STOCKING RATE, CALVING SEASON AND POST-WEANING GROWTH EFFECTS FOR ANGUS CATTLE ON ANNUAL PASTURE

The effects of stocking rate, calving season and post-weaning growth w ere investigated over 3 years for Angus cattle on annual pastures. Ang us cows, mated to Angus bulls for 8 weeks to start calving early summe r (ES), early autumn (EA) or early winter (EW), were stocked at 0.6, 0 .8 and 1.0 cows/ha and calves/ha until their fourth calving ended. Wea ning, at average age 10.5 months, was at the end of October, January o r April. Some calves were slaughtered at weaning and others after a ye ar at 1.4 calves/ha. Late autumn-winter pasture growth [250-3500 kg dr y matter (DM)/ha] was below average in 2 of the 3 years of the study, and spring growth did not vary (overall mean 4400 kg DM/ha). Unseasona ble pasture growth during late summer-early autumn occurred between we aning in EA and EW for years 2 and 3. Milk consumption was an overall average of 4.8 kg/calf.day. The only variation was a higher value in E W in year 2 than in years 1 and 3. Winter calf growth in ES and EA was sometimes affected by year and stocking rate, and overall average spr ing growth was 1.23, 1.33 and 1.13 kg/calf.day in ES, EA and EW, respe ctively. Weaning weight occasionally differed with stocking rate in ES and EA, and tended to differ between years in EW in proportion to the level of unseasonable pasture growth. Overall, carcasses tended to be slightly heavier and fatter in ES but otherwise followed the weaning weight patterns. Minimum cow weight tended to vary with stocking rate in years 2 and 3 and overall increased from ES to EW. Maximum weight a lso differed in these years. Yearly treatment means for average daily weight change during mating were -1.47 to +1.45 kg/cow. Weight gain de clined from ES to EW except for reversal of the ES and EA situations i n year 3 when poor winter pasture conditions followed unseasonable pas ture growth. Average mating weight was greater with the lightest stock ing rate in year 3 and with EW in years 1 and 2. Condition score gener ally followed weight patterns. In the 3 years, calf birth weight tende d to be higher in EW, except for increased birth weight in EA in a yea r of unseasonable pasture growth. Average calving percentage and inter val between successive calvings were 87% and 365 days, respectively, w ith no clear treatment trends. Overall average gross margins/ha ($A) f or the lightest to heaviest stocking rates, respectively, were 126, 14 1 and 142 in ES, 93, 109 and 118 in EA, and 54, 70 and 84 in EW. In ge neral, ES enabled mainly heavier carcasses to be sold at seasonally fa vourable prices but resulted in some calf scours. Relative to ES and E A, EW calving tended to result in less cow stress in most years but he avier birth weights, more dystocia and lighter weaning weights if prol onged unseasonable pasture growth did not occur. Calf response to past ure conditions was generally proportional to calf age, and spring grow th was probably affected by the level of milk consumption and calf gro wth potential relative to age. Post-weaning calf growth did not differ consistently with calving season. The relationship between animal per formance and pasture condition may be useful for assessing different c alving seasons in other environments.