Milk production and feed consumption are reduced automatically in an effort to curtail body heat production when temperatures become elevated. Depressed appetite is the primary cause of reduced milk yields. Heat stress is especially harmful at the peak of lactation. F. A rising temperature above 50 F is more detrimental than a similar fall below 50 F. High humidity adversely affects production only when temperatures exceed 75 F. Provision of shade, use of fans, showers, or refrigerated air alleviate thermal stress. B. Season - Milk yields for the entire lactation are usually greater when the cow calves in the fall.
Yields decrease progressively in freshening occurs in winter, spring, and summer.
The greater production in cows which calve in the fall is probably due to optimal temperatures, absence of flies, and more digestible feeds that are available in the fall, winter, and early spring in comparison with summer conditions. C. Exercise - Moderate exercise is conducive to high milk production. Too much or too little is detrimental. Cows in stanchion barns should be turned out at least once per day for exercise and heat detection. Metabolic Diseases Related to Lactation Milk production starts suddenly and increases daily in early lactation.