Effects of mixing Stylosanthes conserved as hay or silage with corn silage in diets for feedlot beef cattle

The objective of this study was to evaluate the total and partial digestibility, ruminal pH and ammonia nitrogen (NH₃-N) concentration, nitrogen balance (Experiment 1) and performance (Experiment 2) of beef cattle fed diets containing corn silage (CS) and Stylosanthes (silage or hay) as forage source. Treatments were: 1) CS; 2) Stylosanthes silage (StS); 3) Stylosanthes hay (StH); 4) CS + StS (StS-mixed diet); and 5) CS + StH (StH-mixed diet). Experimental diets (125 g CP/kg DM) consisted of 50% forage and 50% concentrate (DM basis). Five cannulated bulls (251 ± 42.6 kg of body weight) were distributed to a 5 × 5 Latin square (Experiment 1). The trial lasted 80 d. The experiment 2 was performed with 40 bulls (360 ± 2.7 kg of body weight) in a completely randomized design and eight replicates during a 99-days period. In experiment 1, CS diet showed greater (P ≤ 0.02) total digestibility of DM, OM, CP and NDF than other diets. Mixed diets had greater (P = 0.02) total NDF digestibility compared to StS and StH. Corn silage showed greater total digestibility of DM, OM, NDF and CP (P ≤ 0.03) compared to mixed diets. Ruminal NDF digestibility was greater (P = 0.03) for CS than other diets. Ruminal pH was greater (P < 0.01) for StS and StH compared to mixed diets. There was a treatment × hour interaction (P = 0.02) for ruminal NH₃-N. In the experiment 2, animals fed CS presented lower (P ≤ 0.03) intake of DM, OM, EE, NDF, iNDF, but greater (P ≤ 0.01) intake of TDN, DOM and NFC than animals fed other diets. The intake of all nutrients, except for NDFi, was greater for mixed diets than StS and StH (P < 0.01). Mixed diets showed greater (P < 0.01) intake of most nutrients compared to CS diet, except for the intake of TDN and DOM, which were similar (P > 0.60). Corn silage showed greater (P < 0.01) digestibility of all nutrients than other diets. Stylosanthes silage and StH had greater (P ≤ 0.03) digestibility of DM, CP and NFC than mixed diets. Average daily gain (ADG) and carcass average daily gain (CADG) were greater (P ≤ 0.03) for CS diet than others, but mixed diets were similar (P ≥ 0.67) to CS. Mixed diets had greater (P < 0.01) ADG and CADG than StS and StH, while StS showed greater (P = 0.05) ADG compared to StH. Carcass yield was greater (P = 0.02) for StH compared to StS. Diets containing 50% CS and 50% StS or StH are alternatives to CS in ration of finishing beef cattle.