PLASMA GLUCOSE CONCENTRATION, SUBCUTANEOUS FAT THICKNESS, AND PUBERTY ATTAINMENT IN NELORE HEIFERS TREATED WITH RECOMBINANT BOVINE SOMATOTROPIN

Abstract Text: In previous research, we observed that Nellore heifers that attained precocious puberty had greater plasma IGF-I but similar plasma leptin concentrations compared with cohorts that attained puberty later. Hence, this experiment evaluated the effects of bovine ST treatment, as an alternative to increase plasma IGF-I concentrations, on plasma glucose concentrations, body fat accretion, and puberty attainment of Nellore heifers. Thirty-one heifers were distributed in groups Treated (n = 16; 348 ± 52 d of age; 259 ± 49 kg of initial BW) or Control (n = 15; 356 ± 40 d of age; 260 ± 38 kg of BW). For 10 months, Treated heifers received 250 mg of sometribove zinc every 14 d, whereas Control heifers concurrently received 2.5 mL of saline. All heifers were maintained on a single pasture and exposed to a teaser bull with a neck-marker device to identify mounted heifers. Ovarian ultrasonography was conducted every 14 d to determine corpus luteum presence. Every 2 months, rump and backfat thickness were also estimated via carcass ultrasonography whereas blood samples were collected. Heifers were considered pubertal when teaser bull activity was observed and a corpus luteum was detected. Age at puberty and fat thickness were analyzed by unpaired t test, whereas plasma glucose concentrations were analyzed by the Mann Whitney test of GraphPad PRISM. No treatment effects were detected (P ≥ 0.30) for puberty attainment, nor heifer age and BW at puberty. More specifically, 7 Treated heifers (593 d of age and 394 kg of BW at puberty) and 7 Control heifers (599 d of age and 411 kg of BW at puberty) reached puberty during the experiment. Backfat thickness was greater (P = 0.03) in Control compared with Treated heifers at 22 mo of age (5.0 vs. 4.0 mm, respectively). Rump fat thickness was also greater (P ≤ 0.05) in Control compared with Treated heifers at 16 mo (5.0 vs. 4.4 mm), 18 mo (5.0 vs. 4.4 mm), 20 mo (5.5 vs. 4.8 mm), and 22 mo of age (5.8 vs. 4.6 mm). No treatment differences were detected (P = 0.46) for plasma glucose concentration (90 vs. 89 mg/dL for Treated and Control heifers, respectively). In summary, Nellore heifers administered bovine ST at the experimental conditions utilized herein had decreased subcutaneous fat accretion, but similar plasma glucose concentrations as well as BW and age at puberty compared with cohorts receiving saline.

Keywords: bovine ST, heifers, Nelore, puberty