INFLUENCE OF POSTPARTUM ENERGY RESTRICTION ON ENERGY STATUS, PLASMA-LH AND ESTRADIOL SECRETION AND FOLLICULAR DEVELOPMENT IN SUCKLED BEEF-COWS

Effects of postpartum energy restriction, parity and time after partur ition on energy status (measured by glucose, insulin, non-esterified f atty acids (NEFAs) and beta-hydroxybutyrate), LH secretion and follicu lar growth were investigated in ten primiparous and nine multiparous s uckled cows. Females were allocated by parity, body mass and body cond ition score at calving to diets supplying either 100% (CE, n = 10) or 70% (LE, n = 9) of energy requirements until day 70 postpartum. Metabo lic parameters were measured every week from calving to day 70 postpar tum. Blood samples were collected at intervals of 15 min for 10 h on d ay 30 and day 50 after parturition for LH measurement. Ovaries were ex amined between days 20 and 30 and days 40 and 50 postpartum by ultraso nography. Energy supply affected mean plasma concentrations of glucose (CE: 0.64 +/- 0.01 g l(-1) versus LE: 0.61 +/- 0.01 g l(-1); P < 0.05 ) and NEFA (CE: 168 +/- 17 mu eq l(-1) versus LE: 309 +/- 18 mu eq l(- 1) P < 0.01) but by day 70 postpartum, glucose and NEFA concentrations were not significantly different between the two groups. LH pulse amp litude and frequency were not affected by energy supply (P > 0.10). Ho wever, at day 30 postpartum, LH pulse frequency was negatively correla ted with plasma concentration of NEFA (r = - 0.61; P < 0.01). Cows fed diets supplying 100% of energy requirements had more large follicles than did cows fed low energy diets (CE: 0.82 +/- 0.05 versus LE: 0.31 +/- 0.05; P < 0.05). The size of the largest follicle was greater in C E cows than in LE cows (CE: 10.2 +/- 0.1 mm versus LE: 8.7 +/- 0.2 mm; P < 0.05). Between 40 and 50 days postpartum, the size of the largest follicle was negatively correlated with NEFA concentration (r = - 0.5 ; P < 0.05). These results suggest that LH pulse frequency might be af fected by energy supply when energy balance was strongly negative, whe reas follicular growth was affected at a later stage, after parturitio n.