Regular weighing of dairy heifers is crucial to ensure animals remain on track to calve at two years of age.

Results from AHDB Dairy's two-year calf to calving project – introduced to help farmers improve calf survival and increase the number of heifers making it into their first lactation – not only found that it is impossible to weight animals by eye but also that weights vary hugely within groups of similarly aged heifers.

The UK-wide initiative saw 12 dairy farms enrolled which acted as hosts for a series of farm meetings on best practice heifer management over the two years.

Six farms were autumn-block calving and enrolled in autumn 2015 and six had a stronger spring calving bias and enrolled in spring 2016. The growth, health and nutrition of 10 heifers on each farm were also monitored every three months.

It’s this growth data that has highlighted the inconsistencies in growth rates within groups of heifers on individual farms and the fact many heifers fail to hit the target growth rates needed to calve in at the most economical age of 24 months.

Some of the key targets set included 50% of mature body weight at 12 months old, 60% at 14 months old and 85% post calving.

“72% of all heifers failed to achieve the target of doubling birth weight by weaning and half were not on target at each, three-monthly weigh point, said AHDB Dairy's technical manager, Andy Dodd who headed up the initiative.

"There was also huge variability within groups. For example, on the Dorset farm, heifers were achieving between 0kg and 2kg of daily live weight gain at six to nine months of age.”

On some farms, 12-15-month-old heifers were also only achieving 0.1kg/day – well below the growth rate needed to hit the right weight to calve at 24 months. On average, heifers need to hit 0.8kg a day to be on track. However, this will vary according to adult cow size on individual farms.

Mr Dodd added: “The results from the 12 farms show it’s impossible to estimate weights by eye or spot variation in growth within a group by looking into a pen. Regularly weighing animals and managing heifers in weight groups is essential to make sure they stay on track.”

The need to continue to weigh animals at grass was also highlighted by the fact the biggest variability in growth rate was seen at the end of the summer across all heifers. This correlated with declining grass quality and insufficient supplementation.

“The Aberdeen farm’s heifers were really consistent when housed inside on the same diet and as soon as they went out to grass, growth dropped off in some animals. Some were 450kg and others were 350kg.”

However, declining growth rate is not an inevitability of grazing, with some farms achieving good consistency in growth rates whilst at grass. Mr Dodd believes more work needs to be done to look at the affect of heifer genetics, however he advised closely monitoring weights at grass.

“If you turn heifers out to grass, weigh them at turn out and then weigh 10% of them, 2-3 weeks later to see if they’ve grown. Split heifers according to weight at grass and supplement those that need it. There is a marked spread in performance within groups so farmers need to target management better to ensure consistencies in growth,” he concluded.