January 2011
Lawrence, L.M. 2011. Broodmare nutrition. UK Bluegrass Equine Digest, October. 2011
Lawrence, L.M. 2011. Managing carbohydrates in equine diets. Kentucky Breeders Short Course, Lexington KY
Lawrence, L.M. 2011. Alfalfa hay for horses. Proc. 31st KY Alfalfa Conference, Lexington KY. Lawrence, L.M. 2011. Forages for horses. In, Proc. Forages at KCA, G. Lacefield Ed., Published by the Kentucky Forage and Grassland Council, Lexington KY