Semen Characteristics and Behavior of Grazing Bulls as Influenced by Shade

Abstract

The efficiency of shades to provide bulls relief from heat stress was studied during the summers of 1977 and 1978. The shades were constructed from steel pipe with expanded metal roof covered with baled straw. Ambient and blackbulk temperatures were more variable in 1977 than in 1978. No consistent influence of shade availability was observed in behavior of the bulls, though during 1978, less time was spent grazing by bulls with access to shade. During both years, standing time was greater (P<.10) by bulls without access to shade. Bulls made little use of the shades in August and September. In 1977, semen motility, movement rate, and percentage live sperm cells were greater (P<.10) from bulls provided shade. Bulls without shade showed a trend for higher numbers of aged acrosomes and abnormal sperm cells. General semen quality was lower in 1978, but no consistent effect of shade was noted, except that abnormal sperm cells were lower from bulls with access to shade. During both years, semen motility was decreased and percentage of abnormal sperm cells was increased 2- to 3-weeks after blackbulb temperatures approached 45 degrees C for several consecutive days.