Effects of trace minerals supply from rumen sustained release boluses on milk yields and components, rumen fermentation and the rumen bacteria in lactating yaks (Bos grunniens)

The experiment was conducted to evaluate trace mineral supplies of iron (Fe), copper (Cu), manganese (Mn), zinc (Zn), cobalt (Co), iodine (I) and selenium (Se) using rumen sustained release boluses on milk yield and milk components, rumen fermentation and the rumen bacteria in lactating yaks. Sixteen multiparous lactating yaks, blocked by parity, liveweight, and milk yield, were randomly assigned to two groups: CON (control group), a high forage diet with no supplemental iron Fe, Cu, Mn, Zn, Co, I and Se; MIN (dietary supplementation of inorganic trace minerals), the CON diet was fed and one rumen sustained release boluses providing inorganic Fe, Cu, Mn, Zn, Co, I and Se were given. The milk yield and lactoferrin concentration were greater ( P < 0.01) in the MIN group than those in the CON group. The MIN group had a higher yield of milk protein ( P = 0.02) and lactose ( P < 0.01) and a lower milk fat content ( P = 0.04) than those in the CON group. Relative to the CON group, MIN group had higher ( P < 0.05) milk content of Ca, P, Mg, Cu, Mn and Fe. The rumen ammonia nitrogen (NH 3 -N) concentration ( P = 0.02) and valerate proportion ( P = 0.01) were higher and acetate proportion were lower ( P = 0.03) in the MIN group than those in the CON group. The relative abundances of Planctomycetes tended to be higher and the Lentisphaerae, Candidatus_Melainabacteria Erysipelotrichaceae_UCG-004 and Tenericutes_bacterium tended to be lower in MIN group. Operational taxonomic units (OTU) unique to the CON and MIN belonged mainly to the phylum Bacteroidetes and Firmicutes, respectively. The relative abundance of Candidatus_Saccharimonas , Erysipelotrichaceae_UCG-004 , Ruminococcaceae_UCG-014 and Ruminococcaceae_NK4A214_group correlated positively with concentration of milk fat and acetate. Relative abundance of Succiniclasticum and Acinetobacter positively correlated with concentration of lactoferrin, milk yield, milk protein yield and milk lactose yield. Overall, these results suggest that trace mineral supply from rumen sustained release boluses has influenced milk yield, milk components and rumen microbiota of lactating yaks, which provides new insights in understanding the trace mineral metabolism, and shed lights on the trace mineral application of yaks and other ruminants lived at Qinghai-Tibetan Plateau. • Supplementation of trace minerals increased the milk yield in lactating yaks. • Supplementation of trace minerals increased the milk protein yield and lactoferrin concentration. • Supplementation of trace minerals altered rumen bacteria.