# Effects of Soybean Meal Replacement on Growth Performance, Rumen Fermentation, Rumen Microorganisms, and Metabolites in Dumont Lambs

## TL;DR

This study explores replacing soybean meal in lamb diets with cheaper protein sources to improve growth and rumen health.

## Contribution

The study identifies optimal soybean meal replacements that enhance rumen fermentation and nutrient metabolism in lambs.

## Key findings

- Replacing soybean meal with urea increased rumen microbial protein and fiber degradation.
- A mix of urea, cottonseed meal, and rapeseed meal improved rumen fermentation and nutrient transport.
- The replacement optimized carbon, nitrogen, and sulfur metabolism in lambs.

## Abstract

The price of soybean meal in China remains high and is mainly dependent on imports. Several factors have caused the price of soybean meal to fluctuate continuously, significantly impacting the sustainable development of China’s livestock industry. Therefore, this article utilises non-protein nitrogen (NPN), cottonseed meal and rapeseed meal as three relatively low-priced protein feed resources to replace part of the soybean meal for feeding Dumont lambs, exploring their effects on growth performance, rumen fermentation, and combined rumen microbial metagenomics and metabolomics to explain the reasons for the changes in phenotypic data. Compared with the soybean meal group, replacing 6.4% soybean meal with 1.5% urea significantly increased the rumen microbial protein (MCP) content, enhanced the degradation ability of fibres, facilitated energy metabolism, and provided a more efficient transportation capacity for nutrients. Replacing 4.3% soybean meal with 1% urea made the microbial composition and metabolic products of Dumont lambs closest to the soybean meal group and had higher MCP content and stronger linoleic acid metabolic ability. In conclusion, with 1% urea + 6.6% cottonseed meal + 5% rapeseed meal instead of all the soybean meal (19%), satisfactory results were obtained, enhancing the feed utilization efficiency and rumen fermentation, and optimizing the synergistic metabolic efficiency of carbon, nitrogen, and sulphur.

This study investigated the effects of replacing part of the soybean meal in the diet of Dumont lambs with urea, rapeseed meal, and cottonseed meal on their growth performance and rumen fermentation and combined rumen microbial metagenomics and metabolomics to explain the reasons for the changes in phenotypic data. Twenty-four healthy male Dumont lambs were divided into four groups: soybean meal group (T1, control group), group with 1.5% urea replacing 6.4% soybean meal (T2), group with 1% urea replacing 4.3% soybean meal (T3), and group with 1% urea + 6.6% cottonseed meal +5% rapeseed meal replacing all soybean meal (19%) (T4), following the principle of equal energy and nitrogen. Urea, rapeseed meal, and cottonseed meal have different degradation rates in the rumen, primarily stimulating arginine biosynthesis, sulphur metabolism, and carbon fixation in photosynthetic organisms through Prevotella genus mediation, thereby influencing the accumulation of metabolites such as 9,10-DiHOME, DG (PGJ2/a-15:0/0:0), isonicotinate and taxifolin, affecting rumen fermentation. Compared with the T1 group, the T2 group showed significantly increased ammonia nitrogen (NH3-N) and microbial protein (MCP) content (p < 0.01) and improved fructose and mannose metabolic capacity (p < 0.05). The T3 group showed a significant increase in total volatile fatty acids (TVFA) and MCP content (p < 0.01), which facilitated the absorption of subsequent nutrients. In the T4 group, different degradation rates of nitrogen resources and rapeseed meal + cottonseed meal contained abundant and complementary amino acids, which improved rumen fermentation, enhanced rumen microbial and metabolite diversity, and optimized the synergistic metabolic efficiency of carbon, nitrogen and sulphur. However, the specific mechanisms of post-rumen metabolism and absorption require further investigation.