Conjugated linoleic acid (CLA), has been shown to have protective effects against various diseases, such as obesity, arteriosclerosis, diabetes, chronic inflammatory diseases, and cancer. This fatty acid in ruminants results from two processes, biohydrogenation, which takes place in the rumen, and de novo synthesis, carried out in the mammary gland, and it has linoleic and α-linolenic acids as its precursors. The amounts of precursors in the diets of animals are related to the amounts of CLA in milk. In the literature review, it was found that the milk of cows fed fresh forage has a higher amount of CLA because they have a higher amount of linoleic acid and α-linolenic acid compared to other foods used in the diets of cows. The amount of CLA precursors in pastures can be increased through agronomic practices, such as nitrogen fertilization, and regrowth age. It is also a technique used to increase the amount of CLA in milk to obtain a greater benefit regarding its nutritional value.

The influence of essential oils (EOs) on gut microorganisms and broiler chicken production was evaluated through the systematic analysis of scientific reports. The present study was focused on the EO antimicrobial activity oriented toward broiler chicken production. There is a great biodiversity of plants, and various compounds with different biological activity have been isolated from them. The EO molecules extracted from plants have been employed recently in livestock feeding. Microbial resistance to antibiotics has led to their reduced use in animal production. To maintain competitive broiler chicken production with reduced antibiotic use, EOs have been explored. In broiler chickens, EOs are supplemented in the diet or drinking water to enhance weight gain and feed efficiency and reduce mortality. EOs are an alternative to antibiotics, and their research is dynamic in poultry production. The present review focused on the antimicrobial activity oriented to broiler chicken production. The search for information in databases used the terms “broiler chicken”, “essential oils” and combined them with the name of the plants. It was detected that the EO of Cinnamon bark or its compound cinnamaldehyde could reduce pathogenic bacteria in the digestive tract and improve intestinal morphology. Essential oils from Cymbopogon spp. and Origanum vulgare had an effect mainly against Gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella spp., and others, and against some Gram-positive bacteria, such as Staphylococcus spp., or yeasts, such as Candida albicans. Essential oils of Cymbopogon citratus acted against Salmonella. Citrus japonica affected Bacillus subtilis, Escherichia coli, and Salmonella typhimurium. Origanum EO improved the antioxidant status and gut health of chickens, while EO of Eucalyptus with carvacrol, thymol, and Citrus lemon improved the productive performance of broiler chickens; also, Citrus spp. reduced the number of oocysts of Eimeria and showed activity against Listeria monocytogenes, Staphylococcus aureus, and Pseudomonas aeruginosa. It is concluded that EOs are a sustainable alternative to antibiotics in the production of broiler chickens. Future research includes the standardization of EO from different plants and active molecules, as well as the interaction with other feed additives and their impact on the health and production of broiler chickens. In addition, safety for consumers and the environment must be considered.

This study evaluated the productive performance and carcass traits of broiler chickens during the warm season in dry tropical conditions. Two hundred, 1-day-old chicks were used. Birds were fed on reduced (RED) and standard (STD) diets, and two essential oils (EOs) levels, 0 and 200 ppm. The RED diets were formulated with 10% less energy and 10% less protein than STD diets. In the starter phase, weight gain was greater (p < 0.01) in birds fed STD than birds fed RED. In the starter phase, productive variables were not affected (p ≥ 0.14) by EOs. In the finisher phase, greater feed intake (p = 0.02) and higher weight gain (p = 0.04) were observed in chickens on STD. Feed conversion ratio was similar (p = 0.97) for STD and RED. Throughout this study (1–42 d), greater feed intake (p = 0.02) and higher weight gain (p < 0.01) were found in chickens on STD. Feed conversion ratio was similar (p = 0.51) for STD and RED. Broiler chickens on EO-supplemented diets had better feed conversion (p ≥ 0.08). Hot carcass weight was greater (p < 0.01) in birds on STD. Greater yields of leg-thigh (p = 0.01), back (p = 0.01), and wings (p < 0.01) were observed in RED. Carcass yields, breast yield, pH, and meat temperature were not influenced (p ≥ 0.14) by nutrient concentrations in the diet. Carcass evaluations were not affected (p ≥ 0.11) by EOs. Body temperature was lower (p = 0.03) in birds receiving RED, however EOs had no effect (p ≥ 0.22) on body temperature. For the length of the study, at 20:00 h, broiler chickens fed on RED diets showed lower (p = 0.04) body temperatures. In conclusion, broiler chickens were under heat stress during the study, and body temperatures were reduced in chickens fed on RED diets or with EOs. Diet modification or EO-supplementation may improve feed conversion, though RED diets may have a negative effect on weight gain or carcass values.