Abstract
Abstract: The objective of this work was to compare genetic evaluations of milk yield in the Gir breed, in terms of breeding values and their accuracy, using a random regression model applied to test-day records or the traditional model (TM) applied to estimates of 305-day milk yield, as well as to predict genetic trends for parameters of interest. A total of 10,576 first lactations, corresponding to 81,135 test-day (TD) records, were used. Rank correlations between the breeding values (EBVs) predicted with the two models were 0.96. The percentage of animals selected in common was 67 or 82%, respectively, when 1 or 5% of bulls were chosen, according to EBVs from random regression model (RRM) or TM genetic evaluations. Average gains in accuracy of 2.7, 3.0, and 2.6% were observed for all animals, cows with yield record, and bulls (sires of cows with yield record), respectively, when the RRM was used. The mean annual genetic gain for 305-day milk yield was 56 kg after 1993. However, lower increases in the average EBVs were observed for the second regression coefficient, related to persistency. The RRM applied to TD records is efficient for the genetic evaluation of milk yield in the Gir dairy breed.
Highlights
Random regression models have been used in different countries for genetic evaluations of productive traits in dairy cattle (Interbull, 2017)
The objective with this work was to compare genetic evaluations of milk yield in the Gir breed, in terms of breeding values and their accuracy, using a random regression model applied to test-day records or the traditional model applied to estimates of 305day milk yield, as well as to predict genetic trends for parameters of interest
The heritabilities for the daily milk yields estimated with the regression model (RRM) ranged from 0.15 to 0.21, which are of similar magnitude to those reported for milk yield in dairy Gir cattle (Herrera et al, 2008; Pereira et al, 2010, 2013a, 2013b; Oliveira et al, 2017)
Summary
Random regression models have been used in different countries for genetic evaluations of productive traits in dairy cattle (Interbull, 2017) These models employ test-day milk yield records instead of estimates of 305-day cumulative milk yield (Y305) data. The Gir (Bos indicus) breed is found throughout Brazil, representing the second largest Zebu population in the country, with a total of 799,284 recorded animals until 2015 (ABCZ, 2017). The ability of this breed to be raised on pasture, as well as its resistance to endo- and ectoparasites and its adaptation to high temperatures, has raised the interest of other tropical countries, resulting in the exportation of semen and animals to Africa and Central and South America and, more recently, to India, where the Gir breed originated from (Pereira et al, 2013a)
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