Composition and processability of milk from older cows : a pilot study on milk quality differences between young and old cows

Sammanfattning: Most Swedish dairy cow’s life expectancy is five years, which is 2.5 lactations. The most common reason for dairy cows being culled are e.g. impaired fertility, mastitis, or low milk yield. Increased cow longevity is associated with animal welfare and would reduce the emission intensity per unit of milk solids per cow. The objective of this study was to investigate the differences in raw milk quality (e.g. composition, SCC, pH, and plasmin- and plasminogen derived activity) and processability of milk (e.g. curd yield, ethanol stability, gel firmness, rennet coagulation time) from cows with different number of lactations, i.e. old cows compared to young cows, and breeds. Milks samples from SRB and SLB cows were collected for this study, eight from each breed. Milk from young SLB cows, had a significant harder gel firmness and shorter rennet coagulation time compared to milk from older cows, however, it was not observed within milk from SRB cows. Within SRB, the difference in SCC was significant between milk from older and younger cows. There was no significant difference in ethanol stability between lactation numbers, but SLB had significantly higher ethanol stability compared to SRB. In milk from SRB cows, the content of βA1-caseins was significantly higher than in milk from SLB cows, whereas SLB milk had significantly higher content of βA2-caseins. Further research with repeated analysis and more individuals is required, to be able to make any conclusions on how the number of lactations of cows affect the processability and quality of milk.