Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2013
Publication Date: N/A
Interpretive Summary: The impact of hot weather on cattle production are varied, ranging from little to no effect in a brief exposure, to death of vulnerable animals during an extreme heat event. Shade has been shown to reduce stress on feedlot cattle. In this study, we investigated how animals of differing coat colors responded to having access to shade. Three hundred eighty four feedlot heifers of different breeds each with a unique coat color were used in this 3-year long study. Each summer a new group of 128 heifers were monitored for 6 – 8 weeks. Cattle were selected by breed, weight, and health status. The colors and associate breeds were: black (Angus), white (Charolais), dark red (composite 1: Pinzgauer x Red Poll x Hereford x Angus cross), tan (composite 2: Charolais x Braunvieh x Limousin x Angus x Hereford cross). Respiration rates and coat surface temperatures were measured twice daily and the heifers were weighed every 28 days. Shade lowered the stress level of all animals, and had a greater impact on the Angus (black) cattle than the Charolais (white) cattle with the two composite breeds (the dark red and tan hided cattle) having an intermediate response. Access to shade did not improve weight gains of any of the breeds.
Technical Abstract: Heat stress in cattle causes decreases in feed intake, growth, and efficiency. In extreme cases, heat stress can cause death of vulnerable animals. A simple shade can reduce the animal's radiant heat load by 30% or more. However, for most feedlots, adding shade structures to all pens is cost prohibitive. The objective of this study was to determine how animals, with known risk factors (color, previous cases of pneumonia, condition score, and temperament) for heat stress, respond to having access to shade. Feedlot heifers (384 animals; 128 animals/year for 3 years) of two breeds (Angus and Charolais) and two composite breeds (MARC I [¼ Charolais, ¼ Braunvieh, ¼ Limousin, ' Angus, and ' Hereford] and (MARC III [¼ Pinzgauer, ¼ Red Poll, ¼ Hereford, and ¼ Angus]) were selected and penned on the basis of weight and breed. Heifers were weighed, condition and temperament scored every 28 days. Heat tolerance was accessed by measurements of respiration rate taken twice daily at 0800 and 1300 h on a preselected group of 64 animals. It was determined that the shade lowered the stress level of all animals, and had a greater impact on the Angus cattle than the Charolais cattle with the two composite breeds (the dark red and tan hided cattle) having an intermediate response. Access to shade did not improve weight gains of any of the breeds.