Estimation of genetic parameters and breeding values from singel- and multiple-trait animal models analyses for friesian cattle in Egypt

The objectives of this study were to estimate genetic parameters and breeding values for some productive, reproductive and growth traits of Friesian cows by using univariate and multivariate animal models analyses. Data on 305-day milk yield (305-dMY), lactation period (LP), number of services per conception (NOS), age at first calving (AFC), birth weight of calf (BW) and weaning weight of calf (WW) from 1011 first lactation records of Friesian cows daughters of 705 dams and 103 sires for a period of 19 years (1977 to 1995) were used to estimate genetic parameters and breeding values. Single- and multi-trait heritability animal models were used to estimate parameters based on restricted maximum likelihood methodology. Fixed effects in the model varied depending on the individual trait. Single-trait analysis of 305-dMY, LP, NOS, AFC, BW and WW, was investigated as a method to genetic parameters and breeding values for individual traits. Multiple-trait analysis (four traits) including 305-dMY, LP, NOS and AFC; and multiple-trait analysis (two traits) included BW and WW were performed. Statistical Analysis System (SAS) was utilizing to investigate the effect of fixed effects on these traits using mixed model procedure. The overall means (t standard deviations) of 305-dMY, LP, NOS, AFC, BW and WW were 2737±25.6 kg, 334±112 day, 2.28±1.86 service, 31.8±5.84 months, 29.0±4.25 and 95.6±9.40 kg, respectively. Minor differences in Heritability estimates (h2) obtained from single versus multi-trait animal model analyses for most studied traits. Heritability estimates for single-traits analysis were 0,27, 0.12, 0.04, 0.25, 0.19 and 0.06 for 305-dMY, LP, NOS, AFC, BW and WW, respectively. Meanwhile, h2 for multiple-traits analysis were 0.28, 0.03, 0.04, 0.31, 0.04 and 0.10 for 305-dMY, LP, NOS, AFC, BW, WW, respectively. Genetic correlations (rG) of 305-dMY and each of fertility traits (NOS and AFC) were unfavourable (0.49 and 0.39, respectively), between NOS and AFC was 0.97 and between BW and WW was 0.71 suggesting that 305-dMY could be considered in a fertility index. However, there were important differences in breeding value predictions for the same trait between single- and multiple-trait analyses. Breeding values for all animals regarding 305-dMY ranged from -3.43 to 5.62. and -4.38 to 7.67 kg for single versus multiple-trait analyses, respectively. The corresponding values for AFC were -4.01 to 7.94 and -3.92 to 6.94 months, respectively. It is recommended that selecting for milk production alone would lead to decline in genetic merit for fertility traits considered here, where milk production has antagonistic rG with NOS. Results of genetic correlations suggest that because of single-trait method is biased due to selection for 305-dMY, a multiple-trait analysis is recommended for production and reproduction traits if all traits are recorded. The genetic parameters estimated from field test records allow to achieve genetic progress in 305-dMY and AFC of Friesian cattle.