Bovine Vaginal Circulation: Changes During Estrous Cycle * R. M. A B R A M S 2 , W . W. T H A T C H E R 3, J. R. C H E N A U L T 3, and C. J. W I L C O X 3 Departments of Obstetrics and Gynecology 2 , and Dairy Science 3 University of Florida Gainesville 32611

between vaginal tissue and arterial blood in sheep (4) and between uterine tissue and arterial blood in cows (9) and sheep (1, 3). Other proof of effects of estrogen on blood flow in sheep has resulted from such techniques as blood flow devices around a uterine artery (8, 10) .and direct collection of uterine venous blood (2). Recent work in normally cycling sheep indicated that significant increases in vaginal thermal conductance, and thus in vaginal blood flow, occur 1 day prior to onset of behavioral estrus (5). If such a change occurs in dairy cattle, advantages of utilizing such information in an AI program are obvious. Our preliminary observations on vaginal thermal conductance (Kvag) in heifers and cows are presented herein.

ABSTRACT

Vaginal thermal conductance was measured in 12 heifers and 7 cows with a gradient layer heat flow probe. Values rose for 4 to 5 days prior to day of behavioral estrus (day 0), with a peak on days - 2 and - 1 , and then declined from day 0 to +5. Curves for heifers were higher than those for cows although there was no evidence that they were n o t parallel. Changes during the estrous cycle appear to result from estrogen-induced alterations in blood flow rate in vaginal tissues. INTRODUCTION

Decision of proper time of artificial insemination (AI) requires processing of considerable information by dairymen. Of greatest importance is presence or absence of behavioral estrus as manifest by increased activity, mounting other cattle, and most importantly standing when mounted. The presence of cervical mucus and, in many instances, swelling and redness of the vulva or vaginal introitus are associated signs of estrus. High plasma estradiol concentrations have been implicated in inducing these physiological changes associated with estrus because of their ubiquitous effects on accumulation of tissue water and on blood flow (4). Direct evidence that estrogens produce vaginal hyeremia in cattle was documented by monitoring vaginal thermal conductance before and after injection of estradiol-17¢3 intravenous (6). Similar estrogen-induced increases in blood flow of the reproductive tract have been inferred from decreases in temperature difference

Received January 14, 1975. 1Florida Agricultural Experiment Station Journal Series No. 5750.

MATERIALS AND METHODS

Design and operating characteristics of the vaginal probe used in these experiments were described (6). Briefly, a copper-constantan thermo-electric gradient layer was glued to the outside of a hexagonal cylinder through which water circulated at 20 C. When this was placed in the vagina, a temperature difference was established across the gradient layer producing an electrical signal proportional to heat flux into the probe. Voltage was recorded and probe removed at the end of 5 rain. Rate of heat transfer or thermal conductance (calories per minute per C difference between vagina and water) is in part determined by rate of blood flow in the vaginal wall. Twelve heifers and seven cows, accustomed to the barn and research protocol, were used to characterize changes in Kvag associated with pre- and post-estrus stages of the cycle. Age, stage of estrous cycle, and parity were known for all animals. Vaginal thermal conductance was recorded daily (n = 163) over 5 to 11 days between days - 1 0 to +12 of the estrous cycle (day of estrus designated day 0). Statistical analysis was by the method of least squares.

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TECHNICAL NOTE RESULTS A N D DISCUSSION

Regression c u r v e s o f vagina] t h e r m a l cond u c t a n c e for heifers and cows are in Fig. 1.

Changes in Kvag for heifers (Kvagtt), cows (KvagC), and p o o l e d within heifers and cows (KvagP) were represented best by 5th, 3rd, and 5th order equations, respectively: [YKvagH = 13.652 -- 2 6 . 0 6 8 X + 71.250X 2 -- 74.448X 3 + 33.1306X 4 5.2725X s ; R ~ = .196. ~-LKvagC = 1.152 + 2 7 . 5 6 0 X - 2 4 . 1 4 5 X 2 + 6 . 5 6 6 X 3 ; R ~ = .193. "QKvagP = 13.144 -- 2 5 . 2 6 7 X + 6 9 . 6 0 5 X 2 - 7 3 . 1 7 9 X 3 + 3 2 . 7 6 3 5 X 4 - 5.2442X s ; R 2 = .162; where X = t i m e in days expressed as deviations from day of estrus plus 11, sum divided by 10, and R ~ = coefficient of multiple d e t e r m i n a t i o n ] . Least squares analysis is in Table 1. Test of h e t e r o g e n e i t y of regression for the fifth order equations (KvagH , KvagC , KvagP) revealed no evidence that curves were not parallel. Vaginal thermal c o n d u c t a n c e regression, pooled within animals, rose rapidly 4 to 5 days prior to day 0 and reached a peak b e t w e e n days - 2 and 1 on the average, w h e n plasma

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FIG. 1. Vaginal thermal conductance changes in heifers and cows during the estrous cycle.

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TABLE 1. Least squares analysis for vaginal thermal conductance (Kvag). Source

d.f.

M.S.

Age group a Among heifersb Among cowsb Common regression (days) c Regression heterogeneity d Residual

1 11 6 5 5 134

39.18"* 5.35** 1.29" * 6.29" * .05 .30

aGroups were heifers and cows. bAnimals nested within age group. Cpooled within age group 5th order regression. dHeterogeneity between two age group 5th order regressions. **P