Effects of supplementing rumen-protected methionine and lysine on milk yield and milk composition in dairy cows

The use of “health-food additives” has gained significant attention within the dairy sector, with a focus on enhancing the nutritional intake of dairy cows to improve their productivity and reproductive performance. This study aims at examining the impact of rumen-protected methionine (Met) and lysine (Lys) supplementation on production and reproductive parameters in a sample of 100 dairy cows, comprising 32 primiparous and 68 multiparous cows with an average of 5.24±2.31 years. The cows’ average milk production was determined to be 24.9±7.40 kg/day. The cows were divided into two groups, one receiving Met/Lys supplementation and the other serving as a control group. The supplemented group demonstrated superior performance in various metrics: milk yield (25.61 kg/day vs. 24.16 kg/day, p < 0.0001), fat (979.02 g/day vs. 874.27 g/day, p = 0.08), protein (843.98 g/day vs. 761.50 g/day, p = 0.10), and lactose content (4.36% vs. 4.21%, p = 0.003). Supplementation also led to elevated levels of butyrate and protein. Notably, the supplemented cows exhibited higher body condition scores (BCS) at different stages of lactation: BCS values of 3.01 at 35 days and 2.80 at 65 days, compared to 2.83 and 2.61 in the control group. Additionally, Met/Lys supplementation resulted in higher levels of albumin (33.22 g/L) and urea (0.20 g/L) in serum samples, with a tendency towards increased levels of ASAT (51.20 U/L). Reproductive performance showed improvements in the supplemented group with a lower number of services per conception (1.88 vs. 2.05), a higher conception rate (44.83% vs. 22.22%), and a higher total pregnancy rate (55% vs. 48%), although these differences were not statistically significant. Thus, the addition of rumen-protected Met and Lys to dairy cow rations shows potential for enhancing milk production and composition, as well as improving specific metabolic and reproductive characteristics.