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Finding the cause of lamb mortality

Lamb mortality rates of 30 - 40% or higher is common, and these losses are often blamed on predation (e.g. foxes, eagles) or cold weather. Over 50 landholders attended information days at Buraja and Howlong last week to hear from specialists about the real cause of losses in lambs.

Dr Gordon Refshauge (NSW DPI) has researched lamb survival and ewe reproduction for many years on thousands of ewes and lambs. In his opinion, the most common cause of lamb death is actually brain or Central Nervous System (CNS) injury during the birthing process. This means frequently lambs taken by foxes or perishing in cold weather, had diminishing chances of survival anyway.

"Most lambs that die look like the lambs that live - so unless you know what to look for, it's hard to identify the real causes", Dr Refshauge says.

Can these losses be avoided? Typically, the answer is yes - but this is dependent on your current levels of loss. Industry benchmarks are 10% of single lambs and 20% of twin lambs however, few producers consistently achieve these rates. To truly understand the losses, pregnancy scanning is required.

70% of lamb mortality between birth and weaning, occurs in the first 48 hours. According to Dr Refshauge, CNS injury can occur through a number of ways including dystocia (a stuck lamb) and the lesser known hypoxia which commonly affects heavy weight lambs enduring longer birth times, and small lambs which are more prone to hypoxia despite normal birth times. Often these lambs eventually die from secondary causes – predation, starvation or cold exposure. Too many ewes in the lambing mob or too many ewes per hectare can also increase the risk of hypoxia by increasing birth time.

Accurate management of the ewe using condition scoring is important to ensure the ewe is in the right condition to achieve optimal birth-weight of lambs.

Genevieve Reardon, Livestock Extension Officer with Murray Local Land Services says;

"Understanding and maintaining optimal ewe condition score leading up to and during lambing can improve birth weight of lambs and significantly reduce lamb mortality rates inmost flocks."

For lambs without CNS injury, optimal ewe nutrition by can significantly help in poor weather, as lighter lambs have fewer reserves to survive. Providing good shelter, especially for twin mobs, lowers wind speed, therefore lowering the chill factor.

The amount of feed available at lambing also has a significant effect on maternal behaviour. Adequate paddock feed during lambing removes the need for the ewe to move away from the birth site to feed and according to recent research by Dr Graeme Martin (University of Western Australia), the ewe only has about 2-4 hours after lambing to bond with the lamb before her hormones change and she becomes repelled by the lamb's smell. Therefore, extended birth times, leaving the lamb to feed, or external factors that scare her from her lamb may result in mis-mothering.

Simply put – lamb survival is optimal when lamb birth-weight is between 4.5 and 5.5kg, or 4-5kg for twins. This results in less hypoxia, fewer dystocia cases, and fewer cold related deaths. Survival rates decrease sharply when lamb birth weights drop below 4kg.

Sam and Jack Talbot from "Kilara" Coreen, said they will be making some management changes as a result of the information days.

"It's been a great day. I've got pretty big mobs and after today I will look at reducing the mob size. We also only wet and dry scan – next time we will scan for twins and singles, so we know what ourreal pregnancy rates are, and we can manage the ewes to keep more lambs alive", Sam said.

You can't control the weather, but you can control your ewes condition score, feed on offer, their ability to rear lambs, to avoid unacceptably high lamb losses.

More information 

Gen Reardon, p: 02 6051 2253, m: 0409 077 254