Influence of the type of energy supply on LH secretion, follicular growth and response to estrus synchronization treatment in feed-restricted sucklerbeef cows

The present experiment aimed to compare the efficiency of supplementation ( +17.5 MJ Net Energy/d starting 47 +/- 4 days after calving) with concentrat e (CS, maize grain, n = 10) or with forage (FS, maize silage, n = 10) in es trus-synchronized (Norgestomet implant 10 days inserted 60 +/- 4 days postp artum + PMSG at implant removal) beef cows previously restricted (47 MJ Net Energy/d, 785 g CP/d, 70% of requirements). The type of diet had no signif icant effect on basal LH concentrations (CS: 0.18 +/- 0.12 vs FS:0.11 +/- 0 .02 ng/mL), LH pulse frequency (CS: 0.7 +/- 0.3 vs FS :0.8 +/- 0.2 pulse/10 h), LH pulse amplitude (CS:0.55 +/- 0.50 vs FS :0.62 +/- 0.50 ng/mL) or es tradiol (E2) concentrations (CS: 3.3 +/- 0.8 vs FS: 4.6 +/- 0.8 pg/mL) 13 d ays after the beginning of energy supplementation. No differences between C S and FS cows were observed for the number of small, medium and large folli cles nor on the size of the largest follicle from 11 days before implant in sertion to implant removal (IR). After IR, an LH surge was observed in 2 of the CS and 4 of the FS cows. The type of energy supplementation had no sig nificant effect on LH (CS: 0.16 +/- 0.06 ng/mL vs FS 0.48 +/- 0.06 ng/mL; P >0.05) or on estradiol concentrations (CS:7.8 +/- 0.2 vs FS: 8.9 +/- 0.2 pg /mL, P<0.10) measured hourly from 29 to 49 h after IR. Cows that ovulated a fter IR tended to have higher E2 concentrations than cows that did not ovul ate (9.4 +/- 0.2 vs 6.3 +/- 0.2 pg/mL, P=0.08). Similar ovulation and pregn ancy rates were observed in CS and FS cows (CS: 6/10 vs FS: 7/10 and CS: 6/ 10 vs FS: 5/10 respectively, P>0.05). To conclude, energy supplementation w ith forage was as effective as energy supplementation with concentrate to i nfluence follicular growth, ovulation and pregnancy percentage after estrus synchronization treatment in diet-restricted beef cows. (C) 2000 by Elsevi er Science Inc.