CROSSBREEDING EFFECTS OF MILK COMPONENTS AND MILK-YIELD OF SLOVAK PIED AND BLACK PIED CATTLE AND THEIR CROSSBREDS

Crossbreeding parameters of production traits of crossbreeding Slovak Pied (PI) and Black Pied (P2) cattle were estimated. The records of 5, 290 first lactation cows during 1984 - 1991 were analyzed. The followi ng traits were analyzed: lactation yield of milk and the content of fa t, protein, lactose, fat and protein, dry matter and free-fat dry matt er. Eleven genetic groups were defined (Tab. II). The mixed model tech nique was used to estimate the genetic group means. The mixed model in cluded the herd effects, joint effects of year and season, the effects of the genetic group, the random effects of sire nested within geneti c group and the regression on the age of the first calving. The cross breeding parameters were estimated by Weighed Least Squares (WLS) from the genetic group means using the reciprocals of the squared standard errors of genetic groups means as weight. The model of D i c k e r s o n (1969) was used. The additive effect, the heterosis and the recomb ination loss were determined. In this investigation maternal heterosis and recombination loss were confounded (E r i c s o n et al., 1988). But the estimate of maternal heterosis in the pilot analysis was non-s ignificant and low. Maternal effects were omitted because the correlat ions between the estimates of crossbreeding effects were increased by involving maternal effects in the model. Milk yield was significantly affected by all effects included in the mixed model. The highest means squares were found for herd and for age of first calving. The genetic groups significantly affected only protein content and free fat dry m atter content. The coefficient of variation for milk yield (20%) was t hree times higher than that for milk components. The lowest coefficien t of variation was found for free-fat dry matter content (2.9 %) and l actose content (3.5 %). The estimates of genetic group means are prese nted in Tab. II and the estimates of the crossbreeding effects are in Tab. III. The milk yield of the genetic groups increased with higher p ercent of Black Pied. The estimated heterosis is positive (S c h u l t e - C o e r n e , B o i e , 1986; V a n d e r W e r f , d e B o e r , 1989; P e d e r s e n , C h r i s t e n s e n , 1989; F r e y e r , P a n i c k e , 199 1) and its absolute value is lower than that of the estimated negative recombination loss. Negative estimate of the recom bination loss have found Fewson et al.(1975), Schulte-Coerne, Boie (19 86), Van der Werf, de Boer (1989) and Distl et al.(1990). The milk fat content of the parent breeds was very similar The estimate of additiv e effect was positive and small. The absolute value of the estimate of heterosis and also the absolute value of the negative estimate of the recombination loss were higher than the estimate of additive effects. A positive estimate of heterosis for milk fat content was found also by G r a m l, P i r c h n e r (1984), P r i b y l et al. (1987), E r i c - s o n et al. (1988), V a n d e r W e r f , d e B o e r (1989), F r e y e r , P a n i c k e (1991). F e w s o n et al. (1 975) and P r i b y 1 et al. (1987) obtained negative estimates of the recombination loss and V a n d e r W e r f , d e B o e r (1989) a positive estimate. The milk protein content was higher for the Slovak Pied breed group. The value of protein content decreased with increasing percentage of B lack Pied cattle in crossbred groups. The estimated additive effect wa s negative. The absolute value of heterosis was a half of the additive effects. A positive estimate of heterosis for milk protein content wa s found by O l d e n b r o e k (1980) and F r e y e r , P a n i c k e (1991). Schulte-Coerne, Boie (1986)and Van der Werf, de Boer (1989) ob tained estimates of heterosis near to zero. The recombination loss was found to be near to zero. These findings are in agreement with those of Van der Werf, de Boer (1989). The genetic group means of lactose co ntent were very similar. The estimated of the additive effects and the heterotic effects were low. A higher value was estimated for the reco mbination loss that was positive. The estimates of the breed group mea ns and the crossbreeding effects for the other analyzed milk component s traits depended on the estimates of fat, milk and lactose contents. They were linear combinations of three basic milk components. A positi ve heterosis for milk yield and also for fat and protein content was f ound but none of the estimates was significant. This is in agreement w ith the results reported by Turton (1981).