title: Relationships of metabolic hormones and serum glucose to growth and reproductive development in performance-tested Angus, Brangus, and Brahman bulls.
abstract: Understanding mechanisms that regulate growth and reproduction are important for improving selection strategies in cattle. In this study, Angus, Brangus, and Brahman bulls (n = 7 per breed) of similar age were selected from a group of 65 weanlings. Bulls were evaluated after weaning (i.e., approximately 6 mo of age) for 112 d for serum concentrations of metabolic hormones and glucose, growth, and reproductive traits. Performance data and blood sera were collected on d 0, 28, 56, 84, and 112. Sera were also collected in periods from d 50 to 59 (56D) and 103 to 112 (112D). Angus bulls were heavier (P < 0.05) throughout the study than Brahman bulls and were heavier than Brangus bulls on d 56, 84, and 112. Initial and final BW for Angus, Brangus, and Brahman bulls were 292.7, 260.6, and 230.4 and 468.3, 435.6, and 350.7 +/- 12 kg, respectively. Conversely, Brahman bulls had greater hip height (P < 0.05) than Brangus, and Brangus were taller (P < 0.05) than Angus. Angus bulls had the greatest (P < 0.05) scrotal circumference (SC) and Brahman bulls the least. Mean SC across days was 31.5, 29.7, and 25.0 +/- 0.6 cm for the three respective breeds. Serum testosterone was greater (P < 0.01) in Angus and Brangus bulls (10.0 and 8.9 +/- 1.4 ng/mL) than in Brahman bulls (4.0 +/- 1.4 ng/mL) throughout the study. After d 112, 100, 86, and 57% of the Angus, Brangus, and Brahman bulls passed a breeding soundness exam (P = 0.51). Serum concentrations of IGF-I and leptin were greater (P < or = 0.06) in Angus bulls on d 56, 84, and 112 than in Brangus and Brahman bulls. Serum concentrations of GH (P < 0.08) and glucose (P < 0.03) were greater in Brangus bulls than in Angus or Brahman bulls throughout the study. Prediction analyses suggested that serum concentrations of leptin could be used to predict (P < or = 0.08) BW and SC (R2 > 0.82) in the 56D and 112D periods among these breeds. Leptin was also useful in predicting (P < or = 0.09) serum concentrations of GH and testosterone in the 112D period (R2 > 0.32). Residual correlation analyses with the effect of breed removed suggested that leptin was correlated (r > or => 0.53, P < 0.05) with both SC and serum testosterone. Angus and Brahman cattle differ in phenotype, level of adiposity, and rate of sexual development. Data herein suggest that these characteristics could be due to varying mechanisms by which metabolic hormones such as leptin, GH, and(or) IGF-I are regulated.
authors.affiliation: Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003, USA. milthoma@nmsu.edu
authors.forename: M G
authors.initials: MG
authors.lastname: Thomas
authors.forename: R M
authors.initials: RM
authors.lastname: Enns
authors.forename: D M
authors.initials: DM
authors.lastname: Hallford
authors.forename: D H
authors.initials: DH
authors.lastname: Keisler
authors.forename: B S
authors.initials: BS
authors.lastname: Obeidat
authors.forename: C D
authors.initials: CD
authors.lastname: Morrison
authors.forename: J A
authors.initials: JA
authors.lastname: Hernandez
authors.forename: W D
authors.initials: WD
authors.lastname: Bryant
authors.forename: R
authors.initials: R
authors.lastname: Flores
authors.forename: R
authors.initials: R
authors.lastname: Lopez
authors.forename: L
authors.initials: L
authors.lastname: Narro
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D001947:Breeding; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood*; D020738:Leptin; D008297:Male; D012098:Reproduction / Q000502:physiology*; D012611:Scrotum / Q000033:anatomy & histology; D012741:Sexual Maturation; D013739:Testosterone / Q000097:blood*; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D020738:Leptin; D013739:Testosterone; D013006:Growth Hormone