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Effect of a teaser bull on ovarian and behavioural activity of suckling beef cows

Abstract:

Two experiments to determine the effect of the presence of the bull on the sexual activity of suckling beef cows were carried out. In Experiment 1, carried out in spring (October-November), 105 cows were allocated to two groups. The treated group (T) was placed in contact with two vasectomised bulls, 58 days postpartum, while the control group (C) was set apart from T and not allowed contact with bulls. Oestrus detection was performed twice a day disregarding the activity of the bull; blood samples were taken every 7 days to determine progesterone levels and to detect ovulations. Observations were made for 28 days. The cows in both groups gained weight during this period. In group T, the proportion of animals in heat and ovulating was higher than in C at the end of the test period (in heat 67.9% vs. 32.7%, P<0.01; ovulating 73.6% vs. 40.4%, P <0.01). In group C, there was a larger proportion of silent heats (42.9% vs. 28.2%). In Experiment 2, carried out in winter (June-July), nine cows were placed in contact with a vasectomised bull within 10 days postpartum (T2), while nine others were set apart and not allowed contact with a bull (C2). For 100 days, oestrus detection was performed twice a day, the ovaries were palpated and blood samples were taken twice a week and cows were weighed weekly. Both groups lost 17% of their weight. There were no significant differences between groups in the interval from parturition to oestrus (T2 55.6 ± 12, C2 67.3 ± 17 days; P> 0.05) and from parturition to onset of ovarian activity determined by rectal palpation (T2 45.6 ± 21, C2 47.2 ± 12 days; P> 0.05). The interval from parturition to ovulation was lower in C2 (T2 53.2 ± 15, C2 36.3 ± 13 days; P < 0.05). In groups C2 and T2 respectively, 89% and 22% of the ovulations were not followed by oestrus. Therefore, contact with a bull results in an increased incidence of oestrus and stimulation of ovarian activity, the latter being observed only under some conditions. © 1987.