Particularly in large individuals, weight loss appears to be due to the logistic constraint operating in late winter. With snowmelt, intake increases rapidly in compensation. However, as the spring flush of vegetation progresses, intake declines until lactation imposes additional demands after calving. The decline in requirements to support lactation is offset by declining forage quality so intake remains high for much of the summer. Seasonal constraints on dry matter intake.
Actual intake is defined as the minim of metabolic, digestive and logistic constraints.
A rather different pattern of constraints operates on weaned calves. Gut fill is predicted to be a major constraint on forage intake until the following spring and summer. Since logistic constraints appear less important, forage quality would be expected to be more important than availability. However, differences in foraging efficiency of large and small animals under harsh winter conditions have received only cursory attention.