Production and Physiological Responses of Dairy Cows to Varying Dietary Potassium During Heat Stress

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Abstract
Objectives were to study influences of heat stress and dietary K content on production and physiological responses of 8 Jersey and 10 Holstein cows blocked by breed and assigned randomly to no shade or shade environments. Each cow received a different dietary K treatment (0.66, 1.08 and 1.64% of dry matter) in each of 3 30-day periods. Rates of K loss from skin were .apprx. 5-fold greater for no shade as for shade cows during the hottest part of the day (13:00-15:00 h). Overall, cows with no shade ate 56% less during the daytime (08:00-16:00 h), 19% more during nighttime (16:00-08:00 h) and 13% less total feed than cows with shade. Interactions of environment and breed with dieatry K treatment suggested differences in feed intake and milk yield responses to increasing dietary K content. Total daily feed intake and milk yield of cows with no shade responded in curvilinear fashion to increasing dietary K responses in shade were small. Largest responses in no shade were as dietary K increased from 0.66-1.08%. Milk yield of Holsteins increased with increasing dietary K, but yield of Jerseys did not. Combined effects of elevated K loss from skin and reduced K and dry matter intake during heat stress suggested that lactating dairy cows may have benefited from supplemental K.