Effect of protein level and source in molasses slurries on the performance of growing cattle fed hay during winter.

Four molasses slurries of varying protein level and source were fed in two performance trials (Year 1, 105 d; Year 2, 92 d) to growing cattle (Year 1, 230 kg; Year 2, 247 kg). Treatments were CONTROL (hay only), MOL (molasses-corn meal), MOL-UREA (molasses-urea-corn meal), MOL-SBM (molasses-soybean meal), and MOL-BF (molasses-urea-corn meal blood meal-hydrolyzed feather meal). Animals on all treatments were offered bermudagrass hay (Year 1: 12.8% CP, 50% TDN; Year 2: 12.8% CP, 54% TDN) and a complete mineral mixture free choice. Each treatment was fed to three pens each year with seven animals/pen. Slurries were offered at 2.1 kg/d (DM) and effects on forage intake, ADG, condition score (1 to 9), hip height, and plasma urea nitrogen were monitored. Treatment effects for Years 1 and 2 were analyzed separately due to treatment x year interactions (P < .15) with respect to ADG, hip height change, condition score change, and feed cost of gain. Supplementation increased (P < .001) ADG over CONTROL in Year 1 (.41 vs .06 kg/d) and Year 2 (.69 vs .25 kg/d), increased hip height change by .02 cm/d (P < .001) in Year 1 and by .01 cm/d (P = .012) in Year 2, and decreased (P < .001) loss of body condition in Years 1 and 2. Molasses-urea showed no advantage over MOL in Years 1 and 2. Natural protein (MOL-SBM and MOL-BF) increased ADG by .10 kg/d in Year 1 (P = .001) and by .06 kg/d in Year 2 (P = .077) compared with MOL-UREA. Daily gain was improved by MOL- BF by .05 kg/d (P = .109) in Year 1 and by .08 kg/d (P = .063) in Year 2 compared with MOL-SBM. Results indicate that growing cattle fed bermudagrass hay during winter respond positively to energy supplementation in the form of molasses. The addition of animal source protein enhanced this response.