Karen Trebilcock

Wintering pregnant cows on fodder beet appears to be affecting the growth of calves, research at the Southern Dairy Hub indicates.

It is early days into the trial and much of the data is still to be analysed, but DairyNZ senior scientist Dawn Dalley, who is managing the research, says the results to date are significant.

Replacement heifer calves born in 2018 at the hub research farm near Invercargill from cows wintered on mainly fodder beet were, on average, 2.5kg lighter and had a smaller stature than those from cows wintered on kale.

“That means at birth they were 10% lighter than the calves from cows wintered on kale which is statistically significant,” Dalley says.

The height, length and girth of the calves were also measured and again the fodder beet calves proved smaller.

‘Farmers have probably never noticed as calves are seldom weighed at birth although a few we have talked to have had their suspicions.’

As well, at nine months of age, the gap in liveweight was still an 8% difference, despite being managed in mixed mobs from three days of age.

The research was presented at the hub’s field day on October 29.

It is the first time a comprehensive study investigating the lifetime performance of young stock from fodder beet and kale systems has been done as New Zealand is one of the few countries in the world where pregnant cows are wintered with fodder beet as a large proportion of their diet.

“When we started the trial our hypothesis was that the calves from cows on fodder beet would be smaller.

“Farmers have probably never noticed as calves are seldom weighed at birth although a few we have talked to have had their suspicions.”

Fodder beet is high in soluble sugars, low in crude protein and low in some essential minerals especially phosphorous.

“We know that protein is needed to build bone and muscle and minerals are required for bone growth.”

Cows at the hub farm were transitioned on to fodder beet or kale at the end of May and stayed on the crop until 10 days before calving in early August.

The cows on fodder beet were offered 10.9 kg drymatter (DM) of fodder beet and 3kg DM of pasture balage per day and the cows on kale got 8.5kg DM of kale, 2.7kg DM palm kernel and 3kg DM of pasture balage.

The winter diet of both groups targeted the same metabolisable energy intake (ME) and was a normal winter diet for cows in Southland.

Dalley says she was surprised the fodder beet calves had not caught up.

“They were in mixed mobs so they all experienced the same feeding conditions until the fodder beet calves (R1s) were introduced to fodder beet in autumn.”

The fodder beet calves were wintered this year on fodder beet and the kale calves on kale and all are being naturally mated with yearling Jersey bulls. Dalley says the in-calf rates and calving dates will be monitored to see if any differences arise between the groups.

As well as the possibility of a lack of protein and minerals in the diets of the calves’ mothers before birth affecting their growth, colostrum volume and quality may also be part of the puzzle.

The fodder beet and kale calves received first and second milking colostrum only from their respective treatment dams until 48 hours of age and then they all received milk pooled from all the cows on the farm.

“We took blood samples from the calves when they were brought into the calf shed and again at 48 hours but we could not get a commercial lab to test the IGG (immunoglobulin) of their blood so instead we used plasma total protein as an indicator of immunity status,” Dalley says.

“The IGG level of the calf’s blood at 48 hours of age should be a good indicator of how good the colostrum intake was and the level of immunity the calf has received from it.

“While the total protein levels in the bloods taken at birth were statistically similar in both groups, it was lower in the fodder beet calves at 48 hours which suggest that their immune status may not have been as good as the kale born calves.”

Data of health incidences from the two mobs has yet to be analysed but Dalley believes there weren’t significant differences, but the lower immunity in the fodder beet calves may have affected growth rates when the calves came under nutritional challenge.

“The research is confounded because the calves were only blood tested when they were brought in, not when they were born – we just didn’t have the resources to do that.

“So we don’t know how much the calves had suckled on their mothers before that first blood test.”

This spring, pooled colostrum samples were sent to a lab for Brix testing which will show if there is a difference in the colostrum quality from cows wintered on fodder beet and the cows wintered on kale.

“There is a lot a data from the weights, stature measurements, blood sampling and animal health events to collate as well to understand the full picture,” she says.

“What farmers should be thinking about is the energy, protein and mineral content of the diet they are feeding different classes of stock, identifying any deficiencies and adjusting the proportions of crop, considering the type of supplement and requirement for mineral supplements to address these.

“They need to be making sure the nutritional requirements of their stock are being met.”