Targets for high-performance weaners in self-replacing flocks

Improving weaner management to reduce mortality and increase growth can improve enterprise performance and reduce costs.

Regardless of whether you are producing merino or maternal weaners, setting reasonable weight and growth targets can improve both the number of replacement ewes to select from, and the number and condition of surplus stock for sale.

Good growth may also allow mating of ewes at 7 months of age, to lamb at 1 year of age. This increases the rate of genetic improvement of your merino flock. As well, having a higher proportion of young sheep in the flock means that the flock has finer wool (on average). Weaners that are growing well or are at target weights are less susceptible to health problems, so you avoid wasting the cost of raising lambs that later die as weaners.

The most important piece of equipment for managing weaners is a set of scales.

Supplementary feeding will be necessary through the summer and autumn. To feed supplements efficiently, it is important to set targets for growth of weaners at various times, and to continually monitor to avoid overfeeding and underfeeding. Table 1 provides a guide to targets, based on a range of adult weights (the average weight of a mature animal in moderate condition).

Table 1 Target weights for weaners at various stages

The first target time is weaning, when lambs should exceed 40 per cent of their mature body weight—for example, a medium-framed merino weaner should be more than 20kg and a larger crossbred weaner more than 25kg. On some properties or in some seasons, this coincides with pasture senescence, so you should use that target.

Weaners that have not met the target weaning weight will need to grow more rapidly after weaning than those that are already there. Lightweight weaners are more likely to die because they have little body reserves (weaners weighing 20kg or less have less than 1kg of fat reserves). Any subsequent weight loss results in the utilisation of vital tissues, leaving them more vulnerable to challenges from chilling, malnutrition, or infections such as flystrike or worms, and often resulting in their death. Even holding them off feed for 24 hours may be fatal for some.

Depending on the time of lambing, weaning is often not far short of when pasture is starting to dry off and drop in quality. Without quality summer feeds such as lucerne, supplements may be required to ensure growth and survival over summer. This means that it is important to draft weaners based on weaning weight and provide preferential treatment to the lighter weaners, continuing to draft off a lightweight and/or poor-doing tail every month thereafter. Targets for growth post-weaning should be at least 2kg per month for 15kg weaners, 1.5kg per month for 20 kg weaners and 1kg per month for weaners weighing 25kg or more.

Table 2 Body weight of weaners at the start of summer, minimum monthly weight gain targets and likely summer mortality risk

The next target is weight at pasture senescence. Weaners need to be above 45 per cent of mature body weight (22.5kg for 50kg adult weight, 25kg for 55kg adult weight). Ewe weaners at first mating should be above 75 per cent of mature body weight. A feasible weaner mortality target is less than 5 per cent for merino flocks and 3 per cent for crossbred flocks.

Having targets for weaner growth provides direction for the allocation of feed resources and management, to reduce mortality and improve performance. To achieve set targets, the most important tool is the use of a set of scales for regular monitoring.

Given the normal variability within any flock, there will always be some sheep that need to grow quite rapidly, as well as sheep that don't. Particularly in a tough year, when feed is tight and supplements are required, the strategy of drafting off the at-risk animals and allocating feed to those in the mob that need it will be more cost-efficient.