Lactation performance of Hereford cows raised in a range system in the state of Rio Grande do Sul

Milk yield of primiparous and multiparous Hereford cows grazing native pastures was studied using 144 lactations from four different years (1995, 1998, 2000, 2001). Estimates of milk yield were obtained every 21-day interval from birth to weaning (189 d) by the weigh-suckle-weigh technique. Effects of year, calving order, pregnancy, calf sex, and sire breed were studied. Multiparous cows (8.27 +/- 0.26 kg/d) yielded more milk than primiparous cows (5.81 +/- 0.25 kg/d) at peak of lactation (42 d). Total milk yield also was higher for multiparous (1,158.34 +/- 25.51 kg/d) compared to primiparous (915.44 +/- 24.47 kg/d). Therefore, the main difference between multiparous and primiparous lactation curves was production at peak although similar lactation persistence was found. All remaining effects did not affect milk yield in the present trial. Milk met calf requirements for maintenance and growth in the first 2 months of lactation and only maintenance requirements until the fourth month.