Abstract
Growth traits were evaluated for 57 Japanese Black (B), 27 Japanese Shorthorn (N) and 26 crossbred calves produced by AI matings of Brahman (Z) sire to B, N and Holstein (H) dams. Significant differences between mating groups existed (P<0.01) for all traits of birth, 3, 7, 12 and 18-mo weights. Calves of ZB, ZN and ZH were 5.0, 10.4 and 11.8kg, respectively, heavier in birth weight than straightbred calves of the corresponding dam breeds. After birth, all crossbred calves exhibited rapid growth ; the 18-mo weights of ZB and ZN were 47 and 46kg, respectively, heavier than those of the corresponding straightbreds. Differences between mating groups were significant (P<0.05, P<0.01, P<0.01) for average daily gains (ADG) from birth to 3, 3 to 7 and 7 to 12-mo, respectively. The ratios of crossbred to corresponding straightbred calves for each ADG exhibited different changes between ZB and ZN as growth proceeded. The ratio for ADG from birth to 3-mo was -3% in ZB, whereas it was 19% in ZN. The different ratio appeared due to a difference in the milk performance between the two dam breeds. The withers heights of ZB and ZN were 6.8 and 4.8cm in 33-mo cows, and 5.9 and 6.4cm in finished fattening steers, respectively, these being taller than those of the corresponding straightbreds. These results indicate that introducing the germ plasm of the Z breed to Japanese beef breeds is useful for increasing the growth potential of calves in the more temperate northeastern area of Japan.
