초록
Daily milk yield estimates were obtained on 74 lactations of 35 Japanese Black cows on weeks 1 to 9, 11, 13, 17, 21 and 26 postpartum using the weigh-suckle-weigh method. The data obtained were analyzed by least-squares procedures according to the models including the following effects; dam, lactation number, season of calving, week of experiment and partial regressions on the lactation number. The overall mean and standard error for daily milk yield was $4.55{\pm}0.04\;kg$. The milk yield declined essentially linearly throughout the experimental period. The main effects of lactation number, season of calving and week of experiment were highly significant. Differences in daily milk yield among cows were significant, and the repeatability was estimated as $0.60{\pm}0.06$. The overall means(kg) and repeat-abilities of cumulative milk yield for 1, 4, 9, 13, 17, 21 and 26 weeks postpartum were 41, 0.08; 166, 0.40; 361, 0.61; 503, 0.66; 632, 0.67; 749, 0.65 and 884, 0.58; respectively. The means of calf weight at birth and 26 weeks weight for different lactations ranged from 25.5 to 33.6 kg and 145.6 to 185.4 kg, respectively. Calf daily gains between experiment weeks were low in earlier stages of lactation.