Níveis de proteína associados a uma fonte de gordura protegida para cordeiros Santa Inês.

Abstract

The objective was to evaluate the effect of diets with different protein levels associated or not with a source of protected fat on the intake and apparent digestibility of nutrients, nitrogen metabolism, ingestive behavior, and performance of feedlot lambs. Sixty-four male lambs, not castrated, crossbred Santa Inês, with average initial weight of 20 ± 1 kg and average age of 90 days, finished in confinement, distributed in a 4X2 factorial, with diets containing four levels of protein: 120, 140, 160 and 180 g CP kg-1 MS, with or without inclusion of 35g kg-1 MS fatty acid calcium salts. The roughage:concentrate ratio was 500 g kg-1 DM of corn silage (Zea mays) and 500 g kg-1 DM of concentrate. The consumption (g kg-1 BW) of CP, EE and CNF increased as a function of the protein content in the diet (P<0.01), while the consumption of DM, NDF and CHOT showed a quadratic effect (P≤0.05) , with reductions from levels 161g, 150g, and 154g PB kg-1 DM, respectively. Apparent protein digestibility increased as a function of protein levels as well as EE with the addition of protected fat (P<0.05). Urinary and fecal nitrogen and retained N increased with the increment of protein in the diet, while N consumption and the fraction absorbed by the animal showed a quadratic behavior (P≤0.05), with a maximum point at 178 g PB kg- 1 MS. Purine derivatives and PB mic followed the same behavior as CMS with a maximum value at the level of 160g PB kg-1 DM. There was an increase in DM and NDF rumination efficiencies (P<0.05) and an interaction effect was observed on rumination time and number of chews per bolus (P≤0.05). There was a linear increase in weight gain (P<0.05), with an estimated value of 302g/day in the highest protein level. Diets with inclusion of up to 160g PB kg-1 DM without the addition of protected fat for Santa Inês lambs, promote increases in the intake and digestibility of nutrients and improve the productive performance of animals.