Yaks living on the Qinghai-Tibetan Plateau for a long time have evolved a series of mechanisms to adapt to the unique geographical environment and climate characteristics of the plateau. Compared with other ruminants, yaks have higher energy utilization and metabolic efficiency. This paper presents possible mechanisms responsible for the efficient energy utilization, absorption and metabolism resulting from the unique evolutionary process of yaks. It is hoped that the information discussed in this review will give a better insight into the uniqueness and superiority of yaks in regards to energy metabolism and utilization compared with cattle and open new avenues for the targeted regulation of energy utilization pathways of other ruminants.

This study aimed to investigate the changes in the blood metabolic profiles of grazing yaks during the cold season to reveal their physiological status and seek the nutrients needed to be supplemented. Six castrated yaks (3 years old) with 166.8 kg (standard deviation = 5.3) of liveweight grazed in the Qinghai-Tibetan Plateau were used as experimental animals without supplementary feeding. Blood samples of each animal were collected in October and December 2015, and March 2016 for the analysis of serum biochemicals and metabolome. Results showed serum indices involved in protein metabolism in grazing yaks showed greater differences during the cold season than the metabolisms of energy or minerals. Cold stress in December had minor effects on the serum metabolic profiles of yaks compared with those in October. Yaks in October and December shared seven differential serum metabolites and enrichments of the “arachidonic acid metabolism” and “glycine, serine, and threonine metabolism” pathways compared with those in March caused by the shortage of feeds. Summarily, the nutrient deficiency would be influential on the physiological status of grazing yaks during the cold season, especially on the protein metabolism, which could be improved by supplementary feeds.

Dietary anthocyanins (ATH) have probiotic and antioxidant functions in humans. They may also have beneficial impacts on rumen microorganisms and subsequently nutrient digestion in cattle. The experiment aimed to study the effects of dietary red cabbage extract (RCE) rich in ATH on rumen fermentation, rumen bacterial community, and nutrient digestibility in beef bulls. Eight Simmental beef bulls and two RCE levels (0 and 120 g/d) were allocated in a replicated 2 × 2 crossover design. Each experimental period included 15 days for adaptation and subsequent 5 days for sampling. The results showed that dietary addition of RCE increased the ruminal concentration of total volatile fatty acids and the molar proportion of propionate, decreased the acetate to propionate ratio, and tended to decrease the molar proportion of acetate, but it did not affect the ruminal pH and the concentrations of ammonia N, microbial CP, monophenols, polyphenols, and total phenolics. ATH was undetectable in the ruminal fluid of beef bulls in both groups. RCE did not affect the alpha diversity of rumen bacterial community, and the relative abundances of major rumen bacteria at the phylum level, but it increased the relative abundances of Ruminobacter and Anaerovibrio and tended to increase the relative abundances of Oribacterium and Monoglobus at the genus level. RCE tended to increase the plasma concentrations of globulin and total protein, but it did not affect the plasma albumin, urea, triglyceride, glucose, and antioxidant activities. Dietary addition of RCE did not affect the apparent nutrient digestibility. In conclusion, the ATH in RCE was highly hydrolysable in rumen fluid. Dietary addition of RCE increased the ruminal concentration of total volatile fatty acids, decreased the acetate to propionate ratio, and slightly modified the rumen bacterial community, but it did not affect the nutrient digestibility and the plasma antioxidants in beef bulls.

Perinatal cows suffer serious physiological stress and energy deficiency. Phytosterols have bioactive functions for gut microbes.

Nitrous oxide (N₂O) is a potent greenhouse gas as well as the key component depleting the ozone sphere of the earth. Cattle have high feed and water intakes and excrete large amounts of urine and feces. N₂O can be produced from cattle excreta during storage and use as fertilizer. Mitigating the N₂O emissions from cattle excreta during production is important for protecting the environment and the sustainable development of the cattle industry. Feeding cattle with low-protein diets increases N utilization rates, decreases N excretion and consequently reduces N₂O emissions. However, this approach cannot be applied in the long term because of its negative impact on animal performance. Recent studies showed that dietary inclusion of some plant secondary metabolites such as tannins, anthocyanins, glucosinolates and aucubin could manipulate the N excretion and the urinary components and consequently regulate N₂O emissions from cattle excreta. This review summarized the recent developments in the effects of dietary tannins, anthocyanins and glucosinolates on the metabolism of cattle and the N₂O emissions from cattle excreta and concluded that dietary inclusion of tannins or anthocyanins could considerably reduce N₂O emissions from cattle excreta.

This trial was conducted to study the effects of dietary rapeseed cake (RSC) containing high glucosinolates (GLS) on rumen fermentation, nutrient digestion and the rumen microbial community in steers. Eight growing steers and four rations containing RSC (GLS 226·1 μmol/g DM) at 0·00, 2·65, 5·35 and 8·00 % DM were assigned in a replicate 4 × 4 Latin square design. The results indicated that increasing RSC levels increased the ruminal concentration of thiocyanate (SCN) (P < 0·01), decreased the ruminal concentration of ammonia nitrogen (NH₃-N) and the molar proportion of isovalerate (P < 0·05), did not affect the ruminal concentration of total volatile fatty acids (P > 0·05), decreased the crude protein (CP) digestibility (P < 0·05) and increased the ether extract (EE) digestibility (P < 0·01). Increasing RSC levels tended to decrease the abundances of ruminal Ruminobacter amylophilus (P = 0·055) and Ruminococcus albus (P = 0·086) but did not affect methanogens, protozoa, fungi and other bacteria (P > 0·05). Increasing RSC levels in the ration did not affect the ruminal bacterial diversity (P > 0·05), but it increased the operational taxonomic units and the bacterial richness (P < 0·05) and affected the relative abundances of some bacteria at the phylum level and genus level (P < 0·05). In conclusion, RSC decreased the ruminal concentration of NH₃-N and the CP digestibility, increased the EE digestibility and partly affected the ruminal bacterial community. SCN, as the metabolite of GLS, could be a major factor affecting these indices.