Published online by Cambridge University Press: 02 September 2010
Sixty Large White ♂ × (Large White ♂ × Landrace ♀) pre-pubertal gilts were allocated at random to one of five treatments. Gilts on treatment A were given oestradiol benzoate (OB) at 160 days of age. They were also given allyl-trenbolone (AT) at 166 days of age for 18 days followed by an injection of gonadotrophins (Gn) at 184 days of age. Gilts on treatment B were given OB and AT, but not Gn. Gilts on treatment C were given OB and Gn, but not AT. Gilts on treatment D were given OB only and gilts on treatment E were given Gn only. Gilts which were in heat after 183 days of age were artificially inseminated twice during the first 2 days of oestrus. All gilts were slaughtered either 20 days after insemination or at 220 days of age if they were still anoestrus.
The percentages of gilts ovulating after Gn injection were 36% (4/11), 91·7% (11/12) and 91·7% (11/12) for treatment groups A, C and E respectively (P < 0·01). Gilts on treatments A, C and E were inseminated at a significantly younger age than those on treatments B and D (P < 0·05). No significant differences were found in ovulation rate or embryo survival between treatments.
The results indicated that the administration of AT prior to Gn injection had an adverse effect on both the percentage of gilts ovulating and the development of embryos.