A comparison of the energy and nitrogen metabolism of broilers selected for increased growth rate,food consumption and conversion of food to gain

1. Calorimetric measurements were made on 5‐week‐old male chickens sampled from the third generation of three lines selected for either increased live‐weight gain (W), food consumption (F), or food conversion efficiency (E). A control line (C) was also measured.

2. Food intake and food conversion ratio were greater (P<0.05) in the F line than in the E and C lines.

3. Metabolisability of the diet was 0.8% higher in the E line than in the other lines.

4. Metabolisable energy (ME) intake and heat production were greater (P<0.05) in the F line than in the E and C lines, and energy balance was greater (P<0.05) in the F than in the W and E lines.

5. During starvation, excreta energy and heat production were greater (P < 0.05) in the F than the other lines.

6. Availability of ME (net energy) was the same (85%) for all lines but calculated daily maintenance energy requirements (kJ ME/kgW) were W, 860; F, 937; E, 796 and C, 810.

7. By 9 weeks the F line contained more fat and less water than lines E and C.     

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.     

Rates of muscle protein breakdown in chickens selected for increased growth rate, food consumption or efficiency of food utilisation as assessed by N tau-methylhistidine excretion

1. N tau-methylhistidine excretion, growth rate, food consumption and body composition was determined in 12 4 to 5 week old chickens sampled from each of 4 lines selected for increased body-weight gain (line W), for increased food consumption (line F), for improved efficiency of food utilisation (line E) or at random (line C), after 12 generations of selection. 2. The use of N tau-methylhistidine as an index of myofibrillar protein breakdown was validated in male and female chickens of lines E and F by following the fate of injected N tau-(14CH3)methylhistidine. Most of the radioactivity (79.3 +/- 1.1%) was excreted in 4 d, with the remainder retained in the carcase. In excreta, 94 +/- 2% of the radioactivity was associated with free N tau-methylhistidine and for the carcase, this value was 88 +/- 3%. 3. In the main experiment, final body weights averaged 497, 651, 588 and 537 g and food: gain ratio averaged 2.47, 2.21, 3.14 and 2.06 for lines C, W, F and E respectively, Carcase protein content (g/100 g body weight) was not different between the lines. 4. N tau-methylhistidine excretion was 5.86, 5.48, 6.43 and 4.99 mumoles/mole carcase-N/d for lines C, W, F and E, respectively. The rate for line F was significantly higher than for lines W and C and that for line E was significantly less than for the control line. 5. The N tau-methylhistidine excretion rate was positively correlated with food: gain ratio. 6. Selection for rapid growth, high food consumption or improved food utilisation results in changes in N tau-methylhistidine excretion which suggest proportionate changes in muscle protein turnover.     

Energy and protein metabolism between 3 and 6 weeks of age of male broiler chickens selected for growth rate or for improved food efficiency

1. A new open-circuit respiration unit consisting of 6 respiration chambers, gas analysis unit and data-acquisition system is briefly described. 2. Energy and protein metabolism in broiler lines selected for improved food efficiency (FC) or for growth rate (GL) were measured weekly from 3 to 6 weeks of age. 3. Gross and apparent metabolisable energy intake per kg W 0.75 was on average higher for GL than for FC chickens without differences in metabolisability. Fed and fasted heat production per kg W 0.75 did not differ between the lines. FC chickens retained less energy per kg W 0.75 than GL chickens. 4. FC chickens deposited much less of the retained energy as fat than their GL counterparts and also showed greater protein conversion efficiency. The leaner composition of the body weight gain in FC chickens was confirmed by the estimated lower fat deposition per kg W 0.75 and by the lower fat protein ratio.     

Temporal secretory patterns of growth hormone in male meat-type chickens of lines selected for body weight gain or food conversion.

1. The pronounced episodic release of chicken growth hormone (cGH) in male broiler chicks, as well as its peak interval of about 90 min was confirmed in this study. 2. Lines selected for 6-week body weight (GL line) or for food conversion between 3 and 6 weeks of age (FC line) not only differ in the selection criteria but also in percentage abdominal fat. 3. The overall mean plasma GH concentration was higher in the FC line in both experiments, and this was only caused by peak amplitudes which were almost twice as high as in the FC line. Peak intervals were identical in both selected lines. 4. These observations suggest that decreased abdominal fat and increased protein efficiency may be genetically linked to increased plasma GH peak amplitude. This, and earlier observations on the effectiveness of pulsatile administration of cGH on the growth of broilers suggest that the biological function of GH may depend on its secretory pattern rather than its mean concentration in plasma.     

Energy and nitrogen metabolism and oxygen use by broilers susceptible to ascites and grown at three environmental temperatures

1. An experiment using respiration calorimetry was performed to examine the energy and nitrogen metabolism of 2 strains of male broilers grown at 3 environmental temperatures; the results were then related to the susceptibility of the strains to the ascites syndrome.

2. Broilers selected for food conversion efficiency were less responsive to environmental temperature than were broilers selected principally for increased weight gain.

3. The susceptibility to ascites of broilers selected for food conversion efficiency may be the result not of a genetic incapacity to use oxygen but of the ability of the bird to maintain growth rate in adverse thermal environments.     

Concentrations of hormones, glucose, triglycerides and free fatty acids in the plasma of broiler chickens selected for weight gain or food conversion

1. The concentrations of growth hormone (GH), insulin-like growth factor I (IGF-I), thyroxine (T4), triiodothyronine (T3), reverse-triiodothyronine (rT3), triglycerides (Tri), free fatty acids (FFA) and glucose (Glu) were determined at 2, 4 and 6 weeks of age in blood plasma of male and female chickens of broiler lines selected for body weight (GL) or food conversion (FC). 2. Plasma concentrations measured in the same animal over a 24 h or a 2 week interval were not significantly correlated with each other. For different traits measured in the same plasma sample only the correlation between T4 and rT3 differed significantly from zero. 3. All traits were dependent on age. Line and sex effects were significant (P less than 0.05) for GH, T4, Tri, FFA and Glu. Additionally, line significantly influenced the plasma T3/T4 ratio and sex influenced plasma rT3. Interactions between line, sex and/or age were seldom significant. 4. Within line and sex, GH (at 6 weeks of age) and T3 (at 4 weeks of age) were negatively, and IGF-I and Tri (both at 6 weeks of age) positively correlated with the amount of abdominal fat at 6 weeks of age. No significant correlation between body weight at 2, 4 or 6 weeks of age and any of the plasma traits was found.     

Temporal patterns of growth hormone, prolactin and thyrotropin secretion in Targhee rams selected for rate and efficiency of gain

Thirteen Targhee rams selected for rate and efficiency of gain for 4 yr (1.5 generations) were compared with 10 rams from a Targhee line with no selection for over 20 yr to determine if selection for these traits would be associated with changes in the secretion of growth hormone (GH), thyrotropin (TSH) and(or) prolactin (PRL). Selected rams exhibited greater birth weight, average daily gain (ADG) and feed consumed/day during a 6-wk individual feeding regimen, and exhibited greater overall ADG during a 16-wk feeding trial as compared with the unselected rams. Temporal blood plasma samples were collected at 15-min intervals for 8 h from each of the 23 rams for hormone analysis. Selected rams exhibited greater overall mean GH (6.1 +/- .4 vs 4.6 +/- .5 ng/ml), overall mean TSH (8.6 +/- 1.2 vs 6.2 +/- .7 ng/ml) and baseline mean TSH (8.0 +/- 1.1 vs 5.6 +/- .5 ng/ml) than the unselected rams. Although the adjusted GH spike amplitude value was higher in the selected line (12.1 +/- 3.0 vs 7.4 +/- .8 ng/ml), this difference was not significant. No differences were observed with any of the variables of PRL secretion. In addition, there were no significant correlations between any of the hormone variables and any of the feed or gain data. These data support the hypothesis that Targhee rams selected for rate and efficiency of gain exhibit higher plasma levels of GH and TSH than unselected rams of the same breed.     

Food intake, growth rate, food conversion and food choice in broilers fed on diets high in rapeseed meal and pea meal, with observations on sensory evaluation of the resulting poultry meat

1. Experiments were done to measure the effects of 100 and 200 g/kg of either pea meal or low glucosinolate, low erucic acid rapeseed meal on food intake and growth, food choice and meat organoleptic quality in broiler chickens. 2. The test diets were formulated to be iso-energetic and iso-nitrogenous with a soy-wheat control diet. In all diets, lysine was fixed at 11.0 g/kg and all other indispensable amino acids were present in excess of requirements. 3. Food intake was little affected by the inclusion of 100 g/kg of pea meal in the diet but 200 g/kg of peas caused a decrease. Rapeseed produced a decrease in food intake at both dietary concentrations. 4. Weight gain was similarly affected, but food conversion from d 0 to d 42 was little affected by the inclusion of either peas or rapeseed. 5. Absolute breast muscle weight was affected by diet but there was no significant difference in breast weight as a proportion of total body weight. 6. From d 7 onwards, selection against the pea-containing diet approached statistical significance. Between d 7 and d 14, birds ate almost twice as much of the control as of the pea-containing diet. Birds offered a rapeseed meal diet ate similar amounts of that and the control diet. 7. The breast meat from birds given 200 g rapeseed/kg was the only meat identified as different but no strong aversion was expressed by the tasting panel.     

Selection for weight gain or food conversion in broilers affects the progesterone production capacity of large folucles in the reproductive adult breeders

1. Selection for leanness by selecting for food conversion (FC‐line) or selection for rapid growth and, thus, a concomitant fat increase (GL line) has also resulted in a lower egg laying rate of the fat birds. In birds of both lines that were effectively laying, plasma progesterone (P4), but not oestradiol concentrations were significantly different, with the lower concentration found in the GL line. This difference could not be attributed to differences in follicle population because this was similar in both groups of selected birds.

2. The in vivo decreased P4 secretion was investigated in vitro using granulosa cells of Fl follicles in a primary cell culture system. Basal P4 secretion tended to be lower in the GL line, whereas LH stimulation resulted in a diminished difference between the two lines. This was mainly caused by a higher relative P4 increase in the GL‐line.

3. Pre‐incubation with FSH increased the LH stimulated P4 secretion equally in both lines, probably through an increase of LH receptors.

4. The results demonstrate that selection for lean or fast growing, fat birds can also change processes apparently unrelated to the selection criteria, but with important effects on reproduction characteristics.     

The effects of dietary energy concentration on growth rate and conversion of energy to weight gain in broiler chickens

Eight diets, their metabolisable energy (ME) concentrations ranging from 2.3 Mcal/kg to 3.6 Mcal/kg (9.6 to 14.1 MJ/kg) were fed to each of four pens of broilers in two trials. Food intake was inversely related to energy concentration but the ME required by each sex to reach a given live‐weight was quite similar. Birds on the diets with a medium energy concentration (about 3.1 Mcal/kg (13.0MJ/ kg)) required slightly less ME than those on other diets and generally reached the required live‐weight earlier than those on other diets. Birds in the first trial required less of any particular diet than their counterparts in the second trial, reflecting the lower ambient temperatures recorded during the latter trial. Mortality recorded from 14 d of each trial was generally lower for birds on the medium energy concentration diets and dressed carcass percentage higher than those on other diets.

The results of the present study are in agreement with the recent recommendation (National Research Council, 1971) of 3.2 Mcal ME/kg (13.4 MJ/kg) for broiler diets. However, it is suggested that minimum and maximum values be given in such recommendations; this would allow greater flexibility and a wider range of ingredients in diet formulation.     

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.     

Social dominance difference,given limited access to common food,between hens selected and unselected for increased egg production

White Leghorn hens, belonging to a population (P) selected on an index for high egg number combined with slightly increased egg size, were compared for social dominance with a control line (R) derived from P in 1958 and reproduced independently over ten generations of random selection. The P line matured 12 d earlier, laid 18 more eggs in the part year to 1st January, had an increased egg production from 1st January to 1st October in the second year, laid heavier (2 g) eggs and had slightly longer shanks than the R line. Body size of the two lines, however, was similar.

Observations on the social dominance of hens were made in pens containing four hungry P‐ and four hungry R‐hens when they were 70 or more weeks of age. Observations focused on the hens’ ability to take and maintain a place at a food trough allowing only limited access. Larger scores, corresponding to high ranks, were given to the hens which were able to spend the most time eating.

Clear‐cut differences of social rank in favour of the selected production line were found in all 20 pens. Phenotypic correlations between production characteristics of individual R‐hens and their social rank scores were in agreement with other studies, showing that within genetic lines hens of high social status matured earlier and had larger body size than the more timid individuals.     

Energy utilization and organ mass of Targhee sheep selected for rate and efficiency of gain and receiving high and low planes of nutrition

Two experiments were conducted to examine changes in usage of energy and visceral organ mass in Targhee lambs selected on the basis of improved rate and efficiency of growth. In Exp. 1, Targhee ram lambs from a breeding line selected for improved growth rate and feed efficiency and a control line that was maintained without selection for 20 yr were provided with either a high (ad libitum) or low (maintenance) plane of nutrition. Rams were slaughtered and weights of the visceral organs were recorded. Analysis of variance, using a factorial model with BW as a covariant, was used to examine effects of lines of breeding, plane of nutrition, interaction between line of breeding and plane of nutrition, and days on feed. Weights of liver, kidneys, rumen, abomasum, and small and large intestines from lambs receiving a high plane of nutrition were, respectively, 39, 25, 12, 28, 40, and 31% greater than weights of those tissues in lambs receiving a low plane of nutrition. Ruminal weights were 13% greater for rams from the select line of breeding than for those from the control line. In Exp. 2, seven Targhee ewe lambs from the select line and eight from the control line were examined for differences in heat production and energy usage by indirect open circuit respiration calorimetry using a completely randomized design. Fasting heat production of lambs from the select line was 7.8% greater than that of lambs from the control line. Partial efficiencies of ME used for maintenance and tissue accretion were not different between lines of breeding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of coccidiosis on growth rate and feed conversion in broilers after experimental infections with Eimeria acervulina and Eimeria maxima

Under experimental conditions, the effects of subclinical Eimeria (E.) acervulina and E. maxima infections on growth and feed conversion in broilers of different ages were analysed. It was concluded that infection with E. acervulina and E. maxima led to a process which was independent of the age at which the birds were infected. The infection adversely affected growth and feed conversion for 2 to 3 weeks, followed by a recovery period of 2 to 3 weeks when compensatory growth took place. From this study it may be concluded that subclinical coccidiosis in the first weeks of life and in the last week of life of broilers does not lead to appreciable damage on growth and feed conversion. Since coccidiosis cannot be avoided in practice, systems in which broilers contact subclinical coccidiosis either in the first weeks of life or in the last week of life should be aimed for. It is suggested that in a coccidiostat programme an efficient anticoccidiosis agent is particularly desirable in the 3rd and 2nd week before slaughter. Examinations performed one week or less before slaughter can hardly be justified, on the grounds that there is a risk of a negative effect on growth an feed conversion due to subclinical coccidiosis.     

Effect of probiotic supplementation on growth,nitrogen utilisation and serum cholesterol in broilers

1. The effect of dietary probiotic supplementation on the growth, nitrogen utilisation and serum cholesterol content of broiler chickens was studied in 2 trials.

2. In experiment 1, the birds receiving the 0, 75, 100, 125 mg probiotic/kg diets had weight gains of 1204.0, 1272.0, 1268.3 and 1210.5 g, respectively at the end of 8 weeks of feeding. The group of birds fed on the 75 mg probiotic supplemented diet retained significantly (P<0.01) more nitrogen than the control birds. Serum cholesterol content was lower in the probiotic‐supplemented birds (93.3 mg/100 ml) compared to the control birds (132.2 mg/100 ml).

3. In the second experiment the probiotic plus antibiotic‐supplemented group of birds had the maximum weight gain (1148.5 g) followed by antibiotic (1141.3 g), probiotic‐supplemented (1128.4 g) and control birds (1045.6 g) after 6 weeks. Nitrogen retention was greatest in the antibiotic—(48.5%) followed by the probiotic—(46.5%), probiotic plus antibiotic‐supplemented groups (46.3%) compared to 40.2% in control birds.

4. The apparent metabolisable energy was greatest in birds receiving the probiotic plus antibiotic‐supplemented diet (12.37 MJ/kg) followed by antibiotic—(12.00 MJ/kg), probiotic‐supplemented birds (11.92 MJ/kg) than in control birds (11.62 MJ/kg). Serum cholesterol was significantly (P<0.01) lower in probiotic‐supplemented birds (86.1 mg/dl) compared to 118.4 mg/dl in control birds.     

Genetic-economic evaluation of traits in a broiler enterprise: reduction of food intake due to increased growth rate

Separate mathematical models for food consumption and growth pattern of broilers were used to derive a combined model to estimate food consumption during the growth period. The model was used to show that each reduction of one day in reaching a fixed body weight would reduce food consumption per bird by 50 to 60 g. Broiler lines with a slow growth rate at an early age and rapid growth rate near market age require appreciably less food overall. This feature should be considered in breeding and feeding programmes.     

The effect of dietary calcium upon growth rate, food utilisation and plasma constituents in lines of chickens selected for aspects of growth or body composition

1. The effect of increasing dietary calcium from 10.3 to 20 g/kg on 5- to 17-day growth performance and plasma minerals, electrolytes, total protein, albumin and glucose in chickens from 4 lines selected for: high 8-week body weight (W), low abdominal fat (L), high abdominal fat (F) or at random (C) was studied in two experiments. 2. High dietary calcium significantly reduced weight gain and plasma phosphate and potassium but increased food:gain ratio, plasma total calcium, glucose and albumin. 3. Significant correlations were found between plasma total calcium and plasma phosphate (r = -0.5, P less than 0.01), plasma total calcium and protein (r = 0.4, P less than 0.01) and between plasma total protein and albumin (r = 0.55, P less than 0.01). 4. Genotypes differed in their response to dietary calcium content. There was a substantial response in line F but little effect in line L. 5. In contrast to the three other lines, in line F high dietary calcium significantly increased plasma ionised calcium without altering plasma phosphate or total calcium concentration. 6. It was concluded that genetic selection has produced lines which vary in their tolerance to high dietary concentrations of calcium. Birds selected for increased fatness were less tolerant to high dietary calcium than their lean-selected counterparts.     

纯中药饲料添加剂对肉仔鸡增重血清激素水平以及尿酸尿素氮的影响

在现代化的肉仔鸡养殖业中，抗生素类药的耐药性和药物残留问题日益突出，饲料报酬低、经济效益差、禽肉不合格检出率高，严格制约了我国肉仔鸡养殖业的发展。中草药具有营养物质与药物的双重作用，且药源广泛，廉价易得，无有害残留，毒副作用小。因此，研制纯中药的肉仔鸡增重保健剂具有重要的现实意义。中药饲料添加剂对肉仔鸡具有促生长作用的报道不少，但大多数停留在观察效果上，很少有更深一步的研究，我们以中兽医学辩证施治为理论基础，以平补消导、健脾理气为组方原则，自拟方Ⅰ和方Ⅱ，试从其影响肉仔鸡的血液激素水平和血浆代谢物方面来探讨中药添加剂的促生长机制。     

Inheritance of plasma insulin-like growth factor-I and growth rate, food intake, food efficiency and abdominal fatness in chickens

1. The inheritance of, and genetic and phenotypic correlations between, plasma insulin-like growth factor-I (IGF-I) and 28-(28dW) and 56-d (56dW) body weight, 28- to 56-d body weight gain (BWG), food intake (FI), food conversion ratio (FCR) and abdominal fatness (AF) at 56 d were determined by sib analyses in a population of 327 pedigreed progeny produced by matings between 18 cockerels and 72 pullets from a broiler strain of chickens bred at random for 8 generations. 2. Plasma IGF-I was measured in fed (IGF-If) and fasted (IGF-I) birds at 42 d. 3. Heritability estimates (sire + dam) were: 28dW 0.35 +/- 0.11, 56dW 0.49 +/- 0.13, BWG 0.51 +/- 0.13, FI 0.55 +/- 0.13, FCR 0.73 +/- 0.14, AF 0.49 +/- 0.13, IGF-If 0.10 +/- 0.08, IGF-Is 0.08 +/- 0.08. 4. The low heritability estimates with their high standard errors for the IGF-I measures precluded the calculation of meaningful genetic correlations between these and the performance traits. There were moderate to strong positive genetic correlations between 28dW, 56dW, FI and AF.