Fertility of yearling beef bulls during mating

Abstract

Crossbred (Bos taurus) yearling beef bulls were assessed for breeding soundness and physical traits prior to multi-sire natural mating at pasture. Bulls (n = 60) were assigned to six groups of nine or 10 bulls and two bull-groups were rotated on 14-day intervals during a 63-day mating season in each breeding herd (n = 3) of 191-196 cows. The remaining bulls (n = 14) were maintained under similar environmental conditions without mating exposure. Bulls were observed during mating and assessed for breeding soundness and changes following mating. Bulls used for breeding (UFB) lost 77 kg of body weight and declined from body condition scores of 6 to 4.5, whereas bulls not used for breeding (NUB) maintained body condition scores of 6 and gained 27 kg. The UFB bulls incurred a 75% total injury rate with 63% incidence of lameness and 12% incidence of reproductive injuries, resulting in a 22% attrition rate. Only 45% were physically sound at the end of mating. Scrotal circumference declined in UFB bulls (À4.58%) and increased in NUB bulls (2.49%). From the 98% BSE-satisfactory rate (UFB) prior to breeding, only 61% were BSE-satisfactory post-breeding. The NUB bulls declined from 57 to 36% satisfactory. The BSE classification was influenced by significant increases in abnormal spermatozoa (primary and secondary), which was significantly associated with injuries incurred during mating. Group and breed differences in injury rates and BSE-status following mating were evident. Environmental conditions and mating activity influenced bull seminal quality and physical condition. Pregnancy rates in all three breeding herds (91-96%) were similar, with insignificant differences between bull-groups; the effects of physical and reproductive changes on individual bull fertility were immeasurable. #

Reproductive success or failure in four breed groups of beef bulls

“…The physical causes of failure are consistent with other findings (McGowan et al, 2002;Cumming, 2003), suggesting that bulls develop problems along their service in the field (Ellis et al, 2005), especially in large natural pasture areas with irregular topography, which requires more physical activity during the breeding season. The mounting activity over the years leads to a natural wear of the bull's physical ability, mainly affecting the locomotor system.…”

“…It is well-documented that bull selection affects the performance of the herd (Parkinson, 2004;Ellis et al, 2005); therefore the use of reliable methods to evaluate the reproductive potential, such as the bull breeding soundness evaluation (BBSE), is critical in ranch management.…”

A Perspective on the Impact of Reproductive Technologies on Food Production in Africa

“…An overall breeding soundness examination (OBE) is a quick, reliable and cost-effective method of screening and classifying bulls in terms of breeding potential (Ellis et al 2005). The latter as well as fertility tests before the onset of the breeding season contribute significantly towards better conception rates in beef herds.…”

Relationship between production characteristics and breeding potential of 25-month old extensively managed Bonsmara bulls

“…Yearling beef bulls are an important component of natural mating schemes and the principal method employed to assess the reproductive potential of the bulls, and thus selection of the bulls, is by overall breeding soundness examinations (OBE) (Ellis et al, 2005). An OBE is a quick, reliable and cost-effective method of screening and classifying bulls in terms of breeding potential and thereby minimizing the use of sub-fertile bulls.…”

“…Yearling beef bulls are typically selected as potential herd sires on their performance in a growth performance test. Data are lacking on the relationship between performance test results and reproductive parameters, but previous results suggested that an unfavourable relationship exists (Ologun et al, 1981;Ellis et al, 2005).…”