From milk to solids – why the weaning transition is a critical stage in dairy youngstock rearing

31 Jul 2021

By Holly Vickery

The milk feeding stage and weaning transition are considered high risk periods for young ruminants, with the highest mortality occurring in these vulnerable first months of life. With the strategy of rearing youngstock naturally with their dams considered unviable for most commercial dairy farms, understanding how to optimise rearing youngstock away from their dams is essential for animal welfare and productivity.   

A particularly important transitional phase during youngstock rearing is that of weaning; the process of a young animal changing from a milk-based diet to one composed predominantly of solid feedstuff. The physiological changes required for successful weaning have been described as a dramatic challenge. A ruminant has four stomach chambers, and for successful weaning to occur they must transition from mono-gastric digestion of milk in the abomasum to digestion of solid feedstuff with microbial fermentation in the rumen. Under natural conditions this change would take place over an extended period involving a gradual reduction in milk intake and subsequent increase in solid feedstuff. However, in systems where youngstock are reared artificially full milk removal takes place younger and without natural cues such as allelomimicry and dams limiting access to milk.  

This presents a challenge – how can these systems ease the weaning transition by ensuring sufficient weight gain and solid feed intake? Developing the chamber of the stomach called the rumen is critical to successful weaning, and its size and functionality is affected by pre-weaning consumption of solid feedstuff. Therefore, it is essential that young ruminants ingest solid feed and forage during the pre-weaning phase in order to develop a fully functioning rumen prior to weaning.

It has been evidenced that ruminants on a restricted milk intake consume more solid feed - however, feeding high or unlimited milk results in increased weight gains and better later-life productivity. Despite these benefits pre-weaning high milk intakes are linked to greater weaning shock by a lack of rumen development. Studies suggest that this can be combatted by using gradual weaning methods, that incrementally reduce milk consumption before full removal, which encourages solid feed intake.

Whilst early weaning is often considered desirable in terms of management (including reducing labour and feed costs), ensuring high growth rates and a successful weaning transition is essential to the welfare of young animals, and is likely to involve strategies that increase solid feed intake before milk access is removed. It seems a critical aspect of rearing young ruminants is in finding a balance between providing high milk intakes whilst ensuring the adequate consumption of solid feedstuff. Further research in this area could have a large impact on animal welfare, as well as the future productivity of the dairy herd.