Comparison of sex-linked dwarf genes in chickens from two sources when introgressed into unrelated genetic backgrounds

1. Sex-linked dwarfing genes from 2 broiler stock origins (EU and US) were each introgressed into 2 White Leghorn populations that had been divergently selected for antibody response to sheep erythrocytes. 2. When the resulting backcrossed populations were 87.5% of their respective. White Leghorn line, non-dwarf pullets were assessed for body weights, shank lengths, immunoresponsiveness, age and body weight at sexual maturity, egg production, average egg weight, and duration of fertility. For measurements where there were no differences between non-dwarf pullets from the 2 origins of the dwarfing genes, then the dwarf pullets (which were full sisters to the non-dwarfs) were compared. 3. Shank length at 8 weeks of age and mature (24-week) body weights were higher for dwarf pullets from EU than US dwarf origin. Immune response and several egg production traits were higher for dwarf pullets from the high antibody backcross than from those of the low antibody backcross. 4. There were few differences in expression of the dwarfing genes from 2 origins in the unrelated backcross populations used in this study. Also each of the dwarfing genes, when introgressed into different genomic backgrounds, was not discernibly different in its expression in terms of antibody response or egg production characteristics.

Developmental stability in different genetic stocks of white rock chickens

Asymmetries were determined for several bilateral traits in females from a line of chickens selected for 39 generations for low 56 day body weight (LWS) and in a subline of LWS where selection had been relaxed for four generations (LWR). Because of reduced food intake under ad libitum feeding, some LWS females do not commence egg production, a condition that can be overcome by relaxing selection for a generation or two. Bilateral traits, measured at 240 days of age in LWS non-layers, LWS layers, and LWR layers, were shank length and diameter, distance between the auditory canal and the posterior junction of the upper and lower mandible, and weight and length of the first primary wing feather. Other traits measured were body weights at 56, 168, and 240 days of age and age at first egg. Fluctuating asymmetry, a good overall measure of developmental stability, was lower in the relaxed than selected line. Means of relative asymmetries were also lower for LWR females than LWS layers and nonlayers which were similar.

Self-selection of dietary protein and energy by broilers grown under a tropical climate: adaptation when exposed to choice feeding at different ages

Three hundred broiler chicks (Hubbard) of both sexes were assigned to five feeding treatments: T0 received a complete diet (control), T1 was a choice feeding system with simultaneous access to an energy-rich feed (ground corn) and a protein concentrate (43.7% CP), and T2, T3, and T4 were introduced to choice feeding after 1, 3, and 5 wk, respectively, of consuming the complete diet. At 1-d-old, T1 chicks showed a marked preference for corn, with only 21.4% of their intake being the protein concentrate diet. Intake of the concentrate progressively increased to 40 to 45% after 3 d of adaptation, resulting in diets with 22.5 to 24.3% CP. When broilers fed the complete diet for 1 to 5 wk (T2, T3, T4) were changed to choice feeding, on the 1st d, their feed choice intake was similar to that of T1 chicks at the same age. Visual observation and tactile assessment of the feed particles during the initial period allowed the chicks to quickly evaluate the new feeds and to adapt their feeding behavior. Although total feed intake to 6 wk of age was not significantly affected by the feeding treatments, broilers on choice feeding selected diets with a lower percentage of CP and had lower live body weights at 6 wk than those fed the complete diet (T0).

Developmental stability in stocks of White Leghorn chickens

The degree of asymmetry in bilateral morphological characters may reflect genetic and environmental stressors. Shank length and diameter, weight and length of the first primary wing feather, and distance between the junction of upper and lower mandibles and auditory canal (face length) were used to classify bilateral types and measure relative asymmetry (RA) in six genetic stocks. The stocks were the S23 generation of White Leghorn lines selected for high or low antibody response to SRBC, sublines in which selection had been relaxed for eight generations, and reciprocal crosses of the selected lines. Differences were found among all stocks for the traits measured. Rankings among traits for RA in descending order were face length, shank diameter, feather weight, and shank and feather lengths. The RA of shank and feather lengths did not differ from each other. An overall RA composed of mean RA of the five traits showed that the two selected lines exhibited greater RA than the crosses between them. The RA of the two lines where selection had been relaxed was similar to that of selected lines. This research suggests that an overall RA created as a combination of RA of several bilateral traits can be a valid measure of genetic stress in chickens and provides a method of comparing developmental stability among populations.

Antibody transmitting ability of hens from lines of chickens differing in response to SRBC antigen

1. Hens from White Leghorn lines selected for high (HA) or low (LA) antibody response to sheep red blood cells (SRBC) were inoculated with 0.1 ml of either 0.25% or 2.50% SRBC suspension. Eggs laid over the next 15 d were grouped into 5, 3-d collection periods and incubated. Maternal antibody titres were determined in chicks at hatch and 7 d after hatch. 2. In a subsequent experiment, hens of the 2 lines were inoculated with 0.1 ml of 2.50% suspension of SRBC, and eggs laid on days 10 to 13 after inoculation were incubated. Maternal antibody titres were determined in 15 and 18-d embryos as well as in chicks at 0, 5, 10, 15, 20, and 25 d after hatch. 3. Dosage of SRBC had no effect on the antibody titres in line HA; however, the higher dosage elicited greater antibody titres than the lower dosage in line LA. 4. Maternal antibodies were detected earlier in chicks of line HA (eggs laid on days 7 to 9) than those of line LA (eggs laid on days 10 to 12) regardless of dosage administered to the hens. 5. In both lines, antibodies specific to SRBC were observed on day 15 of incubation, with the frequency of responders greatest at hatch. The high frequency of HA responders was maintained for 15 d after hatch, whereas there was an immediate decline with age in LA responders. 6. It was concluded that lines HA and LA have diverged in the pattern of maternal antibody levels as a result of the divergent selection for antibody response to SRBC.

Self-selection of dietary protein and energy by broilers grown under a tropical climate: effect of feed particle size on the feed choice

Broilers, 2 wk of age, that had been previously adapted to energy: protein choice feeding, were offered corn (either ground, cracked, or presented as whole grains) and a protein concentrate (43.7% CP) in mash or pellet form. When corn was fed as whole grains, protein concentrate in the selected diet was significantly higher (35.1%) than with cracked corn (29.3%) or ground corn (29.1%). Presenting the concentrate as pellets resulted in a significantly higher concentration in the diet (32.7%) than when mash concentrate was fed (29.6%). Live BW at 4 and 6 wk of age were not significantly affected by feed texture. However, offering corn as whole grains or concentrate as pellets induced a significant improvement in feed efficiency. Total time to eat larger size particles (whole grains, pelleted concentrate) was significantly less than total time to eat ground corn or mash concentrate. Furthermore, the mean duration of the feeding bouts was two times shorter for whole grains (48 s) than for ground corn (98 s) and for pelleted concentrate (56 s) than for mash concentrate (114 s). Chickens ate whole grains or pellets at a significantly slower rate (number of pecks per second feeding time) than when eating ground corn or mash concentrate. There was a rejection during the first 24 h when the form of the concentrate (mash to pellets) was changed. Full adaptation to the new size of the concentrate required about 3 d.

Responses of meat-type chickens to choice feeding of diets differing in protein and energy from hatch to market weight

Chickens from three genetic stocks known to differ in growth potential consumed ad libitum either a single (control) diet or a choice of two diets that differed in protein and energy. Formulation of the choice diets was such that when mixed in specific proportions they provided single diets that decreased in protein and increased in energy over the experimental period. When comparisons of feeding regimens were made at a common age, body weights and feed efficiencies for all stocks were enhanced in chicks fed a single diet. When comparisons were made at a common body weight for controls, chickens fed the single diet were about 15% heavier than those given a dietary choice. For feed efficiency, however, the pattern remained for the faster growing stock whereas there was no difference between feeding regimens for the slower growing stock. Chicks provided a choice of diets had heavier abdominal fat pads and lighter breasts relative to body weight than those fed a single diet. With choice feeding, there were stock by diet interactions for dietary preferences through the first 9 d after hatch. Early on, the interactions resulted from the faster growing stocks exhibiting a greater preference for the diet higher in protein and lower in energy than the slower growing stock. By Day 5, however, the interaction occurred because stocks exhibited either no dietary preference or preferred the diet that was lower in protein and higher in energy. Regardless of genetic stock, at 9 d of age and thereafter there was a clear preference for the diet lower in protein and higher in energy than the diet higher in protein and lower in energy. These data for feed intake were consistent with behavioral observations that showed a preponderance of chicks eating from the feeder containing the diet lower in protein and higher in energy. Compared to a single diet, under choice feeding, energy utilization was negatively influenced more in the faster than slower growing stocks. Protein and sulfur amino acid utilization was not affected by feeding regimen in faster growing stocks, but was enhanced under choice feeding in the slower growing stock. Although lysine utilization was enhanced by choice feeding in all stocks, the effect was greater in the slower than in the faster growing ones. These data demonstrate that although broiler diets are formulated to enhance growth and overall feed efficiency, chicks that are provided a dietary choice of protein and energy do not eat to maximize growth or feed efficiency.

Genetic selection strategies--population genetics

This paper provides an overview of the association between population genetics and selection strategies in poultry. Relationships between artificial and natural selection and among causes contributing to limits to artificial selection are discussed. Homeostasis and resource allocations at the individual and at the population level are reviewed. Examples from poultry demonstrate where human intervention has circumvented biological limits. Lastly, this paper considers the role of population genetics in future breeding strategies for poultry.

Effect of tumor necrosis factor-alpha on progesterone production by granulosa cells in laying hens of different genetic lines

In vitro progesterone production by granulosa cells in the presence or absence of human recombinant tumor necrosis factor-alpha (hrTNF-alpha) was measured at 10, 20, and 30 wk of egg production in White Leghorn hens selected for high (HA)- or low-antibody (LA) response to sheep red blood cell challenge. Isolated granulosa cells from the three largest preovulatory follicles (F1-F3) were incubated with 5 or 250 ng/ml hrTNF-alpha, and progesterone production was determined by the use of a validated radioimmunoassay. F1, F2 and F3 granulosa cells from HA hens produced more (P < or = 0.05) progesterone (140.8, 107.2, and 49.7 ng/ml) than LA hens (109.4, 78.9, and 26.9 ng/ml). The treatment of granulosa cells with hrTNF-alpha consistently inhibited (P < or = 0.05) progesterone secretion by all follicles among HA and LA hens, but not always at both doses. Generally, 5 ng/ml hrTNF-alpha was the maximum inhibitory dose. In the laying hen, a decrease in steroid production in response to cytokines may upset the steroid balance created by follicular hierarchy and inhibit or delay ovulation.

Dietary effects on immune response of fast-growing chicks to inoculation of sheep erythrocytes and Escherichia coli

Responses to SRBC and Escherichia coli inoculations were measured during the early posthatch period in broiler cockerels fed diets differing in nutrient density. Diet A consisted of 20% protein and 2,685 kcal ME/kg and Diet B consisted of 24% protein and 3,146 kcal ME/kg. There was no effect of diet on antibody response of chicks inoculated at 10 d of age with 0.25, 2.50, 5.00, or 25.00% suspensions of SRBC. A significantly larger proportion of chicks, however, produced antibody at the 25.00% than at the 0.25% dosage of SRBC. When inoculated at 15 d of age with 10(-6), 10(-4), or 10(-2) dosage of E. coli, there were no significant diet by dosage interactions for lesion scores, or relative change in BW 24, 48, and 120 h after inoculation. There were differences among E. coli dosages for severity of lesions and mortality, with rankings being 10(-2) > 10(-4) > 10(-6). Lesion scores and mortality were higher for the chicks fed Diet B than those fed Diet A. Also, deleterious effects of E. coli on BW 24, 48, and 120 h after inoculation were greater for chicks fed Diet B than for chicks fed Diet A. Responses to inoculations of SRBC and E. coli of broilers fed a diet with a lower nutrient density were equal or superior to those of broilers fed a diet with a higher nutrient density.

Late embryonic and early posthatch growth of heart and lung in White Leghorn lines of chickens

Growth and development of heart and lungs were measured from day 15 of incubation to 25 days after hatch in lines of chickens that had undergone long-term selection for high (HAS) or low (LAS) antibody titers to sheep erythrocytes. A correlated response to this selection was heavier 28-day body weights for LAS than HAS chickens. In this experiment body weights were heavier in line LAS than HAS from 15 days of incubation to 5 days after hatch and again at 25 days after hatch. Absorption of residual yolk was greater in HAS than LAS chicks. Although there were no differences between lines for absolute heart weights, lungs were heavier in line LAS than HAS at all ages except 20 days after hatch. Relative to body weight, both heart and lung weights declined with age, however, the pattern of decline differed. For this criterium, hearts were larger in line HAS than LAS to 5 days after hatch with no difference thereafter; for lungs lines were similar until 5 days after hatch after which they were larger in LAS than HAS chicks. In all but one case (HAS at hatch) the left:right relationship for lung weights exhibited fluctuating asymmetry with the left minus right character difference having a normal distribution and mean zero. The degree of fluctuating asymmetry, however, varied with age.

Tissue-specific alterations in insulin-like growth factor-I concentrations in response to 3,3',5-triiodo-L-thyronine supplementation in the growth hormone receptor-deficient sex-linked dwarf chicken

Insulin-like growth factor-I (IGF-I) mediates many of the effects of growth hormone (GH). The regulation of IGF-I, independent of GH, is methodologically difficult to assess in vivo, as hypophysectomy results in derangement of many pituitary hormone axes in addition to GH, and a gene knockout model is not available. The recessive sex-linked dwarfing (SLD) gene (dw) in chickens results in a lack of functional target tissue GH receptors due to a variety of molecular defects, which provides a unique model for evaluating GH-independent regulation of IGF-I. In the present study, the impact of 3,3', 5-triiodo-l-thyronine (T3) on circulating and tissue IGF-I was determined in normal versus SLD birds. Adult, nonovulatory female normal and SLD chickens were restrict-fed 40 g of feed/kg bw/day containing 0, 0.5, or 1.0 ppm T3, resulting in supplementation levels of 0 (control), 20 (low dose), or 40 (high dose) microg T3/kg bw/day for 10 days. Samples of GH target tissues including liver, abdominal fat pad, skeletal muscle (pectoralis major), and spleen were extracted and assayed for IGF-I. Plasma T3, T4, GH, and IGF-I were determined by homologous RIA. Tissue GH binding was determined for hepatic membranes by radioreceptor assay. Under control conditions, dwarf chickens were markedly hypersomatotropic (33.3 +/- 4.1 ng GH/ml plasma; mean +/- SEM) compared to normals (2.4 +/- 3.9 ng/ml), and T3 supplementation reduced this to normal levels. Despite the high circulating level of GH in dwarfs, plasma IGF-I was low compared to normal controls (dwarfs 1.5 +/- .9 ng/ml; normals 5. 3 +/- .9 ng/ml; P = 0.004), but this difference was eliminated with low-dose T3. In this study, tissue IGF-I was undetectable in liver and pectoralis muscle in adults (55 weeks of age) of both genotypes, under all treatments. In contrast, adipose tissue IGF-I was relatively high and did not differ (P = 0.84) between genotypes under control conditions (normals 776.5 +/- 236.7; dwarfs 844.6 +/- 236.7 pg/mg protein), but was increased in normals and decreased in dwarfs, resulting in higher levels (P = 0.02) in the normal (1249.9 +/- 200.0 pg/mg protein) than in the dwarf genotype (558.4 +/- 200.0 pg/mg protein) at the higher level of T3 supplementation. This relationship was somewhat reversed in spleen, where T3 tended to decrease tissue IGF-I concentration in normals and increase it in dwarfs. The low level of plasma IGF-I despite nonmeasureable hepatic IGF-I tissue concentrations suggests that IGF-I synthesis by extrahepatic tissues contributes to the circulating pool of IGF-I. The relatively high control levels of adipose tissue IGF-I in the dwarf genotype further suggest that considerable IGF-I synthesis exists that is GH-independent in this extrahepatic tissue. The presence of GH action, however, may mediate the effects of other hormones that can influence local IGF-I production in this tissue, as reflected by the differential response to T3 supplementation between genotypes. The tissue-specific nature of the effect of T3 on IGF-I production supports an additional point of regulation of hormone action at the target tissue level.

Effects of dietary taurine on growth and Escherichia coli resistance in chickens

White Leghorn chicks selected for either high (HA) or low (LA) antibody response to SRBC were used in two experiments to ascertain the effects of differing levels of dietary taurine on growth, levels of taurine in blood plasma, heart, and brain, and response to Escherichia coli inoculation. A different level of dietary taurine was associated with maximal growth in each of the two selected populations. Line HA expressed greater growth with a relatively low level of taurine, whereas Line LA expressed greater growth with a relatively high level of taurine. Line LA chicks had a higher level of taurine in the heart than did Line HA chicks. Although increases in dietary taurine resulted in linear and curvilinear increases in plasma and heart taurine levels, they had no effect on brain levels. No apparent resistance or susceptibility to E. coli exposure was associated with stock or differing levels of dietary taurine.

Long-term divergent selection for eight-week body weight in white Plymouth rock chickens

This paper provides an overview of results from a long-term (38 generations) selection experiment. Lines were developed from individual phenotypic selection for high or low body weight at 8 wk of age. Included are data for the selected lines, sublines in which selection was relaxed, crosses of the selected lines, and sublines in which the sex-linked dw gene was introduced. Periodically (and in some cases every generation) data were obtained for unselected traits. These unselected traits included feed consumption and intake behavior, reproduction, allomorphic relationships, and metabolic, immunological, endocrine, and molecular factors. These responses have been integrated into a resource allocation paradigm.

Immunoresponsiveness in chickens: association of antibody production and the B system of the major histocompatibility complex

Lines of White Leghorn chickens were selected for high or low antibody response to sheep erythrocytes for five generations. The base population from which the experiment started was composed of individuals all of which were heterozygous at the MHC haplotypes B13 and B21. Body weights, egg production traits, and genotypes at the B system were monitored for all individuals in each generation. By Generations 4 and 5 there was separation of the two replicate lines selected for high titer from the two replicate lines selected for low titer. Over the course of the experiment, higher antibody titers and lower BW were associated with B21 and lower antibody titers and higher BW were associated with B13, although these relationships did not occur in every instance. Conclusions were that the B system was associated with antibody response, but that the chickens did not depend entirely upon that association for protection against foreign proteins. Also, the importance of having replicate lines in a selection experiment was shown.

Immunoresponsiveness of fast-growing chickens as influenced by feeding regimen

1. Immunoresponsiveness and disease resistance were measured in broiler males maintained on ad libitum feeding throughout or on alternate-day feeding. Alternate-day restrictions were started 1 and 2 d after hatch so that on any one day there were chicks fed and fasted. 2. Severity of response to E. coli challenge as measured by lesion scores, and mortality was greater for chicks fed ad libitum than those fed on alternate days. For chicks fed on alternate days, lesion scores were lower for those without access to feed for the 24-h period immediately after challenge. 3. Spleen weights, the indicator of response to marble spleen disease virus challenge, were higher for chicks fed ad libitum than those fed on alternate days. 4. Antibody response to sheep red blood cell antigen was not affected by feeding regimen. 5. Ratios of heterophils to lymphocytes were higher for chicks given access to feed for the previous 24-h period than for those fasted during the previous 24-h or those that had been fed ad libitum. 6. Results of this experiment suggest that for alternate-day feeding programs, vaccination be administered on the day that chicks are not fed.

Heterosis and DNA fingerprinting in chickens

Enhancement of performance in traits of economic importance by use of heterosis (hybrid vigor) is routine in poultry breeding. There is, however, no reliable method to predict the level of heterosis that will occur from the mating of individuals from two populations. DNA fingerprints (DFP) were used as a measure of genetic distance between mating pairs of chickens where each individual of a pair was from a different population; the association between that genetic distance and levels of heterosis in the offspring of those pairs was assessed for juvenile BW and for age at production of first egg. There was an inverse relationship between DFP bandsharing level of parents and heterosis in their offspring, suggesting that DFP may be useful in predicting heterosis.

Feeding regimen by sire family interactions on growth, immunocompetence, and disease resistance in chickens

Progeny from matings of 12 sires from a White Plymouth Rock line selected for high juvenile BW and 96 dams from a White Leghorn line selected for low antibody production to SRBC were reared under alternate-day (AD) or ad libitum (AL) feeding regimens. Within a feeding regimen males were heavier than females, and within a sex, chicks fed AL were heavier than those fed AD. Feeding regimen by sire family interactions were significant for BW at 21 d of age for both male and female progeny. The interaction was due to differences among sires in the magnitude of the AD: AL relationship. Product moment correlation coefficients between feeding regimens for male and female progeny of sire families for 21-d BW were essentially zero, which was consistent with the sire family by feeding regimen interactions observed at this age. At 41 d of age, relative to BW, weights of empty esophagus plus crop and of crop contents were greater for AD than AL chicks. There were differences among sire families for crop content and breast weights relative to BW. Lesion scores to Escherichia coli challenge were lower and antibody titers to SRBC antigen were higher in AD than in AL chicks. Sire families differed in antibody titers to SRBC antigen. Feeding regimen by sire family interactions were significant for percentage change in BW 144 h after E. coli challenge and lesion scores were greater for AL than AD chicks.

Growth, immunoresponsiveness, and disease resistance of diverse stocks of chickens reared under two nutritional regimens

Growth, immunocompetence, and disease resistance were measured in a commercial broiler stock (BC), a commercial white-egg-layer stock (LC), and a White Plymouth Rock line selected for high juvenile BW (HW) under dietary regimes differing in protein and energy content. Diet E had 20% more protein and 17% more ME than Diet A. Stock by sex interactions were significant for BW at 28 and 36 d of age because sexual dimorphism occurred at younger ages in the meat than in the layer stocks. When inoculated with .1 mL of a .25 or 2.50% suspension of SRBC, diet by stock interactions were significant for antibody titers 6 d postinoculation (PI) at the lower dosage. Interactions were not present at the higher dosage or for either dosage 13 d PI. Diet by stock interactions were significant at both dosages for change in SRBC titers from 6 to 13 d PI. The interactions resulted from a significantly smaller decline in BC than HW or LC chicks fed Diet A, whereas all stocks responded similarly when fed Diet E. A significant decline in rate of BW gain was observed in chicks inoculated with marble spleen disease virus (MSDV), with the increase in relative weight of spleen significantly greater for LC than HW or BC chicks 6 d PI. When heterophil to lymphocyte ratios were used as an assay of response to MSDV challenge, rations were significantly higher for HW chicks fed Diet A than for chicks fed Diet E and for LC chicks fed Diet E than for chicks fed Diet A, but not different for BC chicks on the two diets.

Stimulation of avian respiratory phagocytes by Pasteurella multocida: effects of the route of exposure, bacterial dosage and strain, and the age of chickens

The effects of the route of exposure (intratracheal [IT], drinking water [DW] and aerosolization [AS]), the age of chickens, and the dose of two vaccine strains of Pasteurella multocida (CU and M-9) on the number, phagocytic proportion and capacity of macrophages, granulocytes and lymphocytes (collectively avian respiratory phagocytes [ARPs]) were analyzed. Administration of P. multocida via the DW even at very high dose failed to stimulate ARPs. In contrast, administration of both strains of P. multocida either IT or by AS resulted in rapid and highly significant increases in the numbers of ARPs. 10 x 10(9) colony forming units (cfu) of aerosolized P. multocidaCU strain activated ARPs maximally in both young (3-6 weeks of age) and old (4-6 months of age) chickens. Old chickens responded in dose dependent manner to 20 x 10(9), 8 x 10(9), and 4 x 10(9) cfu of aerosolized P. multocida CU strain. Young chickens responded significantly only to 8 x 10(9) CU organisms. The M-9 and CU strains had limited differences in inducing migration of ARPs into the respiratory system of chickens or elevating phagocytic proportions and capacity of ARPs. The results indicate that the analyzed factors influence the response of ARPs to P. multocida to various degrees.

Correlated responses to long-term divergent selection for eight-week body weight in chickens: growth, sexual maturity, and egg production

Thirty-six generations of divergent selection for BW at 8 wk of age (BW8) resulted in approximately an eightfold difference between the high (HWS) and low (LWS) lines for this trait. Correlated traits included BW at 4, 24, and 38 wk of age (BW4, BW24, BW38, respectively), age at first egg (AFE), and percentage hen-day egg production (HDP). Responses of BW4 followed the same pattern as that for the selected trait, with the response about five times greater during the first 18 than the last 18 generations of selection in Line HWS and less than two times greater in Line LWS. For BW24 and BW38, correlated responses were greater for LWS than for HWS females without feed restriction, suggesting changes in growth curves after selection age. Although AFE was delayed in both lines, the delay was greater in Line LWS (some individuals of which were anorexic) than in Line HWS and greater in the second half than the first half of the experiment. For pullets that commenced lay, HDP declined slightly in both lines. Correlations between BW at 4, 8, 24, and 38 wk of age were moderate to high and positive in both lines. When feed intake was restricted in Line HWS, however, there were no correlations of BW4 or BW8 with BW24 or BW38. Correlations between AFE and BW at all ages were negative in Line LWS. In Line HWS there were negative correlations of AFE with BW24 and with BW38. Relaxed lines, established periodically during the experiment, were satisfactory monitors of environmental influences for primary and correlated traits.

Intubation of weight-selected chicks with soybean oil or residual yolk: effect on early growth and development

Experiments were conducted to study the role of residual yolk on growth and development of chicks during the 1st wk after hatch. Surgical removal of the yolk sac at hatch reduced early body weight gains. Intubating chicks with a mixture of soybean meal and soybean oil or with residual yolk obtained from chicks at hatch increased body weights and enhanced development of the liver and pancreas. Whereas intubation with residual yolk reduced absorption of yolk sac contents, absorption was similar for chicks that consumed mash ad libitum or were intubated with the soybean meal-soybean oil diet. After cessation of yolk intubation, absorption of residual yolk resumed. Removal of the yolk sac decreased amylase and lipase activity in the pancreas. In the intestinal chyme, activity of amylase, trypsin, and chymotrypsin was reduced by yolk sac removal. Intubation with yolk increased enzyme activity (amylase excepted) in the pancreas or intestinal chyme only in chicks that had their yolk sacs removed. There was evidence that contents of the yolk sac did not enter the intestine via the yolk stalk, but were absorbed directly via the blood.

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%.