Abstract
Background: Antibiotics have been used to maintain animal welfare and improve efficiency for more than 50 years. Recently, the presence of antibiotics was found in the muscle, liver, and kidney of guinea pig carcasses for sale for human consumption, which is a public health issue. Probiotics are supplements of live microorganisms that, administered in adequate doses, could replace growth-promoting antibiotics.
Aim: This study analysed the effect of the administration of an oral probiotic mixture on the productive performance of guinea pigs (Cavia porcellus).
Methods: Fifty male guinea pigs, weaned at 14 days of age, were distributed in a completely randomised design of five treatments with 10 repetitions each. The treatments were: CONTROL, without probiotic; PROB 1, 1 mL of probiotic; PROB 2, 2 mL of probiotic; PROB 3, 3 mL of probiotic; and AGP, 300 ppm zinc bacitracin. The microorganisms used in the probiotic were Enterococcus hirae, Lactobacillus reuteri, L. frumenti, L. johnsoni, Streptococcus thoraltensis, and Bacillus pumilus. Productive parameters were evaluated from weaning to 70 days of age.
Results: No statistically significant difference was found between the treatments on forage DMI, concentrate DMI, or total DMI (p>0.05). Similarly, no statistical difference was found between the treatments in terms of final weight or weight gain (p>0.05). Regarding the feed conversion ratio, there was a significant difference between treatments (p=0.045); the CONTROL group had the highest feed conversion ratio, followed by the AGP group, with the best feed conversion ratio observed in the PROB 3 group (p<0.05). In addition, significant statistical differences were found between CONTROL and PROB 2 (p<0.05). Likewise, a significant linear effect of increasing doses of the probiotic was found (p=0.01), which indicated that the feed conversion was better with a higher dose.
Conclusion: The treatments evaluated in this study had a significant impact on the feed conversion ratio in guinea pigs for fattening. Increasing doses of probiotics had a linear effect on feed conversion ratio.

Key words: antibiotic growth promoter, guinea pig, probiotics, productive parameters