Estimation of broiler responses to increased dietary methionine hydroxy analogue [DL-2-hydroxy-(4-methylthio) butanoic acid] using linear and nonlinear regression models.

As the first limiting amino acid in corn-soy broiler diets, methionine (Met) is supplemented using commercial synthetic sources as demanded to obtain economic feed formulations. The Met analogue DL-2-hydroxy-4-(methylthio)-butanoic acid (HMTBA) is largely utilized with that objective. This study intended to obtain responses of broilers fed with increasing levels of HMTBA, from 28 to 42 d, such that economic returns can be calculated. A total of 2,106 Cobb × Cobb 500 one-day-old male broilers was randomly placed in 81 floor pens (2.7 m2 each). Birds were fed conventional starter (zero to 14 d) and grower (14 to 28 d) diets. Starting at 28 d of age, pens of 26 birds were randomly allocated into 9 feed treatments with 9 replications having increasing supplementations with HMTBA (0.00, 0.07, 0.14, 0.21, 0.28, 0.35, 0.42, 0.49 and 0.56%). These were prepared by mixing different proportions of corn-soy dilution and summit diets, which had the same formulated concentration of nutrients and energy [19.7% CP, 0.90% Ca, 0.45% Av. P, 0.95% digestible Lys, and 3,150 kcal/kg AMEn], with the exception of HMTBA [0.56% in the summit but not supplemented in the corn-soy dilution diet (0.52% digestible TSAA)]]. Growth performance was evaluated until 42 d when carcass yield and commercial cuts were evaluated using 6 birds randomly taken from each pen. Body weight gain (BWG), feed conversion ratio (FCR), proportion of breast fillets, and abdominal fat were adjusted using linear broken-line, exponential asymptotic and quadratic polynomial regression models (P < 0.05). Estimations of maximum responses for supplemented HMTBA by the linear broken-line model were 0.17% for BWG, 0.14% for FCR, and 0.29% for breast fillets. Using exponential and quadratic regressions, optimized HMTBA supplementations were obtained at 0.34 and 0.35% for BWG, 0.20 and 0.33% for FCR, and 0.31 and 0.36% for breast fillets, respectively. Supplemental levels of HMTBA that optimize growth performance and breast meat in male broilers from 28 to 42 d, using different regression models, varied from 0.14 to 0.36%.

Effect of arginine:lysine ratios and source of methionine on growth and body protein accretion in acutely and chronically heat-stressed broilers.

The effect of Arg:Lys, Met source, and time of exposure to heat stress on growth and body protein accretion was tested in acutely heat-stressed (AHS) or chronically heat-stressed (CHS) broilers. Ross 308 1-day-old chickens were raised under normal brooding conditions from 1 to 25 d of age and were then suddenly moved to 32 degrees C (AHS), whereas another group was kept at constant high temperatures throughout the grow-out period (32 degrees C; CHS). From 26 to 33 d of age, both groups were therefore at 32.8 +/- 1.0 degree C. Two rooms were used per environmental treatment. A basal diet deficient in TSAA was supplemented with L-Arg monohydrochloride to achieve Arg:Lys ratios of 0.95 and 1.40. Diets were supplemented with either L-Met, 2-hydroxy-4-(methylthio) butanoic acid (HMB), or DL-Met (DLM) to a level of TSAA 5% lower than requirements. Each Arg:Lys and Met source combination was diluted with a N-free diet to achieve graded levels of CP (0.0, 3.5, 7.0, 10.5, 14.0, and 17.5% CP) and fed to 18 replicates of 3 chickens (3 replicates per level). Treatment effects were obtained by the slope-ratio technique using average daily BW gain and body CP deposition as dependent variables and protein intake as the independent variable. Protein utilization remained unaffected by Met source when fed at high Arg:Lys for birds under AHS and CHS (P > 0.05). However, lower protein utilization was observed in birds fed L-Met in low Arg:Lys compared with those fed DLM (P < 0.05). Birds fed HMB at low Arg:Lys utilized dietary protein better than those fed L-Met only under CHS conditions (P < 0.05). Protein utilization for birds fed HMB was similar to that of birds fed DLM in all instances. It was concluded that Arg:Lys, Met source, and time of exposure to heat stress affected protein utilization in hyperthermic birds.

Concentrations of putrescine, spermidine, and spermine in duodenum and pancreas as affected by the ratio of arginine to lysine and source of methionine in broilers under heat stress.

An experiment was designed to investigate the effect of Arg, Lys, Met, and environmental temperature on broiler performance and associated changes in duodenal and pancreatic polyamines. Two groups of 26-d-old Ross male broilers raised under thermoneutral (TN) conditions were reallocated to 4 rooms kept at heat stress (HS) or TN. Birds were fed equimolar amounts of 2-hydroxy-4-(methylthio) butanoic acid (HMB) or DL-Met (DLM) at requirement levels with Arg:Lys at 0.95 or 1.40. Twelve replicates of 4 birds were offered each diet ad libitum. Body weight gain, efficiency of dietary CP accretion (CPE), feed intake, and feed conversion ratio were ascertained from 26 to 33 d and from 34 to 47 d of age. One bird per cage was killed at 33 and 47 d, and samples of duodenum and pancreas were assayed for putrescine, spermidine, and spermine (Spm), together with estimates of duodenal villus height. From 26 to 33 d, birds fed HMB performed better than those fed DLM, but only at TN conditions. From 34 to 47 d, feeding HMB tended to optimize CPE when added to diets high in Arg. However, lower CPE was obtained when HMB was added to low-Arg diets, whereas birds fed DLM were unaffected by these treatments (P < 0.10). Methionine source, Arg:Lys, or both affected the concentrations of duodenal and pancreatic polyamines, with some changes correlating with performance variables during HS (P > 0.05). It was found that HS caused lower tissue spermidine (P < 0.001) and higher pancreatic Spm (P = 0.08) from 34 to 47 d. Putrescine concentrations were affected by diet and HS, depending on tissue and experimental period. Pancreatic Spm correlated negatively with changes in CPE influenced by Arg:Lys by Met source interaction in chronically heat-stressed birds. The possible association between polyamine metabolism and some of the effects of the Arg:Lys by Met source interaction observed in chronically stressed birds deserves further investigation.

Evidence for 2-hydroxy-4(methylthio) butanoic acid and DL-methionine having different dose responses in growing broilers.

The objective of this study was to compare the gain-response curve to dietary levels of 2-hydroxy-4(methylthio) butanoic acid (HMTBA) and DL-Met (DLM) across 4 floor pen trials in which different diets were used. Six replicates of 38 or 41 birds per pen (trials 1 to 2 and 3 to 4, respectively) were used in a 2 x 3 factorial arrangement. A control with 12 replicates was also included. The 2 Met sources were fed at 3 equimolar levels equally spaced, with the highest level added at requirements from 1 to 48, 49, 43, or 49 d for trials 1, 2, 3, and 4, respectively. Commercial-type TSAA-deficient control diets contained sorghum, wheat, corn, or corn plus meat and bone meal for trials 1, 2, 3, and 4, respectively. Performance improved at all times for most parameters after supplementing with HMTBA or DLM (P < 0.05). No differences were found in the birds fed HMTBA or DLM at any age and trial (P > 0.05), except for trial 1, in which 17-d-old birds performed better when fed HMTBA than DLM (P < 0.05). In each trial, linear, quadratic, and exponential regressions were conducted upon the gain response of birds fed HMTBA and DLM separately. Equations with better goodness of fit were used to compare the estimated gain responses to feeding HMTBA vs. DLM. In 3 trials, the shape of the gain-response curve differed when feeding HMTBA vs. DLM. In trials 3 and 4, feeding HMTBA at commercial levels resulted in greater gain responses than DLM (P < 0.05), whereas, in trials 2 and 4, at very deficient levels, DLM-fed birds outperformed those fed HMTBA (P < 0.05). When the 4 trials were combined, the dose-response curve with the best goodness of fit was linear for HMTBA and quadratic for DLM. It can be concluded that the 2 Met sources have a different dose-response form, HMTBA could outperform DLM at commercial levels, and DLM could outperform HMTBA at deficient levels.

A multiple regression model approach to contrast the performance of 2-hydroxy-4-methylthio butanoic acid and DL-methionine supplementation tested in broiler experiments and reported in the literature.

The purpose of this paper was to compile all available literature comparing the relative performance of 2-hydroxy-4-methylthio butanoic acid (HMTBA) with DL-methionine (DLM) in broiler chickens and using multiple regression techniques, to estimate the predicted dose responses and relative performance of the 2 Met compounds for gain and feed conversion (FC). A database was developed that contained all available broiler studies in which HMTBA and DLM were both present in the same study; weight gain was recorded; Met addition, age of birds, and duration of study were defined; and an unsupplemented control treatment was present. Sixty-two references complied with these criteria and included 100 experiments with 427 observations for HMTBA and 411 for DLM. Multiple regression analysis of the database was used to identify the experimental and dietary conditions that contributed to the gain and FC responses of each source of Met activity. All identified variables contributed similarly to each Met source prediction model and both gain and FC models described a quadratic dose response. Under the average conditions of the database, the predicted responses for gain and FC models did not significantly differ between HMTBA and DLM. However, a trend was observed (P < or = 0.1) for the peak gain response for HMTBA to be numerically greater than DLM, suggesting benefits of HMTBA over DLM in the region of supplementation that is commercially relevant. The experimental and nutritional conditions that contribute to the response to HTMBA and DLM were identified and are discussed in the paper. This statistical approach provided a means to summarize the results obtained from a multitude of studies conducted over the last 5 decades and has provided a meaningful estimate of the relative performance of the 2 sources of Met activity. The lack of differences between the 2 predicted models under experimental and commercial conditions supports an overall conclusion of equal performance of DLM and HTMBA when compared on an equal molar basis.

Effects of acute versus chronic heat stress on broiler response to dietary protein.

Two experiments were conducted to determine broiler response to dietary protein during short (1 wk) or prolonged (>3 wk) heat stress (HS). In experiment 1, 21-d-old birds were kept at 20.3 degrees C (thermoneutral; TN), 27.3 degrees C (medium temperature; MT), or 31.4 degrees C (high temperature; HT) and fed diets with 18, 20, 23, or 26% CP for 21 d. Each treatment consisted of 2 blocks of 3 replicates of 15 birds. In experiment 2, broilers were fed diets with 18 or 26% CP or fed ad libitum 2 diets with 10 or 30% CP. Birds were kept at TN (23.5 degrees C) or slowly introduced to HS from 7 to 14 d of age and kept at HT thereafter (chronic; CHS; 29.4 degrees C), and a third group was moved to HT at 21 d (acute HS; AHS; 29.4 degrees C). There were 16 replicates of 4 chickens per treatment distributed in 2 blocks. Performance, body composition, and protein deposition were ascertained from 21 to 28 d and from 28 to 42 d (short and prolonged exposures, respectively). Feeding high protein diets in experiment 1 resulted in linear improvements in body weight gain and feed:gain (P < 0.001) for MT and HT birds, whereas TN birds exhibited a linear (P < 0.001) response to protein. Feed intake declined as CP increased for HT birds during the third week of the study (P < 0.05). In trial 2, better performance was always observed in TN birds. HS depressed performance, although feeding high CP partially ameliorated this effect under AHS and CHS. Regardless of temperature, choice-fed birds selected high protein diets (mean 25.6% CP) and performed similarly to those fed 26% CP. CHS birds showed similar performance to those under AHS. Efficiency of protein deposition was unaffected (P > 0.05). Level of HS and duration of hyperthermia may determine the response of birds to dietary protein. Discrepancies between the 2 studies in response of birds to protein found after prolonged exposure to HS are discussed in view of the differences in levels of certain amino acids used within each experiment.

Effects of menhaden oil and flaxseed in broiler diets on sensory quality and lipid composition of poultry meat.

1. Three hundred and thirty 1-d-old male broiler chicks from a commercial strain were allocated to 11 dietary treatments comprising combinations of flaxseed at 100 g/kg and menhaden oil (MO) at 7.5 or 15 g/kg. Birds were given the experimental diets 7 or 14 d prior to slaughter. Carcase omega-3 fatty acid profiles and sensory evaluations of different cooked meat portions were carried out. 2. Linolenic acid was preferentially deposited in dark meat and long chain omega-3 fatty acids in white meat. Breast meat sensory quality was not affected in birds given 100 g/kg flaxseed for 14 d (treatment 3), 7.5 g/kg MO for 14 d (treatment 5) or 100 g/kg flaxseed +0.75 g/kg MO for 7 d (treatment 6). In contrast, thigh meat sensory quality decreased in treatments 5 and 6. 3. Feeding flaxseed and MO to birds for just 7 d prior to slaughter resulted in significant omega-3 meat enrichment depending on their dietary concentrations. The linolenic acid and long chain omega-3 fatty acids showed preferential deposition in dark and white meat, respectively, which may affect the sensory quality of various portions differently.

Effect of feeding hens regular or deodorized menhaden oil on production parameters, yolk fatty acid profile, and sensory quality of eggs.

An experiment was conducted to investigate whether feeding menhaden oil (MO) to hens affects egg weight, and whether using deodorized MO (DMO) could ameliorate decreased sensory quality of eggs (characteristic for hens fed high fish oil diets). Two-hundred twenty-four Single Comb White Leghorn hens were allocated to seven dietary treatments comprising either no fish oil, DMO, or regular MO (RMO) at 2, 4, and 6% in commercial-type diets from 19 to 55 wk of age. The data collected were analyzed in four experimental periods (i.e., 0, 2, 6, and 9 mo after feeding MO diets). The sensory evaluation of 2-wk stored eggs from hens fed the 2% RMO, 2% DMO, and control diets was undertaken. Egg weight decreased linearly with increasing MO in all periods tested (P < 0.05). The panelist's scores of aroma, taste, flavor, and acceptability of eggs from hens fed diets containing 2% of either RMO or DMO were lower (P < 0.05) than for control eggs. Greater aftertaste and off-flavors in these eggs were also detected. No differences in sensory quality (P > 0.05) for eggs from hens fed RMO vs. DMO were found. These results suggest that the deodorization of MO does not ameliorate the impaired sensory quality of eggs characteristic of hens fed MO.

Studies on the metabolizable energy content of ground full-fat flaxseed fed in mash, pellet, and crumbled diets assayed with birds of different ages.

Four experiments were carried out to determine the AMEn of ground flaxseed in chickens of different ages and to study the effect of feeding flaxseed in pelleted or crumbled diets on flaxseed AMEn. A corn-soybean meal basal diet was prepared, in which the energy-yielding ingredients were substituted with ground flaxseed at 5, 10, 15, or 20%. Experiments 1, 2, and 3 consisted of these five dietary treatments replicated six times using 9-d-, 6-wk-, and 79-wk-old birds, respectively. A total collection procedure was used to measure diet AMEn, and linear regression analyses were used to calculate the AMEn value of flaxseed for birds at different ages. Experiment 4 involved birds fed either a basal or a 10% ground flaxseed diet prepared as mash, pellets, or crumbles. The flaxseed AMEn values obtained with 9-d- and 6-wk-old chickens were 2,118 and 2,055 kcal/kg, respectively. These values contrast with those of Experiments 3 and 4, in which mature roosters were fed mash diets with AMEn values of 3,560 and 3,654 kcal/kg, respectively. In Experiment 4, a significant improvement in flaxseed AMEn was observed when diets were pelleted or crumbled (4,578 and 4,277 kcal/kg, respectively). We concluded that the difference in AMEn of flaxseed observed in young birds vs. that found in mature birds was likely due to a greater tolerance of the latter to flaxseed, with less evidence of diarrhea. Feeding flaxseed in pellet or crumbled diets can significantly increase AMEn value.