The recent volatility in cost and availability of supplementary protein sources has meant dairy farmers have begun growing their own home-grown protein sources, in particular forage legumes. Legumes are popular due to their ability to fix nitrogen, reducing the reliance on purchased nitrogen fertiliser, and contain high levels of crude protein, reducing the reliance on purchased protein. However, this protein that is available in forage legumes is generally rumen degradable protein, rather than by-pass protein which is also required by dairy cows. However, forage peas contain naturally occurring tannins which can bind to the protein and protect it from microbial breakdown in the rumen, allowing it to become by-pass protein which is available for digestion in the small intestine. Not all the protein will be protected by the tannins and a proportion of it will be digested by the microbes in the rumen.
Why consider forage peas as an alternative source of protein for dairy cows? In the UK, forage pea seeds can be sown in the spring once the soil temperatures have reached between 7 and 8˚C. Forage peas require free-draining sandy soils with a pH between 6 and 7 for successful plant growth and have a short growing season of between 12 and 18 weeks. Forage peas should be harvested at the flowering or flat pod stage to maximise the overall yield. The forage peas can either be harvested as wholecrop silage or wilting can occur prior to being short chopped and ensiled in a pit. Like grass silage, an additive to can be added to aid the ensiling process to reduce nutrient losses, and combined with an airtight seal, will help to ensure high quality silage is produced. Forage peas work well in a rotation to provide a break between cereals and improve soil fertility through the nitrogen fixed by the plants.
Forage peas can also be grown as part of a bi-crop alongside a cereal such as wheat or barley. The difficulty with bi-crops is achieving the optimum time for harvesting to get the maximum nutritive value out of the silage, as the two crops may mature at different rates. Previous studies have shown that the inclusion of a pea-cereal bi-crop in the diet of dairy cows can improve dry matter intakes and milk yield compared to grass silage, or it can replace a proportion of the concentrates and result in similar performance.
Forage pea silage can provide starch, protein, and effective fibre within the diet of dairy cows. Generally, forage pea silage has a dry matter content of between 25 and 35%, however it can be higher depending on the weather on the day of harvesting. Crude protein levels are high compared to grass silage, with values ranging between 17 and 22%. Previous research studies have shown that the inclusion of pea silage in the diet of dairy cows has maintained dry matter intakes and milk yields when compared to a diet containing only grass silage as the forage source. Including forage pea silage within the ration for dairy cows can reduce the reliance on purchased protein sources when the diet is balanced correctly.
As discussed, the inclusion of forage pea silage in the diet of dairy cows can help reduce the costs of supplementary protein sources. If you are considering forage peas as an alternative protein source, please speak to your nutritionist to determine the correct inclusion rates and alteration of concentrates to achieve optimum milking performance of your dairy cows.
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