Are my ewe lambs heavy enough for breeding?
Given the pressures at lambing time, many farmers often decide against lambing down ewe lambs.
However, where the correct management practices are followed and labour is available, it may prove a key way of reducing the cost of rearing replacements, while also increasing flock output and productivity.
Like all activities, there are a number of factors farmers need to keep in mind before contemplating introducing a ram to breed ewe lambs.
Firstly, the weight at mating is one of the most important targets to hit, as this will determine the success of the venture.
Work from Teagasc has indicated that ewe lambs should be 60% of their mature body weight at joining with the ram.
This is critical as ewe lamb weight at joining influences date of puberty, fertility and pregnancy rate. From this work, Teagasc found that increasing the live weight at joining increases the probability of rearing a live lamb, but the appropriate live weight is influenced by ewe genotype.
The above graph outlines the effect of joining weight of ewe lambs – from three different genotypes – on the probability of rearing one or more lambs.
For example, to have a 90% chance of rearing a live lamb, the Belclare and >75% Suffolk ewe lambs would need to be 46kg and 60kg at joining respectively.
Another area that warrants consideration is lambing pattern. As many farmers opt to lamb their ewe lambs after the main flock, a tight lambing pattern is desirable and this can be achieved through the use of the ram effect.
The ram effect can be used to induce ewe lambs to start cycling, provided they are sufficiently close to the time of onset of normal cyclicity, but have not entered their breeding season.
For the ram effect to work, the ewe lambs should have not been in contact (either sight or smell) with rams for the previous month. By introducing a sexually-mature ram – either in the form of teaser or a stock ram fitted with an apron – for a 24 hour period 14 days before mating, the lambing pattern of the ewe lambs can be tightened significantly.
Research from Athenry indicates that the use of the ram effect allows for 70% of the ewe lambs to give birth within a two-week period and 90% to lamb within the space of three weeks.