Cash-converter cows sorted in feed trial

A trial to this effect, running for almost six years at the Westpac Taranaki Agricultural Research Station (WTARS), near Hawera, was instigated because no data was available on this subject for dairying, says Kevin Macdonald, a senior scientist with DairyNZ. He has worked on the trial since it began.  

“We didn’t know whether the cow that produced the most milk ate more or less than the cow that produced a lot less milk. So our aim was to identify gene markers to indicate which were the most efficient converters of feed into product.”

The trial began with calves, about 1050 in feed facilities in New Zealand and a similar number going through a research centre in Australia. “We couldn’t put that many cows through the trial, so the calves were used as a proxy for cows in respect of live weight gain. The calves were 6 – 8 months of age and they were in the pens at WTARS for 60 days. We measured their intake each day and weighed them three times a week. They were fed lucerne cubes imported from Canada for the trial. From these trials we were able to calculate which animals used feed more efficiently than others.”

The use of the lucerne cubes was critical to the trial: moisture levels in pasture can vary, but the cubes provided a consistent feed quality that could easily be weighed  and hence provide accurate data. Kevin Macdonald says while all the animals may have eaten a bit more feed than normal, this didn’t matter because the trial was to obtain accurate data and comparisons.

The results of the calf trials are surprising. The most efficient calves ate up to 20% less feed than the inefficient, suggesting a saving to a farmers of $180-$200 in taking them though from  weaning to when they first calve.

The next stage of the trial has been to see if the feed conversion efficiencies in calves could be translated into lactating cows; the answer is ‘yes’.

Macdonald says the difference in lactation was not as pronounced as in the calves – about 4%. 

Using gene markers LIC identified for ‘residual feed intake’ from the calves, 214 five- and six-year-old cows were selected and bought from Waikato and Taranaki. They were relocated to WTARS and over a season 208 were put through the feed facilities and fed lucerne/pasture cubes imported from Australia. The results were similar to those from the earlier lactating cow trial. The cows identified by the RFI markers as being most efficient were the most efficient.

A trial on 44ha involving 126 of these cows, with a range of stocking rates, is nearing the end of its second lactation. The aim of the trial is to study how cows with differing efficiencies react to a range of stocking rates.

As well as identifying efficient cows, part of the trial measured the amount of methane given off by individual cows, Macdonald says. “When we put the cows through the respiration chambers at the centre for greenhouse gas emissions in Palmerston North there was no difference in the amount of methane being produced from each kg of drymatter eaten. So if efficient cows eat less, and produce the same amount of milk, they will have a lower methane production per kg of MS produced.”

This trial has only involved Holstein Friesian cows. Macdonald says the Australian scientists are planning to do some work with Jerseys and he hopes New Zealand may be able to piggyback off their work.  “Because the results we got from the Holstein Friesians between ourselves and Australia were almost identical, we may be able to rely on their results from the Jerseys without having to do it ourselves. At that point we can look at the kiwi cross.”