Improved winter feeding can increase lamb survival
Updated: Jul 5, 2020
The use of pregnancy scanning to increase the accuracy of feeding and feed allocation have lead to increases in lambing percentages. A body condition score (BCS) of 3.0 during pregnancy has shown to be optimum for ewe survival, lamb survival and lamb live weight gain to weaning.
Only around 35% farmers actually know the live weight of their ewes in autumn, so are unable to make management decisions such as removing light ewes from the mob. Many feed budgeting techniques are based on 'gut feel' or on outdated recommendations for feed requirements, not taking into account the increase in mature ewe size.
Less than 50% of farmers pregnancy scan their ewes, therefore, are unable to preferentially feed multiple-bearing ewes.
The practice of set stocking (continuous grazing) up to 1 month before lambing means that control of pasture intake is lost and depends on the pasture growth rate.
Data collection and improved feeding were implemented with the goal of improving lamb survival and lamb growth to weaning. This paper is a case study and not an experiment, for a full explanation of the two, keep reading.
Lamb survival and weaning weight increased with improved winter feeding over a 4 year period rather than lambing intervention
Increasing feed supply to the ewes by using known feed requirements consistently weaned more lambs at heavier weights and resulted in greater potential revenue compared to the base system using traditional management.
While many changes to farm management and feed production can be made, the major gain in feed supply is through a reduction in summer and autumn feed demand, releasing feed that can be carried into winter.
The study farm was the Freestone farm owned by Landcorp, located in the Te Anau basin. The property is 628 ha and the primary role of the property was to produce maternal composite crossbred rams and terminal Wapiti stags.
Base farm data was collected from 2007 to 2009. Feed budgeting was changed in 2010 from traditional to tailored feed requirements based on measured ewe live weight with feed wastage of 15% factored in. This was then refined in 2011 and 2012.
Feed allocation was changed from monthly to weekly increases during late pregnancy, and set stocking was delayed until the planned start of lambing.
The budgeted aims for pasture covers at lambing were 1650 kg DM/ha for triplet-bearing ewes stocked at 7-8/ha, and 1500 kg DM/ha for twin-bearing ewes stocked at 8-10/ha. To meet this requirement approximately 50-60 ha of crop was required each year, approximately 8-9% of the farm area, at a yield of 15-17 tonnes DM/ha.
This paper is a case study not an experiment. This means that it was an observation style study, as in "we made these management changes... and this is what happened" whereas, an experimental style study would be "we compared all management practices individually and we found that one was better than the other...".
The reason for doing case studies is to provide information of what might happen when there is not much research available on the topic or to see how the research that has been completed is implemented on a farm-scale. This study is the latter, it has been proven that having ewes in good BCS results in improved performance, however many farmers aren't using BCS as a management tool.
Does measuring ewe body condition score and live weight on a farm-scale increase lamb survival?
The feed management changes were implemented from 2010 onwards. The late pregnancy feed allocation was increased from 99 kg DM/ewe to 128 and 144 kg DM/ewe for twin and triplet bearing ewes, respectively. Ewe BCS was maintained at between 3 and 3.5, with BCS loss between scanning and lambing being reduced to zero.
The scanning (blue line) and lambing (purple line) percentages from 2007 to 2012 are shown below in Figure 1.
Overall the number of lambs scanned increased over the 6 year period from 200% to 222%. The number of lambs weaned also increased from 132% to 160%.
The lambing percentage (lambs weaned/ewe mated) was quite variable from 2007-2010. There was a snowfall during lambing in 2008 that resulted in higher than average percentage of lamb losses (47%).
This percentage of lamb losses can be seen in Figure 2 below. The lamb losses were the greatest in 2008 at 47%, however, this was above average due to snowfall during lambing. The lamb losses began in 2007 at 37% and decreased from here to around 30%.
An average lamb mortality rate between scanning and tailing in crossbred ewes is around 20%, however, in high fecund flocks with a large proportion of triplets, this rate can almost double. As this was a flock with high fecund sheep with no lambing intervention the lamb losses were higher on average than the national average.
Lamb wastage declined from 37% in 2007 and 2008, to 25% in 2011 and 2012, though scanning percentage rose by 20%. This increased scanning percentage is likely due to increased triplet lambs, therefore, to maintain a lamb wastage of around 30% while increasing triplet numbers is promising.
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The proportion of scanned triplet-bearing ewes that reared at least 1 lamb is represented below in black (Figure 3). This increased slightly from a low of 62% in 2008 to around 80% in 2011 and 2012. Of these scanned triplet-bearing ewes, the proportion of ewes rearing single lambs remained relatively constant across years.
The proportion of twin- and triplet- rearing ewes increased slightly and fluctuated between the two. This indicates that when the lambing percentage increases, the extra ewes that scan triplets are likely to only loose one lamb to weaning, resulting in the ewe rearing twins to weaning.
Lamb liveweight gain to weaning increased slightly in both twin and triplet bearing ewes as shown below in Figure 4.
Lamb weights increased from 27.5 to 36 kg/lamb at 100 days of age. The increase in the live weight of lambs and ewes at weaning reduced the calculated feed requirements over summer and autumn, potentially releasing 70 to 110 kg DM/ewe to provide feed to meet the extra winter feed requirements. This is due to ewes maintaining a BCS of around 3.0, therefore, do not need to gain much live weight to reach target mating live weight, resulting in lower feed requirements between weaning and mating.
The monitoring of this high fecundity ewe flock in the Te Anau basin demonstrates the process of improved feeding to improve lamb survival and growth to weaning. This case study provides direct on-farm evidence that meeting BCS targets increases lamb survival and lamb liveweight gain to weaning. While this was not a traditional research study, case study's are important to determine if a change measured in a research trial is able to be implemented at a farm-scale.
Farm management changes similar to those carried out on this farm will have differing results for each farm, however, the results from this study indicate that feeding high fecund ewes better over winter can improve overall lamb survival of the flock.
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Johns C, Johns J, Stevens DR (2016). Increasing lamb survival and lamb weaning weight through feeding high fecundity crossbred sheep. In Hill Country Symposium. Grassland Research and Practice Series 16, pp 323-328