Alternatives to soya in the dairy cow diet

This will require analysis of all forages to be fed for accurate rationing and calculation of bought in feed requirements. Feed costs have been challenging so far this year and protein prices are set to remain high this coming winter. Therefore, making sure you are not feeding excess protein will help keep costs to a minimum.

It is a fine balance between providing sufficient protein to support high yielding cows without significantly overfeeding, whilst still maintaining milk output.

Overfeeding protein is wasteful but also has an environmental impact. Excess protein in the diet can lead to increased nitrogen excretion in urine, which can either end up as nitrate in water sources or can be lost to the atmosphere as nitrous oxide, a greenhouse gas which has a global warming potential 298 times that of carbon dioxide.

Research on low protein diets funded by DEFRA and carried out by the University of Reading between 2012 and 2018 examined the effects on lifetime productivity of cows fed a low (14%), medium (16%) and high (18%) crude protein diet over three lactations.

The outcome was that milk production and energy corrected milk yields were similar for cows fed the 16% and 18% protein ration but with the 14% protein ration, milk yield, fat yield and protein yields were lower.

This work was replicated in an on-farm demonstration at SRUC comparing a 15% and 18% crude protein ration between 2016 and 2018.

Over this period cows were grazed during the day in the summer months with access to buffer feed and fed a complete TMR in the winter. The effects on milk production of the two crude protein feeding levels varied over time, partly due to grazing conditions and partly due to changes in forage quality of the grass silage and maize silage.

There were periods where there were no significant differences in milk output between the two groups, with similar dry matter intakes recorded over the winter feeding periods. There were also no obvious effects of lower dietary protein on milk composition.

Butterfat did not vary between the two groups over the summer periods. Over the winter periods butterfat was often higher in the 15% protein fed group. It was rare for there to be any significant difference in milk protein content between the two dietary treatments and more often than not the milk protein level was surprisingly slightly higher in the 15% diet fed group.

Therefore, it can be concluded that with careful rationing and attention to forage changes, milk output and compositional quality can be maintained on lower protein diets.

Care must be taken when formulating lower protein rations as methionine is more likely to be deficient and supplementation of this essential amino acid may be necessary to help maintain milk output and milk protein content.

At the time of the above-mentioned research and on-farm study, 18% crude protein diets were pretty standard for milking cows. While 16% rations are now more the norm, it must be remembered that dairy cows do not have a crude protein requirement, they have a requirement for metabolisable protein which must be met for a given level of milk production. However, crude protein can still serve as a useful indicator of excessive protein supply.

A further thought on protein supplementation this winter is to consider soya alternatives, which should help to reduce your carbon footprint.

Numerous research trials have shown that soya can be easily replaced with a protected rapeseed product to provide quality bypass protein at no detriment to milk output. This is backed up by elimination of soya from SRUC’s three dairy herds 18 months ago.

Alternatively, there are other products on the market that can be used to slow down rumen degradation of protein various sources, therefore increasing the amount of bypass protein available to the cow, which may help to reduce or eliminate the use of soya.

This article has been produced as part of work funded by the Universities Innovation Fund from the Scottish Funding Council.