Relationship between leptin content, metabolic hormones and fat deposition in three beef cattle breeds.

The aim of the study was to determine if cattle breeds differing in their carcass characteristics also differ in the profiles of their leptin and metabolic hormones. Three breeds, Belgian Blue (BB) (n=12), Limousin (L) (n=12) and Aberdeen Angus (AA) (n=12) with varying ability to deposit fat and protein were compared. Blood, muscle and subcutaneous (SC) adipose tissue were sampled. Animal performance, carcass and meat characteristics were determined as well as plasma leptin concentration, leptin gene expression in SC adipose tissue, leptin-receptor gene expression in SC adipose tissue and plasma concentration of insulin, tri-iodothyronin (T3), thyroxin (T4) and cortisol. The BB bulls showed the lowest values of leptin gene expression (P<0.05). Values of plasma leptin concentration and of leptin-receptor gene expression tended to be lower in BB than in the other breeds. For a similar amount of adipose tissue (after normalisation), BB bulls showed a higher ratio of plasma leptin (P<0.05), whereas normalised leptin gene and leptin-receptor gene expressions did not significantly differ between breeds. Belgian Blue bulls also differed in their metabolic hormone profile, tending to show lower values of insulin, T3 and T4 than the two other breeds. Cortisol levels were significantly lower (P<0.05) in BB than in L and AA animals.