Browsing Honors Research Fellows and Undergraduate Research Scholars Theses by Author "Agado, Bryan Joseph"
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Agado, Bryan Joseph (January 11, 2011)[more][less]
Abstract: Identification of feed efficient cattle by determination of residual feed intake (RFI) of individual animals is both laborious and expensive (negative RFI value=efficient; positive RFI value=inefficient). A less costly method to predict RFI is needed. Knott et al. reported that rams with poor feed efficiency (positive RFI values) are more responsive to exogenous adrenocorticotropic hormone (ACTH); thus, we tested the hypothesis that response to an ACTH challenge in Brahman cattle is directly associated with RFI. Brahman bulls (n=12) (390±19 kg BW) and heifers (n=12) (334±12 kg BW), age 15±1 mon, with established RFI values were used. To establish RFI, after the calves were weaned, they were evaluated in separate 70 d test periods for each gender during which the animals were limit fed (2.65% BW/d) in a Calan gate feeding system. The 6 lowest and 6 highest ranking of each gender, males and females, respectively, were used to assess cortisol response to exogenous ACTH, total n = 24. Blood samples were taken via indwelling jugular catheter every 15 min from 3 h prior to challenge through 4 h after challenge at time 0 h with ACTH (0.1 IU/kg BW). Serum concentrations of cortisol were determined by radioimmunoassay using Coat-A-Count kits (intra-assay variation of 7.7% and inter-assay variation of 7.6%). Data were analyzed using GLM specific for repeated measures. Cortisol concentrations were affected by time (P<0.0001) and gender (P<0.005) but were not affected by RFI grouping (P>0.10). Basal cortisol concentrations (M=7±1; F=14±2 ng/ml), peak cortisol concentrations (M=37±3; F=64±4 ng/ml), amplitude of responses (M=31±3; F=49±4 ng/ml), and area under the curves pre-challenge (M=189±30; F=414±60 ng/ml•h) differed (P<0.01) between genders. These data indicate that cortisol response to an ACTH challenge is not a useful predictor of RFI in Brahman cattle. However, a sexual dimorphism in the cortisol response to an ACTH challenge was detected in Brahman cattle.
URI: http://hdl.handle.net/1969.1/93207 Files in this item: 1
RFIonACTHBrahmanFinal.pdf (126.6Kb)
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