PSI-27 Excretion of purine derivatives and rumen microbial protein synthesis in Nelore steers supplemented with low-moisture, sugarcane molasses-based block and fed low-quality forage

Abstract The objective of this study was to determine the effects of supplementation of low-moisture, sugarcane molasses-based block (LMB) on steers fed low quality forage in the excretion of purine derivatives and in the synthesis of ruminal microbial protein. Six rumen cannulated Nellore steers steers (23 months, 350 ± 10 kg) were distributed in a 3 × 3 double Latin square design. The treatments were composed of Brachiaria brizantha ‘Marandu’ hay ad libtum as an exclusive source of bulky (93.65% DM, 3.97% CP and 81.76% NDF) and supplements: complete mineral blend with urea [UR, (urea, salt, mineral-vitamin premix)], a commercial protein supplement [PS, (corn grain, soybean meal, urea, salt and mineral-vitamin premix)] or low-moisture, cooked sugarcane molasses-based protein block [LMB, (cane molasses, cottonseed meal, soybean oil, urea, salt and mineral-vitamin premix)]. Each experimental period lasted 21 days (14 days of adaptation and 7 days of data collection). The total urinary volume was measured for five days in each experimental period. The urine was collected in rubber funnels fixed by elastic loops on the backs of the animals. The urine was conduct through hoses connected to a 20 L polyethylene bucket containing 250 mL of 20% H2SO4 solution. Every 24 hours, the collected urine was homogenized and the total excreted volume was measured. The data were analyzed using Software R, having as fixed effect the treatments and as animal random effect, period, Latin square and error. Supplementation with LMB lead to greater excretion of allantoin (P = 0.046), microbial nitrogen flow (P = 0.023) and higher microbial crude protein (P = 0.023) into the intestine compared to UR and PS. While no effect was observed on total purines and purines absorbed (P > 0.05). Thus, LMB supplementation for rumen cannulated Nellore steers fed low quality forage was effective to improve metabolizable protein supply.