Weighing, Recording & Setting Targets! The Importance of 8-Week Old Weight...

A lamb’s performance is influenced by the ewe’s colostrum and milk production. Meeting a ewe’s energy and protein requirements pre- lambing and in lactation is key for the lamb to have the best start to life and for the ewe to produce as much milk as possible, especially at 3-4 weeks post lambing when peak lactation occurs.

A ewe rearing twins will have a greater nutritional demand than a ewe rearing a single lamb because the twin mother produces 40% more milk. 

A lamb’s rumen will develop as grass and solid feeds, such as creep feeds are introduced. The time to full development will be dependent on lamb breed and nutrition, so in some scenarios can take longer.

The ewes lactation ability is indicated by the lamb’s 8-week weight. If weighing is postponed until weaning, then the ewes maternal ability on early lamb growth is missed. If the flock has a compact lambing period then the mid point of lambing can be used to calculate the 8-week weigh date. Alternatively, if the date of birth is known then an adjusted 8-week weight can be calculated.

At the 8-week weighing, the weight and condition score of the ewes can be recorded as an indication of how much of their body reserves have been used to rear the lambs. 

Recording weights of lambs allows the DLWG to be calculated, however, the birthweight should be accounted for. An example is below, assuming the lamb weighed 4kg at birth.

Setting Targets...

The 8 week weight is classed as a Key Performance Indicator (KPI) which allows targets to be set and performance to be monitored rather than weighing when weaning. Setting realistic targets helps identify lambs which have not met their targets. Possible reasons would be if the lamb is a triplet, had a small birthweight or poor milk production from the ewe. Collecting and analysing the data provides information so that plans can be put into place to prevent the same happening year on year. 

Plan for Poor Performing Lambs...

If lambs are light weights at 8 weeks of age, plans can be implemented so that the lambs are off the farm by the time the next lambing season approaches. These plans could include weaning the lambs early and putting them onto good grazing, introduce creep feeding, sell as stores or sell them to the light lamb market. 

It is also important to set targets for the ewe’s Body Condition Score (BCS) throughout the year to minimise the number of poor performing lambs. Plans could include supplementing thin ewes post lambing, prioritising triplets to the better grazing ground or creep feeding lambs. 

Lambs which have a growth rate of less than 200g/day should be weaned, moved to better grazing and supplementary feed should be considered. 

Nutritional Requirements...

A lamb’s energy requirements depends on the weight and growth rate.

The dry matter intake can be calculated. Lambs consume 4% of their body weight so a 30kg lamb would consume 1.2kg DM. If the forage is 11.5 MJ, the lamb will consume 13.8 MJ/day and should gain 250g per day. 

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