PSX-26 Effect of physically effective neutral detergent fiber and starch inclusion on ruminal motility for feedlot cattle.

Abstract This study was designed to evaluate the effects of physically effective neutral detergent fiber (peNDF) and starch inclusion rate on ruminal motility, pool sizes, and ruminal neutral detergent fiber (NDF) turnover rate in finishing cattle. Eight ruminally cannulated Nellore steers (468.6 ± 87.5 kg), were housed in individual pens (21 m2) and assigned to a replicated 4×4 Latin square design, balanced for carryover effects. The experiment followed a 2×2 factorial arrangement of treatments, with two levels of peNDF (low: 8.5% of diet dry matter (DM) vs. high: 10.3% of diet DM) and two levels of starch inclusion (22.5% vs. 45.0% of diet DM). Concentrate feedstuffs were ground through a 4-mm sieve, and all ingredients were included in the peNDF calculation. Each period consisted of 21 days, including 14 days for adaptation and 7 days of sampling. Corn silage was harvested from a single field and chopped to a theoretical chop length of 2.0 (low peNDF) or 9.0 mm (high peNDF), and included at 20% of DM in all diets. In addition, diets contained finely ground corn grain, soybean hulls, soybean meal, citrus pulp, mineral, urea, and sodium monensin. Dry matter intake, expressed in kg/d and as a percentage of body weight, was not affected by peNDF, starch, or the interaction (P≥0.15). The peNDF inclusion did not affect (P≥0.11) neutral detergent fiber (NDF), and undigested NDF (uNDF) intake. However, feeding high peNDF increased peNDF intake (high: 1.4 vs. low: 1.1 kg; P=0.05). In contrast, feeding high starch decreased NDF (high: 3.0 vs. low: 5.2 kg; P< 0.01), peNDF (high: 2.1 vs. low: 2.3 kg; P=0.05), and uNDF intake (high: 1.4 vs. low: 1.7 kg; P< 0.01). Cattle fed low peNDF and high starch had greater rumen contraction frequency (interaction, P=0.05) when compared with the other treatments. Cattle fed low starch had greater time between contractions (high: 7.7 vs. low: 7.2 s; P=0.03), contraction duration (high: 4.3 vs. low: 3.8 s; P< 0.01), and contraction amplitude (high: 2.8 vs. low: 2.0 mmHg×s; P=0.05). Total ruminal digesta pool size (kg as is), DM, NDF, uNDF, potentially degradable NDF, and NDF passage rate were not affected by peNDF, starch, or the interaction (P≥0.14). Feeding low starch inclusion increased the NDF degradation rate (low: 3.5 vs. low: 1.0 %/h; P< 0.01). Thus, increasing theoretical chop length, a practical approach to manipulate peNDF while keeping the same dietary NDF from roughage had minimal effects on ruminal motility. However, low starch inclusion increased contraction duration, amplitude, and NDF degradation rate. These findings suggest that starch level exerts a stronger influence on ruminal motility in feedlot Nellore cattle than peNDF, with potential implications for ruminal health and nutritional strategies.