Weaning time is looming and farmers are encouraged to consider a number of factors when deciding when to wean, rather than sticking to a specific date every year.
Will Halliday, Beef + Lamb New Zealand’s Senior Advisor Biosecurity and Animal Welfare, says lamb weaning dates should be flexible depending on the season and the market.
“No two seasons are identical so being flexible about weaning dates can be powerful tool. It is important to be monitoring stock condition, feed quality and quantity and market prices to inform the decision about weaning dates.”
He says the goal at weaning is to maximise profit from lamb sales and ensure ewes’ target body condition score is met, so next year’s production is not compromised.
A number of variables should be taken into account when deciding when to wean. These include the age, weights and growth rates of the lambs, ewe condition, feed quality and availability now and over the next three months, the cost of supplements, animal health status of both ewes and lambs and lamb prices, both store and schedule.
Will says growth rates peak when lambs are between three and six weeks of age, but growth rates can stay high in late lactation provided lambs have plenty of high-quality feed available to them.
By eight weeks, lamb growth rates are generally declining with very little growth benefit coming from the ewe’s milk.
However, lambs weaned before six weeks cannot make up for lost milk by consuming more pasture and lambs weaned before eight weeks will typically grow slower than lambs left on their mothers, unless high quality forage is available. This means that if lambs are within 2-3kg of sale weight, they will reach this weight faster if left on the ewe.
Looking after the ewes
Will says ewe condition also needs to be taken into account when deciding on weaning dates. Putting weight back on ewes over summer is relatively expensive, especially in summer-dry regions. It takes 6–7kgDM to put 1kg back on a ewe after weaning.
As a rule of thumb, ewes should be at or above their target mating Body Condition Score at weaning. This makes it easier to maintain condition over summer and manage pastures.
It is easier to put weight back on ewes after weaning, as energy that had been used for lactation is able to be partitioned back into maintenance and building condition. If fed at the same rate as pre-weaning, ewes can gain about 50g/head/day.
For ewes to gain weight at 100g/day, then they usually need a high energy feed such as lucerne or a summer brassica, unless pasture quality is very good.
If the intention is to hold ewe condition post-weaning, then feed intake needs to be reduced by 20%.
For more information about the weaning decision, including different seasonal scenarios, see our factsheet Deciding when to wean your lambs (PDF, 454KB) and also our online learning modules Principles of Feeding: From lambing to weaning and Principles of Feed: Weaning to mating (sheep).