Characterization of productive records of Katahdin sheep and effect of the size of contemporary groups in the genetic evaluation of weaning weight

Abstract

The objective of this research was to characterize the database of the Katahdin sheep breed from Mexico, in order to establish editing and modeling criteria for use in national genetic evaluations of said breed and to compare contemporary groups (CG) of different sizes to determine which size produces greater accuracy of breeding values. The analyzed database contains 92,965 phenotypic and genealogical records. To carry out the descriptive analysis, measures of central tendency and dispersion were calculated, and through univariate ANOVA the influence of environmental factors on growth characteristics was evaluated. The productiva variables were: birth weight (BWT), weaning weight (WWT) and post-weaning daily gain (PWG). Data analysis was performed using R software and genetic evaluation using an animal model was performed using the WOMBAT software. The variables of BWT and WWT were statistically influenced (P < 0.001) by the year and month of birth, sex, herd, age of the mother and the number of lambs per birth. The weighing date also influenced the WWT. The age of the mother and the number of lambs per birth did not influence the PWG. The genetic evaluation analysis showed that the use of CG with 1 or more animals generates a higher accuracy (average=0.43) of the breeding values, but restricting the analysis to only CG with 6 or more animals and at least 2 sires produces a similar accuracy (average=0.37) and hierarchy (Spearman's correlation of 0.89). It is recommended to filter the database by extreme values and eliminate levels with few records for factors such as the age of the mother, herd and year of birth. It is also recommended to use CG with enough records to control or remove part of the environmental effects in a genetic evaluation.