Patterns of change in mature Angus cow weight and fatness during the year.

Abstract

Postcalving cow weight and subcutaneous fatness change patterns were described for 80 mature spring-calving Angus cows. The cows grazed either high (regularly clipped fescue-legume) or low (fescue clipped once) quality pastures. Forage consumption was estimated continuously by an internal (acid detergent lignin)-external (Cr2O3) indicator technique. Milk production (calf-suckle technique) was estimated seven times during lactation. Wither height was measured during the fall after the period of intensive measurment. Angus cows grazing high quality pasture lost an average of 36 kg postcalving, whereas those grazing low quality pasture lost an average of 22 kilograms. Minimum weights were observed about April 1, prior to the season of large pasture quality differences in digestibility of consumed forage. Taller cows, when allowed increased nutrient density during midlactation (high versus low quality), responded by increasing (P < .05) fatness at a more rapid rate than less tall cows. For cows grazing high quality pasture, weight change was independent of level of milk production. Cows grazing low quality pasture and giving relatively large amounts of milk maintained less weight and fat during the middle and last part of lactation than did those giving smaller amounts of milk. Shapes of the curves depicting change in weight and fatness were closely related (P < .01) to digestible dry matter intake. Cows apparently consumed forage in such a manner that they became more alike in both weight and fatness as the grazing season progressed.