Ramón-Moragues, Adrián, Vaggi, Chiara María, Franch-Dasí, Jorge, Martínez-Paredes, Eugenio, Peixoto-Gonçalves, Catarina, Ródenas, Luis, López-Luján, Maria del Carmen, Marín-García, Pablo Jesús, Blas, Enrique, Pascual, Juan José, and Cambra-López, María
Simple Summary: This study aimed to evaluate rabbits' responses to the administration of six organic acids (OAs) through drinking water at three concentrations (pH levels). Animal drinking and feeding behaviour, pH evolution along the animal's gastrointestinal tract, and gastric pepsin activity were monitored in post-weaning rabbits for seven days. The screened combinations were used to identify the optimal OA candidates and pH values, while eliminating those that may exhibit early adverse effects in young rabbits. During our short-term assessment period, the OAs with the greatest potential for use in rabbit farming were formic acid, acetic acid, and citric acid at pH 4. However, further validation with a larger population of animals, and extending the duration of OA supplementation during the growing period could improve performance outcomes and enhance the modulation effect of the gastrointestinal environment. Organic acids (OAs) are employed in animal feed to regulate gastrointestinal disorders and diarrhoea thanks to their ability to modulate the gastrointestinal environment and their antimicrobial capacity. However, there is not enough evidence regarding the most adequate OA and its effectiveness in rabbit farming. Therefore, the aim of this study was to screen and evaluate the response of young rabbits to six OAs, administered via drinking water, at three different concentrations (pH levels). Organic acids (acetic, ACET; formic, FOR; propionic, PROP; lactic, LAC; citric, CIT; and butyric, BUT) were tested at three concentrations (pH 3, 4, and 5). A negative control (CON; non-acidified water) was also included. We used 240 weaned rabbits (28 days old) divided into 2 batches. In each batch, animals were randomly allocated to 1 of the 19 experimental treatments and were housed in group cages of 6 animals per cage, treatment, and batch. Among the 240 rabbits, an additional cage with 6 animals was included to determine the initial physiological state of the animals. All animals were fed with commercial pelleted feed throughout the whole experiment. The duration of the study was 7 days, until 35 days of age. At 31 and 35 days of age, in each batch, three animals per day and treatment were slaughtered. The pH of the digestive contents in the fundus, antrum, duodenum, jejunum, ileum, and cecum, as well as the gastric pepsin enzyme activity, was measured. Water and feed consumption per cage and individual body weight (BW) were recorded daily. The type and dosage of OAs affected water intake. ACET 3, PROP 3, and BUT 3 reduced water intake compared to CON, negatively impacting feed intake and weight gain. FOR and CIT acids led to the highest BW and weight gain at 35 days, compared to PROP, LAC, and BUT (p < 0.05); showing ACET intermediate values. While OAs had limited effects on gastric and small intestine pH, acidified water at pH 4 and 5 lowered ileum and caecum pH (p < 0.05) compared to pH 3. Acidified water at pH 4 showed the highest (p < 0.05) pepsin activity compared to pH 3 and pH 5. Considering the limited sample size and short-term assessment period of our screening test, the OAs with the highest potential for use in post-weaning rabbits were FOR, ACET, and CIT at pH 4. The selected combinations did not exhibit any early adverse effects in young rabbits. These results should be further confirmed in a broader population of animals. It would also be advisable to extend the application of OAs over longer periods to evaluate their effects throughout the entire growing period of rabbits. [ABSTRACT FROM AUTHOR]