Beware over-restricting calf growth, warns SAC
By Jonathan Riley
SOME beef producers are restricting calf growth rates too much in winter and over-estimating the ability of compensatory growth to make up shortfalls in target growth rates.
Compensatory growth takes time and in the north the grazing season is too short for calves to reach optimum weights at housing in their second winter, the Scottish Agricultural Colleges Basil Lowman told the British Grass-land Societys winter meeting at Malvern, Worcs (report p38, 39).
"This is a major reason why cattle are being finished at over 30 months," said Dr Lowman.
He explained that cattle restricted to winter growth rates of 0.5kg – with an average target weight gain of 1kg a day for the first year – needed only to recoup 60kg liveweight at grass after a four-month winter feeding period typical in southern England.
"To reach its target liveweight gain at the end of an eight-month grazing period, the calf in the south would need to grow at 1.25kg a day at grass. But compare this with a calf in the north which, after an eight-month winter feeding period at the same growth rate, would be 120kg below target at turnout," said Dr Lowman.
"With this shorter grazing season some producers are asking cattle to grow at 2kg a day at grass."
Instead Dr Lowman advised feeding cattle a high energy-density diet during the first part of the winter to maximise growth rates. To keep condition scores down at turnout he suggested a switch from concentrates to a roughage-based diet two months before turnout. At this stage the larger animal could eat sufficient silage offered ad lib to maintain growth at 0.8kg a day, he said. "But by reducing concentrate inputs over the two months they will have lost some condition, which will affect their daily liveweight gain at grass.
"For example, a calf at condition score 2 will grow at about 1kg a day, but one at score 3 will grow at only 0.7kg a day," he said.
The switch from concentrate to roughage also allows the rumen bugs to adjust to the changed diet, so growth check at turnout is minimised, he added. *
SACs Basil Lowman:"Dont over-restrict calf growth rates this winter."
ACHIEVING TARGET GAIN
• Dont restrict calf growth rates too much in winter.
• Feed a high energy concentrate diet early on.
• Two months before turnout switch to a forage diet.