Getting cows to bulling weight requires attention

Getting heifers to bulling weight in a low-cost operation is a challenge.

When they are to join the calving block on time, heifers need to be big enough to be sexually mature and mated by a set date. Late calvers are unlikely to make a second lactation in the same herd. This means the emphasis has to be on quality rearing, not lowest cost – and it involves as much measuring and monitoring as milk production from grazed grass.

Such early investment does, however, pay dividends, confirms Staffordshire producer Rupert Major. He runs 380 crossbred cows at Castle Hayes Park near Burton-on-Trent and thinks nothing of feeding a quality milk replacer for at least 12 weeks – some calves are weaned at 16 weeks. In total, this adds up to 50-65kg/head of milk powder consumed. “The cost is insignificant in the overall outlay of producing an animal and works out at 8% of total rearing costs,” says Mr Major. “But the sooner calves get up and running and eating, we will get them to weight. A well-grown heifer eats more summer and autumn grass and is big enough to outwinter on forage crops.”

As well as savings in winter feed and housing, Mr Major finds that stock are far healthier and cleaner from outwintering. “We see no respiratory illness and calves thrive. I’m not saying we never have problems, we just try our hardest to be ahead of them. It’s back to having clear aims and goals,” he says. When calves are at grass, generous stocking rates (30-40 calves on 7ha), plus moving on to fresh ground twice a week, help avoid problems such as coccidiosis. Not surprisingly, therefore, losses (from day one until calving) are well below the target 2%. In the past two years, there have been just four deaths out of 300-plus heifers.

After a decade of rearing crossbred replacements on a budget, Mr Major believes that the most important factor in getting heifers to bulling weight is weaning weight. But, he also emphasises that the focus should always be on maintaining the calving block. In this case, it runs for 12 weeks from 7 February, with heifers calving the week before to give them longer to get back in-calf. “You can’t have low production costs from such a high proportion of grazed grass in the diet, together with economies of scale, without a tight calving block,” he explains.

“So, our mating date is always fixed for 21 April, when the bulls are turned in, and we set our targets along the way based on this. We have to achieve bodyweights and hit our targets on time by managing and manipulating growth rates. When we miss, it’s catastrophic because late-calving heifers are gone in one lactation.”

As in all production systems, a good start in life with plenty of colostrum plays a key role in heifer health and productivity. Calves are therefore picked up twice a day from the calving area and automatically tubed with 2.5 litres of colostrum. They remain on colostrum for three days, before the diet switches to 4.5 litres a head a day of cold milk replacer fed once a day, together with ad lib concentrates amounting to 1kg a head a day. At this stage, calves are housed but have access to an outdoor paddock.

From mid April, Mr Major has youngstock fully turned out and grazing about the farm. At 10 weeks, milk is dropped to three litres a head a day as a prelude to weaning; concentrates continue for a further 2-3 weeks post weaning. Any stock tasks, such as disbudding, are carried out when calves are still on milk to avoid stress and setbacks at weaning. The crucial thing is that weaned calves move about the milking platform: Eating the same leafy quality grass as the milking cows helps rumen development.

Although bulling weight and mating date are fixed targets, weaning weight is always flexible, ranging from 85kg in April, to 120kg for calves weaned in July and August. “It increases as the number of days to mating falls because later-born animals out of the calving spread still need to be mated on the same day. This is why we end up feeding a lot of milk for a long time.”

The remaining weight targets are based on a percentage of the mature weight of the adult herd. This is particularly important with crossbreds because of the lack of uniformity in size and cow type in a herd. At the moment, Castle Park’s mature weight is 480kg. However, this may be revised following a herd weigh-in this summer. Mr Major aims to breed heifers at 60% (280-300kg) of mature weight and calve at 90% with 95% of them calving in the first six weeks.

His other key milestone is to have all heifers at 200kg by early November. This is the basis to withstand outwintering and he finds that good growth rates during good weather give heifers the reserve to tolerate small periods of slower growth in bad weather. On forage crops plus big bale silage, growth rates are 0.5kg/day between mid November and early February. Once heifers are back on spring grass, 0.8kg to 1.0kg/day is possible.

To track progress, calves are weighed five or six times in their first year. Putting youngstock through the weigh crush also allows Mr Major to compare each individual with the rest of the group. But he believes the most useful part of the exercise is to analyse the results on computer and pick out the bottom 10-15% of heifers. “Underweight animals – and they are not always the same animals – need different management because they need to grow faster than their bigger herd mates which can eat more. This is the real challenge,” he says.

Unless he helps them catch up, being under target will significantly affect how these heifers calve the first time, thus impacting on their lifetime productivity. Mr Major’s main method is to remove herd pressure by splitting them off into a separate management group. Being part of a group of just 20-30 animals, instead of 160, is immediately beneficial. In addition, these heifers are on ad-lib grass rather than grazing allocated behind an electric fence. Furthermore, this group is kept on an outdoor feed pad in winter, fed ad lib silage, plus 2kg a head a day of concentrates.

“In our system, management is in place to improve underweight heifers with special treatment at lowest cost. Heifer calves are the most important stock on the farm because they are our future. We get income from our milk, but progress in business comes from rearing replacements: They are our fuel for further expansion.”


Breeding replacements by weight

Heifer rearing targets must be based on a predicted date and age of first calving. But replacement heifers should be bred by weight, not age, if they are to slot into a calving block. This is because the onset of puberty is weight related, says LIC consultant Mike Bailey. “If we delay puberty, we delay calving and heifers that are later in the calving block take longer to get back in-calf again,” he explains.

Late-calving heifers are also more likely to fail to reach a second lactation. Animals either have to be culled from the herd, or risk extending the calving block. NZ figures show that just 55% of replacements selected at birth make it to a third lactation. Growing heifers properly, however, not only minimises losses and maintains a tight calving block, it results in surplus stock which can be sold or used for expansion.

Mr Bailey says that while genetics and environment both affect the age of puberty, it’s the level of nutrition that has the biggest influence. Heifers reaching the correct weight must be sexually mature and cycling. “Previous studies have shown that lower calving rates in lighter heifers were probably caused by a proportion of the heifers being pre-pubertal,” he adds.

“Dexcel results reveal that 100% of Holstein Friesians fed to achieve growth rates of 0.77kg a day, were cycling by Planned Start of Mating. But only 81% of those fed for 0.37kg a day growth were cycling. In Jerseys, 98% of the high feed group were cycling and only 68% of the low feed group.”

Excess growth rates pre puberty have been linked to lower milk production as the developing mammary tissue produces fat cells instead of milk cells. This is why the target is to limit growth rates to achieve 30% of a herd’s mature weight at six months. Aiming for a percentage of a mature weight at key stages in the rearing process is also more practical when dealing with a range of breed sizes, particularly in crossbred herds, says Mr Bailey. And targets should not be based on breed averages or book values: “Weigh your own cows – a number of five to six year olds in the autumn – to determine the mature weight.”

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