Prevention of incubation behavior expression in turkey hens by active immunization against prolactin

The consequences of active immunization against prolactin on expression of incubation, reproductive performance and hormonal profiles were evaluated in turkey hens. Hens were injected weekly for 4 wk starting 8 wk before being submitted to a stimulatory photoperiod and 3 times thereafter at intervals of 4 to 5 wk. The hens were injected i.d. with 0.5 mL of a mixture diluted half in Freund's adjuvant. The mixture was prediluted in .9% saline and contained 100 micrograms of a fusion protein (GST-tPRL), GST, oPRL or vehicle. The results indicate that active immunizations with GST-tPRL or oPRL both induce production of specific prolactin antibodies. The onset of egg production was unaffected but higher egg production was observed for the GST-tPRL immunized hens. No GST-tPRL immunized hens expressed incubation behavior, whereas 20 to 30% of hens in the other experimental groups did so. Apparent hyperprolactinemia was detected by RIA for the GST-tPRL immunized groups starting before photostimulation and lasting until Week 10 of egg production but not in other groups. No significant differences were observed in either plasma LH or estradiol concentrations of immunized and nonimmunized turkey hens. In conclusion, both GST-tPRL or oPRL induced the production of antibodies against prolactin in turkey hens. However, only active immunization using GST-tPRL induced higher antibody titers as well as full prevention of incubation behavior expression. Such a pharmacological approach is of great practical interest, although its uses need to be carefully evaluated under commercial conditions.

Analysis of the β-lactoglobulin locus using the grand-daughter design in the Canadian Holstein population

A total of 185 informative sons from nine heterozygous grandsires were used to study the associations of alleles A and B of the β-LG locus and milk production using the granddaughter design. The average informativeness of the β-LG locus for the nine heterozygous grandsires was 61%. The β-LG locus was found to be significantly associated with milk protein percentage (P ≤ 0.05) across families and (P ≤ 0.01) in one family. The A allele was associated with higher protein percentage EBV (0.096%) than the B allele in that family. There was no association between β-LG and other production traits (milk, fat and protein yields and, fat and percentages). The β-LG locus has a potential use in marker-assisted selection. However, since the association between markers and a given trait is not found in all families, within-family marker selection might be more appropriate due to linkage disequilibrium. Key words: β-lactoglobulin, Canadian Holstein, milk production traits, granddaughter design

A genetic marker in the growth hormone receptor gene associated with body weight in chickens

A genomic clone spanning 16 kb of the GH receptor gene was mapped and used as a probe for identifying restriction fragment length polymorphisms (RFLPs) in chickens. Several strains of meat-type and egg laying chickens were found to segregate for an HindIII RFLP located in the intron preceding exon 4. The polymorphic HindIII site overlapped with a poly(A) signal. Association of the HindIII RFLP with traits was analyzed in a random-bred White Leghorn strain in three generations using either selective or random genotyping. Both methods revealed significant association of the HindIII+ allele (presence of the poly(A) signal) with an increased juvenile body weight (130 days of age). In two meat-type strains divergently selected for size of the abdominal fat pad, the HindIII+ allele was coselected with leanness. The results indicate the presence of a genetic variant of the GH receptor gene which affects growth and abdominal fat deposition and which is relatively frequent in egg laying as well as in meat-type chickens.

Evidence for a genetic variation in the mitochondrial genome affecting traits in White Leghorn chickens

A mitochondrial Mspl RFLP which was coselected with Marek's disease (MD) resistance in White Leghorn chickens was mapped to the NADH subunit IV. The RFLP was due to a transition, resulting in the change of the low-usage threonine triplet ACT (Mspl- allele) to the high usage triplet ACC (Mspl+ allele). Trait association studies within an unselected strain revealed that the Mspl- allele whose frequency was reduced in MD resistant strains was associated with high body weight and high egg specific gravity (a measure of eggshell thickness). Analysis at three different time points indicated a significant interaction between the mitochondrial genotype and the growth hormone genotype in early but not in late adulthood. The analysis indicates that mitochondrial variants may contribute to phenotypic variation in chickens and that such contributions may be dependent on the genetic background.

Restriction fragment length polymorphisms at the ornithine decarboxylase locus associated with milk protein yield in Holsteins

Marker-assisted selection may provide the opportunity to make significant genetic gains in the improvement of economically important traits in livestock (Soller & Beckmann, 1983; Smith & Simpson, 1986). Implementation of this approach will first require identification of candidate genes or anonymous gene markers associated with the traits of interest. Candidate genes are those with a known relationship between physiological or biochemical processes and an economically important trait. In dairy cattle, genes associated with mammary gland growth, development and function are excellent candidate genes for milk production traits.

The polyamines are low molecular mass polycations that influence cell proliferation and growth (Tabor & Tabor, 1984; Pegg, 1986). Ornithine decarboxylase (ODC, EC 4.1.1.17) catalyses the conversion of ornithine to putrescine, the rate-limiting step in polyamine biosynthesis (Pegg, 1986). The level of ODC is induced in quiescent cells exposed to a wide variety of stimuli such as growth hormone, corticosteroids, testosterone and growth factors (Tabor & Tabor, 1984). There is ample evidence that growth factors influence morphogenesis and differentiation of the mammary gland (Imagawa et al. 1994). Trophic hormones that are associated with lactation, such as prolactin and growth hormone, are also required to induce differentiation of bovine mammary epithelial cells (Huynh et al. 1991; Flint & Gardner, 1994), and both mitogenic and lactogenic effects of prolactin, insulin and hydrocortisone appear to be mediated through the polyamine pathway (Rillema et al. 1977; Bedford & Zadworny, 1990; Golden & Rillema, 1993). Strange et al. (1992) have shown that ODC is involved in synthesis of a milk component; ODC has elevated expression in the lactating mammary gland, which declines sharply after weaning. It is therefore possible that particular variants of ODC could be associated with increased mammary gland function and thus influence milk related traits.

The objectives of the present study were to estimate allelic frequencies of ODC polymorphisms in Holstein bulls and to evaluate further the genotypic effects of ODC variants on milk production traits.

Association of endogenous viral genes with quantitative traits in chickens selected for high egg production and susceptibility or resistance to Marek's disease

1. The association of endogenous viral (ev) genes with quantitative traits in 2 genetically distinct sets of White Leghorn strains were investigated. Strain S had been selected for susceptibility to Marek's disease (MD) whereas strain K had been selected for resistance to MD and high egg production and egg weight. 2. In all, 8 ev genes were typed. Ev10, ev19 and 'newB' occurred exclusively in strain S, 'newA' occurred only in strain K, and ev1, ev3, ev6 and ev8 occurred in both strains. 3. Whereas ev6 and ev8 were associated with reduction in egg production rate in strain S, in strain K, the presence of ev3 was associated with increased group specific antigen. 4. The genetic background of the chicken strain may play a role in the way certain ev genes affect traits. 5. It was thought that the position of ev genes on the chromosome may be important and their association with traits of economic importance make them potential genetic markers for uncovering quantitative trait loci.

Bovine ornithine decarboxylase gene: cloning, structure and polymorphisms

Bovine ornithine decarboxylase (ODC) genomic clones were isolated from a bacteriophage lambda DASH genomic library. A total of 9452 bp sequence was determined which covers the entire sequence of the bovine ODC gene. Sequence analysis showed that the bovine ODC gene consisted of 12 exons which encode a protein identical to that inferred from a bovine ODC cDNA. Comparison of the structure and nucleotide sequence of the bovine, human and mouse ODC genes revealed that the gene was highly conserved. Primer extension analysis demonstrated that the transcription start point of bovine ODC mRNA was located 378 bp upstream from the A residue in the translation initiation codon. The 5'-untranslated region (UTR) of ODC mRNA was highly G + C rich, particularly in its 5'-most portion, and computer predictions suggested a very stable secondary structure for this region, with an overall free energy of formation of -134.4 kcal/mol. Conserved sequences and potential promoter elements including a TATA box, a possible CCAAT element, SP1 ranscription factor binding sites (GC boxes) and cAMP response elements (CRE) were identified in the 5'-flanking region of the gene. Two polymorphic restriction sites, a TaqI and a MspI, were mapped to the ODC gene and PCR-based methods for detection of the 2 polymorphisms were developed.

Genetic variability in white leghorns revealed by chicken liver expressed sequence tags

A total of 92 expressed sequence tags from chicken liver (CLEST) were searched for homology with known genes. Among the CLEST, 29% had no sequence similarities with known genes, 34% showed sequence similarity to rRNA, 9% to mitochondrial genes, 23% to known nuclear genes, and 5% to human expressed sequence tags. Among the nuclear CLEST (excluding rRNA), clones with sequence similarity to aldolase B were represented four times, whereas all the other clones represented unique genes. The presence of MspI and TaqI restriction fragment length polymorphisms (RFLP) associated with CLEST were analyzed by bulk Southern blotting in 16 strains of White Leghorn chickens derived from five different genetic bases. No RFLP were observed with rRNA CLEST and a single MspI RFLP was observed with mitochondrial CLEST. The nuclear CLEST with sequence similarity to known nuclear genes were grouped into two classes on the basis of their involvement in intermediary metabolism. Among the nine genes coding for metabolic enzymes, all but one were polymorphic at MspI and/or TaqI sites in at least one of the strains, whereas among the other genes six of nine were polymorphic. The average frequency of clones revealing RFLP per cDNA clone and restriction enzyme for the two classes were 0.7 and 0.3, respectively. The analysis indicated that in White Leghorns, RFLP markers in the vicinity of nuclear CLEST are relatively frequent. Further, RFLP in the vicinity of genes coding for metabolic enzymes were significantly more frequent than near genes coding for other proteins.

Trait association of genetic markers in the growth hormone and the growth hormone receptor gene in a White Leghorn strain

Alleles of the growth hormone (GH) gene and GH receptor (GHR) gene were analyzed for association with juvenile body weight (HBWT), age at first egg (AFE), the hen-day rate of egg production (HDR), egg specific gravity (SPG), and egg weight (EWT) in a strain of White Leghorns. The particular strain segregated at near equal frequencies for two GH alleles defined by differences at three restriction fragment length polymorphisms (RFLP) and for two GHR alleles defined by a single RFLP. The GH genotype was significantly associated with AFE (P < or = 0.04) as well as HDR from 274 to 385 d (P < or = 0.04) and 386 to 497 d (P < or = 0.0003). The GHR genotype (haploid in female chickens) had trends for association with HBW (P < or = 0.06) and HDR from AFE to 273 d (P < or = 0.07). The effects on the egg quality traits SPG and EWT were not significant. Regression analysis revealed that HDR was associated negatively with AFE and positively with HBWT. The slope of the regression line of HDR on AFE varied with the GH genotype, with the effect that the differences in HDR between GH genotypes was relatively small in chickens with early AFE and large in chickens with late AFE. Similarly, the slope of the regression of HDR on HBWT varied between GHR genotypes, with the result that the effect of the GHR genotype on HDR in chickens with low HBWT was opposite to its effect in chickens with high HBWT. The complex relationship between genotypes and traits may reflect gene interaction and indicates that simple models based on additive gene effects may not be adequate for the dissection of the genetic architecture of quantitative traits.

Prevention of the expression of incubation behaviour using passive immunisation against prolactin in turkey hens (Meleagris gallopavo)

The efficacy of injecting antibodies raised against turkey prolactin to prevent the expression of incubation behaviour has been investigated in turkey hens. Medium white turkey hens (n = 15 x 2) were injected three times weekly for 4 consecutive weeks starting on week 5 of egg production. The hens were injected im with a volume of 1 mL per injection for the 1st week and 0.5 mL thereafter, of normal rabbit serum or serum containing antibodies raised against turkey prolactin (Guémené et al, 1994a). None of the 15 passively immunised hens expressed incubation behaviour, whereas, more than half (53%) of the control hens did express it. Plasma prolactin concentrations observed in the two groups presented comparable profiles until week 9 and from week 19 of egg production onward. Differences were, therefore, observed from week 10 until week 17 with the non immunised hens showing higher plasma prolactin concentrations than the immunised ones. This difference was related to the presence of incubating hens in the control group. A higher percentage of non immunised hens disrupted egg production during the course of the study and consequently immunised hens laid more eggs than the control ones. No change in plasma LH and oestradiol concentrations can be related to the immunisation procedure. We conclude that prevention of incubation behaviour can be achieved using passive immunisation against prolactin, prevention which resulted in more egg production under our experimental protocol.

DNA polymorphisms in the chicken growth hormone gene: response to selection for disease resistance and association with egg production

Analysis of the growth hormone (GH) gene in 12 strains of White Leghorn chickens revealed restriction fragment length polymorphisms (RFLPs) at three MspI sites and at a SacI site. Based on linkage disequilibrium analysis, they gave rise to eight different alleles (i.e. combinations of RFLPs), with five occurring at frequencies above 5% in at least one strain. Pairs of GH-RFLPs were at near maximal linkage disequilibrium, suggesting either a lack of recombination or the presence of selection pressure during evolution of the GH gene. Allele frequencies were determined in 12 non-inbred strains derived from three different genetic bases. These strains had been selected either for an array of egg production traits, resistance to Marek's disease or resistance to avian leukosis. Selection for disease resistance was consistently correlated with an increase in the frequency of one of the alleles. One strain segregated for only two alleles, which differed by three RFLPs. Analysis of variance in this strain indicated that the GH allele co-selected with resistance was associated with a delayed onset of ovulation but a higher persistency of ovulation as age progressed, resulting in an overall increase of egg production by 15% (age at first egg to 497 days). The resistance-associated GH allele was dominant for the onset of ovulation and recessive for the persistency of egg production. There was no significant effect of the GH genotype on juvenile body weight, egg weight or egg specific gravity.

Changes in expression of the prolactin and growth hormone gene during different reproductive stages in the pituitary gland of turkeys

The changes in levels of prolactin (PRL) and growth hormone (GH) in plasma and the pituitary gland and their transcripts were measured in turkey hens at different physiological stages by radioimmunoassay and dot blot hybridization analysis, respectively. The levels of tPRL mRNA in the pituitary gland increased from those of the immature group to the egg-laying group, reaching a maximum during the incubation and a minimum during the moulting stages. Changes in pituitary levels of PRL and PRL mRNA followed a similar trend and consequently were highly correlated (r2 = 0.83), whereas a significant but lower correlation was observed between circulating and pituitary levels (r2 = 0.62). Less significant changes were measured for tGH mRNA, with maximum and minimum levels measured in the pituitaries of egg-laying and non-laying hens, respectively. These data suggest that although changes in concentration of PRL are correlated with the reproductive stage of the turkey hen, coordinate changes in levels of GH are not.

Sequence variations in the bovine growth hormone gene characterized by single-strand conformation polymorphism (SSCP) analysis and their association with milk production traits in Holsteins

Sequence variations in the bovine growth hormone (GH) gene were investigated by single strand conformation polymorphism (SSCP) analysis of seven amplified fragments covering almost the entire gene (2.7 kb). SSCPs were detected in four of these fragments and a total of six polymorphisms were found in a sample of 128 Holstein bulls. Two polymorphisms, a T-->C transition in the third intron (designated GH4.1) and an A-->C transversion in the fifth exon (designated GH6.2), were shown to be associated with milk production traits. GH4.1c/GH4.1c bulls had higher milk yield than GH4.1c/GH4.1t (P < or = 0.005) and GH4.1t/GH4.1t (P < or = 0.0022) bulls. GH4.1c/GH4.1c bulls had higher kg fat (P < or = 0.0076) and protein (P < or = 0.0018) than GH4.1c/GH4.1t bulls. Similar effects on milk production traits with the GH6.2 polymorphism were observed with the GH6.2a allele being the favorable allele. The average effects of the gene substitution for GH4.1 and GH6.2 are similar, with +/-300 kg for milk yield, +/-8 kg for fat content and +/-7 kg for protein content per lactation. The positive association of GH4.1c and GH6.2a with milk production traits may be useful for improving milk performance in dairy cattle.

Molecular cloning, tissue distribution, and expression of the prolactin receptor during various reproductive states in Meleagris gallopavo

The primary sequence of the prolactin receptor (PRL-R) in turkeys was deduced from a cDNA clone isolated from a kidney cDNA library and from a polymerase chain reaction (PCR) product. The open reading frame of the turkey PRL-R (tPRL-R) predicted an 831-amino acid protein composed of a leader peptide, an extracellular domain, a single transmembrane domain, and an intracellular domain. The extracellular domain contained two homologous repeat units with 63% amino acid sequence identity to each other. Each repeat unit contained all of the conserved cysteine pairs and a WSXWS motif found in mammalian PRL-Rs. A tPRL-R transcript with a molecular size of about 3000 nucleotides was identified by Northern blot analysis. The tPRL-R transcripts were detected in all 26 tissues examined using reverse transcriptase PCR (RT-PCR). The pituitary gland, hypothalamus, crop sac, duodenum, and gizzard were found to express the highest levels of tPRL-R among the 26 tissues. The expression levels of tPRL-R in 17 tissues were compared using semi-quantitative RT-PCR in nonphotostimulated, laying, out-of-lay, incubating, and maternal hens, and male birds. In most tissues examined there was no obvious relationship between blood levels of PRL, reproductive states, and estimated concentrations of the receptor mRNA. In the pituitary gland and hypothalamus, plasma levels of PRL and levels of tPRL-R transcript were inversely correlated. In the hypothalamus, increasing blood levels of PRL were associated with decreasing levels of the receptor transcript (p < or = 0.05), whereas the opposite was observed in the pituitary gland (p < or = 0.05). These findings support the hypothesis that PRL itself may participate in the neuroendocrine control of incubation behavior through actions on both the hypothalamus via a short-loop feedback mechanism and the pituitary gland via autocrine and/or paracrine effects.

Sequence analysis of the β-lactoglobulin locus in Holsteins identifies two new restriction fragment lengtn polymorphisms

The polymerase chain reaction (PCR) was used to amplify and clone a region from the β-lactoglobulin (β-LG) locus that spanned exons IV and V (849 bp). The DNA was amplified from both AA and BB homozygous individuals and sequenced. Sequence analysis revealed that the intervening intron was 673 bp and that three nucleotide substitutions differentiated the A and B forms of β-LG. One of these substitutions was associated with the amino acid substitution (aspartic acid or glycine in the A and B variants, respectively), and the other two which were not reported previously were present in the intron sequence. These nucleotide substitutions resulted in restriction fragment length polymorphisms (RFLPs) that could be used to genotype individuals. The new restriction sites in the intron would result in a more accurate genotyping of the β-LG gene. Animals with B genotype were positive for the presence of two HaeIII restriction endonuclease sites, and type A animals were negative. Animals could also be genotyped on the basis of a polymorphism at a NlaIV restriction site. Genotyping of a random sample of 129 cows and 99 bull calves in Quebec revealed a frequency of 0.66 for the B allele. A comparison between bulls in current use by the artificial insemination industry (n = 114) and from the earliest years of the industry (n = 70) revealed frequencies of 0.58 and 0.56, respectively. Thus, it is unlikely that the sire selection program has affected the allelic frequency. Key words: β-lactoglobulin, Holsteins, DNA sequence, polymorphisms

A MspI polymorphism in the bovine ornithine decarboxylase gene and its possible association with selection for milk production in Holstein bulls

A polymerase chain reaction (PCR)-based method for detection of a MspI-restriction fragment length polymorphism (RFLP) in the bovine ornithine decarboxylase gene was developed, and the allele frequencies of the polymorphism in two groups of Holstein bulls representing progeny-tested bulls during the 1950s-1960s and 1980s, respectively, were estimated. The frequencies of the MspI(-) allele ere 0.229 and 0.077 and that of MspI(+) were 0.771 and 0.923 in the progeny-tested bulls of the 1950s-1960s and 1980s, respectively. The difference in allele frequencies between the two groups was statistically significant (P < 0.005). Genetic drift could be responsible for the changes in allele frequencies; however, it could also be possible that selection for milk production was associated with the changes of the allele frequencies in the two bull populations.

Presence of an additional PstI fragment in intron 1 of the chicken growth hormone-encoding gene

A previously unreported 196-bp PstI fragment was found in intron 1 of the gene encoding chicken growth hormone (cGH) when a PCR assay for an MspI restriction fragment length polymorphism was established. A pair of PCR primers was designed according to the published cGH sequence and used to amplify a fragment which contained two MspI sites, one polymorphic and another non-polymorphic. However, amplification of genomic DNA from two strains of meat-type chickens and three strains of White Leghorn chickens yielded a PCR product which was about 200 bp larger than expected. The fragment from one of the meat-type chickens was subcloned into the vector pCR-Script SK+, and sequenced. It revealed the presence of an extra fragment of 196 bp which was flanked by the PstI sites and occurred at nt +308 of the previously reported cGH sequence.

Molecular cloning of a bovine ornithine decarboxylase cDNA and its use in the detection of restriction fragment length polymorphisms in Holsteins

A cDNA coding for ornithine decarboxylase (ODC) was isolated from a bovine liver cDNA library. The clone (1758 base pairs) consisted of 5'- and 3'-untranslated regions of 185 and 187 nucleotides, respectively, and an open reading frame of 1383 nucleotides encoding an ODC protein (M(r) 51,342 daltons) of 461 amino acids. Comparison of the nucleotide and the predicted amino acid of the cDNA with other mammalian ODCs showed a very high degree of homology both at the DNA and protein levels. The bovine ODC mRNA was identified by northern blot to be a single species with a molecular size of 2.35 kilobase pairs. Primer extension analysis indicated that the 5'-untranslated region of the bovine ODC mRNA was 312 nucleotides long. Southern blot analysis of bovine genomic DNA revealed restriction fragment length polymorphisms when cleaved with restriction enzymes PstI, MspI, TaqI, and Bg/I.

Development and validation of a homologous radioimmunoassay using a biologically active recombinant turkey prolactin

1. A new homologous radioimmunoassay has been developed for the measurement of turkey prolactin. 2. A 25000 kDa purified recombinant derived turkey prolactin (rtPRL), the biological activity of which was tested using a crop sac assay, was used as immunogen for the production of rabbit antiserum. In this biological test, the rtPRL was as active as the ovinePRL. 3. The radioligand (rtPRL) was labelled with 125I and the assay allowed the detection of standard doses of rtPRL ranging from 400 pg/tube to 50 ng/tube. 4. No cross reaction with chicken luteinising hormone and recombinant chicken growth hormone was detected. 5. The within and between assay coefficients of variability were 5.0 +/- 2.7% and 16.3%, respectively. The overall mean recovery ratio was 1.01. 6. The dose-response curves obtained with serial dilution of plasma and pituitary from turkey hens at different physiological stages and from male turkeys were parallel to those obtained with standard rtPRL. 7. The measured concentration of prolactin was 5 times higher in plasma from incubating than laying turkey hens, and the pituitaries from incubating hens contained 2 and 4 times more prolactin than those of laying and out of lay hens or males, respectively. 8. To further assess the validity of the assay, we measured changes in plasma concentration of prolactin in turkeys following stimulation with chicken vasointestinal peptide (cVIP). A single injection of 1 or 10 micrograms/kg body weight of cVIP to laying hens produced a large and rapid increase in plasma prolactin. 9. This new radioimmunoassay appears to be high for the measurement of turkey prolactin.

Production and characterization of recombinant turkey prolactin

1. Recombinant turkey prolactin (rctPRL) was produced as a fusion protein in E. coli, purified by affinity chromatography followed by cleavage with thrombin. The final yield of the released rctPRL (> 90% purity) was 1-2 mg/l of bacterial culture. 2. Recombinant tPRL co-migrated with the main immunoreactive band (25 kDa) in turkey pituitary extracts and was identical to natural tPRL except for the addition of three amino acids (Gly-Ser-Ser) resulting from the cloning strategy at the amino terminal end. 3. The bioactivity of the rctPRL was equipotent to ovine PRL in a rabbit mammary explant system and in the Nb2 lymphoma mitogenic assay.

Synergism between the endogenous viral loci ev6 and ev9 in inducing immunological tolerance to avian leukosis virus

1. The course of infection by exogenous avian leukosis virus was followed in a commercial strain of White Leghorn domestic fowls by measuring viral antigen in feather pulp and egg albumin. Ten days after hatching, 2 out of 360 birds tested positive and at 286 days of age about 60% of the birds had been antigen positive at least once. 2. Among the antigen positive birds, two groups could be distinguished: those which permanently and those which transiently expressed viral antigen. Permanent antigen expression was associated with low antibody titres, while transient antigen expression was associated with high antibody titres. 3. The strain segregated for the two endogenous viral genes ev6 and ev9, both of which express endogenous viral envelope protein, and have been implicated in affecting immune-responsiveness. The antibody titre in individuals positive for both ev6 and ev9, was significantly lower than in those which had none or only one of the two ev-genes. In addition, individuals positive for both ev-genes occurred more frequently in the group permanently positive for viral antigen than in the group transiently antigen positive. 4. The results indicate that there was a strong synergism between ev6 and ev9 in reducing the antibody response to exogenous avian leukosis virus infection, perhaps by inducing immune tolerance or interfering with antibody formation.

Identification of growth hormone DNA polymorphisms which respond to divergent selection for abdominal fat content in chickens

Two strains of meat-type chickens which had been derived from the same genetic base, but were selected for high or low abdominal fat content, respectively, were analyzed for polymorphisms in the growth hormone gene (GH). A total of four DNA polymorphisms were identified, one at a SacI restriction site and three at MspI restriction sites. Restriction mapping indicated that all polymorphisms were in exons and/or introns and not in flanking regions of the gene. The incidence of GH polymorphisms was determined in 20 chickens from each strain and significant differences were observed for two of the four polymorphisms. Analysis by DNA fingerprinting using (CAC)5 as a probe indicated that the inbreeding coefficient was 0.1 in both strains and that random genetic drift was minimal. Thus, the selection for abdominal fat appears to have affected the frequency of alleles of the growth hormone gene. Whether this is the direct consequence of an altered growth hormone gene on fat metabolism or reflects linkage to an allele of a neighbouring gene remains to be determined.

Developmental expression of the prolactin gene in the chicken

Steady-state levels of prolactin (PRL) mRNA in the pituitary gland during embryonic development were determined by dot blot analyses to relate the changes with those of pituitary and plasma levels of PRL. Steady-state levels of the 1.38-kb mRNA encoding the PRL prohormone remained low until Day 18 of incubation, increased on Day 19 of incubation, and reached maximum levels on the day of hatch but decreased 1 day after hatch. Changes in both pituitary and plasma concentrations of PRL closely mimicked those changes in PRL mRNA levels. Subsequently, both the levels of the pituitary PRL mRNA and PRL remained unchanged whereas those of plasma PRL increased 7 days after hatch. The results indicate that a progressive expression of PRL gene in the pituitary gland occurs 1-2 days before the hatch and concomitant increases in plasma concentrations of prolactin may be associated with physiologic changes in pulmonary respiration and hatching.