Effects of restricted versus conventional dietary adaptation over periods of 6, 9 and 14 days on blood lipopolysaccharide binding-protein concentration of feedlot cattle
Two studies were conducted to determine the effects of restricting intake of the final finishing diet (REST) as a means of dietary adaptation compared with diets increasing in concentrate (STEP) over periods of six, nine and 14 days on blood lipopolysaccharide binding-protein (LBP) concentration of Nellore cattle. The first study was designed as a completely randomized block with a 2x2 factorial arrangement, replicated six times, in which 120 26-months old yearling Nellore bulls (361.3 ± 30.2 kg) were fed in 24 pens for 84 days according to the treatments: STEP for 9-d or 14-d and REST for 9-d or 14-d. The second study had the same design and characteristics just described, in which 120 22-months old yearling Nellore bulls (352.03 ± 19.61 kg) were fed according to the treatments: STEP for 6-d or 9-d and REST for 6-d or 9-d. In each study, 48 animals (two per pen) were randomly chosen for blood collection, which was performed at end of the adaptation period and on day 21 of the studies. Blood samples were collected from the jugular vein, and blood LBP concentration, expressed as ng•mL-1, was determined by using a commercial ELISA kit. For the first study, a significant (P = 0.01) period main effect was observed, in which animals on day 21 presented greater concentrations of LBP than those at end of the adaptation period (128.1 vs. 56.7). A significant (P = 0.01) interaction was observed between protocols and duration of adaptation, where animals in REST protocol of 14-d had greater blood LBP concentration (157.2) than cattle in STEP protocol of 9-d (91.0), which had greater blood LBP concentrations than animals in REST protocol of 9-d (67.3) and STEP protocol of 14-d (54.2). In the second study, no significant (P > 0.10) protocols and duration of adaptation main effects were observed. However, a significant (P = 0.01) period main effect was observed, in which animals on day 21 of the study present greater concentrations of blood LBP when compared to those at the end of the adaptation period (615.3 vs. 136.6). As the normal cattle blood LBP range varies from 50 to 500 ng•mL-1, adapting feedlot Nellore cattle in 14-d, regardless of the protocol, seems to be the most feasible option.
Keywords: acidosis, endotoxin, Nellore