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The assessment of Replacement Heifer Production Efficiencies through Residual Feed Intake and Key Hormone Profiles

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Title: The assessment of Replacement Heifer Production Efficiencies through Residual Feed Intake and Key Hormone Profiles
Author: Smith, Brock Andrew
Department: Department of Animal and Poultry Science
Program: Animal and Poultry Science
Advisor: Miller, Dr. Stephen
Abstract: Biological factors regulating feed efficiency were investigated in replacement beef heifers to establish factors that differ between efficient and less efficient animals. Feed efficiency, measured as residual feed intake (RFI) adjusted for body ultrasound measurements, was determined in forty-seven cross-bred heifers. Reproductive differences between efficient (low RFI) and less efficient (high RFI) heifers were examined. Low RFI heifers had an earlier age at both sexual maturity (P=0.08) and conception (P=0.08), and delivered heavier calves (P=0.006). The potential of fecal progesterone metabolites (FP4M) as an indicator of sexual maturity was examined. Measurements of FP4M present a promising non-invasive alternative technique for determining the onset of sexual maturity. A subset of 36 heifers was used to determine if plasma triiodothyronine (T3) concentrations could be used to predict feed efficiency. Triiodothyronine concentrations a correlation of 0.58 (P=0.001) to those from a quadratic prediction model of RFI in heifers sampled as yearlings.
Description: Research into reproductive characteristics associated with residual feed intake, and to determine the effectiveness of the thyroid hormones as a screening tool for feed efficient animals.
URI: http://hdl.handle.net/10214/5212
Date: 2013-01


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