EFFECTS OF RACTOPAMINE HCL ON PHYSICAL AND REPRODUCTIVE PARAMETERS IN THE HORSE
Kriewald, Russell D.
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The objective of this study was to monitor the effects on physical and reproductive parameters in mares supplemented with Ractopamine HCl (RAC), in an effort to provide some insight concerning the use of RAC in horse diets. Physical deviation was recorded via measurements of body weight (BW), muscle size, and fat deposition. Reproductive deviation was recorded via ultrasonographic measurement of follicular growth and ovulation, while hormonal analyses were conducted for leptin and luteinizing hormone (LH). Data analyses of physical measurements indicated an effect of RAC supplementation (P<.001) as treated horses had a greater increase in BW compared to the controls. Treatment horses increased gaskin circumference (P<.001) compared to horses on the control diet. Both groups showed an increase in rump fat with the treated horses gaining less (P<.05). A similar effect was revealed in body fat percentage (P<.01) with the treated horses gaining less when compared to the controls. No statistical differences were noted for changes in forearm circumference or rib fat. No change was derived for length of estrous or pre-ovulatory follicle size between groups. When analyzing the data from first to last cycle in the treatment group, length of estrous was significantly (P<.05) shortened over the 90-day study. Upon analysis of serum leptin concentrations, the control group had a significantly (P<.001) higher overall concentration as compared to the treated horses; however, no difference was noted for normalized data, though RAC supplementation may have caused the profile of leptin to become more erratic. Analysis of LH concentrations revealed a strong trend (P=0.0527) of RAC-supplemented horses having a lower mean concentration of LH throughout the 90-day study as compared to the controls. Means were also analyzed for day and treatment by day effects, suggesting possible trends (P=0.2944 and P=0.1591 respectively) of seasonality. Area Under the Curve (AUC) was calculated for individual horses and analyzed for treatment effects. Only a trend (P=0.1631) was noted for RAC-supplemented horses having a smaller AUC (80.10 ? 29.72) as compared to the controls (140.60 ? 27.50).