ESTROUS RISE IN BODY-TEMPERATURE IN THE BOVINE .1. TEMPORAL RELATIONSHIPS WITH SERUM PATTERNS OF REPRODUCTIVE HORMONES

Identification and characterization of biological changes which occur near the time of ovulation may eventually provide improved means for determining the timing of this event. A rise in internal body temperature is associated with estrus in dairy cows, but temporal relationships between this temperature rise and other periovulatory events require further investigation. The objectives of this study were: (1) to determine the temporal relationships among changes in serum concentrations of luteinizing hormone (LH), estradiol, progesterone, and changes in body temperature that occur during the periovulatory period, and (2) to assess the consistency among individuals of these temporal relationships by comparing variabilities among cows of intervals between periovulatory events. Vaginal temperature was monitored in eight, nonpregnant, lactating dairy cows using temperature-sensing radiotransmitters. Serum concentrations of progesterone, LH, and estradiol were determined by radioimmunoassay (RIA). Temperature spikes were defined as sustained increases in temperature of ≥ 0.3°C. Intervals between various periovulatory events were calculated (e.g., LH peak to onset of temperature spike, estradiol peak to LH peak, etc.). Variances of these intervals among cows were then compared using an F-test and were considered significantly different if P was <0.05. The duration of elevated temperature averaged 8.14 ± 3.48 h (x ± s.d., n = 7). When variances of intervals were compared, the interval with the lowest variation among cows was the interval between peak LH and the onset of the temperature spike (s.d. = 4.54 h). The variation in this interval, as indicated by s.d., was significantly lower than the variation of the interval from the decline in serum progesterone to peak LH (4.54 h vs. 14.10 h, P < 0.005) and the variation of the interval from peak LH to peak estradiol (4.54 h vs. 11.51 h, P < 0.025). As such, the relationship between the LH surge and the onset of the temperature spike was the most consistent relationship examined. Thus, the temperature spike is a better predictor of the LH surge than the other physiological parameters investigated. Since ovulation occurs within a consistent interval after the LH surge, the temperature spike may be a good predictor of ovulation as well. © 1990.