Lamb mortality - when it occurs, causes and management practices

Lamb mortality impacts on ewe productivity (number of lambs reared per ewe joined), and farm profitability. It is estimated that each 1% change in lamb mortality nationally, is worth approximately €3 million annually. Teagasc Researchers Tim Keady and Dwayne Shiels provide more information.

Main Messages

• Most lamb mortality occurs within 24 hour of birth
• Infection and dystocia are the 2 main causes of lamb mortality and are potentially preventable
• Nutrition management in late pregnancy is key to reducing dystocia and providing adequate colostrum supplies
• Many farmers do not adopt best practices prior to and during lambing
• If you have a problem develop a health plan in association with you vet for the next lambing season

Introduction

Ewes are housed for lambing on 75% of Irish lowland farms. Lamb mortality impacts on ewe productivity (number of lambs reared per ewe joined), and farm profitability. It is estimated that each 1% change in lamb mortality nationally, is worth approximately €3 million annually. Our aim in this paper is to present information on the prevalent causes of lamb mortality and when it occurs on farm. 

When does lamb mortality occur

Most lamb mortality occurs within the first few days after birth. A recent study at Athenry has identified the timing of neonatal lamb mortality (died with 7 days of birth) and the data are presented in Figure 1. Fifty two percent of lambs that die died either, prior to, or at birth. A further 21 % of lamb mortality occurred between birth and 24 hours of age. Thus 73% of all neonatal lamb mortality occurs within 24 hours of birth.

Figure 1: Timing of neonatal lamb mortality

Causes of lamb mortality

The causes of lamb mortality are presented in Figure 2. Infection and dystocia are the 2 main causes of lamb mortality, accounting for 38% and 15%, respectively. Accidents accounted for 8% of lamb mortality. The cause of death was not identified in 28% of the lambs that died. The 2 main causes of neonatal lamb mortality are potentially preventable through the implementation of best known practices prior to and during lambing.

Figure  2.  The causes of neonatal lamb mortality

Management practices on Sheep farms

Approximately 50% of lamb mortality (infection, dystocia) on Irish sheep farms is potentially preventable. The main cause of lamb mortality is infection. Key on farm issues impacting infection are hygiene, colostrum intake and an adequate vaccination programme. Natural colostrum contains IgG which is critical for the transfer of passive immunity to many diseases and infection to new born lambs. Nutrition management in late pregnancy influences colostrum supply. In Ireland 44% of farmers give colostrum to young lambs by stomach tube. The colostrum administered is either sourced from the mother, another ewe, frozen cows colostrum or colostrum substitute (artificial). On 10% of sheep farms artificial colostrum is the only colostrum that is administered to lambs when adequate supply is not available from the mother. Post lambing ewes and their lambs are placed in individual pens on 88% of sheep farms. However, on many farms there are poor hygiene practices in the management of individual pens. Only 41% of Irish farms clean and disinfect individual pens after each ewe vacates.   

The main cause of dystocia is inadequate nutrition management which results in lambs been either over or under weight at birth. To implement an effective nutrition plan it is necessary to know silage feed value, expected lambing date and expected litter size. Use of a raddle during the mating season and changing the colour frequently enables the prediction of expected lambing date. Only 60% of farmers raddle their rams during the joining period and of these only 70% change the colour every 2 weeks or more frequently. Only 69% of farmers pregnancy scan their ewes. Consequently many farmers are unable to implement an effective pregnancy nutrition plan as they do not know expected lambing date and/or litter size.

Lamb mortality on your farm

Lamb mortality includes all lambs that die up to weaning including abortions and stillbirths. All lambs that die should be recorded on a record sheet. Other information recorded should include date of death, age at death, litter size, symptoms/cause of death. This information will identify if there is a lamb mortality issue, the potential causes and can be used by veterinary practitioners to develop a flock health plan to reduce mortality in future lambing seasons and thus increase flock profitability.