Characterizing feedlot heifer response to environmental temperature

Authors: Brown-Brandl, Tami; JONES, DAVID - University Of Nebraska

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2015
Publication Date: 4/11/2016
Citation: Brown-Brandl, T.M., Jones, D.D. 2016. Characterizing feedlot heifer response to environmental temperature. Transactions of the ASABE. 59(2):673-680. https://doi.org/10.13031/trans.59.10855.

Interpretive Summary: Extreme summertime conditions can have negative impacts on growth, performance, and can cause death in vulnerable animals. A study was conducted over a three-year period to evaluate the characteristics that contribute to heat stress. Three hundred eighty four feedlot heifers representing black, dark red, tan, and white breeds were evaluated over a three-year period to evaluate characteristics that contribute to heat stress. Animals of each color were assigned to pens with and without shade structures. It was determined that color plays an important role in heat stress. Animals that were less responsive to heat stress gained more weight than those with a higher responsiveness. Shade had a greater impact in darker colored breeds (black and dark red), and lowered responsiveness in tan cattle but did not impact the responsiveness in white heifers.

Technical Abstract: It has been shown that feedlot cattle vary in their response to environmental temperature. There is a need to develop a parameter to summarize those varied responses, i.e., a heat stress phenotype. The goal of this investigation is to quantify animal response to environment by describing each animal with a parameter and to investigate how this parameter is impacted by management practices. Responsiveness was determined to be a useful parameter to describe the impact of dry-bulb temperature (tdb) on respiration rate (RR) of feedlot heifers. Responsiveness was defined as the slope of RR to tdb. It is a valid and useful parameter because it expresses a single value for each animal that includes the dynamic interaction of RR and tdb. Using the responsiveness parameter, it was determined that unshaded feedlot cattle had a lower responsiveness than shaded cattle. It was noted that there were a range of responsiveness values for all colors of cattle tested; thus, it is likely that there is genetic variation in this parameter. This parameter may prove useful for genomic analysis of heat stress. In shaded animals, the effects of color were minimized. Therefore, dark breeds and composite breeds (Angus and dark red MARC III composite) showed more of a reduction in responsiveness than tan-colored MARC I composites, while Charolais heifers showed no response to shade. While responsiveness was shown to be a useful parameter, it may not be optimal, and other candidate parameters need to be explored.