Increasing ovulation rate and lambing percentage by active immunization against androstenedione in dairy sheep breeds

A total of 1200 ewes, two hundred from each of six dairy breeds-the Karagouniko (K), the Serres (S), the Vlachiko (V), the Florinis (F), the Kimis (Km) and the Chios (Ch)-were used to examine the efficacy of a new immunogen (androstenedione-7a-HSA + DEAE-dextran) in improving reproductive performance. Ewes of each breed were randomly allotted to two groups, the control and the treated. Treated ewes were given two injections of 2 ml immunogen three weeks apart, while the control ewes were untreated. Rams were introduced to all ewes after the second injection. Twenty ewes in each group for each breed were laparotimized 7 to 10 days post-mating. Incidence of estrus and mating, the ovulation rate (OR), lambing percentage (Lp. 100), litter size (LS), and lamb (LbW) and litter weight (LW) were recorded. The OR was increased in immunized ewes compared to controls from 1.60, 1.46, 1.50, 2.50, 2.50 and 2.90 to 2.50, 2.06, 2.20, 3.20 (P<0.05), 4.20 and 4.80 (P<0.01), respectively, in K, S, V, F, Km and Ch breeds. No significant difference on Lp. 100 was observed between control and treated ewes of all breeds. The LS was increased in immunized ewes by 17, 20, 18, 28, 57 and 0 lambs compared to control ewes in K, S, V, F, Km and Ch breeds, respectively; however, the increase was statistically significant (P<0.05) only in Km and F breeds. The LbW was decreased in immunized ewes compared to controls; however, the decrease was statistically significant (P<0.05) only in the V breed. When compared to control ewes the LW was greater in immunized ewes of S, K, Km and F breeds while in Ch and V breeds LW was smaller. It was concluded that an increase in ovulation rate by active immunization against androstenedione may not be reflected in an increase of litter size in dairy sheep. Breed differences must be considered when producers intend to use this technique to improve litter size.