Genetic parameters for test-day milk yield, 305-day milk yield, and lactation length in Guzerat cows

Abstract

a b s t r a c tMilk production in tropical environments requires the use of crossbreeding systems including breeds well adapted to harsh conditions, but with lower productivities when compared to specialized breeds. Besides the genetic improvement for milk production, lactation lengths also need to be studied for most of these breeds. Accordingly, genetic parameters were estimated for 305-day cumulative milk yield (MY305), test-day milk yield (TDMY), and lactation length (LL) using information from the first lactations of 2816 Guzerat cows selected for milk production in 28 herds in Brazil. Contemporary groups were defined as herd, year and season of the test for TDMY, and as herd, year and season of calving for MY305 and LL. Variance components were estimated with the restricted maximum likelihood method under a multi-trait animal model. Heritabilities estimated for TDMY ranged from 0.16 to 0.24, and were 0.24 and 0.12 for MY305 and LL, respectively. Genetic correlations were high and positive, ranging from 0.51 to 0.99 among TDMY records, from 0.81 to 0.98 between each TDMY and MY305, and from 0.71 to 0.94 between each TDMY and LL. Genetic parameters obtained in this study indicated the possibility of using test-day records for the prediction of breeding values for milk yield in this population of the Guzerat breed. The use of TDMY as selection criteria would result in indirect gains in MY305 and LL. However, the highest response to selection for MY305 would be obtained by direct selection for this trait.

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

“…The heritability estimates obtained by the TDMO ranged from 0.15 (first month) to 0.27 (third month), and the estimates in the initial lactation phase were lower than those obtained by the RRMs. These heritability estimates are similar to those obtained by Santos et al (2013b) for the Guzerat breed, and by Ledic et al 2002 for the Gyr breed, which ranged from 0.16 to 0.24 and from 0.14 to 0.24, respectively. However, Herrera et al (2008) found the highest heritability estimates, from 0.14 to 0.34 for Gyr breed, while Bignardi et al (2008) found the lower estimates, which ranged from 0.07 to 0.19 for the Holstein breed.…”

“…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.…”

“…For better data consistency and correct estimation on the genetic parameters, cows with unknown cause for the cease of lactation and less than four records in different categories were excluded from the analyses. This procedure had previously been adopted by Santos et al (2013b), so that animals with 90 to 120 days in lactation had all the monthly records, and those with lactations less than 90 days, whose cause of drying is unknown, were discarded.…”

Phenotypic and genetic parameters for selected production and reproduction traits of Mpwapwa cattle in low-input production systems

“…The estimates for LMY and 305LMY were higher compared with previous studies of improved zebu in low-input production systems in sub-Saharan Africa (Ilatsia et al, 2007;Badri et al, 2011). Conversely, the repeatability estimates for LL was moderate, but consistent with other studies of improved zebu in the tropics (Ilatsia et al, 2007;Badri et al, 2011;Santos et al, 2013). The repeatability estimates for production traits indicate that selection of the best cows to be kept in the herd for production could be done with some degree of precision based on estimates for LMY, 305LMY and LL of the cows.…”

Estimates of genetic and crossbreeding parameters for 305-day milk yield of Girolando cows

“…Strategies for crossbreeding Bos taurus taurus with Bos taurus indicus are important in Brazil to achieve the balance between yield and adaptability of animals to adverse conditions in the country (Santos et al 2013) and explore the benefits of heterosis and complementarity originated from the crossbreeding between different breeds (Canaza-Cayo et al 2014).…”