Influence of distillers grains with solubles on bull growth and reproductive traits

This study evaluated the effects of offering growing bulls a diet with 40% modified wet distillers grains plus solubles (MWDGS; dry matter [DM] basis) on growth, composition, hoof scores, and reproductive performance. Simmental × Angus bulls (n = 28) were stratified by body weight (BW; 316 ± 29 kg), sire, and day 0 semen production (Y/N) and assigned into one of six pens. Pens were randomly assigned to one of two dietary treatments (n = 3 pens/treatment): 1) offered free-choice access to a corn-based diet with no MWDGS (CON) or 2) offered free-choice access to a diet with 40% MWDGS (DST; DM basis). Bulls were offered treatments for 140 d and, then, switched to a free-choice, common, low-energy diet for an additional 70 d. Bull BW, body condition score (BCS), hip height (HH), ultrasound (rump fat depth [RF], 12th rib fat thickness [BF], marbling score [MS], and longissimus muscle depth [MD]), hoof evaluations, breeding soundness examination (BSE), and semen evaluations were performed on days 0, 28, 56, 84, 112, 140, 175, and 210. There was a tendency (P < 0.09) for a treatment × time effect for BW. Bulls fed DST tended (P ≤ 0.10) to be heavier on days 28 and 56 than CON bulls. A treatment × time effect was detected (P < 0.01) for RF. Bulls fed DST had greater (P = 0.02) RF on day 84 than CON bulls. Treatment × time and treatment effects were detected (P ≤ 0.05) for BF, in which DST bulls had greater (P ≤ 0.05) BF on days 84, 112, and 175 and tended (P ≤ 0.10) to be greater on days 56 and 210 than CON bulls. A treatment × time effect was detected (P < 0.02) for percentage of major sperm defects. Bulls fed DST had a greater (P < 0.01) percentage of major sperm defects on day 140 than control bulls. There was a tendency (P = 0.09) for a treatment × time effect for percentage of sperm with proximal droplets. Bulls fed DST had a greater (P = 0.01) percentage of sperm with proximal droplets on day 140 than CON bulls. In conclusion, offering growing bulls a diet with 40% MWDGS (DM basis) resulted in heavier BW at days 28 and 56, increased RF at day 84, and increased BF and increases in both major sperm defects and sperm with proximal droplets at day 140. However, after 70 d on the common low-energy diet, there were no carryover effects for any growth, composition, hoof, or reproductive measures except for a tendency for BF.