Let’s bring the sow back to “balance”, Part 1

Let’s bring the sow back to “balance”, Part 1

Modern hyperprolific sows and their piglets face numerous challenges during their lives. Rearing a litter is not an easy task in itself, let alone with improved genetics resulting in increasing litter sizes, longer duration of farrowing, milk production being an issue, lower birth weight, decreased vitality of piglets and an increasing risk of stillbirths. However, we do have a tool to mitigate the challenges around farrowing: by adjusting the dietary electrolyte balance (dEB) of the gestation and lactating rations of the sow we can provide an optimum calcium supply, a nutrient of critical importance around farrowing.

Living organisms are characterised by the capability of adjusting to changes in the internal and the external conditions in order to maintain their biological stability. This is what we call homeostasis.
Homeostasis means maintaining certain variables within pre-set limits, with maintaining a stable ion concentration – including the concentration of hydrogen ions – in body fluids being one of these important variables. pH is the negative decimal logarithm of H+ ion concentration and is characteristic for the concentration of acids and bases. If the equilibrium is not maintained, it may lead to disruptions in the metabolic functions of the body (Aoi and Marunaka, 2014). pH disturbances might lead to loss of functionality in the immune system or the nervous system, affect enzyme activity and cause gastric ulcers or lesions in the stomach (Machida, 1981).

External factors such as feed can influence pH. Generally speaking high protein feed ingredients lead to higher acid production than high carbohydrate ingredients. Ambient temperature also influences pH. When the barn is overheated, at farrowing or in the summer periods of heat stress, animals start hyperventilating, which depletes the CO2 in the blood, potentially leading to respiratory alkalosis, meaning that the pH of the blood becomes more alkaline. The health status of the animal also affects pH, with vomiting and diarrhoea causing fluid and electrolyte loss. Diarrhoea is a common problem in pigs, leading to metabolic acidosis, a decrease in blood pH (Quiniou 2018).

Electrolytes play a major role in maintaining the pH, as well as the water and electrolyte balance of the body. Electrolytes are minerals found in body fluids that carry an electric charge. They dissociate into ions when dissolved in water. The electrical charge of the ions can be positive (cations) or negative (anions). Cations such as sodium (Na+), potassium (K+), calcium (Ca 2+) and magnesium (Mg2+) ions increase blood pH, while anions such as chloride (Cl), phosphate (PO4 3-) and sulphate (SO4 2-) decrease the pH of blood. When formulating diets it is important to consider the mineral composition, since it affects the performance of the animals significantly. Monovalent ions such as Na+, K+ and Cl ions are used most commonly to calculate the electrolyte balance.  More precise, but more complex calculations also include bivalent ions (SO4 2-), although this method requires more chemical analyses. The formula itself shows the balance between the positively charged cations and the negatively charged anions in the feed. The result is expressed in milliequivalents (mEq), as the expression of concentration per kg of feed dry matter. The result shows if the ions included in the formula will shift metabolic processes towards increasing or decreasing acidity. Feed with higher dEB values will shift metabolic processes in a more acidic direction by increasing gastric HCl production, while lower dEB levels in feed will increase NaHCO3 secretion of the pancreas (Babinszky and Halas, 2019).

Dietary electrolyte balance (dEB) is most commonly calculated by the following formula (Babinszky and Halas, 2019):

dEB (mEq/kg) = 1000 x [Na(g/kg)/23.0 + K(g/kg)/39.1 – Cl(g/kg)/35.5]

Adjusting the electrolyte balance of sow rations promotes calcium (Ca) mobilisation that influences colostrum production and the duration of farrowing. Sows will give birth to a minimum of 20 piglets, which puts strain on both the sow and the piglets, since the length of farrowing will increase with litter size. Prolonged farrowing requires more calcium to support uterine contractions, increased milk production leads to a higher risk of health issues such as MMA (metritis-mastitis-agalactia) syndrome, while the number of stillborn piglets increases and the average birth weight and vitality of the piglets is lower (Potthast, 2022).

When considering the physiological effect of calcium in the transition period, we can conclude that while feed intake decreases at farrowing, calcium requirement increases during and after farrowing because of the uterine contractions and the start of milk production (Gao et al., 2019). In order to meet increased calcium requirements, the sows need an adequate dietary calcium supply and also be able to mobilise calcium from the bones. Calcium mobilisation is a hormonally regulated process that is inactive during gestation and is activated 24-72 hours before farrowing (Fthenakis, 2022). This activation might be delayed in case of larger litters, leading to hypocalcaemia and consequently prolonged duration of farrowing, lower colostrum secretion and a delay in the start of milk production (Helvoirt-Kremers, 2015).

To promote calcium mobilisation from the bones, the electrolyte balance of the ration must be adjusted a week before farrowing. If possible, provide transition feed, or if technology does not allow it, pay special attention to not feed lactation rations any earlier than 5 days before farrowing, as the higher calcium level of the lactating ration will restrict calcium mobilisation and the hormonal processes.

Pregnant sows are transferred to the farrowing unit around day 110 of gestation. Farrowing usually takes place on day 117 from the day of insemination. Modern sow nutrition has adopted the concept of using transition feed in this period, which is unfortunately not an option in most of Hungarian farms where only one type of feed, lactation feed can be fed at the farrowing unit. This means that setting the proper electrolyte balance of gestation and lactation rations has become more important in meeting the calcium requirements of the sow.

Generally speaking, lactation rations must have lower dietary energy balance values per kg than gestation feeds (Quiniou, 2018). The sow must be able to fill up its calcium and phosphorus reserves in the bones by the time lactation comes, so it can rely on calcium mobilisation to supply enough calcium for supporting uterine contractions during farrowing and the start of milk production. A higher electrolyte balance compared to lactation feed can be achieved by providing a cation excess, since the positively charged ions will increase blood pH. This will trigger a reaction of the pituitary gland, as it will try to normalise blood pH, a process that will promote calcium storage in the bones. Lactation feeds, on the other hand, must contain less cations that anions. An anion excess will decrease blood pH, shifting it towards acidosis. So when sows begin to eat lactation rations following the transfer to the farrowing unit, the feed has a lower electrolyte balance than the previous gestation feed. Chloride content increases in the sows blood due to the lactation feed, which causes H+ ions, cations to be expelled from the cells. This shifts blood pH towards a more acidic value. To compensate this, the sow will release calcium from the bones to act as a buffer. This process, triggered by lowering the electrolyte balance of the feed, promotes calcium mobilisation from the reserves (bones) to support uterine contractions, quicker and easier farrowing, and a better induction of colostrum and milk production (Helvoirt-Kremers, 2015).

A lower electrolyte balance in lactation rations does not only lower blood pH, it also lowers urine pH, which can lead to a decrease in total bacterial count in the urine and a decreased risk of urogenital infections (Cheng et al., 2015).

Figure 1 displays results published by DeRouchey et al. (2003), indicating that using a feed with a lower electrolyte balance increased survival rates in piglets, as well as the number of piglets weaned.


The dietary electrolyte balance value (dEB) of the ration can be influenced by changing the ratio of the raw materials used. Table 1 shows sodium, potassium and chloride contents of various types of feedstuffs and the dietary electrolyte balance values calculated from these data. The results indicate that feedstuffs rich in protein are also rich in potassium, meaning that their electrolyte balance will be high, in comparison to the dEB values of cereals and by-products. Optimising dEB is a raw material and farm specific task, and using feed additives is an additional tool to achieve optimum values.


In summary we can say that optimising the dietary cation-anion balance of gestation and lactation sow rations plays a key role in supporting the health of the sows and mitigating the problems of the periparturient period. Optimising dietary electrolyte values contributes to a shorter the duration of farrowing, promoting uterine contractions, inducing the secretion of colostrum and milk, increasing the number of live born piglets and decreasing health issues in sows in the postpartum period, thus providing a good basis to swine breeding.

Our team at Bonafarm-Bábolna Takarmány Ltd. is committed to the concept of innovative sow and piglet nutrition. We take great care to provide the best advice and products that will increase the efficiency and the productivity of your operations. Our colleagues are always there for you, the partnership for us means working for your success also!


Babainszky és Halas (2019): Innovatív takarmányozás, Akadémiai Kiadó, pg. 124-129.
Potthast PhD (2022): Why is it important to shorten farrowing time?, Pig Progress, 14-09-2022
Fthenakis PhD (2022)- Parturient Paresis in Sheep and Goats, (Milk Fever, Hypocalcemia, Lambing Sickness), MSD Manual, Veterinary Manual
v. Helvoirt-Kremers (2015)-Don’t forget the sow’s electrolyte balance, All About Feed, Feed Additives, 25.02.2015.
M. DeRouchey, J. D. Hancock3 , R. H. Hines, K. R. Cummings4 , D. J. Lee, C. A. Maloney, D. W. Dean, J. S. Park, and H. Cao (2003)-Effects of dietary electrolyte balance on the chemistry of blood and urine in lactating sows and sow litter performance, Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
Gao , X. Lin , C. Xie , T. Zhang , X. Wu, Y. Yin (2019)-The time of Calcium Feeding Affects the Productive Performance of Sows, Animals, 4 May 2019; 9(6):337
Quiniou PhD (2018)-Electrolyte balance in pig and sow diets: an often forgotten feed formulation element, Swine Conference 2018, from Sow to Meat Quality – Presentation
Machida (1981)- a Study of Intragastric pH in Patients with Peptic ulcer–with Special Reference to the Clinical Significance of Basal pH value, Gastroenterologia, Japonica Vol. 16, No. 5, The Japanese Society of Gastroenterology
Aoi és Y. Marunaka (2014): Importance of pH Homeostasis in Metabolic Health and Diseases: Crucial Role of Membrane Proton Transport, Hindawi Publishing Corporation BioMed Research International, Volume 2014, Article ID 598986, pg 8.
S. Cheng, L. Wang, X.L. Chen, B.M. Shi , A.S. Shan (2015)-Effects of dietary electrolyte balance on the performance, plasma biochemistry parameters and immunoglobulin of sows during late gestation and lactationAnimal Feed Science and TechnologyVolume 200, February 2015, pg 93-101.

Fédra Borbély
junior product manager
Bonafarm-Bábolna Takarmány Ltd.


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