Research Abstracts

Proceedings of the Equine Nutrition and Physiology Symposium, June 1999

The following research papers were presented at the Equine Nutrition and Physiology Symposium, June 2-5, 1999, in Raleigh, North Carolina. Abstracts have been prepared and personal comments added to increase the relevance of the research.

Fresh grass constitutes the majority of the diet of many horses in the spring and summer. Grass contains large volumes of water soluble carbohydrates such as sucrose, fructose, glucose and fructans. Researchers are proposing that fructans can cause laminitis, much like grain overload. Fructans cannot be digested in the small intestines of horses but are rapidly, but selectively, utilized by certain microbial species at the expense of others. If large amounts of carbohydrates such as starch and, possibly, fructans are "dumped" into the hind gut, there may be a rapid change in the hind-gut microbial population. It is thought that large numbers of dying bacteria release toxins which then elicit the onset of laminitis. Levels of fructans vary throughout the day with the highest concentrations around midday. (Comment: The research would suggest that individual animals or breeds such as ponies, who are prone to laminitis, should not be on pasture during the midday period. Horses should be introduced to pasture slowly over 5 - 7 days to allow their intestinal flora to change. Feeding of hay, each day for a week, prior to the horse(s) being placed on pasture, will lessen the chance of abrupt intestinal changes.)

Reference: Longland A.C., Cairns A.J., Humphreys M.O., Seasonal and Diurnal Changes in Fructan Concentration in Lolium Perenne: Implications for the Grazing Management of Equines Pre-disposed to Laminitis.

Weanlings, which were allowed exercise through either continuous access to pasture or partial access to pasture, had greater cannon bone (third metacarpal bone) densities than weanlings which were continuously confined to stalls. Stalling of weanlings will prevent the normal mineral deposition of the cannon bone and may be detrimental to the future athletic ability of the horse. (Comment: Bone is continually changing and the architecture of that bone will change to adapt to the requirements placed on the bone. Continuously confined horses will have lower bone density than horses which receive exercise regularly.)

Reference: Bell R.A., Nielson D.N., Waite K., Heleski C., Rosenstein D., Orth M., Influencing of Housing on Third Metacarpal Bone Mass in Weanling Horses

Mares supplemented with corn oil had a 4.2-fold increase in immunoglobulin G concentration in their colostrum collected 6 to 12 hours after foaling. Researchers wanted to determine if the vitamin E content of corn oil (327 IU/kg) was the contributing factor. The colostrum of mares fed a diet containing 160 IU/kg of vitamin E had higher concentrations of immunoglobulins IgG, IgA and IgM than the colostrum of mares fed 80 IU/kg vitamin E. The post suckling immunoglobulin levels were correspondingly higher for the foals from the mares fed the higher level of vitamin E. (Comment: The vitamin E intakes of 80 and 160 IU/kg of dry matter are very low in comparison to National Research Council maximum tolerable levels of 1,000 IU/kg of dry diet or 20 IU/kg of body weight. Observations on myopathies (disease of the muscle) that respond to vitamin E and/or selenium suggest an interrelationship between these two nutrients. Owners must be careful of the over-supplementation of Vitamin E and selenium when several sources are supplying these nutrients.)

Reference: Hoffman R.M., Morgan K.L., Lynch M.P., Zinn S.A., Faustman C., Harris P.A., Dietary Vitamin E Supplementation in the Periparturient Period Influences Immunoglobulins in Equine Colostrum and Passive Transfer in Foals

It is often very difficult to determine the amount of feed horses are eating when on pasture. A novel system of using external markers was developed and used on horses. The technique involves the feeding of a marker in a "greenola bar" and then measuring the levels of the marker in the manure and determining the intake from the dilution of the marker. Feed intakes of 3.3 % of body weight were estimated. (Comment: For the typical 1,000 lb. horse, this means that the horses were consuming 33 lbs. of dry matter daily or, on an as-fed basis, almost 100 lbs. of grass. The National Research Council (NRC) estimates that a mature horse will consume 1.5-2% of its body weight in total dry matter daily. These horses consumed almost l.5 times more than NRC would have predicted.)

Reference: Holland J.L., Kronfeld D.S., Cooper W.L., Ordakowski A.L., Hargreaves B.J., Sklan D.J., Harris P.A., Pasture Intake in Mature Horses

In a study of 633 foaling mares, there was no significant difference in foal mortality rates between a farm with minimum foaling management (a pregnant mare urine farm) and an extensively managed farm where foalings were closely monitored. Foal losses included immune deficiency associated with partial or failure of passive immunity transfer to the foal with the colostrum, mal-presentation, genetic defect, predation and drowning. Foal mortalities were 5-7%. Eighty-eight percent of the mortalities were before day 6 of age.

Reference: Burwash L.D., Pritchard J., Coleman R.J., Foal Mortality on Extensively Managed Farms

Fifteen riding horses from a university riding program were used in a study to assess the physiological responses to transport for 24 hours in a commercial horse van. All horses had previous hauling experience. They were provided with alfalfa hay and were offered water at all stops during the trip. The water came from the home farm. The blood parameters cortisol, neutrophil to lymphocyte ratio, hematocrit, aspartate aminotransferase (AST) were elevated both during transport and recovery. Lactate and creatine kinase (CK) were elevated during the recovery. Body weight was decreased by 6% upon unloading and recovered to a 2.4% loss within three hours with ad libitum access to water. However, body weights did not recover to pre-transit weights until after 24 hours. Many of the measures of stress, dehydration, muscle metabolism alterations and immune compromise did not return to normal following 24 hours of recovery. (Comment: Horses which are transported long distances and expected to compete to their peak performance should have a recovery time of a few days prior to competing. Water should, preferably, be from the home farm and be available at regular intervals or continuously during transit.)

Reference: Stull C.L., Rodiek A.V., Physiological Responses of Horses to 24-Hours of Transportation

Ammonia levels in poorly ventilated horse barns can rise to levels potentially harmful to the equine respiratory tract. Horses were placed in a four-stall, center-isle-type barn with dirt floor stalls for 14 days. The stalls were bedded with straw and cleaned daily. The stalls were bedded to maintain a 25-cm depth to the straw. Ammonia levels at the stall floor level rose from 2.5 ppm to 218 ppm. by day 14. At the horses head level, ammonia levels rose to 15 ppm. An ammonia absorbing compound was effective in reducing ammonia levels at the stall floor level. (Comment: The high ammonia levels at the floor level are extremely important to foals and horses who tend to lie down in their stalls).

Reference: Pratt S.E., Lawrence L.M., Barnes T., Powell D., Warren L.K., Measurement of Ammonia Concentration in Horse Stalls

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