ABSENCE OF RESPONSE TO ESTRUS INDUCTION AND SYNCHRONIZATION TREATMENTIS RELATED TO LIPID MOBILIZATION IN SUCKLED BEEF-COWS

Energy status, follicular growth, oestradiol and LH secretion were inv estigated in 17 suckled Charolais cows synchronised 59.0 +/- 3.6 days after calving with a 10 day ear implant containing 3 mg of Norgestomet . The cows received 3 mg of Norgestomet and 5 mg of oestradiol valerat e by IM injection at implant insertion (day 0) and 600 IU PMSG at impl ant removal (day 10). They were artificially inseminated (Al) 48 and 7 2 h after implant removal. Energy status was assessed by measuring wee kly plasma concentrations of non-esterified fatty acids (NEFA), beta h ydroxy-butyrate (BHB), glucose and insulin 7 weeks before AI. Progeste rone plasma concentrations were measured during the same period to ass ess the presence of a functional corpus luteum. Follicular growth was followed daily by ultrasonography from day -3 to day 13. Oestradiol se cretion was measured on day -3, day 6 and day 10 from five hourly samp les. Oestradiol and LH plasma concentrations were measured hourly from 29 to 48 h after implant removal for seven cows. Cows were checked fo r pregnancy by ultrasonography 45 days after AI. Pregnant cows (P) wer e compared with non-pregnant cows (NP) for energy status, follicular g rowth, and oestradiol secretion by split-plot ANOVA. Two cows (11.8%) were cyclic before treatment, seven ovulated after treatment (41.2%) a nd five were found pregnant 45 days after Al (29.4%). There was no dif ference in body condition score and body weight between P and NP cows on day 0 (2.5 +/- 0.2 and 685 +/- 24 kg vs 2.5 +/- 0.1 and 670 +/- 13 kg; P > 0.05). Mean plasma NEFA concentrations before treatment were s ignificantly lower in P than in NP cows (218 +/- 29 mu eq/L vs 279 +/- 18 mu eq/L; P < 0.05). No significant differences between P and NP co ws were found for BHB, glucose and insulin concentrations. P cows pres ented more medium sized follicles (5 mm less than or equal to diameter < 10 mm than NP females during the period of observation (2.65 +/- 0. 19 vs 2.50 +/- 0.12; P = 0.05). Plasma oestradiol concentrations were not different between P and NP cows on day -3 (8.4 +/- 0.7 pg/mL vs 7. 7 +/- 0.4 pg/mL, P > 0.05), day 6 (10.4 +/- 0.6 pg/mL vs 9.8 +/- 0.4 p g/mL, P > 0.05) but were higher in P than in NP cows on day 10 (10.9 /- 0.6 pg/mL vs 7.8 +/- 0.4 pg/mL; P < 0.05). After implant removal, o estradiol secretion only increased in P cows and a LH peak occurred wh ereas no increases in oestradiol (11.0 +/- 0.4 pg/mL vs 6.3 +/- 0.3 pg /mL, P < 0.05) and LH (6.0 +/- 0.5 ng/mL vs 1.2 +/- 0.5 ng/mL, P < 0.0 5) secretion were observed in NP cows. The conclusion was that follicu lar growth, oestradiol secretion, ovulation and pregnancy rate after o estrus synchronisation treatment are related to mobilization of energy stores before treatment in suckled beef cows in the same body conditi on score.