Interactive effects of dietary amino acid density and environmental temperature on growth performance and expression of selected amino acid transporters, water channels, and stress-related transcripts.

Exposure to heat stress (HS) is one of the challenges facing the broiler industry worldwide. Various nutritional strategies have been suggested, such as altering dietary concentrations of some nutrients. Thus, we evaluated feeding different amino acid (AA) densities on live performance, Pectoralis (P.) muscles, and expression of selected AA transporters, water channels, and stress-related transcripts in a fast-growing broiler strain. Ross 308 chicks (n = 576) were randomly assigned to 4 dietary treatments (24 reps, 6 chicks per rep), differing in AA density (110, 100, 90, and 80% of a breeder's AA specifications). During 24 to 36 days of age, half of the birds were kept at a thermoneutral (TN) temperature of 20°C, whereas the other half were subjected to HS at 32° C for 8 h daily, making the treatment design a 4 × 2. The results revealed no interaction between housing temperature and AA density on growth performance or P. muscles weights. Feeding 80% AAs depressed BWG, FCR, and P. muscles at 36 d (P < 0.001). There was an interaction (P < 0.001) between AA density and temperature on the expression of all examined genes. Reducing the AA density beyond 100% upregulated the expression of AA transporter (CAT1, B0AT, b0,+AT, SNAT1, LAT1), HSP70, HSP90, glucocorticoid receptor (GR), and AQP3 in the TN birds' jejunum. Whereas in the HS birds, inconsistent expressions were observed in the jejunum, of which CAT1, B0AT, and LAT1 were markedly downregulated as AA density was reduced. In P. major of TN birds, reducing AA density resulted in upregulating the expression of all AA transporters, HSP70, GR, and AQP1, while downregulating HSP90 and AQP9. In contrast, AA reduction markedly downregulated CAT1, B0AT, and LAT1 in the P. major of HS birds. These findings indicate that the dietary AA level alters the expression of various genes involved in AA uptake, protein folding, and water transport. The magnitude of alteration is also dependent on the housing temperature. Furthermore, the results highlight the importance of adequate AA nutrition for fast-growing chickens under HS.

Nutritive value and the maximum inclusion level of pennycress meal for broiler chickens.

Two experiments were conducted to evaluate the nutritive value and maximum safe level (MSL) of pennycress meal (PM) for broiler chicks. In experiment 1, a total of 480 chicks was fed either mash or crumbled diets containing zero, 5, 10, or 15% PM for 18 d (8 diets; 6 replications per diet). In experiment 2, a total of 660 chicks was fed mash diets containing zero, 3, 6, 9, 12, or 15% of either PM or canola meal (CM; a comparative reference) for 14 d (11 diets; 6 replications per diet). Analytical results show that PM is a good source of protein (∼31% CP) and it is very comparable to CM (∼36% CP). However, it contains higher erucic acid (∼1.68 vs. < 0.021%), glucosinolates (sinigrin) (∼63.5 vs. <0.163 µmol /g), and crude fiber (18.60 vs. 9.27%) compared to CM. In experiment 1, increasing PM from zero to 15% resulted in linear reductions (P < 0.05) in FI, BWG, and FCR at 10 days. Above 10%, performance responses were affected for FI and BWG at 18 d, respectively. An estimated MSL of 10% PM based on orthogonal contrast was optimal for satisfactory FI and BWG. The MSL as estimated by broken-line linear (BLL) and broken-line quadratic (BLQ) models was 9.12 ± 0.50 and 7.0 ± 1.27%, respectively. In experiment 2, growth performance at 14 d was reduced above 9% due to PM inclusion. CM inclusion did not affect growth performance at 14 d, suggesting 15% to be safe. The MSL for maximum growth performance varied depending on the statistical analysis as follows: 12% by orthogonal contrast and LSD, 15% by the Scheffé test, 10.84 ± 0.57 by BLL, and 8.61 ± 1.29 by BLQ. In conclusion, PM can be included in broiler starter diets as a protein source but its inclusion should be limited to no more than 8.5%. Different statistical procedures give different MSL and this should be considered when interpreting the data.

Estimation of the maximum safe level of feed ingredients by spline or broken-line nonlinear regression models.

The use of non-linear regression models in the analysis of biological data has led to advances in poultry nutrition. Spline or broken-line nonlinear regression models are commonly used to estimate nutritional requirements. One particular application of broken-line models is estimating the maximum safe level (MSL) of feed ingredients beyond which the ingredients become toxic, resulting in reduced performance. The objectives of this study were to evaluate the effectiveness of broken-line models (broken-line linear or BLL; and broken-line quadratic or BLQ) in estimating the MSL; to identify the most efficient design of feeding trials by finding the optimal number of ingredient levels and replications; and to re-estimate the MSL of various test ingredients reported in the nutrition literature for comparison purposes. The Maximum Ingredient level Optimization Workbook (MIOW) was developed to simulate a series of experiments and estimate the MSL and the corresponding descriptive statistics (SD, SE, CI, and R2). The results showed that the broken-line models provided good estimates of the MSL (small SE and high R2) with the BLL model producing higher MSL values as compared to the BLQ model. Increasing the number of experimental replications or ingredient levels (independently of each other) reduced the SE of the MSL with diminishing returns. The SE of the MSL was reduced with increasing the size (total pens) of the simulated experiments by increasing either the number of replications or levels or both. The evaluation of MSLs reported in the existing literature revealed that the multiple range procedure used to determine the MSL in several reports can both overestimate and underestimate the MSL compared to the results obtained by the broken-line models. The results suggest that the broken-line linear models can be used in lieu of the multiple range test to estimate the MSL of feed ingredients along with the corresponding descriptive statistics, such as the SE of the MSL.

Quantitative estimates of the optimal balance between digestible lysine and the true protein contents of broiler feeds.

Typical poultry feed formulation models have been developed for meeting the minimum specifications of the essential amino acids (EAAs), ignoring the importance of providing precise levels of the non-essential amino acids (NEAAs) that are required for maximum performance. Including true protein (TP) values in these models in relation to EAAs can most accurately account for the requirements of all amino acids (AAs) in the ration (essential, non-essential and excess EAAs). Data from recent research reports on the digestible lysine (dLys) requirements for maximum weight gain and minimum feed conversion ratio (FCR) were compiled from the literature. dLys requirements and the TP contents of the feeds were recalculated based on common ingredient composition values. Broken-line linear (BLL) and broken-line quadratic (BLQ) models were fitted to the data and compared. The dLys requirements of broilers (g/kg diet) for body weight gain (BWG) and FCR were found to increase linearly as a function of the true and crude protein contents of the diet. These relationships were not affected by either age or sex. As chickens aged, the dLys requirements decreased. However, the dLys requirement to TP ratio did not change with age for BWG or FCR. For maximum BWG and minimum FCR, the dLys requirements were estimated from the prediction models to be 4.92% ± 0.51 and 5.58% ± 0.70 of the TP level of the diet, using the BLL models, respectively. The good linear relationship between the dLys requirement and TP level allows the prediction of the variables from each other for use in feed formulation to represent the requirements of both EAAs and NEAAs. The dietary dLys requirements were estimated to be lower using the BLL vs. the BLQ models. TP was a better predictor of dLys requirements than crude protein (higher R(2) values).