There are many factors that influence reproductive performance of ewes including, breed, genetics, season, time of year, disease, condition score, and nutrition. However, there are also products on the market to enhance reproductive efficiency. Reproductive failure should be investigated if the flock has a high rate of scanned lambs that do not amount to weaned lambs as, in a lot of cases, lamb survival is often the issue. This is not only a straight economic loss but it also costs energy for the ewe to grow the foetus for no gain. It is pointless to increase the number of foetuses conceived if lamb survival is an issue. Some Victorian figures from the South West Monitor Farm Project from 2003-2005 showed that the average lamb marking percentage for Merinos was 78% (56-100%) and Prime lambs averaged 99% ranging from (60-143%).
Merinos have a lower ovulation rate compared to British breeds and their crosses, due to producing fewer eggs at ovulation. Some breeds and strains such as those that have the Booroola gene have more multiple births but unless management conditions are exceptional with excellent pasture and shelter provided, lamb survival is poor and reproductive wastage occurs. Products such as Ovastim increase ovulation rates and result in increased numbers of twins and triplets in British breeds and crossbreds but it is not recommended for Merinos.
Nutrition is the key factor controlling the condition score of ewes. Condition score is one of the most important factors in determining conception rates, with condition score 3 targeted as the ideal score. The weight of maidens at mating has a large impact on conception rates; maiden ewes should be 75-80% of their mature body weight. Flushing to improve ovulation rates is a common practice particularly with ewes being mated on poor quality pasture where a legume grain such as lupins are given 2 weeks prior to mating. Some producers move ewes to green feed two weeks before mating and they remain on that feed until the rams are removed. Research into flushing has highly variable results and the benefits of flushing are not always clear.
The length of time for joining varies highly between properties for various reasons. Sheep are seasonal breeders and are stimulated to cycle once the day length begins to shorten, from March to June. Merinos are the least seasonal, followed by short wool British breeds such as the Poll Dorset. Long wool breeds such as Border Leisters are very sensitive. Time of joining for many is largely determined by many as what is the most profitable which is often related to matching feed demand with feed supply and reducing the supplementary feeding costs. This is often where products such as ‘Regulin’ can come into play, or strategies such as the use of teaser rams. A 5-6 week joining period providing ewes are in adequate condition should allow ewes to cycle twice and to get in lamb. A tighter joining reduces the tail end and at weaning (unless you are split weaning) allows for all lambs to be weaned early rather than waiting for all lambs dropped to reach a minimum weight and the ewes can then recover for the following joining.
There are a few infectious diseases that cause abortions or newborn lamb deaths. These include vibrosis, toxoplasmosis, listeriosis and salmonellosis. Sub clover cultivars such as Yarloop and Dwalganup can have high levels of oestrogenic compounds and can result in temporary or permanent infertility particularly after long term and repeated exposure. Brucellosis causes infertility in rams and while ewes do not remain infected from season to season, rams do. Depending on the severity of the infection, a ram may be completely infertile or have reduced fertility. Pregnant ewes infected with Brucellosis can have inflammation of the placenta which can reduce birth weights of the lambs.
Increasing reproductive efficiency is pointless unless lamb survivability is outstanding. There are silver bullets on the market to improve reproductive efficiency but for many producers focusing on nutrition and condition score would have the greatest benefit. For those who are managing ewes in condition score three and have a high lamb survivability, looking at options to enhance reproductive efficiency is an avenue to investigate. Reproductive efficiency can be a key profit driver of the sheep enterprise if you can maximise the foetuses conceived into weaned lambs.
See below a link to MLA’s Making More from Sheep – Wean More Lambs
19 April 2016
Article compiled by Penny Moorhouse and Tiffany Bennett