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

[摘要] English: A study to evaluate the effect of season (ambient temperature, daylight length andrelative humidity) and nutrition on the reproductive potential and sexualcharacteristics of young Boer goat bucks was carried out between June (winter) andNovember (spring), 2000. This study was carried out at the University of the FreeState 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 bodyweight. 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 totalmixed diet based on Themeda triandra (Red grass) summer hay, supplemented withmaize 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 tothe observation period, all the bucks were subjected to a prescribed diet foradaptation, for a period of 4 weeks. Then 2 weeks prior to the observation period ofthis 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 artificialvagina. Apart from the different nutritional management, both groups were housedand 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 andspring). In order to have a more realistic and accurate measurement an average of thetwo measurements taken per week (i.e. semen volume, mass motility etc.) was used asa measurement for the respective week. The following semen parameters wereevaluated: 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 skinthickness and libido) as well as rectal temperature and body weight was recordedevery 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 youngBoer goat bucks observed during this trial, were markedly influenced by the week(season) in which semen was collected, although no clear seasonal trend wasobserved. In general the animals on the higher nutritional plane diet tended to recordhigher serum testosterone levels and superior semen and testicular characteristicscompared to those from the group maintained on a lower plane of nutrition. Thesedifferences however were only significant at certain times of the observation period. Itcan be also concluded that the Boer goat buck maintains its libido and satisfactorypotential fertility (testicular characteristics and semen quality) during the winter(outside the natural breeding season). The effect of season and nutrition on thefertility of Boer goat bucks would have been better evaluated, had this study beencarried out for all 4 seasons of the year and the nutritional differences been moreextreme.

[发布机构] University of the Free State