Determination of adjustment factors of milk yield according to mature age in Brown Swiss breed cattle

Abstract

The study investigates environmental adjustment factors, specifically age and seasonal correction factors, to refine milk yield estimates in Brown Swiss cattle. The methodology includes the analysis of milk yield data (1987-2023 years) from 19,042 records spanning 10,127 cows across T & uuml;rkiye, employing three methods-simple average, polynomial regression, and gross comparison. These factors aim to standardize milk yield to a mature equivalent basis, ensuring fair comparisons by accounting for systematic environmental influences such as calving season and age. This adjustment enhances the precision of genetic trend evaluations and aids in selecting superior breeding stock, ultimately improving dairy farming productivity and genetic advancements. The adjustment factors for milk yield for 305-day were calculated taking into account 22 different age groups and 4 seasonal groups. The ages of cows calving in spring, summer, fall and winter months to reach 305-day milk yield at mature age were 64-66 months, 52-54 months, 58-60 months and 37-39 months, respectively. The current results therefore show that cows that calve in winter reach mature age earlier than cows that calve at other times of the year.