Estrogen concentrations in milk at estrus and ovulation in dairy cows

Abstract

The objective of this study was to determine the efficacy of using milk estradiol-17β (E 2) sampled during regular milking periods as a predictor of estrus in dairy cows. Twenty-three primiparous Holstein cows received radiotelemetric transmitters on day 16 of the estrous cycle (day 0=estrus) for continuous monitoring of behavioral estrus. Milk and blood samples were collected every 12 h at each milking, from day 18 of the estrous cycle until the fourth milking after the onset of estrus, for radioimmunoassay of E 2. Onset of estrus was indicated by the first standing event identified by radiotelemetry. Ultrasound examination of ovaries was conducted daily in a subset of cows ( n=17) from day 18 until ovulation was confirmed. Statistical analysis involved utilization of Pearson correlation to observe any association of mean plasma and milk E 2 concentrations. Intervals from highest measured plasma and highest measured milk E 2 until the first expression of standing behavior and intervals from highest measured plasma and highest measured milk E 2 until ovulation were compared using Student’s t-test. Repeated measures were utilized to evaluate the effect of day and time on milk E 2 concentration. Chi-square procedures were utilized to detect differences in actual time of onset of estrus compared to the expectation of random time of onset of estrus throughout the 24 h day. Mean duration from highest measured milk E 2 until onset of standing behavior was 21±3.7 h and until ovulation was 46.7±5.3 h. Mean duration from onset of standing behavior until ovulation was 26.4±4.2 h. Mean milk E 2 concentrations increased ( P<0.01) from the fourth milking period before estrus to the milking period immediately before the first expression of standing behavior, followed by a reduction ( P<0.01) in mean concentrations at the milking immediately after the onset of estrus.