Butyrate Supplementation for Swine (Part 1)
Continuing from our previous article discussing the various types of sodium butyrate supplementation for poultry and essentially choosing the right one for your needs, this article serves to be a guide towards choosing a suitable type of butyrate add additive for swine.
Before we move on, it should be acknowledged that the gastrointestinal tract (GIT) of swine is much longer compared to poultry. Furthermore, piglets have a much shorter GIT compared to grower/finishers, sows and boars causing the relative retention times (RT) of corresponding GIT positions to differ greatly. The small intestine of a newborn pig is about 2 to 4 m long and will grow to 16 to 21 m by the time they reach full maturity. In the first 10 days of life, pig's intestines are said to increase 80% in length and 30% in diameter thus doubling their absorptive capabilities. However, the relative pH of the corresponding GIT positions will not differ by much. Keeping that in mind, this article discusses the importance of product releasing site for uncoated and coated butyric acid products and the effects they bring to the animal.
Which type of butyric acid is for my pigs?
There are currently many types of butyric acid feed additive available on the market, we have butyrate salts, mono-, di- and triglycerides. Amongst the butyrate salts, there are coated and uncoated versions with different coating technologies or internal structures. The efficiency of sodium butyrate, calcium butyrate and tributyrin, depends upon the pKa value of butyric acid and pH of the corresponding part of the digestive system. At a pH of 4.82, butyric acid remains in equilibrium between butyric acid, and butyrate and hydrogen ions. If the pH of a medium is less than the pKa value of butyric acid, most of the molecules of butyric acid remain un-dissociated. It is important to understand pKa because butyric acid and butyrate exerts different functions in the intestines, and it allows us to understand how butyrate salts or esters work in the animal’s body.
In terms of choosing a butyric acid additive the most common question asked is “Which is the best?”. Honestly, “the best one” depends on your needs and if the product can release butyric acid at your desired releasing site to exert your desired effects. In the following discussion, we will categorize the butyric acid feed additives into unprotected and protected (fat coated) forms whereas tributyrin is categorised in the protected form because it mainly works starting the small intestines.
Swine feed retention times
Before moving on to understanding the actions of protected and unprotected sodium butyrate in swine, we should establish an understanding of the feed retention times and relative pH of the different segments of the pig gastrointestinal tract (GIT). This allows us to deeper understand the bioavailability of butyric acid as it travels in the GIT. The gastric retention time (RT) has been reported to be 1.5-6hrs in pigs and the pH ranges from 2 to 4 (Davies et al., 2001; Henze et al., 2018). Therefore, for any form of butyric acid supplementation to target only the hind intestines, it needs to be able to withstand 1.5-6hours of acidic conditions within the stomach before moving on to releasing butyric acid in the small and large intestines.
What happens when different types of butyrate are ingested?
Unprotected sodium butyrate:
- Butyrate salt starts dissolving and forms butyric acid after ingestion.
- The stomach has an acidic pH; thus, it allows butyric acid to stay in its un-dissociated form. Butyric acid modulates MUC gene expression in goblet cells which improves the properties of the mucus layer thus improves the protection of the stomach! At the same time parietal cells expression is also improved allowing in increase in HCl secretion thus improving the digestion and acidity in the stomach. In grower, finishers, sows and boars, the stomach food retention time is much longer, thus the bactericidal effects of undissociated butyric acid can reduce the bacterial load that moves into the small intestines and proximal colon of the swine.
- When the left-over butyric acid enters the proximal small intestine, it will dissociate into butyrate and hydrogen ions. Here, butyric acid is readily absorbed by enterocytes via passive diffusion and used to increase villus length and cells turnover. It should be noted that since piglets have a much shorter GIT length, the butyric acid that flows into the proximal small intestines could be much more compared to a more mature animal.
- Due to the higher pH in the small and large intestines, butyric acid becomes dissociated into butyrate ions which can be absorbed as a source of energy as well, which require different methods for their absorption.
→ Via diffusion
→ Via HCO3- exchange method
→ Via active transport (MCT1 & SMCT1)
Coated butyrate is usually used in older pigs such as growers, finishers, sows, and boars. The reason behind this is simply because the digestive tract of older animals is much longer compared to younger animals and the feed retention time in the stomach is much longer. Unprotected butyric acid would have mostly exerted its effects in the stomach due to the longer stomach feed retention times leaving less butyric acid to exert effects in the small intestinal and the hindgut.
One study showed that supplementing 6-week-old piglets with 800mg/kg sodium butyrate had a significantly higher ADG on the first 14 days post treatment, but the advantage did not carry on through to 56 days of treatment (Piva et al., 2002; Table 1). This is because cell proliferation occurs more actively during the early weaning period when the small and large intestines are rapidly increasing in size (Sakata and Setoyama, 1997).
Protected sodium butyrate:
Protected forms of butyrate usually refer to butyrate salts coated with vegetable fat or esterified forms such as tributyrin or monobutyrin.
- Protected forms of butyrate usually prevents butyric acid from being released earlier on in the digestive tract (i.e., the stomach) and allows for slow release of butyric acid starting the small intestines as its’ outer coating is broken down by lipase, releasing the inner contents of butyrate salts. Although there are some gastric lipase activities in the stomach, its total activity is much lower compared to pancreatic lipase (Jensen et al., 1997; Liu et at., 2001). Butyrate salt that is exposed starts dissolving and forms butyric acid.
- Butyric acid released in the proximal small intestine dissociates into butyrate and hydrogen ions because the pH of the small intestines is higher than the pKa of butyric acid. Here, butyric acid is readily absorbed by enterocytes via passive diffusion and used to increase villus length and cells turnover.
- From here on, the mechanism is similar to unprotected sodium butyrate (4).
Targeted release of butyrate in the small intestines and hindgut allows for increased villi proliferation and differentiation which improves intestinal integrity. It allows for increase of villi to crypt ratio which translates to increase in absorption efficiency and lesser energy demand for cell turn overs.
When comparing the effects of protected sodium butyrate and monobutyrate glycerides on 21-day-old piglets, Mallo (2012) found no differences in growth performance (Table 2) but higher concentrations of butyric acid and VFA in the colon of protected sodium butyrate fed animals. This suggests that both protection techniques lead to similar growth performance results.
Gastrointestinal disturbances during pre and post weaning conditions cause large economic losses in pig industry. Naturally, piglets are usually weaned at around 12-17 weeks old, but for commercial producers to push for reproduction and economical productivity, piglets are instead weaned much earlier at 3-4 weeks old. The weaning transition is a complex period during which the piglets must cope with many stress factors such as separation from their mother, mixing with other litters in a usually new environment and turning over to a less digestible solid creep feed from highly digestible liquid milk. The situation remains same when the new-born piglets are offered with solid creep feed from the 10th day after birth. Weaning exacerbates the level of general stress in these immature animals. When not managed properly, the weaning stresses result in low feed intake, body weight loss, high incidence of diarrhoea and even lead to death and economical loss to the producers.
To be continued...Watch this space for PART 2.
By Kayla Wong, Technical Specialist, Manuka Biotech