Course: Winter Health | Last Updates: 7th October 2015
Changing from grass to silage and concentrates or to intensive grain diets can cause problems in cattle of all ages, but youngstock being weaned at the same time as being housed can face the biggest challenge.
Patience is a virtue at this time. If you rush the transition growth rates will suffer and serious health problems including scours and pneumonia could follow. It’s therefore incredibly important to get nutrition right.
Why is a gradual change needed?
The rumen is designed to break-down fibre. It contains billions of microbes which work together to form a continuous fermentation system to digest this material.
Any change in nutrition needs to be done slowly to give the rumen time to adapt.
It works best when operating in slightly acidic conditions, about pH 6-7. Switching from grass to silage, which has been partially fermented, contains a lot of protein breakdown products and fewer sugars which can throw the system out of balance.
The problem increases when grain is added, as it is high in starch which is rapidly fermented and causes excess acid production.
An acidic rumen slows down bacterial fermentation of fibre, and in severe cases can even stop it. This slows the passage of feed through the gut, which reduces intake.
It takes a ruminant three weeks to get used to a different ration so that the microorganisms inside it can adapt.
What do you need to consider before changing rations?
Firstly you need to assess your animals and what you require them to achieve over the winter period.
Whether you are rearing, growing or finishing, each stage is nutritionally very different and has different energy requirements to ensure efficient and gradual growth.
You also need to quantify your feed stocks so you know what you have available over the winter period and ensure you have the necessary forage, energy and protein available to put together a ration.
You should already have some idea of the tonnage of cereals available to you, but to calculate what silage you have in the clamp you can make a basic calculation of 650-700kg of silage/cubic metre.
Once you know your volumes, it is incredibly important to get it analysed so you know its quality and nutritional value.
What’s the best way to introduce a silage-based diet?
Patience is a virtue, so when you bring an animal in, start with grass silage and slowly introduce concentrate to given them time to adapt.
One of the biggest problems with changing diets is it causes stress on the animal, which has a big impact on how it settles down, so anything you can do to reduce stress is important.
Starting to feed them concentrates while they are outside can help them adapt in plenty of time. I would recommend starting to feed them a month or six weeks ahead of housing with a compound in the feeder.
It is worth remembering the autumn flush of grass is likely to be low in dry matter and the energy density could be low, and that’s where early feeding of concentrates can really come in – not only does it get them acclimatised to the new feeding system, but it keeps liveweight gains up.
Get the silage tested at least three times over the winter, especially if you are feeding from a clamp. Nutritional value varies from field to field and with different fermentation, so it’s important to check it regularly.
Each animal has a maintenance requirement to sustain its body weight, then you build on the ration to increase weight. If you have a 400kg animal, it will need 65kJ of energy, plus an additional 15-25kJ for growth.
There is no hard and fast rule on the amount of feed each animal requires, so it’s a good idea to take professional advice from a nutritionist to help you calculate your herd’s requirements.
What if you’re using straw?
Straw is a much poorer feed than grass or silage as it is high in fibre but low in metabolisable energy and crude protein levels. It is not well digested, so stock will need more concentrate and protein supplement. The same principles should be used for the transition as before.
Remember to keep the forage element of the final diet at about 40% of the overall dry matter and no lower than 30%, otherwise the increased starchiness interferes with fibre digestion and you won’t get the benefits of the fibre.
How do you help suckled calves?
Suckled calves are often weaned at housing and it’s a critical issue to get right.
I would advise creep feeding at least six weeks prior to weaning to get the calves used to concentrate in the diet and maintain growth rates as their mother’s milk output diminishes in the autumn.
Creep feeding also helps reduce the stress of changing both diets and housing, which in turn can help protect against the risk of pneumonia.
To check you are getting calf nutrition right, the critical thing is to weigh the calf as soon as it is weaned. Give it a month to settle down, then weigh it again. If it has not put on reasonable weight, you know there is a problem.
If you continue to weigh them at two month intervals throughout the winter period that will help you keep track of how they are doing. They should be gaining 0.8-0.9kg/day, if that’s not the case then it gives you time during the winter to change the ration and get their weight at the level you need it to be.
Intensive diets: How quickly can you introduce grain?
Managed carefully, grain-fed animals will gain weight quickly, with suckled calves ready to be sold at 13-15 months.
Again though, it is important to be patient and make the change between feeds a gradual one.
If you want to finish suckler bulls on a grain-based system, they should have grain added to their creep. With spring-born bull calves, you should start creep-feeding from May-June so that when they come to be housed they are used to the feed.
Some people try to increase the amount of grain they are fed immediately after being weaned and housed, but I would recommend starting with a forage-based ration and increasing it by 0.5kg/head every three or four days to give the animal time to acclimatise.
Supplementing the animal’s feed at the start with something with higher digestible levels such as oats and high-fibre soya hulls can also help, as they are much more rumen-friendly.
Clean, long straw should also be supplied to appetite in the first few weeks while concentrate is gradually increased. While it will only account for about 10-15% of the dry matter in the diet, it will get them chewing, which produces saliva and helps neutralise acid in the rumen.
It is also important to remember that while all diets should be supplemented with vitamins in minerals, it is essential to use a calcium-rich supplement in an intensive grain diet to keep bones strong and healthy.
- Avoid sudden changes in diet when housing stock – ensure a three-week transition to minimise problems
- Get silage analysed so you know its nutritional value and supplement it if necessary
- In intensive systems, build grain into their diet slowly and provide long, clean straw
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