Two decades ago, during the 1980s, nutritionists became aware of the importance of so-called acid binding factors in the formulation of piglet creep and weaner diets. The story has advanced considerably since then. The consideration of formulating to achieve a negative electrolyte balance is now recognised to cover a wide spectrum of pig feeds, not merely those for young pigs.

Once the factors themselves had been quantified, the underlying theory was soon defined as the identification and manipulation of the acid binding or buffering capacity of the feed. A function of the ingredients used and their inclusion rate, this can be expressed as the amount of normal hydrochloric acid that would be required per unit of feed to establish and maintain a pH of 4.0 or less in stomach contents entering the duodenum.

The figure of 4.0 is significant because it is the pH level above which the pepsinogen/pepsin production in the animal’s digestive process slows down. Pepsin is the primary enzyme in protein digestion. With less of the enzyme produced, more of the protein in the feed stays undigested as it moves through the small intestine to the large intestine. The material thus provides nutrients for the multiplication of potentially pathogenic organisms that would otherwise be present in only relatively small quantities.

An increased pH level in the lower gut is also beneficial for this multiplication of pathogens. They invade the small intestine, where their toxic metabolic by-products are absorbed to cause disease symptoms such as those seen with acute E. coli infection. In other words, the enteric health of the pig should be better if its feed is more acidic than alkaline.

High performance

While nutritionists have progressed in establishing new parameters required for the formulation of ideal pig diets, the geneticists have also made rapid progress in selecting animals with ever-increasing performance potential. These high-performing pigs obviously require high-density diets in order to express their full genetic productivity.

But the increased levels of essential amino acids and minerals found in diets of high density raise the acid binding activity of the diet. It has a less acidifying effect and therefore greater possibility of causing disease problems.

Experience with high-performance animals during the recent past has shown that such problems are not only manifested during the weaner stage. They can also occur during the grower phase, in the form of symptoms including the so-called red gut associated with campylobacter infections.

The acid binding syndrome must be interrupted in order to prevent the feed’s pH level becoming critical. In simple language this means that the nutritionist must either add acidifiers to the diet or select a combination of ingredients of a more acidic (less alkaline) nature.

The second option -- that of selecting combinations of ingredients with low buffering capacity -- attacks the root of the problem, giving a more nutritionally correct and effective diet. The correctness of the diet can be calculated using acid binding capacity data or electrolyte balance information. These two concepts are closely correlated, since diets with a negative electrolyte balance have a lower buffering capacity than those with a positive balance.

Dietary electrolyte balance is estimated by calculating the difference in equivalent mass of cations and anions (positively and negatively charged electrolyte atoms/molecules) represented in the diet. A very simple, but rather extreme, example of negative electrolyte balance is the acid naturally present in the stomach. This is hydrochloric acid. Its formula of HCl shows that it is formed from the cation hydrogen (H) and the anion chlorine (Cl). Whereas H has a mass of 1, however, the mass of chlorine is 35 so the result is a negative balance of minus 34 - confirming that hydrochloric acid is extremely acidic!

By contrast, hydrochloric acid has a potassium salt in the form of potassium chloride (KCl) in which the electrolyte balance is positive. Since potassium has an equivalent mass of 39 compared with the 35 of chlorine, the balance is plus 4.

An assessment along these lines should be done of the dietary cation/anion difference of the pig’s feed. The aim is to achieve a negative balance in order to make more nutrients available to the animal while decreasing their availability to pathogens in the large intestine.

There are times when the feed formulation does not achieve the required negative electrolyte balance, such as can happen with very high density creep diets. The corrective action in that case would be to calculate an appropriate quantity of acidifier and incorporate it in the feed formula.

As greater demands are placed on the genetically superior pig’s performance, larger quantities of nutrients must be made available to the animal and metabolised by it. A limiting factor here is likely to be the volume of the gut, whether we are talking about the young growing pig of less than 60 kilograms in weight or the lactating sow suckling 10 or more vigorous piglets.

Lactating sows and gilts

Compared with the dietary needs of the growing pig, however, the requirements of the lactating sow or gilt are a little more complex. They look simple enough at first, in that the assurance of optimum availability for the nutrients in a high-density lactation diet is again obtained by using negative electrolyte balance formulation techniques. But these should be integrated with measures to avoid the sow’s blood-sugar level reaching an unnecessarily high peak immediately after feeding. High blood sugar levels at farrowing result in piglets that do not feel hungry and are therefore less active in their search for a teat and the vital initial colostrum.

It is an important consideration both in the heavily pregnant sow and in one that has newly farrowed. There have been good results from the pre-farrowing introduction of lactation diets that comply both on electrolyte balance and on blood-sugar factors. It has simplified the management of feeding in the farrowing house and at the same time has led to heavier litters at weaning.

For a high-density lactating diet to be also used as a pre-farrowing ration, it must comply with the following requirements:

(a) Digestible energy should be at least 14.3 mJ per kilogram;

(b) The total fat level should exceed 55g per kilogram --- i.e. the ratio between fat-derived and carbohydrate-derived energy should be narrowed;

(c) The feed should include180mg of trivalent chromium (as chromium-picolinate or nicotinate) per metric ton, as an insulin extender;

(d) Pre-farrowing females should be fed the diet for at least six days prior to their expected farrowing date;

(e) The pre-farrowing sow’s daily allowance should not exceed the equivalent of 40 mJ DE (approximately 2.75kg of total feed). Sows with a condition score in excess of 3.5 and all gilts should receive not more than 2.25kg daily.

(f) Preferably, the daily allowance should be split equally between two feeds, most likely given in the morning and late afternoon.

Pre-farrowing use of a diet that complies with the above recommendations meets the demands for a laxative feed which will not induce high blood sugar levels in the sow and her unborn foetuses. The high fat/oil level gives soft slightly loose dung three days after commencement of feeding. It also combines with the insulin extending effect of the chromium to maintain relatively steady blood sugar levels so that newborn piglets are active and enthusiastic sucklers.

By using this type of lactation diet pre-farrowing, the sow and her gut microflora are already adapted before birth of the piglets, so her appetite and milk production increase steadily from day one of lactation.

Critics of this practice often suggest the alternative of a low-energy feed, bulked with an equivalent mass of bran or other fibrous material to give an alleged satiation effect and so make the sow less hungry and more restful. Observation of several thousand farrowings during the past decade has shown no difference in a sow’s pre-farrowing behaviour when fed the recommended lactation diet or the low-energy pre-farrowing diets. A major disadvantage of the low-energy/high-bulk diet is the combination of the increased fibre and, in particular, potassium levels associated with the bran inclusion. They give rise to major changes in gut micro-organism populations and a decrease in the negativity of the electrolyte balance. This in turn leads to a longer period being needed for the sow to adapt to the lactation diet when it is introduced.

When used pre-farrowing, however, the high-density lactating diet must have a negative electrolyte balance of at least 10meq/100g and comply with all requirements (a) to (f) listed above. Lactation performance and the need to use only one feed in the farrowing house are the main benefits.