Webinar offers advice on maximising liveweight gains for lambs

Lamb management post-eight weeks was the subject of a recent SAC Consulting webinar, with one of the organisation’s senior consultants, Poppy Frater, advising on maximising liveweight gains and weighing techniques.

A daily liveweight gain target of 320gms/day was appropriate for eight-week-old lambs, said Ms Frater.

“This target will help to achieve an average lamb weight of 30kgs for a group that is to be weaned at 90 days. Ewes’ milk is extremely nutritious and it is important to maximise ewe milk volume and quality, by keeping her healthy and giving her access to good-quality grazing.

“A young lamb is an efficient converter of feed, so attention to nutrition in the early stages will pay dividends later on. Its average weight gain potential will fall sharply post-weaning, with a figure of 150gms/day on pasture including silage aftermath and 180gms/day on re-seeded grass containing a high percentage of white clover.

“Post-weaned lambs on alternative feeding systems have greater potential and 200gms/day could be expected for groups on forage rape, turnips, plaintain and chicory swards, with 300gms-plus if they are creep-fed and given access to red clover grazing.”

Regular weighing was essential for monitoring weight gain and Ms Frater offered some advice on the procedure. She suggested that best practice is to monitor lambs at eight weeks and 14 weeks, followed by weighing at regular intervals thereafter.

Poppy Frater of SAC Consulting

“Scales should be checked before weighing by calibration with a known weight, such as a bag of feed,” she said. “It is best to separate lambs into relatively uniform groups for assessment. Some examples of this practice would include mobs of Mule singles, hill lambs, or twin lambs of roughly the same breeding.

"Where possible, lambs should be weighed at the same time of day while at grass because the effect of gut-fill can add 5kgs to individual figures. This time of day should be applied to further weighing sessions, as it will increase accuracy.

“For mobs of an even weight and size, a minimum of 36 lambs should be weighed in one session, with the three lightest and the three heaviest removed from the group. Ideally, 56 lambs should be weighed, as this will give an accurate picture of the average weight gain that is being achieved.”

Creep feeding lambs help them maintain a healthy weight

There can be a temptation for producers to select the best lambs for weighing, but she advises against the practice.

“This system will not give a representative sample. Instead, take a random selection of lambs using an equal sample from the front, middle and the back of the mob. If using a batch system, where 300 lambs are being moved through the yards in groups of 30, weighing the third and seventh groups is recommended.”

Lambs on a rotational grazing programme will usually give the best utilisation performance and Ms Frater offered some management pointers taken from previous research studies.

“The grass height should be no lower than 5cms at any stage and the addition of legumes and herbs will improve liveweight gains. Paddock size will be linked to group size, but smaller areas tend to be more effective.

"I would start by creating paddocks of up to two or three hectares for 200-250 ewes with lambs and graze them over three days, followed by a 21-day rest period. The other option is to split a field in half and move the stock between the two sections.

“The rest periods can be adjusted depending on conditions,” she said. “If the grass length exceeds 8cms during the grazing round, the rest period should be decreased. Conversely, resting should be extended if it has been grazed to below 8cms. If a leader/follower system is applied by introducing cattle, the sheep should be no more than two paddocks behind. Mowing can also be useful to manipulate the sward height to the optimum figure.”

For set-stocking, aim to keep the grass within the 6 to 8cm zone.

“There should also be as a little stem and dead material as possible. While adhering to these figures will maximise weight gains, removing the lambs at a pasture height of 3-4cms may have benefits for pasture quality.”

Trace element intake was linked to performance, with the correct balance essential for reaching growth rates targets, she stressed.

“Trace element deficiencies can be highly localised and while soil testing is helpful as a guide, it is only a starting point. Herbage analysis can also be misleading due to various interactions between minerals.

“The most accurate results will be obtained from the results of blood and tissue testing. Where feasible, a sample of roughly eight animals should be blood-tested tested for each management group. Among the most critical trace elements are cobalt, iodine, selenium and copper. If these are out of balance there is a risk that target liveweight gain figures will be compromised,” said Ms Frater.