PLASMA HORMONES AND METABOLITES IN CATTLE IN RELATION TO BREED (BELGIAN-BLUE VS HOLSTEIN) AND CONFORMATION (DOUBLE-MUSCLED VS DUAL-PURPOSE TYPE)

Four Belgian Blue double-muscled type (BBDM) bulls, four Belgian Blue dual-purpose type (BBDP) bulls and four Holstein bulls were used in a fattening trial in order to relate differences in the extent of muscle development and adiposity to differences in digestibility, endocrine status, protein and lipid metabolism. The larger muscle development in BBDM animals was associated with a trend to higher nitrogen retention , higher food conversion efficiency (p<0.05) and lower apparent digest ibility (p<0.05). No difference was found between the groups for plasm a glucose concentration. Higher creatinine, lower alpha-amino nitrogen , lower triglycerides and higher non-esterified fatty acid plasma leve ls were observed in BBDM as compared to Holstein bulls (p<0.05), the B BDP group being intermediate. A trend to a higher cholesterol plasma r evel was found in BBDM animals. There was no difference between the th ree groups in plasma fatty acid composition, except for the C-14:0 con tent. Some of the differences in plasma metabolites were related to ca rcass composition and endocrine regulation, a decrease in muscle devel opment and an increase in adiposity being associated with lower growth hormone production (p<0.05) and higher insulin (p<0.05) and IGF(1) se cretions. The insulin/growth hormone ratio at the end of the fattening period was 0.0011, 0.0018 and 0.0069 in BBDM, BBDP and Holstein bulls , respectively, and was directly associated with fat deposition.