Puberty and early reproductive performance in sheep rams lambs

The attainment of puberty and early breeding performance in the ram lamb have been much less well studied than in the ewe lamb. There are very limited data available and only a few breeds have been included in such investigations. Sexual development and the attainment of puberty in ram lambs appear to be controlled by a mechanism, involving the brain and the anterior pituitary gland, which regulates both the synthesis and release of gonadotropic hormones. The completion of spermatogenesis, marked by the release of spermatozoa, is preceded by a steady rise in the level of androgen secretion and enhanced development such as testes descent and the breakdown of preputial adhesions, which are also under endoncrine control, are normally completed before puberty is attained. The length of the spermatogenic cycle is regarded as a biological constant, with spermatogenesis in the growing ram lamb proceeding in a way similar to that in the fully mature adult ram. However, the maximal efficiency of spermatogenesis, as indicated both by the quanlity of the spermatozoa produced, is not achieved until several months after puberty has been attained. In the work reviewed, it has been difficult to separate the effects of genetic and environmental factors. Sexual development, as indicated by the growth of reproductive organs and by the completion of spermatogenesis, appears to be more closely related to body growth than to chronological age. The level of nutrition during rearing, as reflected in growth rate and general body development, can have a marked influence on puberal development. Although the level of nutrition is probably of the greatest importance, other environmental factors such as daylight, an possibley temperature may effect sexual development and the attainment of puberty in ram lambs. However, there is a lack of critical work in this field. Certain forms of sexual behaviour may be noted in ram lambs at an early age. However, sucessful copulation with ewes does not take place until some time after physiological puberty has been attained. Selected ram lambs which produce semen of reasonably good quality may be used successfully for breeding, either by natural mating or by artificial insemination reduced generation interval resulting from the use of ram lambs for breeding may be of particular importance in performance - and progeny - testing programmes. Thus, information can be obtained on the breeding value of the ram at an early age. Genetic improvement may be further accelerated by breeding their female progeny as ewe lambs. There is no evidence to indicate that the use of ram lambs for breeding has any adverse effects on their subsequent growth and development