Changes in leptin and metabolite concentrations over time in finishing beef steers and heifers

Abstract Text: Leptin is a hormone produced in adipocytes that is involved in the control of feed intake, growth, and carcass composition.  The objective of this experiment was to determine if the changes in plasma leptin and metabolites over a feeding period differed between steers and heifers.  Composite breed cows were bred to working ranch bulls representing Angus, Charolais, Gelbvieh, Limousin, Red Angus, and Simmental breeds to produce calves with a wide range in DMI and growth.  Steer (n = 127) and heifer (n = 109) progeny were fed a finishing ration individually for 84 d with BW recorded every 21 d.  Blood samples were collected on d 1, 42, and 83 via jugular venipuncture and plasma was analyzed for leptin, glucose, and lactate concentrations.  Body composition was evaluated by ultrasound between d 93 and 97.  Data were analyzed using the mixed procedure of SAS.  Fixed effects included breed, sex, and time, and sire was included as a random effect.  All 2-way interactions were tested and removed if not significant (P > 0.05).  Time was treated as a repeated measure with animal as the subject.  There was a time × sex interaction (P < 0.001) for leptin concentration, indicating that heifers had greater leptin concentrations than steers on d 1 and 42, but concentrations were not different on d 84.  Heifers had greater plasma glucose concentrations than steers (P < 0.001), but both sexes decreased from d 1 to 42 (P = 0.013) and reached a nadir, not changing on d 83.  Heifers also had greater lactate concentrations (P < 0.001), and both sexes tended to have greater lactate concentrations on d 42 than d 1 (P = 0.059), and d 83 was intermediate.  A mixed model was also used to determine the effect of sex on body composition and carcass characteristics.  Breed and sex were included as fixed effects and sire was a random effect.  Heifers had slightly more back fat than steers (P = 0.017), but had larger LM area as measured by ultrasound (P < 0.001) and at slaughter (P = 0.014).  Leptin concentrations increase over the finishing period in both steers and heifers but at a greater rate in steers, which could be due to heifers reaching a fatness endpoint earlier than steers.  USDA is an equal opportunity provider and employer.

Keywords: Feedlot cattle, leptin, growth, efficiency