Abstract
Starch-rich diets are a commonly adopted strategy in order to sustain high milk yields in dairy cows. However, these diets are known to increase the risk of gut dysbiosis and related systemic health disorders. This study aimed to evaluate the effects of supplementing a clay mineral-based feed additive (CM; Mycofix® Plus, BIOMIN) on fecal microbiota structure, fecal short-chain fatty acid (SCFA) fermentation, serum metabolome, and liver health in primiparous (PP, n = 8) and multiparous (MP, n = 16) early-lactation Simmental cows (737 ± 90 kg of live body weight). Cows were randomly assigned to either a control or CM group (55 g per cow and day) and transitioned from a diet moderate in starch (26.3 ± 1.0%) to a high starch diet (32.0 ± 0.8%). Supplementation of CM reversed the decrease in bacterial diversity, richness, and evenness (p < 0.05) during high-starch diet, demonstrating that CM supplementation efficiently eased hindgut dysbiosis. The CM treatment reduced levels of Lactobacillus in PP cows during starch-rich feeding and elevated fecal pH, indicating a healthier hindgut milieu compared with that in control. Butyrate and propionate levels were modulated by CM supplementation, with butyrate being lower in CM-treated MP cows, whereas propionate was lower in MP but higher in PP cows. Supplementing CM during high-starch feeding increased the concentrations of the main primary bile salts and secondary bile acids in the serum and improved liver function in cows as indicated by reduced levels of glutamate dehydrogenase and γ-glutamyl-transferase, as well as higher serum albumin and triglyceride concentrations. These changes and those related to lipid serum metabolome were more pronounced in PP cows as also corroborated by relevance network analysis.
Highlights
High-producing dairy cows have increased energy requirements associated with milk production
The risk of health disorders deriving from impaired liver function is especially high during early lactation [2], and the disorders induced by high-grain diets further compromise liver function by enhancing the release and translocation of microbial endotoxins into the systemic circulation [1] as well as impairing the hepatic lipid and bile acid metabolism [3]
In the last week of high-starch feeding, CM-supplemented cows tended to have a higher fecal pH than cows offered the control diet (p = 0.07), whereas fecal lactate concentration tended to be higher during the 1st (p = 0.06) and 2nd weeks (p = 0.08) of high-starch feeding in those cows
Summary
High-producing dairy cows have increased energy requirements associated with milk production. Recent research showed major metabolic shifts in bile acid metabolism in response to high-starch diets [4], and this finding was consistent with increased liver enzyme concentrations, e.g., aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH), γ-glutamyl-transferase (GGT), and alkaline phosphatase (AP) during early lactation [5]. These effects were pronounced in primiparous cows, highlighting the already suspected role of parity in the ability of cows to cope with starch-rich diets [6]. These metabolic derailments substantially impair animal health and welfare, decrease productivity, and constitute important economic losses for the dairy industry [7]
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