Limited multiple ovulation in heifers fed high plane of nutrition before PMSG stimulation and steroid hormone concentrations in single, twin and multiple ovulators.
Limited multiple ovulation (2-4 CL's) in heifers was attempted by feeding a low or a high plane of nutrition during an estrous cycle and injecting a low dose of PMSG at day 16 of that cycle. Multiple ovulation was achieved in 52% of the 19 dairy x beef crossbred heifers that received 1200 I.U. of PMSG. The ratio of the number of heifers which ovulated between 2-4 follicles to those ovulating 1 and more than 4 was higher (P<0.05) in heifers which were fed a high plane of nutrition than in those which were fed a low plane of nutrition. Thirty-six hours after the PMSG injection and prior to estrus, the concentration of E(2)-17beta was less in heifers with 1 growing follicle developing into 1 CL than in heifers with 2 or >2 growing follicles developing into CL's (P<0.01). Heifers with >2 growing follicles developing into CL's had more E(2)-17beta than those which eventually formed 2 CL's (P<0.01). Moreover, in heifers with >2 CL, E(2)-17beta concentration increased regularly until at least 96 hrs after the PMSG injection, while in heifers with 1 CL or 2 CL's, the concentration plateaued at 60 hrs after the PMSG injection. Progesterone concentration during proestrus was lower in heifers that developed >2 CL's than in those with 1 or 2 CL's (P<0.05).
Dufour
J J
JJ
Research Station, Agriculture Canada, Lennoxville, Quebec JIM IZ3, Canada.
Adelakoun
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V
Matton
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