NATTAPHON CHONGKASIKIT1, JOHN DAVID KABASA2, KESINEE GATPHAYAK1, THERDCHAI VEARASILP1
1Chiang Mai University, Department of Animal Science, Thailand
2Georg-August-Universität Göttingen, Institute of Animal Physiology and Animal Nutrition, Germany
Phenotypic and genetic correlations show relationships between phenotype and genotype traits. These parameters are important especially in multi-trait selection and improvement programs because they are used in the calculation of selection responses. However, phenotypic and genotypic correlations differ among populations due to genetic and environment differences. The objective of this study was to estimate the phenotypic and genetic correlation among systematic factors, production traits, and fertility traits of Northern Thai dairy cattle population. Reproduction traits, milk yield, and milk contents were measured using 2,764, 1,673 and 391 heifers respectively. The number of sires ranged from 85-570, resulting in fairly small progeny group sizes of 4.2-4.6 in average. Genetic correlations were based on the animal model, employing restricted maximum likelihood calculation. The fixed effects were herd-year, season, and % of Holstein-Friesian (HF). The co-variable was days in milk.
The results revealed that phenotypic correlations between % HF and milk contents ranged between -0.076 and 0.030, and that between % white colour and milk contents between - 0.122 and 0.049. Phenotypic correlations between age at first calving and milk contents ranged between -0.048 and 0.043, while that between age at second calving and milk contents between -0.142 and 0.079. The phenotypic and genetic correlations between milk contents ranged between -0.091 and 0.286 and 0.008 and 0.283 respectively. Meanwhile, phenotypic and genetic correlations between the different fertility traits ranged between 0.054 and 0.858 and 0.007 and 0.613 respectively. The results suggest that genetic correlation between fertility and milk yield is neutral, while that with the different reproduction traits: service period, insemination index and calving interval is clearly positive (r = 0.3-0.6). This indicates an autocorrelation of the same genetic phenomenon.
Keywords: Dairy Cattle, Genetic correlation, phenotypic correlation