191 Effects of feeding strategy on growth performance and semen quality of developing bulls

The use of high-energy diets to develop bulls is perceived to influence semen quality, yet little research has been conducted using iso-caloric diets that differ in form or feeding management strategy. Therefore, the objective of this experiment was to evaluate the effects of two feeding strategies on growth performance and semen quality of developing bulls. Angus bulls (n = 48; 332 ± 47 d of age) were stratified into one of sixteen drylot pens before pens were randomly assigned to one of two iso-caloric diets: a total mixed ration (TMR; n = 8 pens) or a component-based ration (COMP; n = 8 pens) fed for 84 d. Rumen pH was continuously monitored via rumen boluses and dry matter intake (DMI) was measured daily throughout the experiment. Backfat thickness and hoof conformation were measured on d 0 and 84, with body weight measured and semen collected at 21-d intervals. Semen was assessed for progressive motility, total sperm per ejaculate, and sperm cell morphology. Data were analyzed via ANOVA utilizing JMP 13.0. Bulls fed the COMP ration had a greater DMI (P < 0.01) and ADG (P < 0.01), but similar feed efficiency (P = 0.21) when compared to TMR-fed bulls. Bulls fed COMP tended to have a lower mean rumen pH (P < 0.10). Additionally, COMP-fed bulls had greater backfat thickness (P < 0.01) but similar hoof conformation scores (P = 0.26) when compared to TMR-fed bulls on d 84. Feeding strategy did not affect progressive motility (P = 0.34), total sperm per ejaculate (P = 0.81), or percent morphologically-normal sperm (P = 0.31). These results suggest that the feeding strategies utilized in this experiment affected growth performance, rumen pH, and adiposity without influencing semen quality of developing bulls, and therefore should not be expected to influence breeding soundness examination outcomes.