پژوهشهای علوم دامی ایران (Apr 2016)
Genetic analysis of production traits of Holstein cows in the Mediterranean climate of Iran using random regression and animal model
Abstract
Introduction Productive traits such as milk production and fat and protein percentage have economic importance in the livestock industry. Accurate prediction of breeding value of animals is one of the best tools available for maximizing response to selection program. It is a fact that the main objective of the breeding program, is to achieve the maximum economic benefit. For breeders of dairy cattle, milk, fat, and protein are the main sources of income that are the most important traits in the firm goals. For evaluating the dairy cattle based on these traits (milk production, fat, and protein percentage), prediction of breeding values is essential. The present study was performed in order to estimate the genetic and phenotypic parameters and genetic and phenotypic trends of production traits in the Mediterranean climate of Iran (including; Ardebil, Hamadan, East and West Azerbaijan and Zanjan provinces) using 105118 records for Test Day and 30985 records for 305-day lactation records Related 8808 Herd of first lactation Holstein Cattle calving between 2003 to 2013. All records collected by Animal Breeding Center of Iran. Materials and Methods Records were edited using Fox pro 8.0 and ACCESS 2010 software and the wrong and unusual records were removed from the dataset. All analyses were performed using the RR (random regression) routine of the WOMBAT software package using AIREML algorithm on Linux operation system. Test day records were analyzed with the following random regression model (RRM): Where; Pk; kth fixed effect of province, YSl; lth fixed effect of year-season of calving, Yklimnptv; test day record i obtained at dimt of cow p calved at the nth age group in herd-test day m, HTDm; fixed effect of mth herd-test date, Cf; The fth fixed regression coefficient for calving age, agen; The nth calving age, k; The order of fit for fixed regression coefficients (k=4), βr; The rth fixed regression coefficient, ka; The order of fit for additive genetic random regression coefficients, kp; The order of fit for permanent environmental random regression coefficients, αpr; The rth random regression coefficient of additive genetic value for pth cow, γpr; The rth random regression coefficient of permanent environmental effect for pth cow, ∅r)dimt (; The rth coefficient of Legendre polynomials evaluated at days in milk t, emnptv; is The residual effect. Results and Discussion The heritability of milk yield, fat percentage, and protein percentage during days 5 to 305 of lactation were 0.07 to 0.2, 0.019 to 0.041, and 0.019 to 0.217, respectively. The repeatability of milk yield, fat percentage, and protein percentage during this period of lactation were 0.65, 0.09, and 0.16, respectively. The study of production traits suggested that during the last 10 years in the Mediterranean climate of Iran, Genetic trend of Milk production was positive, but the genetic trend of fat and protein percentage, negative or zero. Figures 2 and 3 clearly indicate that using both types of records; test day records and 305-corrected records, genetic trend for milk production compared with fat and protein percentage was positive and increasing. Heritability of production traits in early lactation was low. The great influence of environment on animals and the negative energy balance are the reasons for the low heritability in this period (2). This amount was being increased and reaches its maximum in the second half of lactation. Increased heritability in the second half of lactation is a function of increasing additive genetic variance and sharp decline in the variance of permanent environment. Similar trends for the results of other studies were reported in the country (1, 14). Conclusion Recent studies showed that the accuracy of test day records using random regression method was higher than 305 days lactation records. The results of random regression method and Test Day records showed that the heritability of milk production is the highest and heritability of fat percentage is. Result of this study showed that, during the last 10 years (from 2003 to 2013) in the Mediterranean climate of Iran, Genetic trend was positive in the amount of milk production, but genetic trend of fat and protein percentage, negative or near zero.
