Growth and plasma thyroid hormone concentrations of chicks fed diets deficient in essential amino acids

Low-Protein Diets Differentially Regulate Energy Balance during Thermoneutral and Heat Stress in Cobb Broiler Chicken (Gallus domesticus)

The objective was to assess whether low-protein (LP) diets regulate food intake (FI) and thermogenesis differently during thermoneutral (TN) and heat stress (HS) conditions. Two-hundred-day-old male broiler chicks were weight-matched and assigned to 36 pens with 5-6 chicks/pen. After 2 weeks of acclimation, birds were subjected into four groups (9 pens/group) including (1) a normal-protein diet under TN (ambient temperature), (2) an LP diet under TN, (3) a normal-protein diet under HS (35 °C for 7 h/day), and (4) an LP diet under HS, for 4 weeks. During HS, but not TN, LP tended to decrease FI, which might be associated with a lower mRNA abundance of duodenal ghrelin and higher GIP during HS. The LP group had a higher thermal radiation than NP under TN, but during HS, the LP group had a lower thermal radiation than NP. This was linked with higher a transcript of muscle β1AR and AMPKα1 during TN, but not HS. Further, LP increased the gene expression of COX IV during TN but reduced COX IV and the sirtuin 1 abundance during HS. The dietary protein content differentially impacted plasma metabolome during TN and HS with divergent changes in amino acids such as tyrosine and tryptophan. Compared to NP, LP had increased abundances of p_Tenericutes, c_Mollicutes, c_Mollicutes_RF9, and f_tachnospiraceae under HS. Overall, LP diets may mitigate the negative outcome of heat stress on the survivability of birds by reducing FI and heat production. The differential effect of an LP diet on energy balance during TN and HS is likely regulated by gut and skeletal muscle and alterations in plasma metabolites and cecal microbiota.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Selected metabolic, epigenetic, nitration and redox parameters in turkeys fed diets with different levels of arginine and methionine

The amino acid guidelines formulated by British United Turkeys postulate higher levels of lysine (Lys) in turkey diets than those recommended by the National Research Council. However, any modifications in the Lys content of turkey diets should be accompanied by changes in the inclusion rates of other amino acids, including methionine (Met) and arginine (Arg). The research hypothesis postulates that the appropriate inclusion levels and ratios of arginine and methionine in turkey diets with high lysine content can improve the antioxidant status of turkeys without compromising their metabolism. The aim of this study was to determine the influence of different Arg and Met ratios in Lys-rich diets on biochemical indicators, redox status and epigenetic changes in turkeys. The turkeys were assigned to six groups with eight replicates per group and 18 birds per replicate. Six feeding programs, with three dietary Arg levels (90%, 100% and 110%) and two dietary Met levels (30% and 45%) relative to dietary Lys content were compared. During each of the four feeding phases, birds were fed ad libitum isocaloric diets with high Lys content. Our results show, that in growing turkeys fed diets with high Lys content, the inclusion rate of Arg can be set at 90% of Lys content with no negative effects on their antioxidant status, metabolism or performance. Diets with high Arg content (110% Lys) are not recommended due to the risk of lipid and protein damage, and an undesirable increase in insulin and T4 levels. Regardless of dietary Arg levels, an increase in the Met inclusion rate from 30% to 45% of Lys content minimizes the oxidation of lipids, proteins and DNA, and increases the antioxidant defense potential of turkeys.

Growth performance and accretion of selected amino acids in response to three levels of dietary lysine fed to fast- and slow-growing broilers

Literature data indicate that feed intake is sensitive to the dietary Lys content particularly in fast-growing birds. From a conceptual and a practical viewpoint, an interaction between genotype (i.e., fast-growing vs. slow-growing birds) and dietary Lys content is of interest, but it needs confirmation owing to a dearth of studies addressing this issue. A study was conducted with 266 Cobb 500 birds and 266 Thai native crossbreed birds serving as models for fast-growing broilers (FGB) and slow-growing broilers (SGB), respectively. Within genotype, chicks were randomly allocated to diets containing either a high (H-LYS = 1.36%), medium (1.17%), or low Lys (1.01%) content. Growth performance and the accretion of protein and selected amino acids were determined in birds from 1 to 21 d of age. Treatments were arranged in a factorial design with 6 replications/treatment. Low Lys vs. H-LYS caused a 42.1% lower feed intake in FGB (P < 0.001), but not in SGB (P = 0.596). The feed conversion ratio (FCR (g feed/g BW gain)) was lowest in FGB (P < 0.001) and increased with decreasing dietary Lys contents (P < 0.001). The Lys induced increase in FCR, however, was more pronounced in SGB (P = 0.025). The absolute protein gain (g/bird) was influenced by the Lys content of feed and decreased by ∼54% and ∼23% in FGB and SGB, respectively (P < 0.001). The efficiency (% of intake) of protein accretion was found to be greater in FGB (P ≤ 0.001) and decreased with decreasing dietary Lys (P ≤ 0.001). The efficiency of Lys accretion was found to be negatively affected by the dietary Lys content in FGB (P < 0.001) but not SGB (P_{genotype × dietary Lys} = 0.008). It can be concluded that a dietary Lys content of 1.01% does not safeguard both growth performance and body protein accretion efficiency in both FGB and SGB. The suboptimal growth performance in FGB, but not SGB, is partially counteracted by a Lys-induced reduction in feed intake.

Thyroid hormones in diabetes, cancer, and aging

Thyroid function is central in the control of physiological and pathophysiological processes. Studies in animal models and human research have determined that thyroid hormones modulate cellular processes relevant for aging and for the majority of age‐related diseases. While several studies have associated mild reductions on thyroid hormone function with exceptional longevity in animals and humans, alterations in thyroid hormones are serious medical conditions associated with unhealthy aging and premature death. Moreover, both hyperthyroidism and hypothyroidism have been associated with the development of certain types of diabetes and cancers, indicating a great complexity of the molecular mechanisms controlled by thyroid hormones. In this review, we describe the latest findings in thyroid hormone research in the field of aging, diabetes, and cancer, with a special focus on hepatocellular carcinomas. While aging studies indicate that the direct modulation of thyroid hormones is not a viable strategy to promote healthy aging or longevity and the development of thyromimetics is challenging due to inefficacy and potential toxicity, we argue that interventions based on the use of modulators of thyroid hormone function might provide therapeutic benefit in certain types of diabetes and cancers.

Effects of reducing dietary amino acid density and stocking density on growth performance, carcass characteristics, meat quality, and occurrence of white striping in broiler chickens

A 49-day trial was conducted to determine the impact of dietary amino acid (AA) density and stocking density (SD) on growth performance, carcass traits, meat quality, and white striping (WS) occurrence in broiler chickens. Two hundred eighty-eight Ross 308 male broilers consisting of 6 replicate cages with 8 broilers per replicate were used. Treatments were arranged in a 3 × 2 factorial and consisted of 3 AA densities (normal, 10, or 20% lower than normal) and 2 different SD (high 35 kg/m² or low 26 kg/m²). Breasts were classified as normal, moderate, and severe for WS. Data were analyzed as a completely randomized design using the GLM procedure. Decreasing AA density decreased overall growth performance, carcass, breast yields, and fillet dimensions linearly, while leg and rib cage yields increased linearly (P < 0.01). High SD decreased hot carcass, breast, wings, and rib cage weights in birds fed normal AA diets (P < 0.05). High SD increased the length of breast fillet (P < 0.05). Cooking loss, breast lightness (L∗), and redness (a∗) at 48 h postmortem increased linearly with decreasing AA density, while ultimate breast pH (pH_u) and nitrogen content decreased linearly (P < 0.05). The occurrence of normal, moderate, and severe WS fillets was 45.3, 49.1, and 5.6%, respectively. As the dietary AA density decreased, the occurrence of no WS breast fillets increased linearly, whereas the occurrence of moderate WS fillets and mean WS score decreased linearly (P < 0.05). SD did not affect the occurrence of WS. Severe WS fillets were heavier and had higher cranial thickness, pH_u, and fat content and lower yellowness (P < 0.05), but water-holding capacity, nitrogen content, L∗, and a∗ value did not differ among different WS scores. Taken together, WS occurrence and severity increased with higher growth rate. Growth depression created by lowering dietary AA density regardless of SD resulted in a decrease in mean WS score, but it also compromised the growth and meat quality.

The effects of lignocellulose supplementation on laying performance, egg quality parameters, aerobic bacterial load of eggshell, serum biochemical parameters, and jejunal histomorphological traits of laying hens

This study was performed to investigate the effects of lignocellulose supplementation (LS) on performance parameters, egg quality, aerobic bacterial load of eggshell, serum biochemical parameters, and jejunal histomorphological traits of laying hens between 18 and 38 wk of age. A total of 640 pullets at 16 wk of age were allotted to 4 treatment groups as 0 kg (control, CONT), 0.5 kg, 1 kg, and 2 kg LS per ton of feed. Body weight (BW), daily feed intake, egg production (EP), egg weight (EW), and efficiency of feed utilization (EF) were determined as the mean of each 3-wk period between 18 and 38 wk of age. Laying hens in the 1 kg LS group had a higher BW mean (1632.1 g, P < 0.001). The highest mean value of EP and EW were observed in 1 kg LS group (81.8% and 57.3 g, respectively), whereas the lowest values were found in the 2 kg LS group (78.6% and 54.4 g, respectively, P < 0.001). The mean of EF was the lowest in the 1 kg LS group (2.72, P < 0.001). There was a decline in eggshell breaking strength and eggshell thickness in the 2 kg LS, when compared with the 0.5 and 1 kg LS groups (P < 0.001). The total aerobic bacterial load of the eggshell was the lowest in the 1 kg LS group (4.7 log₁₀ cfu/mL). The level of aspartate amino transferase and alanine amino transferase showed an increment in both the CONT and 2 kg LS groups (P < 0.001). The high level of LS (2 kg per ton of feed) caused a decline in the levels of IgY, IgA and IgM, when compared to the 0.5 and 1 kg LS groups (P < 0.001). Laying hens in 0.5 and 1 kg LS groups had longer villus height (1335.9 μm) in the jejunum than the others (P < 0.001). These findings showed that the 1 kg LS per ton of feed improved EP and EW, eggshell quality, immunoglobulin levels and intestinal morphology, and decreased the total aerobic bacterial load.

Growth performance, pH value of gizzard, hepatic enzyme activity, immunologic indicators, intestinal histomorphology, and cecal microflora of broilers fed diets supplemented with processed lignocellulose

This study was performed to investigate the hypothesis that supplementation of processed lignocellulose (PL) in the diets of broilers has a positive effect on growing performance, pH value of gizzard, hepatic enzyme activity, immunologic indicators, histomorphological character of small intestine, and cecal microflora populations. A total of 720 one-day-old Ross 308 broiler chicks were allotted to 4 treatment groups and fed maize−soybean meal based diets. The basal diet was supplemented with PL with an amount of 0 kg (control), 0.5 kg, 1 kg, and 2 kg per ton feed. Growing performance parameters, were determined weekly until 35 D of age. Blood samples for enzyme activities and immunoglobulins, jejunum and cecum samples for histomorphological characters for villus growth, and microbial population were collected from 12 broilers from each group. At 35 D of age, body weight of broilers supplemented with 1 kg of PL was found to be the highest with a value of 2305.0 g, when compared to the broilers supplemented with control, 0,5 and 2 kg of PL groups (2154.0, 2201.0, and 2141.7 g, respectively, P = 0.001). An increased activity of aspartate amino transferase (AST) was observed in the control and 1 kg PL supplementation groups (633.6 and 597.4 IU/L, respectively), whereas alkaline phosphatase (ALP) activity was the highest in the control group (5404 IU/L, P < 0.05). Broilers in the control group had the lowest level of IgY and IgA (122.2 and 25.8 mg/dL, respectively, P < 0.05). Villus height increased by 22.0%, 40.7%, and 34.8% in 0.5, 1, and 2 kg PL supplementation groups, respectively, when compared to the control (P < 0.001). The processed lignocellulose supplemented as 1 kg of PL decreased the average count of Staphylococcaceae, E. coli, and Enterobacteriaceae, whereas it increased the population of Lactobacillus spp. in the cecum (P < 0.05). These data indicate that the supplementation of processed lignocellulose had positive effects for performance via changes in hepatic enzyme activities, immunoglobulin levels, villus growth in jejunum, and microflora in cecum.

Assessing the response of hen weight, body composition, feather score, egg quality, and level of excreta nitrogen content to digestible balanced protein intake of laying hens

Ideally balanced dietary protein is critical for laying hen egg production and feed efficiency, but also affects other important characteristics. This research was designed to study the nonegg production and feed intake response of Lohmann-LSL Lite hens to 550, 625, 700, 775, and 850 mg d−1 of amino acid balanced digestible lysine (Dlys) from 27 to 66 wk of age. Data collection included hen weight (HW), feather scoring, tissue weights, egg specific gravity, egg component weights, and excreta nitrogen (N) content. The experiment was a completely randomized design and level of significance was fixed at P ≤ 0.05. Hen weight (quadratic, Q), pectoralis muscle (absolute, % – Q), and abdominal fat (absolute – linear, L; % – Q) increased with increasing Dlys intake. Although gastrointestinal segment weights and lengths were affected by Dlys intake, interpretation of results was confounded by other aspects of diet composition. Hen feather score (L) and excreta N content (Q) increased, and egg shell quality (L) decreased with increasing Dlys intake. Absolute egg component weights increased with Dlys intake, but effects on proportional weights were Q and relatively minor. In conclusion, balanced Dlys intake affected a variety of practical nonproduction characteristics in laying hens.

Growth performance, duodenal morphology and the caecal microbial population in female broiler chickens fed glycine-fortified low protein diets under heat stress conditions

1. This study was undertaken to examine the effect of feeding glycine (Gly)-fortified low protein (LP) diets on the growth performance, duodenal morphology and caecal microbial populations of broiler chickens raised under unheated, cyclic or constant heat stress environmental conditions. 2. From d 1 to 21 (starter phase), an equivalent number of birds were fed either a normal protein (NP) diet or a LP diet fortified with Gly. From d 22 to 42 (grower phase), an equivalent number of birds from each starter diet were distributed to one of the following dietary groups: (i) an NP diet during the starter and grower phases (NPNP), (ii) an NP diet during the starter phase and a LP diet during the grower phase (NPLP), (iii) an LP diet during the starter phase and an NP diet during the grower phase (LPNP) or (iv) LP diets during both phases (LPLP). 3. Commencing from d 22, an equivalent number of birds from each dietary group were exposed to (i) 23 ± 1°C throughout (unheated), (ii) 34 ± 1°C for 7 h each day from 10:00 to 17:00 (cyclic heat) or (iii) 34 ± 1°C throughout (constant heat). 4. Feeding the LP diet during the starter phase resulted in feed intake (FI), weight gain (WG), feed conversion ratios (FCR) and energy efficiency ratios (EER) similar to those for the NP diet. The birds fed the LP diet had a significantly higher protein efficiency ratio (PER) compared with the birds fed the NP diet. 5. During the grower phase, there were significant diet × temperature interactions for F, WG, FCR, PER, EER, villus height, crypt depth and caecal Clostridia. The birds fed the NPLP and LPLP diets had lower FI, WG and EER, higher FCR, shorter villus height and crypt depth and higher caecal Clostridia compared with the birds fed LPNP and NPNP diets under constant heat stress. However, feeding birds the NPLP and LPLP diets resulted in FI, WG, EER, FCR, morphology parameters and caecal Clostridia equivalent to the birds fed LPNP and NPNP diets, as well as improved PER, under unheated and cyclic heat stress conditions. 6. In conclusion, our results indicate that Gly-fortified LP diets can be fed to broilers under normal and acute heat stress environmental conditions without any adverse effects on performance. However, the use of such LP diets can be detrimental to broilers under chronic heat stress conditions.

Effects of Dietary Protein on Thyroid Axis Activity

Thyroid hormones (TH) are essential for the normal development and function of every vertebrate. The hypothalamic-pituitary-thyroid (HPT) axis is regulated to maintain euthyroid status. One of the most influential environmental factors that determines HPT axis activity is nutrition. Both food availability and substrate diversity affect thyroid hormone economy. The present paper aims to summarize literature data concerning the influence of the amount and the type of protein on thyroid axis activity. This review sheds light on the contribution of a low-protein diet or insufficient intake of essential amino acids to TH abnormalities. We believe that the knowledge of these dependencies could improve the results of nutritional interventions in thyroid axis disorders and enhance the efficiency of animal breeding.

Dietary deficiency of essential amino acids rapidly induces cessation of the rat estrous cycle

Reproductive functions are regulated by the sophisticated coordination between the neuronal and endocrine systems and are sustained by a proper nutritional environment. Female reproductive function is vulnerable to effects from dietary restrictions, suggesting a transient adaptation that prioritizes individual survival over reproduction until a possible future opportunity for satiation. This adaptation could also partially explain the existence of amenorrhea in women with anorexia nervosa. Because amino acid nutritional conditions other than caloric restriction uniquely alters amino acid metabolism and affect the hormonal levels of organisms, we hypothesized that the supply of essential amino acids in the diet plays a pivotal role in the maintenance of the female reproductive system. To test this hypothesis, we examined ovulatory cyclicity in female rats under diets that were deficient in threonine, lysine, tryptophan, methionine or valine. Ovulatory cyclicity was monitored by daily cytological evaluations of vaginal smears. After continuous feeding of the deficient diet, a persistent diestrus or anovulatory state was induced most quickly by the valine-deficient diet and most slowly by the lysine-deficient diet. A decline in the systemic insulin-like growth factor 1 level was associated with a dietary amino acid deficiency. Furthermore, a paired group of rats that were fed an isocaloric diet with balanced amino acids maintained normal estrous cyclicity. These disturbances of the estrous cycle by amino acid deficiency were quickly reversed by the consumption of a normal diet. The continuous anovulatory state in this study is not attributable to a decrease in caloric intake but to an imbalance in the dietary amino acid composition. With a shortage of well-balanced amino acid sources, reproduction becomes risky for both the mother and the fetus. It could be viewed as an adaptation to the diet, diverting resources away from reproduction and reallocating them to survival until well-balanced amino acid sources are found.

Nutrition and immunity: the effects of the combination of arginine and tryptophan on growth performance, serum parameters and immune response in broiler chickens challenged with infectious bursal disease vaccine

To explore the effects of the combination of tryptophan (Trp) and arginine (Arg) on growth performance, serum parameters and immune response of broiler chickens challenged with intermediate plus strain of infectious bursal disease virus vaccine, an in vivo experiment was conducted. A corn-soybean meal-based diet containing different levels of Arg and Trp was used. Cobb500 male broiler chickens from 0 to 49 days of age were subjected to a diet supplemented with the combination of Trp and Arg. Growth performance parameters and serum parameters were measured at 27 and 49 days of age. To evaluate the immunomodulatory effects of the combination of Trp and Arg on the challenged chickens, we measured the serum levels of interferon-α, interferon-γ and immunoglobulin G at 27, 35, 42, and 49 days of age. The results showed that the three evaluated immune system parameters including interferon-α, interferon-γ and immunoglobulin G were significantly enhanced after treatment. This enhancement resulted in the recovery of infectious bursal disease virus-infected chickens compared with controls as confirmed by histopathological examinations. Moreover, serum parameters such as albumin and total protein increased, whereas the treatment decreased (P<0.05) the feed:gain ratio, aspartate amino-transferase, alkaline phosphatase, lactic dehydrogenase, triglyceride and cholesterol. These findings suggest that the combination of Arg and Trp has a regulatory effect on growth performance. Moreover, it modulates the systemic immune response against infectious bursal disease.

Assessment of the Efficacy of L-Lysine Sulfate vis-à-vis L-Lysine Hydrochloride as Sources of Supplemental Lysine in Broiler Chickens

In this study the effects of L-lysine hydrochloride (containing 78.8% available lysine as crystalline lysine) and L-lysine sulfate (containing 51% available lysine in bacterial cell mass) as source of supplemental lysine in broiler chickens was assessed. The basal diet was supplemented with either L-lysine hydrochloride or L-lysine sulfate to meet lysine requirement. Lysine supplementation irrespective of source improved (P < .05) live weight and food conversion. Live weight and food conversion ratio of the L-lysine sulfate group was superior (P < .05) to the L-lysine hydrochloride group. Supplementation of lysine to the basal diet improved breast meat yield (P < .05). Meat protein content and protein accretion increased (P < .01) when L-lysine sulfate was supplemented. Nutrient metabolizability, N retention, protein utilization efficiency and live weight gain : lysine intake ratio also improved (P < .01) with L-lysine sulfate. A fasting trial conducted after the completion of the feeding trial indicated that the birds receiving L-lysine sulfate retained more of their live weight than the control and the L-lysine hydrochloride dietary groups (P < .05). It was concluded that due to the retained bacterial cell mass, L-lysine sulfate may be a superior source of supplemental lysine than L-lysine hydrochloride for broiler chickens.

The avian thyroid gland

There has been a considerable amount of research regarding the function of the avian thyroid gland, particularly in chickens. There is also more information on diseases of the avian thyroid gland, although it is usually in the form of case reports. This article covers a limited amount of material on the structure and function of the avian thyroid gland and its diseases.

Long-term effects of early life L-arginine supplementation on growth performance, lymphoid organs and immune responses in Leghorn-type chickens

The effects of a short-term dietary arginine supplementation after hatching on subsequent growth and the immune system were assessed in growing male Leghorn-type chickens. An arginine-deficient basal diet (67 g/kg) supplemented with 0 (control), 2.7 (LA) or 5.4 (HA) g L-arginine/kg, was offered ad libitum to 1-d-old male ISA Brown chicks for 4 weeks, then all birds were offered ad libitum a commercial pullet grower feed (8.9 g arginine/kg) for another 8 weeks. Supplemented birds had higher growth rates and feed intake than control birds during the 4-week supplementation period, but these effects did not persist into the subsequent periods. When the supplementation ceased at week 4, no differences in lymphoid organ weights relative to body weight (BW), primary serum antibody levels against sheep red blood cells (SRBC) or cutaneous reactivity of toe webs to phytohaemagglutinin (PHA) were detected. LA-fed birds had lower immunoglobulin (Ig) G levels against bovine serum albumin (BSA) than the control at week 4, but this effect did not persist at weeks 8 and 12. No difference in anti-BSA IgM levels was detected among birds at week 4; at week 12, however, the LA-fed birds had a significantly higher anti-BSA IgM level than the control. An increased anti-SRBC antibody level and a reduced relative bursa weight in HA-fed birds were evident at week 8, without any prior effects. It is concluded that short-term supplementary L-arginine had minimal effects on immunity, but some enhancement of SRBC antibody responses in later stages of growth was observed with previous L-arginine administration.

Effects of lysine deficiencies on plasma levels of thyroid hormones, insulin-like growth factors I and II, liver and body weights, and feed intake in growing chickens

Adequate (1.10%) and deficient (0.88, 0.66, and 0.53%) levels of Lys were fed to broiler chicks from 9 to 23 d of age. Groups fed the control diet (1.10% Lys) were also pair-fed daily with each deficient group. Compared with the free-fed control, graded decreases in feed intake occurred as the deficiency worsened, and these were significantly different with 0.66 and 0.53% Lys. Growth decreased significantly with each deficient level of Lys compared with the free-fed control and was always significantly lower than in the pair-fed control groups in each set. Plasma triiodothyronine (T3) was elevated in chicks fed 0.88 and 0.66% lysine but not with 0.53% when compared with the full-fed control treatment. However, in deficient chicks receiving 0.66 and 0.53% Lys, T3 levels were significantly higher compared with their pair-fed controls. Plasma T4 was not significantly different between any treatments. Liver weights decreased significantly at each level of Lys deficiency, but most of the differences disappeared when expressed relative to body weight. Plasma insulin-like growth factor (IGF)-I decreased significantly with the most severe Lys deficiency. However, it decreased to a similar degree in the pair-fed controls, showing that this effect was primarily due to the lower feed intake. Plasma IGF-II levels did not differ between any treatments. No correlations were evident between thyroid hormones and IGF-I or IGF-II values. We concluded that the primary effect of Lys deficiency was an elevation in plasma T3 levels without accompanying changes in plasma T4. No effect of the Lys deficiency per se on plasma IGF-I and IGF-II and liver weights relative to body weights was found.

Effects of methionine deficiencies on plasma levels of thyroid hormones, insulin-like growth factors-I and -II, liver and body weights, and feed intake in growing chickens

We showed previously that Met deficiency at 0.25% of the diet causes elevations in plasma triiodothyronine (T3) in broilers. In the present study, plasma levels of thyroid hormones as well as insulin-like growth factors (IGF)-I and -II were measured in chicks fed 3 deficient levels of total Met. Control (0.5%) and Met-deficient diets (0.4, 0.3, and 0.2%) were fed to male broilers from 8 to 22 d of age. Additional groups of control chicks were pair-fed with the Met-deficient ones. Chicks receiving 0.4% Met increased feed intake by 10% with no significant change in body weight. The more severe Met deficiencies of 0.3 and 0.2% caused graded reductions in feed intake and weight gain. However, corresponding pair-fed control chicks were significantly heavier. These changes suggest more marked alterations in metabolic processes with 0.3 and 0.2% Met than with 0.4% Met. Liver weights were heavier in chicks fed 0.3 and 0.2% Met but not 0.4%. Plasma T3 was higher in all deficient chicks compared with the free-fed control, which was significant only with 0.3% Met. However, with 0.3 and 0.2% Met, plasma T3 was significantly elevated compared to pair-fed controls. Plasma thyroxine (T4) was lower in all deficient groups, which was significant only with 0.2% Met, whereas no significant differences occurred between deficient chicks and their pair-fed controls. Plasma IGF-I levels were not significantly different, but they were consistently lower in deficient chicks and deserve further study. Plasma IGF-II was significantly less in chicks fed 0.2% Met compared to pair-fed controls suggesting that Met deficiency interferes with IGF-II metabolism. We concluded that a deficit of dietary Met altered plasma T3 and IGF-II levels, but the effect was dependent on the degree of deficiency.

Influence of dietary arginine concentration on lymphoid organ growth in chickens

In vivo effects of graded dietary levels of arginine on the body and lymphoid organs were investigated using Cornell K strain chickens of the B15/B15 haplotype. Two-week-old birds were fed an arginine-deficient basal diet (0.53% arginine) supplemented with additional arginine (up to 1.0% L-arginine to the diet). At four weeks of age, body weight, lymphoid organ weight, and concentrations of amino acids in plasma were measured. Arginine supplementation produced significant increases in plasma arginine (from 200 nM in chicks fed the basal diet to 2,000 nM in chicks receiving the 1.5% arginine diet) and ornithine concentrations (from 17 nM in chicks fed the basal diet to 500 nM in chicks receiving the 1.5% arginine diet). The arginine-deficient diet reduced body weight gain (P < 0.0001) and thymus, spleen, and bursa of Fabricius weights (P < 0.05). In contrast to the bursa weight, the thymus and spleen weights, as percentages of body weight, were also decreased (P < 0.05). This study suggests that arginine markedly influences lymphoid organ development, with a more pronounced effect on the thymus and spleen than on the bursa of Fabricius.

Growth, feed intake, and plasma thyroid hormone levels in chicks fed dietary excesses of essential amino acids

The consequences of dietary excesses of 10 essential amino acids, His, Ile, Phe, Trp, Val, Arg, Leu, Lys, Met, Thr, on growth, feed intake and plasma levels of triiodothyronine (T3) and thyroxine (T4) in growing chicks were investigated. Each amino acid was added to a starter ration to bring it to a level 2.84x above the National Research Council (1984) requirement. Excesses of all amino acids except His and Leu caused significant reductions in weight gain. Of the amino acid excesses that reduced growth, only Trp and Val did not also reduce feed intake. Gain:feed decreased significantly only in chicks consuming excess Arg, Lys, Phe, and Trp. Chicks fed excesses of Ile and Val had plasma T3 levels that were statistically higher than control levels; none of the other amino acid excesses significantly altered blood concentrations of this hormone. Compared to the control, plasma T4 levels were not significantly altered by the amino acid excesses, but there was a significant difference between Trp and Val, the latter being lower. This study shows that high dietary levels of essential amino acids cause depressions in weight gain and feed intake, and, with Ile and Val, these depressions are accompanied by elevations in plasma T3 levels. Otherwise, the amino acid excesses had little effect on plasma levels of thyroid hormones.