Effect of nutrition on testicular traits of tropically adapted yearling beef bulls

Abstract

The effects of different management practices on testicular development of young Bonsmara bulls fed a high energy (HE), medium energy (ME) and low energy (LE) diet after weaning were determined. Testicular histology and seminal traits were examined together with scrotal circumference (SC) development over an 84-day performance test trial period. The SC differed significantly (P < 0.001) between HE-, ME- and LE-fed bulls. Seminal traits, such as semen concentration were significantly (P < 0.001) lower in bulls fed the HE diet (1.3 ± 0.134) compared with those fed the ME diet (2.4 ± 0.18) and LE diet (2.6 ± 0.16). Similarly, linear movement of sperm was also affected by diet and movement was slower (P < 0.05) in bulls fed the HE diet (1.7 ± 0.30) compared with bulls fed the ME diet (2.2 ± 0.31) and LE diet (3.1 ± 0.23). The percentage total major (P < 0.001) and total minor (P < 0.05) sperm defects were also greater in the HE-fed bulls (27.1 ± 6.82 and 7.4 ± 0.91) compared with the ME-fed bulls (9.7 ± 1.45 and 5.5 ± 0.87) and for the LE-fed bulls (5.4 ± 1.26 and 3.9 ± 0.58). Dietary energy level (P < 0.05) influenced the percentage inactive seminiferous tubuli, with bulls fed the HE diet having 35% more seminiferous tubules classified as inactive compared with those bulls fed ME and LE diets. Scrotal fat deposits were higher (P < 0.05) in bulls fed the HE diet (243.4 ± 21.59 g) compared with those fed the ME (110.0 ± 12.1 g) and LE (88.4 ± 9.65 g) diets. Feeding HE diets to young bulls probably reduces their reproductive potential.