TheBullLady
Well-known member
GENETICS VS. BOVINE RESPIRATORY DISEASE
Researchers at the U. S. Meat Animal Research Center, Clay Center, Nebraska, analyzed over 110,000 records from various breeds and crosses collected over a 20-year period to study possible genetic effects on incidence of Bovine Respiratory Disease (BRD) in beef calves, whether from viral, bacterial, or mycoplasmal causes. Spring-born calves were vaccinated with 8-way clostridial and 5-way leptospirial vaccines at average age of 42 days and boostered with those vaccines at average age of 165 days (about 30 days before weaning), along with a modified-live viral vaccine at that time. Average incidence of BRD was 10.5% (ranging from 3.3% for the lowest year to 23.6% for the highest) of which 13.1% died (so, there was 1.4% overall death loss due to BRD). There were two peaks in incidence, from birth to 20 days of age and again from 70 to 100 days of age. Difficult birth resulted in more BRD. Overall, British crosses had lower incidence than purebreds, and British X Continental or tropically-adapted breed crosses were lower than British crosses. Based on heritability estimates, it was stated that "selection for BRD could be effective provided all animals are challenged adequately with the disease". That is, it might be possible to increase genetic resistance in a population over time but only by exposing every animal, even those not resistant, a mixed blessing at best. Interestingly, there was a negative genetic correlation between direct and maternal effects. The authors speculated that dams superior for providing resistance to their calves may delay development of their calf's immune system. (J. Animal Sci. 83:1247)
Researchers at the U. S. Meat Animal Research Center, Clay Center, Nebraska, analyzed over 110,000 records from various breeds and crosses collected over a 20-year period to study possible genetic effects on incidence of Bovine Respiratory Disease (BRD) in beef calves, whether from viral, bacterial, or mycoplasmal causes. Spring-born calves were vaccinated with 8-way clostridial and 5-way leptospirial vaccines at average age of 42 days and boostered with those vaccines at average age of 165 days (about 30 days before weaning), along with a modified-live viral vaccine at that time. Average incidence of BRD was 10.5% (ranging from 3.3% for the lowest year to 23.6% for the highest) of which 13.1% died (so, there was 1.4% overall death loss due to BRD). There were two peaks in incidence, from birth to 20 days of age and again from 70 to 100 days of age. Difficult birth resulted in more BRD. Overall, British crosses had lower incidence than purebreds, and British X Continental or tropically-adapted breed crosses were lower than British crosses. Based on heritability estimates, it was stated that "selection for BRD could be effective provided all animals are challenged adequately with the disease". That is, it might be possible to increase genetic resistance in a population over time but only by exposing every animal, even those not resistant, a mixed blessing at best. Interestingly, there was a negative genetic correlation between direct and maternal effects. The authors speculated that dams superior for providing resistance to their calves may delay development of their calf's immune system. (J. Animal Sci. 83:1247)
