Endocrine and reproductive response of beef cows to PMSG.

Thir ty-one 3-year-old Angus cows and 23 2-year-old Angus heifers were randomly allotted to two t rea tment groups to examine the influence o f PMSG on endocr ine and reproductive responses. Sixteen cows and 11 heifers received a single subcutaneous inject ion of 2,000 IU PMSG on day 17 o f the estrous cycle (Trt 17); 15 cows and 12 heifers received 1,500 IU PMSG on day 5 and 2,000 IU on day 17 (Trt "5, 17). Plasma progesterone, estradiol and LH concent ra t ions were quant i f ied in jugular b lood col lected at regular intervals during the t rea tment cycle. Trea tment with PMSG on days 5, 17 resulted in increased estrous cycle lengths in bo th cows (P<.05) and heifers (P<.10) compared to a single t r ea tmen t on day 17. The