Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 15, 2009
Publication Date: September 6, 2009
Citation: Hall, M. 2009. Heat Stress Alters Ruminal Fermentation and Digesta Characteristics, and Behavior in Lactating Dairy Cattle. In: Proceedings of Eleventh International Symposium on Ruminant Physiology, September 6-9, 2009, Clermont-Ferrand, France. p. 204-205. Technical Abstract: In a study designed to assess the impact and interaction of nonfiber carbohydrates (NFC) and ruminally degradable protein (RDP) on ruminal characteristics and animal behavior, animals experienced heat stress in the first period (HS), and no/greatly reduced heat stress (NHS) in the second period, allowing a comparison of the effects of environment as a period effect on animal responses. The study was carried out as an incomplete partially balanced Latin square design with a 2 x 2 factorial arrangement of treatments (trt) and two 21-d periods. Eight ruminally cannulated Holstein dairy cows were randomly assigned to a series of dietary trts: supplementation with the nonfiber carbohydrates (NFC) sucrose (SUC) or corn starch (STA) at 10% of diet DM, and relative modification of dietary ruminal protein degradability (RDP) by supplementation with 48% soybean meal (+RDP) or expeller soybean meal + 48% soybean meal (-RDP). All diets contained 33% corn silage and 22% alfalfa silage, on a DM basis. Diets were formulated to contain 30% NDF, 17.3% CP, and 41% NFC. Cows were offered the diets ad libitum. Sample and data collections were made in the last 7 d of each period. During HS, animals had greater respiration rates (69 breaths/min) and rectal temperatures (39.0C) than did animals during NHS (41 breaths/min, 38.4C; P<0.01). DM intake tended to be lower during HS than NHS (21.9 and 34.8 kg; P=0.15). Rumination (403 and 486 min/d; P=0.07) tended to be lower, and Eating time was lower (190 and 242 min/d; P<0.01) for HS than for NHS. Ruminal pH (6.03 and 5.82; P<0.01) and organic acid concentration lower (147 and 174 mM; P<0.01) for HS than for NHS. In addition to the slightly decreased intake for HS, these values may be due to the decreased DM% of rumen digesta (13.8% and 15.6%; P<0.01), reduced digesta DM kg (12.5 and 13.7 kg; P=0.02), and tendency for increased digesta liquid kg (77.6 and 73.8 kg; P=0.08) for HS and NHS, respectively. That ruminal fermentation and digesta characteristics and behavior changed with changing HS or NHS, suggest that such environmental changes may alter nutrients available to the animal, passage kinetics, and maintenance requirements, thus affecting animal performance.