Oral Presentation The Annual Scientific Meeting of the Endocrine Society of Australia and the Society for Reproductive Biology 2014

Intensive feeding and management reduces semen quality of Santa Gertrudis bulls (#7)

Matthew Callaghan 1 , Juan Hernandez Medrano 2 , Viv Perry 2
  1. School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, South Australia, Australia
  2. School of Veterinary and Medical Science, University of Nottingham, Sutton Boddington, LE12 5RD, UK

Breeding bulls in northern Australia are commonly fed high energy diets post weaning. This practice is associated with a reduction in the reproductive potential of these bulls (Holroyd et al. 2005). This study examines alternative practices prior to pre-sale feeding that may alleviate deleterious effects and investigates factors leading to such perturbation.
Primiparous Santa Gertrudis beef heifers with bull calves (n = 61) were randomly allocated to high (H) or low (L) nutrition during the pre-weaning period. Pasture construed the only component of L diet whilst H dams accessed protein pellets ad libitum during lactation. Bull calves were weaned at 6.5 months of age, aggregated into a single group and grazed common pastures until 22 months of age. A subset of bulls (n = 34) were then paired with bulls reared on the same property on the basis of weight, age and semen parameters. Bulls were group housed and fed total mixed rations containing hay and concentrates until sale at 26 months of age.
Intensive feeding was associated with deleterious effects upon semen morphology at 32 and 82d after commencement (p ≥ 0.05). This was accompanied by increased levels of cortisol (p ≥ 0.01). Cortisol was negatively correlated (P ≥ 0.01) with testosterone pre and post feeding (r ≥ - 0.53). Cortisol was negatively correlated with normal morphology pre-feeding but not at 32d. Bulls that received H nutrition pre-weaning had a tendency for improved normal semen morphology (p=0.07) and higher levels of testosterone (p ≥ 0.01) pre and post feeding.
This study shows that the known negative effects of intensively fed and managing bulls upon semen is associated with elevated circulating cortisol. This may act upon GnRH release, thereby reducing testosterone levels essential for spermatogenesis. Further, improving pre-weaning nutrition may reduce these negative effects suggesting an alternative management strategy.

  1. Holroyd, R. G. et al. 2005. Bullpower: Delivery of adequate normal sperm to site of fertilisation. Final Report Project NAP3.117. p 23-45. Meat and Livestock Australia, Sydney.