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The respective investigations were carried out on 16 groups of bull sires, lathers of the subsequent generation of reproductors, including 13 groups of bulls of the Polish black-and-white breed (BW), 2 groups of purebreed Holstein-Friesian (HF) and 1 group of interbreed crosses (BW x HF). The total number of sons amounted to 427 heads and the numbers of groups varied from 9 to 74 sons. The results obtained prove a highly significant (P ≤ 0,01) effect of fathers on the body weight of sons on the 120th, 300th and 400th day of life, body weight gains from the 121st to the 400th day of life, height at withers and chest girth. The best results with regard to the traits analyzed were obtained by sons of the Centaur bull, a purebreed Holstein-Friesian and the worst by sons of the black-and-white Rolek bull.
The most cases of statistically significant differences between bull calves of different were found in rearing stations where the traits formed at a more favourable level. The investigated traits for all genotype groups of bulls assumed significantly different values in particular years of rearing. Crosses (BW × HF) reached higher body weight and higher daily weight gains than the inland BW bulls. The height at withers depended on the genotype and the interaction: genotype x rearing year. The bulls were the taller the greater was the HF blood addition. The chest girth depended on the genotype and rearing year The smallest was recorded in the BW bulls. The measurement coefficient depended, first of all, on the genotype. The highest values of this index were found for BW bulls; the higher was the HF blood addition the lower was the massiveness index. To the A and B class the lowest number of BW bulls was assigned, whereas the highest number of bulls assigned to these classes was of bulls of the genotype of 50% and 75% HF.
A review of performance testing of the dual-purpose yearling bulls in Poland in the period of 1971 - 1989 is given. Evolution of testing and selection methods in the above period are discussed. Considering the results of all papers presented in the present issue a general conclusion is drawn about the necessity of BLUP method introduction in estimation of breeding value of performance tested bulls.
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