Relationship between milk storage characteristics and the short-term response of dairy cows to thrice-daily milking

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Abstract
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 (8/16 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 (8/8/8 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.