By Eric van Heugten, North Carolina State University Department of Animal Science Professor
Fats and oils are often used in the swine industry to increase the energy density of diets and improve growth and feed efficiency in swine. These lipids are derived from a variety of sources and may include rendered animal fats, restaurant grease, vegetable oils, including oils from distiller’s dried grains with solubles, and blended fats and oils. Therefore, the composition and quality of supplemental lipids can vary considerably.
We were particularly interested in the oxidative stability of lipids (level of peroxidation or rancidity). Lipid peroxidation is a complex process that results in the degradation of lipids. It starts with the formation of free lipid radicals and hydroperoxides, which can subsequently react with other unsaturated fatty acids to form additional hydroperoxides. Hydroperoxides are then decomposed into secondary and tertiary oxidation products. Saturated lipids are less prone to peroxidation, and peroxidation rates increase with increasing degree of unsaturation of lipids. The degree of lipid peroxidation is very difficult to characterize because the compounds that are produced are unstable and decompose as peroxidation progresses.
Nonetheless, it is important to determine the oxidative quality of lipids used in swine diets because lipid peroxidation products can induce oxidative stress, compromise immunity, decrease intestinal function and reduce growth performance. Indeed, we previously demonstrated that forced lipid peroxidation of soybean oil, using heat and oxygen perfusion, progressively increased markers of peroxidation with increasing time of exposure, resulting in decreased feed intake (by up to 7%) and growth rate (by up to 9%) when fed to nursery pigs.
In addition, digestibility, absorptive capacity and morphology of the intestine were compromised with increasing peroxidation. The response of pigs to peroxidation products appears to be progressive and a minimum threshold for lipid peroxidation above which detrimental effects are manifested likely exists.
Previous research clearly demonstrated that lipid peroxidation negatively affects cell integrity and increases oxidative stress, which can compromise health status. Nevertheless, no information exists with regard to the impact of lipid peroxidation on health, viability and mortality of pigs housed under the rigors of commercial conditions, such as population density and greater immune stress than a laboratory environment. Accordingly, we conducted a study to determine the impact of lipid peroxidation in nursery pigs housed under commercial conditions on growth performance, morbidity and mortality (Smith et al., 2016).
The study was conducted at a commercial research facility located in Illinois owned and operated by Hanor Co., using 2,200 gilts and castrates (Camborough derivative x PIC TR-4 sire; 5.95 ± 0.2 kilogram body weight) housed in a total of 100 pens with 22 pigs per pen. Pigs were fed one of five dietary treatments (20 pens per dietary treatment). Dietary treatments consisted of five degrees of peroxidation to present a dose response challenge of increasing peroxidation: no peroxidation, low, medium-low, medium-high and high peroxidation.
Treatments were administered for the duration of the nursery phase (43 days). Peroxidation was accomplished by exposing a restaurant-grade control corn oil to heat (65 degrees C) while bubbling air through the oil at a constant rate of 20 liters per minutes for 12 days. Peroxidation of the oil by using heat and air exposure was clearly achieved as shown by increased peroxidative markers (Table 1). Control corn oil was added to experimental diets at 5% and represented the no peroxidation treatment, while peroxidized corn oil was added to diets at 5% representing the high peroxidation level. Intermediate diets were blended on the farm using a feeding system that blends, weighs and records feed delivered to individual pens.
Average gain of the pen of pigs was reduced linearly when pigs were fed diets with increasing levels of peroxidation (Figure 1). Pen gain was calculated by difference of the total weight of pigs in the pen at the end of the study and the total weight of pigs in the pen at the start of the study. Thus, this measure considers only the pigs that finished the study and gives no value to pigs that died or were culled, which is practically relevant. Indeed, peroxidation increased death losses and the number of pigs that were culled (pigs that weighed less than 13.6 kilograms at the end of the nursery), and decreased the number of full-value pigs available to enter the finisher (Figure 2). The reduction in pen gain was primarily due to death losses and increased number of small (no-value) pigs, indicating that pigs that survive and are successfully treated have the ability to gain similarly, regardless of peroxidation level of the diet. The number of pigs treated with injectable medication and the number of pigs pulled increased linearly with increasing levels of peroxidation.
Although the impact of peroxidized lipids on growth performance may appear to be subtle, we demonstrated, under field conditions, that increasing the level of peroxidation resulted in a dose-related increase in mortality, number of pigs medicated and number of pigs that were excessively light. This resulted in a reduced number of pigs and a lower total pig weight by the end of the nursery. The financial value of retaining viable pigs is a powerful driver of return over investment. The challenge that remains is to define the acceptable levels of the several oxidation markers of a lipid quality control program for oil and fat sources. This application is probably most important for weaned pigs as compared to older growing pigs and sows, and responsiveness may vary with age at weaning and robustness of genetic lines used.
Also collaborating on this research are David Rosero, nutritionist and research scientist for Hanor Co. LLC, Franklin, Ky.; and Dean Boyd, adjunct professor at North Carolina State University Department of Animal Science, and technical director and nutritionist for Hanor Co. LLC, Franklin, Ky.