Desempenho e aproveitamento pós-ruminal do amido em tourinhos Nelore e Angus alimentados com dietas com grãos de milho inteiro e sem volumoso

Abstract

The objective of this study was to evaluate the performance and the postruminal starch utilization of Nellore and Angus young bulls fed a diet containing whole shelled corn without forage or a diet containing corn silage more concentrate. Thirty-six young bulls (18 Nellore and 18 Angus) with an average initial age of 20 months and initial live weight of 381 ± 11.8 kg were used for this study. The study was performed in a completely randomized design, with a factorial arrangement of 2 x 2 (two breeds and two diets). The diet with corn silage contained 30% forage and 70% corn and a soybean meal-based concentrate. The diet with the whole shelled corn contained 85% whole shelled corn and 15% soybean meal and a mineral-based premix. The comparative slaughter of eight animals was conducted at the beginning of the experimental period for the determination of carcass gain. The animals were weighed at the beginning and end of the trial period in order to obtain the average daily gain (ADG). The digestibility determination occurred during the days 48 and 50 of the experimental period. The ruminal pH was measured using an intra-ruminal bolus obtained at the end of the experiment. After slaughter, the hot carcass weight (HCW) was determined, and measurements were taken of the ribeye area (REA) and subcutaneous fat thickness (SFT). Samples were taken from the pancreas to analyze α-amilase pancreatic acitivity; duodenum and jejunum for maltase activity and liver to analyze PCK1 gene expression. It was not observed interaction between breed and diet for the performance characteristics and Ruminal pH (P > 0.05). Greater dry matter intake (DMI) (P < 0.01), ADG (P < 0.01) and feed efficiency (P < 0.01) were observed in animals of the Angus breed compared with Nellore cattle. The feeding of the diet containing whole shelled corn resulted in a lower mean ruminal pH value (P = 0.04) and tended to reduce the ADG of the animals (P = 0.08) as well as the DMI (P < 0.01), which resulted in animals with greater feed efficiency (P = 0.01). The whole shelled corn diet had greater DM, NDF and starch digestibility (P < 0.01). Angus animals had greater starch digestibility (P = 0.03). However, the activity of α-amylase was greater in the Nelore animals (P < 0.01), and had no diet effect (P = 0.52). In the duodenum, maltase activity was greater in the animals fed corn silage and concentrate (P = 0.02). Feeding with whole shelled corn diets is indicated for the finishing of beef cattle in feedlots because this diet promotes greater feed efficiency. Nellore animals have low capacity to digest starch. However, they don’t have less α-amylase and maltase activity, compared to Angus. Dry matter and starch digestibility increased when animals fed whole shelled corn diets without forage.