Advice on feeding silage to youngstock

Some dairy farmers often introduce silage to heifer diets too early, which can be dangerous. Cargill’s heifer specialist Bianca Theeruth answers key questions about feeding silage to youngstock.

Target growth rates

  • By three months old a typical Holstein should be around 120kg and the aim is to maintain a growth rate of between 750g and 850g/day
  • The aim is for a heifer to be 375kg at 15 months old and ready for breeding
  • Growth rates are linear – it’s not a ‘stop start’ effect

What are the problems associated with feeding silage to young heifers?

A three-month old heifer will have a functional rumen, but it will not be fully developed and will only amount to 65% of the four stomach compartment. This will increase to 80% in the mature ruminant.

In most cases, the animal is not physically capable of achieving the intakes of silage required to meet its nutrient requirements.

The nutrients are simply not concentrated enough. Compared with concentrate feed, silages have a very high water content and the lactic acid produced when the silage is broken down in the rumen can reduce the pH, leading to metabolic problems such as acidosis.

The young heifer will not produce the amount of saliva of an adult cow to help neutralise this acid.

Could there be exceptions to feeding silage to youngstock, as some farmers may have silage ear-marked for these young heifers?


In exceptional cases where top quality silage is available, it could be included as part of a TMR. This could only be possible if the silage analysis clearly showed at least 30% DM and an ME of 10.7MJ/kgDM.

It is important the silage is dry. Wet and acidic silages are unpalatable and this will affect intakes.

And the concentrates in the TMR must be carefully balanced and adjusted regularly with up-to-date silage analyses.

See also: Feeding a TMR to youngstock increases weight gains

Quite often farmers save poorer silages to feed to their heifers. Is this a cardinal sin?

Yes. They shouldn’t be fed anything that you wouldn’t feed to the milking herd. I’ve seen cases of farmers feeding mouldy silages to heifers in an effort to avoid waste.

Although the effects are not seen immediately – as they might be in the milking herd – they will manifest themselves in the long term through reduced growth rates, health and possibly fertility problems. Heifers are an investment and the future of the milking herd and need to be managed with care.

What is your advice to farmers?

Avoid the temptation to move the weaned heifer on to an adult cow ration too quickly. Think carefully before feeding silage – grass or maize. But ideally keep to a ‘Goldilocks’ diet of straw, concentrate and water in the post weaning and early growth phase.

Acetic acid production in the rumen from the breakdown of silages will hinder papillae development; these papillae are so important for absorption and increasing surface area of the rumen.

Conversely, the break down products of straw – butyric and propionic fatty acids –   encourage the rumen bug populations and the straw provides valuable scratch factor. All these factors encourage the rumen wall to thicken and become more vascularised with increasing numbers of papillae

And a high grain diet will also aid rapid rumen development compared to high milk or forage diets. High quality, more digestible feeds and forages that contain rapidly degradable energy for the rumen encourage faster rumen development.

How often should heifers be attended to?

Don’t neglect feed management even if the young heifers are in a yard away from the milking herd. They should be fed twice a day, making sure they have ad-lib access to fresh feed. Push up and clean up feed; these young heifers cannot grow if they can’t reach the feed or it’s old and stale.

Good feed management and quality rations for these young ladies will have lasting effects.