3/04/2007
Lamb growth rate has a big influence on the overall performance of your sheep flock. At this stage March born lambs are still very much dependent on their dam's milk, but over the next few weeks these lambs will start consuming larger amounts of grass to supplement the ewe's milk.
Achieving high growth rates at all stages of the production cycle is important if target drafting dates are to be met.
If growth rates fall below the target level then lamb drafting will be delayed and lambs will end up competing with the ewes for grass pre-mating.
Pre-weaning is the most important time to watch both ewe and lamb nutrition. Target lamb growth rate (see Table) for the period from birth to weaning should be 275g per day over the entire period (birth to 14 weeks of age).
This will result in a liveweight gain of about 2kg per week. Contrast this with a potential liveweight gain of around 0.7-1.0 kg week post-weaning and it is easy to see that where liveweight gain is compromised pre-weaning it will take two to three times as long to make up this lost ground post-weaning.
Think back to last year. What was the average weight of your lambs at weaning time?
If it was less than 32kg then you need to look at your system. There are lots of different factors that will influence lamb growth rate, but the main one is flock nutrition.
Milk yield
Provided that your ewes are healthy and free from disease such as mastitis etc., the amount of milk that they produce will be directly related to the quality and quantity of feed that is available. For the first 5-6 weeks of their lives, lamb thrive is influenced by the milk yield of the dam. The dam's milk yield in turn is influenced by the supply of grass available.
Forcing ewes during this period of the production cycle to graze lower than 5cm will hit milk production and reduce lamb liveweight gain. Where adequate grass is not available at this time of year concentrates need to be feed to make up the shortfall.
Concentrate feed
Concentrates are an expensive substitute for poor grassland management. While concentrates have an important role to play in the sheep production cycle they should be used as a compliment to and not a substitute for good grassland management/high quality winter forage.
Grassland management
Contrary to what many farmers believe, managing your grass to achieve high lamb thrive need not be complicated. Good quality leafy grass will achieve the liveweight gain targets set out in the Table.
To achieve these targets careful attention needs to be paid to the height of the grass that is being offered to the ewes and lambs. The target heights that lambs should be grazing to pre-weaning are March/April 5cms, May 6cms, June 7cms, July 8cms.
Measuring grass heights
There are a number of ways in which you can measure grass height. A rising plate metre is the most accurate way of measuring grass height. A ruler is the next best alternative.
Maintaining quality
As the post grazing height increases it will become more difficult to keep on top of grass quality. This is where creep grazing comes in. Where the lambs are creep grazed ahead of the ewes, the ewes can be left to clean up the pasture (6 weeks post lambing ewe milk yield is dropping). Where creep grazing is not practised you will need to start topping pastures in May.
Challenge
My challenge to every sheep farmer is to try this for a few weeks. It is a simple system. Measure the grass in the field where the sheep are grazing and once it reaches the target height move them on. At weaning time you will have heavier lambs and no need for creep feed to get them there.
