Effect of Methionine Analogues on Growth Performance, Serum Biochemical Parameters, Serum Free Amino Acids and Rumen Fermentation of Yaks

SIMPLE SUMMARY: Yaks (Bos grunniens) are one of the most remarkable domestic animals; however, they generally suffer from malnutrition for almost 8 months of the year, which results in yaks displaying a circannual rhythm with seasonal changes. Yaks are ruminant animals whose utilization of dietary nitrogen efficiency is only about 15.9–19.0%; a large amount of N is excreted in feces and urine. A nutritional method could be taken to improve the utilization rate of dietary nutrients and regulate the synthesis of protein. Methionine makes up the first two limiting amino acids in a corn–soybean-meal-based diet for ruminants; therefore, we added the methionine analogues to the diet to investigate its role in yaks, eventually to find an efficient way to feed yaks. ABSTRACT: This experiment was conducted to investigate the effects of methionine analogues 2-hydroxy-4-methylthio butanoic acid isopropyl ester (HBMi) on growth performance, nutrient apparent digestibility, serum metabolite, serum free amino acids, and rumen fermentation parameters of yaks. Twenty-four male Maiwa yaks (252.79 ± 15.95 kg) were randomly allocated to four dietary treatments: basic diet (CON), or three HBMi (MetaSmart (MS); Adisseo Inc., Antony, France) supplementation treatments: MS1 (5 g), MS2 (10 g), and MS3 (15 g). The results showed that the increase in the supplemented MS levels linearly increased the average daily gain (p < 0.05), while the serum alkaline phosphatase activity and malondialdehyde content were increased when yaks were fed with 15 g/d MS (p < 0.05). The diet supplemented with MS linearly increased the percentages of glutamic acid and proline, and linearly or quadratically decreased the percentages of isoleucine, phenylalanine, and valine (p < 0.05). Furthermore, supplementation of 10 g/d and 15 g/d MS increased ruminal microbial crude protein (p < 0.05). The ratio of acetate to propionate in the MS2 group was lower than those in CON and MS1 groups (p < 0.05). In summary, a diet supplemented with 10 g/d MS could be an effective way to improve the growth performance of fattening yaks without negative effects.