Effect of the inclusion of lysine and methionine on the nutritional performance and ingestive behavior of lambs

Abstract

Lysine and methionine are the most limiting amino acids for ruminants; their inclusion in the free form is not effective, since they are quickly degraded by ruminal microorganisms, making the fulfillment of the requirements of metabolizable protein difficult. The objective of this study was to evaluate the effects of including different levels of lysine and methionine, protected from ruminal degradation, in the diet of lambs; more specifically, their effects on intake, digestibility, nitrogen balance and ingestive behavior. The experiment was conducted at the Experimental Farm Capim Branco, Federal University of Uberlândia, from September to October 2016. Five 1/2Dorper x 1/2Santa Inês lambs, at approximately eight months of age and an average weight of 50 kg, were distributed in a 5x5 Latin square design, with five treatments and five replicates. The treatments consisted of different levels (0 g, 8 g, 16 g, 24 g and 32 g) of lysine and methionine added to the diet, protected from ruminal degradation (MicroPEARLS LM ®). The feed was composed of corn silage and concentrate (30V: 70C), offered twice daily at 08h00 and 16h00. The experiment lasted 75 days and was divided into five phases. Each phase lasted 15 days, with 10 days for adaptation of the animals and five days of data collection. The animals were kept in individual metabolic cages, with a feeder, drinker and salt shaker. A digestibility assay was performed to determine the consumption and apparent digestibility coefficients of dry matter (DM), crude protein (CP), neutral detergent fiber and acid (NDF/NDA). Urine volume and density, stool weight and fecal score, nitrogen balance and ingestive behavior were recorded. In relation to metabolic and body weight, DM intake (kg day-1) presented a positive linear response with the inclusion of amino acids, as well as the CP intake, NDF intake, ingested nitrogen and nitrogen balance, which were positive in all treatments. There was no difference (P < 0.05) in the digestibility coefficients of DM, CP and NDF. Water consumption was high in all treatments, but did not differ by treatment (P > 0.05). Ingestive behavior was not influenced (P > 0.05). The inclusion of up to 32 g of protected lysine and methionine increases DM and nutrient intake, without negatively affecting digestibility. The high CP intake induced an increase in the urinary nitrogen excretion, and consequently, an increase in the energy expenditure.