With cattle housed early in parts of the country this year, silage stocks will need to be stretched to last the winter. This is often achieved by including straw in the diet to add bulk and maintain intake. However, in terms of actual feed value, straw adds very little to the mix. However, could straw completely replace the need for grass silage in the dry cow diet?

The process of treating straw with ammonia is by no means new technology. This week I visited the farm of Peter Robertson near Peterhead in Aberdeenshire who has been feeding ammonia straw to his cows for over 20 years now. Effectively what it does is increase the feed value of straw to moderate-quality hay.

The main component of straw is fibre, this includes cellulose and hemicellulose which can be digested by ruminants. Some of this fibre is bound to lignin which is not digestible. The role of ammonia is to destroy the link between digestible and indigestible fibre and so these fractions become available to the animal.

Typically this is done with wheaten straw as barley straw is preferably retained for bedding purposes. However, in terms of feed value there is little difference between treated straw types.

Bales can be stacked and covered with plastic, individually wrapped or most commonly wrapped with a tube-line wrapper. This sees bales wrapped end to end in long lines, with four layers of plastic recommended for ammonia treatment (inset picture below).

A truck with a treatment tank then drives along the row and injects ammonia into each bale and seals the plastic again. It is recommended that bales are treated for a minimum of three weeks prior to feeding. In order to eliminate the strong smell of ammonia, bales must also be opened 24 hours prior to feeding.

For spring-calving cows, housed in good condition at a body condition score (BCS) of three or above, ammonia straw can be used as the sole diet in order to calve down at a target BCS of 2.5. However, condition needs to be closely monitored throughout the winter, with thin or older cows needing some supplementation. Intake for a typical 700 to 750kg late-maturing breed type cow is in the region of 8-10kg per day. Adequate dry cow minerals must also be fed throughout the winter.

Costs for ammonia treating straw start at €27 (£24) per tonne up to 50t, with slightly better rates available for higher quantities. This year straw is trading between €55 and €61 (£50-55) per tonne baled in northeast Scotland. This translates to a daily feed cost of between €0.82 – 0.88 per day plus minerals.

Benefits

It must be said that this system works best on mixed tillage and beef enterprise farms. Feeding straw eliminates the requirement for silage for cows, therefore the grassland area on the farm can be reduced to match grazing requirements plus higher-quality silage targeted for young stock on farm.

Also in years with difficult harvest conditions when getting straw baled dry or soil contamination can be an issue, treating with ammonia within 24 to 48 hours will preserve straw and inhibit mould growth.

As the majority of cattle in Scotland are straw-bedded, feeding ammonia straw means cattle are much drier in the dung compared to grass silage diets therefore significantly reducing the amount of bedding required. Farmers also report less instances of coughing and pneumonia around housing time when feeding treated straw.

While options for treating straw this winter have passed, it may be a route that can be explored in the future. When compared on relative feed value, grass silage, especially lower-quality mid 60s DMD “cow silage” is an expensive crop to produce. This option would eliminate silage requirements for dry cows, allowing farmers to carry more stock during the grazing season and target higher-quality grass silage for young stock.