INFLUENCE OF FLUSHING ON LH-SECRETION, FOLLICULAR-GROWTH AND THE RESPONSE TO ESTRUS SYNCHRONIZATION TREATMENT IN SUCKLED BEEF-COWS

The effects of energy supplementation (flushing) on LH and estradiol s ecretion, follicular growth and the response to estrus synchronization treatment (Norgestomet+PMSG initiated 41.9+/-3.4 d after calving) wer e investigated in 16 suckled beef cows fed either 70% (Group C, n=8) o f energy requirements from calving to 3 wk after AI or fed the same re stricted diet until 11 d before synchronization and then were suppleme nted with 2 kg concentrate until 3 wk after Al (Group S, n=8). Concent rations of LH and estradiol 17 beta were measured from 3 sampling peri ods : 25 and 39 d after calving and between 29 and 49 h after implant removal. Ovaries were examined by ultrasonography 11 d before treatmen t to implant withdrawal OR). The effects of energy level, day (or hour ) of observation and corresponding interactions were tested on repeate d measurements by split-plot ANOVA. No positive effect of flushing was observed on characteristics of LH secretion on Day 39. However, the s ize of the largest follicle and the number of large follicles were hig her in Group S than in Group C cows,respectively, 7 and 9 d after the beginning of flushing to 2 d after the start of treatment. After IR, t he estradiol secretion tended to be higher in Group S than in Group C cows (9.8+/-0.4 pg/mL vs 7.2+/-0.2 pg/mL; P=0.06), but no effect on LH secretion was observed. After implant removal 12 cows ovulated (Group S:7/8 vs Group C:5/8; P>0.05), 7 were pregnant at 21 d after AI (Grou p S :6/8 vs Group C :1/8; P<0.05) and 4 at 45 d after AI (Group S: 4/8 vs Group C 0/8; P>0.05). To conclude, flushing had a positive effect on follicular growth, which does not seem to be mediated by LH. In cow s fed a restricted diet, flushing enhanced follicular growth, increase d the fertilization rate and/or reduced early embryonic death. (C) 199 8 by Elsevier Science Inc.