| Goat milk is favoured by consumers for its richness in nutrients and bioactive substances,that is widely used in the processing of dairy products.Milk composition varies according to genetics,season,lactation period and parity,which leads to variable levels of protein,fat,lactose and other nutrients.At present,the main nutrients in milk are mainly studied using milk composition analysis techniques,but the research of the biological function and the process of changes in the production of small molecule metabolites in milk are lacking.Therefore,in order to investigate the quality and breed characteristics of Dazu black goat milk and the effect of litter size and season on its nutritional composition,this study combined milk composition analysis and non-targeted metabolomics techniques to study Dazu black goat milk and its influencing factors from both macroscopic and microscopic aspects,providing a theoretical basis for further exploration of the molecular mechanisms and biological processes underlying the changes in goat milk composition.This study was carried out in the following experiments:（1）30 animals from each group of Dazu black goats（DBG）,Saanen goats（SG）and Holstein cattle（HC）of similar body weight,body condition,parity,and lactation period.（2）20 Dazu black goats each group from high litter size（HLS）and low litter size（LLS）of similar body weight,body condition,lactation period and parity were selected.（3）30 Dazu black goats each group from summer（S）and winter（W）with similar body weight,body condition,lactation period and parity.All milk samples were collected and tested for milk composition and data from the DBG vs SG,DBG vs HC,SG vs HC,HLS vs LLS and S vs W comparison groups were analysed using a one-way ANOVA.After obtaining milk sample metabolic data,multivariate statistical analysis was performed for each group to screen the differential metabolites among the comparison groups.Hierarchical cluster analysis and KEGG pathway analysis were used to reveal the metabolic pathways and biological functions involved in the differential metabolites.The main results are as follows:1.Comparative analysis of milk composition and metabolomics in Dazu black goat,Saanen goat and Holstein cattle.The results of milk composition analysis showed that milk fat:DBG>SG>HC;protein:DBG>SG>HC;lactose:DBG>HC>SG;solids-not-fat:DBG>HC>SG.The metabonomics results showed that 51,99 and 81 differential metabolites were screened from the DBG vs SG,DBG vs HC and SG vs HC comparison groups,respectively.The metabolic pathways involved in the differential metabolites of the three comparison groups include:glycerol phospholipid metabolism,amino sugar-nucleotide sugar metabolism,phenylalanine tyrosine tryptophan biosynthesis,phenylalanine metabolism,nicotinic acid-nicotinamide metabolism,fructose-mannose metabolism,sphingolipid metabolism,alanine-aspartate-glutamate metabolism,tricarboxylic acid cycle,aminoacyl t RNA biosynthesis,glycolysis gluconeogenesis,glycine-serine-threonine metabolism arginine biosynthesis,glutamine-glutamate metabolism,and histidine metabolism.2.Effect of different litter size on milk composition and metabolites in Dazu black goat milk.The results of milk composition analysis and metabolomics showed no significant differences in the content of milk fat,proteins,lactose,solids-not-fat and small molecule metabolites between HLS milk and LLS milk.3.Effect of different seasons on milk composition and metabolites of Dazu black goat.The results of milk composition analysis showed that milk fat:W>S;protein:W>S;lactose:W>S;solids-not-fat:W>S.The results of metabonomics showed that 52 differential metabolites were screened between S milk and W milk,and the metabolic pathways involved were glycerol phospholipid metabolism,arginine biosynthesis,histidine metabolism,arginine-proline metabolism,glutamine-glutamate metabolism and vitamin B6metabolism.Conclusions:（1）Data on the milk composition and metabolic profile characteristics of Dazu black goat were obtained by comparative analysis of milk from Dazu black goat,Saanen goat and Holstein cattle.（2）Litter size does not significantly affect the content and composition of nutrients and metabolites in the milk of Dazu black goat.（3）Seasonal factors significantly influenced the content and composition of nutrients and metabolites in the milk of Dazu black goat.Seasonal changes mainly affect lipid metabolites,and the biological functions of differential metabolites are mainly related to kid growth and development,lipid metabolism,immune regulation,heat stress and energy supply. |
