Improvements in piglet thermoregulation
Higher iron doses may enhance energy utilization in post-weaning phase
By Molly Jones, Tom Petznick, Emily Pratt, Wesley Lyons and Chris Olsen
Iron supplementation in neonatal piglets is a long-established practice, as piglets are born with limited iron reserves and receive insufficient levels from the sow’s milk1. Piglets have enough iron support to growth up to about seven days of age. With advancements in genetics, today’s high-performance pigs require a reassessment of the once standard 200mg iron dose. Optimizing injectable iron dosage has been the focus of recent research showing that higher iron doses offer multiple benefits to both pigs and producers. Notably, these studies have shown that pigs receiving two, 200mg doses of iron before 10 days of age have improved average daily gain from wean to market and are approximately 7 pounds heavier at marketing compared to those that receive just one 200mg dose2,3.
A study investigating differential gene expression in response to varying iron doses reported changes in the expression of numerous genes of interest in wean pigs. Interestingly, the TRPV1 gene had a > 4.0-fold increase in expression in piglets receiving two, 200mg doses of iron dextran4. This gene encodes for Transient Receptor Potential Vanilloid-1 which is a sensory receptor involved with the detection and regulation of body temperature5. These findings prompted the primary objective of this project, which was to evaluate the relationship between injectable iron dose and piglet body temperature during and after weaning.
On a 4,500-head commercial sow farm in Nebraska, 16 crossbred gilts of similar size and weight were enrolled within 24 hours of birth and evenly allotted to the control (200mg iron) or treatment (400mg iron) group. At enrollment, birth weights and hemoglobin levels were recorded, and ear tags were placed for individual identification. At three days of age, all piglets received a 200mg dose of Uniferon® iron dextran, and treatment pigs received an additional 200mg dose three days later.
To monitor body temperature without repeated handling, a novel device (Thermochron® DS1921G) was programmed to record a temperature reading every five minutes. These data loggers were attached to the skin in the axillary region to obtain 1,621 readings from each pig over the span of 12 hours pre-weaning through five days post-weaning. One day prior to weaning, body weight and hemoglobin were measured, and data loggers were affixed to the piglets.
To attach the loggers, piglets were first anesthetized with an intra-muscular tiletamine/zolazepam/ketamine/xylazine injection, and axillary skin was shaved and cleaned with surgical scrub. Loggers were secured with an adhesive medical patch then sutured around the circumference of the patch with 2-0 Vicryl® using aseptic technique. Once recovered from anesthesia, piglets were returned to their respective litters before weaning the next morning.
Times for all pig movement events and environmental conditions at the nursery site were recorded. On the day of weaning, transport took just under 40 minutes in mild weather, at 74°F and cloudy. The ambient temperatures in the nursery throughout the rest of the week remained within expected ranges for summertime in Nebraska (Figure 1).
At the conclusion of the data collection period, patches and sutures were removed to retrieve the data loggers. Figure 2 shows the average temperatures of the pigs in both the treatment and control groups, with the dashed line representing the expected normal body temperature (101.5°F). Throughout the collection period, there are clear daily patterns during which control pigs’ temperatures consistently drop lower than the treatment pigs, even in a warm, summer environment. The treatment group exhibited an overall mean temperature that was 0.5°F higher than the control group, but the p-value is just 0.12 (Table 1). It is possible, however, that a significant difference could have been found with a larger sample size.
There was a noticeable spike in the temperature of both groups post-placement that lasted 10 hours (Figure 3). The control pigs had a higher mean temperature over this period and exhibited greater variability overall, with higher maximums and lower minimums compared to the treatment group (Table 2).
Aside from the differences of our two treatment groups, the obvious temperature spike during that 10-hour period post placement is a critical finding, where individual piglets reached temperatures as high as 105.8°F. This is valuable insight into the level of fever and stress that piglets experience during their first day in the nursery and is an area of opportunity for future research into how to mitigate thermal stress during this time.
Given that this project was completed in the summer, replicating the project in winter would be helpful to understand if the differences seen between our two treatment groups are amplified in a colder climate. Additionally, differing transport times in a variety of environmental temperatures may influence the level thermal stress wean pigs experience during this period. These pigs had just a 40-minute transport time, but many wean pigs are routinely moved from the East Coast to the Midwest for their nursery and finishing phases, which could impact the level of thermal stress experienced.
Altogether, the additional 200mg dose of iron resulted in improved thermoregulation, bringing their average temperature closer to normal (101.5°F) during the evaluation period. Thermal stress can negatively affect pig health and divert energy away from growth. Improved thermoregulation with higher iron doses, potentially driven by increased TRPV1 expression, may enhance energy utilization in the post-weaning phase, thus contributing to the improved wean-market growth performance reported in previous studies.
References:1Mahan, D., Vallet, J. (1997). Vitamin and mineral transfer during fetal development and the early postnatal period in pigs. Journal of Animal Science.
2Gomez Cruz F., Krantz, S., Lyons, W. Pierce, J. L. (2024). Comparison of 200 mg injectable iron dextran vs 400 mg in either a single timepoint or split-dosed into two timepoints on growth and hemoglobin in pigs from birth to end of finishing. American Association of Swine Veterinarians Annual Meeting.
3Chevalier, T., Lyons, W., Paczosa, D., Rentfrow, G., Lindemann, M. (2023). A second iron injection administered to piglets during lactation improves hemoglobin concentration, growth performance, and carcass characteristics at slaughter. Journal of Animal Science.
4Pierce, J., Lyons, W., Chevalier, T., Lindemann, M. (2024). Effects of a second iron-dextran injection administered to piglets during lactation on differential gene expression in liver and duodenum at weaning. Journal of Animal Science.
5Lezama-García, K., Mota-Rojas, D., Pereira, A., Martínez-Burnes, J., Ghezzi, M., Domínguez, A., Gómez, J., de Mira Geraldo, A., Lendez, P., Hernández-Ávalos, I., et al. (2022). Transient Receptor Potential (TRP) and Thermoregulation in Animals: Structural Biology and Neurophysiological Aspects. Animals.
Jones is a Ph.D. candidate with North Carolina State University College of Veterinary Medicine; Petznick is a swine practitioner and Pratt is an associate veterinarian, both with ArkCare; Lyons is veterinary technical services director and and Chris Olsen is a technical services manager, both with Pharmacosmos US.
