Lamb survival and group size

It is estimated that over 10 million lambs in Australia die each year within 48 hours of birth. These are worth over $700 million to the industry, not to mention an animal welfare concern; however on average lamb survival rates have not changed in 20 years. The Lamb Survival Initiative estimates that an extra lamb surviving to turnoff is worth $55 after costs. Poor weather and predators are significant causes of death, but losses from mis-mothering can be reduced through improved genetics and management. Improved management in late pregnancy can provide immediate results, and an appropriate mob or group size can help achieve this.

Too big a group risks ewes and lambs being disturbed by other sheep during the first few hours post lambing. This is when the ewe bonds to the lamb, and the lamb needs to get colostrum and the maternal antibodies to combat disease. Twin lambs are at a greater risk due to smaller birth weights, and reduced contact with the mother. Ewes carrying multiple lambs and in-experienced maiden ewes should be kept in separate smaller groups, and scanning is essential to achieve this. In deciding on mob sizes farmers should also account for the cost of extra fencing, and the additional cost of managing extra groups. The ‘Making More from Sheep’ programme suggests the following mob or group sizes:

  • Twin bearing mature ewes: 100-250
  • Single bearing mature ewes: 400-500
  • Single bearing maiden ewes: 250-400

The Bred Well Fed Well Programme gives a maximum of 150 for twin bearing maiden ewes. Reducing the number of lambs per day by can also improve the opportunities for bonding. Although smaller group sizes do incur extra costs these are outweighed by the returns from improved lamb survival rates.