Partição energética e produção de metano em novilhas das raças Guzerá e Nelore submetidas a diferentes planos nutricionais

Abstract

The objective of this study was to evaluate food and energy intake, nutrient digestibility, nitrogen balance, performance, energy partition, diet energy density and methane production in Guzerá and Nelore heifers submitted to two nutritional plans (restricted and ad libitum). The experiment was conducted at the Veterinary School of the Federal University of Minas Gerais located in the city of Belo Horizonte-MG. Were used twelve heifers feed individually with diets based on corn silage and concentrate, in proportion voluminous : concentrate 66:34 and 68:32 concentrate based on dry matter. The diets was formulated to allow gains of 0.200 and 1.0kg/day, corresponding to the restricted period and ad libitum, respectively. The experimental design was completely randomized and the two races represented the two treatments. In the restricted period there was no statistical difference (P>0.05) for food andenergy consumption, nitrogen balance, performance, energy partition, methane production and dry matter digestibility, organic matter, ethereal extract, crude protein, cellulose, hemicellulose, non-fibrous carbohydrates, carbohydrate fraction B2 and crude energy. There was a statistical difference (P<0.05) for the digestibility of the fiber in neutral detergent, fiber in neutral detergent corrected for ash, fiber in neutral detergent corrected for protein, fiber in acid detergent and fibrous carbohydrates, with Guzerá animals presented larger digestibility values (621.15, 680.91, 631.97, 587.88 and 694.14g/kg, respectively) compared to the Nellore breed (582.41, 648.01, 593.48, 508.50 and 662.82g/kg, respectively). In the ad libitum period, there was a difference (P<0.05) only for food consumption and Guzerá animals showed higher consumption in all analyzed variables, for the digestibility of ethereal extract and fibrous carbohydrates, with Guzerá animals presented higher values (695.95 and 597.71g/kg) compared to Nelore (626.82 and 571.22g/kg). For nitrogen ingested, nitrogen lost in urine, total nitrogen excreted and for the ratio between nitrogen absorbed in the gastrointestinal tract and metabolic weight, and the Guzerá breed presented higher values (193,17, 62,17,130,19g/day, 2,27, 1,53 and 1.47g/kg PV0.75, respectively) compared to the Nellore breed (172.27, 52.39, 113.67g/day, 2.05, 1.35 and 1.32g/kg PV0.75, respectively). There was also a statistical difference (P<0.05) for the consumption of crude energy, digestible energy, metabolizable energy (Mcal/day and Kcal/kgPV0.75) and energy loss in the form of urine as a percentage of gross/day), and the animals of the Guzerá breed presented higher values (36.10, 24.32, 20,71Mcal/day, 424.17, 285.73, 243,26 Kcal/kgPV0.75 and 1,49Mcal/day, respectively) in comparison to the Nelore animals (31.83, 21.23, 18.15Mcal/day, 377.82, 252.03, 215.42Kcal/kgPV0.75 and 1.11Mcal/day, respectively). Likewise, there was a difference (P<0.05) relating to the production of methane with the intake of fiber in acid detergent and the consumption of digestible organic matter, neutral detergent fiber corrected for ash and protein, acid detergent fiber, hemicellulose and cellulose, and Guzerá animals showed lower values (81.99, 29.75, 85.42, 144.66, 179.65 and 161, 39g/kg, respectively) compared to Nellore (86.50, 31.70, 93.84, 154.95, 195.46 and 174.21g/kg, respectively). It was concluded that, although there was similarity in the performance, metabolizable, dietary relationship between EM/ED between the two races, the genetic factor in the ad libitum period influenced food and energy consumption, nitrogen balance, methane production per unit of product as well as the digestibility of the fibrous fractions of the food in both periods.