The performance, carcass traits, and litter humidity of broilers fed increasing levels of glycerine derived from biodiesel production were evaluated. In this experiment, 1,575 broilers were distributed according to a completely randomized experimental design into five treatments with seven replicates of 45 birds each. Treatments consisted of a control diet and four diets containing 2.5, 5.0, 7.5, or 10% glycerine. The experimental diets contained equal nutritional levels and were based on corn, soybean meal and soybean oil. The glycerine included in the diets contained 83.4% glycerol, 1.18% sodium, and 208 ppm methanol, and a calculated energy value of 3,422 kcal AMEn/kg. Performance parameters (weight gain, feed intake, feed conversion ratio, live weight, and livability) were monitored when broilers were 7, 21, and 42 days of age. On day 43, litter humidity was determined in each pen, and 14 birds/treatment were sacrificed for the evaluation of carcass traits. During the period of 1 to 7 days, there was a positive linear effect of the treatments on weight gain, feed intake, and live weight gain. Livability linearly decreased during the period of 1 to 21 days. During the entire experimental period, no significant effects were observed on performance parameters or carcass traits, but there was a linear increase in litter humidity. Therefore, the inclusion of up to 5% glycerine in the diet did not affect broiler performance during the total rearing period.

Two experiments were carried out to determine which factor influences weight at hatch of broiler chicks: breeder age or incubated egg weight. In Experiment 1, 2340 eggs produced by 29- and 55-week-old Ross® broiler breeders were incubated. The eggs selected for incubation weighed one standard deviation below and above average egg weight. In Experiment 2, 2160 eggs weighing 62 g produced by breeders of both ages were incubated. In both experiments, 50 additional eggs within the weight interval determined for each breeder age were weighed, broken, and their components were separated and weighed. At hatch, hatchlings were sexed and weighed, determining the average initial weight of the progeny of each breeder age. Data were analyzed using the Analyst program of SAS® software package. In Experiment 1, the weight difference between eggs produced by young and mature breeders was 10.92 g, and the component that mostly influenced this difference was the yolk (7.51 g heavier in mature breeders, compared with 4.23 g difference in albumen and 0.8 g in eggshell weights). Hatchling weight difference was 9.4 g higher in eggs from mature breeders. In Experiment 2, egg weight difference was only 0.74 g, but yolk weight was 4.59 g higher in the eggs of mature breeders. The results obtained in the present study indicate that hatchling weight is influenced by egg weight, and not by breeder age.

Feed is responsible for about 70% of broilers production costs, leading to an increasing number of studies on alternative dietary products that benefit bird performance and lower production costs. Since the 1950s, antimicrobial additives are the most frequently used performance enhancers in animal production and their positive results are observed even in high-challenge conditions. Since the 1990s, due to the ban of the use of some antibiotics as growth promoters and the growing trend of the public to consume natural products, plant extracts have been researched as alternatives to antibiotic growth promoters. The first study that evaluated the antibacterial activities of plant extracts was carried out in 1881; however, they started to be used as flavor enhancers only during the next decades. With the emergence of antibiotics in the 1950s, the use of plant extracts as antimicrobial agents almost disappeared. There are several studies in literature assessing the use of plant extracts, individually or in combination, as antimicrobials, antioxidants, or digestibility enhancers in animal feeds. Research results on the factors affecting their action, such as plant variety, harvest time, processing, extraction, as well as the technology employed to manufacture the commercial product and dietary inclusion levels show controversial results, warranting the need of further research and standardization for the effective use of plant extracts as performance enhancers, when added to animal feeds. This article aims at presenting plant extracts as alternatives to antibiotics, explaining their main modes of action as performance enhancers in broiler production.