In this post, we’ll cover research findings on the use of pellet diets for feeding pigs, exploring both the benefits and drawbacks of this feeding method. In addition, we’ll discuss the importance of reporting confidence intervals and the limitations of relying on a single study to draw reliable conclusions.
Diverse studies on the use of pellet diets in swine nutrition have yielded contradictory results, with some indicating positive effects and others negative ones. A closer look at the experimental conditions, however, reveals a consistent pattern. Figure 1 depicts a meta-analysis indicating that pelleting may have positive effects when using fewer animals, but as the number of animals increases, the benefits may diminish and even lead to lower productivity compared to mash diets.
The empirical data shows that pelleting has an effect on G:F ratios relative to mash diets ranging from +6.2 to -5.40%. Experiments with fewer animals revealed greater benefits from pellet diets, while as the number of animals increased closer to typical commercial conditions (1200 head), the benefits of pelleting reduced. Myers et al. (2013) who found a 5.4% reduction in G:F ratios of pellet diets compared to mash diets attributed this reduction in efficiency to poor pellet quality (a high proportion of fines) resulting in pigs sorting through and wasting feed. Furthermore, poor pellet quality could have been exacerbated by feeder management because, according to Myers et al. (2013), feeders were adjusted to their respective settings on day 0 and the settings were maintained throughout the study (d 0 to 104 post wean). In a second study, Myers et al. (2013) adjusted feeders throughout the study to maintain feeder pan coverage of 40 to 60% and observed a 3.2% improvement in G:F due to pellet diets. However, Myers et al. (2013) reported that “due to variation in pellet quality and flow ability among batches of feed, maintaining proper feeder adjustments proved rather difficult”. In addition, De Jong et al. (2016) observed a 5.7% improvement in G:F ratio due to pelleting, but they also reported a 3.8-fold increase in pigs removed from pellet fed pens due to stomach ulceration. Thus, the improved G:F observed by De Jong et al. (2016) could be attributed to the removal of less robust pigs from the experiment. The preceding observations indicate that the utilization of pellets in pig production can be problematic.
According to the meta-analysis, pelleting increases G:F by 1.4% in commercial conditions (1200-head barn). However, by taking confidence and prediction intervals into account, a more accurate interpretation of this improvement may be obtained. In statistics, the confidence interval of a mean is a range of values that is likely to contain the true mean with a certain degree of confidence (usually 95%). A prediction interval, on the other hand, is a range of values that is likely to contain the possible outcomes with a certain degree of confidence. Based on the data from the meta-analysis shown above, a confidence interval of -0.65 to 3.4% was calculated for a 1200-head barn, indicating that the true G:F ratio difference could fall within that range. Moreover, the prediction interval for the improvement in G:F is estimated to be between -4.1 to 6.8%, which suggests that if the experiment were repeated in commercial conditions, the range of G:F differences could be expected to fall within that range.
Assuming that a pig consumes approximately 650 lbs of feed during its lifetime, a 1.4% increase in its G:F ratio would result in a decrease in feed intake of about 9 lbs (650 × 0.986 = 641). This decrease would translate into savings of roughly $1.8 (assuming a feed cost of $0.20/lb). However, pelleting one US Ton of feed (2000 lbs) costs around $7, which means that the pelleting cost per pig would be $2.2 (7 × 641/2000). Consequently, based on the sample mean, using pellet diets could result in a loss of approximately $0.40 per pig. Taking into account the cost of pelleting and the prediction interval, using pellet diets for pigs in commercial settings could result in a net difference between +6.5 and -7.5 dollars per pig. In addition, considering the confidence interval of the mean and pelleting costs, in the long run the practice of providing pigs with pellets may result in a net difference between +2 and –3 dollars per pig. The previous calculations only consider feed processing costs; however, there may be additional labor costs associated with adjusting the feeders as well as animal mortality losses due to ulceration.
Furthermore, given that the data used in the meta-analysis came from experiments involving highly skilled personnel who were likely meticulous in their execution of the study, it is possible that the use of pellet diets in commercial settings could potentially have even more negative effects. This is because real-world scenarios present greater challenges in feeding practice management and execution, which may exacerbate the negative effects associated with pellet diets.
Hence, while a single study involving fewer than 500 pigs may conclude that pellet diets improve G:F ratios substantially, a more comprehensive analysis of multiple studies does not appear to support the use of pellet diets in pigs under commercial conditions (1200-head barns). When drawing conclusions from our data, we must remember that they can only be made within the range over which the data was collected. We must acknowledge the experimental conditions and recognize that our findings may not be applicable in other contexts. Overgeneralization can affect our ability to analyze a phenomenon objectively, leading to biased knowledge.
Final remarks:
The inclusion of confidence and prediction intervals alongside means can enhance the accuracy of interpreting study results. For instance, simply reporting that pellet diets improve G:F ratios by 1.4% under commercial conditions may suggest a consistently positive outcome. By contrast, when confidence and prediction intervals are incorporated and reveal negative values, it becomes apparent that using pellets may result in economic losses. Moreover, if the apparent 1.4% benefit is linked to a low P-value, such as in this case (P=0.009), it can intensify the misleading sense of certainty regarding the results. Despite being derived from a meta-analysis, the average improvement of 1.4% is based on a subset of the population, so there is still uncertainty about the true effect. Encouraging researchers and journals in animal science to incorporate confidence and prediction intervals in addition to p-values, can lead to a more precise depiction of the potential outcomes of different interventions.
Finally, it is important not to becoming overly attached to our data, as even if our research demonstrates that a particular intervention has clear positive effects, these effects may not necessarily transfer to other situations, such as commercial pig farming conditions.
Questions to the reader:
- What, in your opinion, is the reason for the continued promotion of pellet diets for pigs by a number of companies in the swine industry?
- Is the potential decrease in productivity attributable to the pellet process itself or to ineffective management?
Thanks for reading, and I hope you found this post helpful!
Christian Ramirez-Camba
References:
Amornthewaphat, N., Hancock, J. D., Behnke, K. C., McKinney, L. J., Starkey, C., Lee, D., Jones, C., Park, J., & Dean, D. (2000). Effects of feeder design and pellet quality on finishing pigs.
Ball, M., Magowan, E., McCracken, K., Beattie, V., Bradford, R., Thompson, A., & Gordon, F. (2015). An investigation into the effect of dietary particle size and pelleting of diets for finishing pigs. Livestock science, 173, 48-54.
Boler, D. D., Overholt, M. F., Lowell, J. E., Dilger, A. C., & Stein, H. H. (2015). Effects of Pelleting Growing-Finishing Swine Diets on Growth, Carcass, and Bacon Characteristics. 15th Annual Midwest Swine Nutrition Conference Proceedings, Indianapolis, Indiana, USA, September 10, 2015,
De Jong, J. A., DeRouchey, J. M., Tokach, M. D., Dritz, S. S., Goodband, R. D., Woodworth, J. C., & Allerson, M. (2016). Evaluating pellet and meal feeding regimens on finishing pig performance, stomach morphology, and carcass characteristics. Journal of Animal Science, 94(11), 4781-4788.
Medel, P., Latorre, M., De Blas, C., Lázaro, R., & Mateos, G. (2004). Heat processing of cereals in mash or pellet diets for young pigs. Animal Feed Science and Technology, 113(1-4), 127-140.
Myers, A., Goodband, R., Tokach, M. D., Dritz, S., DeRouchey, J., & Nelssen, J. (2013). The effects of diet form and feeder design on the growth performance of finishing pigs. Journal of Animal Science, 91(7), 3420-3428.
Nemechek, J., Fruge, E., Hansen, E., Tokach, M. D., Goodband, R. D., DeRouchey, J. M., Nelssen, J. L., & Dritz, S. S. (2012). Effects of diet form and feeder adjustment on growth performance of growing-finishing pigs.
O’Meara, F. M., Gardiner, G. E., O’Doherty, J. V., & Lawlor, P. G. (2020). The effect of feed form and delivery method on feed microbiology and growth performance in grow-finisher pigs. Journal of Animal Science, 98(3), skaa021.
Potter, M., Tokach, M. D., DeRouchey, J. M., Goodband, R. D., Nelssen, J. L., & Dritz, S. S. (2009). Effects of meal or pellet diet form on finishing pig performance and carcass characteristics.
Steidinger, M., Goodband, R., Tokach, M., Dritz, S., Nelssen, J., McKinney, L., Borg, B., & Campbell, J. (2000). Effects of pelleting and pellet conditioning temperatures on weanling pig performance. Journal of Animal Science, 78(12), 3014-3018.
Yang, J., Jung, H., Xuan, Z., Kim, J., Kim, D., Chae, B., & Han, I. K. (2001). Effects of feeding and processing methods of diets on performance, morphological changes in the small intestine and nutrient digestibility in growing-finishing pigs. Asian-Australasian Journal of Animal Sciences, 14(10), 1450-1459.