GENETIC TRENDS IN MILK YIELD AND SOME REPRODUCTIVE TRAITS OF HOLSTEIN FRISIAN CATTLE

Istraživanja genetskih promena u proizvodnji mleka i nekim svojstvima plodnosti (trajanje steonosti i scrvis pcrioda) Holštajn goveda izvedena su na 12.335 laktacija kod 4.700 krava koje potidu od 53 različita oca, a u vremenu od 1978 do 1988 godine. Ocene genetskih parametara utvrđene u datim istraživanjima u granicama su literaturnih izvora. Promene nastale nakon selekcije krava na mlečnost nisu se odrazile značajno na trajanje steonosti. Iako produženje servis perioda pri selekciji na 4 % MKM nije visoko, ipak dobijeni trend povrđuje pretpostavku da utvrđene promene mogu imati značajne posledice.Investigations of genetic trends in milk yield and some reproductive traits (period of pregnancy and service period) of Holstein cattle were carried out in 12,335 lactations of 4,700 cows of 53 different siries in the period from 1978 to 1988. Estimations of genetic parameters made in these investigations were within the limits found in literature. Trends after the selection of cows for milk yield did not reflect significantly on the duration of pregnancy. Although the extension of the service period in selection for 4 % MKM was not high, the trend obtained confirms the supposition that the established changes can have significant effects. 16