The effect of season and nutrition on the reproductive potential and sexual characteristics of Boer goat bucks

English: A study to evaluate the effect of season (ambient temperature, daylight length and relative humidity) and nutrition on the reproductive potential and sexual characteristics of young Boer goat bucks was carried out between June (winter) and November (spring), 2000. This study was carried out at the University of the Free State campus in Bloemfontein, South Africa. Twelve Boer goat bucks with a mean initial age of 12 months were used in this study. These bucks were divided into two similar experimental groups, with regard to body weight. A high nutritional plane diet was randomly allocated to one group (Group H) and a low nutritional plane diet was allocated to the other group (Group L). The total mixed diet based on Themeda triandra (Red grass) summer hay, supplemented with maize meal, molasses, HPK 40, HPK 60 and lucerne at two different nutritional levels (High and Low) was given ad lib to the two respective experimental groups. Prior to the observation period, all the bucks were subjected to a prescribed diet for adaptation, for a period of 4 weeks. Then 2 weeks prior to the observation period of this trial, each group received their respective treatment diets. During these 6 weeks, the experimental bucks were trained for semen collection with the aid of an artificial vagina. Apart from the different nutritional management, both groups were housed and managed under similar conditions. Semen samples from each buck were collected by means of an artificial vagina. Semen was collected twice weekly throughout the observation period (winter and spring). In order to have a more realistic and accurate measurement an average of the two measurements taken per week (i.e. semen volume, mass motility etc.) was used as a measurement for the respective week. The following semen parameters were evaluated: semen volume, semen colour, mass motility, sperm concentration, percentage live sperm and percentage abnormal sperm. Other sexual characteristics (serum testosterone concentration, scrotal circumference, testes volume, scrotal skin thickness and libido) as well as rectal temperature and body weight was recorded every second week concurrently with semen collection. The environmental factors (ambient temperature, daylight length and relative humidity) were recorded daily. From this study it can be concluded that the semen and sexual characteristics of young Boer goat bucks observed during this trial, were markedly influenced by the week (season) in which semen was collected, although no clear seasonal trend was observed. In general the animals on the higher nutritional plane diet tended to record higher serum testosterone levels and superior semen and testicular characteristics compared to those from the group maintained on a lower plane of nutrition. These differences however were only significant at certain times of the observation period. It can be also concluded that the Boer goat buck maintains its libido and satisfactory potential fertility (testicular characteristics and semen quality) during the winter (outside the natural breeding season). The effect of season and nutrition on the fertility of Boer goat bucks would have been better evaluated, had this study been carried out for all 4 seasons of the year and the nutritional differences been more extreme.