Maximising mating performance is important as this sets the potential number of lambs that can ultimately be produced.
Factors that influence mating performance include:
Younger ewes (hoggets and two-tooths) begin cycling later and are in heat for shorter periods. They are also less likely to search out the ram, have lower ovulation rates and higher rates of embryonic loss. For these reasons it is common to mate them separately from the mixed age (MA) ewes.
For each flock there should be an ideal target mating weight which corresponds to an average BCS of 3. This mating weight then becomes the target for the start of mating each year and if achieved, helps to maintain consistent performance between years.
Genetics plays a significant part in determining the likely mating performance - about 70% of the mating performance is influenced by genetics1.
Ewes are seasonal breeders and cycling is induced by decreasing day length. If ewes are mated too early there will be a decrease in the mating performance, with less multiples and more dry ewes.
Shearing ewes within a month of mating or during mating can stop them cycling and result in more late lambs being born. This will have a dramatic effect on lamb weaning weight and the time it takes to finish lambs. Avoid shearing ewes at this time.
Shearing rams within 6-8 weeks before mating can lead to temporary infertility and a poor mating performance. Avoid shearing rams at this time.
Gastrointestinal parasites can have a negative impact on the mating performance of ewes. Particularly hoggets and two-tooths.
The effect between farms is often very variable and depends on the degree of parasite challenge that the ewes are under from the infective larvae on pasture.
Performing faecal egg counts on ewes pre-mating can be useful in assessing the challenge.
Sporidesmin, the causative toxin produced by the fungus Pithomyces chartarum not only damages the liver of ewes leading to ewe wastage but can also have a direct effect on the mating performance of the ewe flock. Both ewes and rams can be affected leading to more dry ewes and less multiple lambs. The degree of impact will depend on the amount of toxin exposure (spore counts) and the degree of susceptibility of the flock (genetic tolerance).
Selenium deficiency can lead to a lower implantation rate of eggs into the uterus. This is often seen as a higher dry rate.
Sperm is produced 8 weeks before it is used. Any management practices or disease processes that course significant stress or an increased body temperature can kill this semen, rendering the ram temporarily infertile. Preparation of the rams for mating should be completed at least 2 months prior to mating.
Ram ratios: usually 1-2 rams per 100 ewes. If hogget rams are used the ratio needs to be 1 per 50 ewes.
Rams should be fit, not fat (BCS 2.5-3.5).
Only buy rams from Brucellosis accredited studs.
Testicles should be firm, large and symmetrical.
By the end of two cycles (34 days) 95-98% of ewes should be pregnant.
The majority of factors that influence the mating performance of ewes are under the influence of the farmer and are dependent on their management decisions.
Why mate hoggets?
Carrying stock for a shorter period of time before you get income from them.
Potential reduction in generation interval.
More lambs produced on farm in a given year.
Increased lifetime performance of the ewes.
More mouths to eat surplus feed in spring.
Early screening tool for fecundity.
Limitations of hogget mating
Low and variable reproductive performance.
Lambs small and of low value.
Increased feed demand
Increased feed requirements during autumn and winter.
Need for adequately grown hoggets at eight months of age.
Potential for decreased two-tooth and MA ewe performance.
Factors influencing success
The minimum mating weight for hogget's should be 40kg.
Winter growth rates
The greater the mating weight, the lower the winter growth rates need to be.
Hoggets need to grow at approximately 135g/day during winter2 (see fig 1 below).
Hoggets are more likely to abort due to infectious diseases. Consider vaccinating for
Introduce teasers 17 days before mating.
Use mature rams at 1:50 -1:75.
Length of mating
Restrict the mating length to avoid late lambs, with teasers 26 days (17+9).
Long acting drenches
These have been shown to increase both hogget weight and lamb weights at weaning3.
Hogget weight: 2.3-2.7 kg.
Lamb weight: 1.4-3.97 kg.
Wean lambs early to give the hogget time to get back up to weight for mating as a two-tooth.
Figure 1: Impact of hogget growth rates on breeding performance2.