Evaluation of Selection Practices in Three Lines of Beef Cattle
Selection practices in three synthetic lines of beef cattle were evaluated based on data collected over 12 to 13 years. Sires from the Jersey, Angus and Simmental breeds were mated to three lines of foundation crossbred dams to produce first generation progeny. Subsequent calves were produced mating crossbred parents of the same generation. Crossbred sires were selected based on an index that included hip height and weight at weaning. At Rhodes, a total of 2.84 to 3.07 generations of selection have been carried out. This provided a mean generation interval of 4.33, 4.23 and 4.58 years in small, medium and large lines, respectively. At McNay, the corresponding generation interval values were 4.15 years for small and medium lines and 5.29 years for the large. The mean weighted sire selection differential for the index in the small line was 1.28 s/generation. In the medium cattle these values were -.57 s/generation (Rhodes) and -.36 s/generation (McNay). For the large synthetic cattle the index differential ranged from .71 s/generation at McNay to .92 s/generation at Rhodes. Of the total mean parental selection differential, sire contribution ranged from 86% to 95%. Selection differential values for components of the index indicated that the index equations often favored weaning weight, and this was very pronounced in the medium line. Regardless of the line, selection criteria have been strictly followed. However, all the maximum potential sires have not been utilized.