نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم دامی، دانشکده کشاورزی و صنایع غذایی، واحد علوم و تحقیقات تهران، دانشگاه آزاد اسلامی، تهران، ایران
2 گروه علوم دامی، دانشکده کشاورزی، واحد ورامین-پیشوا، دانشگاه آزاد اسلامی، ورامین، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
111543 records of first calving test day milk production with three milking times during the years 1983 to 2016 were used for 142 herds in the Breeding Center data file. The dairy cows under study had 10 test day records. Variables from the herd-year-calving combination as random effect and herd-test-month-age combination at the time of record as fixed effects were created for each animal. Average milk yield in hot and dry climate was higher than hot and wet climate. The average traits of milk fat and milk protein percentage in hot and dry climates were higher than hot and wet climates, but somatic cell traits were higher in hot and wet climates. The phenotypic variance of milk yield was higher in hot and dry regions in all ten test day records. The phenotypic variance of milk fat percent was higher in hot and dry area on the first, second, fifth and sixth test days. The average genetic variance of milk fat percentage in hot and wet region at 9 test day records was higher than in hot and dry region. Phenotypic variance of milk protein percentage in hot and dry area was higher than in hot and wet regions in all test days. In countries where calving occurs throughout the year, mastitis is dependent to the pattern of growth of pathogens in different seasons and years. Changes in animal physiological conditions (calving and changes in breast status) increase the number of somatic cells in milk, which has a physiological effect. As a result, the interaction of genotype and environment changes the ranking of male cows in high-yield, medium-yielding and low-yielding herds. In other words, male cows that have a high corrective value in high-yielding herds may not have the expected yield in low-yielding herds.
کلیدواژهها [English]