Effects of active immunisation of female lambs against androstenedione on LH secretion, onset of puberty and ovulation rate

Abstract

The aim of this experiment was to determine if immunisation of ewe lambs against androstenedione would increase luteinizing hormone (LH) pulse frequency and advance the time of onset of puberty. Belclare Improver ( n = 35) and Improved Galway ( n = 18) ewe lambs were randomized to treatments as follows: (1) control, (2) immunisation with an androstenedione-protein conjugate (Fecundin, Glaxo Animal Health, U.K.) on two occasions, 9 August and 7 September. Ewe lambs were bled for determination of antibody titres, progesterone and LH concentrations. They were also checked for oestrous behaviour and examined by endoscopy to monitor ovulatory activity. Immunisation against androstenedione did not affect date or age of first ovulation or first oestrus. However, it did increase ( P < 0.01) ovulation rate at first ovulation in Belclare Improver (1.18 and 1.77 in control and immunised ewes, respectively) and in Improved Galway ewe lambs (1.23 and 1.35 in control and immunised ewes, respectively). Ovulation rate at first oestrus was increased ( P < 0.05) in Belclare Improver (1.51 and 1.97 in control and immunised ewes, respectively) and in Improved Galway ewe lambs (1.29 and 1.53 in control and immunised ewes, respectively) and there was a significant breed effect. Immunisation increased ( P < 0.05) LH pulse amplitude (1.39 and 1.81 for control and immunised) but had no effect on any other characteristic of LH release. Immunisation of prepubertal ewe lambs against androstenedione increased ovulation rate and LH pulse amplitude but did not affect the time of onset of puberty.