关键词: 可溶性蛋白, 甲烷排放, 后备牛, 生长性能, 瘤胃微生物

Abstract:

【Objective】Soluble protein ( SP ) can be rapidly degraded and utilized by microorganisms in the rumen. Through the analysis of the changes of soluble protein in the diet, the rumen microorganisms and their metabolites were analyzed to explore the effect of soluble protein on methane emission. 【Method】A total of thirty healthy, five-month-old Holstein heifers (94.55 ± 6.27 kg body weight) were randomly allocated to three dietary treatments (n=10 per group). All groups were fed a diet with a 60:40 concentrate-to-roughage ratio. The three dietary treatments differed only in their soluble protein (SP) content, expressed as a percentage of total dietary dry matter: Diet 1 (6.00% SP), Diet 2 (6.48% SP), and Diet 3 (6.96% SP). Following an eight-week feeding period, methane production was measured over three consecutive days, and rumen fluid samples were collected for subsequent analysis.【Result】(1)The daily gain of Diet 3 was significantly higher than that of Diet 2 and Diet 1 during 29-56 days in the whole experimental period (P<0.05 ),There was no significant difference in dry matter intake during the whole experimental period (P>0.05).No significant differences in methane emissions were observed among the treatment groups(P>0.05), while methane to body weight ratio, Diet 2 was significantly higher than Diet 3 and Diet 1 ( <0.05).In the rumen fermentation parameters, the ammonia nitrogen content increased first and then decreased with the soluble protein content. The content of volatile fatty acids was the highest in Diet 3. (2) In microbial diversity, there was no significant difference in ACE, Chao1, Shannon and index among the three groups (P>0.05); at the phylum level, Bacteroidetes in Diet 3 was lower than that in Diet 2 and Diet 1. At the genus level, Prevotella in Diet 2 was slightly higher than the other two groups. LEfSe analysis identified microbial taxa with LDA scores greater than 4.5 in the Diet 3 group, which included Pseudoruminococcus、Streptococcaceae、Veillonellales、Streptococcus_mutans、Ruminiclostridium_josui、Prevotella_histicola、Prevotella_veroralis.(3) There were 240 significantly different metabolites between Diet 1 and Diet 3, 109 significantly different metabolites between Diet 2 and Diet 1, and 60 significantly different metabolites between Diet 3 and Diet 2. Among them, the differences in metabolites were mainly in organic acids and their derivatives, lipids and lipid molecules. The metabolites of succinic acid, 23-demethoxycholic acid, spermidine, histidine, threonine and glutamine increased significantly with the increase of SP content. D-erythritol-4-phosphate, isocitrate, leucine and other metabolites were enriched in Diet 1. (4)There was a significant positive correlation between Veillonella and propionic acid. Ruminiclostridium _ josui, Prevotella _ veroralis and Streptococcus _ mutans were significantly positively correlated with Histidine, threonine and glutamine.【Conclusion】Increasing the level of soluble protein (SP) in the diet improved the average daily gain of heifers and concomitantly exerted a moderate inhibitory effect on methane emissions per unit of body weight. Furthermore, the higher SP level promoted the colonization of beneficial bacteria such as Prevotella, which facilitates volatile fatty acid (VFA) production. These shifts in the rumen enhanced the synthesis of energy and amino acids through ruminal metabolism, thereby potentially supporting immune function.

Key words: soluble protein, methane emissions, reserve cattle, growth performance, rumen microorganisms