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United States Department of Agriculture

Agricultural Research Service

Title: Influence of Breed, Heterozygosity and Disease Incidence on Estimates of Variance Components of Respiratory Disease in Preweaned Beef Calves

Authors
item Snowder, Gary
item Van Vleck, Lloyd
item Cundiff, Larry
item Bennett, Gary

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 2, 2005
Publication Date: May 20, 2005
Citation: Snowder, G.D., Van Vleck, L.D., Cundiff, L.V., Bennett, G.L. 2005. Influence of breed, heterozygosity and disease incidence on estimates of variance components of respiratory disease in preweaned beef calves. Journal of Animal Science. 83:1247-1261.

Interpretive Summary: Respiratory disease in young calves is the leading economically important disease in young calves in the USA. The objective of this study was to characterize genetic and environmental factors influencing bovine respiratory disease (BRD) in beef cattle. Records from nine purebred and three composite breeds and a variety of crossbred types produced over a 20 yr period (1983 to 2002) were evaluated for breed and crossbreeding effects on the incidence of BRD. Crossbred types for calves were defined by generalized breed origins: British, Continental, and Tropically adapted. The overall average incidence of BRD was 10.5 percent with a mortality rate of 13.1%. Respiratory disease in this herd followed a standard epidemiological pattern of initial introduction reaching an epidemic stage at 70 to 170 d of age followed by a period of rapid decline to weaning. Calves born with extended birthing difficulty were more likely to develop BRD than calves born with no or little birthing difficulty. Heritability estimates for resistance to BRD were low and ranged from 0.00 to 0.26. Braunvieh and MARC I composite calves had the highest incidences of BRD. There were few other significant differences among all other breeds studied. Crossbred calves that were Continental by British or Tropically adapted by British breeds had a lower incidence of BRD than calves of British by British breeds. Results from this study indicate that genetic selection for resistance to pulmonary diseases can be successful. However, the low heritability of resistance suggests that the rate of improvement for disease resistance will be slow. An alternative approach would be to develop a humane and effective way to challenge all animals for resistance to BRD to correctly identify the animal's level of resistance.

Technical Abstract: The objective of this study was to characterize genetic and environmental factors influencing bovine respiratory disease (BRD) in beef cattle. Records from nine purebred and three composite breeds and a variety of F1 and three way crosses including progeny of 12 additional different sire breeds produced over a 20 yr period (1983 to 2002) were evaluated for breed and heterozygosity effects on the observed incidence of BRD. Heterozygosity fractions for calves and dams were defined by generalized breed origins: British, Continental, and Tropically adapted. Variance components were estimated for each pure and composite breed, and across all breeds and crossbreds. The effect of incidence of observed BRD was determined by comparing groups of low and high years of incidence. Respiratory disease in this herd followed a standard epidemiological pattern of initial introduction reaching an epidemic stage at 70 to 170 d of age followed by a period of rapid decline to weaning. Estimates of heritability of incidence of BRD were low and ranged from 0.00 to 0.26 with overall estimates of 0.07 and 0.19 depending on the data set analyzed. The highest incidence of BRD in preweaned calves occurred in the Braunvieh breed (18.8 percent). The genetic correlation between the direct and maternal genetic effects was generally large and negative suggesting dams genetically superior for resisting BRD raise calves more susceptible. Possibly, maternally superior dams provide passive immunity to their calves which delays the development of the calves' direct immune system making it more prone to BRD during the preweaning period. Heterozygosity of calves reduced the incidence of BRD when compared with purebred cattle. Calves that were Continental by British or Tropically adapted by British breeds had a lower incidence of BRD than calves of British by British breeds. As the annual incidence of BRD increase there was an associated increase in the heritability estimate. The estimated heritability based on an underlying continuous scale was large (h2 = 0.48 inferring response to selection for BRD resistance could be large if the phenotype for BRD resistance was known.

Last Modified: 10/22/2014
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