Effects of dietary n-6:n-3 fatty acid ratio on growth performance, plasma fatty acid profile, intestinal morphology, and immune function of pigs

Highlights

• The increasing dietary n-6:n-3 fatty acid ratio altered plasma n-6 and n-3 fatty acid concentration as well as n-6:n-3 fatty acid ratio, and might influence the intestinal morphology during the nursery phase.

• The increasing dietary n-6:n-3 fatty acid ratio did not generally affect growth performance or the skin inflammation response of pigs in the nursery and/or grower phases.

• The extremely low dietary n-6:n-3 fatty acid ratios might have negative effects on the growth performance of pigs during the nursery phase.

Abstract

A total of 185 crossbred pigs (Yorkshire x Landrace; 20.7 ± 2.5 d of age and 6.7 ± 1.1 kg BW) from 3 weaning groups were used to evaluate dietary n-6:n-3 fatty acid (FA) ratios on nursery and growing pigs. Within each weaning group, pigs were blocked by BW and randomly assigned to 1 of 5 dietary treatments in a randomized complete block design with balanced sex and 4 or 5 pigs/pen within each block. The dietary treatments were: 1) low n-6:n-3 FA ratio (LO): 5.0% menhaden oil (MO) and 0.0% corn oil (CO); 2) low-medium n-6:n-3 FA ratio (LO-MED): 3.5% MO and 1.5% CO; 3) medium n-6:n-3 FA ratio (MED): 1.5% MO and 3.5% CO; 4) high-medium n-6:n-3 FA ratio (HI-MED): 0.2% MO and 4.8% CO; and 5) high n-6:n-3 FA ratio (HI): 0.0% MO and 5.0% CO. The diets were fed in 2 phases as d 0 to 28 (nursery phase) and d 29 to 70 (grower phase). In vivo cell-mediated immune response was assessed on d 14 and 28 for Group 1 and 2 by measuring the inflammatory response to an intradermal injection of 100 µL of phosphate buffered saline (PBS) or phytohemagglutinin (PHA, 0.5 mg/mL of PBS). One pig was euthanized from each pen in Group 1 and 2 at the end of the nursery and grower phase to assess intestinal morphology. During the nursery or grower phase, average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio were not affected by increasing dietary n-6:n-3 FA ratios (P > 0.16). However, pigs fed the LO diet had lower (P < 0.05) ADG and ADFI compared to those fed diets containing greater n-6:n-3 FA ratios during the nursery phase. Increasing dietary n-6:n-3 FA ratio altered plasma n-6:n-3 FA ratios on d 15 and d 29 (quadratic, P < 0.01). In vivo cell-mediated immune response to PHA did not differ among treatments. Duodenum and jejunum villus height and villus height:crypt depth ratio did not differ among pigs on different treatments at the end of either the nursery or grower phase (P > 0.10). Jejunum crypt depth increase in a quadratic manner at the end of the nursery phase (P < 0.05) but not at the end of the grower phase (P > 0.10). In summary, increasing dietary n-6:n-3 FA ratios altered plasma n-3 FA concentration and n-6:n-3 FA ratio and might influence the intestinal morphology, but did not generally affect growth performance or the skin inflammatory response of pigs in the nursery or grower phases.

Introduction

Omega-6 fatty acids (n-6 FA) and omega-3 fatty acids (n-3 FA) are two classes of essential FA that have important physiological functions with both being critical for good health and normal development (Simopoulos, 2006). The n-6:n-3 FA ratios in western human diets are between 15 and 17, whereas the ideal dietary n-6:n-3 ratio, as recommended by a panel of lipid experts, is around 2 (Simopoulos et al., 1999). A high n-6 FA consumption and a high dietary n-6:n-3 FA ratio are reported to lead to the pathogenesis of many diseases, such as cardiovascular disease, cancer, and inflammatory and autoimmune diseases (Simopoulos, 2002). This has lead to investigations into increasing the n-3 FA content of animal products to alter the total dietary ratio in human diets. Kouba and Mourot (2011) reviewed previous studies and concluded that feeding animals with diets containing greater concentrations of n-3 FA (mainly from linseed supplementation) leads to a significant improvement of tissue n-3 FA concentrations in animal products (egg, meat, and milk). Additionally, increasing n-3 FA concentration in animal feed was also shown to benefit animals per se, especially for swine. Several studies reported that increasing dietary n-3 FA concentrations promoted growth performance of weanling and growing-finishing pigs (Luo et al., 2013; Duan et al., 2014; Shin et al., 2017), alleviated the stress induced by LPS challenge or weaning of nursery pigs (Liu et al., 2013; Li et al., 2014); and greater n-3 FA concentrations in sow diets improved conception rate, piglet weight gain during lactation, and n- 3 FA concentrations in various tissues of piglets (Binter et al., 2011; Perez Rigau et al., 1995; Yin et al., 2017).

Fish oil (FO) is considered as an excellent source to supply n-3 FA in swine diets. It has been reported that FO increased tissue n-3 FA concentrations of weanling and suckling pigs compared to palm oil or linseed oil, when supplemented in the nursery (2.5%) or sow diets (2.0%), respectively (Tanghe et al., 2015; Komprda et al., 2017). However, other studies show that greater inclusion rates of FO (7.0% or 10.5%) might suppress the growth performance and immunity of nursery pigs (Turek et al., 1996; Luo et al., 2013).

The objectives of this study was to evaluate the effects of increasing dietary n- 6:n-3 FA ratio, which was established by using different combinations of menhaden oil (MO) and corn oil (CO), on growth performance, plasma FA profile, intestinal morphology, and immune function of pigs during the nursery and grower phases.