Effect of chronic cyclic heat stress and supplemented inorganic and organic zinc source levels on grow-finish pig growth performance and estimated body composition

Authors: Mills, Kayla; MAHONEY, JULIE - United Animal Health; DUTTLINGER, ALAN - Country View Family Farms; ELEFSON, SARAH - Baylor College Of Medicine; RADCLIFFE, JOHN - University Of Kentucky; RAMBO, ZACH - Zinpro Corporation; RICHERT, BRIAN - Purdue University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2024
Publication Date: 4/2/2024
Citation: Mills, K.M., Mahoney, J.A., Duttlinger, A.W., Elefson, S.H., Radcliffe, J.S., Rambo, Z.J., Richert, B.T. 2024. Effect of chronic cyclic heat stress and supplemented inorganic and organic zinc source levels on grow-finish pig growth performance and estimated body composition. Translational Animal Science. 8. Article etxae029. https://doi.org/10.1093/tas/txae029.
DOI: https://doi.org/10.1093/tas/txae029

Interpretive Summary: Heat stress is a physiologic state where an animal can no longer properly regulate its body temperature during spikes of heat waves. It has been well documented that heat stress can negatively impact feed intake, growth performance, and carcass characteristics in swine. Pigs that are in the finishing months of growth prior to going to market are particularly sensitive to heat stress and cost the U.S. swine industry one billion dollars annually. There are several ways heat challenges can be mitigated to reduce the negative impacts of heat stress during warmer temperatures, one of which being nutrition. Zinc (Zn) supplementation in pigs has proved to lessen the negative effects of heat stress during intense, short heat events. However, the effectiveness of Zn supplementation during cyclic heat stress that mimic true summer weather patterns has yet to be explored. In addition, Zn can come in different forms (inorganic vs. organic) where organic is more easily absorbed by the animal than the other. Therefore, the objective of this study was to identify the optimal supplementation level and form of zinc to mitigate the negative effects of long-term, cyclic heat stress in finishing swine. Six hundred cross-bred pigs were housed under thermoneutral (TN) or cycling heat (HS) conditions simulating summer heat with acute 3-day heat waves for a 70-day study. There was a total of six diets varying in Zn level and source, each increasing in a stepwise manner in the amount of Zn included. Pigs were randomly allotted to 1 of 12 temperature and diet treatment combinations. At the conclusion of the study, HS pigs were found to be 9 pounds lighter at market when compared to their TN counterparts, had lower overall average daily gain, and average daily feed intake, but tended to have a greater gain:feed ratio. In addition, pigs under HS had less back fat at the 10th rib, a smaller loin eye area, and a greater calculated percent lean. Pigs supplemented with 50 inorganic and 60 organic mg/kg Zn under HS conditions were affected the least by the summer heat simulation. Therefore, our results indicate that a Zn blend of 110 mg/kg may be helpful to feed finishing swine during summer heat events to prevent loss in growth performance.

Technical Abstract: Zn supplementation has proved to mitigate effects of heat stress with varying effects evident with Zn source during acute heat events. However, the effects of Zn supplementation during long-term summer weather patterns have yet to be explored. Therefore, the objective of this study was to identify the effects of supplementation source and level of Zn to mitigate the negative effects of long-term, cyclic heat stress in finishing swine. Six hundred cross-bred pigs were housed under thermoneutral (TN) or cycling heat (HS) conditions simulating summer heat with acute 3d heat waves for a 70d study. TN conditions were 16.7-18.9°C throughout the study. HS pigs were housed at the same temperature as TN from d0-18, then 28°C/24°C for 12h/12h on d18-21, followed by 30°C/26.7°C for 12h/12h on d24-70, except during acute heat (32-33°C/29-30°C, 12h:12h) on d21-24, 42-45, and 63-66. Treatments were arranged in a 2×6 factorial with main effects of environment (HS vs. TN) and dietary available zinc supplementation: 1) 50 mg/kg ZnO; 2) 130 mg/kg ZnO: 3) 50 mg/kg of organic Zn (Availa®Zn); 4) 50 mg/kg ZnO + 40 mg/kg organic Zn); 5) 50 mg/kg ZnO + 60 mg/kg organic Zn; and 6) 50 mg/kg ZnO + 80 mg/kg organic Zn. Pigs (5/pen) were blocked by initial BW (72.2 kg) and randomly allotted to 1 of 12 temperature and diet treatment combinations across 10 replicates. Body weight and feed intake were determined at the beginning and end of each acute heat event. All pigs were ultrasonically scanned at the 10th rib to predict loin muscle area (LMA), backfat (BF), and percent lean. Data were analyzed by the MIXED procedure in SAS with pen as the experimental unit. At d63 HS pigs were lighter (P<0.01), had lower overall ADG (P<0.01) and ADFI (P<0.01). A diet by environment interaction was observed for overall ADG (P=0.04) with diet 5 HS pigs having a 3.9% reduction in ADG whereas diet 6 had 14.4% reduction in ADG, while under TN temperatures diet 6 had the greatest overall ADG of all treatments. Other diets were intermediate in their ADG under both HS and TN conditions. Pigs under HS had less BF at the 10th rib (P<0.01) and a smaller LMA (P<0.01), and a greater calculated percent lean (P=0.04). Our results indicate that a blend of supplemental Zn sources at 50/60 mg/kg may mitigate the reduction in growth performance due to HS. While not directly contrasted, the NRC requirement of 50 mg/kg Zn may be too low to optimize finishing pig growth performance under both TN and HS conditions.