Effects of Altering the Omega-6 to Omega-3 Fatty Acid Ratio in Starter Diets on Piglet Inflammatory Response

Weaning is a critical time in a piglet’s life. They are exposed to many new stressors, including immune challenges. These stressors can lead to reduced feed intake and growth, and an inflammatory response will be generated. Although a certain degree of inflammatory response is beneficial during this time, an over-production of immune cells can be detrimental, leading to increased muscle degradation and reduced protein synthesis.

The n-3 FA’s are anti-inflammatory, and are known to have many different health benefi ts in a variety of species. Also, n-3 FA’s can alter the body’s release of cytokines, (proteins secreted by immune cells in response to stimuli) which assist in regulating the inflammatory response. Some of the most important pro-inflammatory cytokines are tumour necrosis factor (TNF-α), interleukin (IL)-1, IL-6 and IL-8.

This project was designed to determine if feeding a diet high in n-3 FA’s post-weaning could alter the inflammatory responses of piglets by reducing production of pro-inflammatory cytokines and improving piglet performance during an E. Coli LPS challenge. 

Figure 1. Average rectal temperatures of pigs treated with lipopolysaccharide (LPS) or saline after consuming varying n-6 to n-3 fatty acid ratios for one week in the nursery. No eff ect of diet was found for body temperature at time zero prior to challenge; P > 0.05. No diet x challenge interaction was observed; P > 0.05.

Weanling pigs (n=120) were randomized to one of fi ve dietary treatments immediately post-weaning (d 26 ± 2 days of age). Diets were formulated to contain varied n-6:n-3 FA ratios and consisted of a control (tallow based), plant based ratios of 10:1, 5:1, 1:1, and a fi sh based 5:1 ratio. Piglets were housed in groups of 2, and were given 6 days to acclimate to their surroundings and new diet prior to undergoing an inflammatory challenge. Piglets were then randomized to a challenge control group (saline injected) or to an LPS injected group (n=10/challenge/diet) and moved into individual pens for the 24 hour challenge period. Rectal temperatures were recorded at 0, 1, 2, 3, 4, 5, 6, 12 and 24 hrs post injection and blood samples were collected at 0, 2, 6 and 12 hrs post injection for cytokine analysis (IL-1β, IL-6, Il-8, TNF-α). 

Figure 2. Diet by challenge interaction of plasma interleukin (IL)-6 concentration (mean
SEM) for piglets injected with saline or lipopolysaccharide (LPS) when consuming varied n-6 to n-3 ratios post-weaning. P Values: Diet <0.01, Challenge 0.03, and D x C 0.01

 

Figure 3. Diet by challenge interaction of plasma interleukin (IL)-6 concentration (mean +/- SEM) for piglets injected with saline or lipopolysaccharide (LPS) when consuming varied n-6 to n-3 ratios post-weaning. P Values: Diet 0.08, Challenge <0.01, and D x C 0.13

Piglets that were challenged with LPS consumed less feed and had reduced growth rates relative to those piglets who received a saline injection during the challenge period (P < 0.01).

Rectal temperatures were unaffected by dietary treatment (P > 0.05), but maximum body temperature was 1.8 oC higher in pigs injected with LPS relative to the saline controls, regardless of dietary treatment group (P < 0.01). Figure 1 shows the effects of starter diet and challenge on rectal temperatures for piglets throughout the 24 hour challenge period.

The area under the curve (representing cumulative output for the period) for plasma IL-6 was greater in pigs consuming the 5:1 plant based diets relative to those consuming the other diets (P < 0.01), as was the area under the curve for those injected with LPS. A diet x challenge interaction was present for plasma IL-6, with piglets consuming the 5:1 plant based diet having an increased response when injected with LPS (P = 0.01; Figure 2). Similarly, there was a tendency for pigs consuming the plant based 5:1 diet to have increased plasma IL-8 during the inflammatory challenge period (P = 0.08). There was also a tendency for a diet x challenge interaction, with pigs consuming the 5:1 plant based diet having a greater response when injected with LPS relative to the other diets, as shown in Figure 3. 

Altering the n-6 to n-3 fatty acid ratio in the diets of newly weaned pigs can aff ect how they respond to immune challenges. Pigs consuming the intermediate n-6 to n-3 ratio of 5:1 had increased production of pro-inflammatory cytokines when challenged with LPS. Further work is required to determine the overall impact of these changes and how we can utilize them to help alleviate the post-weaning growth lag observed in the nursery. 

Strategic program funding was provided by Sask Pork, Alberta Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund. Specifi c funding for this project was provided by Alberta Livestock and Meat Agency (ALMA) and Vandeputte s. a., Belgium.