EFFECT OF UNILATERAL ONCE OR TWICE-DAILY MILKING OF COWS ON MILK-YIELD AND UDDER CHARACTERISTICS IN EARLY AND LATE LACTATION

Twelve multiparous British Friesian cows in early (40 +/- 23 d in milk ; n = 6) or late (216 +/- 17 d in milk; n = 6) lactation were used to study the effects of milking frequency on yield, udder volume and mill i storage within the udder. After a 2 week control period of twice dai ly milking, diagonally opposed udder halves within a cow were milked o nce or twice daily for 3 weeks. Milk yield was 28-38% lower from the h alves that were milked once daily than from halves that were milked tw ice daily. The loss of milk yield, expressed as a decrease in the rela tive milk yield quotient (an index that accounts for pretreatment diff erences): was greater for cows in early than in late lactation (0.59 v . 0.68). Empty udder-half volume was not decreased by once daily milki ng, suggesting that no cell loss occurred. Instead, once daily milking reduced the secretion efficiency (units of milli. per unit of empty u dder half volume) by 46 and 27% respectively in early and late lactati on; thus, at least part of the loss was due to reduced metabolic activ ity of tile mammary epithelium. There were positive correlations betwe en the relative milk yield quotient and the proportion (r = 0.804) or volume (r = 0.644) of cisternal milk in the glands that were milked on ce daily. These results confirm that, during extended milking interval s, milk loss was smallest for cows that stored a larger proportion of milk in the gland cistern.