fatty acid requirements in pigs

Dietary fatty acids have been shown to be potent mediators of physiological processes related to body composition, brain and cognitive development as well as immune function. There is emerging evidence to suggest that type of fat fed during gestation as well as the relative proportions of different fatty acids in the diet influence these outcomes. More recently, nutritionists have investigated the potential benefits of fatty acids for their use in animal production. In the present study, two trials were performed to investigate the effects of feeding gilts gestation and lactation diets enriched with saturated fatty acid (SFA) or n-3 or n-6 polyunsaturated fatty acids (PUFA) on the behaviour, growth, performance and body composition of their progeny. Dietary fatty acids influenced the reproductive performance of gilts and the behaviour, growth and health status of their progeny. Feeding n-6 PUFA diets post-weaning significantly reduced the growth and performance of progeny compared with pigs fed SFA or n-3 PUFA diets. Furthermore, the health status of pigs fed n-6 PUFA-enriched diets post-weaning was significantly compromised. These results are in agreement with published findings in other species and may be a consequence of the dietary n-6:n-3 PUFA ratio. This paper presents a summary of current findings and compares the results to those in the available literature.

Piglet pre-weaning mortality is an important source of loss for the Australian pig industry and has been estimated to account for 13% of piglets produced (Australian Pork Limited, 2008). Genetic selection for a leaner genotype, which has been shown to produce piglets that are less physiologically mature at birth, could be contributing to these losses (Rooke et al., 2000). The maternal diet has also been shown to influence the growth and development of offspring. A growing body of evidence in other species suggests that the types of dietary fatty acid in the maternal diet during gestation have physiological outcomes for foetal development and the piglet post-partum. These postnatal effects include altered cognitive development, gene expression and energy metabolism (Wainwright, 2002). Animals are unable to synthesise n-6 or and n-3 polyunsaturated fatty acids (PUFAs) and therefore these must be supplied in the diet either in their long-chain form or as their precursors, linoleic acid (LA 18:2n- 6) and α-linolenic acid (ALA 18:3n-3), respectively. Confounding this requirement is competition between n-6 PUFA and n-3 PUFA for the same elongation and desaturation enzymes that produce long-chain PUFAs. Thus the relative proportions of n-6 PUFA and n-3 PUFA consumed in the diet significantly influences the synthesis of long-chain PUFAs.

Despite the known importance of fatty acids, limited research has been conducted on the fatty acid requirements of gestating sows. NRC (1998) recommendations only provide for n-6 PUFA for grower-finisher pigs (LA: 0.1% of the diet) and no recommendations have been made for n-3 PUFA (Rooke et al., 1998). There appears to be a requirement for specific fatty acids by the developing embryo and the foetus (Perez Rigau et al., 1995). Brazle et al. (2009) reported that the maternal diet can affect the fatty acid composition of the conceptus as early as day 19 of pregnancy and that embryonic docosahexaenoic acid (DHA; 22:6n-3) is 6–12 times greater than the maternal concentration by day 40 of pregnancy. As commercial pig diets are based on cereals that are rich sources of n-6 PUFA, it may be necessary to supply long-chain n-3 PUFA to the foetus during this period (Rooke et al., 1998).

In a recent study comprising two animal trials, gilts were fed one of three fatty acid treatment diets prior to mating and throughout gestation. These diets were enriched with sources of saturated fatty acid (SFA), n-3 PUFA and n-6 PUFA (Table 1).

Table 1. Summarised fatty acid profiles fed gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA during the third trimester in Trial 1.

Figure 1. Timeline for feeding of diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA to gilts in Trials 1 and 2.

The amounts of fat of each source added to the diets and the period of time offered are shown in Figure 1. Progeny were maintained on the same dietary treatment as their dams after weaning in Trial 1. However, in Trial 2, a subset of animals from the n-3 PUFA and n-6 PUFA litters were fed SFA diets post-weaning and compared with their litter mates who continued with the same dietary treatment as their dam. Outcomes measured as a part of these trials included reproductive performance, piglet behaviour, energy metabolism, carcass composition and the growth and performance of gilt progeny. This paper provides a review of some of the known physiological effects of dietary fatty acids and compares these with the findings of our study.

Dietary fatty acids are of particular importance for foetal development because they are incorporated into all cell membranes (Binter et al., 2008) and are involved in the regulation of processes such as gene expression and hormone and eicosanoid production (Simopoulos, 2004; Ibrahim et al., 2009). Fatty acids have also been implicated in improvement of fertility in dairy cows (Zachut et al., 2010) and improved reproductive performance in sows (Mateo et al., 2009). Webel et al. (2003) demonstrated improved embryo survival when sows were supplemented with n-3 PUFA; however, the mechanism responsible remains undefined. Maternal nutrition has a pronounced influence on foetal development during the final trimester of gestation (Brazle et al., 2009). This period is when development of the brain and retina is most rapid (Rooke et al., 1998). Because grain-based maternal sow diets contain little n-3 PUFA, scope may exist to improve both sow reproductive performance and post-partum piglet survival (Mateo et al., 2009).

Although there is evidence suggesting a positive role for n-3 PUFA in sow nutrition, few studies have assessed performance in gilts fed diets differing in fatty acid composition (Estienne et al., 2008). Diets high in n-3 PUFA have been associated with increased gestation length and birth weight in humans (Olsen et al., 1992; Koletzko et al., 2008), rats and pigs (Rooke et al., 2001a). Conversely, diets high in n-6 PUFA are thought to be associated with a higher risk of preterm labour in humans (Wathes et al., 2007) and have been shown to reduce gestation length in rabbits (Allen and Harris, 2001) and sheep (Elmes et al., 2005; Capper et al., 2006).

In the current study, dietary treatment had no significant effect on the reproductive performance of gilts in Trial 1. In Trial 2, feeding gilts diets enriched with n-6 PUFA significantly reduced (P < 0.05) the number of piglets born alive, significantly increased (P < 0.05) the number of mummified foetuses and numerically increased (P = 0.2) the number of stillborn piglets compared with gilts that were fed litters SFA or n-3 PUFA (Table 2).

This effect has not been reported previously. However, Perez Rigau et al. (1995) postulated that proportions of n-6 PUFA and n-3 PUFA in maternal sow diets may influence embryo survival. In the present study, a positive trend was evident for an increase in piglets born alive with an increase in the proportion of dietary n-3 PUFA. The data from our current study support the notion that the dietary n-6:n-3 PUFA ratio affects embryo or foetal survival. Gestation length and piglet birth weight were not significantly affected by dietary fatty acid treatment. There was no treatment effect on the number of piglets weaned or their body weight at weaning.

Table 2. Trial 2 treatment mean (± SEM) litter characteristics for gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

The association between brain fatty acid content, brain development and neonatal behaviour is well documented (Wainwright, 2002; McCann and Ames, 2005; Fedorova and Salem, 2006). Long-chain PUFA such as arachidonic acid (AA; 20:4n-6) and DHA (22:6n-3) are widely reported to be important for maintaining normal brain structure and function (Takeuchi et al., 2003; Demar et al., 2006). Previous work has shown that AA (20:4n-6), eicosapentaenoic acid (EPA; 20:5n-3) and DHA (22:6n-3) accumulate predominantly in the brain and retina of developing foetuses during the third trimester (Clandinin et al., 1980). Innis (2007a) reported benefits of n-3 PUFA supplementation on cognitive development in piglets and Rooke et al. (2001a) demonstrated beneficial effects of n-3 PUFA supplementation of the diets of gestating and lactating sows on the growth and survival of their progeny. An inadequate supply of these fatty acids has been associated with impaired visual acuity and cognitive development in humans (Innis, 1991) and experimental animals (Rooke et al., 1998). Previously, Rooke (2001b) demonstrated that piglets from sows fed tuna oil from day 92 of gestation through to term tended to contact the udder and suckle significantly earlier than piglets from sows fed a basal diet or a tuna oil supplemented diet on days 63–91 of gestation. Similar results have also been reported by Capper et al. (2006), who showed a decreased latency for neonatal lambs to suckle from ewes fed fish oil from day 110 of gestation to term compared with lambs from ewes fed a basal diet that contained no added long-chain n-3 PUFA.

The results from Trial 1 in the current study showed that piglets born to n-3 PUFA gilts had significantly reduced rectal temperatures at birth and were the only progeny to have an increased temperature 60 min postpartum (Table 3).

Table 3. Treatment mean (± SEM) litter characteristics for gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

Piglets from the n-3 PUFA-supplemented gilts tended to make contact with the udder and suckle earlier compared with piglets from either SFA- or n-6 PUFA-treated gilts. Compared with piglets of the n-3 PUFA group, progeny of the SFA group took 1.6 and 9.6 minutes longer to reach the udder and to suckle, respectively, and progeny of the n-6 PUFA treatment group took 4.2 and 7.9 minutes longer to reach the udder and to suckle, respectively. The time taken by piglets between contacting the udder and suckling (latency) was also reduced with maternal n-3 PUFA dietary supplementation. There was a significant interaction (P = 0.04) between birth weight and treatment for time taken to suckle (Figure 2).

Figure 2. Relationship between body weight and the time taken to suckle for progeny from gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA during gestation.

Figure 3. Mean (± SEM) whole brain tissue fatty acid content (g per 100 g) for selected fatty acids from oneday- old piglets from gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA during gestation.

As birth weight increased, there was a corresponding decrease in the time taken by SFA and n-3 PUFA piglets to reach the udder and suckle. In contrast, for piglets from the n-6 PUFA group, the amount of time taken to reach the udder and suckle increased as birth weight increased. Brain tissue of piglets from the n-3 PUFA group showed greater incorporation of both EPA (20:5n- 3) and DHA (22:6n-3) compared with brain tissue of the SFA and n-6 PUFA groups (Figure 3).

Incorporation of total SFA and monounsaturated fatty acid into brain tissue was not affected by maternal dietary fatty acid source, and similar amounts were incorporated in all three treatment groups.

Although neonatal behaviour after maternal dietary n-3 PUFA supplementation has been described, there are no reports on the relationship between birth weight and suckling behaviour of piglets from gilts supplemented with n-6 PUFA. Innis and de La Presa Owens (2001) showed that the fatty acid composition of the developing foetal rat brain is very sensitive to changes in the maternal dietary n-6:n-3 PUFA ratio. The DHA (22:6n-3) content and the n-6:n-3 PUFA ratio in whole brain tissue of progeny from the n-6 PUFA-treated gilts was similar to that of progeny from the SFA group. The significant incorporation of long-chain PUFA into brain tissue of progeny from the SFA and n-6 PUFA groups supports the notion that there is a specific requirement for n-3 PUFA for brain development and function (Amusquivar et al., 2008). In the present study, brain fatty acid profiles were obtained for piglets of average body weight. The amount of n-3 PUFA incorporated into brain tissue may depend on body weight and could vary between regions in the brain, as demonstrated by Carrie et al. (2000).

Dietary fat is a concentrated source of energy and acts as a carrier for fat-soluble vitamins A, D, E and K (Rossi et al., 2010). Furthermore, their use in animal feed has been shown to improve diet palatability and to reduce dust during processing. There appears to be little information on the comparative effects of feeding sources of SFA, n-3 PUFA and n-6 PUFA to gilt progeny on their growth and development.

Performance data for the post-weaning period in Trial 1 are shown in Table 4.

Table 4. Performance data (± SEM) for Trial 1 gilt progeny fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA during the post-weaning period.

Voluntary feed intake of pigs from the n-6 PUFA treatment group was significantly lower (P < 0.05) than that of the SFA and n-3 PUFA treatment groups for each week of the post-weaning period. The total voluntary feed intake for the post-weaning period for pigs fed the n-6 PUFA diet was equivalent to 50% and 53% of the total feed consumed by the SFA and n-3 PUFA treatment groups, respectively. There was no significant difference in body weight between treatment groups at weaning. However, 7 days post-weaning, pigs of the n-6 PUFA treatment group were significantly lighter (P < 0.05) than pigs of the SFA and n-3 PUFA treatment groups, which did not differ in live weight. This pattern persisted for the remainder of the post-weaning period (Figure 4) and through to the completion of the trial.

The results for Trial 2 supported those for Trial 1. No significant differences in body weight occurred at weaning (day 23). Pigs from the n-6 PUFA/SFA treatment group were significantly heavier than pigs from the n-6 PUFA treatment group 14 days post weaning (Figure 5).

Figure 4. Trial 1 post-weaning treatment mean (± SEM) body weight for pigs fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

Figure 5. Trial 2 post-weaning treatment mean (± SEM) body weight for pigs fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA (*P < 0.05)

This significant difference continued throughout the trial and became significant for all other treatment groups relative to the n-6 PUFA group 21 days postweaning. Progeny that were maintained on n-6 PUFA diets post-weaning showed significant reductions in feed consumption and growth throughout the trial (Table 5).

Interestingly, there was no growth setback for n-6 PUFA progeny that were fed SFA diets post-weaning. The findings show that progeny post-weaning growth was negatively affected by n-6 PUFA diets.

Table 5. Treatment means (± SEM) for voluntary feed intake, body weight and feed-to-gain ratio for post-weaning pigs fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

Dietary fatty acids have been shown to modulate body composition in chickens (Newman et al., 2002), humans (Micallef et al., 2009) and rats (Storlien et al., 1991). Specific fatty acid subtypes have also been shown to affect insulin sensitivity and energy partitioning (Couet et al., 1997). Improved sensitivity to insulin results in increased protein retention (Bergeron et al., 2007) and, in chickens, has been associated with greater muscle mass (Newman et al., 2005). Bee et al. (2002) showed that energy supply and specific fat sources alter lipid deposition as well as the fatty acid composition of porcine adipose tissues. Diets rich in n-3 PUFA have been associated with reduced feed intake, increased energy expenditure and lower fat mass (Kratz et al., 2009), whereas diets containing high proportions of either SFA or n-6 PUFA are thought to contribute to the development of disorders associated with metabolic syndrome, such as diabetes (van Dijk et al., 2009).

In Trial 1, the respiratory exchange ratios (RERs) of male progeny from gilts fed SFA, n-3 or n-6 PUFA diets were measured to determine which type of substrate was oxidised for energy production. Piglets fed n-6 PUFA had higher RER values than those fed SFA (P = 0.05) (Table 6).

Table 6. Mean (± SEM) respiratory exchange ratios of male progeny from gilts fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

The higher RER for the n-6 PUFA group indicates greater carbohydrate oxidation compared with piglets from the SFA or n-3 PUFA groups. The lower RER values for piglets fed SFA is indicative of greater lipid oxidation compared with piglets fed the n-6 PUFA diets. When body composition was measured using computed tomography, no effect of fat source on carcass composition was identified. Feeding different fatty acid subtypes to finisher pigs had no significant effect on the proportion of individual carcass components (bone, lean tissue, adipose tissue and water) (Table 7).

Table 7. Mean (± SEM) carcass composition of finisher pigs fed fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA as determined by computed tomography.

However, pigs from the SFA and n-3 PUFA treatment groups had greater (P < 0.05) increases in bone weight during this period compared with pigs fed the n-6 PUFA diet. These results may be indicative of a species difference or may be because the amount of fat in the diet was insufficient to affect body composition. Diets in this study were enriched with 3% fat whereas a poultry study detected effects on body composition when the diet contained 8% fat (Newman et al., 2002).

The effects of dietary fatty acids on postprandial inflammation have been linked to the quantity of fat, the proportion of SFA and the ratio of n-6:n-3 PUFA (Margioris, 2009). Several animal and epidemiological studies have shown that disturbances in the uterine environment may program the foetus for the development of diseases in later life (Barker, 2002; Ibrahim et al., 2009). In the present study, no mortalities were observed in the first trial, which was conducted in a controlled environment. However, in Trial 2, which was conducted on-farm, animals fed n-6 PUFA were 13 times more likely to die than pigs from the SFA treatment group (Table 8).

Table 8. Frequency of mortality and morbidity in Trial 2 grower-finisher pigs fed diets containing saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (PUFA) or n-6 PUFA.

These effects could not be attributed to differences in susceptibility to a specific disease. The increased propensity for mortality was unique to pigs from n-6 PUFA litters that were maintained on n-6 PUFA diets post-weaning. Piglets from n-6 PUFA litters that were fed SFA diets post-weaning had no mortalities.

Chronic illnesses such as diabetes, obesity and atopic diseases are increasingly thought to be a consequence of foetal programming (Enke et al., 2008). It is widely accepted that AA (20:4n-6) and its derivative eicosanoids upregulate the inflammatory response and that eicosanoids derived from EPA (20:5n-3) and DHA (22:6n-3) reduce the production of inflammatory cytokines such as interleukin-1, interleukin-6 and tumour necrosis factor-α and play roles in preventing future allergies (Cetin et al., 2009). Diets containing high levels of n-6 PUFA promote synthesis of inflammatory cytokines and eicosanoids (Innis, 2007b). This connection between increased dietary n-6 PUFA consumption and inflammation could have predisposed progeny to an increased risk of health complications and failure to mount an adequate immunological defence against environmental pathogens in a commercial environment. This finding demonstrates that the proportions of dietary n-6 PUFA and n-3 PUFA may be important for pig health and should be considered when formulating diets.

The results from this work show that the type of dietary fat fed to gilts influences reproductive performance, post-weaning progeny growth and the health status of grower-finisher pigs. Continued consumption of n-6 PUFA-rich diets had detrimental outcomes in both trials. Treatment diets in both trials were formulated to be isoenergetic, isonitrogenous and contained similar ingredients with the only difference being the type of dietary fat used. For these reasons, it is suggested that the dietary n-6:n-3 PUFA ratio is important for the growth and development of pigs. This is in agreement with an increasing body of evidence showing that the dietary n-6:n-3 PUFA ratio is a potent mediator of physiological outcomes (Simopoulos, 1991; Calder et al., 2009; Calder, 2010).

This project was supported by the CRC for an Internationally Competitive Australian Pork Industry.

This paper was presented at the Recent Advances in Animal Nutrition (RAAN) - Australia, July 2011. Engormix.com thanks for this huge contribution.