K. Stelwagen et Ch. Knight, EFFECT OF UNILATERAL ONCE OR TWICE-DAILY MILKING OF COWS ON MILK-YIELD AND UDDER CHARACTERISTICS IN EARLY AND LATE LACTATION, Journal of Dairy Research, 64(4), 1997, pp. 487-494
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.