Advice on grazing management for dairy heifers

Well-managed rotational grazing for dairy replacements can produce cost-effective growth and train calves to become effective grazers. However, it is important to recognise the limitations in their first grazing year.

Herds turning out their weaned calves for the first time need to be sure that rumens have developed, says grazing consultant Sean Chubb of LIC.

This is usually reflected by concentrate intakes of at least 1kg a head, or 1.5kg in mob-reared calves (to allow for some calves eating more, others less, than the target).

See also: Benefits of weighing dairy heifers to improve efficiency

“Research shows that at a minimum of six weeks of age, calves should be OK to take on grass, but they still need concentrates and hay/straw as they adjust slowly to nibbling grass. Typically, you can wean them off straw in a month and concentrates in two months,” he says.

Sean warns that weaned calves cannot graze covers higher than 2,800kg/dry matter (DM)/ha, or hit a residual of 1,500kg DM/ha.

For the first couple of months at grass, he recommends they just take off the top 2.5-3cm before moving onto a fresh bite. By late summer, when fully grazing, they should be able to graze down to 1,600-1,700kg DM/ha.

“As they get older – by 12 months – you can push them a bit harder, to 1,500kg. R2s [rising two-year-olds] can be treated like a cow and go into covers of 3,000-3,200kg on the shoulders of the season, although they might not hit residuals,” he says.

Timing and choice of paddock

However, using dairy heifers to clean out paddocks rejected by cows will curtail growth rates, as they tend to be pushed to graze it down, so will be underfed. “Cows have left this grass for a reason,” he points out.

Also, heifers need leafy material for growth, but where paddock covers are really high, grass will start to be growing stem at the bottom and, in May, this stem begins to harden.

“Plant energy content begins to fall, and so heifers are getting lower energy and you are slowing down their growth.”

Unless replacements go in 21 days (to allow for regrowth) after cows have grazed a paddock, Sean advocates using a mower to correct poor residuals.

Exceptions may be where there is only one paddock a week to graze down, or a break of some good-quality grass has been left as well.

Putting heifers before cows in the rotation is also unlikely to be successful because older cows do not like to graze grass that has been made unpalatable by saliva, urine or dung, Sean says.

“If it is followed by rain and left for 20 days, it’s less of an issue, but grazing two to three days later is not good unless you are really stuck for paddocks.”

Where heifers are on a leader-follower system, he advises running leaders two to three weeks ahead, so that followers graze quality not “scraps”.

“In a rotation, youngsters might not eat as quickly, and you might need to skip a couple of paddocks for followers to keep their distance,” he adds.

Farms operating a separate heifer-grazing platform are reminded to measure outputs as well as inputs. This means grass quality, daily growth rates, and heifer weights.

“If you weigh heifers, you can allocate grass accordingly.

“A heifer needs high quality – 12MJ/kg ME [metabolisable energy] – for muscle growth, even if she can utilise the rougher stuff, so it’s important to monitor the outputs of daily liveweight gain and in-calf rates.”

Monthly weighing

Weighing every four to six weeks is necessary to keep track of target daily liveweight gains, agrees vet Ginny Sherwin, clinical associate professor at Nottingham University.

However, she says that a management plan needs to be devised before weighing, so that it can be actioned on the day.

“[When you weigh] use marker spray to put a red blob on the back of those heifers below target.

“You don’t have to go back to the office to make some calculations and take action in a couple of days – you can decide there and then.

This might be separating heifers into different groups, or running a leader-follower system, or feeding concentrates,” she explains.

Data from regular weighing can be used to make concentrate supplementation more precise, adding or removing it from the diet according to grass quality.

Monthly weighing also means that no calves get too behind in growth rates but can soon catch up with the rest of the group.

Lean growth

The aim is to have lean skeletal growth, and this is most efficient at a younger age when feed conversion efficiency is highest.

“It’s worth putting concentrates in earlier, rather than during winter housing. It costs more to get that growth later.

“Trying to grow in-calf heifers faster is not good: [target] a steady 0.6kg/day so they calve at 90% of the mature cow bodyweight.”

Grazing intakes

“When dry matter is low, calves are going to need to eat a lot of grass to get their energy requirements,” she says.

“Even where grass averages 12.6MJ of metabolisable energy [ME], a 3-4-month-old calf needs 32MJ [of ME] a day to grow 0.8kg/day.

“This means we are asking them to eat 13kg of grass [freshweight] when their rumen is still in development.

“We know that a 500kg grazing mature cow eats 15kg DM/day. But this cow is a very efficient grazer, not a picky calf.”

Feeding some form of fibre – such as chopped straw in barrels – in the paddock will offset low-fibre spring grass and help develop rumen size and papillae health, says Ginny.

However, she points out that feeding supplements should not attract badgers.

“Ideally, rotate so that calves are not on the same pasture for more than three days, and avoid using troughs on the floor.

“The best badger-proof troughs are off the ground with high sides or removed at the end of feeding. Some people can also run heifers into a shed for feeding.”