Published online by Cambridge University Press: 02 September 2010
Sixty Large White d♂ × (Large White ♂ × Landrace ♀) pre-pubertal gilts were allocated at random to one of five treatments. Treatment consisted of a combination of three factors to induce puberty and maintain cyclicity: the administration of exogenous oestradiol benzoate (OB), the application of an orally active synthetic progestagen, allyl-trenbolone (AT), and exposure to mature boars. Treatment A gilts were given OB at 160 days of age (15 μg/kg body weight). This was followed by the administration of 20 mg/day of AT from 166 days of age for 18 days. These gilts were also allowed exposure to a mature boar for 30 min/day from 160 days of age until they were mated. Treatment B gilts were given OB at 160 days of age and were allowed boar exposure from 160 days of age but were not given AT. Treatment C gilts were given OB and AT but were not allowed exposure to a mature boar. Treatment D gilts were not given OB at the beginning of the experiment but were given AT for 18 days from 166 days of age and were allowed boar exposure. Treatment E gilts were not given any exogenous hormones but were allowed boar exposure from 160 days of age. The dose of OB was split equally into three bolus injections given on consecutive days beginning at 160 days of age. All gilts were mated twice during the first 2 days of their second oestrous period, and were slaughtered at either 25 days post coitum or at 220 days for anoestrous gilts.
The percentages of OB-treated gilts with normal oestrous cycles (oestrous cycles of between 15 and 30 days from one oestrus to the next) were: 91·7%(11/12), 45·5%(5/ll) and 58·3%(7·12) for gilts in treatments A, B and C respectively (P < 0·05). The OB-treated gilts (treatments A, B and C) attained puberty at a significantly younger age than did the control gilts in treatment E (F < 0·05). No significant differences were found in ovulation rate and the percentage embryo survival between treatments.
The results demonstrate that the combination of AT and boar exposure was an effective means of maintaining oestrous cycles in OB-treated gilts.
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