Increased responsiveness to dietary lysine deficiency of pectoralis major muscle protein turnover in broilers selected on breast development

It has been previously established that growth and carcass qualities of chicks are modified by genotype and dietary amino acid supply. In this study, we evaluated the effects of lysine deficiency and genetic selection on muscle protein metabolism. Chicks originating from an experimental line selected for breast development (QL) and its control line (CL) were provided ad libitum access to isoenergetic diets containing 20% crude protein but differing in their lysine content (0.75 or 1.01%). Protein fractional synthesis rates (FSR) were measured in vivo in the pectoralis major and sartorius muscles of 3-wk-old chickens (flooding dose of [3H]phenylalanine). Fractional breakdown rates (FBR) were estimated as the difference between synthesis and deposition. Lysine deficiency reduced (P < 0.001) growth performance and muscle weights and increased (P < 0.05) muscle FSR, capacity for protein synthesis (muscle RNA:Protein, Cs) and FBR. Although QL birds grew faster and had heavier pectoralis major muscles than CL birds (P < 0.05), there was no line difference in sartorius weight (P = 0.15). No difference between the lines was observed in sartorius protein metabolism (P > 0.14). In the pectoralis major muscle, chicks of both lines receiving an adequate lysine intake also exhibited similar protein turnover rates. However, in chicks fed the lysine-deficient (0.75% lysine) diet, FSR and Cs were higher in QL than in CL chicks (P < 0.05), and FBR tended (P = 0.07) to be higher in QL chicks. This increased protein turnover in the QL birds on the lysine-deficient diet suggests that the responsiveness of muscle protein metabolism to amino acid supply is modified by genetic selection for breast development.     

Comparative responses of genetically lean and fat chickens to lysine,arginine and non‐essential amino acid supply. I. growth and body composition

1. Three experiments were performed to study the effects of amino acid imbalance on the growth of genetically lean (LL) or fat (FL) male chickens from 28 to 42 d of age. In experiment 1, five concentrations of digestible lysine were compared (4.75, 6.75, 7.75, 8.75 and 9.75 g/kg). In experiment 2, four concentrations of digestible arginine were compared (6.53, 7.69, 8.84 and 10.0 g/kg). In experiment 3, three diets were compared: a high‐protein diet (189 g CP/kg), a low‐protein diet containing added essential amino acids (EAA) (144 g CP/kg) and this low‐protein diet supplemented with 40 g/kg of non‐essential amino acids (NEAA) (glutamic acid + aspartic acid).

2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake.

3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens.

4. Similar growth rates, although slightly lower in FL, were obtained with low‐ and high‐protein diets. However, NEAA supplementation of the low‐protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines.     

The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens

1. Growth performance between 28 and 49 d of age and carcase composition at 49 d in genetically lean (LL) and fat (FL) broilers fed on diets varying in non-essential amino acid (NEAA) concentrations were compared in 2 experiments. In experiment 1, 3 crude protein (CP) contents (133, 155, and 178 g/kg) were compared. In experiment 2, 4 CP levels (131, 150, 170 and 189 g/kg) were compared. All diets were supplemented with synthetic amino acids to cover the EAA requirement of the LL birds. 2. Weight gains of FL chickens were not affected by dietary treatments, while those of LL increased when CP level increased. 3. Reducing CP content always increased body lipids, abdominal fat and food conversion ratio in both lines in both experiments; however, the effect on abdominal fat was more pronounced in the FL birds. 4. Reducing CP concentration always decreased breast muscle proportion in both lines in both experiments, even when growth rate was not affected by CP. 5. It is concluded that LL chickens require diets more concentrated in NEAA than fat chickens and that there seems to be an effect of NEAA on breast muscle development.     

Further investigations on protein requirement of genetically lean and fat chickens

1. Genetically lean (LL) or fat (FL) chickens were fed from 28 to 42 d of age on one of 6 diets with different protein contents (from 73 to 208 g/kg). In order to keep a constant amino acid balance the experimental diets were made by diluting a well-balanced protein-rich diet with a protein-free diet. 2. Dietary protein influenced the growth rate of both genotypes similarly. However, maximum weight gain was reached in LL at a lower protein intake than in FL. 3. Regression between total protein gain (body protein + feather protein) or body protein gain and protein intake exhibited significantly different slopes, that of LL being superior to that of FL. 4. At a given protein intake, feather protein gain was also superior in LL to FL. Moreover feather protein, as a percentage of total protein gain, was superior in LL to FL. When the dietary protein fell below 126 g/kg, feather protein represented a higher proportion of total protein gain. 5. Multiple linear regressions of protein intake (as the dependent variable), and body weight and protein gain or weight gain (as the independent variables) suggest that the maintenance requirement for protein is similar in both lines but that the protein efficiency for growth is significantly superior in LL. 6. In a second experiment both genotypes were offered either a single high protein diet (232 g/kg) or a single medium protein diet (186 g/kg) or had free-choice between a high (269 g/kg) and a low protein (145 g/kg) diet. In free-choice feeding, FL chickens selected an overall dietary protein content which was significantly lower (179 v. 200 g/kg) to that of LL. In both genotypes, free-choice feeding led to fatter and less efficient chickens than predicted by the linear regression between adiposity or food conversion and protein content.     

Effect of a major gene for growth on protein synthesis in mice

Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) X (whole body protein), was greater (P less than .001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P less than .001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P less than .05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%.     

Comparative responses of genetically lean and fat broiler chickens to dietary threonine concentration

Genetically lean (LL) or fat (FL) male broiler chicken's were fed on 5 diets containing either 3.80, 4.27, 4.75, 5.22 or 5.70 g true digestible threonine per kg. Threonine deficiency induced a more pronounced reduction in growth in the LL than in the FL but did not influence abdominal fat and breast muscle proportions in either line. Plotting weight gain or protein gain against threonine intake suggests that the requirement of both lines is very similar in terms of mg per g of gain. Thus food intake or appetite should account for differences between genotypes. Requirement for true digestible threonine was estimated as 10.70 mg per g of weight gain or 63.8 mg per g of protein gain, using a linear regression approach. The quadratic polynomial equations suggest that the requirements are 13.9 and 12.4 mg digestible threonine per g of gain for LL and FL respectively.     

Effect of exogenous corticosterone in genetically fat and lean chickens

1. The effects of daily injections of corticosterone (1 or 5 mg/bird) on growth, fat deposition, liver lipid and plasma concentrations of uric acid, glucose, insulin and growth hormone were studied using genetically selected lines of fat (FL) and lean (LL) chickens. 2. Both doses of corticosterone depressed body weight gain and increased the liver lipid and the abdominal fat to the same extent in both lines. 3. In both lines, corticosterone caused a dose-dependent increase in the plasma concentrations of uric acid, glucose and insulin in the fasted and refed states. 4. In untreated birds, plasma concentrations of growth hormone (GH) were slightly higher in FL than in LL chickens and slightly decreased during refeeding. The response was not modified by injection of 1 mg corticosterone. Injections of 5 mg decreased plasma GH in both lines in the fasting state and in LL chickens during refeeding. In contrast, the same dose increased GH in FL chickens during refeeding. This contradiction remains unexplained. 5. The results suggest that corticosterone sensitivity is not involved in difference of fattening between FL and LL chickens.     

Muscle protein turnover in chickens selected for increased growth rate, food consumption or efficiency of food utilisation: effects of genotype and relationship to plasma IGF-I and growth hormone

1. Rates of muscle protein turnover, growth, and food consumption were determined in 4 lines of chickens selected for either weight gain (line W), food consumption (line F), efficiency of food conversion (line E), or at random (line C) and in two Australian commercial broiler strains (S and H). These measures were related to body composition and the circulating concentrations of plasma growth hormone (GH) and IGF-I. 2. N tau-methylhistidine excretion was 10-14% higher in line F and 7-13% lower in line E compared to line C, showing divergence in the rate of muscle protein breakdown with selection. 3. There were no differences between the 4 experimental lines (W, F, E and C) in muscle protein fractional synthesis rates, whether calculated from N tau-methylhistidine excretion or measured directly by 3H-phenylalanine incorporation. 4. No consistent differences were found between lines in circulating concentrations of either GH or IGF-I but plasma IGF-I concentrations were positively correlated over all lines with protein accretion rates. There was a strong inverse correlation over all lines between the rates of protein degradation and FCR. 5. The correlated responses in protein degradation rates are consistent with the notion of a positive genetic association between the overall efficiency of food utilisation for growth and the efficiency of protein metabolism.     

Are genetically lean broilers more resistant to hot climate?

1. Genetically lean (LL) or fat (FL) male chickens were exposed to either high (32°C) or control (22°C) ambient temperature up to 9 weeks of age. They were fed on one of two isoenergetic diets differing in protein content: 190 or 230 g/kg.

2. At 22°C, weight gain of LL broilers was the same as in FL chickens, but at the high temperature LL birds grew to a greater weight than FL ones.

3. Food conversion efficiency was not affected by ambient temperature in LL chickens but was depressed in FL ones at 32°C.

4. Increasing dietary protein content did not alleviate heat‐induced growth depression irrespective of the genotype.

5. Gross protein efficiency was higher in LL chickens and was less depressed at 32°C than in FL birds.

6. Fat deposition decreased with increasing protein concentration at normal temperature in both genotypes; at high temperature, high protein content enhanced fatness, particularly in LL chickens.

7. Thus, genetically lean broilers demonstrated a greater resistance to hot conditions: this was indicated by enhanced weight gain and improved food and protein conversion efficiencies.     

Responses of body composition, growth and food efficiency to dietary protein in genetically lean and fat broilers up to seven weeks of age

1. Growth, food intake and abdominal fatness were measured at 7 weeks of age in male and female broilers from genetically lean and fat lines fed on isoenergetic diets containing 160, 190, 210, 230 and 260 g crude protein/kg from hatching. 2. The mean proportions of abdominal fat decreased from 39 to 20 g/kg body weight in the fat line and from 26 to 11 g/kg in the lean line over this range of protein concentrations. 3. Protein requirements, for optimum growth as a proportion of the diet did not differ between the lines but the lean line was less tolerant of inadequate dietary protein. 4. In birds fed on the same diet, conversion efficiencies of food (FCE) and dietary protein (PCE) were always superior in the lean line but energetic efficiency (EE) was similar in good growing birds of both lines. 5. When dietary protein was adequate for growth and body compositions were equalised in the two lines (by feeding higher protein diets to the fat line), lean line birds had 10% better FCE, 6% better EE and 33% better PCE. 6. It is concluded that genetic selection is a more effective and economic means of producing leaner broilers than dietary manipulation.     

Energy exchanges of broilers, selected for fatness and leanness, on diets with and without a repartitioning agent.

1. Two experiments were undertaken for 3 or 5 d in respiration chambers, on two experimental lines of broiler chickens (aged 25-38 d) selected for leanness and fatness. Diets were without or with 0.4 mg cimaterol per kg. 2. The lean line with sexes combined (experiment 1), or with females only, had a significantly greater heat production than the fat line. Net availability of metabolisable energy for gain (kg) was 0.54 for the lean birds and and 0.84 for the fat birds. 3. Cimaterol did not have an effect on any of the variables examined.     

Effects of dietary lysine intake during lactation on blood metabolites, hormones, and reproductive performance in primiparous sows

Effects of three dietary lysine (protein) concentrations during lactation on metabolic state, protein metabolism, reproductive hormones, and performance were investigated in 36 primiparous sows. Sows were assigned randomly to one of three diets containing .4% (low lysine, LL), 1.0% (medium lysine, ML), or 1.6% (high lysine, HL) total lysine from intact protein sources. All diets contained 2.1 Mcal NE/kg and exceeded the recommended requirements for all other nutrients. Actual lysine intakes over an 18-d lactation were 16, 36, and 56 g/d for sows fed LL, ML, and HL, respectively. Fractional breakdown rate of muscle was determined on d 4 and 15 of lactation by using a three-compartment kinetic model of 3-methylhistidine metabolism. Increasing lysine intake during lactation did not affect fractional breakdown rate of muscle on d 4 of lactation but decreased it on d 15 (P < .05). Sows fed LL had a reduced number of LH pulses on d 12 and 18 (P < .05) and reduced serum estradiol (E2) concentration on d 18 of lactation compared with sows fed ML and HL treatments. However, LH pulses and E2 concentrations were similar between ML and HL treatments (P > .35). Increasing lysine intake increased serum urea nitrogen (SUN) and postprandial insulin concentrations (P < .05) during lactation but had no effect on plasma glucose concentrations (P > .20). Sows fed HL had greater serum IGF-I on d 6 and 18 than sows fed ML (P < .05). Number of LH peaks was correlated with serum insulin concentration 25 min after feeding on d 6 and 18 (r = .31 to .41; P < .1) and pre- (r = .33 to .46) and postprandial (r = .30 to .58) SUN concentrations (P < .05) during different stages of lactation. Results indicate that, compared with medium lysine intake, low lysine intake increased muscle protein degradation and decreased concentrations of insulin, SUN, and estradiol and LH pulsatility. In contrast, high lysine (protein) intake increased SUN, insulin, and IGF-I, but did not increase secretion of estradiol and LH compared with medium lysine intake. Furthermore, nutritional impacts on reproduction may be mediated in part through associated effects on circulating insulin concentration.     

Effects of divergent selection for incidence of tibial dyschondroplasia (TD) on purebred and crossbred performance. 1. TD incidence and calcium and phosphorus plasma concentrations

1. The effect of divergent selection for high (H) or low (L) incidence of tibial dyschondroplasia (TD) for 7 generations on blood calcium (Ca) and phosphorus (P) concentrations was studied. 2. The chicks used in this experiment were obtained from diallel crosses between H and L lines to obtain HH, HL, LH, and LL lines. A random-bred control (CC) line was also used. 3. The chicks were reared under standard management conditions. Body weight and plasma Ca and P concentrations were measured at 2, 4, and 7 weeks of age. Incidence of TD was recorded at 4 and 7 weeks. 4. Although HH birds had lower body weights than the other lines, there was no significant effect attributable to line selection for body weight at 2, 4, and 7 weeks of age. 5. The LL line birds had no incidence of TD at 4 weeks of age; however, the incidence of TD in LL line birds was 5.3% at 7 weeks of age. The incidence of TD was higher in HH line birds than the other line at 4 and 7 weeks of age. 6. Plasma Ca and P concentrations and Ca:P ratios increased with age. These results showed that HH line birds had higher plasma Ca, lower plasma P and higher Ca:P ratios than birds of the LL line.     

Comparative responses of genetically lean and fat chickens to lysine,arginine and non‐essential amino acid supply. II. plasma amino acid responses

1. Three experiments performed to study the effects of amino acid imbalances on the growth of genetically lean (LL) and fat (FL) male chickens from 28 to 42 d of age were described by Leclercq et al. (1994). The plasma amino acid concentrations of birds on selected treatments from that paper are reported here. In experiment 1, three dietary concentrations of digestible lysine were compared (4.75, 6.75 and 7.75 g/kg). In experiment 2, two dietary concentrations of digestible arginine were compared (6.53 and 10.00 g/kg). In experiment 3, three diets were compared: a high‐protein diet (189 g CP/kg), a low‐protein diet containing added essential amino acids (144 g CP/kg), and this low‐protein diet supplemented with 40 g/kg of non‐essential amino acids (NEAA; glutamic and aspartic acids).

2. The present results are compared with two earlier reports on the same genotypes. The LL consistently had lower plasma concentrations of me‐thionine, cystine, phenlyalanine, isoleucine and valine, and higher concentrations of histidine, than the FL chickens. In 4 of 5 experiments, LL leucine concentrations were lower, and glutamic acid, tyrosine, glutamine and alanine were higher, than in the FL. The other amino acids measured; arginine, lysine, aspartic acid, glycine and serine, exhibited variable responses among the experiments.

3. When the limiting essential amino acids, lysine and arginine, were added to a deficient diet, the plasma concentration of the supplemented amino acid increased while the others remained constant or decreased.

4. When glutamic and aspartic acids were added to the low protein diet, plasma amino acid responses were similar to those of adding a limiting amino acid to a deficient diet, except that alanine exhibited a dramatic increase.

5. Although there were genotype by diet interactions for several amino acids, the interactions were caused by differences in the degree of the responses, not in their direction.

6. These results suggest that the FL and LL genotypes do not utilise various amino acids with the same efficiency and, as a consequence, the ideal profile of dietary amino acids should not be the same for both lines. The results support the hypothesis that selection for fatness and leanness changed the amino acid requirements independently of the: effects of food intake.     

Energy and nitrogen retention and loss in broiler chickens genetically selected for leanness and fatness

1. A breeding programme based on the assessment of the body fat content of broilers by measurement of plasma very low density lipoprotein concentration has resulted in 2 lines with significantly different body fat contents. 2. Energy and nitrogen intake and retention were measured in 63- to 70-d-old females from each line during 5-d periods of indirect chamber calorimetry. Results obtained by this technique were compared with results from a previously published growth trial incorporating carcase analysis at 49 d. 3. Body weight, metabolisable energy intake, heat production, energy retention and efficiency of energy retention did not differ significantly between the fat and lean lines. 4. The proportion of energy retained as crude protein and the efficiency of crude protein retention were significantly greater in the lean line. 5. In terms of whole-body energy and nitrogen exchanges, the essential difference between the lines was therefore in the partition of the same quantity of retained energy between fat and protein deposition. 6. The results were consistent with a higher rate of breakdown of amino acids in the fat line; because heat production did not also increase, a greater proportion of retained energy therefore became available for storage as fat.     

Influence of energy intake on growth and utilisation of dietary protein and energy in germ-free and conventional chicks

The effect of metabolisable energy (ME) intake on the growth and utilisation of dietary protein and energy in germ-free (GF) and conventional (CV) chicks was investigated in two experiments. In experiment 1 a high energy diet (HED, 14.8 kJ ME/g) and a marginally-adequate energy diet (AED, 11.7 kJ ME/g) were fed to the GF and CV chicks at 240 g/2 birds/10 d. In experiment 2 a diet with 13.7 kJ ME/g was fed at 118 g (low level, LL) or 128 g (high level, HL)/bird/10 d. Body weight gain, protein retention and protein retention rate were similar in GF and CV chicks on both AED and HED in the first experiment, but in the second were higher in GF than in CV chicks. The increased ME intake of the CV chicks in experiment 2 may be too small to compensate for the increased requirement. ME intake was significantly higher in the CV chicks than in the GF chicks, whereas energy retention was similar in both groups.     

Injection of porcine growth hormone releasing hormone gene plasmid in skeletal muscle increases piglets' growth and whole body protein turnover

The aim of the current study was to investigate the effects of a porcine growth hormone releasing hormone (pGHRH) gene plasmid injection in piglets on growth performance and whole body protein turnover. Sixty male Canadian Landrace × Chinese Taihu piglets were assigned to an intramuscular injection of 0 (control), 0.25, 0.5, 1 and 2 mg. All pigs were fed with the same diet (crude protein: 239.8 g/kg, digestible energy: 14.28 MJ/kg) at ad libitum intake. Protein turnover was determined on the 22nd day with a three-pool model by using a single-dosage, end-product analysis method with ¹⁵ N-glycine as a tracer. Injection of the pGHRH gene plasmid increased the piglets' growth rate, altered feed intake and decreased feed conversion ratio. It increased plasma growth hormone releasing hormone (GHRH), growth hormone (GH), insulin-like growth factor-I (IGF-I) and somatostatin but reduced serum urea and triglyceride. It reduced the urinary nitrogen excretion and led to higher nitrogen retention as well as the efficiencies of nitrogen retention and digestible N utilization. It increased the rates of protein synthesis, protein breakdown and net protein gain. Excretion of endogenous urinary nitrogen was reduced and nitrogen reutilization rate was improved. Conclusions: Injection of the pGHRH gene plasmid in skeletal muscle stimulated GHRH, GH and IGF-I excretion in piglets. Protein deposition was increased by an increase in protein synthesis and a smaller increase in protein breakdown, which was accompanied by reducing amino acid oxidation and increasing nitrogen reutilization.     

Feed intake pattern of broiler chickens under intermittent lighting: Do birds eat in the dark?

This paper reflects the results of a short experiment conducted in parallel with a larger trial which aimed to test the assumption that ‘consumption of feed by broiler chickens during periods of darkness is largely negligible’. To that effect, on d 31, feeders of birds raised under intermittent lighting (IL), i.e. 1 h of light [1L]:3 h of dark (3D):1L:3D:1L:3D:1L:3D:2L:6D, were weighed at the onset and at the end of each period of darkness (or scotoperiod). Moreover, in order to compare the feeding behavior of IL birds with that of broilers raised under continuous lighting (CL, i.e. 18L:6D), their feeders were weighed in parallel and at the same time points. On d 31, feed intake of IL birds during scotoperiods represented 45% of their 24 h feed intake. Both CL and IL birds presented anticipatory feed intake prior to the long nocturnal period of darkness (6D), as well as higher feed intake right at the onset of lighting at 06:00. Feed intake of CL birds during the 6D nocturnal scotoperiod was negligible at around 2% of their total feed intake. Intermittent lighting birds exhibited excitement at the start of each hour-length scotoperiod and, within that time, ingested around 2.5 times the amount of feed ingested by CL birds. Although short, this study revealed several interesting observations which might be worth further exploring in a larger, lengthier, behavior-focused experiment. Amongst other factors, it might be interesting to understand whether the high feed intake observed during scotoperiods for IL birds in reflective of the whole flock or rather a coping mechanism developed mainly by hierarchically lower-ranking birds to achieve their daily feed intakes requirements.     

Relative responses of protein turnover in three different skeletal muscles to dietary lysine deficiency in chicks 1

1. The effect of lysine deficiency was analysed on muscle protein turnover in 2‐, 3‐ and 4‐week‐old growing broilers. Protein fractional synthesis rates (FSR, in %/d) were measured by a reliable in vivo technique (flooding dose of L‐[4‐³H] phenylalanine) in the Pectoralis major (PM), the Anterior latissimus dorsi (ALD) and the Sartorius (SART) muscles. Protein fractional breakdown rates (FBR, in %/d) were estimated as the difference between the synthesis rates and the growth rates of tissue protein.

2. Lysine deficiency resulted in significant increases in muscle FSR and FBR. When expressed in absolute rates (g/d), tissue protein deposition was reduced whatever the tissue. This phenomenon was accompanied by decreased protein synthesis (ASR).

3. The protein turnover responsiveness to the lysine deficiency appeared to depend on the studied muscle, since the PM muscle was the most sensitive whereas the SART and ALD muscles presented a lower sensitivity.