Seasonal variation in voluntary feed intake and growth in cashmere bucks fed ad libitum diets of low or high quality

Abstract

The effects of season and diet quality on voluntary feed intake and growth were examined in mature cashmere bucks over a 16 month period at Wollongbar (29¦S., 153¦ E.). Three-year-old bucks were individually housed under natural photoperiod and fed ad libitum diets of High (pelleted lucerne, CP 17.6%, ME 8.3 MJ/kg) or Low (pasture hay; CP 6.9%, ME 6.6 mJ/kg) quality, between July 1988 and Oct. 1989 (n = 6/treatment). Bucks on both diets exhibited a seasonal pattern in voluntary feed intake with maximal intakes during spring and summer, and minimal intakes during autumn. The pattern appeared to be circannual with high intakes during spring of both years. Liveweight also varied with season peaking in mid to late summer and reaching a seasonal nadir in late autumn or early winter. Change in liveweight was closely associated with digestible energy intake ( r = 0-87, P < 0.001) resulting in a growth cycle closely resembling that of voluntary feed intake. In both treatments, bucks lost weight throughout autumn, while growth rates were maximal between mid-winter and mid-spring. Diet quality did not alter the magnitude of the autumnal decline in liveweight with bucks losing 7.6% (Low) and 7.8% (High) of liveweight during this period. However, bucks on the high quality diet exhibited significantly elevated growth rates between mid-winter and mid-spring. We conclude that mature cashmere bucks exhibit an annual growth cycle with weight loss during autumn and maximal weight gains between mid-winter and mid-spring; that the growth cycle is driven primarily by changes in voluntary feed intake; and that increasing diet quality does not reduce the autumnal decline in liveweight but significantly increases liveweight gain during the seasonal peak in growth.