Induction of pulsatile LH release, FSH release and ovulation in post-partum acyclic beef cows by repeated small doses of Gn-RH

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Abstract
Five acyclic spring-calving beef cows (20-40 days post partum) were bled eveXy 15 min for 60 h and thereafter every 6 h for 5 days. Gonadotropin releasing hormone (5 .mu.g) was injected every 2 h for 48 h, starting 12 h after sampling began. Pulsatile patterns of LH [luteinizing hormone] release occurred synchronously in response to injection and 4 of the 5 treated animals subsequently ovulated and completed at least 1 full ovarian cycle. Four of 6 similar control cows were bled every 10 min for 8 h periods at equivalent times post partum. Pulses of LH were seen after day 25 post partum with a mean pulse frequency of 0.5/h. There was little evidence of a discrete pulsatile mode of FSH release in any of the treated or control cows. The time to the first significant progesterone rise in the 4 treated and ovulating cows (34.5 .+-. 5.6 days post partum) was significantly shorter (P < 0.05) than in the 6 control animals (66.3 .+-. 11.4 days).