R. A. Pym

Transcripts of the MHM region on the chicken Z chromosome accumulate as non-coding RNA in the nucleus of female cells adjacent to the DMRT1 locus

The male hypermethylated (MHM) region, located near the middle of the short arm of the Z chromosome of chickens, consists of approximately 210 tandem repeats of a BamHI 2.2-kb sequence unit. Cytosines of the CpG dinucleotides of this region are extensively methylated on the two Z chromosomes in the male but much less methylated on the single Z chromosome in the female. The state of methylation of the MHM region is established after fertilization by about the 1-day embryonic stage. The MHM region is transcribed only in the female from the particular strand into heterogeneous, high molecular-mass, non-coding RNA, which is accumulated at the site of transcription, adjacent to the DMRT1 locus, in the nucleus. The transcriptional silence of the MHM region in the male is most likely caused by the CpG methylation, since treatment of the male embryonic fibroblasts with 5-azacytidine results in hypo-methylation and active transcription of this region. In ZZW triploid chickens, MHM regions are hypomethylated and transcribed on the two Z chromosomes, whereas MHM regions are hypermethylated and transcriptionally inactive on the three Z chromosomes in ZZZ triploid chickens, suggesting a possible role of the W chromosome on the state of the MHM region.

Village poultry: still important to millions, eight thousand years after domestication

Village poultry make a significant contribution to poverty alleviation and household food security in many developing countries. This contribution by village poultry to livelihoods can also support HIV/AIDS mitigation and wildlife conservation initiatives. Appropriate interventions focussing on the factors limiting productivity of the different production systems must be tailored according to country and local conditions. The contrast between the type of support in relation to the production systems that might be promoted in export-oriented countries such as Thailand, in comparison to others such as Mozambique and Lao PDR is discussed. A review of the benefits and costs of inputs comparing small scale commercial poultry and scavenging village poultry production systems in different countries taking into account the bio-risks for each production system demonstrates the overall efficiency of the village production system and provides an insight into why this system has continued to thrive into the 21st century.

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.

Effects of dietary calcium, available phosphorus and vitamin D on growth rate, food utilisation, plasma and bone constituents and calcium and phosphorus retention of commercial broiler strains.

1. The effects of different dietary concentrations of calcium (Ca), available phosphorus (AP) and vitamin D (D) on 5- to 16-day growth performance, and aspects of calcium and phosphorus (P) metabolism of chickens from three commercial strains were studied in two experiments. 2. Increasing dietary Ca reduced weight gain, tibia Ca and P content and increased plasma total Ca, Ca consumption and excretion, whilst dietary Ca at 32 g/kg increased tibia Ca:P ratio, plasma ionized calcium and reduced plasma P, tibia ash, P excretion, excreta moisture and Ca retention. 3. Increasing dietary AP reduced plasma total and ionized Ca and excreta moisture and increased P consumption and excretion, plasma P and tibia ash. 4. The addition of vitamin D increased plasma total and ionized Ca, tibia Ca:P ratio and reduced plasma sodium and P concentrations. 5. Strains differed in their tibia contents of Ca and Ca:P ratios, in response to Ca, AP and vitamin D diets whilst they differed in Ca excretion and excreta moisture caused by feeding either dietary Ca or AP. 6. It was concluded that dietary Ca, AP, vitamin D and strain of broiler chickens influenced the metabolism of Ca and P and that, as a consequence, the tolerance to high dietary Ca. A lean strain of chickens tolerated high dietary calcium better than its fat counterparts.

Rates of muscle protein breakdown in chickens selected for increased growth rate, food consumption or efficiency of food utilisation as assessed by Nτ‐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.

Village, chicken production in Myanmar - purpose, magnitude and major constraints

The main objective of this work was to describe the characteristics of and major constraints to village chicken production in Myanmar. Data on village chicken production, health, husbandry and marketing were collected in 296 households in 10 villages in the Yangon division of Myanmar in November 2003. The average flock size in the study area was about 30 birds, comprising 12 chicks, 12 growers, 4 hens and 2 cocks. Disease as a cause of mortality was more prominent in growers and adults, while predation and exposure to unfavourable environmental conditions were major causes of mortality in chicks. The main predators identified were: birds, rats, snakes, dogs and cats in 32, 31, 17, 15 and 3% of households respectively. Two main strategies were identified to improve village chicken production: vaccination as a means of protecting birds against Newcastle disease and confinement rearing and supplementary feeding of chicks, as a means of reducing the attrition rate of young chicks. This is the first survey conducted describing village chicken population structure and productivity in Myanmar.

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.

Protein utilisation and turnover in lines of chickens selected for different aspects of body composition

1. Protein utilisation and turnover were measured in male chickens sampled from a line selected for high breast yield and a randombred control line (lines QL and CL, experiment 1) and in male chickens sampled from lines selected for either high or low abdominal fatness (lines FL and LL, experiment 2). In each experiment, 18 birds per line were given iso-energetic (12·9 MJ ME/kg) diets containing either 120 or 220 g CP/kg from 21 to 29 d (experiment 1) and 33 to 43 d (experiment 2). 2. Measurements were made of growth rate, food intake, body composition, excreta production and Nτ-methylhistidine excretion as a measure of myofibrillar protein breakdown, and fractional rates (%/d) of protein deposition, breakdown and synthesis were calculated. 3. In experiment 1, there were no significant differences between the line means for the fractional measures of protein turnover, but there was marked differential response in the two lines in the fractional rates of protein deposition, breakdown and synthesis, to increase in protein intake. The positive slope of the regressions of fractional (%/d) protein deposition and synthesis rates on protein intake (g/d/kg BW) were approximately 1·4- and 2·0-fold higher respectively in the QL than the CL line birds, and the negative slope of the regression of fractional breakdown rate on protein intake was approximately threefold greater in the CL than the QL line birds. 4. In experiment 2, fractional deposition rate was 6·2% lower, but fractional breakdown rate 9·4% higher in the LL than the FL birds, whilst there was essentially no difference in response of the FL and LL birds in the components of protein turnover to increase in protein intake. Line differences in deposition and breakdown rates were thus a reflection of the considerably higher (20%) food and hence protein intake in the FL than the LL birds. 5. The differential line responses in protein turnover in the two experiments suggest that selection for increased breast muscle yield and for reduced body fatness manipulate different physiological pathways in relation to protein turnover, but neither selection strategy results in an improvement in net protein utilisation at typical levels of protein intake by birds on commercial broiler diets, through a reduction in protein breakdown rate.

Evaluation of strategies to improve village chicken production-controlled field trials to assess effects of Newcastle disease vaccination and altered chick rearing in Myanmar

Previous research identified Newcastle disease and poor management of chicks (birds younger than 6 weeks of age) as major constraints to village chicken production in Myanmar. Based on these findings, controlled trials were conducted in 124 randomly selected households in nine villages in Myanmar over a period of 12 months to evaluate strategies to enhance survival of village chickens. Two intervention strategies were assessed: Newcastle disease vaccination using the thermostable I-2 vaccine and changes to the management of chick rearing (confinement and supplementary feeding). These interventions were applied in two trials: (1) a randomised controlled trial to compare I-2 vaccination, altered chick management and no intervention (apart from placebo treatment) at household level and (2) nested within this trial, a double-blinded controlled trial at bird-level to compare serological titres between I-2 vaccinated and placebo-treated birds both between and within households. Outcomes measured in the first trial were crude incidence rate of mortality, proportional mortality rate for deaths due to disease stratified by age group of birds and mortality attributed to Newcastle disease, number of sales, income from sale of birds, consumption of birds and hatching of birds. Odds of having protective titres two weeks after vaccination were up to 125 times higher in I-2 vaccinated birds and up to 47 times higher in control birds in contact with I-2 vaccinates compared to birds without I-2 contact. Vaccination against Newcastle disease reduced the proportions of mortalities assumed to be caused by disease in growers and chicks. Crude mortality incidence was lower in households that applied management changes to chick rearing. In household-months when birds were sold, numbers sold were higher and income from sale of birds were about 2.50 US dollars per month higher in households allocated to altered chick management. Altered chick management resulted in more households having hatchings of chicks. After a lag period of 7 months, these households were also more likely to consume home-produced chicken meat. This 7-month period reflects the age when birds are consumed and sold and highlights the lag periods that should be expected before beneficial effects of interventions focussed on chicks occur. This field research has shown that I-2 vaccination markedly increases the prevalence of protective titres and reduces proportions of mortality attributed to disease and that chick management using confinement and supplementary feeding can improve health and production of village chickens. These interventions are simple and sustainable intervention strategies.

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.