Deciding when to wean lambs is a significant decision to make on the farm and it’s not an easy call to make. With science telling you that you can wean from six weeks onwards and tradition saying to keep them on as long as possible, how do you decide? Sometimes it is your own choice and other times it is decided by the weather and seasonal conditions. 

To understand how to wean lambs successfully, I think it is important to have an understanding of what is going on with the lamb's digestive system during this time. Lambs are not born ruminants. For the first three weeks of life, a lamb's digestive system is closer to that of a human or a pig and then it slowly transitions into a ruminant over the course of five weeks

NON-RUMINANT PHASE (WEEKS 1-3) 

At this stage, a lamb's diet is made up of nearly 100% milk. However, the rumen is not designed to digest milk. So, during the digestive process, the milk bypasses the rumen entirely via the oesophageal groove (an organ that directs milk from the throat towards the abomasum) where it can then be digested properly. The levels of volatile fatty acid (V.F.A) concentrations in the rumen are very low at this stage (however they are still present) and whatever grass enters the rumen remains relatively undigested. At this stage, the rumen capacity is around 6ml and the surface is relatively smooth.

TRANSITIONAL PHASE  (WEEKS 3-8)

At around three weeks of age, the lamb begins to eat more forage, the rumen begins to expand and a population of microbes begin to establish (with volatile fatty acids (VFA) and ammonia concentrations rapidly increasing at this age). Papillae, tiny structures on the rumen wall, begin to increase in length during this time (as long as there is enough fibre present in the diet). Papillae are important as they increase the surface area of the rumen, improving nutrient absorption within the rumen. The most significant increase in rumen volume happens from five weeks onwards, levelling out at around eight weeks.

ADULT RUMINANT (WEEK 8 ONWARDS)

By week eight, the rumen is functioning as it would in an adult sheep. At this point, the ratio of rumen to liveweight is relatively stable and the lamb maintains this ratio throughout its adult life. The papillae length is established and set by this time. Throughout this whole process, the abomasum remains roughly the same size.

So, when to wean?

So, as you can see, healthy development from the pseudo-monogastric system that a lamb has at birth to a fully functioning rumen is critical for creating a sheep that can efficiently digest and utilise forage throughout their adult years. And, from eight weeks of age, a lamb is a full ruminant and therefore can be weaned off milk if necessary. Lambs can even be weaned at six weeks (this comes with risks but, if managed correctly, can work well). So why is it we hear of people keeping lambs with ewes past 14 or 15  weeks, if not more?

This brings me to my next point … and my favourite graph:

This graph shows that by week 12 milk is such an insignificant part of a lamb’s diet that there is no need for them to be with their dam, especially when their dams are grazing all of the spring pasture and shedding worm eggs all over what grass is left. It takes so much more energy to turn grass into milk to feed a lamb than the lamb just eating the grass itself. For the sake of a small amount of milk, is it worth keeping them with the ewes? 

Also, this graph shows the average lactation curve of a ewe. In harder years, the amount of milk a lamb will be receiving from its dam will be even less, and the need to wean early even more obvious.

And it is not only the lambs that benefit from being weaned. In a season with limited grass, lambs and ewes end up competing for the best grazing. Early weaning in this scenario can reduce the strain on pastures, allowing lambs to access more nutrients while giving ewes a chance to recover their condition without the lactation demand. Ewes typically start producing less milk after the peak lactation period (around three to four weeks postpartum), so keeping them with lambs beyond eight weeks might mean both are nutritionally disadvantaged. Once ewes dry off, their dry matter (DM) requirements drop significantly and they can put back on any weight they may have lost during pregnancy and lactation. The longer they have to improve their condition, the better off they will be at the following joining and are more likely to scan multiples.

So, now that you have this knowledge of what’s going on inside of the lamb, and what the respective demands of the ewe and lamb are, all that is left in this equation is the seasonal conditions. 

By the start of lambing, you will have a fair guestimate of the amount of grass you will have in six weeks (which, if the season isn’t going well, would be the earliest you could successfully wean lambs). This gives you six weeks to set the lambs up for a successful early weaning. If the season is going well, you can still set yourself up for better weaning results by thinking ahead and making more informed decisions. As Rob Bell said in our podcast interview with him, think about the weaning process as a production phase, not just a day on the calendar.

The first step, regardless of when you wean, is establishing what feed the weaned lambs will be going onto. Ideally, all lambs need to be weaned onto a high-quality, high-protein feed. But, if you are weaning earlier, the quality of this feed needs to be even higher. If weaning onto pasture, aim for 1200-1500 kg DM/ha of high-quality perennial pasture containing at least 20% legume. 

Once you have decided on your choice of weaning tucker, it’s time to start either building that feed base up (and ensuring pastures are kept clear of sheep to reduce the worm burden) or start establishing how you are going to feed concentrates and ensure you have the infrastructure to do it well. 

Be it grass, crop or barley, a lamb should be exposed to their feed source whilst still with their dams - this is known as imprint feeding. Most commonly, this is done with grain, but can also be done with crops. A trial showed higher post-weaning growth rates in lambs weaned on lucerne when the lambs and dams were put on the crop a week before weaning, and then the dams were removed, in comparison to putting the lambs on the lucerne after weaning with no prior exposure to the crop. With grain, the same applies. It is recommended to expose the lambs to the feed (and the method of feeding) at least three times before they are weaned. 

Weaning onto grain is an art. And, rather than re-inventing (or re-writing) the wheel, here is a fantastic document provided by ProAgni explaining the best protocols for weaning onto grain. It can be found here. 

Once you have the feed and feeding method established, it is then time to think about the process of weaning. There is no denying it is a stressful situation for a lamb. All of a sudden its feed source and companion has been taken away. Imprint feeding removes one of these stressors but not all of the stress. 

If possible, draft lambs to size at weaning. Any lamb weaned under 40% of their standard reference weight should be separated from those above that threshold to ensure they have the best chance of survival and reaching their goal weight. To quote Rob Bell again, if a jockey and a rugby player had access to an all-you-can-eat buffet, you know who’s going to get more food and who’s getting less. If you can split your tops, mids and tails, you will get better weight gains all around. 

There is so much to weaning and it would take far more than a single article to cover all of the different kinds of weaning practices. If you would like some advice specifically on early weaning (five to eight weeks) then let us know. 

Ultimately, weaning should be seen not just as a set date but as part of a larger, ongoing management strategy. Weaning lambs is a complex process that is influenced by various factors, a few of which are completely out of our control. By understanding what is happening inside the lamb’s digestive system, and planning carefully for weaning, you can feel comfortable knowing you’ve made an informed decision that optimises your lamb's growth and your ewe's ongoing health.