| North
Dakota Agricultural Research North Dakota State University, Fargo, ND 58105
Water
intake and confinement effects on estrogen and
cortisol production in pregnant mares (continued) |
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Abstract |
 Results and
DiscussionRecorded daily ambient temperatures varied from maximums of 18oF to minimums of -20oF during the urine collection period. Temperatures inside the barn were maintained above freezing (32oF to 48 oF). Urinary output based on a 12-hour collection was measured for each treatment group. Urinary volume averages were 1.62 pints for water-restricted confined mares (Group I); 1.93 pints for water-restricted, exercised mares (Group II); and 1.82 pints for ad libitum water, confined mares (Group III). The mares that were allowed 1 hour free exercise had slightly greater (P<.05) urinary output than those mares that were confined at all times. Urinary E2 and cortisol concentrations in pregnant mares are presented in Table 1. Manipulating the water intake of pregnant mares in long-term confinement appears to affect urinary E2 concentration. Mares that were confined but had free access to water (Group III) had greater E2 concentrations (P<.0001) than mares that were confined and had restricted access to water (Group I; Figure 1 – b&w graph – 30KB gif). Estradiol concentrations were not different (P>.05) between confined mares (Group I) and those that were exercised daily during the 14 day sampling period (Group II; Figure 2 – b&w graph – 29KB gif), although the exercised group had slightly greater E2 concentrations on 11 of 14 days.
Discussion Pregnant mares that were allowed 1 hour per day of exercise were found to have elevated urinary cortisol concentrations. James et al. (1970) studied the effect of exercise on cortisol levels in racehorses and found that the horse was not greatly influenced by exercise unless it is of greater magnitude than established training regimes. The mean urinary cortisol concentrations in all treatments (Table 1) were lower than previously reported plasma-based data for pregnant mares at rest (Hoffsis et al., 1970). James et al. (1970) established that normal plasma cortisol values in horses range from 3 to 13 ug/100 ml, and that urine sample concentrations parallel these values. In addition plasma cortisol concentrations were not affected by age, sex, pregnancy, or time of day (Hoffsis et al., 1970). Mal et al. (1991b) reported that confined mares appear to exhibit intermediate cortisol values, sometimes being the same as pasture mares or total isolation mares. Temperature data collected during the sampling
period from north central North Dakota weather
stations indicated minimum daily temperatures
were below 32oF each day. Houpt and
Houpt (1988) reported that cold environmental
temperatures negatively affect behavior in horses
in separated conditions, that is, horses that
were in a pen alone but had contact with other
horses in adjacent pens. Their hypothesis (when
an animal is prevented from exhibiting a normal
behavior such as walking, trotting, cantering,
and standing, the behavior will be amplified once
the restraint is removed) did not hold true when
their experimental horses were exposed to
temperatures below freezing. In our study the
mares demonstrated increased activity when
exercised and often circled the paddock several
times at a trot or canter before returning to the
in-gate. This increased daily activity coupled
with exposure to extreme cold temperatures during
the sample collection period could have been a
factor in the observed elevated cortisol
concentrations. Christison, G. I., and H. D. Johnson. 1972. Cortisol turnover in heat-stressed cows. J. Anim. Sci. 33:1005-1010. Cymbalyk, N.F. 1989. Water balance of horses fed various diets. Equine Prac. 11:19-24. Friend, T. H., and G. R. Dellmeier. 1986. Recent developments in stress research. Prof. Anim. Sci. 2:(2) 1-6. Ginther, O.J. 1992. Reproductive Biology of the Mare: Basic and Applied Aspects, (2nd Ed.). Equservices, Cross Plains, Wisconsin. Hoffsis, G. F., P. W. Murdick, V. L. Tharp, and K. Ault. 1970. Plasma concentrations of cortisol and corticosterone in the normal horse. Am. J. Vet. Res. 31(8):1379-1387. Houpt, K. A., and T. R. Houpt. 1988. Social illumination preferences of mares. J. Anim. Sci. 66:2159-2164. James, V. H. T., M. W. Horner, M. S. Moss, and A. E. Rippon. 1970. Adrenocortical function in the horse. J. Endocrinol. 48:319-335. Mal, M. E., T. H. Friend, D. C. Lay, S. G. Vogelsang, and O. C. Jenkins. 1991b. Behavioral responses of mares to short term confinement and social isolation. Equine Vet. Sci. 11:96-102. McCall, C. A., G. D. Potter, J. L. Kreider, and W. L. Jenkins. 1987. Physiological responses in foals weaned by abrupt or gradual methods. J. Equine Vet. Res. 76:368-374. Monfort, S. L., N. P. Arthur, and D. E. Wildt. 1991. Monitoring ovarian function and pregnancy by evaluating excretion of urinary oestrogen conjugates in semi-free-ranging Przewalski's horses (Equus przewalskii). J. Reprod. Fertil. 91:155-164. Nett, T. M., D. W. Holtan, and V. L. Estergreen. 1973. Plasma estrogens in pregnant and postpartum mares. J. Anim. Sci. 37:962-970. Terqui, M., and E. Palmer. 1979. Oestrogen pattern during early pregnancy in the mare. J. Reprod. Fertil. 27(Suppl.):441-446. Thompson, D. L. Jr., F. Garza,
Jr., P. S. Mitchell, and R. L. St. George. 1988.
Effects of short-term stress, xylazine
tranquilization and anesthetization with xylazine
plus ketamine on plasma concentrations of
cortisol, luteinizating hormone, follicle
stimulating hormone and prolactin in
ovariectomized pony mares. Theriogenology.
30:(5)937-946.
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