PS4-24. Eating Behavior and Particle Sorting of Feedlot Nellore Cattle Fed Diets Varying in Physically Effective Neutral Detergent Fiber and Starch.

Abstract

This study was designed to evaluate the feeding behavior and particle sorting of feedlot Nellore cattle fed diets varying in physically effective neutral detergent fiber (peNDF) and starch. Eight ruminally cannulated Nellore steers (468.6 ± 27.2 kg) were assigned to a replicated 4 × 4 Latin square design, balanced for carryover effects, with 21 d experimental periods, and housed in individual pens (21 m²). Treatments were arranged in a 2 × 2 factorial arrangement, consisting of two levels of peNDF (8.5 vs. 10.3% of dietary dry matter [DM]) and two levels of starch inclusion (20 vs. 40% of dietary DM). Diets were formulated using corn silage, finely ground corn grain, soybean hulls, soybean meal, citrus pulp, mineral, urea, and sodium monensin. The peNDF concentration was adjusted by modifying the theoretical chop length of the corn silage, and all dietary ingredients were considered in the peNDF calculation. Eating behavior was assessed from d 17 to d 21 of each experimental period using a video monitoring system (iM5 SC, Intelbras, São José, SC, Brazil), with a single camera positioned to record two pens (n = 4). Animal activities were recorded at 5 min intervals over a continuous 96 h period. No interaction between peNDF and starch levels was observed (P ≥ 0.11) for any of the variables evaluated. Initial body weight (BW), dry matter intake (DMI; kg/d or % of BW), neutral detergent fiber (NDF) intake, undigested NDF (uNDF) intake, time spent eating or drinking, number of meals per day, DMI per meal, meal length, and eating rate of DM were not influenced by peNDF level (P ≥ 0.11). However, steers fed diets containing 10.3% peNDF had greater peNDF intake (P = 0.05), spent less time resting (P = 0.04), and more time ruminating (P = 0.05) compared with those fed 8.5% peNDF. The starch level did not affect DMI (kg/d or % of BW) or any of the evaluated eating behavior variables (P ≥ 0.07). Diets with 20% starch resulted in greater NDF (P < 0.01), peNDF (P = 0.05), and uNDF intake (P < 0.01) than diets containing 40% starch. Particle sorting for fractions retained on the 19, 8, and 4 mm sieves, as well as particles smaller than 4 mm, was not affected by peNDF level, starch level, or their interaction (P ≥ 0.06). Thus, increasing theoretical chop length, a practical strategy to manipulate peNDF while maintaining constant dietary NDF from roughage, may enhance rumination activity without negatively impacting DMI or particle sorting. In contrast, variation in starch level has a limited effect on eating behavior in feedlot Nellore cattle.