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MANAGING PIG VARIATION What a difference the weight makes! Dr. Brian Hardy Any failure to stay within the weight range specified by a slaughter outlet is likely to be expensive, so ways of reducing or managing within-group variation deserve the finishing manager’s attention. Variation in the weight at which pigs are marketed is a major concern for the swine industry in North America as elsewhere. Many of the abattoirs (packers) in Canada and the USA are attempting to slaughter at a more uniform weight. Some have put a very tight weight range on their payment grids. The actions open to producers in responding to this need to hit the core on the grid provided a fascinating session at the 2004 Banff Pork Seminar in Alberta, Canada. The following remarks are abstracted from papers by 2 speakers, Dr. John Patience of Prairie Swine Centre (Canada) and Dr. Mike Tokach of Kansas State University (USA). They pointed out that understanding variation and how to deal with it would become increasingly important to all pig producers. As more farms use all-in/all-out systems, their operators will have to watch both the average growth rate for a finishing barn and the range of weight within the house. The lighter pigs are the most expensive part of the weight distribution curve as they dictate when the barn can be emptied. On other units the producers are forced to sort pigs carefully prior to shipping, in order to reduce the financial penalty associated with falling outside the ideal weight range. Talk of distribution curves raises the point that a basic knowledge of some statistical terms is required to appreciate variation. A “bell curve” shows the distribution of measurements within the population. The curve can be normal (looks like a bell) or skewed (has a bias to one side). Mean is the average value for the whole population, minimum the lowest value and maximum the highest. Range is the difference between minimum and maximum values. Standard Deviation (SD) is a measure of dispersion. A high SD value indicates greater variation within the group. Coefficient of Variation (CV) is the SD expressed as a percentage of the mean value. Table 1 shows some typical numbers from Canada to illustrate all of these. For management purposes, the Banff speakers explain, a target Coefficient of Variation of 20% would be considered acceptable for weight at weaning. This target would drop to 12-15% for pigs coming out of the nursery and again to 8-12% for finishing pigs at market weight. Is the actual farm CV above target? Then consideration should be given to reducing the variability. Is it on target? Then consider ways of managing the variation. Table 1. Measured variation in body weight at three ages within an unselected population of pigs at Prairie Swine Center Elstow Research Farm
Patience et al. (2004) The speakers said producers should enlist the assistance of their nutritional or veterinary adviser to help them study variation on their farm and generate a plan of action. Generally only 80% of the genetic potential is achieved at farm level due to ‘environmental’ limitations that include inadequate availability of feed and water spaces and also crowding of pigs through overstocking of pens. A major cost associated with variation is that the barn is under-utilized. Say the enterprise operates on 3-site production with a finishing barn turnover of 16 weeks. In this example, reducing the grow-out period by 2 weeks could cut the overall floor area needed by 13%. Assuming a finishing space costs US$230 per pig, this saving represents US$1.25 per pig sold. Producers should find the packer grid that best suits their pig population variation or consider marketing heavy and light pigs to more suitable outlets. We’ve heard that methods to deal with variation in market weight can be divided into 3 areas. The first of these aims at achieving an artificial reduction, most commonly either by sorting into pens according to size or by cross fostering between litters. Both techniques will tend to reduce variation within the pen, but may also cut the daily gain of the whole population and so do not always achieve the desired outcome. To reduce variation, there is the option of split-sex housing: because castrates grow faster than gilts, the rooms or houses can be managed accordingly. But the farm needs to have a large number of pigs each week to apply this strategy. Mixing pigs over time to separate the sexes in one barn can have drawbacks associated with age and health differences. Rearing gilt progeny separate from those of older parities is used on some farms. This so-called segregated parity flow can lead to healthier pigs and less variation. A higher health status in the herd in general, will have a similar effect. This can be seen in all-in/all-out systems, which may have a CV of 7.5%, compared with a CV of 8.8% for continuous flow. Other options include using opportunity barns to accommodate the smallest pigs (5-25% of the population) and even to flow them through separate nursery and finishing sites. This gives the opportunity to feed supplemental milk replacer and any specialised diets to ‘normalise’ growth rate. Alternatively, recognising these pigs will be slower growing and will take longer to reach market weight means that variation within the original weaning group is not changed, but variation within the normal barn is reduced by removal of these small pigs. As Table 2 illustrates, variable weaning age is one of the biggest contributors to variation in market weight. Variation increases as weaning age is reduced, since younger pigs tend to grow slower than older pigs. Where pigs are weaned over a 7-day period, the final market weights will vary both through having some younger animals and from the range of weight gains around each age group. Possible answers are either multiple weaning per week or raising the average weaning age. Table 2. Influence of weaning age on weight and variation in pig weight
Main et al. (2004, in press) Increasing the farrowing capacity by 50% of one week's farrowing requirement will allow the weaning age to be increased by 3 days. Putting sows into the farrowing crate closer to the point of farrowing allows for an increase in the lactation length. Early weaning of the larger pigs in the litter may actually increase market variation, however. Equally, take a careful look at the cost: benefit ratio of any steps taken to increase the weight gain of the smallest pigs. Such increases can be achieved by split suckling, using complex nursery diets, use of supplemental milk or fostering onto sows with a higher milk yield. But these techniques do not reduce variation very much. Some help in reducing variation may be available from the selection of sire lines with similar growth potential. Unfortunately, its impact could be lessened by the farm’s own ‘environment’. Feeding multiple diets within a group is also potentially helpful. Adding 5-6% fat to increase the energy concentration of the diet fed to the smaller pigs will allow them to grow faster. This can lead to an extra 3-5 kg of gain in the total finishing period. Adequate water access is critical to reducing variation. Feed-grade antibiotics have been cited to reduce variation by increasing health status and allowing the smaller pig to grow faster. Prompt treatment of clinical disease will also bring about a reduction. To manage variation, you want to keep the CV percentage on your unit at about the current target level. One point to realize is that increasing the growth rate of the entire group will not reduce variation, or the need to sort pigs at market weight. It will, however, increase the weight of the slow-growing pigs. So it is worth considering how to raise the group’s overall rate of weight gain. That could be by using genetics capable of a high growth rate under commercial farm conditions, for example, or by feeding of Ractopamine (Paylean), if approved. Also think about the sow in this respect. Feeding in gestation should promote not only litter weight but also the number of muscle fibres in each unborn pig as this can affect later lean growth. Use sows of high milking ability. Encourage a high feed intake in lactation to increase weaning weights. Then, for the grow-finish stage, raise the energy concentration in the diet and feed correct amino acid levels. These may need to be slightly higher than the levels associated with cost/kg gain, particularly in the later finishing stages. This article was published in PIG INTERNATIONAL (April 2004) Close
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