Influence of milk removal on patterns of luteinizing hormone (LH) in dairy cows and LH and prolactin (PRL) in crossbred sows

Abstract

Two experiments were conducted to evaluate the effect of mild removal, either by machine milking or suckling, on peripheral patterns of LH and PRL. In Experiment 1, blood samples were collected at 10-min intervals for 12 continuous hr beginning at 0600 hr from five lactating Holstein cows 12 [plus or minus] 2 days postpartum and again three days following the first observed estrus. On the day of blood sample collection, cows were machine-milked at 0400, 1400, and 1600 hr. Plasma levels of LH were quantitated by radioimmunoassay (RIA). The data were analyzed using both time and frequency domain methods of time series analysis. In the second experiment, blood samples were collected at 10-min intervals for 10 continuous hr beginning at 0700 hr from six intact and five ovariectomized multiparous crossbred sows, each nursing eight pigs, on either day 13, 14, or 15 postpartum. The pigs were allowed to suckle for five min at 0700, 0800, 0900, 1500 and 1600 hr. Following the 0900 suckling, litters were removed from the sows for 6 hr. Plasma levels of LH and PRL were quantitated by RIA. Due to the small number of observations during the periods of suckling and the dependent nature of the data, conventional statistical methods (t-test, interventional analysis, etc.) could possibly be misleading; therefore, the characteristic behavior of the data were described by visual appraisal. Systemic levels of LH fluctuated in a pulsatile manner in Holstein cows early postpartum (12 [plus or minus] 2 days) and three days following the first observed postpartum estrus. In four cows, the pulses were relatively small (ΔLH, .2-2.75 ng/ml) and occurred rather frequently (5-12 pulses/12 hr). In the remaining animal, the pattern of LH was obviously different in that basal levels during the initial segment of blood sample collection were 6- to 12-fold higher than levels in the other four cows. The results of this study indicate that rhythmic patterns of LH occurred in cows 12 [plus or minus] 2 days postpartum and on day three following the first observed postpartum estrus. The results further indicate that precisely controlled milking stimuli did not acutely affect the pulsatile release of LH in postpartum Holstein cows during either blood collection period; however, conclusions regarding a chronic effect could not be substantiated by these data...