A study of sexual development in ram lambs

Abstract

Two experiments were designed to study the effect of rearing method, female company, and repeated libido and semen tests on the pattern of sexual development of ram lambs. Four artificial rearing treatments (AR) were compared with natural rearing (NR) in one experiment and four artificial compared with three natural rearing treatments in a second experiment. Lambs on AR treatments in both experiments, as well as naturally reared lambs in the second experiment, were reared with or without females either before and/or after weaning. Half the lambs in the second experiment were libido and semen tested, and their mean plasma testosterone level was also measured, while the rest were only tested at the end of the experiment. The effect of method of rearing and female company on body growth, testes diameter, libido and semen quality were also investigated.A close relationship was found between body weight and sexual characteristics (for example, testis diameter, semen traits, libido, testosterone level and age at the onset of sexual maturity). NR resulted in faster growth than AR but was not appreciably different from early weaned-naturally reared treatments. It was also observed that mating performance improved steadily with advancement in age and increase in body weight. The onset of sexual maturity was attained at a minimum of 23 kg body weight and a minimum of 198 days of age. However, the heavier the lamb when sexually mature, the better its mating performance.Previous libido tests of ram lambs improved their subsequent mating performance, but had no effect on semen quality. However, libido tests did not improve the performance of those ram lambs which did not exhibit initial libido.It is suggested that early weaning at 2 months of age could be a suitable system for ram lambs weaned off their mothers for breeding purposes. These lambs should be reared as an all-male group but libido tested at monthly intervals commencing at 3 months of age. The criteria for selecting these lambs at an earlier age should be body weight and testis diameter.

Reproductive and sexual behaviour development of dam or artificially reared male lambs

“…Al-Nakib et al [30] observed that lambs reared with their mother presented an earlier sexual development and a delayed sexual interest in oestrus ewes compared to artificially reared lambs. However, it is important to highlight that in the study of Al-Nakib et al [30] the amount of food that was offered to lambs artificially reared was not adjusted in relation to that received by lambs reared with their mothers, and thus, lambs reared with their mothers had greater body weight than those reared artificially. Although there were differences between both groups of lambs, in male lambs, prepuberal reproductive development is strongly influenced by body weight [31,32], confounding both effects.…”

Comparative performance of Omani goats and sheep

“…Young bucks showed some inferiority in their fertilizing ability compared to the experienced mature adults, and the gap was even wider between rams and young ram lambs, making the use of ram lambs for breeding purposes inadvisable. This problem in young ram lambs has been identified by many breeders and research workers (Dyrmundsson & Lees 1972;Zenchak & Anderson 1980;Al-Nakib et al 1986). The latter authors attributed this problem to the social environment under which these animals were reared, which adversely affected body growth and hence other correlated traits directly involved in sexual development.…”

Sexual activity and puberty in pure Awassi and crosses and backcrosses with Charollais and Romanov sheep breeds

“…Puberty can be defined as the time period when fertile spermatozoa are present intheejaculate (Beardenand&Fuquay 1997). Many sheep producers tend to use a relatively high percentage of ram lambs in their breeding program by 7 months of age (Al-Nakib et al 1986). Thus, they benefit from accelerating genetic improvement by using young rams for breeding (Price et al 1991).…”