THE MULTIPLE (PART) LACTATION MODEL FOR T HE EVALUATION OF DAIRY-CATTLE .1. ESTIMATION OF GENETIC-PARAMETERS

Genetic parameters using new data from Friesian cows of Lower Saxony w ere estimated for the multiple (part)lactation model used in Germany f or the evaluation of dairy sires and cows. The results may be summariz ed as follows: Genetic correlations for the three 100-days parts of th e first lactation are about .90 between successive parts whereas a gen etic correlation of .65 to .75 between parts one and three shows that these parts may be considered as different traits. The correlations be tween the parts of the first lactation and the entire second lactation are at most .85. The genetic correlation between part two of the firs t lactation which itself exhibits a close relationship with the entire first lactation and the second lactation is about .85. Estimates of h eritabilities are higher than previously reported for German data but are in good agreement with today's REML-analyses for the international Holstein-Friesian world. The third part of the first lactation is inf luenced by additional environmental effects which lead to comparativel y low estimates of heritabilities. The recording of production in this part of the lactation should be improved since this would be of subst antial help when selecting for animals with higher persistency.