Formulating for Optimum Gut Health and Performance in Swine
Optimal gut health is fundamental to good life time performance in pigs. Successful and welfare friendly pig production requires a solid appreciation of the interactions which occur between nutrition, gut physiology and immunity (Kelly and King, 2001). Events like heat stress also add an environmental factor into the list of considerations.
When formulating diets for pigs it is essential to consider not only the nutritional requirements for efficient growth, but also the nutritional and non-nutritional requirements of the immune system, the intestinal tract, and the commensal microflora. This paper will explore the nutritional factors which require consideration when formulating for optimal gut health and performance in modern pig production.
Dealing with the immature piglet
When formulating young pig diets it is essential to ensure that the interaction between nutrition, gut physiology and immunity is the focus point. Weaning is a challenging event which can result in suboptimal performance and immunity for the life time of the pig (Kelly and King, 2001). The introduction of solid feed is challenging, but nutritional tools are available to assist us. Controlled exposure of bacterial and feed antigens to the pigs’ immune system is essential for the effective development of the mucosal immune system. It is important to maintain an efficient balance between the developing regulatory and effector functions of the immune system (Kelly and King, 2001).
From a feed antigen perspective this is best achieve by exposing piglets to a broad range of raw materials at low inclusion rates whilst they are still consuming sows milk. This allows their immune system to recognize feed ingredients and avoid or reduce transient hypersensitivities, (Bailey et al., 1994) which can be metabolically costly. Gradual introduction of raw materials like soya bean meal and legumes which are known to cause sensitivities is also advisable. Raw material selection should focus on processed or simple carbohydrates (cooked cereals and sugars), high quality animal proteins (fish, blood, meat, plasma, egg), milk products and beneficial fats (fish, algal, coconut).
The practice of creep feeding has more to do with exposing pigs to feed and bacterial antigens than supplying pigs with significant amounts of nutrients. In a simple commercial experiment, the introduction of creep feed 9 days prior to weaning (at day 27) resulted in a 45% reduction in the removals from the nursery for reasons of mortality and morbidity (P=0.07, Edwards et al., 2011).
From a bacterial antigen perspective it is important to control exposure. A weaning event which results in excessive regulatory or effector functions can result in a long term inability to mount an appropriate response to mucosal antigens (Kelly and King 2001). Controlled exposure can be achieved by the use of functional feed ingredients and additives. It is not easy (nor necessarily helpful) to eliminate all bacterial antigens by the use of feed additives like spray dried porcine plasma, hyper-immunized egg proteins, copper, phytogenics, yeast fractions, organic acids etc., we can reduce the quantity or pathogenicity of these microbes but still allow the immune system to recognize the antigen for future reference.
We also have the opportunity to manipulate the microflora by the use of prebiotics and/or probiotics. These can improve piglet performance by reducing the risk of bacterial related disease and generating the production of metabolic compounds which benefit the health and maturity of the pig (e.g. polyamines, volatile fatty acids). Research outcomes are also demonstrating that fiber has a role in establishing and maintain gut health in pigs. In situations where their is a risk of undigested protein entering the large intestine of pigs, the addition of a fermentable fiber source provides a preferential substrate for bacterial fermentation in the hind gut which is associated with positive health benefits.
Maximize digestive capacity
Appreciating the limitations of the digestive capacity of the pigs at different developmental stages is another important aspect of successful formulation for optimal gut health. It is important to remember that the development of the digestive system is largely dependent of substrate, so practices which enhance feed intake in newly weaned pigs will accelerate the digestive development.
The utilization of supplementary enzymes (phytase, non-starch polysaccharide enzymes, protease, cellulose, pectinase, amylase) to support efficient digestibility of feed stuffs is recommended where substrates are significant. Nutritionists also need to think about potential antagonists in the diet which may limit enzyme efficacy (e.g. zinc, pelleting temperatures). Some enzyme like phytases are more effective when offered in combination with acidifiers (Blank et al., 2012). In addition to this, it is important to support the pigs own digestive capacity by considering dietary factors including keeping the acid binding capacity of feeds offered to young pigs low, and the electrolyte balance optimal for efficient nutrient absorption, as well as protein and mineral digestion (Guzman-Pino et al., 2015). Some phytogenic products are also able to enhance digestive functions in the pig and lead to improved feed conversion efficiency and reduce the risk of health challenges associated with undigested protein and ammonia emissions.
Dietary protein quality versus quantity
Lowering dietary protein is seen as a way to improve gut health, reduce environmental pollution and make better use of expensive protein meals. Protein quality (digestibility) is of more importance than crude protein level in influencing gut health (Wellock et al., 2009). Pig feed producers though have to find a balance between diet costs and raw materials quality which does not always favor highly digestible protein meals for pigs. Using lower protein diets successfully requires greater nutritional discipline and an increased use of synthetic amino acids. Firstly diets must be formulated to the full 10 essential amino acids, and when very low protein levels are used, there is a need to also monitor the non-essential amino acids. The objective of nutritionist should be to meet the protein requirement of the pigs by formulating diets to standard ileal digestible amino acids with as little excess or non-digestible protein in the diet as possible. This ultimate means using highly digestible protein sources and the full range of available synthetic amino acids. Experiments which have only formulated to the first 5 limiting amino acids have found that reducing crude protein levels result in suboptimal performance (Nyachoti et al., 2006, Wellock et al., 2006).
Lowering dietary protein as a means of maintaining gut health is mostly relevant in the period immediately post weaning. As the pig matures its tolerance improves and the need to contain protein levels for this purpose wanes. Nitrogen loading of the environment is an independent consideration.
Raw material quality
Modern NIR technology now allows us to know more detail than ever before about raw materials. This technology should be utilized to ensure that we meet the nutrient requirements as best we can. We can even obtain full amino acid profiles for grains, soya and canola which detail the digestibility. Fiber profiles on grains are also useful to determine the amount and type of enzymes to use.
Avoiding contaminants like mycotoxins which cause health challenges, gut irritation, immune suppression, and inflammation are also import. Rapid testing for mycotoxins is a valuable tool the industry should utilize.
Conditionally essential nutrients
There are a number of nutrients which have important roles in health, immunity and gut function at critical times. These nutrients include glutamine/glutamate, arginine, vitamin E, threonine, tryptophan and sulfur amino acids (cysteine + methionine).
Glutamine/glutamate is an important nutrient for gastrointestinal maintenance and function. Sow’s milk is rich in free glutamine (21%) and glutamate (9.8%) (Wu and Knabe, 1994). Glutamine is the only free amino acid which is known to increase as lactation progresses (Wu and Knabe, 1994). However piglet feeds (especially low protein diets) can be deficient in glutamine relative to sow’s milk. Supplementary glutamine has been shown to prevent villus atrophy, enhance feed intake and feed efficiency as well as maintain antioxidant status in weaner pigs (Watford, 2015). Supplementation in lactating sows has been shown to improve the transfer of glutamine to piglets via milk and reduce body weight loss in sows (Watford 2015). Supplementation of glutamine and glutamate in late gestation and lactation has been shown to improve the lipid content of colostrum and milk (Bignell, 2014).
Arginine is an important nutrient for maintaining the gastrointestinal tract and also in injury healing (Wu et al., 2009). Arginine is important for innate and acquired immunity and sufficient arginine is required for defense against viruses, bacteria, fungi, protozoa and parasites. Supplemental arginine has been shown to enhance cellular and humoral immunity in early weaned pigs (Tan et al., 2009). Supplemental arginine (1%) has been shown to improve body weight gain and feed conversion in newly weaned pigs (He et al., 2009). Arginine supplementation has been shown to maintain gastrointestinal integrity and reduce the incidence of diarrhea when included at modest (0.7%) rather than high levels (1.2%, Zhan et al., 2008). Arginine is commonly in excess in the diets of pigs relative to the requirements recommended for efficient lean growth. However, research outcomes suggest that arginine may be conditionally essential to piglets during the acute post weaning phase especially if glutamine is limiting.
Threonine, tryptophan and the sulfur amino acids are required to support immune responses in the face of health challenges and poor sanitation (Capozzalo et al., 2015, Kim et al., 2012, Van der Meer et al., 2015). It is estimated that the requirement of these amino acids may be up to 20% higher relative to lysine during challenge events.
Gut stability in adult pigs
A stable gut environment is equally important in adult pigs. Disturbances to the microbial balance in the gut can lead to discomfort and compromise performance and in extreme instances death. Some of the factors which can destabilize the gut include:
a) Feeding frequency – Irregular feed intake and in particular ‘out of feed’ events can be quite stressful to the gut. A lack of food in the gut can result in a decline in the gut architecture which results in a compromise to its digestive and absorptive function, leading to undigested material flowing into the lower bowel on realimentation. This increase in fermentable substrate can result in bacterial proliferation and a shift in the microbial balance leading to inflammation, gas production and endotoxin release. The symptoms that emerge are, twisted bowel, enterotoxemia, prolapse, diarrhea and commonly death.
b) Specific feed stuffs – sudden marked changes in the composition of the diets have the propensity to alter the microbial balance and create gastrointestinal stress. This is particularly for highly fermentable components such as wheat and legumes. Anti-nutritional factors in some feedstuffs can also be a source of gut irritation e.g. tannins, trypsin inhibitors, phytohaemagglutanins, alkaloids, mycotoxins, rancid fats, biogenic amines etc.
c) Particle size – Although fine grinding tends to improve the digestibility of feedstuffs it also increases the risk of gastrointestinal disturbances and damage (irritation, inflammation, keratinization, ulcers). Dietary fiber plays a key role in gut stability but fine grinding of fibrous components can remove much of their functional properties. In adult sows coarse grinding and/or mash feeding often promote gut stability.
d) Feed hygiene – Feed is a perishable item and needs to be managed to preserve its integrity. Whether feed is in bags or bulk silos it needs to be turned over regularly to prevent oxidation, purification, mold and mycotoxins, rodent damage and loss of vitamin potency. Precautionary addition of antioxidants, mold inhibitors or mycotoxin binders into the feed is recommended where the risk is apparent.
These factors can combine to magnifying the risk e.g. finely ground, pelleted, wheat based diets fed irregularly would be a high risk. By the time symptoms such as sudden death from twisted bowel emerge it is likely that a large proportion of the herd is uncomfortable and performing sub-optimally.
How heat stress complicates matters
When pigs experience heat stress they try to reduce the heat production by reducing their movement and reducing their feed intake. The body also redistributes blood flow away from the gastrointestinal tract to the outer extremities as a way to improve heat loss. These physical and metabolic responses to heat stress can potentially create gastrointestinal challenges. Altered passage rates of digesta, together with increased intestinal permeability can create opportunities for undesirable shifts in microflora, and increased absorption of toxins (Gabler and Pearce, 2015). Nutritional strategies should consider the physical and metabolic changes and adopt practices which minimize them. These include not only formulation to reduce the heat increment (less fiber and protein, more fat) and control of electrolyte balance but also the use of osmoregulators like betaine or marine kelps, the use of chromium or cinnamon to improve thermal tolerance and the use of appropriate feed additives to reduce the bacterial load (organic acids, phytogenics, yeast fractions) and support the vulnerable intestine with antioxidants like vitamin E, vitamin C, organic selenium, polyphenols (Cottrel et al., 2015). In-water application of nutrients (vitamins, minerals, acidifiers, electrolytes, peptides) is also worth considering to aid in maintaining gut integrity whilst the animals are off feed.
Formulating for optimal gut health is about understanding the physiological changes, immune development, environmental factors and the dynamic nutritional needs of the pig and how these factors interact. It is also about refining our nutritional approach to limit excessive nutrients and at the same time avoid nutritional deficiencies. There are a good selection of available raw materials which can be used in combination with good formulation practices to favorably manipulate the bacterial colonization of the gastro intestinal tract and ultimately support the immune development and response capabilities of the pig. Understanding the need for specific conditional essential nutrients at critical time points is also important to minimize the effects of environmental and health challenges.