Comparison of random regression models to estimate genetic parameters for milk production in Guzerat (Bos indicus) cows

Abstract

ABSTRACT. Random regression models have been widely used to estimate genetic parameters that influence milk production in Bos taurus breeds, and more recently in B. indicus breeds. With the aim of finding appropriate random regression model to analyze milk yield, different parametric functions were compared, applied to 20,524 test-day milk yield records of 2816 first-lactation Guzerat (B. indicus) cows in Brazilian herds. The records were analyzed by random regression models whose random effects were additive genetic, permanent environmental and residual, and whose fixed effects were contemporary group, the covariable cow age at calving (linear and quadratic effects), and the herd lactation curve. The additive genetic and permanent environmental effects were modeled by the Wilmink function, a modified Wilmink function (with the second term divided by 100), a function that combined third-order Legendre polynomials with the last term of the Wilmink function, and the Ali and Schaeffer function. The residual variances were modeled by means of 1, 4, 6, or 10 heterogeneous classes, with the exception of the last term of the Wilmink function, for which there were 1, 3, 6, or 10 classes. The models gave similar hereditability estimates, ranging from 0.20 to 0.33. Genetic correlations between adjacent records were high values (0.83-0.99), but they declined when the interval between the test-day records increased, and were negative between the first and last records. The model employing the Ali and Schaeffer function with six residual variance classes was the most suitable for fitting the data.

Random regression models to estimate genetic parameters for milk production of Guzerat cows using orthogonal Legendre polynomials

“…The magnitude of the heritability estimates found in the present study is similar to those reported by Olori et al (1999), Cobuci et al (2005), and Bignardi et al (2009) for the Holstein breed. Similar results (0.20 to 0.33) were found by Santos et al (2013a), who used RRM with parametric functions for Guzerat breed. When RRMs were used with parametric functions in Gyr dairy cows, Herrera et al (2008) found similar estimates to those found here.…”

“…(Tables 3 and 4). The genetic correlation estimates obtained with the RRMs were high and near the unity for the adjacent records, with the values declining as the interval between the test-day records increased (Tables 3). The same tendency was reported by Bignardi et al (2009) for the Holstein breed, by Kettunen et al (2000) for the Ayrshire breed, by Herrera et al (2008), and Pereira et al (2013b) for the Gyr breed, and Santos et al (2013a) for the Guzerat breed, all of them using parametric function. The three RRMs (Leg.3.5.6, Leg.3.6.6 and Leg.6.6.6) showed negative genetic correlation estimates between milk yield in the first and in the last test-day records, but of small magnitudes.…”

“…When the parametric function was used in Gyr data, Herrera et al (2008) did not estimate negative genetic correlations, while Pereira et al (2010) reported negative genetic correlations between test-day records at the beginning and at the end of lactation. For Guzerat breed, Santos et al (2013a) found -0.15 and -0.03 for genetic correlation between records at the beginning and at the end of lactation, with Wilmink and Ali & Schaeffer function respectively. However, Santos et al (2013b), using a multi-trait model, estimated values which ranged from 0.91 to 0.56 between all monthly milk yields.…”

Cluster analysis of breeding values for milk yield and lactation persistency in Guzerá cattle

“…Genetic correlations (Table 1) between monthly milk yields ranged from -0.03 to 0.95 and the lowest or negative estimates occurred between yields at the beginning and end of lactation. Similar results have been reported by SANTOS et al (2013) for Guzerá cattle. Phenotypic correlations (Table 1) were all positive and ranged from 0.18 to 0.81.…”

“…Production continued in the second month of lactation (8.98±4.14kg) and subsequently decreased after the third month until the end of lactation (5.44±2.53kg). The heritabilities of TDMY (Table 1) were higher than those reported by SANTOS et al (2013) for the same breed. These authors estimated a higher heritability in the second month (0.35) and a lower heritability in the eighth month of lactation (0.18).…”