Effect of immunization of ewes against prostaglandin F-2α on the life-span of corpora lutea and oestrous behaviour during two breeding seasons

Abstract

Two adjuvants, Freund's complete adjuvant (FCA) and GNE (proprietary product; Intervet Ltd, The Netherlands), were used to immunize cyclic Finnish Landrace ewes (4-6/treatment) against a prostaglandin F-2α-human serum albumin (PGF-HSA) conjugate. Ewes were randomized to the following treatments: (a) control-untreated, (b) control-5 mg HSA in FCA (control-HSA), (c) 5 mg PGF-HSA in FCA (FCA-5 mg), (d) 15 mg PGF-HSA in FCA (FCA-15 mg), (e) 5 mg PGF-HSA in GNE (GNE-5 mg) and (f) 15 mg PGF-HSA in GNE (GNE-15 mg). Ewes were monitored for oestrus (twice daily) and ovarian activity (progesterone concentrations in blood samples taken twice weekly) for 2 consecutive breeding seasons. In the first breeding season, the mean number of oestrous periods detected was 6.0, 5.7, 0.0, 0.2, 1.8 and 0.5 in control, control-HSA, FCA-5 mg, FCA-15 mg, GNE-5 mg and GNE-15 mg-assigned ewes, respectively [pooled standard error of difference (s.e.d.) = 1.2]. A persistent CL formed, on average, 10.0, 10.0, 29.8 and 32.5 days after primary immunization (pooled s.e.d. = 14.6) in 6/6 FCA-5 mg, 6/6 FCA-15 mg, 5/6 GNE-5 mg and 4/4 GNE-15 mg-assigned ewes, respectively; these CL were maintained for, on average, 138.7, 139.0, 127.8 and 129.0 days, respectively (pooled s.e.d. = 15.9). Antibody titres (log transformation of dilution of plasma that bound 40% of radiolabelled PGF), determined monthly, did not decline during anoestrus and therefore high antibody titres persisted into the second breeding season [3.5, 3.1, 2.3 and 2.5; FCA-5 mg, FCA-15 mg, GNE-5 mg and GNE-15 mg, respectively (pooled s.e.d. = 0.5)]. The first CL formed after ovulation at the onset of the second breeding season was maintained for, on average, 134.8, 145.8, 139.0 and 116.5 days (pooled s.e.d. = 15.7) in 5/6 FCA-5 mg, 5/6 FCA-15 mg, 2/6 GNE-5 mg and 2/4 GNE-15 mg-assigned ewes, respectively. These results demonstrate the efficacy of a PGF-HSA conjugate to induce a persistent CL which lasted for ~ 135 days and suppressed oestrous behaviour. These CL regressed during anoestrus and the first CL of the second breeding season persisted for a similar length of time.