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

Abstract

The objective of this work was to estimate covariance functions for additive genetic and permanent environmental effects, as well as to obtain genetic parameters for buffalo test-day milk yield using random regression models on Legendre polynomials (LPs). A total of 2,538 test-day milk yield (TDMY) records from 516 first lactation records of Khuzestan buffalo, calving from 1993 to 2009 and belonging to 150 herds located in the state of Khuzestan, Iran, were analyzed. The residual variances were modeled through a step function with 1, 5, 6, 9, and 19 classes. The additive genetic and permanent environmental random effects were modeled by LPs of days in milk using quadratic to septic polynomial functions. The model with additive genetic and animal permanent environmental effects adjusted by cubic and third order LP, respectively, and with the residual variance modeled through a step function with nine classes was the most adequate one to describe the covariance structure. The model with the highest significant log-likelihood ratio test (LRT) and with the lowest Akaike information criterion (AIC) and Bayesian information criterion (BIC) was considered to be the most appropriate one. Unexpected negative genetic correlation estimates were obtained between TDMY records of the twenty-fifth and thirty-seventh week (-0.03). Genetic correlation estimates were generally higher, close to unity, between adjacent weeks during the middle of lactation. Random regression models can be used for routine genetic evaluation of milk yield in Khuzestan buffalo.

Optimization of test day for milk yield recording and sire evaluation in Murrah buffaloes

“…Sesana et al (2010) also found higher permanent environmental variances at early stages of lactation in milking buffalo while Madad et al (2016) reported highest permanent environmental variances in mid of lactation which was contradictory to the present findings. Katneni (2007), also obtained higher additive genetic and permanent environmental variance at the initial stage (0.991 and 1.716 kg 2 ) and end of lactation (1.997 and 2.019 kg 2 ) using LP function but obtained values were higher for additive genetic variance and lower for permanent environment variances in contrast to present estimates.…”

“…They estimated that genetic variances were higher (0.41) in the first month of lactation (DIM 30), declined to a value of (0.16) up to seven test days (DIM 210), and then increased to a maximum estimated value of (0.72) at DIM 270 for Iranian buffaloes. Similar findings using RRM were reported by Madad et al (2016) and Sesana et al (2010) and , who reported that Brazilian Murrah and Iranian Khuzestan buffaloes had higher additive genetic values for the first 2 weeks of lactation. Contrary to the present results, Tonhati et al (2008) reported lower estimates of the additive genetic variance at the beginning and end of lactation using a bivariate animal model.…”

“…They have also mentioned the presence of negative correlation among test day yields for the permanent environment effects in Iranian buffaloes. Madad et al (2016) and Sesana et al (2010)also found negative correlation among different test days for the permanent environment among different lactation weeks in Brazilian Murrah and Khuzestan buffaloes which were in contrast to the present finding.…”

“…Breda et al (2010), Geetha et al (2007), Katneni (2007), Madad et al (2013, 2016) and Sesana et al (2010) using RRM also reported high genetic correlation estimates between successive TDMY records in buffaloes. Negative genetic correlation estimates between early and late TDMY records, in dairy cattle using RRM, have also been reported by Bignardi et al (2009), Brotherstone et al (2000a, 2000b); Kettunen et al (2000), López‐Romero and Carabaño (2003), Madad et al (2013), and Rekaya et al (1999) have also found negative genetic correlations for milk yield between the DIM 270 and DIM 90–180 in Iranian buffaloes.…”

“…Only a few studies are reported on buffaloes (Brazilian Murrah, Khuzestan and Iranian buffaloes) where test-day milk yield was used for estimation of genetic parameters with random regression analysis (Madad et al, 2013(Madad et al, , 2016Sesana et al, 2010). Therefore, it is crucial to use these models for genetic evaluation of Murrah buffaloes in India.…”