Nutritional parameters and rumen microbiome quantification of beef cattle supplemented with ruminally degradable protein in tropical pasture

Abstract

The hypothesis of the present study is that supply the requirements of ruminally degradable protein (RDP) during the dry-rainy and rainy-dry transition seasons improves productive performance, nitrogen metabolism and the rumen microbial population of grazing beef cattle. Thus, three experiments were carried out at the sector of Beef Cattle in the Experimental Farm of the Federal University of Mato Grosso, to evaluate supplementation strategies in the ruminal microorganisms, nutritional parameters and performance of Nellore bulls on grazing. Nutritional characteristics: Eight rumen cannulated Nellore bulls (388 ± 25 kg) were used in a replicated 4 x 4 Latin square design. The treatments were: Control (mineral supplement) and supplements with Low-RDP, Medium-RDP, and High-RDP that provided 9; 47 and 82% of the RDP requirements for Nellore bulls, an average daily gain of 550g. In animal performance, 48 Nellore steers (300 ± 20 kg) were used. The treatments were Control (mineral supplement) and LowRDP, Medium-RDP and High-RDP which provided 8; 43 and 76% of the requirements in RDP. Crude protein intake was higher (P<0.001) in bulls consuming supplement with High-RDP, intermediate in Medium-RDP, and lower in Low-RDP and Control. The forage intake (g/kg BW) was higher in the Control, Medium-RDP and High-RDP treatment compared to the Low-RDP (P=0.026). The total digestibility of organic matter and non-fibrous carbohydrates ware greatest (P<0.05) for supplemented bulls compared to the Control. Supplementation increased average daily gain (ADG) compared with Control (P<0.05). The supply of Medium-RDP increased the ADG by 56% compared to the control (P=0.017). Therefore, supplementation with Medium-RDP increased the use of forage, the digestibility of nutrients, positively influencing the performance of Nellore steers in tropical pastures in the dry-rainy season. In experiment 2, eight rumen cannulated Nellore bulls were used in a replicated 4 x 4 Latin square design. Treatments included: Control (mineral supplement) and supplement with Low-RDP, Medium-RDP and HighRDP, providing 7, 33 and 71% of the RDP requirements for Nellore bulls. Supplemented bulls showed higher intake of crude protein and non-fibrous carbohydrates when compared to the control (P<0.001). In addition, the High-RDP supplementation strategy provided a 60% increase in nitrogen retention (P<0.001) compared to the Control. Therefore, supplementation with High-RDP end Medium-RDP increased the digestibility of nutrients and the efficiency of nitrogen use of Nellore bulls in tropical pastures in the rainy-dry season. In experiment 3, two studies were conducted in dry-rainy and rainy-dry seasons to investigate the microbial population of the rumen of Nellore bulls in topical pasture. In both studies, 4 Nellore bulls cannulated in the rumen were used, in a 4x4 Latin square design. The treatments were the same as in experiments 1 and 2, respectively. The supplementation strategies with supply of the requirements in RDP did not influence the abundance of bacteria, archaea, protozoa and fungi (P>0.05) in the two evaluated seasons. However, the rainy-dry season has increased by 21; 35; 33; 29; 20; 31 and 47%, respectively, in the proportion of F. succinogenes, R. albus, R. flavefaciens, S. ruminantium, B. fibrisolvens, fungi and protozoa, when compared to the dry-rainy season. The supplement with High-RDP in the dry-rainy and rainy-dry seasons provides greater availability of ruminal nitrogen and does not alter the growth of the main species of ruminal bacteria from grazing bulls. Therefore, supply the requirements for ruminally degradable protein provides better use of nitrogen and the performance of beef cattle during transition seasons. In addition, the ruminal microbiota is influenced by the seasons, as well as the quality and availability of the tropical grass.