Research On The Effects Of Nutritional Regulation Of Amino Acids And Minerals For Milk Quality And Ruminal Ecosystem In Lactating Yaks And Its Calves

Yak production depends on the vast natural grassland in the Qinghai-Tibet Plateau.However,serious grassland degradation and prominent ecological environment pressure caused by animal husbandry production had affected the sustainability of yak production.In addition,yaks have been raised in shed or half shed-feeding,but the nutrition management measures matched with this model are imperfect.Therefore,the objectives of this study were to investigate the effects of supplementing amino acids and minerals on milk yield and milk components,and rumen microbiome of lactating yak and its calves.Thirty-two and sixteen lactating yaks and its calves were selected to study the supplementary effects of amino acids and minerals,respectively.Thirty-two lactating yaks with parity（2-3）,body weight（169±15 kg）,milk yield（1.02±0.13 kg/d）and lactating period in 90 d were randomly assigned into one of four treatments:control（CON;basal diet without adding rumen-protected amino acid）,and the basal diet supplemented with RPM（50.0 g/yak/d）,RPL（66.7 g/yak/d）or RPML（12.5 RPM g/yak/d and 50 g RPL/yak/d）.The experimental period comprised 40 days with 10 days of adaptation followed by 30 days of data collection.The diets offered and the refusals were recorded daily.Samples of diets were collected on days 2,9,16,23,and 30 of the experimental period.Milk yields were recorded on days 2,9,16,23,and 30 of the experimental period.Milk samples and rumen fluid sampling of individual yaks were collected on days 16,23,and 30 of the experimental period for measurements of milk components,rumen fermentation parameters and rumen microbiome.And more,sixteen lactating yaks with parity（2-3）,body weight（175±10 kg）,milk yield（1.18±0.18 kg/d）and lactating period in 90 d were randomly assigned into two treatments:control（CON;basal diet without adding rumen sustained-release boluses）and mineral group（MIN;basal diet adding rumen sustained-release boluses）.The experimental period and sampling procedure are similar to previous described trial.Results as following shown that:1.The milk yield,dry matter intake（DMI）,lactoferrin（LF）,the yield of milk components（milk protein,fat,and lactose）,and energy-corrected milk for the RPM and RPML group were greater than those of the CON and RPL groups（P<0.05）.The RPM group had a lower ruminal p H（P<0.05）,whereas the RPML group had higher ammonia nitrogen than did the RPM,RPL,and CON groups（P<0.05）.RPM supplementation increased the concentration of butyrate and valerate as compared with the other three groups（P<0.05）.The relative abundance of Proteobacteria,Rikenellaceae_RC9_gut_group,and Prevotella₁ was increased in the RPM,RPL,and RPML groups（P<0.05）,respectively.Operational taxonomic units（OTU）unique to the RPL and RPML groups belonged mainly to phylum Bacteroidetes,whereas the majority of OTUs unique to the RPM group belonged mainly to phylum Firmicutes.Redundancy analysis showed that the relative abundance of Fibrobacter and Selenomonas₁ was positively correlated with milk yield,propionate,valerate,butyrate,and total volatile fatty acids.Also,the relative abundance of Candidatus_Saccharimonas,Ruminococcaceae_UCG-014,Rikenellaceae_RC9_gut_group,and Erysipelotrichaceae_UCG-004 was positively correlated with concentrations of milk protein,isovalerate,and isobutyrate.The relative abundances of planctomycetes in calves rumen of RPM group was greater than that of the CON,RPL and RPML groups（P<0.05）.2.The milk yield,LF,the yield milk protein and lactose were greater in the MIN group than those in the CON group（P<0.05）,while the fat and casein content of the MIN group were lower than those of the CON group（P<0.05）.The MIN group had a higher rumen NH₃-N concentrations and molar proportion of valerate（P<0.05）,and a lower molar proportion of acetate（P<0.05）.OTUs 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 milk fat.The relative abundance of Prevotella₁ and Succiniclasticum were positively correlated with milk protein and casein.The molar proportion of acetate and A:P positively correlated with Rikenellaceae_RC9_gut_group,Christensenellaceae_R-7_group,candidatus_Saccharimonas,Erysipelotrichaceae_UCG-004,Ruminococcaceae_UCG-014,and Ruminococcaceae_NK4A214_group.There was no effect on rumen fermentation parameters and rumen microbiome of yak calves among treatment.In conclusion,supplementation of 50 g/d RPM increased DMI,milk yield,milk protein content,lactoferrin of lactating yaks.In addition,OTUs unique to the yaks of RPL and RPML groups belonged mainly to the phylum Bacteroidetes,whereas the majority of OTUs unique to the yaks of the RPM group belonged mainly to the phylum Firmicutes.Nevertheless,RPAA may have had an independent and additive positive effect on milk components and yield in lactating yaks,but more research on AA requirements will be required to determine the effects of supplementation of RPAA.Supplemental rumen sustained-release boluses increased milk yield,concentrations of protein,lactose,and lactoferrin.Supplemental rumen sustained-release boluses changed the rumen fermentation parameters,specific bacterial abundance tended to be changed.The calves of RPM group had a higher relative abundances of planctomycetes than other three treatments.