As part of the ongoing effort to reduce greenhouse gas emissions of the Irish dairy industry, there is an increased focus being placed on imported feedstuffs, particularly protein.

For most of the year, supplementary protein is not required in dairy cows because grass is very high in protein.

For example, a 12% to 14% protein dairy nut is more than adequate in terms of supplementing cows at grass.

However, when milking cows are housed and fresh grass is not a part of the diet protein suddenly becomes a limiting factor.

Because grass silage is low in protein and because maize silage is particularly low in protein a high protein concentrate is required to balance the diet and achieve the desired 15% to 17% dietary crude protein target.

This has normally been achieved by including soya bean meal in the diet. This is a very high protein feed of up to 50% crude protein.

The problem with soya bean is that it cannot be grown in Ireland and so it must be imported, either from North or South America.

Soya bean meal from South America carries a higher environmental burden because farmers there are burning down rainforests to plant soya.

Teagasc research at Johnstown Castle has shown that when compared to feeding a diet consisting of homegrown protein sources, the carbon footprint lifecycle analysis of Brazilian soya-based rations is 32% higher. This is after taking into account all the carbon emissions associated with getting that imported soya bean into the cow.

Sources

However, the study has shown up some challenges with feeding homegrown protein sources. For one thing, animal performance suffered.

Beans are a protein source that can be grown in Ireland.

Although the diets were balanced in terms of crude protein and energy concentration, homegrown diets containing beans and rapeseed meal didn’t perform as well in terms of milk yield, fat and protein content as the imported protein sources such as soya bean meal and maize distillers. See Table 1.

The study was conducted over an eight-week period on autumn-calving cows and both treatment groups were fed a base forage diet of maize and grass silage.

According to researcher Michael Dineen, the study is set to run again this winter but with some tweaks.

The focus area is on adjusting the diet to overcome inadequate mobilisation of protein and amino acids.

Despite the reduction in animal performance, the carbon footprint of the milk produced using homegrown protein was substantially reduced.

UCD has been carrying out trials on native grain and report significant reductions in greenhouse gas emissions and no impact on animal performance, although this has been on spring-calving cows where protein is not as limiting as it is in a winter milk scenario.

A new study is commencing at Johnstown Castle looking at the impact of red clover silage.

The thinking here is that this high protein forage would reduce the amount of supplementary protein required in the diet.

Red clover silage has a typical crude protein of 16% to 20% compared to 12% for grass silage and just 8% for maize silage or fodder beet.

As protein becomes more of a limiting factor in winter milk herds, the continued use of maize or wholecrop wheat silage will need to be questioned because of how much supplementary protein is required to balance the diet.

While they are high energy feeds, forages that are high in protein are likely to become more important as locally grown energy sources such as cereals are readily available as a form of supplement.