Effect of Rumen Protected Methionine Supplementation on Protein Digestibility and Milk Protein Content in Lactating Sapera Dairy Goats

Aims: To evaluate the effects of rumen protected methionine (RPM) supplementation at different levels on crude protein digestibility, nitrogen utilisation, microbial protein synthesis, and milk protein content in Sapera dairy goats. Study Design: A randomised block design was used with 4 dietary treatments and 5 replicates. The treatments were T0 (without supplementation RPM), T1 (1 g/100 g CP RPM), T2 (2 g/100 g CP RPM), and T3 (3 g/100 g CP RPM). The measured parameters included crude protein (CP) intake and digestibility, faecal and urinary nitrogen excretion, microbial protein synthesis, and milk protein content. Place and Duration of Study: The in vivo study was conducted at Nio Farm, Pedurungan, Semarang, Indonesia, while the in vitro analyses were conducted at the Laboratory of Nutrition and Feed Science, Faculty of Animal and Agricultural Sciences, Diponegoro University, Semarang, Indonesia, from June to September 2025. Methodology: Twenty lactating Sapera dairy goats were allocated to four treatments based on their average daily milk production. The experimental period lasted 45 days, consisting of an adaptation period, a 30-day treatment period, and a total collection period. Parameters included CP intake and digestibility, faecal and urinary nitrogen excretion, microbial protein synthesis, and milk protein contents. Data were analysed using ANOVA at a 5% significance level, followed by Duncan’s multiple range test when significant differences were detected. Results: RPM supplementation did not significantly affect CP intake or digestibility. However, it significantly affected faecal nitrogen, urinary nitrogen, and microbial protein synthesis. The best response was observed in T1, which showed lower faecal and urinary nitrogen excretion and the highest microbial protein synthesis (17.43). Milk protein content was also significantly increased, with the highest value observed in T1 (3.586%). Conclusion: Rumen protected methionine supplementation at 1 g/100 g CP showed the most favourable response, particularly in improving nitrogen utilisation, microbial protein synthesis, and milk protein content in Sapera dairy goats.