PLASMA-INSULIN, METABOLITE CONCENTRATIONS, AND CARCASS CHARACTERISTICS OF JAPANESE BLACK, JAPANESE BROWN, AND HOLSTEIN STEERS

To characterize some of the physiological features of Japanese beef br eeds, plasma concentrations of insulin and metabolites and carcass com position were measured in five Japanese Black, five Japanese Brown, an d four Holstein steers (6.2 mo; 164 kg). The steers were raised under typical feeding conditions in Japan until they were slaughtered at 600 to 700 kg BW. Blood samples were collected at 8 mo of age (average BW , 194 kg) and at 300, 400, 500, and 600 kg BW. Plasma insulin concentr ations increased with BW in all three breeds and were greater (P < .05 ) in Japanese Blacks than in the Japanese Browns or Holsteins at 400 a nd 600 kg BW. The Japanese Blacks exhibited lower(P < .05) plasma gluc ose levels at 300, 400, and 600 kg BW compared with Holsteins. Regardl ess of the breed, plasma urea nitrogen (PUN) concentrations increased with BW. The two Japanese breeds had greater (P < .05) PUN levels than Holsteins at 300 and 600 kg BW. Total cholesterol and phospholipid co ncentrations tended to decrease above 300 kg BW in the Holsteins; howe ver, the concentrations of both metabolites were elevated in the steer s of Japanese breeds at 500 and 600 kg BW (P < .05). Breed did not aff ect the plasma concentrations of albumin, triglycerides, and NEFA. The Japanese breeds had higher P < .01) dressing percentage, greater(P < .05) carcass fat proportion, and a lower proportion of carcass bone (P < .01) than the Holsteins. These results indicate that there are bree d differences in plasma levels of insulin and certain metabolites and carcass composition among Japanese breeds and Holstein.