The development of sexual activity, sperm production, semen characteristics, testis growth and body size was studies in 10 male sheep (ram lambs) of the Romanov breed and 11 of the Finnish Landrace breed between the ages of 4 and 15 months.
The sexual responses, observed daily for 40 days from the age of 4 months, developed earlier and more intensively in the Romanov than in the Finnish ram lambs, being fully developed in the former breed after 4 days as compared with 14 days in the latter breed. All lambs of both breeds, however, were considered capable of impregnating females by 5 months of age.
In both breeds there was a considerable delay between the onset of sexual maturity and the time at which it became possible to collect semen by means of an artificial vagina. Successful collection was not achieved until the age of 11 months, there being no difference between breeds in this respect.
Subsequent semen production increased to the 14th month of age, with little difference between breeds. Respectively for Romanov and Finnish rams at this age (±s.e.), the mean ejaculate volume was 0·85 + 0·062 and 0·77±0·052ml; motility 64·6 ± 1·62 and 59·7±l·66%; sperm concentration 4·75±0·198 and 4·7 ± 0·197 ×1012perl; number of sperm per ejaculate 4 09±0·338 and 3·63 ±0·259 × 109; and fructose concentration 6·84 × 0·2606 and 4·87 ± 0·2707g/1. In the 15th month there was a tendency for these values to decline except in the case of sperm concentration and, hence, total sperm number.
Mean live weight and size increased until the 14th month and there was no difference between breeds, but testis length and diameter were greater in the Romanov rams at this age.