The rate of live-weight gain was measured for two groups of dairy heifers in winter; one group had access to shelter for 18#x2013;22 h per 24 h, whereas the other group never had access to shelter. Both groups grazed on pasture for 4#x2013;6 h during the day. In a second experiment the oxygen consumption of young Friesian bulls and mature Jersey cows was measured using a face-mask; the animals were kept in stalls outdoors in an exposed location. The provision of shelter, in association with a relatively dry ground surface, increased the rate of live-weight gain of the heifers in the two years by 3.6 and 7.2 kg per head over periods of 54 and 44 days respectively. Heat production of the Friesian bulls and Jersey cows was increased by the climatic conditions on only a few occasions when wind speed was high and rain was falling; under these conditions apparent body insulation was 0.19#x2013;0.31#xB0;c m2/W and 0.11#x2013;0.19#xB0;c m2/W for the Friesian bulls and Jersey cows respectively. It was calculated that under windy, wet conditions the lower critical temperatures of the cattle were between + 7 to + 24#xB0;c if fed on a maintenance level of feeding. However, the heat production of the cattle was apparently not increased during several nights when ground frosts were recorded.
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