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Journal of Animal Science Abstract - Animal Production

Effects of bovine somatotropin administration on growth, physiological, and reproductive responses of replacement beef heifers1

 

This article in JAS

  1. Vol. 91 No. 6, p. 2894-2901
     
    Received: Nov 08, 2012
    Accepted: Feb 13, 2013
    Published: November 25, 2014


    2 Corresponding author(s): reinaldo.cooke@oregonstate.edu
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doi:10.2527/jas.2012-6082
  1. R. F. Cooke 2,
  2. D. W. Bohnert*,
  3. C. L. Francisco*†,
  4. R. S. Marques*,
  5. C. J. Mueller and
  6. D. H. Keisler§
  1. Oregon State University – Eastern Oregon Agricultural Research Center, Burns 97720
    Faculdade de Medicina Veterinária e Zootecnia, UNESP – Univ Estadual Paulista, Campus de Botucatu, Departamento de Produção Animal, Botucatu, SP, Brazil, 18618-970
    Oregon State University – Eastern Oregon Agricultural Research Center, Union 97720
    Division of Animal Sciences, University of Missouri, Columbia 65211

Abstract

This experiment compared growth, body composition, plasma IGF-I and leptin, and reproductive development of beef heifers receiving or not recombinant bovine ST (BST) beginning after weaning until the first breeding season. Fifty Angus × Hereford heifers (initial BW = 219 ± 2 kg; initial age = 208 ± 2 d), weaned at approximately 6 mo of age, were assigned to the experiment (d 0 to 210). On d 0, heifers were ranked by initial BW and age and assigned to 1) treatment with BST or 2) saline control. Heifers assigned to the BST treatment received subcutaneous (s.c.) injections containing 250 mg of sometribove zinc whereas control heifers received a 5-mL s.c. injection of 0.9% saline every 14 d. Treatments were initiated on d 14 and last administered on d 196. Heifers were maintained on separate pastures harvested for hay the previous summer according to treatment and received grass and alfalfa hay at a rate to provide a daily amount of 7.0 and 1.0 kg of DM per heifer, respectively. Heifer shrunk BW was collected on d 1 and 211 for heifer ADG calculation. Blood samples were collected weekly from d 0 to 210 for determination of plasma progesterone to estimate puberty attainment as well as plasma concentrations of IGF-I and leptin in selected samples. On d 0, 63, 133, and 189, heifers were evaluated for intramuscular marbling, LM depth, and backfat thickness via real-time ultrasonography. No treatment effects were detected (P = 0.27) for heifer ADG (0.49 vs. 0.51 kg/d for control and BST heifers, respectively; SEM = 0.02). Mean backfat thickness was lesser (P < 0.01) in BST heifers compared with control cohorts (3.56 vs. 3.92 mm, respectively; SEM = 0.08). Heifers receiving BST had greater plasma IGF-I concentrations compared with control cohorts 7 d after treatment administration (treatment × day interaction; P < 0.01). Mean plasma leptin concentrations were lesser (P = 0.05) in BST heifers compared with control cohorts (1.82 vs. 2.03 ng/mL, respectively; SEM = 0.07). Onset of puberty was hastened in BST heifers compared with control cohorts (treatment × day interaction; P = 0.04). In summary, a greater proportion of BST heifers reached puberty during the experiment compared with control cohorts, despite lesser plasma leptin concentrations, backfat thickness, and similar ADG. Hence, circulating IGF-I was positively associated with hastened puberty attainment independently of growth rate, circulating leptin concentrations, and body fat content of replacement beef heifers.

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