Phenotypic variation in live weight and live-weight changes of lactating Holstein-Friesian cows

This study quantified individual phenotypic variation in live weight and li ve-weight changes during the first three lactations and estimated the effec ts of age, lactation week and pregnancy on live weight. Data comprised week ly averaged live weight (calculated from daily observations) during 452 lac tations of 239 Holstein-Friesian cows. Unadjusted mean live weights were 55 3 (s.d. 50), 611 (s.d. 55) and 654 (s.d. 57) kg during first, second and th ird parity, respectively. Estimated effect of growth during parity was 46, 52 and 23 kg for the first three parities. Mean maximum weight loss was 26, 22 and 22 kg for first, second and third parity and variation was large am ong individuals. Week of lactation when cows had their maximum weight loss ranged from 7 weeks in first lactation to 13 weeks in third lactation. Esti mated maximum effect of pregnancy on live weight during the lactation varie d from 27 to 59 kg. Phenotypic variance in live weight increased with parit y. Repeatabilities of live-weight observations within parity were 0.85. Acr oss parities, high repeatabilities were found for calving weight and mean l ive weight but not for parameters associated with maximum weight loss. Corr elations between weekly means and mean live weight during the whole of lact ation were high. It was concluded that single live-weight observations of h eifers are a good measurement of mean live weight during the first three pa rities.