| Abstrakt: |
Twenty-eight Hereford × Angus cows (4 yr of age) were used to determine the effects of pre- and postpartum dietary energy on performance and reproductive function in suckled beef cows. The experiment was designed as a 2 × 2 factorial with cows receiving either 70 (L) or 150% (H) of NRC recommended level of dietary energy before and(or) after parturition, resulting in four treatment combinations (L-L, L-H, H-L, H-H). Prepartum diets were fed for approximately 110 d, and postpartum diets were fed until either 10 d after the second postpartum ovulation or 150 d postpartum for those cows that failed to ovulate. Cows receiving low compared with high levels of energy before calving lost more (P<.01) weight, body condition, subcutaneous fat, and longissimus muscle area before parturition and had calves with lighter (P<.01) birth weights. Cows receiving low compared with high levels of energy postpartum lost more (P< .01) weight, body condition, and longissimus muscle area after parturition. Low levels of energy before and after parturition decreased (P<.01) milk production and calf weight at 70 d of age. Rates of cervical and uterine involution were unaffected by dietary energy treatments. Cows receiving high levels of energy prepartum had increased (P< .01) mean concentrations and pulse frequency of LH in serum after parturition, and cows receiving high levels of energy postpartum had increased (P< .05) pulse frequency of LH. Low levels of energy postpartum decreased (P<.01) appearance rate of small (5.0 to 7.9 mm) and large (≥ 10 mm) follicles, and low levels of energy prepartum decreased (P<.02) appearance rate of large follicles based on transrectal ultrasonography. Cows receiving high levels of energy prepartum had shorter (P< .02) intervals from parturition to ovulation, and a higher (P< .01) percentage of the cows that received high levels of energy postpartum ovulated by 150 d postpartum. In summary, prepartum level of dietary energy influenced birth weight and weight gain of calves, milk production, concentrations and pulse frequency of LH in serum, appearance rate of large follicles, and the interval to first ovulation. Postpartum level of dietary energy influenced milk production, weight gain of calves, pulse frequency of LH, appearance rate of small and large follicles, and the percentage of cows that ovulated after parturition. |
