Tibetan sheep are better able to cope with low energy intake than Small-tailed Han sheep due to lower maintenance energy requirements and higher nutrient digestibilities

Targeted Screening of Fiber Degrading Bacteria with Probiotic Function in Herbivore Feces

Cellulolytic bacteria with probiotic functions play a crucial role in promoting the intestinal health in herbivores. In this study, we aimed to correlate the 16S rRNA gene amplicon sequencing and fiber-degrading enzyme activity data from six different herbivore feces samples. By utilizing the separation and screening steps of probiotics, we targeted and screened high-efficiency fiber-degrading bacteria with probiotic functions. The animals included Maiwa Yak (MY), Holstein cow (CC), Tibetan sheep (TS), Southern Sichuan black goat (SG), Sichuan white rex rabbit (CR), and New Zealand white rabbit (ZR). The results showed that the enzymes associated with fiber degradation were higher in goat and sheep feces compared to cattle and rabbit's feces. Correlation analysis revealed that Bacillus and Fibrobacter were positively correlated with five types of fiber-degrading related enzymes. Notably, the relative abundance of Bacillus in the feces of Tibetan sheep was significantly higher than that of other five herbivores. A strain TS5 with good cellulose decomposition ability from the feces of Tibetan sheep by Congored staining, filter paper decomposition test, and enzyme activity determination was isolated. The strain was identified as Bacillus velezensis by biological characteristics, biochemical analysis, and 16S rRNA gene sequencing. To test the probiotic properties of Bacillus velezensis TS5, we evaluated its tolerance to acid and bile salt, production of digestive enzymes, antioxidants, antibacterial activity, and adhesion ability. The results showed that the strain had good tolerance to pH 2.0 and 0.3% bile salts, as well as good potential to produce cellulase, protease, amylase, and lipase. This strain also had good antioxidant capacity and the ability to antagonistic Staphylococcus aureus BJ216, Salmonella SC06, Enterotoxigenic Escherichia coli CVCC196, and Escherichia coli ATCC25922. More importantly, the strain had good self-aggregation and Caco-2 cell adhesion rate. In addition, we tested the safety of Bacillus velezensis TS5 by hemolysis test, antimicrobial susceptibility test, and acute toxicity test in mice. The results showed that the strain had no hemolytic phenotype, did not develop resistance to 19 commonly used antibiotics, had no cytotoxicity to Caco-2, and did not have acute toxic harm to mice. In summary, this study targeted isolated and screened a strain of Bacillus velezensis TS5 with high fiber-degrading ability and probiotic potency. This strain can be used as a potential probiotic for feeding microbial preparations for ruminants.

Comparative analysis of genome-wide copy number variations between Tibetan sheep and White Suffolk sheep

The DNA copy number variations (CNVs) are widely involved in affecting various kinds of biological functions, such as environmental adaptation. Tibetan sheep and White Suffolk sheep are two representative indigenous and exotic breeds raised in Sichuan, China, and both of them have many contrasting biological characteristics. In this study, we employed high-throughput sequencing approach to investigate genome-wide CNVs between the two sheep breeds. A total of 11,135 CNV regions (CNVRs) consisting of 6,488 deletions and 4,647 duplications were detected, whose length ranged from 1,599 bp to 0.56 Mb with the mean of 4,658 bp. There were 281 CNVRs segregated between Tibetan sheep and White Suffolk sheep, and 18 of them have been fixed within both breeds. Functional analyses of candidate genes within the segregating CNVRs revealed the thyroid hormone signaling pathway and CTNNB1 gene that would be responsible for differential biological characteristics of breeds, such as energy metabolism, seasonal reproduction, and litter size. Furthermore, the segregating CNVRs identified in this study were overlapped with many known quantitative trait loci that are associated with growth, testis weight, and reproductive seasonality. In conclusion, these results help us better understanding differential biological characteristics between Tibetan sheep and White Suffolk sheep.

Effect of dietary Agriophyllum squarrosum on average daily gain, meat quality and muscle fatty acids in growing Tan lambs

The herb A. squarrosum is reputed to possess medicinal properties for humans, and has the potential to be a feed resource for livestock. We hypothesized that this herb would improve the meat quality of lambs. To test this hypothesis, 24 Tan ewe-lambs (27.7 ± 0.45 kg) were offered diets containing 0 (CON), 100 (AS₁₀₀), 200 (AS₂₀₀) and 300 (AS₃₀₀) g A. squarrosum/kg DM, and average daily gain, carcass traits, blood metabolites, meat quality and fatty acid profiles were determined. Drip loss % and cooking loss % decreased with the AS₁₀₀ and AS₂₀₀ diets (P < 0.05). Dietary A. squarrosum reduced muscle fiber area and diameter and increased density of the meat (P < 0.05), which indicated that the meat was more tender. The concentrations of C10:0 and C18:1n-9 t were 1ower and of C17:0 and C18:3n-3 were greater in the AS₂₀₀ and AS₃₀₀ treatments than CON (P < 0.05). Our results suggest that feeding lambs up to 200 g/kg DM of A. squarrosum can increase the water-holding capacity and L* value of meat without compromising growth. Further research is needed to determine the optimal level.

Rumen microbiota of indigenous and introduced ruminants and their adaptation to the Qinghai–Tibetan plateau

The grassland in the Qinghai–Tibetan plateau provide habitat for many indigenous and introduced ruminants which perform important ecological functions that impact the whole Qinghai–Tibetan plateau ecosystem. These indigenous Tibetan ruminants have evolved several adaptive traits to withstand the severe environmental conditions, especially cold, low oxygen partial pressure, high altitude, strong UV radiation, and poor forage availability on the alpine rangelands. Despite the challenges to husbandry associated with the need for enhanced adaptation, several domesticated ruminants have also been successfully introduced to the alpine pasture regions to survive in the harsh environment. For ruminants, these challenging conditions affect not only the host, but also their commensal microbiota, especially the diversity and composition of the rumen microbiota; multiple studies have described tripartite interactions among host-environment-rumen microbiota. Thus, there are significant benefits to understanding the role of rumen microbiota in the indigenous and introduced ruminants of the Qinghai–Tibetan plateau, which has co-evolved with the host to ensure the availability of specific metabolic functions required for host survival, health, growth, and development. In this report, we systemically reviewed the dynamics of rumen microbiota in both indigenous and introduced ruminants (including gut microbiota of wild ruminants) as well as their structure, functions, and interactions with changing environmental conditions, especially low food availability, that enable survival at high altitudes. We summarized that three predominant driving factors including increased VFA production, enhanced fiber degradation, and lower methane production as indicators of higher efficiency energy harvest and nutrient utilization by microbiota that can sustain the host during nutrient deficit. These cumulative studies suggested alteration of rumen microbiota structure and functional taxa with genes that encode cellulolytic enzymes to potentially enhance nutrient and energy harvesting in response to low quality and quantity forage and cold environment. Future progress toward understanding ruminant adaptation to high altitudes will require the integration of phenotypic data with multi-omics analyses to identify host-microbiota co-evolutionary adaptations enabling survival on the Qinghai–Tibetan plateau.

A comparison of average daily gain, apparent digestibilities, energy balance, rumen fermentation parameters, and serum metabolites between yaks (Bos grunniens) and Qaidam cattle (Bos taurus) consuming diets differing in energy level

Yaks (Bos grunniens), indigenous to the harsh Qinghai-Tibetan Plateau, are well adapted to the severe conditions, and graze natural pasture without supplements all year round. Qaidam cattle (Bos taurus), introduced to the Qinghai-Tibetan Plateau 1,700 years ago, are raised at a lower altitude than yaks, provided with shelter at night and offered supplements in winter. Based on their different backgrounds, we hypothesized that yaks have lower energy requirements for maintenance than cattle. To test this hypothesis, we measured average daily gain (ADG), apparent digestibilities, energy balance, rumen fermentation parameters, and serum metabolites in growing yaks and cattle offered diets differing in metabolizable energy (ME) levels (6.62, 8.02, 9.42 and 10.80 MJ/kg), but with the same crude protein concentration. Six castrated yaks (155 ± 5.8 kg) and 6 castrated Qaidam cattle (154 ± 8.0 kg), all 2.5 years old, were used in 2 concurrent 4 × 4 Latin square designs. Neutral and acid detergent fiber digestibilities were greater (P < 0.05) in yaks than in cattle, and decreased linearly (P < 0.05) with increasing dietary energy level; whereas, digestibilities of dry matter, organic matter, crude protein and ether extract increased (P < 0.05) linearly with increasing energy level. The ADG was greater (P < 0.001) in yaks than in cattle, and increased (P < 0.05) linearly with increasing energy levels. From the regressions of ADG on ME intake, the estimated ME requirement for maintenance was lower (P < 0.05) in yaks than in cattle (0.43 vs. 0.57 MJ/kg BW^0.75). The ratios of digestible energy (DE):gross energy and ME:DE were higher (P < 0.05) in yaks than in cattle, and increased (P < 0.05) linearly with increasing dietary energy level. Ruminal pH decreased (P < 0.05), whereas concentrations of total volatile fatty acids (VFAs) and ammonia increased (P < 0.01) with increasing dietary energy level, and all were greater (P < 0.05) in yaks than in cattle. Concentrations of ruminal acetate and iso-VFAs were greater (P < 0.05), whereas propionate was lower (P < 0.05) in yaks than in cattle; acetate decreased (P < 0.001), whereas butyrate and propionate increased (P < 0.001) linearly with increasing dietary energy level. Serum concentrations of β-hydroxybutyrate were lower (interaction, P < 0.001) in yaks than in cattle fed diets of 9.42 and 10.80 MJ/kg, whereas non-esterified fatty acids were greater (interaction, P < 0.01) in yaks than in cattle fed diets of 6.62 and 8.02 MJ/kg. Concentrations of serum leptin and growth hormone were greater in yaks than in cattle and serum insulin and growth hormone increased (P < 0.01) linearly with increasing dietary energy level. Our hypothesis that yaks have lower energy requirements for maintenance than cattle was supported. This lower requirement confers an advantage to yaks over Qaidam cattle in consuming low energy diets during the long winter on the Qinghai-Tibetan Plateau.

Differences between Yaks and Qaidam Cattle in Digestibilities of Nutrients and Ruminal Concentration of Volatile Fatty Acids Are not Dependent on Feed Level

The Qinghai–Tibetan Plateau (QTP) is characterized by highly fluctuating seasonal pastures. Yaks (Bos grunniens) graze at higher altitudes than Qaidam cattle (Bos taurus), but the two bovine species co-graze in their overlapping ranges. We hypothesized that yaks would digest nutrients to a greater extent and utilize energy more efficiently than cattle at low dietary intakes, but the difference between bovine species would not be apparent at high intakes. To test this hypothesis, six yaks (203 ± 6.0 kg) and six Qaidam cattle (214 ± 9.0 kg), all 3.5-year-old castrated males, were used in two concurrent 4 × 4 Latin square designs with two extra steers of each species in each period. The digestibilities of dry matter, organic matter, crude protein, ether extract, neutral and acid detergent fiber were greater (p < 0.05) in yaks than in cattle and decreased linearly (p < 0.05) when feed level (FL) increased. The average daily gain (ADG), the ratios of digestible energy (DE) to gross energy and metabolizable energy (ME) to DE, and ruminal total volatile fatty acids and ammonia-N concentrations were greater (p < 0.001) in yaks than in cattle and increased linearly (p < 0.001) when FL increased. Based on the regression equations of ADG on ME intake, the daily ME requirement for maintenance in yaks was 0.53 MJ BW−0.75 d−1, which was lesser (p < 0.05) than the 0.62 MJ BW−0.75 d−1 in cattle. We concluded that: (1) when differences between breeds emerged, the differences existed for all FLs; (2) maintenance energy requirement was lesser and ADG was greater in yaks than in cattle; (3) the digestibilities of nutrients were greater in yaks than in cattle when consuming only oat hay pellets. These findings indicate that yaks adapt to fluctuating dietary intakes in harsh environments by having a low energy requirement and high digestibility of nutrients, independent of the FL.

Small intestinal morphology and sugar transporters expression when consuming diets of different energy levels: comparison between Tibetan and small-tailed Han sheep

Some non-structural carbohydrates, especially starch, escape ruminal fermentation, are converted into glucose, and are absorbed from the small intestine. This glucose provides an important source of energy, and its usage is more efficient than glucose from carbohydrates which are fermented as short chain fatty acids in the rumen and, subsequently, undergo hepatic gluconeogenesis. Tibetan sheep graze on the harsh Qinghai-Tibetan Plateau (QTP) all year round and their carbohydrate and energy intakes fluctuate greatly with seasonal forage availability. Consequently, a high capacity to absorb glucose from the small intestine would be particularly beneficial for Tibetan sheep to allow them to cope with the inconsistent dietary intakes. This study examined how the small intestinal morphology and sugar transporters' expression of Tibetan and Small-tailed Han (Han) sheep respond to fluctuating energy intakes under the harsh conditions of the QTP. Han sheep graze on the QTP only in summer and are generally raised in feedlots. Twenty-four Tibetan sheep and 24 Han sheep, all wethers, were assigned randomly to four groups (n = 6 per breed/group), with each group offered a diet differing in digestible energy content: 8.21, 9.33, 10.45 and 11.57 MJ/kg DM. After 49 d, all sheep were slaughtered, tissues of the small intestine were collected, and measurements were made of the morphology and glucose transporters and the related regulation gene expressions. At intakes of low energy levels, Tibetan sheep had a greater villus surface area in the duodenum, jejunum and ileum and higher mRNA expression of sodium-dependent glucose transporter 1 in the duodenum and ileum (P < 0.05) than Han sheep. In the glucose transporter 2 (GLUT2) mediated glucose absorption pathway, Tibetan sheep had higher GLUT2 and taste receptor family 1 member 2 and 3 mRNA expressions than Han sheep in the duodenum, jejunum and ileum (P < 0.05). We concluded that the differences between breeds indicated a greater glucose absorption capacity in the small intestine of Tibetan than Han sheep, which would confer an advantage to Tibetan over Han sheep to an inconsistent energy intake on the harsh QTP. These findings suggested that ruminants raised under harsh environmental conditions with highly fluctuating dietary intakes, as is often the case in grazing ruminants worldwide, are able to absorb glucose from the small intestine to a greater extent than ruminants raised under more moderate conditions.

Hypothalamic regulation of energy homoeostasis when consuming diets of different energy concentrations: comparison between Tibetan and Small-tailed Han sheep

Seasonal energy intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau (QTP) fluctuates greatly and is often well below maintenance requirements. The aim of this study was to gain insight into how the hypothalamus regulates energy homoeostasis in Tibetan sheep. We compared Tibetan and Small-tailed Han sheep (n 24 of each breed), which were each allocated randomly into four groups and offered one of four diets that differed in digestible energy densities: 8·21, 9·33, 10·45 and 11·57 MJ/kg DM. Sheep were weighed every 2 weeks, and it was assumed that the change in body weight (BW) reflected the change in energy balance. The arcuate nucleus of the hypothalamus in Tibetan sheep had greater protein expressions of neuropeptide Y (NPY) and agouti-related peptide (AgRP) when in negative energy balance, but lesser protein expressions of proopiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART) when in positive energy balance than Small-tailed Han sheep. As a result, Tibetan sheep had a lesser BW loss when in negative energy balance and stored more energy and gained more BW when in positive energy balance than Small-tailed Han sheep with the same dietary intake. Moreover, in the hypothalamic adenosine monophosphate-activated protein kinase (AMPK) regulation pathway, Tibetan sheep had greater adenosine monophosphate-activated protein kinase-α 2 protein expression than Small-tailed Han sheep, which supported the premise of a better ability to regulate energy homoeostasis and better growth performance. These differences in the hypothalamic NPY/AgRP, POMC/CART and AMPK pathways between breeds conferred an advantage to the Tibetan over Small-tailed Han sheep to cope with low energy intake on the harsh QTP.

Energy substrate metabolism in skeletal muscle and liver when consuming diets of different energy levels: comparison between Tibetan and Small-tailed Han sheep

The energy intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau (QTP) varies greatly with seasonal forage fluctuations and is often below maintenance requirements, especially during the long, cold winter. The liver plays a crucial role in gluconeogenesis and skeletal muscle is the primary tissue of energy expenditure in mammals. Both play important roles in energy substrate metabolism and regulating energy metabolism homeostasis of the body. This study aimed to gain insight into how skeletal muscle and liver of Tibetan sheep regulate energy substrate metabolism to cope with low energy intake under the harsh environment of the QTP. Tibetan sheep (n = 24; 48.5 ± 1.89 kg BW) were compared with Small-tailed Han sheep (n = 24; 49.2 ± 2.21 kg BW), which were allocated randomly into one of four groups that differed in dietary digestible energy densities: 8.21, 9.33, 10.45 and 11.57 MJ /kg DM. The sheep were slaughtered after a 49-d feeding period, skeletal muscle and liver tissues were collected and measurements were made of the activities of the key enzymes of energy substrate metabolism and the expressions of genes related to energy homeostasis regulation. Compared with Small-tailed Han sheep, Tibetan sheep exhibited higher capacities of propionate to glucose conversion and fatty acid oxidation and ketogenesis in the liver, higher glucose utilization efficiency in both skeletal muscle and liver, but lower activities of fatty acid oxidation and protein mobilization in skeletal muscle, especially when in negative energy balance. However, the Small-tailed Han sheep exhibited higher capacities to convert amino acids and lactate to glucose and higher levels of glycolysis and lipogenesis in the liver than Tibetan sheep. These differences in gluconeogenesis and energy substrate metabolism conferred the Tibetan sheep an advantage over Small-tailed Han sheep to cope with low energy intake and regulate whole-body energy homeostasis under the harsh environment of the QTP.

Comparison between Tibetan and Small-tailed Han sheep in adipocyte phenotype, lipid metabolism and energy homoeostasis regulation of adipose tissues when consuming diets of different energy levels

This study aimed to gain insight into how adipose tissue of Tibetan sheep regulates energy homoeostasis to cope with low energy intake under the harsh environment of the Qinghai-Tibetan Plateau (QTP). We compared Tibetan and Small-tailed Han sheep (n 24 of each breed), all wethers and 1·5 years of age, which were each divided randomly into four groups and offered diets of different digestible energy (DE) densities: 8·21, 9·33, 10·45 and 11·57 MJ DE/kg DM. When the sheep lost body mass and were assumed to be in negative energy balance: (1) adipocyte diameter in subcutaneous adipose tissue was smaller and decreased to a greater extent in Tibetan than in Small-tailed Han sheep, but the opposite occurred in the visceral adipose tissue; (2) Tibetan sheep showed higher insulin receptor mRNA expression and lower concentrations of catabolic hormones than Small-tailed Han sheep and (3) Tibetan sheep had lower capacity for glucose and fatty acid uptake than Small-tailed Han sheep. Moreover, Tibetan sheep had lower AMPKα mRNA expression but higher mammalian target of rapamycin mRNA expression in the adipocytes than Small-tailed Han sheep. We concluded that Tibetan sheep had lower catabolism but higher anabolism in adipose tissue and reduced the capacity for glucose and fatty acid uptake to a greater extent than Small-tailed Han sheep to maintain energy homoeostasis when in negative energy balance. These responses provide Tibetan sheep with a high ability to cope with low energy intake and with the harsh environment of the QTP.

Carcass parameters and meat quality of Tibetan sheep and Small-tailed Han sheep consuming diets of low-protein content and different energy yields

Today, consumers are very health conscious and are more aware of the nutritional value of food, especially of meat, than they were in the past. The aim of this study was to evaluate the carcass parameters and meat quality of Tibetan sheep and Small-tailed Han sheep when consuming a diet of low-protein (~7%) and different energy yields (digestible energy, 8.21, 9.33, 10.45 and 11.57 MJ/kg) in the cold season. Twelve sheep of each breed were divided randomly into four treatments of different diets with three replicates per treatment per breed. Crude protein of the meat decreased linearly (p < .05), whereas energy increased linearly (p < .05) with an increase in energy level. Tibetan sheep tended to have a higher (p < .1) dressing percentage and rib eye area, while live body weight and hot carcass weight did not differ between breeds but increased linearly (p < .01) with an increase in energy level. Water holding capacity, as indicated by pressing loss and drip loss, did not differ between breeds and was not affected by dietary energy. The concentration of n-3 polyunsaturated fatty acids (PUFAs) was greater in Tibetan sheep meat but saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and n-6 PUFA did not differ between breeds. With an increase in energy content of the diet, SFA decreased (p < .05), whereas MUFA increased (p < .05). The n-6:n-3 PUFA ratio was lower (p < .001) in Tibetan sheep meat, while the atherogenic index did not differ between breeds, but tended to decrease (p < .1) with an increase in dietary energy content. The essential amino acid (EAA) content and ratio of EAA:NEAA (non-essential amino acid) were close to the world standards for healthy meat. In summary, (a) Tibetan sheep meat was preferable to Small-tailed Han sheep meat, although differences between breeds were small; and (b) some carcass parameters and meat quality were improved with an increase in dietary energy level when a low-protein diet was offered.

Diversity and Composition of Rumen Bacteria, Fungi, and Protozoa in Goats and Sheep Living in the Same High-Altitude Pasture

Simple Summary

Tibetan goats and sheep graze together but have different growth performances, immune responses, and feeding preferences in the Tibetan pasture. Rumen microbiota composed of bacteria, fungi, and protozoa are necessary for a healthy ruminant. Therefore, in this study, we comprehensively describe composition and diversity of bacteria, fungi, and protozoa in the high- altitude rumen. Compared with sheep, the bacteria that degrade crude protein and produce volatile fatty acids (VFA) were increased in the rumen of goats (Saccharofermentans and Lachnospiraceae_XPB1014) (p < 0.05). In addition, when compared with goats, the fungi and protozoa that degrade fiber were increased in rumen of sheep (Neocallimastigaceae and Metadinium) (p < 0.05). Furthermore, VFA were significantly increased in the rumen of goats compared with sheep (p < 0.05). The VFA level was consistent with differences in the microbiota composition in the rumen between goats and sheep. Under mixed grazing conditions, goats tend to select a high-crude protein diet that is good for growth, whereas sheep tend to select a high-lignin diet that is difficult to digest. Therefore, the different microbiota in the rumen of goats and sheep may be explained by dietary preference.

Abstract

Environmental adaptation of ruminants was highly related to microbiota in the rumen. To investigate the diversity and composition of bacteria, fungi, and protozoa in the rumen of high-altitude animals, amplicon gene sequencing was performed using rumen fluid samples derived from both Tibetan goats and sheep at the same pasture in a highland (altitude > 4800 m). Between these two species, the ruminal bacteria and fungi were significantly different at multiple taxonomic levels. The alpha diversity of bacteria was significantly high in goats (p < 0.05). One hundred and sixty-four and 29 Operational Taxonomy Units (OTUs) with significant differences were detected in bacteria and fungi, respectively. The abundance of bacteria, fungi, and protozoa in the rumen was characterized at multiple taxonomic levels, and we determined that Firmicutes, Bacteroidetes, Neocallimastigomycota, and Ciliophora were the most abundant bacteria, fungi, and protozoa. The family Neocallimastigaceae and the genus Metadinium had cellulose degradation capacity in the rumen with high abundance, thereby, suggesting that fungi and protozoa played an essential role in rumen fermentation. In addition, by comparing microbiota in the rumen of goats and sheep it was found, that the fiber-degrading fungi genus (Cyllamyces) was increased in the rumen of sheep (p < 0.05) whereas VFA-producing bacteria (Saccharofermentans and Lachnospiraceae_XPB1014) were increased in the rumen of goats (p < 0.05). Interestingly, in the rumen, no differences in protozoa were observed between goats and sheep (p > 0.05). Furthermore, when compared to sheep, level of acetic acid, propionic acid, and total volatile fatty acid (TVFA) were significantly increased in the rumen of goats (p < 0.05). Taken together, these results suggested microbiota in the rumen drive goats to better adapt to high-altitude grazing conditions.

Tibetan sheep have a high capacity to absorb and to regulate metabolism of SCFA in the rumen epithelium to adapt to low energy intake

The nutritional intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau is often under maintenance requirements, especially during the long, cold winter. However, they have adapted well and even thrive under these conditions. The aim of the present study was to gain insight into how the rumen epithelium of Tibetan sheep has adapted to the consumption of low-energy-level diets. For this purpose, we compared Tibetan and small-tailed Han sheep (n 24 of each breed, all wethers and 1·5 years of age), which were divided randomly into one of four groups and offered ad libitum diets of different digestible energy (DE) densities: 8·21, 9·33, 10·45 and 11·57 MJ DE/kg DM. The Tibetan sheep had higher rumen concentrations of total SCFA, acetate, butyrate and iso-acids but lower concentrations of propionate than small-tailed Han sheep. The Tibetan sheep had higher absorption capability of SCFA due to the greater absorption surface area and higher mRNA expression of the SCFA absorption relative genes than small-tailed Han sheep. For the metabolism of SCFA in the rumen epithelium, the small-tailed Han sheep showed higher utilisation of the ketogenesis pathway than Tibetan sheep; however, Tibetan sheep had greater regulation capacity in SCFA metabolism pathways. These differences between breeds allowed the Tibetan sheep to have greater capability of absorbing SCFA and better capacity to regulate the metabolism of SCFA, which would allow them to cope with low energy intake better than small-tailed Han sheep.