The dynamics of changes in performance indices in a holstein-friesian cross-breed cow herd

Research was based on data from a herd of Black-and-White breed cows which had an average milk yield ca. 7000 kg per cow per year. Upgrading crossing with Holtein-Friesian breed (HF) was employed in the herd and over 15 years of the breeding scheme the percentage of HF blood increased from 18 to 87% . Evaluation and comparative analysis of performance indices (length of per formance, life-time milk production and per 1 year of performance) for 16 g roups (2448 animals in total) of cows which started production between 1979 -1994 were carried out. A tendency to shorten the length of performance was observed in proportion to the increase of HF genes which greatly influenced and lowered life-time milk production. A speedy improvement in milk yield per one year of perform ance due to an increase in HF blood share of up to 75% was noted. Stagnatio n in milk yield was observed in the next generations of hybrids with more t han 75% share of HF genes.