The Feed Acidifying Power Database (NIC2025) has been updated! A further advancement in the digestive system for precise acid use! (Part 1)

Weaning is a critical stage in the growth and development of piglets. As is well known, for economic reasons, early-weaning strategies are commonly employed in swine production ( 25 or 28 age in days). However, during the entire nursery phase, the piglets’ digestive system is not yet fully developed; gastric acid levels cannot be maintained at the lactational (high-lactose fermentation) level, and pepsinogen cannot be efficiently converted into pepsin. This results in incomplete protein digestion and subsequent digestive dysfunction. Undigested proteins entering the intestine allow opportunistic pathogenic microorganisms to proliferate excessively, disrupting the intestinal microecological balance, damaging the small intestinal mucosal barrier, and causing an imbalance in small intestinal water and electrolyte metabolism, leading to increased water content in the chyme. On the other hand, insufficiently digested proteins that reach the hindgut continue to undergo putrefaction, producing harmful substances such as amines that injure the colonic mucosa, impairing the colon’s water reabsorption function and further increasing the water content of the chyme, ultimately resulting in fecal moisture content exceeding 20% , i.e., the observed symptoms of diarrhea. NIC (Acid Innovation Center) research has found that during the rearing phase, undigested protein in the intestine accounts for 40-60% The origin lies in the inactivation of pepsin, which is associated with 40% Chyme in the stomach pH higher than 4.0 consistent with the observations ( n=100 ) ( NIC ， 2022-2024 Unpublished data).

Although in terms of physical length, the small intestine accounts for 60-70% , the large intestine accounts for 20-30% , the stomach seems to occupy a negligible part 3-5% , but from the perspective of volume, the stomach's capacity is comparable to that of the large intestine and is approximately equal to the total capacity of the small intestine. 60-80% Moreover, pepsin—the major enzyme system for protein digestion—is also present in the stomach, yet the stomach’s role in gut health is largely overlooked in practical piglet rearing and nutrition! Therefore, under antibiotic-free conditions, maintaining gastrointestinal health in nursery piglets hinges first and foremost on preserving normal gastric function.

As previously mentioned, the primary cause of nutritional diarrhea in weaned piglets is insufficient gastric acid secretion due to delayed stomach development after weaning. Solutions include using highly digestible ingredients, reducing dietary protein levels, or employing therapeutic antibiotics and vaccines at the farm level; historically, the most convenient and cost-effective approach was direct antibiotic supplementation in feed. However, growing concerns about food safety and human medicine risks stemming from antibiotic residues and bacterial resistance now threaten public health and production, prompting China to ban antibiotics in feed during the 14th Five-Year Plan period and further reduce their use in animal husbandry by the 15th Five-Year Plan. Consequently, the role of antibiotics in the livestock industry will continue to diminish.

The effectiveness of formulating nursery pig diets lies in maximizing weight gain potential, reducing diarrhea, and ensuring economic feasibility. High‑digestibility protein ingredients typically command higher purchase prices; however, lowering the total protein content may hinder the full realization of production potential. Therefore, selecting protein ingredients with appropriate digestibility and enhancing gastric protein digestibility through the exogenous addition of acidifiers have become trade-offs considered by nutritionists. The number of acidification agents is also used from AGP of the time 1-3kg/T Promoted to prohibited use AGP period's 3-5kg/T , both the European Union and China’s current feed industry follow broadly similar patterns.

The main components of acidifiers used in the feed industry are medium-strength acids such as lactic acid, citric acid, and formic acid ( pKa Between 3.0-5.0 Inside) , Because the digestion of dietary protein results from the combined action of four major enzyme systems—pepsin, trypsin, chymotrypsin, and carboxypeptidase—common acidifiers primarily target the stomach to maintain a normal digestive environment there. In contrast, due to factors such as bile, the normal conditions in the pig’s intestinal tract are... pH It is in 5.5-7.0 Fluctuations: Conventional doses of acidifiers rarely affect intestinal pH fluctuations by more than 10% Therefore, the primary nutritional role of acidifiers is to facilitate protein digestion in the stomach, while protein digestion in the small intestine is hardly directly affected by acidifiers. Consequently, acidifiers can serve as a major facilitator of gastric protein digestion, particularly during the nursery phase. Due to advances in acid–base theory, the scope and implications of acidity are continually expanding; Acid Innovation Center ( NIC ，2021 ) argues that the new type of acidifying agent is not based on the amount of hydrogen ions it provides, but rather on its electron-accepting capacity under broader conditions; therefore, these novel acidifiers possess new functions such as improving digestibility, inhibiting and killing bacteria, reducing inflammation and oxidative stress, and decreasing viral load. Conventional acidifiers are primarily intended to support protein digestion in the stomach; thus, NIC It is suggested that replacing the concept of “chemical (acidifier)” with “functional (digestive) acid” may be more accurate, while also distinguishing the functions of intestinal acid preparations: specifically, the primary function of intestinal antibacterial acids is to inhibit bacteria, which differs from digestive acids. Classical acidifiers are often conflated conceptually, making it difficult to differentiate the functional roles of acids in the stomach and intestines, thereby hindering the precise application of acids.

Reasonably incorporating digestive acids into weanling pig diets can increase gastric acidity; from a formulation perspective, selecting an appropriate acid-binding capacity is crucial—data-driven approaches are key.

Acid-binding capacity: This refers to the ability of a diet to bind acids, representing the buffering capacity of a given mass of feed against acidic substances. It is expressed as the amount of acid bound by the feed and thus reflects the diet’s acid–base balance; consequently, it is also known as dietary acid neutralization capacity, acid buffering capacity, or acid-binding coefficient. Both domestic and international researchers have primarily focused on dietary acid-binding capacity in weaned piglets, with particular attention to the optimal conditions within their stomachs. pH The scope is 3.0~4.0 , therefore, the dietary acid-binding capacity of piglets is usually defined as the amount required to 100 kilogram feed pH The value drops to 4.0 The millimoles of hydrochloric acid required.

Testing method: Take evenly 100g Air-dried sample, ground through 60 Eye, add 200mL Distilled water, stir evenly with a glass rod and soak at room temperature. 20 minutes, then heat in a constant-temperature water bath to 37 ℃ Remove and place on a magnetic stirrer; maintain the temperature at during stirring. (37±1)°C Within, will pH The working electrode is inserted into the solution, and then use 1mol/L Titrating with hydrochloric acid while stirring, and recording. pH The value is 4.0 (or 3.0 The volume of hydrochloric acid consumed at that point is then converted into millimoles of HCl, which represents the acid-binding capacity of the feed sample.

( 1 ) Reduce the acidity in the piglet's stomach pH value, improve the digestibility of weaned piglets’ diets

Compared with adult pigs, the gastric environment of piglets is pH Values are usually high, overall NIC ( 2021-2024 ) The study found that, 60 Among piglets of a certain age, there are 40% Chyme one hour after eating pH Value greater than 4.0 . Pepsin is essentially an enzyme that functions at low pH Proteases that are active in the environment, the activity of pepsin is dependent on the environment pH It is extremely sensitive and rapidly inactivated under neutral or slightly alkaline conditions; only when exposed to a suitable acidic environment does the zymogen convert into an active enzyme, with its optimal pH For 1.0-3.0 , if in the stomach pH > 5.0 , resulting in an abrupt loss of most activity. To address these issues, adding digestive acids to the diets of weaned piglets is an effective strategy, and identifying optimal digestive acid formulations will become another research focus for precision nutrition in the industry.

( 2 ) The composition of digestive acids and the dosage of additives affect gastrointestinal microbial balance.

Piglets have limited digestive capacity; undigested dietary protein in the stomach ferments in the intestine, producing ammonia and toxic polyamines, which raise intestinal pH. This pH The changes disrupted the gut’s normal microecological balance, notably inhibiting the growth of beneficial bacteria such as lactobacilli. At the same time, it favored a neutral environment ( pH value 6~7 However, various pathogenic microorganisms such as Escherichia coli, Salmonella, Staphylococcus, and Clostridium can proliferate rapidly, and the growth of these pathogens can lead to diarrhea in piglets. In addition, NIC It was found that formic, citric, and fumaric acids exhibit strong inhibitory effects on both harmful and beneficial bacteria; in contrast, lactic and phosphoric acids demonstrate relatively better digestive acidification, effectively suppressing harmful bacteria while still allowing a large population of beneficial bacteria to survive. Therefore, optimizing the type and composition of digestive acids can help restore intestinal microecological balance, thereby reducing diarrhea and mortality in piglets.

The preceding article delved into the critical role of the gastric digestive environment, the functional significance of digestive acids, and the quantitative implications of acid-binding capacity. The next installment will focus on the progress in developing the Acid-Binding Capacity Database (NIC2025), the characteristics of acid-binding capacity across various feed ingredients, and strategies for its application in weaner pig diets. Stay tuned!

Written by: Kuai Yunyi

Hu Youjun

Zhao Xiaonan

Wen Wei

Review: Hu Youjun