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

Summary. Five acyclic spring-calving beef cows (20–40 days post partum) were bled every 15 min for 60 h and thereafter every 6 h for 5 days. Gn-RH (5 µg) was injected every 2 h for 48 h, starting 12 h after sampling began. Pulsatile patterns of LH release occurred synchronously in response to injection and 4 of the 5 treated animals subsequently ovulated and completed at least one 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 approximately Day 25 post partum with a mean pulse frequency of 0·5 per 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).