A study was conducted to investigate the effects of Bacillus amyloliquefaciens CECT 5940 as a direct-fed microbial (DFM) alone or in association with bacitracin methylene disalicylate (BMD) in broilers under enteric pathogen challenge. A total of 1,530-day-old male Cobb500 chicks were randomly assigned to 5 treatments, with 9 replicate pens with 34 birds each. Treatments included positive control (PC, basal diet without additives or challenge); negative control (NC, basal diet without additive and challenged birds); NC + 0.05 g/kg BMD; NC + 1 g/kg DFM (106 CFU B. amyloliquefaciens CECT 5940/g of feed); and NC + 0.05 g/kg BMD + 1 g/kg DFM. The challenge consisted of oral gavage with Eimeria maxima and Clostridium perfringens inoculum. Body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) were evaluated on days 21, 35, and 42. Ileal and cecal content were collected on days 21 and 28 for C. perfringens enumeration by real-time PCR assay and the intestinal health was evaluated by scores. Uniformity (UN), carcass (CY), and breast meat yields (BMY) were evaluated on day 42. After 14 and 21 d post-inoculation, birds in the challenged groups had significant lower FI and BWG compared to the PC group (P < 0.05). However, the groups receiving DFM, BMD, or its combination presented better FCR, CY, BMY, UN, and lower incidence of footpad lesion and litter quality visual scores, compared to the NC group without feed additives (P < 0.05). Mortality was not affected by treatments (P > 0.05). Broilers fed DFM, BMD, or its combination presented lower C. perfringens in ileal content at 21 and 28 d compared to NC group without additives (P < 0.05) and also maintained gut health by keeping the frequency of ballooning, abnormal content, and swollen mucosa comparable to the PC group (P > 0.05). The study indicates that Bacillus amyloliquefaciens CECT 5940 is effective as BMD to provide similar performance and gut health in challenged broilers.

A total of 56 Hy‐line W‐36 hens from 28 to 30 weeks were used on nitrogen balance (NB) trial to estimate daily N maintenance requirements (NMR) and the genetic potential for daily N retention (NRmaxT). The treatments consisted of six graded levels of nitrogen in the diets (N1 = 8; N2 = 16; N3 = 24; N4 = 32; N5 = 40; and N6 = 48 g N/kg of feed), formulated using the dilution technique. The regression analyses between nitrogen intake and excretion were performed to fit the exponential function and to determine the NMR = 292 mg/BWkg 0.67, which was applied for further calculation of NRmaxT = 1,883 mg/BWkg 0.67. A second NB trial was conducted, and a total of 96 Hy‐line W‐36 hens were used in the same period to estimate the ideal amino acid ratio (IAAR). Twelve treatments with eight replicates and one bird per cage were used. A balanced diet (BD) was formulated to meet the IAAR and the requirement of other nutrients for pullets. The limiting diets were formulated diluting BD with cornstarch and refilled with synthetic AAs and other feed ingredients, except for the AA under study. In each trial, the data of nitrogen intake, excretion, deposition and retention were obtained in a NB trial. The IAAR determined by Goettingen approach was Lys 100, Met+Cys 88, Trp 21, Thr 69, Arg 109, Val 90, Ile 75, Leu 127, Phe+Tir 110, Gly+Ser 73 and His 29%. The IAAR determined by Louvain approach was Lys 100, Met+Cys 88, Trp 21, Thr 69, Arg 104, Val 91, Ile 78, Leu 121, Phe+Tir 119, Gly+Ser 77 and His 29%.

The current feeding programs used for broiler breeder hens need information on how to make use of the genetic potential more efficiently by modelling the amino acid (AA) requirements. Thus, this study aimed to determine the model parameters for maximum nitrogen retention (NR max T), nitrogen maintenance requirement (NMR) and the efficiency of lysine utilization (bc −1) to determine the lysine (Lys) requirements of broiler breeder hens. Nitrogen balance trials were performed in two periods (I: 31-35 wks and II: 46-50 wks). Seven dietary treatments were used with eight replicates and one hen per cage; the treatments consisted of seven diets with protein levels ranging from 58.8 to 311.9 g/kg of feed, with Lys being limiting in the dietary protein (c = 3.91 g of Lys in 100 g of CP). For each period, nitrogen intake (NI), nitrogen excretion (NEX), nitrogen in egg mass (NEM), nitrogen deposition (ND) and nitrogen retention (NR, NR = ND + NEM + NMR) were obtained in a N balance trial of 25 days. The NMR was calculated as the intersection point of the exponential curve between NEX and NI at NI = 0. The NR max T and b (slope related to protein quality) were estimated by the exponential fit between NR and NI. The Lys efficiency bc −1 was obtained dividing b by c. The likelihood ratio test for the model parameters yielded 255 mg/BW kg 0.67 for NMR, 0.000117 for b and 1684 mg/BW kg 0.67 (period I) and 1484 mg/BW kg 0.67 (period II) for NR max T. The necessary Lys intake dependent on NR and Lys efficiency was derived by the equation Lys = (lnNR max T-ln(NR max T-NR))/(16 × bc −1). Lys intakes required to achieve 0.80 times the maximum potential (NR max T) were 915 mg and 876 mg in the period I and II, respectively. For broiler breeder hens, assuming 0.80 times the NR max T value and average efficiency of Lys utilization, 6.02 g/kg (31-35 wk) and 5.96 g/kg (46-50 wk) digestible dietary Lys were observed as optimal digestible Lys concentration in the diet (corresponding to 152 and 147 g of daily feed intake, respectively). Results of model calculations need verification in performance trials with evaluation of nitrogen deposition and varying dietary Lys efficiencies.

1. A nutrition model is described that may be used to optimise the amino acid nutrition of laying-type pullets prior to the onset of lay. It is not a method of optimising lifetime laying performance. 2. The potential growth and composition of the body, feathers, ovary and oviduct are described from hatching to the age at which sexual maturity is attained, from which the daily amino acid and energy requirements for the average individual in the population can be calculated. 3. There are two parts to the approach used, the first being a description of the model itself and the second being a description of how the required information was gathered. A number of assumptions made in developing the model are discussed. 4. The rates of maturing of the body, feather-free body and body protein of the DeKalb pullets used were shown to be constant at 0.017/d and those of feathers at 0.02/d. These are considerably slower than those of the oviduct and ovary (0.139 and 0.084/d respectively). The ovary attained a higher mature weight (78.4 vs. 58.7 g) than the oviduct. 5. The age at which the growth of the reproductive organs is initiated in the model is defined by the user. The daily amount of threonine required to meet the requirements for maintenance and potential growth of the developing tissues and organs is calculated for each day of the growing period from hatching to the age at which the first egg is laid. A method of calculating the required daily concentration of threonine in the feed is described, from which a feeding programme may be derived. 6. For the model to produce an optimum economic feeding programme for a population of laying-type pullets, more information than is available from this study is required. These issues are discussed in the paper.

A digestibility assay was conducted in order to determine the digestibility coefficients (DC) of amino acids of feed ingredients in cecectomized adult roosters. In total 48 cecectomized adult roosters were used to assess the coefficient of digestibility of 7 ingredients: corn, soybean meal, soybean concentrate, corn gluten meal, wheat bran, peanut meal, and feather meal. Each ingredient was replicated six times and a group of 6 rooster was used to measure endogenous amino acid losses. After 48 hours of fasting, the roosters were tube fed 20g of ingredients tested twice during a day. At 12 hour-intervals excreta and endogenous losses were collected and immediately freezedried for further chemical analysis. At the end of the assay, excreta were weighed and samples of ingredients, excreta, and endogenous losses were pooled and analysed for dry matter, nitrogen and amino acid content. The coefficients of indispensable amino acids for the most feed ingredients assessed in the current research were similar to published literature like AMINODat ® 5.0 and the 4 th edition of the Brazilian Tables for Poultry and Swine, except feather meal, in which only digestible Trp and Thr content were similar to literature. Particularly, the coefficients for some amino acids like Arg and Gly exhibited large discrepancies from literature in almost all the feed ingredients assessed herein. In general, using cecectomized adult roosters proved to be a reliable technique to assess the digestibility of feed ingredients used in poultry diets.

Experiments were conducted to estimate daily N maintenance requirements (NMRs) and the genetic potential for daily N retention (NRmaxT) of pullets in growth phase. Three nitrogen balance trials were conducted, and a total of 48 Hy‐line W‐36 pullets were used in each trial in age periods (starter: 14–28, grower: 56–70 and developer: 98–112 days). The treatments consisted of six graded levels of nitrogen in the diets (L1 = 8, L2 = 16, L3 = 24, L4 = 32, L5 = 40 and L6 = 48 g N/kg of feed), formulated using the dilution technique. The regression analyses between nitrogen intake and nitrogen excretion were performed to fit the exponential function and to determine the NMR. The daily NMRs that were estimated at 294, 331 and 355 mg/BWkg0.67 for the initial, grower and developer periods, respectively, were applied for further calculation of NRmaxT as the threshold value of the function between N intake and daily N balance. The NRmaxT was estimated by a statistical procedure following several iteration steps by the Levenberg–Marquardt algorithm until the sum of the squares of the residual was minimized. The NRmaxT was estimated at 3,200, 2,633 and 1,826 mg/BWkg0.67 for starter, grower and developer periods respectively. The determined model parameters were the precondition for modelling of the amino acid requirement based on an exponential N‐utilization model and depended on performance and dietary amino acid efficiency. This procedure will be further developed and applied in the subsequent study.

An experiment was conducted to evaluate broiler chicken performance and carcass yield in response to carbohydrase supplementation (Xylanase and Betaglucanase; XB) and association of carbohydrase and phytase (PHY). A total of 1,920 day-old male broiler chicks (Cobb 500) were distributed in a completely randomized design with 8 treatments and 8 replicates each, allocated in 64 pens with 30 chicks each. The treatments were: Positive Control (PC); Negative Control (NC): reduced ME [-120kcal/kg (Starter) and -170kcal/kg (Finisher)]; NC + XB [50g/ton]; NC + XB [100g/ton]; NC + XB [150g/ton]; NC + XB [50g/ton] + PHY [100g/ton]; NC + XB [100g/ton] + PHY [100g/ton]; NC + XB [150g/ton] + PHY [100g/ton]. The inclusion of XB (150) and XB (50, 100, and 150) associated with phytase increased feed intake than positive control when considering the total rearing phase. The feed conversion ratio of all broilers fed diets with energy reduction were worse than positive control, even with the addition of enzymes, and did not differ between them. There was no significant effect of treatments on carcass parameters.

Context Genetic improvements in modern strains have led to continuous increments in broiler growth rates, which, as a consequence, have resulted in higher economic returns for broiler producers over the last decades. Aim The present study was conducted to characterise the potential growth of the body and feathers of Cobb 500, Hubbard Flex and Ross 308 male and female broilers, as well as to assess the changes in chemical composition that occur up to 16 weeks of age. Methods Birds were fed isoenergetic diets divided in four phases and formulated to marginally exceed the nutritional requirements of the strains throughout the growing period. They were maintained in a controlled environment so as not to limit growth. A dual energy X-ray absorptiometry (DXA) scanner was used to follow the in vivo body composition of 12 broilers of each strain and sex (total of 72 broilers), and the feather weight and composition was determined in four birds of each strain and sex selected at intervals during the growing period (total of 288 broilers) through comparative slaughter with later chemical analysis. Key results Parameters of Gompertz growth curve to describe the strains were estimated for body and feather weight as well as for the growth of their chemical components. Conclusion Differences in the growth rates between strains were evident, indicating the possible differences in selection methods used by geneticists in the different breeding companies. These genetic parameters would explain part of the variation on broiler´s performance which impacts on the way they should be fed and housed during growth. Implications The accurate description of genetic growth potential is useful information to be associated with factorial models that predict nutritional and feed intake requirements of birds. The main advantage of DXA technology is to decrease the variation of body deposition on the Gompertz model, resulting from the use of the same bird throughout its life. Despite the speed of obtaining chemical values of the body, the method is unsuitable for measuring the growth of feathers, which is also important data to be collected and related to the broiler strains.