ACCOUNTING FOR THE EFFECTS OF ENVIRONMENT ON THE NUTRIENT-REQUIREMENTS OF DAIRY-CATTLE

The maintenance requirements of the Cornell Net Carbohydrate and Prote in System were revised to evaluate the effects of activity, temperatur e, and humidity. Four dairy heifer situations were simulated (1 = clea n and dry, 2 = moderately matted hair coat, 3 = condition 2 plus 10-cm lot mud from November to March, and 4 = condition 1 plus 16-kph wind) to represent typical conditions of the northern and southwestern US. In the northern condition, predicted daily gain was 0.88, 0.60, 0.53, and 0.68 kg/d for the four environmental situations; corresponding val ues for the Southwest were 0.88, 0.88, 0.78, and 0.88, Environmentally neutral daily gain was 0.94 kg/d to a BW of 603 kg at first calving a t 20.3 mo of age. Calving age was increased when environmental stress extended the age at which puberty weight was reached. Calving weight w as decreased when environmental stress occurred after conception. Twel ve environmental conditions (variable temperature, humidity, and housi ng) for lactating dairy cows were simulated. At 30 degrees C and no ni ght cooling, predicted milk production decreased 2.6 and 11.9 kg/d at 20 and 80% humidity, respectively. Increased activity reduced predicte d milk production to 0.4 to 1.3 kg/d in confinement scenarios and to 0 .9 to 7.5 kg in grazing scenarios.