Dietary Energy Levels Affect Rumen Bacterial Populations that Influence the Intramuscular Fat Fatty Acids of Fattening Yaks (Bos grunniens)

Abstract

The yak rumen microflora has more efficient fiber-degrading and energy-harvesting abilities than that of low-altitude cattle; however, few studies have investigated the effects of dietary energy levels on the rumen bacterial populations and the relationship between rumen bacteria and the intramuscular fatty acid profile of fattening yaks. In this study, thirty yaks were randomly assigned to three groups. Each group received one of the three isonitrogenous diets with low (3.72 MJ/kg), medium (4.52 MJ/kg), and high (5.32 MJ/kg) levels of net energy for maintenance and fattening. After 120 days of feeding, results showed that increasing dietary energy significantly increased ruminal propionate fermentation and reduced ammonia concentration. The 16S rDNA sequencing results showed that increasing dietary energy significantly increased the ratio of Firmicutes to Bacteroidetes and stimulated the relative abundance of Succiniclasticum, Saccharofermentans, Ruminococcus, and Blautia populations. The quantitative real-time PCR analysis showed that high dietary energy increased the abundances of Streptococcus bovis, Prevotella ruminicola, and Ruminobacter amylophilus at the species level. Association analysis showed that ruminal acetate was positively related to some intramuscular saturated fatty acid (SFA) contents, and Prevotella was significantly positively related to intramuscular total polyunsaturated fatty acid content and negatively related to intramuscular total SFA content. This study showed that high dietary energy mainly increased ruminal amylolytic and propionate-producing bacteria populations, which gave insights into how the effects of dietary energy on rumen bacteria are related to intramuscular fat fatty acids of fattening yaks.

Dynamics of rumen bacterial composition of yak (Bos grunniens) in response to dietary supplements during the cold season

“…The genus Ruminobacter is mainly responsible for degrading starch into acetate and propionate in the rumen (Hamlin & Hungate, 1956). The abundance of this genus in the rumen has been reported to be associated with concentrate diet in Holstein Cows (Wang et al, 2020), which is in agreement with our results. The genus Oscillospira is the first reported bacteria to be involved in plant cell wall degradation (Yanagita et al, 2003), which might explain its abundance in GG and OG groups.…”

“…High forage content in GG and CG groups increased the proportion of acetate and decreased propionate, which is in agreement with other study (Agle et al, 2010). Similar results were reported in the rumen of yak fed high forage diet compared to concentrate diet (Wang et al, 2020) and in a study conducted on Holstein cows when fed a high concentrate diet compared to a high forage diet (Wang et al, 2020). We also recorded higher proportions of isobutyrate and isovalerate in the CG group compared to GG and OG groups, which are similar to results reported in yaks fed concentrate diet (Liu et al, 2019a).…”

“…It is also reported to promote the growth of bacteria and prevent rumen acidosis (Bryant, 1956). Therefore, the high abundance of Selenomonas in the CG group might be related to the availability of more fermentable substrate compared to other groups, in agreement with the previous studies (Kim et al, 2018;Hu et al, 2020) who reported that a moderate increase in dietary energy increased the abundance of Selenomonas in the rumen of yak. Although in the present study no significant correlation was observed between genus Corynebacterium and ruminal butyrate proportions, this genus is known to be able to utilize carbohydrates to produce butyrate in the rumen (Douglas & Gunter, 1946), which might explain the higher proportion of butyrate observed in the CG group compared to other groups.…”

“…Studies have reported that many factors can contribute to define the rumen microbiota, specifically diet (Tremaroli & Bäckhed, 2012;Wang et al, 2018). Several studies have reported distinct variations in the rumen microbial community of cows when fed different dietary fiber (Thoetkiattikul et al, 2013) and diets with different concentrate to forage ratios (Wang et al, 2020), indicating a clear influence of diet on the microbiota. So, a comprehensive understanding of the rumen microbial community and what are the changes it undergoes due to different type of diets is important to enhance the welfare, health, and production of livestock.…”

Rumen Bacterial Community of Grazing Lactating Yaks (Poephagus grunniens) Supplemented with Concentrate Feed and/or Rumen-Protected Lysine and Methionine

“…Accounting for 87.1% of the total detected OTUs, Bacteroidetes and Firmicutes were the dominant phyla in the rumen bacterial community, which indicates that they play an important role in the bacterial ecology and the degradation of substrates in grazing, lactating yaks. Similarly, Bacteroidetes and Firmicutes constituted the majority of bacteria in cattle [ 30 ], dairy cows [ 31 , 32 ], growing yaks [ 33 ] and other lactating yaks [ 28 ].…”