RELATIONSHIP BETWEEN MILK STORAGE CHARACTERISTICS AND THE SHORT-TERM RESPONSE OF DAIRY-COWS TO THRICE-DAILY MILKING

Twenty lactating dairy cows were used to investigate the relationship between the site of milk storage in the udder and the short-term response to thrice-daily milking. Cisternal and alveolar milk volumes were measured 8 h after an ordinary morning milking by catheter drainage and machine milking with oxytocin respectively. The response to thrice-daily milking was assessed using a half-udder technique and the relative milk yields quotient (RMYQ). Over the first 7 days, both halves were milked twice daily (8116 h intervals) and milk yields over the final 4 days of this period were higher for left fore/right hind (LF/RH) (12.4 (s.e. 0.85) kg/day) than for RF/LH (10.5 (s.e. 0.63) kg/day) which was milked after LF/RH throughout the experiment. Over the following week, LF/RH quarters were milked an additional time (81818 h intervals) and yields over the final 4 days were increased (15.7 (s.e. 0.95) kg/day) compared with control quarters (9.8 (s.e. 0.73) kg/day). In a final 4-day period, animals were milked twice daily and half udder yields were 13.1 (s.e. 0.89) kg/day and 10.6 (s.e. 0.77) kg/day respectively. Differences between yields from the two halves of the udders were highly significant in all 3 weeks of the experiment (P < 0.001). Cistern milk yield as a proportion of total milk yield at 8 h (cistern proportion) averaged 0.170 (s.e. = 0.0275; range 0.020 to 0.334) and tended to be greater for multiparous (0.215, s.e. 0.0279) than for primiparous animals (0.118, s.e. 0.0437; P = 0.076). During the periods of twice-daily milking, the proportion of milk yielded from LF/RH quarters was not significantly related to cistern proportion (P = 0.70 and 0.43 for weeks 1 and 3 respectively). However the response to thrice-daily milking, assessed as RMYQ, was significantly related to cistern proportion both when changing up to, and down from, thrice-daily milking (P < 0-01). Animals with low cistern proportions showed larger responses to thrice-daily milking. There was a significant relationship (P < 0.05) between the responses on changing up to, and down from, thrice-daily milking. Primiparous animals tended to exhibit smaller declines on returning to twice-daily milking than multiparous animals with equivalent responses to thrice-daily milking