Journal of Animal Science, Vol 72, Issue 10 2703-2708, Copyright © 1994 by American Society of Animal Science

JOURNAL ARTICLE

Body energy reserves influence the onset of luteal activity after early weaning of beef cows

D. K. Bishop, R. P. Wettemann and L. J. Spicer
Animal Science Department, Oklahoma Agricultural Experiment Station, Stillwater 74078-0425.

The influence of body energy reserves on the onset of luteal activity and concentrations of LH and IGF-I in serum was evaluated in postpartum anestrous beef cows after early weaning. Multiparous Hereford and Hereford x Angus cows (n = 24) were fed during gestation to establish body condition scores between 3 and 6 (BCS, 1 = emaciated; 9 = obese) at parturition. Concentrations of progesterone in plasma were determined weekly for 5 wk postpartum (PP). Anovulatory cows and their calves (n = 19) were confined in stalls on d 40 +/- 3 PP. Jugular cannulas were inserted on d 44 +/- 3 PP, and calves were weaned (d 0) the following day. Blood samples were collected from all cows for 4 h (every 10 min) before weaning and on d 1, 2, 4, 6, 8, and 10 after weaning and LH was quantified. Progesterone was quantified in daily blood samples until d 10, and in samples taken twice weekly until d 46. Within 25 d after weaning, 100% of the cows with BCS < or = 5 at weaning (n = 7) had initiated luteal activity, whereas only 43% (P < .01) of the cows with BCS < 5 (n = 12) had luteal activity. Mean serum IGF-I concentrations were correlated with BCS (r = .50; P < .05). Frequency of LH pulses was influenced (P < .01) by body condition at weaning but was not influenced by day after weaning. The number of LH pulses at weaning, serum IGF-I, and the interval to the onset of ovarian activity after early weaning of anestrous beef cows were influenced by BCS.

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