E. A. Dunnington

Jungle fowl-domestic fowl relationships: a use of DNA fingerprinting.

There has been a long and continuing interest among poultry breeders and scientists in relationships of domestic fowl with their jungle fowl ancestor. Recent commercial practices in poultry breeding have greatly changed and improved the meat and egg stocks available for the production of food. There is concern, however, that artificial selection for traits of economic importance has caused a narrowing of the genetic base and subsequent reduction in genetic variability. Because continued progress in the achievement of increased growth or egg production depends heavily on genetic variability, its present status is of interest. Current techniques in molecular biology allow estimations to be made of genetic distance among populations. This paper reviews DNA fingerprinting in poultry using results from this technique to survey genetic diversity among jungle fowl, domestic fowl representative of stocks from several decades ago and todays commercial broilers and layers. The genetic distance between wild jungle fowl and layers has been found to be similar to that between wild jungle fowl and broilers. Within the two types of modern commercial fowl there is less genetic diversity among broiler than layer stocks.

Long-term selection for 8-week body weight in chickens - direct and correlated responses.

SummaryA bidirectional selection experiment for 8-week body weight in chickens was conducted. In addition to 27 generations of selection, random samples were chosen from each selected line in generations 6, 13, 19 and 26 to initiate lines in which selection was relaxed. Genetic change was evident in the selected high-weight line through the first 75% of the study after which response in the direction opposing selection occurred. Selection for low body weight resulted in considerable reduction in body size, particularly in the last quarter of the study. Correlated responses evaluated were body weight at several ages, conformation, age at onset of lay, various reproductive and egg quality traits and ratio (female: male) of some traits. Data from lines where selection was relaxed indicated that natural selection opposed artificial selection with the effects greater in later generations.

Aspects of food intake restriction in young domestic fowl: metabolic and genetic considerations

This paper reviews the literature on the response of young domestic fowl to various food restriction patterns. Emphasis has been given to anatomical, endocrine and immunological factors and their interactions with the genetic background. Under restricted feeding (limitation of the amount or time of access to food) chickens learn quickly to ingest the allocated quantity of food within a short period of time. When exposed to a single sequence of food removal and restoration, body weight losses are reduced for non-adapted compared with adapted individuals, for light breeds compared with heavy breeds, and for older compared with younger chickens. Adaptation to food restriction includes increased capacity and slower evacuation of the gastrointestinal tract (mainly the storage organs) to increase the supply of nutrients during the periods of food deprivation; increased hepatic lipogenesis and glycogen synthesis during the feeding cycle; and decreased heat loss on days of food deprivation. Synthesis and secretion of digestive enzymes in response to intermittent feeding has been found to be population dependent and consistent with the hypothesis that the amount of intestinal chyme mediates the synthesis and excretion of digestive enzymes from the pancreas. Numerous hormones are directly or indirectly involved in the metabolic responses to food restriction. Hyperinsulinaemia, increased plasma levels of growth hormone, triiodothyronine, thyroxine and plasma prolactin have been observed after the reintroduction of full feeding. It is suggested that the altered hormonal environment induced by food restriction contributes to a metabolic situation that may enhance immunocompetence.

Food intake adjustments of chicks: Short term reactions to deficiencies in lysine, methionine and tryptophan

1. Two experiments were conducted to compare food intake responses of broiler chicks fed diets varying in lysine, methionine, and tryptophan. Diet D was formulated to create simultaneous deficiencies of lysine, methionine, and tryptophan. Diet A matched National Research Council (1984) recommendations for broilers, and diets B and C were, respectively, 2:1 and 1:2 mixes of diets A and D. 2. Short-term food intake can provide information on the sequences of adaptation of chicks to a diet deficient in essential amino acids. 3. Chicks consumed 26% less of diet D than A during the first 24 h posthatch. When chicks fed diet A or D to 7 d of age were then fed one of 4 diets singly, within 24 h intake was lowest for chicks fed diet D. Within 48 h, food intake of diet C was more than that of diet D and less than that of diet A, while for diet B intake was more than of diet D but not different from diet A. 4. In the second experiment, chicks were fed diet A to 8 d and then diets A or D alone or given a choice of diets A and D from 8 to 20 d of age. Within 4 to 8 h, food intake of chicks fed diet D alone decreased markedly followed by partial recovery within 24 h. In a choice setting, consistent preference of Diet A over Diet D was observed within 7 h followed by stabilisation at about 65% diet A to 35% diet D. 5. Chicks fed diet D alone from 8 to 20 d of age, then placed in the same choice situation preferred diet A to D with a delay of less than one h and stabilisation at about 85%. Chicks provided a choice of diets A and D from 8 to 20 d, and then diet D alone reduced their food intake more quickly than those not given a choice initially. 6. Broiler chicks appear to react to amino acid deficiencies within a short period (hours) by adjusting their feed intake and/or selection. The response is influenced by age and prior experience.

Food restriction early or later in life and its effect on adaptability, disease resistance, and immunocompetence of heat‐stressed dwarf and nondwarf chickens

1. Dwarf and nondwarf chickens placed under 60% food restriction from either 4 to 6 (early) or 24 to 26 (late) days of age were exposed to high ambient temperatures (35 +/- 2 degrees C) from 36 to 43 d of age. 2. As measured by heterophil/lymphocyte (H/L) ratios, stress response to food restriction was similar at both ages for dwarfs while less at the younger than the older age for nondwarfs, resulting in a significant food restriction interaction of genotype by age. 3. Nondwarf chickens food restricted at the younger age had smaller increases in H/L ratios, improved resistance to marble spleen disease infection and greater growth than those restricted at the older age or fed ad libitum in response to the high ambient temperatures. 4. For dwarf chickens feeding regimen had no influence on response to the environmental insults. 5. Antibody response to sheep erythrocyte antigen was not affected by genotype or feeding regimen.

Anorexia and sexual maturity in female white rock chickens. I. Increasing the feed intake

Long-term selection for low juvenile body weight has resulted in a line of chickens where sexual maturity is retarded or prevented because of anorexia.Ad libitum-fed pullets which had not commenced egg production by 240 days of age were randomly assigned to be force-fed or fedad libitum. Increasing food intake via force-feeding caused a significantly greater proportion of females to commence egg production than was noted forad libitum-fed controls. Moreover, of those pullets that commenced lay, age at onset was significantly earlier in those force-fed than in those fedad libitum.

Inhibition of adrenal steroidogenesis, food restriction and acclimation to high ambient temperatures in chickens

1. White Plymouth Rock chickens placed under 60% food restriction or ad libitum feeding, with or without metyrapone treatment, from either 4 to 6 (early) or 24 to 26 (late) d of age were exposed to high ambient temperatures (35 +/- 2 degrees C) from 36 to 43 d of age. 2. Stress attributable to fasting was not manifested through leucocytic alteration when food-restricted chicks were supplemented with an adrenal blocking chemical, metyrapone. 3. Provision of metyrapone during the fasting period resulted in inferior compensatory growth during refeeding. 4. Exposure to high temperatures from 36 to 43 d of age did not cause an elevation in the heterophil:lymphocyte (H/L) ratios of chicks that had eaten metyrapone-treated food ad libitum during the neonatal stage. 5. During heat exposure, chicks that had been subjected to early 60% restriction with non-metyrapone-treated food had lower H/L ratios and improved resistance to marble spleen disease infection.

Effects of dietary corticosterone in young leghorn and meat‐type cockerels

1. Cockerels from meat-type (MT) and Leghorn (LG) stocks were fed on diets containing 0, 20, or 30 mg corticosterone/kg from 1 to 22 d after hatching. 2. Within MT and within LG stocks, responses to dietary corticosterone inclusion rates were similar; however, patterns differed between these major classes resulting in stock X diet interactions. 3. Traits responding to different inclusion rates of corticosterone in a dissimilar manner for MT and LG chickens included: immunoresponsiveness, body weight, efficiency of food utilisation, feathering; relative weights of liver, spleen, bursa, testes, breast and abdominal fat pad, as well as the proportion of liver lipid. 4. No differential responses occurred for relative adrenal weight, plasma xanthophyll concentrations, proportion of breast lipid and abdominal fat, or surface and cloacal temperatures. 5. Results indicated genetic differences in thresholds for response to corticosterone and in degree of response once thresholds were reached. Within populations, sensitivities varied between target organs.

Mating frequency in male chickens: long-term selection

SummaryTwenty-three generations of bidirectional selection in male chickens (Gallus domesticus) for number of completed matings resulted in widely diverse mating behavior in the high and low lines. Selection caused a steady increase in cumulative number of completed matings (CNCMs) of the high line with a realized heritability of 0.18±0.02. In contrast, selection for decreased CNCMs caused many males to pass a threshold below which they would not mate naturally. Changes in male mating behavior were not accompanied by changes in mating behavior of females.

Growth related traits in body weight selected lines and their crosses reared under different nutritional regimens

1. Four populations--two that had undergone 37 generations of selection for high (HH) and low (LL) body weight, and reciprocal crosses between them (HL and LH) were fed two diets differing in protein and energy. Diet A, under which selection had been made, contained 200 g protein and 11.23 MJ/kg. Diet E contained 240 g protein and 13.16 MJ/kg. 2. Body weight and feed efficiency were measured weekly from hatch to 56 d of age at which time oesophagus, abdominal fat pad, heart, liver and lungs were removed and weighed. At 35 d of age chicks were inoculated with sheep erythrocytes (SRBC) and antibody titre was measured 6 d later. 3. Chicks fed diet E were heavier than those fed diet A. HH chicks were heavier than LL chicks with HL and LH chicks intermediate to the parental lines. LH chicks were heavier than HL ones reflecting large maternal effects. 4. Food efficiencies among stocks and diets were consistent with those for body weight, with HH > LH > HL > LL and E > A. Relative differences between diets were similar across ages and heterosis for food efficiency was about 15%. 5. Relative to body weight, oesophagus and liver weights were heavier in chickens fed diet A than fed diet E. The pattern reversed for abdominal fat pad. 6. Antibody to SRBC antigen was greater in the crosses than in line HH and in cross HL than line LL, with heterosis of 70%.