| Abstract: | Ten primiparous heifers were used in this experiment to evaluate the effects of suckling and nonsuckling on return to estrus and circulating serum levels of luteinizing hormone and prolactin. Three suckled heifers returned to standing estrus at a mean interval of 76 days. Five nonsuckled heifers returned to estrus within 43 days but the interval was not significantly different from that of the suckled heifers (P>.05). The postpartum serum LH values for three nonsuckled and two suckled heifers ranged from a low value of .4 ng (NIH-LH-B8)/ml to a high value of 65 ng/ml. Each heifer exhibited a sharp LH peak of 10.5 ng/ml to 65 ng/ml of serum during the period of standing estrus. One suckled animal exhibited an LH peak 28 days prior to her first observed standing estrus. ... |
|---|