Date of Award
Master of Science (MS)
Committee Member 1
Committee Member 2
John S. Radcliffe
Three studies were conducted for this thesis. In study 1, effects of antimicrobials on nutrient digestibility and retention of 18 to 20-kg pigs was investigated. The study used a randomized complete block design (RCBD) with 4 treatments and 6 replicate pigs in individual metabolism crates per treatment. The four treatments consisted of, negative control (NC) devoid of antimicrobials with 0.41% total P and 0.71% Ca, NC with 55 mg/kg carbadox (Mecadox 10, Phibro Animal Health), 44 mg/kg tylosin (Tylan 40, Elanco Animal Health), and 11 mg/kg virginiamycin (Stafac 20, Phibro Animal Health). A 5-d total collection period with chromic oxide used as an initiation and termination marker for feces followed a 5-d adaptation period. Supplementation with carbadox increased (P < 0.05) energy (E) digestibility and retention relative to pigs fed the NC diet. Overall, supplementation of an antimicrobial did not significantly influence DM, P, and Ca utilization; however, specific antimicrobial supplementation influenced N digestibility and E utilization.
Study 2 was conducted to determine the impact of antimicrobials on phosphorus digestibility with or without the addition of phytase in pigs. A total of 72 crossbred barrows between 18 and 20-kg BW were assigned in a RCBD in a 3 x 3 factorial arrangement of antimicrobials (none, 44 mg/kg tylosin, or 28 mg/kg virginiamycin) and phytase (0, 500, or 1500 FTU/kg) in a corn-soybean meal diet deficient in P, 0.38% available P, 0.58% Ca. The results showed that supplementation with tylosin decreased (P < 0.01) DE and ME; however, final BW, DM, N, E, Ca, and P apparent digestibility and retention were not significantly influenced regardless of antimicrobial supplementation. Increased levels of phytase supplementation improved (P < 0.05) final BW, DM, N, E, DE, ME, Ca and P utilization regardless of antimicrobial supplementation. Overall, nutrient utilization was not significantly affected by antimicrobial supplementation, but addition of phytase improved all nutrient utilization criteria.
Study 3 was conducted to determine the impact of antimicrobials on phosphorus digestibility with or without the addition of phytase in broiler chickens. A total of 720, 5-d post hatching, male Ross 708 broilers were assigned to 9 treatments with 10 replicates in a RCBD in a 3 x 3 factorial arrangement of antimicrobials (none, 44 mg/kg tylosin, or 11 mg/kg virginiamycin) and phytase (0, 500, or 1500 FTU/kg) in a corn-soybean meal diet deficient in available P. Supplementation with antimicrobials improved (P < 0.05) gain-to-feed ratio, and tylosin supplementation improved (P < 0.05) tibia ash percent. Increased levels of phytase supplementation improved (P < 0.01) growth performance and tibia ash regardless of antimicrobial supplementation. The addition of phytase linearly improved (P < 0.01) apparent ileal digestibility (AID) and apparent retention of P regardless of antimicrobial supplementation. Adding phytase to diets supplemented with tylosin or virginiamycin linearly improved (P < 0.05) retention of Ca, while phytase addition to the NC diets linearly decreased retention of Ca. Overall, supplementation of antimicrobials did not significantly influence AID and retention of DM, E, N, Ca, and P, however, supplementation of increased phytase levels improved growth performance, tibia mineralization, AID and retention of P.
McCormick, Katherine A., "Impact of antimicrobials with or without the addition of phytase on phosphorus digestibility and utilization in swine and broiler chickens" (2014). Open Access Theses. 217.