Deaths and disposals in lines selected for milk yield and control lines of Jersey cattle

Deaths and disposals of Jerseys from birth to 120 d of first lactation during a selection experiment were summarized. Cows were randomly assigned to the high milk yield and young sire lines. Service sires were bulls with the highest estimated breeding value for milk for the high milk line and a collection of all young unproven bulls available in AI in 1967. Cattle that were unsuitable for conditions of normal herd management were candidates for culling. Culling of uncalved heifers and of lactating cows was also permitted to maintain group sizes. Culling for herd reduction was random. Culling for low milk yield was permitted after cows reached 120 d of first lactation. Death and disposal data were analyzed through 120 d of first lactation. By 120 d of first lactation, 29.6% of females born to the young sire line had died or been involuntarily removed compared with 29.8% born to the high milk yield line. Deaths were 54.8% of total losses for the high milk yield line compared with 58.4% for the young sire line. Stillbirths were a larger proportion of total losses for animals in the high milk yield line (21.4%) than for those in the young sire line (15.3%). The most frequent cause of death was scours and pneumonia during 1st mo of life for animals in both lines. Selection of sires for high milk yield does not decrease total survival rates through the early first lactation.