Effects of corn and molasses supplements with and without feed additives on performance, voluntary intake, and digestive function in cattle fed bermudagrass hay

Abstract

lonophores and bambermycins have improved gain of growing cattle fed forage based diets when mixed in grain or mineral supplements. In limited research monensin has not improved gain of growing cattle when fed in molasses based liquid feeds offered at 2 kg/d or more and the efficacy of bambermycins in this supplement has not been evaluated. Growing cattle fed bermudagrass hay were supplemented with 1.57 kg TDN from corn-urea (CU) or molasses-corn gluten meal (MCG) , without and with monensin or bamberirrycins. Cattle fed supplements without antibiotics gained .62 kg/d. Monensin increased gain .035 kg/d in CU and decreased gain .029 kg/d in MCG. Bambermycins increased gain .106 kg/d in CU and .042 kg/d in MCG. Monensin decreased hay intake .14% of BW while bambermycins increased hay intake .14% of BW in Year 1 and had no effect in Year 2, Monensin increased the difference between observed and predicted gains (an estimator of feed efficiency) .102 and .026 kg/d in CU and MCG, while bambemrycins increased that difference .063 and .041 kg/d in CU and MCG, respectively. Effects of CU or MCG with and without bambermycins on feed intake and digestive function were evaluated in two 4 x 4 Latin squares with ad libitum and restricted intake. Bambennycins increased total DM intake .08% of BW but did not affect digestibility. Bambennycins increased ruminal pH (6.63 vs 6,52), decreased butyrate molar proportions (9.8 vs 10.6), and did not affect acetate :propionate ratio (C2:C3) and microbial N efficiency. Ruminal pH, total VFA, VFA molar proportions, and CjtCj exhibited a supplement by time post feeding interaction (P < .07). Steers fed CU had higher (P < .033) apparent (3.59 vs 2.99 g N/100 g OM) and true (2.47 vs 2.19 g N/100 g OM) microbial N efficiency, and higher ruminal feed CP degradability (69.2 vs 58.9%) than those fed MCG. Monensin improved gain in cattle fed corn but did not improve gain in cattle fed molasses supplement. Bambermycins improved gain in cattle fed corn and molasses supplements but this effect was greater in corn than in molasses. Increased gain due to bambermycins was not explained by changes in digestive function.