| dc.description.abstract | Insulin-like growth factor-I (IGF-I) is a growth hormone that acts as a key modulator of the growth axis. Serum and plasma concentrations of IGF-I have been linked to economically important traits in beef cattle.
In order to determine whether concentrations of IGF-I differed among breeds of beef cattle, plasma samples from purebred and crossbred animals were analyzed. Two calf crops were derived from three-breed diallel matings using temperate and tropically-adapted breeds of cattle. The breeds consisted of temperate Bos taurus (A; Angus), tropical Bos indicus (B; Brahman), and tropical Bos taurus (R; Romosinuano). Plasma samples were obtained from 10 heifers and 10 steers of each breed-type at weaning, and two dates post-weaning. Concentrations of IGF-I were determined by radioimmunoassay (RIA). Breed differences were observed (P < 0.001). Relative to the temperate Bos taurus breed, IGF-I was greater in tropically-adapted breed-types.
In an effort to select for the improvement of economically important traits, experiments were performed to explore the possible use of concentration of IGF-I and temperament assessment as tools for selection. Using a Calan gate system, 3 Brahman heifer crops were fed during70-day trials. Performance and feed intake data were collected to determine feed efficiency. Temperament, determined by exit velocity and pen score, was evaluated at weaning. Serum samples were taken at weaning and days 0 and 70 of each trial. Concentrations of IGF-I and cortisol were determined by RIA. Correlations including IGF-I were weak (P > 0.05). Temperament had no significant effect on RFI but may affect ADG.
In an attempt to examine the relationship between IGF-I and RFI, body weight and feed intake data were collected during individual finishing phase feeding trials, on steers at El Reno, OK. The breeds consisted of temperate Bos taurus (A; Angus), tropical Bos indicus (B; Brahman), and tropical Bos taurus (R; Romosinuano). Plasma samples were obtained from 10 steers of each breed-type at weaning and days 0 and 60 of each finishing phase. Concentrations of IGF-I were determined by RIA. Correlations between IGF-I and RFI were weak (P > 0.05). Breed and year significantly influenced RFI (P < 0.01). | en |
