The microflora of the digestive tract in poultry has not been fully characterised. The withdrawal of antibiotic growth promoters (AGPs) resulted in increased interest in the role of microflora of the digestive tract and its control, particularly in birds exposed to feed containing alternatives to AGPs. We studied the effects of a feed complement (Lactobacillus spp.) on broilers, from the farm and during processing. Growth and feeding (feed intake, daily body weight gain) were monitored regularly. The levels of digestive flora in the caeca of animals were monitored throughout the trial as follows: total coliforms, Clostridium perfringens, Enterococcus and lactic acid bacteria during the breeding period; thermophilic coliforms, Staphylococcus aureus, Pseudomonas and lactic acid bacteria during processing. Samples were taken from neck and thigh skins. Pseudomonas and lactic acid bacteria were counted twice, i.e.: the day of slaughter and seven days after chilling at 4 °C to assess the effect of the product on the shelf life of chicken meat. No significant effect of the lactic acid feed supplement was found among the bacteria studied in caecal samples. The lactic acid feed supplement did not modify the bacterial count in animals at the processing plant level. It had no positive effect on the shelf-life duration of the products. Our findings showed a significant improvement in growth performance (P=0.049) for broilers receiving 105 cfu/ml of the lactic acid strain. At this concentration, the product had a positive effect (P=0.031) on the health of the birds, tending to prevent diarrhoea in the first days of fattening. We did not detect any significant effect of the higher (106 cfu/ml) concentration.