Precocious puberty in tamoxifen‐treated cockerels: Hypothalamic gonadotrophin‐releasing hormone‐I and plasma luteinising hormone,prolactin, growth hormone and testosterone

1. The administration of the anti‐oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin‐re‐leasing hormone (cGn‐RH‐I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels.

2. The increase in hypothalamic GnRH‐I content which occurs during sexual development was advanced in TAM‐treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth.

3. Plasma LH concentrations behaved similarly and were higher in the TAM‐treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM‐treated than in control birds; plasma GH values were not consistently affected by TAM treatment.

4. Both the growth and the involution of the bursa of Fabricius in the TAM‐treated cockerels preceded that in the control chicks.

5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.     

Plasma lipoprotein concentration as an indicator of fatness in broilers: Effect of age and diet

1. The relationships between plasma very low density lipoprotein (VLDL) plus low density lipoprotein (LDL) triglyceride concentrations at 3 and 7 weeks of age and body fat content at 7 weeks were studied in male and female broiler grandparent stock fed on diets containing about 25 or 90 g fat/kg.

2. Plasma VLDL plus LDL triglyceride concentrations were similar in males and females and only slightly higher in birds fed on the high‐fat diet. Concentrations at 3 weeks were similar to those at 7 weeks.

3. Body fat content was correlated more closely with plasma VLDL plus LDL triglyceride measured at 7 weeks than at 3 weeks.

4. Phenotypic correlations between body fat content and plasma VLDL plus LDL triglyceride concentrations at 7 weeks were 0.47 and 0.43 for males and females respectively fed on the high‐fat diet and 0.70 and 0.60 for males and females fed on the low‐fat diet.

5. Phenotypic correlations between body fat content and measurements with an abdominal caliper were 0.35 and 0.49 in birds fed on the high‐ and low‐fat diets respectively.

6. A possible procedure for selecting for leanness in broiler breeding programmes on the basis of measurements of plasma VLDL plus LDL triglycerides is discussed.     

Selecting broilers for low or high abdominal fat: Initial observations

1. Two lines of broiler breeders were selected for three generations using a high (fatty line) or a low (lean line) ratio of abdominal fat to live weight as criterion in males at 9 weeks of age.

2. The heritability of this character remained high in both lines.

3. By the third generation, the progress achieved was much more marked in males than in females. The difference between the females of both lines was nevertheless significant.

4. The differences between the two lines were already discernible at 4 weeks of age.

5. Selecting for low or high abdominal fat content was accompanied by a better food conversion ratio in males of the lean line.

6. Selecting for the amount of abdominal fat produced similar effects on the other fatty deposits.     

Effect of strain,sex and stocking rate on the performance and carcass yield of caged broilers

1. Performances of two broiler strains grown in cages at two different stocking rates to 8 weeks of age were compared.

2. High stocking rate (18 birds/m²) adversely affected weight and food conversion efficiency. Performance of females was more sensitive to stocking rate than that of males. Stocking rate x strain interactions in weight and food conversion efficiency at 8 weeks were highly significant.

3. Carcass dissection showed a marked difference between males and females.

4. Stocking rate merits further attention in respect of strain and sex.     

Activities of chicks in their home cages and in an open field

1. Previous work has shown that there are sex differences in the open‐field behaviour of 7‐d‐old domestic chicks. General activity is higher in females, whereas males respond by sitting or lying. It could be argued that such findings merely reflect the fact that females are generally more active than males. In the present study, therefore, a number of behaviour patterns were recorded both in the chicks’ home cages and in an open field or novel environment.

2. Differences in behaviour between the two sexes were found in the open field as before but not in the home cage.

3. This suggests that there is a genuine dichotomy between males and females in their responses to a novel environment.

4. The quantitative changes in behaviour patterns seen when chicks are moved from their home cage environment to a strange open field are consistent with the hypothesis that a novel environment evokes fear, especially in males.     

Growth and the plasma concentrations of growth hormone and prolactin in chicks: Effects of “environmental enrichment”, sex and strain

1. The effects of including novel objects in the environment ("environmental enrichment “) on body‐weight gain, relative body‐weight gain, gain : food ratio, plasma growth hormone (GH) and prolactin concentrations in male and female broiler and layer chicks was investigated.

2. Environmental enrichment improved body‐weight gain, relative body‐weight gain and gain: food ratio but had no effect on circulating GH or prolactin concentrations.

3. Weight gain and gain : food ratio were greater in the broilers than in the layer chicks, while plasma GH and prolactin (females only) concentrations were less.

4. There were no sex differences in weight gain and relative weight gain but gain : food ratio was significantly greater in females than in males. In both strains plasma GH concentrations were higher in males than in females and prolactin concentrations were higher in male than in female broilers.     

Effects of ageing and gonadal steroid hormones on prolagtin concentration in the anterior pituitary of the chicken

1. Effects of ageing and gonadal steroid hormones on pituitary prolactin (PRL) concentration in the chicken were investigated.

2. No difference was found in the qualitative electrophoretic patterns of the anterior pituitary homogenates at different ages and between the sexes.

3. Pituitary PRL concentrations in males were generally higher than in females.

4. Pituitary PRL concentrations in castrated immature cockerels were higher than in intact birds, while PRL concentration was depressed by the injection of testosterone propionate or oestradiol benzoate.

5. Prolactin concentration in intact immature cockerels was decreased by daily injection of testosterone or oestradiol for 3 weeks but not by injection of the hormones for 1 week.     

Agonistic interactions in developed and undeveloped breeds of chickens

1. Agonistic interactions were observed over a 24‐week period in Rhode Island Red and in Nigerian local fowl aged 32 weeks or 12 weeks at the start of the experiments.

2. Agonistic interactions were both more numerous and more severe (fights and peck avoidances) in groups of the local breed than in those of Rhode Island Reds.

3. The outcome of severe interactions favoured local males and Rhode Island females in the first experiment and Rhode Island males in the second.

4. Small body and comb size might account for the relatively high number of agonistic interactions and the submissiveness of local females and young males while physical strength or some other breed characteristic might account for the high number of agonistic interactions of local males as well as their dominance in breed encounters.     

Divergent selection of lean and fat lines of broilers over eight generations using plasma very low density lipoprotein as selection criterion

1. Male and female broilers from a male grandparent line have been selected over 8 generations on the basis of low or high plasma very low density lipoprotein (VLDL) concentration. This has given lines of lean and fat broilers.

2. Plasma VLDL concentration in the two lines has diverged steadily and showed a 7‐fold difference in the 8th generation.

3. Divergence of other traits, including abdominal and total body fat, body protein and conversion efficiencies of food and dietary protein has continued but body weight has not changed with selection.

4. Divergence of body composition and nutrient conversion relative to a commercially selected control line derived from the same origin as the experimental lines has been slightly greater for the fat line.

5. In the lean line, females have been more responsive to selection with the result that body compositions of lean line males and females at 7 weeks have become quite similar.

6. Plasma VLDL concentration decreased little in the lean line over the later generations and showed a lower phenotypic correlation with abdominal fatness than in the fat line in the 8th generation. A limit to selection for body fatness using this criterion may be approaching in the lean, but not in the fat, line.     

Effect of age and sex in determining cognitive ability in Vanaraja chickens

(1) To evaluate the cognitive ability of male and female Vanaraja birds, three hundred and sixty 1-d-old sexed chickens were reared under similar conditions in three treatment groups with 4 replicates in each group: 120 females in Treatment 1, 120 males in Treatment 2 and both males and females (60 + 60) as a mixed group in Treatment 3.

(2) To assess learning ability, the birds were trained in T- and Y-mazes and tested at 3-week intervals in 4 test schedules (21, 42, 63 and 84 d). The birds were put into tonic immobility (TI) in each test schedule.

(3) In each maze test, the latency to find the feed was regarded as a successful completion of the task. In the TI-test, the time taken to stabilise on a plane surface after swinging in the hanging cradle for 20–25 s was recorded.

(4) The results indicated that male birds appeared to be cognitively superior to females in terms of learning and cognitive evolution in all the mazes, but by d 84, the females performed as well as the males. With increasing age, spatial memory gathering and processing improved. In the TI-test, the effect of sex or grouping system had no significant effect on the performance of birds at the various ages.     

Effect of age and sex on the composition of muscle and skin from a commercial broiler strain

1. The effects of age and sex have been studied on the proximate composition and inorganic constituents in breast, thigh, drumstick and skin from a commercial British broiler strain (Ross 1).

2. Protein content generally increased with age in all muscles and decreased in skin. Protein content in skin of males was always higher than that in females.

3. Moisture content in all muscles decreased with age. In the skin, moisture decreased with age considerably more in females than in males.

4. Fat content increased with age in all tissues, while ash content of breast, thigh and skin decreased with age.

5. Phosphorus, chloride, magnesium and potassium all decreased with age in all the tissues. Thigh and skin calcium content were affected by age, as was the sodium content of drumstick and skin.

6. The sex effect on the inorganic constituents was variable.     

Effects of regular handling on growth in male and female chicks of broiler and layer strains

1. The effects of regular handling on growth and gain: food ratios in male and female chicks of layer (two strains) and broiler strains were examined from hatching to 3 weeks of age.

2. Growth was significantly enhanced by regular handling in broilers and the females of the layer strains and gain : food ratios were generally greater in the handled birds.

3. There were no significant treatment effects on growth or gain : food ratios in males of the layer strains.

4. Males had higher relative weight gains and gain : food ratios than females.     

Effects of male body weight,strain and dietary protein content on fertility and musculo‐skeletal disease in naturally mated broiler breeder males

1. The effects of male body weight at mating and different rates of gain on overall fertility were studied in two strains of broiler breeder males fed on a diet containing 160 or 120 g crude protein/kg. Sexual activity, musculo‐skeletal disease and culling were also assessed.

2. There were no differences in early fertility between males weighing 3–0 or 3–5 kg at the start of the mating period, or between males gaining 1.0 or 1.5 kg body weight from mating to 60 weeks of age.

3. There were no differences in fertility between males fed on the two diets differing in crude protein content.

4. One strain of male had lower fertility than the other and this was associated with a greater weight of breast muscle, lower frequency of observed copulations and a higher number of incompleted matings.

5. Sexual activity declined and the number of spermatozoa trapped on the perivitelline membrane increased with age.

6. There were no differences among the treatments in the prevalence of musculo‐skeletal lesions (destructive cartilage loss). As a proportion destructive cartilage loss occurred in 0^‐67 of the males at 66 weeks of age. Degeneration of the antitrochanter was present in 3 of 50 females examined and a cartilage flap in the medial condyle of the tibiotarsus occurred in 15 of these birds.

7. Beak lesions were the most important cause of male culling which averaged 0–24 as a proportion of the males at the start of the experiment.     

Directional selection for growth at two ambient temperatures in Coturnix coturnix japonica 1

1. Four lines of quail; random‐selected, male‐selected, female‐selected and male‐ and female‐selected lines, were subjected to 37 ± 1.6 °C from 3 to 5 weeks of age while another four lines, similarly selected, were reared at room temperature (15 to 27 °C).

2. Selection for increased growth was practised for two generations using ten females and five males as parents in each line.

3. A significant interaction between time and temperature was observed in the third generation progeny; when exposed to heat stress, the stress‐adapted lines showing a superior growth rate.

4. A sex × temperature interaction was also observed and was due largely to the control females being more sensitive to stress than the males.

5. A cumulative realised heritability estimate of 0.47 ± 0.15 for 5‐week body weight was obtained.     

A simple caliper technique for the estimation of abdominal fat in live broilers

1. A caliper technique for estimating the amount of abdominal fat in live broilers is described.

2. Sixty‐three male and 47 female broilers sampled at 63 d of age from an unselected control line were used to examine the accuracy of the caliper measure in predicting abdominal fat.

3. Phenotypic correlations between caliper measure and the proportion of abdominal fat were + 0.80, +0.79 and +0.81 in males, females and the heaviest 20% of males respectively.

4. The application of the technique as an indirect means of selecting for decreased abdominal fat in commercial broiler breeding programmes is discussed.     

Changes in body and organ weights of Japanese quail selected for 6‐week body weight 1

Three populations of Japanese quail, selected over 13 generations for increased body weight, a randomly selected base population and reciprocal backcrosses of selected lines to the control were studied. Live body weight and weights of liver, testes, oviducts and carcasses were obtained to assess the effects of selection.

At 6 weeks of age a 20 g. difference in live body weight existed between selected line and base population. Sexual dimorphism in live body weight in favour of females appeared at 3 weeks of age and increased with age. A 5 g. difference in 6‐week body weight between female backcross progeny from sires from selected lines and those sired by males from the base population suggested an influence of sex‐linked genes. At 8 weeks of age the weight of females of both reciprocal back‐cross types significantly exceeded the average of females from the selected lines suggesting that female reproductive organ weight had increased under selection as well as heterosis. Carcass weight of selected females was lower than for corresponding males, a reversal of the sexual dimorphism displayed by the controls.

Reciprocal differences in liver weight between backcross females, but not males, suggested an effect of sex‐linked genes.

Testis as well as oviduct weights of quail from selected lines were substantially greater than from controls.     

Growth hormone and prolactin secretion in growing domestic fowl: Influence of sex and breed

1. Plasma growth hormone (GH) and prolactin concentrations were measured between 1 and 24 weeks of age in both sexes of a laying strain of chickens and from 1 to 9 weeks of age in broiler cockerels.

2. GH and prolactin concentrations were highest in young birds and higher in males than in females.

3. In both sexes GH and prolactin concentrations were correlated inversely with age and body weight and positively with relative weight gain.

4. Differences in growth rate between broilers and layers were related to differences in blood GH concentrations.

5. Water deprivation for periods of 6, 12, 18 or 24 h increased plasma prolactin markedly but did not affect GH secretion significantly.     

The relationship between hatching egg weight and subsequent performance of broiler chickens

Small eggs constitute a high proportion of the eggs laid by pullets. The literature shows that chick hatching weight is strongly correlated with egg weight, but evidence on the influence of egg weight on hatchability and subsequent performance of chicks is less certain.

The aim of this experiment was to determine the profit returned at 12 weeks by broiler chickens hatched from eggs ranging in weight from 44 g. to 58 g. at one gram intervals and to determine how competitive and separate rearing might modify the relationship.

A total of 6000 eggs were collected during 10 days from a 28‐week‐old, broiler breeding flock and graded into the above mentioned egg weight classes. From these, a total of 3480 day‐old broilers were housed. Each egg weight class was equally represented and balanced for sex.

Hatchability and fertility showed no consistent trend with egg weight for eggs above 46 g., but below the 47 g. level there was a trend of declining fertility and hatchability.

A strong positive relationship was found between the weight of the chick at 1 day of age and egg weight for both males and females with no significant difference overall in body weight between the two sexes.

Body weight to 12 weeks was found to be strongly related to egg weight, in a linear fashion, though this influence declined with age.

There was a greater influence of egg weight on body weight at all ages in the separate rearing treatment compared with competitive rearing but this was not significant after 10 weeks.

Egg weight had an important bearing on body weight and profit at 12 weeks, but no effect on food conversion or mortality.

The increased profit over food costs per 100 day‐old chicks was found to be 52.75 cents for the separately reared birds respectively for each 3 g. increase in egg weight.     

Physiology of the growing and adult goose

The packed cell volume, haemoglobin concentration, erythrocyte sedimentation rate and specific gravity and percentage water of whole blood and plasma were determined at 4‐week intervals in male and female Pilgrim goslings from 1 to 20 weeks of age and in adult geese at 4‐ to 5‐week intervals from 34 to 59 weeks of age.

All parameters studied increased during the growing period except erythrocyte sedimentation rate which declined. There were no significant sex differences at any time during this period.

The packed cell volume of adult males remained relatively constant from 34 to 50 weeks while that of the females declined. After 50 weeks the female level began to rise in contrast to a decline in the males so that the values were about the same for both sexes at 59 weeks. Differences between sexes were highly significant between 43 and 50 weeks.

Changes in haemoglobin content and whole blood specific gravity were positively correlated with changes in packed cell volume while changes in erythrocyte sedimentation rate were negatively correlated.

Plasma specific gravity of adult males remained relatively constant whereas that of females decreased prior to commencement of egg production at 43 weeks, then increased significantly and remained significantly above the male level for the remainder of the adult period.     

Rearing temperature and the meat yield of broilers

1. One hundred and twenty (60 male and 60 female) 21‐d‐old Ross 1 broiler chicks were reared in cages in rooms kept at 21°C or 31°C and were killed at body weights of 1.0, 1.5, 2.0, 2.5 or 3.0 kg.

2. Birds reared at either of the two temperatures ate similar quantities of food to reach their slaughter weight although at 31°C they took longer to reach it.

3. The meat yields of the birds at each slaughter weight were similar at both rearing temperatures, but at body weights greater than 2.0 kg, the broilers reared at 21 °C had more breast meat than those reared at 31°C.

4. Females ate more food than males to reach each of the slaughter weights. The females deposited more fat and had a greater skin weight than the males and, although they had a similar amount of total meat, they had more breast meat.