MMN November 2024 – Should You Feed Silage to Weaned Calves?

There is a lot of debate around whether weaned dairy calves can be fed on a grass silage-based ration. Standard industry guidance for years has been to feed weaned calves on straw and concentrates until around six months of age before transitioning them to a silage-based ration. The reason for this is that the rumen is not fully developed until five to six months of age and is therefore not able to fully digest and utilise a fermented feed such as grass silage. However, many farmers do feed weaned calves on grass silage and seem to have no problem with it.

With high prices for straw, some farmers may be tempted to try and reduce straw requirements (and concentrate feed costs) and feed dairy calves on a silage-based ration earlier than normal. If so, there are a number of things to be aware of:

 

• Calves may not produce sufficient saliva to effectively buffer acidic rumen contents from the fermentation of silage and concentrates, especially where low fibre and wetter, more acidic silages are fed. More saliva will be produced by feeding straw as opposed to silage and so hay would be a good compromise between the two.

 

• Silage-based rations tend to be fed with less concentrates compared to a straw-based ration, therefore there will be more acetic acid produced in the rumen from silage fermentation. Acetic acid is less favourable for papillae development in the rumen wall and papillae are important to increase the surface area for nutrient absorption in the rumen.

 

• A higher concentrate diet (starch) drives more butyrate and propionate production in the rumen, aiding papillae development.

 

• Straw aids development and thickening of the muscular layer of the rumen wall and its “scratch factor” also helps normal papillae development.

 

• Calves will produce wetter faeces when fed on silage, meaning a wetter, dirtier environment with a greater coccidiosis risk.

Therefore a straw and concentrate based ration will be more favourable for faster rumen development, which in theory should aid better nutrient absorption and growth.

There is little scientific evidence regarding the use of grass silage for weaned dairy calves and effects on performance. However, if you are looking to move calves onto a silage-based diet earlier than normal, here are some tips:

 

1. Drier, less acidic silages are more favourable for intakes. Aim to feed silage that is over 30% dry matter. If a wetter, more acidic silage must be fed, consider feeding a rumen buffer.

 

2. Know the quality of the silage being fed. Get it analysed so your nutritionist can advise on the required protein content of the concentrate and recommended feeding rate to achieve the target growth rate.

 

3. Gradually introduce silage, while still providing straw and increase the silage inclusion over a period of 7-10 days to ensure gradual adaptation of the rumen bugs to the change in forage.

 

4. Concentrates - a lower protein concentrate will likely be required with silage compared to when feeding straw (depending on the silage analysis). Make sure the change in concentrate is also gradual and they are mixed for a few days, gradually increasing the proportion of the new concentrate.

 

5. Ensure calves have been fully weaned off milk for a minimum of two weeks before making any change to their diet and any change should be done gradually.

While often the best silage quality is kept for the milking herd, silage quality for calves also needs to be excellent and any silage with the presence of moulds should be avoided. Also, poorly fermented silages will be less palatable, reducing dry matter intake. Maximising dry matter intake of forage will be crucial to support high growth rates when feeding less concentrates compared to a straw- based system.

 

lorna.macpherson@sac.co.uk; 07760990901