High mortality and poor performance in Merino lambs post-weaning is a well documented problem especially in the higher rainfall regions of eastern Australia. It is a significant industry problem not only because of lost production but it is also a very important animal welfare issue (Hatcher et al, 2008). We sought address this by monitoring weaned Merinos and also by actively intervening and making recommendations whenever we felt it was warranted. We therefore set management targets that we hoped we could assist our producers to achieve. These targets were to keep the mortality rate at 5% or less per annum, to grow the lambs at at least 0.5 kg per month (about 16 g/hd/day) and to keep faecal egg counts below 400 epg.
After surveying the Merino breeders in our Board we asked for expressions of interest in participating further in a trial to monitor the growth, health and mortality of Merino weaners. Eleven producers from across the Board agreed to participate. At our initial visit at weaning we individually tagged about 200 usually ewe weaners. We then weighed and fat scored these lambs. We then blood tested them for glutathione peroxidise and vitamin B12 levels and collected samples for a faecal egg count. We planned to inspect the pastures that the lambs were to be weaned onto but almost all were weaned onto grain making this irrelevant. However we checked the water source to assess suitability for lambs. We also examined the lambs for concurrent diseases such as diarrhoea, flystrike and arthritis.
We weighed and fat scored the 200 tagged lambs three more times at approximately three month intervals and then weighed them again pre-joining this year (2008).
As can be seen from following table, weaning weights averaged 15.3 kg. This is very light reflecting the exceptionally poor season and particularly the failed spring in 2007. Nonetheless all producers were able to manage their lambs to grow at an average of 71g/hd/day well above our target of 16g/hd/day in the critical months after weaning. Producers almost all did this by continuing lambs on grain. Only one farmer was able to wean his lambs onto green feed and grow them without supplementary feed.
While the average mortality rate was 7.7%, 7 of the 11 producers were able to achieve our target of 5% or less.
|Flock ID||Weaning weight||Weight 3 mo post-weaning||Growth rate g/day||Weight 6 mo post weaning||Growth rate g/day||Overall growth rate g/day||Mortality rate %|
We collected blood and faeces from a sample of the lambs at weaning and collected faeces at each subsequent visit. The central tablelands has large areas especially to the east that are known to be selenium deficient and a small pocket known to be cobalt deficient. However tests for selenium (GSHPx) and cobalt (B12) were all normal at weaning. We have no known areas of copper deficiency but have areas with soils high in copper. Blood copper levels were normal except on one property where some tests were marginally high.
Strongyle egg counts at weaning were zero on all properties except one. Almost all lambs had low to moderate levels of Nematodirus . Despite the low egg counts drenching at weaning was always recommended.
At each visit we noted weaners affected by diseases such as flystrike, arthritis and diarrhoea. In this dry year these diseases had a negligible prevalence and impact on the health of lambs in the trial.
The producers in this trial were able to manage their lambs to grow usually with an acceptable mortality rate despite the very tough season and low weaning weights. Only one producer to the northeast of Bathurst had sufficient rain to wean and grow lambs on green feed. The others were able to do this by feeding lambs grain. Introduction to grain was usually smooth because the lambs had become accustomed to grain feeding prior to weaning.
Graph 1 shows that mortality rates were strongly related to weaning weight on all properties. However the graph also shows that some producers were able to manage even very small weaners to grow with low mortality rates.
Despite the low faecal egg counts at weaning, drenching was always recommended. This is because very small lambs have very few body reserves and have virtually no immunity to parasites. These egg counts are almost certainly is an underestimate of worm burdens in lambs that may have only been grazing and so picking up worm larvae for the last 2-3 weeks.
From the first year of our trial we learned that weaning weight is critical. This can best be achieved by good ewe nutrition. We also learned however that ever very small lambs can survive if they make a smooth transition to grain. In this year concurrent diseases such as flystrike, internal parasites, trace mineral deficiencies, arthritis and diarrhoea were not problems however in other years this will not be the case.
Concurrent diseases must also be managed vigilantly in young Merinos with very poor body reserves.
We thank Central Tablelands RLPB and NSW DPI for providing the resources to run this trial. We also wish to acknowledge Pfizer for helping fund it.