The study was done by research scientist Lorna McNaughton and LIC intern Rhiannon Handcock, who is about to start her PhD in the area of heifer management.
McNaughton has been involved in recent research work behind recommended liveweight targets for New Zealand dairy heifers with the aim of maximising those animals’ performance once they enter the herd. Other researchers have shown that failing to achieve these target weights can mean lower milk production and lower reproductive performance.
The work McNaughton did with Thomas Lopdell two years ago showed heifers that were heavier before calving produced more milk in their first lactation than those which were lighter. A 1% increase in target liveweight equated to an extra 23.2 litres of milk, which at a 9% milksolids (MS) test meant a 2.09kg MS gain. For a 500kg cow the increase would be 2.25kg MS.
Further research demonstrated the reproductive benefits of heifers reaching liveweight targets. Table 1 shows the expected benefit in milk production and reproduction for a heifer that reaches her liveweight target at 22 months, compared with a heifer that is 10% or 20% behind target.
Data from 600,000 heifers born from 2006 to 2010 showed many failed to meet their liveweight targets, with 53% of six-month-old heifers more than 5% below their target liveweight. This increased to 61% when they were 15 months old then 73% at 22 months.
The aim of the most recent study was to see if dairy heifer rearing weights had improved since the 2012 study.
“We wanted to revisit the area because there have been a lot of messages to farmers from DairyNZ and LIC that if their heifer weights fall behind targets, particularly during winter, it’s hard to catch up,” McNaughton said.
For the research Handcock searched the LIC database across the national herd to extract liveweights, liveweight Breeding Values (BV), breed data and birth dates of heifers born between 2011 and 2014. After cleaning the dataset there were more than 2.6 million records on almost 656,000 animals. She then calculated their expected mature liveweight and target liveweights at various stages of growth.
DairyNZ targets of 30% at six months, 60% at 15 months and 90% at 22 months and actual liveweights achieved were compared for the 2011 to 2014-born heifers at these ages. These were then compared with the 2006-10 born heifers after their data was re-evaluated to provide a direct comparison because of the significant changes in liveweight BVs earlier this year. At all ages higher numbers of heifers in the recent study were at and above target liveweights compared with the earlier one. The 15-month-old and 18-month-old heifers showed the greatest increases in those at or above target weights, an improvement from 43% to 68% for the first group and from 46% to almost 75% for the older group of animals.
McNaughton said she had hoped there would be an improvement in heifer liveweights seen when the data was analysed.
“But I was really surprised at how much they had improved,” she said.
“It shows what farmers can do once they have identified a problem.”
She said the results of the earlier study only started being talked about in the 2012-13 season. With the higher milk payouts of that time farmers could see the value of increased milk production from better-quality young stock coming back on to their farms from graziers.
“It starts with your calves,” she said.
“If you don’t do a good job of them they can struggle the whole way.”
Farmers grazing young stock onfarm were paying more attention and being more vigilant about weighing them regularly. Scales were cheaper to buy and since the introduction of MINDA weights it was easier to monitor individual heifer weight.
The latest study showed just over 9% of 2011-14 born heifers were at risk of not reaching puberty coming into mating.
“Our initial work showed that 30% of heifers were at risk, so this is a huge improvement,” McNaughton said.
The dataset was subdivided by breed. A lower percentage of Jersey heifers were at or above target at most ages compared with crossbreds and Friesians.
McNaughton said Friesian and crossbred heifers generally did better in hitting or exceeding liveweight targets.
“We don’t know so more research is needed.”
A continuing area of concern is heifer weights at 22 months. The advantage the 2011-14 born heifers had at 15 months had almost disappeared. This coincides with the time when many heifers return from grazing. The 90% of mature liveweight target at 22 months has a significant effect on future milk production, so it is an important target to reach.
Handcock will now, as part of her PhD, look further into heifer growth patterns.
“We suspect there is an optimum,” McNaughton said.
“Poorly grown heifers are at risk but the larger ones, which are far exceeding targets, might be too.”
The Massey and Lincoln trial, which is at the early planning stage will study 2015-born heifers through to 2018. It will look at both milk production and reproduction, which McNaughton said had been a neglected area since the 1990s. Work published in 2005 by Dr Kevin MacDonald and Dr John Penno when they were at Dexcel looked into heifer planes of growth, but the animals were treated with CIDRs and no reproduction effects of different liveweights were observed.
And when it comes to milk production, the latest study shows heifers from 22 to 24 months old were on average between 8% and 11% below target. That meant a loss of between 18.2 and 23.6kg MS in their first lactation, and even at the forecast Fonterra payout of $3.85/kg MS that means more than $90/heifer.
Doing it right
Farmers should be regularly monitoring heifer liveweights by weighing at specific times and charting their animals’ progress. While many weigh 20% of their heifers at random, the more animals they weigh the stronger the indications will be of any problem so the sooner they’re able to intervene.
“If they have a good eye for stock they can be bang on with their feeding,” McNaughton said.
But discussion group results often showed this ability was limited to just a few farmers out of a large number who thought they could accurately guess young stock weights. They also needed to remember eye appraisal was only relative to the particular mob they were casting their eye over, and not other animals.
“Heifers with small frames can look good but still be underfed and they won’t catch up with the rest of the mob for a long time,” she said.
Grazing companies agreed supplementing heifers was generally required over winter, which could be with the cheapest feed available.
“That message seems to have been taken on board by farmers,” she said.
A lot were paying their graziers more, which they regarded as fair value so long as they were getting good animals back on their farms.
“But that probably feels painful at the moment.”
McNaughton was hearing of more farmers rearing young stock themselves and said there was no reason it couldn’t be done well. The low payout also meant some farmers were talking about rearing fewer heifers for a couple of seasons. If they had a good repro programme they could probably get by with a lower replacement rate in their herd.
“Their vet is a good first port of call to draw up a plan.”
Avoiding the pitfalls
Not getting heifers in-calf and coming into the herd producing well is a big waste, which could easily be rectified, Lorna McNaughton says.
“You can treat heifers pretty badly and they may still get in-calf, but they may calve late and struggle to conceive early when they are in the herd.”
A common hiccup with maintaining heifer liveweights could be farmers forgetting about paying enough attention to young stock in their first winter.
“They’re very tied up with calving and if young stock are wintered on the home farm they can be competing with the herd for grass,” she said.
“It’s always a hard call and particularly so with the current payout.”
Some farmers might not have their farms set up well for regularly weighing their stock.
“Their yards may not be suitable for handling young stock because they’re got everything set-up for milking,” she said.
“But there are weighing services out there and they may be the answer.”
