Dr Jeff Cave, Senior Veterinary Officer
As we move towards winter sheep producers may begin to see cases of pregnancy toxaemia or twin lamb disease in their ewes.
Twin lamb disease occurs when ewes have an inadequate energy intake during the last 4 to 6 weeks of pregnancy.
During this final period of pregnancy, ewes' energy needs increase substantially, as she is providing energy for both herself, and her rapidly growing lamb.
Ewes that are carrying twins are particularly susceptible, hence the name. In fact a ewe carrying twins has one and a half times the energy requirements of a ewe with a single lamb, and more than twice the energy requirements of a dry ewe.
Table below - energy requirements in megajoules (MJ ME/day) for sheep maintained at Condition Score 3 with single lambs or twin lambs.
Sheep weight (without foetus) kg |
Dry mature |
Late Pregnant – single (twins) |
Ewe and lamb – single (twins) |
|---|---|---|---|
Medium frame 50 kg |
8 |
12 (15) |
19 (23) |
Large frame 60 kg |
9 |
14 (18) |
21 (27) |
Large frame 70 kg |
10 |
16 (20) |
24 (30) |
Sheep fed in containment areas generally require 10–16% less energy compared with animals walking around paddocks looking for feed.
An outbreak of twin lamb disease is often triggered by stress and environmental conditions that cause a low intake of food such as during yarding or holding off feed or severe weather conditions.
Affected ewes usually appear dopey, blind and unresponsive. The condition may progress over several days.
The presence of affected ewes is an indication that all is not well in the remainder of the flock.
Many other ewes may also be sub-clinically affected and may progress to become further cases of twin lamb disease.
Twin lamb disease occurs because of a breakdown of body fat at a rate with which the ewe's liver is unable to cope.
As a result, on autopsy an affected ewe's liver will appear swollen, yellow, crumbly and greasy.
Affected ewes can occasionally be successfully treated by an energy-rich drench such as glycerine provided the drench is given during the early stages of the disease.
More importantly, good quality supplementary feeding should be given to those ewes most at risk.
Increasing the ewe's energy intake through appropriate ration formulation during the last 8 weeks of pregnancy can prevent twin lamb disease.
