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Abstract Body weight (BW) gain is highly correlated with profitability and positively associated with feed efficiency and reduced environmental impact of beef production. Fiber stimulates rumination which is essential for digestion, nutrient absorption, and maintenance of animal health. The quantity and quality of fiber in the diet affect BW gain and feeding and rumination patterns. Forage neutral detergent fiber (fNDF) has a key role in regulating intake and health. This study tested two levels of forage inclusion NDF on performance and feeding behavior of Nellore bulls. Corn silage was the source of forage fiber, diets had 12% or 7% fNDF [23.3% or 13.6% in the total dry matter (DM). Diets had 64% and 73.5% ground corn, and 0.2 and 0.5% potassium chloride respectively for 12% and 7% fNDF. Both treatments included soybean meal (1.5%); cottonseed (7%), urea (1.2%), mineral mixture (2.7%) and monensin (25 ppm). Diets were formulated to meet protein and mineral requirements with RLM model (rlm.app.br). Nellore bulls (n = 40; BW = 460 ± 38 kg and an average age of 20 mo) were fed for 50 d after 21 d adaptation. Each animal was considered as experimental unit in a completely randomized design. On d 21 and 42 behavior was evaluated every 10 min for 24 h. Feed intake was measured using Growsafe feeders. Average daily gain (ADG) was estimated by linear regression based on BW (without fast) obtained in real time scales at the water trough. Data were evaluated by SAS PROC GLM. Daily gain (1.71 vs. 1.43 kg/d, P = 0.0002), DM intake (10.97 vs. 10.00 kg/d, P 0.001) and feed efficiency (0.154 vs. 0.139, P = 0.04) were greater for the 12% fNDF treatment. Likewise, rumination time was greater for the 12% fNDF compared with the 7% fNDF treatment; 356 and 275 min/d respectively (P = 0.0005). Animals fed 12% fNDF had longer rumination times and improved performance compared with those fed 7%. There were no differences in the number of visits to the troughs or in total feeding time (P 0.05), with mean visits of 15.17 and 15.43, and feeding times of 145.6 and 146.8 minutes for the 12% and 7% fNDF diets, respectively. Linear correlation between ADG and rumination time was positive r = 0.49 (P 0.03) and r = 0.28 (P 0.23), indicating that rumination is associated with an increase in ADG. Coefficient of variation for ADG was 13.4 and 27.2% for 12 and 7% fNDF diets, with greater variability for the low fiber diets. The results highlight the importance of providing adequate forage to feedlot cattle. Results are consistent with previous work from our group demonstrating that the maximum performance is achieved at around 11 to 13% fNDF. Bulls fed 12% fNDF diets had greater BW gain, higher rumination and reduced ADG variation compared with those fed 7% fNDF diets.
Souza et al. (Sun,) studied this question.