The interaction of fiber, supplied by distillers dried grains with solubles, with an antimicrobial and a nutrient partitioning agent on nitrogen balance, water utilization, and energy digestibility in finishing pigs1

The objective of this study was to determine if a higher-fiber diet alters the response of finishing pigs to an antimicrobial (tylosin phosphate [TP]) and a nutrient partitioning agent (ractopamine HCl [RAC]) in terms of N and water utilization and energy digestibility. Seventy-two gilts (initial BW = 107.4 ± 4.2 kg) were blocked by weight and allotted to 1 of 8 dietary treatments. Treatments were arranged as a 2 × 2 × 2 factorial: distillers dried grains with solubles (DDGS; 0 vs. 30%), RAC (0 mg of RAC/kg and 0.70% standardized ileal digestible [SID] Lys vs. 5 mg of RAC/kg and 0.95% SID Lys) and TP (0 vs. 44 mg of TP/kg). Pig was the experimental unit, with 9 replications per treatment. Pigs were housed in individual metabolism crates and fed treatment diets for 17 d. Feed was provided twice daily, as much as the pigs could consume within 1 h per meal, and water was provided to the pigs between feeding periods, ad libitum. Fecal and urine collection occurred on d 7 and 8 and on d 15 and 16, for sampling periods 1 and 2, respectively. Pigs fed the DDGS diets had reduced ADG (P < 0.001) and ADFI (P < 0.0001). The apparent total tract digestibility (ATTD) of N and GE were lower for the 30% DDGS diets than the 0% DDGS diets (P < 0.0001). Ractopamine improved ADG (P < 0.0001), G:F (P < 0.0001), and N retention (P < 0.001) and tended to increase daily water intake (P < 0.10). Pigs fed RAC had higher N intake and urinary excretion and lower N retention in Period 2 than in Period 1 (P < 0.05), indicating a decline in the response to RAC over time. Tylosin phosphate did not affect ADFI or G:F but did improve ATTD of N (P < 0.05). There was a tendency for a TP × DDGS interaction (P < 0.10) for ADG, where TP tended to increase ADG in pigs fed 0% DDGS diets (P < 0.10) but not in pigs fed 30% DDGS diets (P > 0.10). Pigs fed DDGS diets had higher N intake (P < 0.01) and higher fecal (P < 0.0001) and urinary (P < 0.01) N excretion with no difference in N retention (g/d). Overall, RAC increased N retention by 33% (P < 0.0001) and the response to RAC was similar in both corn–soybean meal–based and corn–soybean meal–DDGS–based diets. Tylosin phosphate tended to improve growth performance in pigs fed corn–soybean meal–based diets but not in diets containing 30% DDGS; however, this response was not explained by changes in N balance or in energy digestibility.