Abstract
Breeding for disease resistance is a challenging but increasingly necessary objective to overcome the issues with the reduced use of antibiotics and growing concern for animal welfare while limiting economic losses. However, implementing such strategies is a complex process because animals face numerous diseases, and the environments on selection farms differ from those on commercial farms. We evaluated whether selection for resistance to non-specific diseases based on a single visual record in selection (S) and challenging (Ch) environments is possible. Records from 23,773 purebred rabbits born between 2012 and 2016 were used in this study. After weaning (at 32 days of age), 17,712 rabbits were raised in the S environment and 6,061 sibs were raised in the Ch environment. Clinical signs of disease were recorded for all animals at the end of the test, at a single time point, at 70 or 80 days of age. The causes of mortality occurring before the end of the test were also recorded. Three disease traits were analyzed: signs of respiratory disease, signs of digestive disease, and a composite trait (Resist) taking into account signs of digestive, respiratory and various infectious diseases. This latter composite trait is proposed to capture the global resistance to disease. All disease traits were binary, with 0 being the absence of symptoms. Two production traits were also recorded: the number of kits born alive (4,121 litters) and the weaning weight (13,090 rabbits). Disease traits were analyzed with animal threshold models, assuming that traits are different in the two environments. Bivariate analyses were carried out using linear animal models. The heritabilities of the disease traits ranged from 0.04 ± 0.01 to 0.11 ± 0.03. The genetic correlations between disease traits in both environments were below unity (≤ 0.84), indicating genotype by environment interactions. Most of the genetic correlations between disease and production traits were not significantly different from zero, except between the weaning weight and Resist_S, with a favorable correlation of −0.34 ± 0.12. Given these genetic parameters, for the same level of exposure of rabbits to pathogens, the expected response to selection is a reduction of disease incidence of 4–6% per generation.
Highlights
Breeding for disease resistance is becoming increasingly important to reduce the use of antibiotics and address the growing concern for animal welfare
Genotype by Environment (G×E) interactions exist for this trait between selection and challenging environments
Longterm prediction of the genetic gain is difficult, due to the probable changes in disease epidemiology caused by selection
Summary
When the selection environment differs considerably from commercial environments (i.e., the higher biosecurity level of selection environments entails a lower expression of disease) little or no selection pressure is applied on this trait To implement such selection, there is still a need for phenotypes that can be measured, at a reasonable cost (Merks et al, 2012). Previous studies have shown that simple health records, measured once on growing animals of the selection nucleus, can be used to improve disease resistance (Eady et al, 2007; Garreau et al, 2012; Gunia et al, 2015) It is not known if such selection will be beneficial for maintaining the health and productivity of animals reared in commercial conditions. We assessed the expected genetic progress for disease resistance for various selection strategies, including records from different environments in the genetic evaluations
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