A NOTE ON ATTAINMENT OF PUBERTY OF SEPTEMBER-BORN EARLY-MATURING EWE LAMBS IN RELATION TO LEVEL OF NUTRITION

The attainment of puberty in September-born early-maturing ewe lambs was studied at Zaragoza (latitude 41-degrees 40' N). Thirty twin Salz females were allocated to two groups receiving two nutrition levels after 3 months of age: high (500 g/day lucerne hay and 500 g/day concentrate) (H) and low (500 g/day lucerne hay) (L). Oestrus was detected daily by aproned rams. Corpora lutea were counted after oestrus and plasma progesterone levels monitored each week. In the first breeding season (January to February) the percentage of females showing sexual activity (silent ovulation or oestrus and ovulation) was higher in the H compared with the L group (67 and 20%; P < 0.05). Nonpubertal oestrus before the main breeding season was detected in 67% of animals. In the main breeding season and for H and L groups respectively, percentage of females showing silent ovulation before puberty was 67 and 33% and mean age at puberty extended to 319 (s.e. 4.8) and 314 (s.e. 3.7) days. Ovulation rate at puberty was 1.73 (s.e. 0.13) and 1.33 (s.e. 0.15) respectively (P < 0.05).