Animal and veterinary scientists working at the USDA experiment station at Clay Center, Nebraska monitored health events and growth performance in a population of range beef calves in order to identify associations of these factors with passive immune status. Although this study was published over 15 years ago, it is still relevant today. Blood samples were collected at 24 hours postpartum from 263 crossbreed calves to determine the amount of passive maternal immunity that had been obtained from colostrum. Growth performance and health events in the study population were monitored from birth to weaning, and after weaning throughout the feeding period. The lowest levels of passive immunity were observed among calves that were sick or died prior to weaning.
Calves with inadequate passive immunity had a 5.4 times greater risk of death prior to weaning, 6.4 times greater risk of being sick during the first 28 days of life, and 3.2 times greater risk of being sick any time prior to weaning when compared to calves with adequate passive transfer. The risk of being sick in the feedlot was also three times greater for inadequate compared to adequate calves. Passive immune status was indirectly associated with growth rates through its effects on calf health. Sickness during the first 28 days of life was associated with a 35 pound lower expected weaning weight. Respiratory disease in the feedlot resulted in a .09 lb lower average daily gain. (Source: Wittum and Perino. 1995. Am. Journ. of Vet. Med. Vol. 56:1149.)
Thus, passive immunity obtained from colostrum was an important factor determining the health of calves both pre- and post-weaning, and indirectly influenced calf growth rate during the same periods. To optimize the colostrum production by first calf heifers, they should be in excellent body condition (BCS=6) at calving and have been raised with a proper health/vaccination program.