Association of endogenous avian viral and endogenous viral genes with feed conversion and six-week body weight in broilers.

The consistency of the effect of selection on the frequencies of endogenous avian viral (eav) and endogenous viral (ev) specific restriction fragment length polymorphism (RFLP) bands was studied in two broiler lines selected from a single base population and in an F2 population derived from a reciprocal cross of both lines. One broiler line (FC line) was selected for low feed conversion ratio and the other line (GL line) was selected for high 6-wk body weight. In the F2 population, the band frequencies were determined in groups representing separate tails of the distribution of two production traits, namely, low feed conversion ratio between 29 and 42 d of age and body weight at 42 d of age. The F2 population consisted of 288 females belonging to 24 full-sib families. To rule out family effects, the tails for these production traits were composed by either the best or by the worst female performer for each trait in each full-sib family. In total, 29 HindIII-eav, 34 MspI-eav, and 21 BamHI-ev bands could be distinguished by RFLP analysis. This report describes the influence of selection on 11 potentially interesting bands. Two bands, the 9.5-kb HindIII-eav and the 15-kb MspI-eav band, which were found both in higher frequencies in the parental FC line, were also found in higher (P < or = .05) frequencies in the F2 tail with a favorable feed conversion ratio. A third band, the 6.5-kb HindIII-eav band, present in lower frequencies in the parental GL line, was also present in lower (P < or = .05) frequencies in the F2 tail of birds with heavy body weight.

Endogenous proteolytic enzymes in chicken muscles. Differences among strains with different growth rates and protein efficiencies.

The theory that net muscle growth is, at least partly, regulated by catabolic factors has been tested in order to set up an animal model to study meat aging and post-mortem tenderization. Male and female chickens of a layer strain (White Leghorn), a commercial broiler strain (Ross), and two experimental broiler lines (designated GL and FC) were used to estimate differences in proteolytic enzyme activities in the breast muscles. The GL and the FC lines were selected for high body weight gain and high feed efficiency, respectively. At 6 wk of age the birds were slaughtered and the activities of endogenous proteinases and their specific inhibitors in breast muscles measured. The Leghorns showed significant differences in all traits compared with the three broiler genotypes. Within the broiler types, FC birds tended in the direction of the Leghorns and GL birds in the opposite direction. Ross birds were intermediate between FC and GL birds. All types and sexes differed significantly in slaughtering weight. Feed conversion ratio and protein conversion ratio were highest for Leghorns. The FC birds showed the lowest feed conversion. Ross and GL birds showed intermediate values. The Leghorns showed higher calpain activities and lower calpastatin activity than the three broiler genotypes. The FC broilers showed intermediate calpain and calpastatin activities but higher cathepsin H and total cystatin values. The GL broilers showed lower cathepsin B, D, and H activities. In all cases the Ross broilers showed intermediate values. From these figures it is concluded that the strains of birds used in this study can be used as a natural source of variability to study the mechanisms involved in post-mortem proteolytic degradation and thus in the study of muscle tenderization and meat aging. It is also concluded that it could be very interesting to study the behavior of the different proteolytic systems more carefully in relation to muscular growth characteristics and compare them to anabolic factors involved in muscle growth.

Fertility rate of daily collected and cryopreserved fowl semen.

Semen was collected for 4 consecutive d individually from experimental broiler breeder males that had not been massaged for 7 d. The semen was mixed and diluted with the Beltsville Poultry Semen Extender with dimethylsulfoxide (DMSO) as cryoprotectant and cryopreserved. After thawing of the semen, hens were inseminated and fertility over 1 wk after a single insemination with the cryopreserved semen was determined. The overall fertility rate in this experiment (83 to 93%) was high, compared with the generally reported fertility rate of frozen-thawed fowl semen. The fertility rate of the semen collected on Days 3 and 4 was significantly higher than that of semen collected on Day 1 or 2, indicating that frequent collection over the 4-d period enhances the fertility rate of the semen.

Effect of dialysis before storage or cryopreservation on fertilizing ability of fowl semen.

Semen of broiler breeder males was collected and used for artificial insemination. Semen was used undiluted and diluted and both inseminated immediately after collection. Only diluted semen was used after storage. Half of the semen samples to be stored were first dialyzed. Storage of fresh, diluted semen was for 4 or 24 h at 5 C or by cryopreservation. The Beltsville Poultry Semen Extender was used for dilution and dimethylsulfoxide (DMSO) was used as cryoprotectant. Fertilizing ability was determined as the percentage fertilized eggs of eggs collected from Day 2 to 17 after a single insemination. Dialysis had a small positive effect on fertilizing ability of semen stored for 24 h. Dialysis before cryopreservation did not improve fertilizing ability. The effects of storage for 4 h were only apparent in eggs collected 9 or more d after insemination. Semen stored for 24 h gave reduced fertilizing ability in the 1st wk after insemination, especially when no dialysis was applied.

The effect of environmental temperature on episodic growth hormone release of meat-type chickens selected for 6 week body weight or for improved feed efficiency between 3 and 6 weeks of age.

The effect of a high (33 degrees C) compared to a normal (23 degrees C) ambient temperature on the pulsatile release of growth hormone (GH) has been studied in 4-week-old, cannulated male meat-type chickens selected for high body weight (GL line) or for improved feed efficiency (FC line). When reared in the normal temperature environment, overall circulating mean and amplitude GH values of FC chickens were significantly higher than those of GL chickens. There were no differences in GH pulse length or frequency between genotypes. The high rearing temperature completely abolished the pulsatility of GH in the plasma in both lines, but without affecting overall mean GH levels.

Influence of pre-incubation treatment on hatching results of broiler breeder eggs produced at 37 and 59 weeks of age.

1. The influence of temperature in the nest box, temperature during storage, storage time and pre-setting temperature on the hatchability of broiler breeder eggs produced by birds of 37 and 59 weeks of age was examined. 2. All treatments that can be characterised as being less optimal for embryo survival than the control treatment affected the hatchability of fertile eggs more in the case of eggs produced by older birds. 3. A higher temperature in the nest box, longer storage periods, higher storage temperature, especially at longer storage periods, and higher pre-setting temperature significantly reduced the hatchability of fertile eggs from the older birds. 4. For the younger birds, a significant reduction of hatchability was found only for the longest storage period.

Plasma levels of growth hormone and insulin-like growth factor-I and -II from 2 to 6 weeks of age in meat-type chickens selected for 6-week body weight or for feed conversion and reared under high or normal environmental temperature conditions.

The aim of this study was to compare the effect of high (33 degrees C) and normal (33-20 degrees C) rearing temperature on growth and plasma levels of the somatotrophic hormones of 2 genetic lines of broiler chickens selected for 6-wk body weight (GL-line) or for feed conversion between 3 and 6 wk of age (FC-line) or for feed conversion between 3 and 6 wk of age (FC-line). Blood samples were collected weekly and analysed for growth hormone (GH) and insulin-like growth factors (IGF)-I and -II levels by RIA. The growth-depressing effect of the HT-treatment was more pronounced in the heavier GL-line and in males. A similar age-related pattern for all hormones studied was observed with the highest levels between 2 and 4 wk of age. FC-line chickens and males had consistently higher plasma GH levels than GL-line chickens and females respectively. No consistent effect of rearing temperature on plasma GH levels were observed. At 2 wk of age, HT-treatment resulted in higher plasma IGF-I levels while this was reversed from 3 wk of age onwards. GL-line chickens had significantly higher plasma IGF-I levels at 2, 3 and 4 wk of age. No consistent effect of sex on plasma IGF-I levels could be observed. For the whole period studied, GL-line chickens had significantly higher plasma IGF-II levels than FC-line chickens. No consistent effect of sex or temperature treatment on plasma IGF-II levels was observed.

Abdominal adipose tissue from broiler chickens selected for body weight or for food efficiency differ in in vitro lipolytic sensitivity to glucagon and to chicken growth hormone, but not to dibutyryl cAMP.

1. Differences in responses to lipolytic agents have been investigated in vitro in abdominal adipose tissue from lines of broiler chickens selected for body weight (GL, a 'fat' line) or for food efficiency (FC, a 'lean' line). 2. Dibutyryl cyclic adenosine monophosphate stimulated in vitro lipolysis, as measured by the glycerol release, by adipose tissue from GL or from FC chickens to the same extent. 3. Glucagon stimulated glycerol release from adipose tissue from FC chickens, but not from GL chickens. 4. Adipose tissue from GL chickens was much more sensitive to chicken growth hormone (GH) compared to FC chickens. 5. It is concluded that the selection criteria applied influenced the number of adipose GH and glucagon receptors, the number of adipose GH receptors being lower and of glucagon receptors being higher in FC chickens compared to GL chickens.

Endogenous viral genes in thirteen highly inbred chicken lines and in lines selected for immune response traits.

Thirteen highly inbred lines of chickens of Leghorn, Spanish, and Egyptian Fayoumi origin, four partly inbred Leghorn lines selected for MHC alleles and immune response to GAT (Ir-GAT), and two replicated, noninbred Leghorn lines divergently selected for multiple immune response traits were subjected to molecular genotyping for endogenous viral (ev) gene sequences. In all highly inbred lines of Leghorn origin, ev1 alone or both ev1 and ev2 were observed. The Spanish and Fayoumi lines had three and five ev genes, respectively, most of which were not readily identifiable with standard Leghorn ev gene loci. The Leghorn lines selected for MHC and Ir-GAT had ev1 fixed in the population. Differences in ev3 and ev5 gene frequency were associated with Ir-GAT in the B1 haplotype, but not in the B19 haplotype. In the noninbred lines, which were divergently selected for multiple traits of immune responsiveness, ev6 and ev9 differed in frequency between lines, and both were in lower frequency in the lines selected for high immunoresponsiveness. These two ev genes are the only ones known in White Leghorns that have the gs-chf+ phenotype [expressing chicken helper factor (chf) but not expressing group-specific antigen (gs)].

Growth hormone response to TRH in male broiler chickens selected for body weight gain or food conversion and reared at either a moderate or a high ambient temperature.

The aim of the present experiment was to study the growth hormone (GH) response upon thyrotropin releasing hormone (TRH) challenge (2 micrograms/kg body weight) in broiler chickens selected for body weight gain (GL line: fat line) or for feed efficiency (FC line: lean line) reared at either a moderate (33-23 degrees C) or high (33 degrees C) ambient temperature. A higher plasma GH level at 5 min after TRH administration was observed in the high temperature conditioned chickens of both lines. Also at high ambient temperature, an enhanced GH decrease between 15 min and 30 min post-injection and a higher acute elimination rate was calculated compared to moderate ambient temperature. A significantly higher GH secretory response was observed in the leaner FC line chickens, which was probably related to the more pronounced pulsatory GH secretion rate in these chickens. There was no difference in GH acute elimination rate between both lines in both environments. No interactions between line and rearing temperature for these parameters of GH dynamics were observed.

Different endogenous viral loci in Cornish and White Plymouth rock chickens.

Endogenous viral (ev) loci were studied in three broiler lines. In 5 birds of each of line cw1 and line cw2 (White Plymouth Rock lines) 19 and 14, respectively, different SstI ev-junction fragments were found, while in 8 R line birds (Cornish type) 15 different Sst I junction fragments were found. Further characterization of the line R loci with a second restriction enzyme, BamHI, revealed that these junction fragments represent 25 different loci, of which at least 21 have not been reported previously. SstI RFLP analysis of progeny from crosses between chickens of the three broiler lines and White Leghorns demonstrated that within line R and cw1 approximately 90% of the ev loci were hemizygous. In line cw2 at least 50% of the ev loci were hemizygous. There was no evidence for polymorphic loci, and only two ev loci were found to be linked genetically. Intertype crosses revealed that overall differences in the RFLP patterns observed between Cornish, White Plymouth Rock and White Leghorn chicken lines were due to the presence of different ev loci in each of the lines rather than to polymorphism. The few shared ev loci always contained similar allelic fragments.

Concentrations of hormones, glucose, triglycerides and free fatty acids in the plasma of broiler chickens selected for weight gain or food conversion.

1. The concentrations of growth hormone (GH), insulin-like growth factor I (IGF-I), thyroxine (T4), triiodothyronine (T3), reverse-triiodothyronine (rT3), triglycerides (Tri), free fatty acids (FFA) and glucose (Glu) were determined at 2, 4 and 6 weeks of age in blood plasma of male and female chickens of broiler lines selected for body weight (GL) or food conversion (FC). 2. Plasma concentrations measured in the same animal over a 24 h or a 2 week interval were not significantly correlated with each other. For different traits measured in the same plasma sample only the correlation between T4 and rT3 differed significantly from zero. 3. All traits were dependent on age. Line and sex effects were significant (P less than 0.05) for GH, T4, Tri, FFA and Glu. Additionally, line significantly influenced the plasma T3/T4 ratio and sex influenced plasma rT3. Interactions between line, sex and/or age were seldom significant. 4. Within line and sex, GH (at 6 weeks of age) and T3 (at 4 weeks of age) were negatively, and IGF-I and Tri (both at 6 weeks of age) positively correlated with the amount of abdominal fat at 6 weeks of age. No significant correlation between body weight at 2, 4 or 6 weeks of age and any of the plasma traits was found.

Variations in endogenous viral gene patterns in White Leghorn, medium heavy, White Plymouth Rock, and Cornish Chickens.

The endogenous viral (ev) gene patterns of White Leghorn (WL; 6 lines), medium heavy (MH; 4 lines), White Plymouth Rock (WPR; 8 lines), and Cornish types (2 lines) of commercial chickens were compared. Southern blot analysis of SstI-digested genomic DNA of 151 chickens revealed that the number of ev gene-containing fragments in a chicken from the MH, WPR, or Cornish type is about twice twice the number of that in WL chickens. Also, the number of hybridizing fragments of different size found within one line was twice as high in the broiler (on average 16.0 bands per line) and MH lines (20.5 bands per line) than in the WL lines (10.0 bands per line). In studies with subregion-specific probes, all ev fragments detected contained the env (3') part of the viral genome. Only eight ev fragments, found in 7 animals of 2 lines, lacked the gag (5') part of the viral genome. Studies with the ev-1-specific flanking probe, pGd111, revealed that ev-1 is commonly present in the DNA of the WL chickens, but not within the DNA of the WPR chickens. The results suggest that use of the standard nomenclature for the ev genes based on restriction fragment length is not feasible within the WPR, MH, and Cornish lines because of the complexity of the ev gene patterns found within these lines.

Fat deposition in a broiler sire strain. 3. Heritability of and genetic correlations among body weight, abdominal fat, and feed conversion.

Body weight, abdominal fat, and feed conversion were measured in ad libitum-fed pedigreed chickens of four lines selected from a broiler sire strain. Lines were selected for four generations for a low amount of abdominal fat (AF), a favorable feed conversion (FC), a high body weight after restricted feeding (GR), and a high body weight after ad libitum feeding (GL). A total of 2,400 pedigreed chickens from three hatches were reared by line in groups on litter and 864 chickens were tested for individual feed conversion in individual cages. The h2 from the sire component for the four lines combined were for body weight, .27 (litter) and .22 (cages); for weight of abdominal fat, .54 (litter) and .40 (cages); for percentage abdominal fat, .53 (litter) and .45 (cages); and for feed conversion, .44 (cages). Analysis within line and sex indicated that, in the relatively fat GR and GL lines, sex-linked inheritance could be involved for abdominal fat. In the leaner AF and FC lines this was not the case. Genetic correlations (sire estimate) for the four lines combined were, between body weight and weight of abdominal fat, .58 (litter) and .55 (cages); between body weight and percentage abdominal fat, .36 (litter) and .47 (cages); between body weight and feed conversion, .16 (cages); between weight of abdominal and feed conversion, .43 (cages); and between percentage abdominal fat and feed conversion, .44 (cages). Genetic correlations did not differ significantly between sexes, but in the AF and FC lines, the genetic correlation between body weight and abdominal fat was higher (AF: .80, FC: .76) than in the GR (.14) and GL (.68) lines.

Fat deposition in a broiler sire strain. 4. Performance of broiler progeny of four differently selected sire lines.

Cocks from four lines selected for a low amount of abdominal fat (AF), a favorable feed conversion ratio (FC), and high body weight after restricted (GR) or ad libitum (GL) feeding were mated to commercial broiler breeder hens. A total of 3,600 broiler progeny in three hatches from these matings was reared by line in litter pens. At 41 days of age GR and GL line progeny had significantly heavier body weights, poorer feed conversion ratio, and higher percentages of abdominal fat than AF and FC line progeny. At comparable body weights (AF, 1,893; FC 1,918; GR, 1,848; and GL, 1,897 g) feed conversion was most favorable for FC line progeny (1.72), AF and GL line progeny did not differ (1.77), and GR line progeny had the poorest feed conversion ratios (1.79). The AF line progeny had the lowest percentage abdominal fat (1.88%), followed by FC line progeny (2.20%), GL line progeny (2.91%), and GR line progeny (3.10%). As in the pure lines, selection for body weight after restricted feeding was not effective in obtaining leaner and more efficient chickens. When compared with differences between pure lines, results of the broiler progeny matings indicate that body weight, feed conversion, and percentage abdominal fat are inherited largely in an additive manner.

Fat deposition in a broiler sire strain. 5. Comparisons of economic efficiency of direct and indirect selection against fatness.

In a simulation study, selection for weight gain in a broiler sire strain was compared with 1) one and two stage index selection for weight gain and feed conversion and 2) weight gain, slaughter yield, and percentage abdominal fat. Weight gain per day was assigned an economic value of 1.138 Dutch cents (ct)1/g; feed conversion, -138.18 ct/1.0; slaughter yield, 0 or 7.55 ct/%; and percentage abdominal fat, 0 or -10 ct/%. When selection was completely or almost completely (as in two stage selection) based on weight gain, percentage abdominal fat increased; otherwise it decreased. Weight gain, feed conversion, and slaughter yield improved with all selection methods examined. Due to the high positive correlation between feed conversion and percentage abdominal fat, selection for an index of weight gain and feed conversion gave about the same reduction in percentage abdominal fat as selection for an index of weight gain, slaughter yield, and percentage abdominal fat. Selection response of the four traits was dependent more on selection methods than on sets of economic values. Based on economic values, selection for an index of weight gain and feed conversion gave 1.70 to 3.35 times the financial gain of selection for weight gain only, and selection for an index of weight gain, slaughter yield, and percentage abdominal fat gave 1.15 to 3.12 times that attained by selection only for weight gain. The extra financial gains exceeded by far the estimated additional costs of the index selection methods.

Genetic analysis of the humoral immune response of White Leghorn chicks.

Total agglutinin antibody titers, 2-mercapto ethanol (2-ME) sensitive and 2-ME resistant antibody titers were determined in 598 White Leghorn chicks after intramuscular injection with sheep red blood cells. Antibody titers were determined on day 0 and on days 3, 7, 10, 13 postinjection. Mean total tier (5.2, log2 value) was highest on day 7. Females showed a significantly higher response to injection with sheep red blood cells than males. Also, significant hatch effects were noted. Heritability estimates generally varied from 0 to .5 for all parameters. In the earlier stages of the immune response the sire estimate of heritability for total and 2-ME sensitive antibody titer was higher than the dam estimate. Additive genetic correlations between 2-ME sensitive (days 3 to 13) and resistant (days 7 to 13) antibody titers were negative, varying from -.30 to -.93. The response to selection for total antibody titer is, therefore, not easily predicted.