Investigation of milk quality differences between young and old cows

This study aimed to investigate if the number of lactations or breed, affects milk quality parameters, i.e. protein profile, gross composition, pH, somatic cell count, and processability, i.e. rennet coagulation time (RCT), gel firmness, and curd yield for the two major breeds of Swedish dairy cows. In this study, 116 milk samples from Swedish Red and White (SRB) and Swedish Holstein (SLB) cows were collected in herds participating in an ongoing research project. Fresh milk samples of the individual animals were pooled separately for young and old cows. pooled milk samples (PM) were used in all analyses. The protein composition of milk samples was investigated by capillary electrophoresis, in order to evaluate the variation in protein profile from different lactation numbers and breeds. In milk from SRB cows, the content of βA1-caseins was significantly higher than in milk from SLB cows, whereas SLB milk had a significantly higher content of βA2-caseins. Additionally, milk from SRB cows had a numerically higher content of fat and total solids, and higher relative concentrations of SFA, UFA, MUFA, PUFA, C14:0, C16:0, C18:0, and C18:1C9, compared to milk from SLB cows. Milk from older SLB cows had a higher gel firmness and shorter rennet coagulation time compared to milk from young cows, however, opposite results were observed within milk from SRB cows. There was no significant difference in ethanol stability, and SCC between young and old cows, but SLB had significantly higher ethanol stability compared to SRB. Several statistically significant correlations were found within the data, including rennet coagulation time (RCT) and gel firmness; curd yield and SCC; RCT and βA1-CN; RCT and βA2-CN. Overall, there were few variations in milk composition and processibility between young and old cows. These results demonstrate that older cows could be retained in dairy production but more extensive studies are needed in order to support the results. Keywords: milk quality, lactation number, gel firmness, rennet coagulation time, Swedish Holstein, Swedish Red and White.