The influence of loss and gain of body mass on ovarian activity in beef cows

Author: B.P. Louw, C.R. Thomas & A.W. Lishman
Year: 1988
Issue: 1
Volume: 18
Page: 1 - 7

Ovarian activity was studied in 36 dry, Bos taurus cows fed to achieve different rates of body mass loss and gain in a 2 x 2 factorial experiment. Cows were fed hay to supply either 70% (Treatments 1, 2) or 40% (Treatments 3, 4) of their ME requirements for maintenance until they became anoestrus. Following a 90-day period during which body mass was maintained the animals were fed hay ad lib. and either 1 kg (Treatments 1, 3) or 4 kg (Treatments 2, 4) of maize per cow per day until they resumed luteal activity. During the initial 14 days after maize feeding commenced each cow was weighed every second day in order to obtain an estimate of gutfill. Oestrous activity was monitored twice daily by observing marker bulls joined with cows. Ovarian activity was assessed each week throughout the trial by palpation of the ovaries per rectum. Ovarian activity did not cease in four cows, despite a loss of about 31% of initial mass. One cow died during the course of the experiment. Thirty one cows lost approximately 100 kg or 21% of their initial mass, and 1,1 condition score points over a period of about 5 months before they became anoestrous. Treatment did not influence mass and condition losses and gains and the time taken for cows to cease and resume ovarian activity. Gutfill was estimated at 25,9 ± 10,5 kg. Cows were between 35 and 57 kg heavier (P < 0,01) at the resumption than at the cessation of ovarian activity. The estimate of gutfill in each cow was subtracted from the actual mass at resumption of ovarian cycles. At the resumption of ovarian activity the mean adjusted mass (389,9 ± 44,9 kg) was significantly (P < 0,01) greater than that at the cessation of ovulatory cycles (368,6 ± 39,1 kg). The mean condition score at resumption of ovulation (2,35 ± 0,34) was also significantly (P < 0,01) higher than that at cessation of ovarian activity (1,72 ± 0,37). Treatment did not influence conception rates in cows. Over all treatments 85% of the cows conceived to service at the resumption of ovulatory activity.





Keywords: anoestrus, beef, body mass, Cows, ovarian activity
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