Short communication: Changes in the composition of yak colostrum during the first week of lactation

Although the great interest has been paid to colostrum utilization for calves, no systematic studies evaluating the compositional changes of yak colostrum during the first week after parturition have been reported. The aim of this study was to elucidate such postpartum nutritional changes. Colostrum samples from 12 multiparous (2-7 lactations) yaks, grazed on alpine pasture, were collected at exactly 1, 24, 48, 72, 96, 120, 144, and 168 h postpartum. Gross composition (fat, total solids, protein, and ash) were measured, as well as fat and water-soluble vitamins, fatty acid and mineral composition, and IgG. The colostrum, collected 1 h postpartum, had the highest concentrations of crude protein, total solids, ash, vitamin A and E, β-carotene, and most minerals (Na, Mg, Zn, Cu, and Fe). These components decreased rapidly within 24 h. Similarly, at 24 h postpartum, IgG content decreased to 7.5% of the value (87.78 mg/mL) at 1 h postpartum. In contrast, the concentration of vitamin C increased from 1 to 24 h and then decreased consistently thereafter to the lowest value at 168 h. Phosphorus and Ca contents showed an increasing trend from 24 to 168 h after calving. Lactose content increased from 2.88% at 1 h to 4.96% at 48 h postpartum and was steady to 168 h. Total n-3 fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, and n-3-to-n-6 fatty acid ratio were proportionally similar as a percentage of total fatty acid methyl esters during the first 168 h of milk production. However, the proportion of total n-6 fatty acid content to total fatty acid methyl esters decreased from 3.07% at 1 h to 2.60% at 24 h. In summary, experimental results indicate colostrum should be provided to yak calves as soon as possible after birth to provide nutrients and enhance passive immunity.