phenotypic correlations

In this study, records of 64220 first lactation dairy cows were used. Data were collected from 749 herds during 1996 to 2009 by the Animal Breeding Center of Iran. Data included of production (305 d milk yield, 305 d fat percentage, 305 d protein percentage and lactation length) and reproduction (dry days, age at first calving, calving interval and days open) traits. Data analysis was performed by restricted maximum likelihood procedure using DFREML software. The estimated heritabilities of milk yield, fat percentage and protein percentage and lactation length were 0.197, 0.282, 0.333 and 0.031, respectively. The estimated heritabilites of dry days, age at first calving, calving interval and days open were 0.015, 0.079, 0.035 and 0.036, respectively. Genetic correlations between production traits were from 0.52 for milk yield and fat percentage to 0.74 for fat percentage and protein percentage. Genetic correlations between reproduction traits were from 0.07 (age at first calving and calving interval) to 0.95 (dry days and calving interval). Estimated genetic correlation between production and reproduction traits were from -0.63 (milk yield and dry days) to 0.96 (lactation length calving interval). Considering negative genetic correlation between production and reproduction traits, planning of selection programs in dairy cows based on a combination of production and reproduction traits is recommendable.

In this study, calving records of 4221 Iranian native buffaloes from 621 herds which were collected by the Animal Breeding and Livestock Products Improvement Center of Iran from 2003 to 2010 were used to estimate heritability, genetic and phenotypic correlations between milk production, milk fat production, age at first calving and first calving interval using univariate and bivariate animal models. The highest and the lowest heritabilities were estimated for milk production (0.46±0.01) and first calving interval (0.01±0.29), respectively. Heritability estimates for age at first calving and milk fat production in the studied population were 0.21±0.21 and 0.27±0.17, respectively. Positive and high genetic correlation between milk yield and milk fat production (0.55) in this study indicated that milk fat increased along with increasing in milk production. Negative and medium genetic correlation between milk production and age at first calving (-0.25) indicated that genetic selection for milk production cause decrease in age at first calving. Positive and high genetic correlation between age at first calving and first calving interval (0.96) indicated that selection based on lower age at first calving cause reduced first calving interval.