A team of researchers from the State University of Santa Catarina, the Federal University of Santa Maria and the Federal University of Rio Grande do Sul in Brazil explored the use of glycerol monolaurate (GML) or lauric acid as an alternative to antimicrobial use in the diets of broiler chickens.
The group published the research in Microbial Pathogenesis.
“The aim of this study was to evaluate whether [the] addition of GML as replacement for antibiotics has positive effects on health and performance of broiler chickens,” the researchers said.
They found that birds receiving the largest amount of supplemental GML – T300 – had higher body weights, daily weight gain and total weight gain than those on the control feed. The group also had the best feed conversion ratio (FCR).
Chicken receiving the GML supplemented diet T300 also showed reduced amounts of Eimeria spp. oocysts compared to the control, they said. Plasma total protein levels, globulins, uric acid and glucose were increased for birds on the GML-inclusive diets compared to the control.
“GML can be a molecule capable to replace zinc bacitracin, one of the most [widely] used antimicrobial agents [in] the Brazilian poultry industry,” the researchers said. “The antimicrobial and anti-parasitic actions of GML improved animal health and influenced positively the weight gain in the termination phase.”
Adding 300 mg/kg GML to the feed benefited production and improved growth performance, they added.
Improving production, replacing antimicrobials
The poultry industry has a continuing interest in finding feed additives that boost animal productivity and product quality while supporting zootechnical performance and lowering production costs, they said.
Adding sub-therapeutic amounts of antimicrobial drugs to broiler chicken diets is a common practice in the production industry, they said. “The beneficial effects of such practice on animal production are linked to improvement on weight gain and feed conversion, and reduction on animal mortality,” they added.
However, there is an increasing concern about the use of small amounts of antimicrobial drugs in animal feed generating a risk for human health with the emergence of bacterial resistance to antimicrobials, said the researchers. There also are concerns about the potential presence of residues in poultry products, which could provoke allergic reaction and toxicity.
Why glycerol monolaurate?
Several non-medicated additives have been explored to replace the use of antibiotics in animal feed following public campaigns to ban the use of antimicrobials in poultry production, the researchers said.
Past research with glycerol monolaurate (GML) found that the additive demonstrated an antimicrobial property when added to piglet diets, they said.
“GML is a monoester with 12 carbon atoms formed by the combination of glycerol and lauric acid, possessing a large range of pharmacological properties, such as bactericidal, fungicidal, and virucidal. GML is recognized as a food safe emulsifier (GRAS) approved by Food and Drug Administration (FDA), being considered a non-toxic compound even at relatively high dose levels.”
However, most work with the additive focused on its potential as a food preservative, they said. Little is known about its use as an animal feed additive.
Feeding trial details
During the 42-day feeding trial, 240 day-old broiler chicks received one of four diets, the researchers said.
The diets included a corn and soybean meal basal diet, they said. The control group received the basal diet with 60ppm of the antibiotic zinc bacitracin and 80ppm of the coccidiostat salinomycin through day 35 (T0), and the experimental feeds included the basal diet, salinomycin through day 35, and one of three levels of GML at 100, 200 or 300mg/kg – diets T100, T200 and T300, respectively.
Birds were weighed on days 1, 7, 21, 35 and 42 of the feeding trial, they said. Daily weight gain (DWG), feed consumption (FC) and feed conversion were calculated at the end of the period.
Fecal samples were collected on days 21 and 42 for bacteriological and parasitological analysis, the researchers said. Blood, kidney, liver and intestine samples were taken on day 42 for analysis and histopathology.
Total carcass weight was noted and breast muscle was evaluated for meat parameters including pH, color and water retention, they said.
Birds on the T300 diet had a higher body weight than those on the control diet at day 42, the researchers said. The birds also had better weight gain and average daily weight gain along with a lower feed conversion compared to the control.
“Regression analyses revealed that 300 mg/kg GML was the dose that animals expressed the maximal performance,” they said.
No significant difference in mortality was noted during the trial, they said.
Birds getting the GML feed additive presented lower numbers of oocysts on day 42 compared to control group birds, the researchers said.
“It is important to emphasize that animals supplemented with GML on the diet until 42 days of life remained with low levels of oocysts eliminated on feces (T100) or ceased the elimination (T200 and T300), which suggests that GML can interfere on parasite multiplication in the intestine. However, this mechanism remains unknown.”
Total bacterial and E. coli counts were similar for all birds by day 42, they said.
“No significant difference was observed among groups regarding erythrocyte and leukocyte counts, hematocrit level, and hemoglobin concentration, as well for lymphocyte, heterophil, monocyte, and eosinophil counts,” they said. “No significant difference was observed among groups regarding serum levels of albumin, triglycerides, and cholesterol at each evaluated period.”
Birds on the GML diets did display higher serum levels of total protein than those on the control diet, they said. Birds receiving the T300 diet had higher serum globulin levels, those on both the T200 and T300 diets saw higher serum glucose, and serum uric acid levels were increased for birds on the T100 and T300 feeds.
Birds receiving the T100 diet had superior carcass yield for the breast cut, the researchers said. However, results were similar for all birds for the weight of carcass, leg, wings, back and perineal fat, pH and color.
Water retention capacity was reduced in the breast muscle for chickens on the GML-supplemented feeds, they said.
No hepatic or renal lesions were found in any of the birds, however, some gut fragments presented immature forms of Eimeria, they said. “Parasite oocysts were observed in the intestinal lumen only in groups T0 and T100,” they added.
Source: Microbial Pathogenesis
Published online ahead of print: doi.org/10.1016/j.micpath.2019.02.005
Title: Glycerol monolaurate in the diet of broiler chickens replacing conventional antimicrobials: Impact on health, performance and meat quality
Authors: B. Fortuoso, J. dos Reis, R. Gebert, M. Barreta, L. Griss, R. Casagrande, T. de Cristo, F. Santiani, G. Campigotto, L. Rampazzo, L. Stefani, M. Boiago, L. Lopes, R. Santos, M. Baldissera, R. Zanette, T. Tomasi, A. Da Silva