Hybrid Chickens Research Articles

Alkaline Phosphatase Isozyme System, Akp-2, in the Chicken

An electrophoretic variation of the chicken plasma alkaline phosphatase was observed in the region migrated more anodally than that of the fast component reported by Law and Munro (1965). Some of chickens possessed a band in the region, while the others lacked it. Mating experiments suggest that the band is controlled by a resessive allele (Akp-2a) and a dominant allele (Akp-2o) at an autosomal locus. The band appears in plasma of the bird homozygous for the allele Akp-2a.Gene frequency of Akp-2a in Barred Plymouth Rocks, commercial egg-type hybrid chickens (Rhode Island Red×Rhode Island White), White Leghorns, and commercial meat-type hybrid chickens (White Cornish×White Plymouth Rock) was 0.54, 0.52, 0, and 0, respectively.

Effects of battery gage shape and dietary energy regulation on the performance of laying hens offered diets containing dried poultry manure

1. About 3000 medium‐weight hybrid chicks were used in a factorial experiment involving two “chick” treatments: diets containing 0 and 50 g dried poultry manure (DPM)/kg; three “grower” treatments, diets with and without 50 g DPM/kg given ad libitum and regulated amounts of the diet with DPM; five “layer” treatments: diets with 0, 100 or 200 g DPM/kg given ad libitum and regulated amounts of diets containing 110 and 220 g DPM/kg and two shapes of layer cages: deep (conventional) and shallow. 2. Chick diets had no significant effects on rearing or subsequent laying performance. 3. Food‐regulated pullets were 7% lighter than pullets given the DPM diet ad libitum at 18 weeks but consumed 12.5% less food; growing treatments had no significant effect on subsequent egg production. 4. Hens housed in shallow cages laid 10.3 eggs/bird‐housed more than those in deep cages, produced 3.8% greater egg mass, consumed 2.7% less food and produced fewer damaged (cracked, broken and hair‐cracked) eggs (P< 0.001). 5. DPM‐co...

Studies on experimental tenosynovitis in light hybrid chickens

A group of light hybrid chicks was inoculated via the footpad at 1-day-old with an avian reovirus isolated from ruptured gastrocnemius tendons, and were housed with a similar number of uninoculated chicks (in-contacts) from the same hatch. Though all inoculated birds showed swellings of the injected leg after 7 days, lesions of tenosynovitis did not develop in the other leg or in either leg of in-contacts until they were 6- to 7-weeks-old. Lesions in leg tendons, and particularly the digital flexors, persisted in both inoculated and in-contact birds until the termination of the experiment at 33 weeks of age. Reovirus was recovered for varying periods from the trachea, intestine, hock and footpad of inoculated chickens commencing 1 week after infection, and from the same tissues of in-contacts but from 2 weeks, and generally for shorter periods. In both groups virus persisted for at least 13 weeks in the hock joint or surrounding tissues and cloacal swabs were positive between the 14th and 16th weeks after inoculation. Fluorescent antibody staining demonstrated penetration of the virus into the tendons. Precipitating antibodies to the reovirus were detectable in both groups between the 3rd and 24th weeks after infection.

Effects of different lighting regimes on diurnal feeding patterns of the domestic fowl

1. Male hybrid chicks were, from hatching, subjected to either a 12‐h photoperiod with uniform light intensity or a 12‐h photoperiod with a simulated “dawn” and “dusk” or to continuous light. 2. At 10 weeks of age the birds exposed to “dawn” and “dusk” were significantly heavier than those exposed to 12 h uniform illumination and these were heavier than those in continuous light. 3. From 15 to 25 weeks of age the birds in continuous light showed a marked diurnal rhythm in food intake, eating most in the period corresponding to normal daytime, while all birds subjected to 12‐h photo‐periods ate most at the end of the day, apparently having learnt to anticipate when their day would end. 4. When the birds subjected to continuous light were given one of the two 12‐h photoperiods, those given 12 h of uniform light intensity started by eating most food in the mornings, but later ate more towards the end of the day, while those with the “dawn” and “dusk”, ate more food at the end of the day during most of the 20...

CHIMAERISM OF IMMUNOCOMPETENT CELLS IN ALLOGENEIC BONE MARROW-RECONSTITUTED LETHALLY IRRADIATED CHICKENS

Injection of parental bone marrow cells into 12-day-old lethally irradiated F1 hybrid chickens resulted in chimaerism of donor-type graft-versus-host (GVH)-reactive cells and suppression of antisheep red blood cell antibody response. These manifestations of a chronic graft-versus-host reaction were prevented by pretreatment of the donor marrow with specific anti-T cell globulin. In some chimaeras donor-type GVH-reactive cells developed gradually from T cells precursors of donor origin. Transplantation of spleen and marrow cells from sheep red blood cell-primed F1 hybrid donors into lethally irradiated parental recipients resulted in the loss of memory potential within 1-2 weeks of transfer, whereas donor-type IgG allotype synthesis was preserved. Injection of goat antichicken thymocyte serum to recipients 1 day before reconstitution enabled the antibody response of memory cells at 1-2 weeks, although it failed to prevent their rejection by 8-9 weeeks after transplantation. Split chimaerism of donor-type GVH-reactive cells was demonstrated in chickens which had previously rejected the B cells derived from the same graft.

Effects of group size on the feeding behaviour and growth of chicks

1. The aim of the study was to see if social facilitation of feeding has a lasting effect on the growth of chicks. 2. In two experiments, newly hatched hybrid and Brown Leghorn chicks were reared in isolation and in small groups of different sizes, and their growth, food intake and feeding activity were measured for several eeks. 3. Initially, chicks of both strains grew faster when they were grouped than when they were in isolation, as a result of a more efficient conversion of food rather than as a result of increased consumption. 4. Later, chicks in the largest groups converted their food less efficiently, possibly because of increased disturbance. 5. From 6 to 12 weeks, when the chicks were in larger cages, growth rate was not affected by group size, but food intake and food conversion were affected differently in the two strains. 6. In general, the isolated chicks ate about the same amount as the grouped ones, and it is doubtful whether social facilitation of feeding occurred at all in these experiments.

Studies on reducing the crude protein content of feeds fed to chicks and young hens (laying stock)

2 rearing trials were carried out on a total of 8550 hybrid chicks (White Leghorn) to investigate in which way food mixtures containing reduced levels of crude protein (supplemented or unsupplemented with amino acids) might influence the growth of chicks and young hens. Decreases from 21.5% to 16.5% in the crude protein content of chicken feed and from 15% to 13% in feeds feed to young hens (greater than 8 weeks of life) did not reduce the live weight of birds at the end of the rearing period to any appreciable extent. No clearly defined differences were found to exist between the different types of feed tested concerning the amount of food and energy consumed per unit of weight gain and the mortality rate among the birds; it was shown, however, that the demand for crude protein per unit of weight gain was clearly reduced in birds reared at the lower crude protein level. For young hens receiving the diet poorer in protein the date when the birds began laying was slightly delayed. Otherwise, no statistically significant differences were found to exist between the young birds fed varying levels of crude protein, concerning the age at 50% laying performance and other parameters that are characteristic of the entire laying period (laying performance, weight of individual eggs, food consumption, mortality, fertilization of hatching eggs, hatchability of eggs). It appears that the feeding of a reduced protein diet to chicks and young hens (laying stock) did not have any detrimental effect on the growth and later laying performance of the birds. Apart from the fact that the demand for protein feeds is considerably reduced during the rearing period the costs of feeding per bird can also be cut down.

Growth and behaviour of chicks fed on pellets or mash

Synopsis Newly hatched hybrid and Brown Leghorn chicks were fed on diets in either pellet or mash form and growth and feeding behaviour were studied. The mash was made by re‐grinding the pellets. All chicks fed on pellets were heavier after 40 d, but had eaten no more than those fed on mash. The apparent digestibilities of pellets and mash were about the same in the hybrid chicks but was greater for mash than pellets with the Leghorn birds. All chicks fed on mash spent more time feeding than those fed on pellets, but the times spent on drinking and resting were similar with both food forms. Chicks which were given a choice of food form consistently preferred mash to pellets. It is concluded that pelleted food was converted more efficiently than mash mainly because chicks spent less time feeding on pellets and so expended less energy, and in the case of the Leghorns there may have been improved digestibility when the food was pelleted.

The Relationship between Hatching Time and Sex-ratio in Chicks

The relationship between hatching time and sex-ratio in chicks was investigated in connection with breed and age of their parents, laying season and egg size. The chicks used were 3 strains of White Leghorn (W.L.) and hybrids between Rhode Island Red (R.I.R.) male and Rhode Island White (R.I.W.) female and between W.L. male and Barred Plymouth Rock (B.P.R.) female, and the reciprocal hybrid of the latter. Chicks that hatched alive were classified according to time intervals of every 2 or 3 hours after the start of hatch and sexing was done immediately after hatch.Female chicks tended to hatch earlier than males and the difference in hatching time between males and females varied among the breeds or the strains used, especially in the hybrid between R.I.R. male and R.I.W. female.Female chicks hatched earlier than males in proportion to the increase of age of their parent stocks in the hybrid between R.I.R. male and R.I.W. female, whereas no difference was observed among the other breeds used.In general, hatching time also might be earlier during the hot season than during the cold. This was clearly shown in the R.I.R. male: R.I.W. female hybrid and the difference of hatching time between the two sexes was more distinct in the hot season than in cold in this hybrid.Large eggs tended to hatch earlier than small ones in the R.I.R. male: R.I.W. female hybrid and vice versa in the Shaver strain of W.L. Eggs of medium size showed less difference in hatching time between the two sexes than those of larger or smaller size in hybrid chicks from R.I.R. male and R.I.W. female.It might be concluded from the results that the hatching time and the sex-ratio are affected considerably by the breeds or the strains of their parents.

Immunocompetent cells in the chicken: II. Synergism between thymus cells and either bursa or bone marrow cells in the humoral immune response to sheep erythrocytes

Newly hatched F 1 hybrid chicks isogenic for the strong B histocompatibility locus were rendered immunologically incompetent by cyclophosphamide treatment and x-irradiation. They were then injected intravenously with thymus, bone marrow, or bursa cells together with sheep erythrocytes (SE) and received another iv injection of SE 3 days later. Splenic plaque-forming cells (PFC) and serum hemagglutinins were assayed 7 days after transfer. At donor ages of 14–26 days, cells from thymus (T) and bone marrow (BM) showed synergism when injected together, as indicated by a significantly higher geometric mean of PFC per recipient spleen in the BM + T group than in the BM group. The response of the T group was extremely low. With thymus and bursa cells from 6- to 28-day-old donors, significant synergism was demonstrated in 3 of 9 individual experiments. However, almost all the other 6 experiments showed marked differences in the same direction, and the combined probability for all experiments was < 0.001. The most striking demonstration of thymus + bursa synergism was made in 2 experiments using 1-week-old donors. Bone marrow cells from 1-week-old donors failed to cooperate with thymus, as did BM cells from older bursectomized agammaglobulinemic donors. This suggests that B cells from bone marrow originate in the bursa. Thymus-bursa cooperation was somewhat difficult to demonstrate in individual experiments using donors over 1 week of age, owing to the occurrence of some responses with bursal cells alone and to variability of response within bursa or bursa + thymus recipient groups. Synergism between thymus and bursa cells was more consistently demonstrable when irradiated normal spleen or low doses of bone marrow cells were added. These additions led to an increased response and a lowered coefficient of variation in the thymus + bursa recipient groups. The ‘third’ cell type needed for optimal response by the thymus and bursa cells together was tentatively identified as a macrophage.

Differentiation of male chick oviducts under hormonal stimulation.

Abstract Hybrid chick embryos with a sex-linked marker were treated with estradiol benzoate. After hatching, females and intersexual males were treated with a combination of estradiol benzoate and testosterone enanthate. After 1 wk of treatment, a histological study of their oviduets was made. Oviduels from intersexual males responded to hormonal stimulation by differentiating typical infundibular and albumen-secreting portions. Albumen-secreting glands contained granules with the same characteristies as those previously deseribed in oviducts of normal hens. These results demonstrate that oviduets of intersexual males can complete their differentiation.

EFFECTS OF MICROWAVE RADIATION ON GROWTH AND REPRODUCTION OF TWO STOCKS OF CHICKENS

White Leghorn hybrid and broiler type chickens were subjected to continuous wave (CW) microwave radiations, at a frequency of 6 GHz and at densities of 0.02 and 400 pw/cm2. The birds were exposed continuously from hatching, throughout the growing and reproductive period, to 420 days of age for broiler-type stock and to 476 days of age for egg-type stock. Microwave treatment of birds had no significant effect on growth rate, feed efficiency, egg production and quality, hatchability, and mortality in either type or stock.

Feeding layers with different levels of energy and protein in the Eastern Province of Saudi Arabia.

Three hundred day-old Single Comb White Leghorn hybrid chicks were kept in insulated units with ventilators and 930 in traditional open-air units under a corrugated galvanised sheet roof in Saudi Arabia. All were fed on a standard diet. Growth in both groups was almost equal, but feed conversion was slightly more favourable in the insulated house. Overall mortality was considered to be favourable. The remaining 995 pullets, when of laying age, were divided into 8 groups, 2 of which were kept in the insulated units, and the rest in open-air units. During the laying period, 4 groups were fed on a high-energy (HC) mash and 4 on low-energy (LC) mash. A 17-h lighting schedule was maintained. Feed intake and energy and protein conversion were higher in the LC groups, while gross feed conversion was better in the HC group and the hens tended to be slightly heavier. There was no difference in egg production between feed groups, but that of hens in insulated units was higher than that of hens in open units. Mortality was higher in the HC group, the main cause being visceral lymphomatosis, and higher in the open housed groups, where 33 died from heat stroke in July, than in the insulated units. The authors conclude that the favourable aspects of the HC feeding were offset by the higher mortality and the higher feeding costs, and so the LC mash might be more profitable. I. F. la C. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Aflatoxin effects in livestock.

AbstractFeeding trials were conducted with swine, beef cattle, dairy cattle and poultry to determine adverse effects, if any, of graded levels of aflatoxins in rations. In addition, samples of meat, eggs and milk from these animals were analyzed chemically to determine if aflatoxin was transmitted into these products. In growing‐fattening swine, no evidence of toxic effects was observed when the aflatoxin level fed was 233 ppb or less. In a swine reproduction experiment, no adverse effects were detected in pigs produced from sows fed 450 ppb aflatoxin. No toxic effects were observed at levels of 300 ppb or lower in cross‐bred beef steers fed aflatoxin rations for 4.5 months. Using recognized chemical methods, we detected no aflatoxin in meat from swine and cattle fed rations containing 800 and 1000 ppb of aflatoxin, respectively. In dairy cows, weekly intakes of 67 to 200 mg of aflatoxin B1 per cow produced 70 to 154 ppb aflatoxin M1 in lyophilized milk. Rapid disappearance of aflatoxin M1 in the milk took place after withdrawal of aflatoxin from the ration. No adverse effects were discernible in broilers fed from one day to eight weeks of age a ration containing 400 ppb aflatoxin. Lyophilized meat from broilers fed 1600 ppb aflatoxin for eight weeks contained no detectable aflatoxin. Striking differences in aflatoxin susceptibility were observed in 17 different breeds and strains of poultry and game birds fed from two to six weeks of age a ration of 800 ppb aflatoxin B1. New Hampshire chicks and turkey poults were highly susceptible to aflatoxin in contrast to the resistance of Barred Rock and Australop chickens and guinea fowl. Hybrid chicks from a New Hampshire‐White Leghorn cross were highly resistant to aflatoxin. Eggs and meat from White Leghorn hens fed a ration containing 2700 ppb aflatoxin contained no detectable aflatoxin.

GROWTH AND REPRODUCTION OF CHICKENS SUBJECTED TO MICROWAVE RADIATION

White Leghorn hybrid chickens of different ages were subjected to CW microwave radiations at a frequency of 6 GHz and at densities of 0.02 and 400 picowatts/cm3. Microwaves were produced by a Varian LD 807 travelling wave tube. Continuous or periodic exposure of chickens during the growing stage did not affect their growth or feed conversion efficiency in comparison with non-treated controls. Hens subjected continuously, from 1 day old, to microwave treatment at the low or high densities showed significantly higher percent hen-day rate of lay, during 169 to 476 days of age, and significantly lower egg weight than the untreated birds. The low-density treatment resulted in significantly higher fertility than the high level of treatment. Egg quality, mortality and several other traits studied were unaffected by the treatments.

Transfer of antibody production with cells from bursa of Fabricius.

F(1) hybrid chicks isogenic for the strong B histocompatibility locus and for most weak H-loci were X-irradiated on day 1 after hatching, injected intraperitoneally on day 2 with dispersed cells of bursa, spleen, or thymus from 4- or 10-wk-old F(1) hybrid donors, and immediately challenged by the same route with either Brucella abortus, sheep erythrocytes, or a mixture of both together. The agglutinin titers were measured in sera obtained 1 wk later. With 4-wk-old donors, a greater primary response to Brucella abortus was obtained after transfers of cells from bursa than from spleen, while thymus was much less effective. With 10-wk-old donors, the decreasing order of response was spleen, bursa, thymus. Only splenic cells were effective in transferring a response to sheep erythrocytes, at either donor age. In tests of synergism by cell mixtures from pairs of organs, the only positive finding was a modest augmentation of titer against sheep erythrocytes by bursa + spleen as compared with spleen alone. Bursal cells from 6- or 10-wk-old donors were effective in transferring a response to sheep erythrocytes when antigen injection was delayed until 5 days after cell transfer. Splenic cells from hormonally bursectomized donors were ineffective in transferring a primary response, even when the donors had been injected with antigen 1 wk before transfer. Preimmunization of normal donors led to marked increases in the responses to Brucella abortus produced by transferred splenic or thymic cells. With bursal cells, an increased response was obtained only if the interval between preimmunization and transfer was 17 rather than 7 days. With the 17-day interval, both bursal and thymic cells could also transfer a response to sheep erythrocytes. The primary sera to Brucella abortus produced after transfers of bursal or splenic cells contained almost entirely 19S antibodies. A 7S component was found in all the secondary sera tested.

Assessment of resistance to infectious diseases in birds of line selected against neoplasms

As a result of specific selection by CAM-test, two lines of chickens with increased resistance to infection with pathogens of Marek's disease and lymphoid leukemia of the group were created: D-2 - on the basis of Leghorn breed, P-2 - Poltava clay. The D-2 resistance index was 50.5%; P-2 79.3% against control, D-4 - 11.0% and P-37 - 58.8%. Selection by CAM - test helped to increase the bird's resistance to leukemia. When artificially infected with the leukemia virus, subgroups A of the selected lines were probably (at P &lt;0.01) more resistant to leukemia than non-selected. A similar pattern of resistance to leukemia was observed in natural infections.&#x0D; The bird of line D-2 was more resistant to Marek's disease: the percentage of deaths from this disease in it was 7.0, while in line D-4 (initial, unselected) and 15.5% of the initial population (not vaccinated bird). After vaccination, the number of deaths from Marek's disease decreased to 0.11% and 1.33%, respectively, the named lines. Line P-2 did not show a probable increase in resistance to tumors caused by Marek's disease in comparison with control P-1. Lines P-2 and D-2 during specific selection did not reduce their resistance to the most common bacterial pathogens (E. coli, S. pullorum), did not differ from unselected lines on the sensitivity of the main immunocompetent organs to vaccination (La-sota, smallpox vaccine), as well as the introduction of thymus - and bursa-dependent antigens.&#x0D; In most cases, both interbreed and interlinear hybrids have an intermediate inheritance of resistance to infection by oncornaviruses, ie hybrids occupied the middle position between more or less resistant baselines.&#x0D; The hybrid bird, obtained using lines resistant to neoplasms, at the age of 30 weeks had an egg weight of 52-54 g, at the age of 6163 g, and the average for the year - 58-60 g. The egg mass in the best combinations is 14-15 kg. The age of 50% egg production varied significantly depending on the year of the study, the quality of the young and the time of its transfer to poultry houses. Under optimal conditions, the bird reached 50% of egg production at the age of 160-165 days, but the weight of eggs at this age is low - 47.9 - 48.6 g.&#x0D; As a result of tests of the best laying on the initial and middle laying hens revealed a combination of B-7 x D-2, from which for 72 weeks of life received 230 eggs per initial and 244.2 eggs - on the average laying hen at the weight of eggs at the age of 30 weeks 52.7 g and 52 weeks - 63.1 g. However, the preservation of these hybrid chickens was lower by 2.3%, compared with P-2xD-2. The registered death from neoplasm was 0.9% of the initial population against 0.45% in P-2 x D-2.&#x0D; At the same time, chickens of the B-7xD-2 hybrid combination received 9.7 more eggs per average laying hen than other hybrids tested in the same poultry house under the same conditions (250.2 eggs vs. 240.5). A characteristic feature of the tested combinations is their reduced susceptibility to neoplasms, the frequency of registered neoplasms did not exceed 1%, while the rest of the chickens of this poultry departure from the neoplasm was 1.75%, ie 2 times more.

The Host Range of BRYAN Strain Rous Sarcoma Virus Synthesized in the Absence of Helper Virus

SUMMARY Different L-R ‘non-producer’ cell lines synthesized one of two types of RSV(O), distinguishable by host range. RSVα(O) has no known natural host. RSVβ(O) is infectious for Japanese quails, European pheasants and some Brown Leghorn, White Leghorn and Reaseheath I × C hybrid chickens. The host range of RSVβ(O) is distinct from other avian tumour viruses. Host susceptibility to RSVβ(O) is genetically determined in a complex and as yet unclear way. It is not correlated with response to the A, B, and C sub-groups of avian tumour viruses or with presence of the natural antigen which reacts in the COFAL test: nor is it sex-linked. RSVβ(O) is not markedly oncogenic in hamsters. The difference between RSVα(O) and RSVβ(O) did not appear to be a heritable property of the RSV particle but depended on the type of host cell in which the virus was cloned. Synthesis of RSVβ(O) occurred only after passage through COFAL positive host cells. The possible control of the infectious properties of RSVβ(O) by a helper virus present in an elusive form in permissive hosts is discussed. A stock of inactivated Sendai virus commonly used for cell fusion was apparently contaminated with an active avian leukosis virus.

Development of black down feathering in hybrid chick embryos (cross New Hampshire male with light Sussex female) after pituitary implantation.

Hypophysen von embryonalen oder alteren Huhnern wurden in die Bauchhohle von 5 Bruttage alten Hybriden der Huhnerkreuzung New Hampshire ♂ × Light Sussex ♀ implantiert. Vom 12. Bruttage an zeigen die Embryonen beider Geschlechter ein Gebiet mit schwarzer Daunenpigmentierung am Hinterkopf. Implantationen mit anderen Geweben und Injektionen mit synthetischen Hormonen blieben ohne Erfolg, ausgenommen ACTH und MSH, die schwach positiv waren. Die Ansicht, dass das Melanozyten-stimulierende Hormon (MSH) fur die verfruhte Entwicklung des schwarzen Nackenkragens der Light-Sussex-Rasse verantwortlich ist, wird durch die Beobachtung erhartet, dass das Gebiet uber der Epiphysis cerebri von schwarzem Gefieder entblosst bleibt.

The Effect of Climate on the Growth Performance of Populations of Broiler Chickens

The average hatching weight of chicks was heavier during summer than during other seasons of the year. Hatching weight was found to be correlated with bodyweight at nine weeks of age. The advantage in favour of the summer hatched chicken explains in part the farming community’s opinion that the summer chicks are better than other chicks. The climate affected the growth rate of hybrid chicks only in early life; within the temperature range 55–80°F, temperature influenced the bodyweight gain only during the brooding period and after this age body size was the important factor determining succeeding weight gain. Le poids moyen des poussins qui venaient d’éclore était plus élevé pendant l’été que pendant les autres saisons de l’année. On a trouvé que ce poids à l’éclosion était en corrélation étroite avec le poids des poussins de 9 semaines. Cet avantage des poussins éclosant l’été explique en partie l’opinion des éleveurs, suivant laquelle les poussins nés en été sont meilleurs que les autres. Le climat n’affectait la croissance des poussins hybrides que juste après leur naissance; entre 55 et 80°F, la température n’influençait l’augmentation de poids que pendant la couvée des poussins et, après cette période, leur taille était le facteur déterminant pour qu’ils parviennent à peser plus. Das Durchschnittsgewicht geschlüpfter Kücken war während des Sommers etwas höher als während der anderen Jahreszeiten. Das Gewicht 9 Wochen alter Kücken entsprach dem Gewichtsverhältnis nach dem Schlüpfen. Der Vorsprung der im Sommer gebrüteten Kücken erklärt teilweise, warum die ländliche Bevölkerung der Meinung ist, dass Sommerkücken besser sind als andere. Das Klima beeinflusst die Wachstumsrate gekreuzter Kücken nur in den frühen Lebensstadien; innerhalb der Temperaturspanne von 55–80°F beeinflusste die Temperatur die Gewichtszunahme nur während der Brutperiode; später war die Körpergrösse der massgebende Faktor, der die Gewichtszunahme bestimmte. El peso medio de incubación de los pollitos fué mayor durante el verano que durante otras estaciones del año. Se observó que el peso de incubación estaba correlacionado con el peso del cuerpo a las 9 semanas de edad. Las ventajas a favor de los pollitos incubados en verano explica en parte la opinión de las comunidades granjeras de que los pollos de verano son mejores que los otros. El clima afectó el índice de crecimiento de los pollitos híbridos únicamente en sus primeras etapas de vida; dentro de una temperatura oscilante entre los 55–80°F, la temperatura sólo influenció el aumento del peso del cuerpo durante el período de empolladura, y después de esta edad, el tamaño del cuerpo fue el factor importante que determinó el aumento de peso subsiguiente.