Farm Ireland

Thursday 24 May 2018

Lambs are growing at a slower rate, but this is to be expected

Lamb growth rates to nine weeks of age at Lyons are a bit behind target, but this is hardly surprising given the poor weather and grass growing conditions since early April.

Our twin lambs are averaging just under 300g/day from birth and averaging 23.5kg liveweight at nine weeks of age.

This is back on growth rate up to five weeks of age, but this is to be expected. The young suckling lamb is the most efficient converter of nutrients into weight gain on the sheep farm. The ratio of milk dry matter intake by the young lamb to live weight gain is approximately 1:1. This conversion rate disimproves to the point where store lambs need up 15kg of feed drymatter in order to gain just 1kg in liveweight.

Lambs are almost entirely dependent on the milk of the ewe for the first 6-8 weeks of life. They then become more dependent on solid feed intake. However, lambs' efficiency drops once they become dependent on solid feed.

The importance of solid feed increases where stocking rates are high, litter sizes are large, grass is scarce, where ewes are in poor condition at lambing, or where creep concentrates are offered from an early age.

This year we are seeing ewes that were slightly under-nourished in late pregnancy producing lower growth rates from their lambs. This is largely as a result of the lower ability of these ewes to produce milk in early lactation.

The triplet lambs are receiving 410g/day of creep feed and are growing at 270g/day. We would not usually creep-feed these lambs but difficult grass growth conditions have dictated otherwise. Grass growth rates are now improving, though still below normal. Daily growth rate was 38kg DM/ha in the week to May 8 but this then increased to 54kg DM/ha during the following week.

For mid-season flocks weaning will be taking place in the next 4-6 weeks. Approximately 14 weeks is the target weaning age when lambs weigh 31kg (twins) and 36kg (singles).

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When weaning is carried out at 12-14 weeks, some ewes will still be milking at up to 60pc of their peak yield. In order to reduce udder damage, the feed supply to the ewes should be greatly reduced at this time. At weaning, ewes should not be housed for more than 3-5 days and subsequently put on to the barest grass field available, to guard against grass tetany.

Where weaning is not timed correctly it will tend to occur too late, rather than too early. For the lamb to compensate for the loss of milk from the ewe, they must be able to consume extra solid feed. The target should be 4-7g of grass drymatter for every gram reduction of milk solids. In practice, a lamb will tend to be drinking about 0.5l a day at weaning. This equates to about 90g of solids which will require 360-600g of grass drymatter to replace. Research suggests that the lamb must be at least 11 weeks before this can occur. Late weaning can result in thin ewes and the less efficient use of grass.

Trace element deficiencies are a recurring issue on sheep farms. Last year we used cobalt boluses for the first time on a portion of the flock and are using these again this year across the entire flock.

Traditional dosing, while popular, is less than optimal for cobalt deficiency as the majority of the dosed cobalt is excreted within 2-3 days of dosing, therefore requiring frequent dosing. There are a number of question marks over slow release boluses also but the theory behind them at least offers a better option.

Dr Tommy Boland lecturers in sheep production at UCD.

Indo Farming