Abstract
Flavonoids played critical roles in stabilizing microbial homoeostasis when animals suffered exoteric stresses. However, whether flavonoids attenuated heat stress of dairy cows is still not clear. Therefore, in the present article, flavonoids extracted from honeycomb were supplemented to investigate the production, digestibility, and rumen microbial metabolism responses of cows under heat stress conditions. A total of 600 multiparous dairy herds were randomly allotted into the control treatment (CON), the heat stress (HS) treatment, and the honeycomb flavonoids supplement under heat stress conditions (HF) treatment for a 30-day-long trial. Each treatment contains 4 replicates, with 50 cows in each replicate. Production performances including dry matter intake (DMI), milk production, and milk quality were measured on the basis of replicate. Furthermore, two cows of each replicate were selected for the measurement of the nutrient digestibility, the ruminal fermentable parameters including ruminal pH, volatile fatty acids, and ammonia-N, and the rumen microbial communities and metabolism. Results showed that HF effectively increased DMI, milk yield, milk fat, and ruminal acetate content (p < 0.05) compared with HS. Likewise, digestibility of NDF was promoted after HF supplement compared with HS. Furthermore, relative abundances of rumen microbial diversities especially Succiniclasticum, Pseudobutyrivibrio, Acetitomaculum, Streptococcus, and Succinivibrio, which mainly participated in energy metabolism, significantly improved after HF supplement. Metabolomic investigation showed that HF supplement significantly upregulated relative content of lipometabolic-related metabolites such as phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, and phosphatidylethanolamine, while it downregulated biogenic amines. In summary, HF supplement helps proliferate microbial abundances, which further promoted fiber digestibility and energy provision, and ultimately enhances the production performances of dairy cows under heat stress conditions.
Highlights
Heat stress traditionally refers to the combination of the excessive heat accumulation and the reductive heat dissipation, which may seriously induce fervescence [1, 2], the reduction of feed intake [3], the turbulence of rumen microbiota, and the reduction of milk production of dairy cows [4]
Temperature and relative humidity of each treatment were recorded in five different locations, and the temperature humidity indexes (THI) was calculated based on the average temperature and humidity
THI provided a confirmation of the occurrence of heat stress
Summary
Heat stress traditionally refers to the combination of the excessive heat accumulation and the reductive heat dissipation, which may seriously induce fervescence [1, 2], the reduction of feed intake [3], the turbulence of rumen microbiota, and the reduction of milk production of dairy cows [4]. Disorders of ruminal microbial ecosystem and the following declines of nutritional digestibility when subjected to heat stress mainly caused the reduction of dairy production [15, 16]. The most critical point in attenuating heat stress is the re-establishment of the physiological thermal energy balance between heat acquisition and heat dissipation through the regulation of ruminal microbial community and nutrient metabolism. Flavonoids extracted from honeycomb were supplemented to investigate the productive, rumen microbial, and rumen metabolism responses of cows under heat stress conditions, which aimed to provide a selectable suggestion for dairy production. We hypothesized that flavonoids help promote the proliferation of fiber-degrading bacteria, following the regulation of energy metabolism, and enhanced the production performances of dairy cows
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