Effects Of Weaning On Growing Foals

Every foal must be weaned from its dam at some point. However, when and how the weaning process is undertaken may have significant effects on the growing horse. One of the physiological responses often noted at weaning is a reduction in rate of weight gain.

In a study on Thoroughbred farms in Central Kentucky, average daily gain in the week following weaning was reduced to 33% of the rate observed before weaning. Average daily gain rebounded in the second week following weaning and then averaged about 68% of the preweaning rate in the next 8 weeks. An interesting finding was the reduced radiographic density of the cannon bone after weaning. However, in a later study at the University of Kentucky, a similar reduction in radiographic bone density was not observed after weaning.

The difference in the results may be related to the way the foals were managed at weaning. IN the first study, many of the foals were confined to stalls for several hours each day following weaning; whereas in the University of Kentucky study, foals were maintained on pasture approximately 22 hours per day and were placed in stalls only at feeding. A Michigan study recently reported that stalled yearlings also had a reduction in radiographic bone density that was not observed in age-matched controls maintained on pasture.

Another goal of the University of Kentucky study was to evaluate effect of age on weaning. Foals were weaned at either 4.5 months of age or 6.0 months of age. To compensate for possible seasonal effects, foals were matched so a 6-month old foal and a 4.5-month old foal were weaned on the same day and then kept in the same pasture. Although it was suspected that younger foals would be affected by weaning more than the older foals, weaning at an older age did not reduce the depression in average daily weight gain observed in the first week after weaning. Furthermore, at 8 months of age, there was no difference in either height at the withers or body weight between the two weaning groups.

Researchers in Virginia and New Jersey have compared single and paired weaning. In each case, foals were separated from their dams and placed in box stalls, either alone (single weaning) or with another foal (paired weaning). The Virginia Tech study found that although single-weaned foals tended to be more vocal than paired-weaned foals, cortisol responses indicated that paired weaning was more stressful than single weaning. In the Rutgers, New Jersey, study single-weaned foals had normal cell-mediated immune responsiveness whereas this response variable was depressed in the pair-weaned foals. Both studies concluded single weaning was less stressful than paired weaning.

—Dr. Laurie Lawrence, Equine Disease Quarterly, funded by Lloyd's, London, Brokers

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