The last decade’s unprecedented rise in litter size has resulted in an increased number of fallback pigs. Fallback pigs are those that fail to achieve performance in the barn equal to that of their contemporaries. Pigs can be born as fallbacks, in that they have a lighter birth weight. However, pigs with normal or heavy birth weights can become fallback pigs due to poor nutrition, environmental conditions, disease or other, as yet unknown, reasons. Whatever the cause, these pigs compromise barn throughput, result in weight penalties at market, and may reduce barn flow. There is little research concerning the factors that affect fallback from normal production. A better understanding of these factors may allow for the development of environmental or nutritional interventions to control their prevalence, thereby maximizing the production efficiency, throughput, and profitability of a barn. Therefore, the overall objective of this study was to develop an understanding of the underlying biology of the fallback pig, which hopefully will lead to improved management practices in the barn. The specific objectives of this experiment were to: 1) identify differences in the biology and physiology, and thus the growth and metabolism, between fallback pigs and their heavier, faster growing counterparts; 2) determine if these differences result from variations in small intestine structure or function; and 3) determine the role of blood chemistry and immune status in fallback from normal performance. To accomplish these objectives, 120 weanling pigs were utilized in growth, metabolism, and comparative slaughter experiments. Forty barrows from each of the lightest, median, and heaviest 10% pigs at weaning were placed in individual crates with slatted floors, allowing for fecal and urine collection. Eight pigs from each weaning weight category were harvested on d 5 post-weaning as the initial slaughter group. The remaining 32 pigs in each category were part of the metabolism group, and were utilized in a growth and metabolism experiment and were then slaughtered. After the completion of the live animal component of the experiment, pigs within each initial body weight (BW) category were further stratified into the slowest, median, or fastest 33% average daily gain (ADG) categories. This resulted in a total of nine treatments. Fallback pigs were designated as those belonging to the slowest ADG category from either the lightest or median BW categories. In contrast to our initial hypothesis, there was no effect of treatment on feed efficiency, which suggests that improvements in ADG were primarily driven by ADFI. Kidney and intestine weights, as well as protein and fat deposition rates were affected by both BW and ADG category, even when equalized per unit of body weight. These variations confirm that fallback pigs differ in both their biology and physiology compared to their heavier, faster growing contemporaries.
In order to further understand why these differences in carcass composition occur, the digestibility of nutrients and efficiency of energy utilization were measured and found to be maximized by pigs in the median ADG categories. While it may be more intuitive for these to be maximized by the fastest ADG categories, experiments by other researchers largely agree with our findings. Additionally, bicarbonate levels in the blood were highest in the two extreme categories: the slowest ADG, lightest BW category and the fastest ADG, heaviest BW category. Bicarbonate is a measure of acid-base balance, and the variation in its measurement is further evidence that both the poorest and highest performing pigs may have poorer physiological regulation compared to their contemporaries. These differences in nutrient digestibility, energy utilization, and blood metabolites underscore the importance of managing the entire variation of a population, and not just the poorest performers. There were no distinct patterns in differences in small intestine structure or function, nor were white blood cell or lymphocyte concentrations affected by fallback status. Thus, all pigs in the experiment, even fallback pigs, appear to have had similar health status.
Taken together, these results suggest that the underlying cause for fallback from performance lies jointly with poor feed intake and poorer utilization of absorbed nutrients. There is still little explanation as to the root cause of poorer nutrient utilization. While this experiment has made immense strides toward identifying management strategies that are more calculated and economical, the next phase of research must be undertaken in a commercial environment, in order to answer questions that could not be addressed in this experiment. Indeed, we are currently collaborating with veterinary pathologists, an Iowa pork producer, and IPPA to evaluate the broader factors affecting fallback from performance in a commercial facility. In this experiment, we have characterized the biological and physiological differences in fallback pigs and identified the underlying causes for fallback from performance. This, combined with our understanding of factors in a commercial environment, will allow us to determine management strategies that may be critical to maintaining profitability in the pork sector. For more information, contact John Patience at [email protected] or at 515-294-5132.
