Effect of substituting steam-flaked corn for course ground corn on in vitro digestibility, average daily gain, serum metabolites and ruminal volatile fatty acids, and bacteria diversity in growing yaks

Abstract

Yaks are well adapted to the Qinqhai-Tibetan Plateau and, traditionally, only grazed natural pasture all year without supplements. Today, however, yaks are also raised in feedlots; consequently, more information is needed in choosing optimal feeding regimes. This study examined the effects of substituting steam-flaked corn (SFC) for coarse ground corn (CGC) on average daily gain (ADG), in vitro true digestibility (IVTD), concentrations of ruminal volatile fatty acids (VFAs) and serum metabolites, and rumen bacterial diversity of growing yaks. Twenty-one, 2-year-old male yaks (138 ± 37.3 kg) were divided randomly into 3 groups (n = 7 per group) and received a total mixed ration (TMR) for 143 days. The TMR contained 446 g corn per kg dry matter (DM), but the ratio of CGC: SFC differed among the three groups as: 1) 100:0 (SFC0), 2) 50:50 (SFC50), and 3) 0:100 (SFC100). To maintain conditions similar to the feedlots, the yaks were fed as a group and feed intake was recorded daily. The yaks were weighed on 6 occasions during the study and ADG was calculated for each yak from the regression equation of body weight (BW) on days of treatment. On the morning of d 144 before feed was offered, jugular vein blood was collected to measure the concentrations of serum metabolites, and rumen contents were collected to determine ruminal VFAs, fermentation parameters and bacterial diversity. The daily dry matter intake (DMI) averaged between 6.08 and 6.15 kg per yak for the three dietary treatments and the IVTD increased with an increase in SFC (P < 0.05). The ADG was higher (P < 0.05) by 13.2% (812 vs 717 g/d) in the SFC100 group than in the SFC0 group while the ratio of the average daily DMI per yak to the average ADG per yak was lowest numerically for the SFC100 group (7.51), followed by the SFC50 group (8.46) and then the SFC0 group (8.66). The serum concentrations of alkaline phosphatase (ALP), serum urea-N, and triglycerides (TG) decreased (P < 0.05) but of aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and total cholesterol (TC) increased (P < 0.05) with an increasing proportion of dietary SFC. The greater serum concentration of LDH and lesser concentration of serum urea-N suggests that the SFC50 and SFC100 groups were proliferating cells at a faster rate and depositing more protein in muscle tissue than the SFC0 group, as the ADG increased with an increase in the level of dietary SFC. The ruminal concentrations of VFAs increased and of NH3-N decreased with an increase in the proportion of SFC. The rumen bacterial diversity did not differ among dietary groups; Bacteroidetes and Firmicutes were the dominant phyla and Prevotella and Succiniclasticum were the dominant genera in all dietary treatments. These results demonstrated that increasing the proportion of SFC could improve IVTD, ruminal concentration of VFAs, ADG and the group DMI to ADG ratio.