The beneficial effects of probiotics on performance parameters of broilers have been demonstrated in previous reports. Jahanbani et al. (2016) investigated the effect of Enterococcus facium isolated from the intestine of Coracias garrulus and Lactofeed® probiotic on the carcass characteristics and performance indicators of broilers. Body weight values were higher in broilers receiving E. facium and Lactofeed®, and FCR was lower in birds that received probiotics in drinking water compared to controls. However, BWG and FCR in the present experiment showed a significant influence of treatment only in week 5 (data not shown). In addition, Jahanbani et al. (2016) observed that E. faecium and Lactofeed® decreased serum cholesterol and triglycerides, also increasing the antibody response against sheep red blood cells. The authors postulated that the ingestion of E. facium isolates or Lactofeed® probiotic in drinking water or by spraying increases the body weight and FCR, also improving the immune system function and the intestinal microbiota of broilers.
Poorghasemi et al. (2017) evaluated the effect of Lactofeed® probiotic addition in combination with different fat sources in the feed of broilers on performance, carcass characteristics, and lipid concentrations. Similar to our study, the authors observed no significant changes in BWG, FI, and FCR between controls and supplemented groups. Also, as found in this work, there were no significant changes between controls and probiotic-only supplemented groups in the fat content of breast, thigh, liver, heart, and abdomen. The complete digestion and absorption process of nutrients is fundamental for higher performance, and intestinal microbiota has an essential role in these activities. In this context, probiotics exert positive effects on the host health, as they improve gut microbiota by reducing the activity of pathogenic bacteria and, consequently, improving the FCR values (Poorghasemi et al., 2017). According to a review by Jadhav et al. (2015), several studies showed probiotics effectiveness in improving growth rates and body weight gain in broilers. They also observed positive effects on feed intake, as reported in this study. Other important findings were decreased mortality and possible reduction in cholesterol in the serum and in meat. However, the appropriate dose of probiotic is still a matter of discussion, taking into account the contradictory results on the effect of probiotics on carcass characteristics of broilers (Jadhav et al., 2015).
Islam et al. (2008) observed that the addition of 0.5% citric acid increased the BWG of broilers, when compared with the controls during weeks 0-5 of age, also increasing feed consumption at 2nd and 3rd weeks of age and providing higher feed conversion during weeks 0-5 of age. However, this treatment did not affect carcass characteristics, as observed in our study. The authors concluded that the dietary inclusion of 0.5% may increase the live weight gain and improve the feed conversion of broilers. In the present experiment, we found significant influence at week 1 for BWG and FCR in chickens receiving water supplemented only with citric acid. Citric acid can be an excellent alternative to growth promoters based on antibiotics, as it may improve the gut health, growth rate, feed efficiency, bone mineral content and density, and carcass quality (Islam, 2012), although more studies are necessary to clarify its mode of action and the best concentrations to be applied in commercial broiler operations. Islam (2012) reported that up to 6% citric acid may be added to broiler diets without hampering performance. Best performance parameters were observed with 0.5% and 0.75% citric acid in mash and commercial pelleted diets, respectivelly. Citric acid may also enhance non-specific immunity as well as antibody titers against Newcastle disease. Although addition of citric acid in drinking water may not affect performance, low doses may improve the intestinal health by decreasing the load of pathogenic bacteria and increasing mineral availability to birds. These effects can also compensate for the lower performance of broilers fed diets with reduced protein and energy levels. Accordingly, Khan & Iqbal (2016) found that ingestion of citric acid, whether in association with other organic acids, presented antimicrobial activity and good effect on the poultry gastrointestinal tract, also improving the digestibility of major nutrients, and stimulating the natural immune response.
Fascina et al. (2012) included phytogenic additives and organic acids in the diet of broiler chick, and evaluated their effects on the digestibility of nutrients, performance, and carcass characteristics of broilers. The authors also observed that organic acids alone or in combination with phytogenic additives improved broiler performance, when compared with broilers submitted to diets containing an antibiotic enhancer at 42 days of age, and improved carcass characteristics. According to Araujo et al. (2019), the lack of effect of the probiotic and/or organic acids added to feed can be associated with proper environmental conditions, good management practices, and quality of feeds. However, there is evidence that the inclusion of organic acids in the feed of broiler may influence gastrointestinal bacteria, reduce the counts of pathogens, and mostly control the development of some competitive bacterial species [16]. Therefore, the acidification of the diet inhibits this competition for nutritional factors and may possibly reduce the production toxic metabolites by pathogenic bacteria and increase the weight gain. Inhibition of potential growth of pathogenic bacteria in the diet and in the gastrointestinal lumen are also beneficial to host health (Hassan et al., 2010).
In the present experiment, supplementation with probiotics and citric acid did not affect any of the carcass characteristics, except for the total carcass weight of birds receiving probiotic and 0.2% of citric acid. Previous studies did not describe any effects of probiotics and/or organic acids on the carcass parameters evaluated. Barbieri et al. (2015) analyzed the effect of a probiotics and/or organic acids on the performance of broilers challenged by three Eimeria species. The authors found mild alterations in the microbiota and morphology of the intestines of broilers fed these supplements, but there was no significant change in the performance at slaughtering. In another report, the inclusion of organic acid significantly increased BWG, although no effect on this variable was observed on feed consumption and feed efficiency in different growth phases (Agboola et al., 2015). Moreover, a lower feed : gain ratio was observed in the negative control diet, although this parameter was significantly improved by organic acid and probiotics in the initial growth phase. In contrast, Araujo et al. (2019) concluded that supplementation with probiotic and/or organic acids resulted in lower performance of broilers challenged by Eimeria species (E. acervulina, E. maxima, and E. tenella), when compared with chickens receiving antibiotics.
In conclusion, supplementation of drinking water with probiotic Lactofeed® and 0.2% of citric acid significantly increased feed intake of Ross 308 broilers within the first 21 days, as well as their body weight after 42 days and total carcass weight at slaughtering. Although no significant changes were observed in other performance parameters, serum biochemistry and relative weight of organs of broiler from the treatments tested, water supplementation with probiotic and 0.2% of citric acid is a promising strategy to enhance growth performance in broilers.