Random regression models to estimate genetic parameters for test-day milk yield and composition in Iranian buffaloes

Abstract

Abstract. The objective of this study was to estimate genetic parameters for milk yield and milk percentages of fat and protein in Iranian buffaloes. A total of 9,278 test-day production records obtained from 1,501 first lactation buffaloes on 414 herds in Iran between 1993 and 2009 were used for the analysis. Genetic parameters for productive traits were estimated using random regression test-day models. Regression curves were modeled using Legendre polynomials (LPs). Heritability estimates were low to moderate for milk production traits and ranged from 0.09 to 0.33 for milk yield, 0.01 to 0.27 for milk protein percentage and 0.03 to 0.24 for milk fat percentage, respectively. Genetic correlations ranged from −0.24 to 1 for milk yield between different days in milk over the lactation. Genetic correlations of milk yield at different days in milk were often higher than permanent environmental correlations. Genetic correlations for milk protein percentage ranged from −0.89 to 1 between different days in milk. Also, genetic correlations for milk percentage of fat ranged from −0.60 to 1 between different days in milk. The highest estimates of genetic and permanent environmental correlations for milk traits were observed at adjacent test-days. Ignoring heritability estimates for milk yield and milk protein percentage in the first and final days of lactation, these estimates were higher in the 120 days of lactation. Test-day milk yield heritability estimates were moderate in the course of the lactation, suggesting that this trait could be applied as selection criteria in Iranian milking buffaloes.

Estimation of genetic parameters for test-day milk yield in Khuzestan buffalo

“…Heritability estimates obtained by the 3.3.het9 model varied from 0.53 in the first week to 0.04 in the thirty-third week. When the estimates of heritabilities for milk yield at early lactation were ignored, heritability for milk yield was higher than that reported by Hurtado-Lugo et al (2006) for Murrah buffalo in Colombia (0.01 to 0.20), but similar to that obtained by Chakraborty et al 2010, Breda et al (2010), and Madad et al (2013b), who found that the heritability estimates for test-day milk yield were low to medium in milking buffalo. Hurtado-Lugo et al (2006) and Tonhati et al (2008) analyzed TDMY records of milking buffalo by finite models and observed a similar trend for heritability estimates to that obtained in the present study from the thirteenth to the twenty-fifth week, with values ranging from 0.19 to 0.30 and from 0.16 to 0.20, respectively.…”

“…Likewise, Sesana et al (2010) compared different structures of permanent environmental variances using RRM and found higher variance estimates at early lactation in milking buffalo. Madad et al (2013b), using RRM in dairy buffalo, also reported high additive genetic variance in the early months of lactation, despite observing lower variances.…”

“…Breda et al (2010) found that the peak TDMY of Murrah buffalo occurred around the eleventh week of lactation, whereas Hurtado-Lugo et al (2006) reported the greatest values of TDMY close to the middle of lactation in North Colombia buffalo. According to Madad et al (2013b), the peak milk yield of Iranian buffalo occurred on the ninetieth day of lactation.…”

Estimates of genetic parameters for fat yield in Murrah buffaloes

“…Madad et al . [ 20 ] observed that heritability estimates ranged from 0.03 to 0.24 for TD fat percentages in Iranian buffaloes. Ibrahim et al .…”

Parâmetros genéticos e fenotípicos do perfil de ácidos graxos do leite de vacas da raça holandesa

“…Observa-se que, embora a diferença entre o valor mínimo e máximo tenha sido discreta, houve uma tendência decrescente do inicio ao final da lactação para as estimativas da VG. Tal tendência também foi observada por Pool et al (2000) e Madad et al (2013). Para a VP, as estimativas variaram de 0,022 a 0,038 g/100g de leite 2 , também diminuindo da fase inicial ao final da lactação.…”