Increasing shade area in feedlot heifers during heat stress: physiological and performance parameters.

Heat stress is a great challenge for feedlot operations established in arid zones. The aim of this study was to evaluate if increasing shade area in the pen improved physiological and productive variables in feedlot heifers under hot climate. A total of 510 European and Zebu heifers were randomly assigned to six pens which were divided in two treatments: (1) three pens with 100 heifers each with a shade area of 2.7 m2/head (control group [C]); and (2) three pens with 70 heifers each with a shade area of 3.7 m2/head (treated group [T]). Physiological variables respiratory frequency (RF) and body surface temperature (BST) of several anatomic regions were taken from 30 heifers per treatment (i.e., 10 heifers/pen). Feed intake on pen basis was recorded weekly and heifers were individually weighted on days 1, 26, and 66 of the study to calculate performance variables. Relative humidity (RH) and ambient temperature (AT) were recorded and used to estimate the temperature-humidity index (THI). Data was analyzed with analysis of variance. The average THI during the study was 81.7 units, which was categorized as dangerous heat stress. In both shaded areas, European heifers showed higher (P < 0.05) RF than Zebu heifers. In the afternoon, the temperature of head, neck, loin, paddle, and belly was higher (P < 0.05) in C compared with T. Heifers under T showed better (P < 0.05) daily weight gain (DWG), total weight gain (TWG), feed conversion (FC), and feed efficiency (FE) than heifers in C, with no effect on dry matter intake (DMI). Results indicate that during hot summer months, Zebu showed more tolerance to heat stress than European heifers; however, heifers under a shade area of 3.7 m2/head had better productive performance than those under a shade area of 2.7 m2/head during the finishing phase of the feedlot. Increasing the shade area in the finishing phase of beef cattle on feedlot improved some physiological and productive responses during heat stress.

Climate change vulnerability of confined livestock systems predicted using bioclimatic indexes in an arid region of México.

Climate change is a major world-wide challenge to livestock production because food security is likely to be compromised by increased heat stress of the animals. The objective of this study was to characterize, using bioclimatic indexes, two livestock regions located in an arid zone of México, and to use this information to predict the impact of global warming on animal production systems of these regions located in the state of Baja California (México). A 5-year database (i.e., 2011 to 2015) consisting of about one million data points from two zones (i.e., coast, valley) from four meteorological stations in the north of Baja California were used. Bioclimatic indexes were constructed for the four types of livestock production systems most common in this region, being: dairy cattle, beef cattle, sheep, pigs. The temperature-humidity index (THI) thresholds used to classify heat stress were determined and scaled for each livestock species as: THIbeef and THIpig 74 units; THImilk 72 units; and THIsheep 23 units. Statistical differences between indices were detected (P < 0.01) during summer for the valley and coast zones as (THIbeef = 72.9 and 51.8; THImilk = 80.6 and 67.4; THIpigs = 83.9 and 65.2; THIsheep = 29.5 and 20.1 units). Coast zone weather did not suggest vulnerability of livestock production systems to heat stress at any time of the year, but heat stress risk during summer for valley zone dairy cattle, sheep and pigs was classified as severe, but lower for feedlot cattle. Prediction models showed significant adjustment just in the coastal zone for THImilk, THIsheep, and THIsheep, suggesting more impact of global warming during summer in the coastal zone. Use of management strategies to reduce heat load of domestic animals during summer in northern Baja California is essential to maintain their productivity, with more emphasis in the valley zone.