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Stutz, W. A., Topliff, D. R., Freeman, D. W., Tucker, W. B., Breazile, J. W., & Wall, D. L. (1992). Effects of dietary cation-anion balance on blood parameters in exercising horses. Journal of Equine Veterinary Science, 12(3), 164–167.
Abstract: Summary Four geldings and four mares of primarily Thoroughbred and Quarter Horse breeding were used in simultaneous 4x4 Latin square experiments to test the effects of dietary cation-anion balance (DCAB), defined as meq ((Na+K)-C1)/kg diet dry matter, on blood pH, blood gases, acid-base status and plasma glucose in horses at rest and following anaerobic exercise. Four diets, consisting of a base concentrate of corn, soybean meal and cottonseed hulls fed in a 60:40 ratio with Bermudagrass hay, were formulated to provide a DCAB of 5 (L=Low), 107 (ML=Medium Low), 201 (MH=Medium High) and 327 (H=High) meq ((Na+K)-C1)/kg diet dry matter. Calcium chloride and ammonium chloride were added to treatment L and ML and sodium bicarbonate and potassium citrate were added to treatment H to achieve the desired cation-anion balance. Treatment MH was not supplemented and served as the control treatment. Prior to the experiment, horses performed six weeks of long, slow, distance (LSD) work. During the experimental periods, horses were subjected to an exercise regimen alternating LSD with an interval training protocol 6 days/week. Venous blood pH, pCO2 and bicarbonate levels were significantly lower in horses at rest consuming diet L versus diets MH and H. Blood pH and acid-base parameters decreased with decreasing DCAB. There were no significant differences in blood pH or acid-base parameters between treatments, after anaerobic exercise. Plasma glucose concentrations for treatment L were significantly lower than treatment H at 10, 20, and 30 minutes post-exercise. These data suggest that DCAB has significant effect on acid-base status and indicate that horses consuming diets with low DCAB may experience a metabolic acidosis.
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Covalesky, M. E., Russoniello, C. R., & Malinowski, K. (1992). Effects of show-jumping performance stress on plasma cortisol and lactate concentrations and heart rate and behavior in horses. Journal of Equine Veterinary Science, 12(4), 244–251.
Abstract: Summary Effects of show jumping competition on stress levels in horses was examined. Twenty-six homes were sampled in both show and farm environments from three levels of show experience schooling, (least experience, n=11); intermediate, (moderate experience, n=6); open, (most experience, n=9). Blood samples were taken at 6 time points; 3 at the horse show and 3 at the home farm (baseline at rest, pre-schooling and post-performance over a jump course). Stress responses were assessed through comparison of the behavioral response of the horses (determined by a subjective scoring system) to plasma cortisol (F) concentrations. Physical exertion was evaluated by heart rate (HR) and plasma lactate (L) concentrations. Schooling jumpers displayed higher baseline F concentrations than open jumpers (83g±9.2 vs 46.4±10.2 ng/ml, respectively; p<.05); but not when compared to intermediate jumpers (66.2 ± 13.7 ng/ml; p>.05) at the horse show. At the farm, there were no differences in F concentrations between experience levels at a time point (p<.05). Least experienced horses displayed higher F values at rest at the show compared to the home farm. At the show, open jumpers had higher L concentrations post-exercise compared to intermediate horses (40.3±3.4 vs 25.5±4.0 mg/dL, respectively; p<.05); but were not different compared to schooling jumpers (34.8±2.0 mg/dL; p>.05). There were no differences in heart rates or behavior score between experience levels at specific time points at either the show or farm (p>.05). Low positive correlations were found between HR and F (r=.24, p<.05); HR and L (r-.48, p<.05); and HR and behavior (r=.22, p<.05). Results suggest that conditioned jumpers that have previously been exposed to horse show environments do not appear stressed during acute show-jumping competition.
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Dugatkin, L. A., & Godin, J. G. (1992). Reversal of female mate choice by copying in the guppy (Poecilia reticulata). Proc Biol Sci, 249(1325), 179–184.
Abstract: Ever since Fisher (1958) formalized models of sexual selection, female mate choice has been assumed to be a genetically determined trait. Females, however, may also use social cues to select mates. One such cue might be the mate choice of conspecifics. Here we report the first direct evidence that a female's preference for a particular male can in fact be reversed by social cues. In our experiments using the Trinidadian guppy (Poecilia reticulata), this reversal was mediated by mate-copying opportunities, such that a female (the 'focal' female) is given the opportunity to choose between two males, followed by a period in which she observes a second female (the 'model' female) displaying a preference for the male she herself did not prefer initially. When allowed to choose between the same males a second time, compared with control tests, a significant proportion of focal females reversed their mate choice and copied the preference of the model female. These results provide strong evidence for the role of non-genetic factors in sexual selection and underlie the need for new models of sexual selection that explicitly incorporate both genetic and cultural aspects of mate choice.
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Harkins, J. D., Kamerling, S. G., & Church, G. (1992). Effect of competition on performance of thoroughbred racehorses. J Appl Physiol, 72(3), 836–841.
Abstract: The effect of competition and the influence of age and sex on performance were examined in a study of 18 Thoroughbred racehorses. The horses performed two solo and two competitive runs at 1,200 and 1,600 m for a total of eight runs. No group ran faster during competition, which may have been a reflection of the quality of horses used for this study and their susceptibility to stress-induced impairment of performance. Males showed no significant difference between competitive and solo run times, whereas females were consistently slower during competition. Males ran significantly faster than females in all runs. There was no difference in run times due to age, which may have been due to the high mean age (5.9 yr) of the group. The slower competitive run times may have occurred because of an earlier onset of fatigue when compared with solo runs. Plasma lactate was significantly greater for the 1,200-m competitive than for the solo runs.
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