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THE TALE OF GOAT S1 CASEIN

THE TALE OF GOAT S1 CASEIN. E. Manfredi SAGA, INRA de Toulouse, France. Context : dairy goat production Biology : protein, DNA, RNA, cell biology Effects of the polymorphism : dairy performances, feed utilization, dairy products Selection : simulations, use in practice.

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THE TALE OF GOAT S1 CASEIN

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  1. THE TALE OF GOAT S1 CASEIN E. Manfredi SAGA, INRA de Toulouse, France

  2. Context : dairy goat productionBiology : protein, DNA, RNA, cell biologyEffects of the polymorphism : dairy performances, feed utilization, dairy productsSelection : simulations, use in practice • s1- Casein polymorphism

  3. CONTEXT • s1- Casein polymorphism

  4. Dairy goat products • Diversity of products • milk: fluid whole or skimmed, powder • cheese • yoghurt, ice-cream, butter, candies • In Europe, milk is mainly used for labelled cheese making, with specific market demands • Cheese yield is heavily dependent on protein content of milk • Goat milk benefits from a ‘natural’ and ‘healthy’ image. • Genetic origin of nutritional and dietetic properties ?

  5. Issues in the 80’s Contents g/kg 40 4 • Yield kg 1 20 days Low protein and fat contents in middle lactation Seasonality : concentration of kidding dates in winter months  deficient cheese processing

  6. BIOLOGY : protein, DNA, RNA… • s1- Casein polymorphism

  7. Research in the 80’s : The protein • 4 main caseins: s1, s2, ,  • s1-casein : variable structure , variable expression • AllelesSynthesis rate • A, B, C high • E medium to low • F, G low • O null • Grosclaude et al. (1987)

  8. Cas-s1 polymorphism – Breeds • Breed Alleles • A, B, C E F • Maltese 0.6 0.1 0.3 • Murciana 0.3 0.6 0.1 • Alpine (France) • unselected 0.2 0.3 0.5 • dams of bucks 0.4 0.3 0.3 • Jordana et al. (1995), Ramunno et al.(1991), Grosclaude et Martin (1999)

  9. Research in the 90’s : DNA, RNA Reference A : 19 exons, 17.5 kb • Leroux et al. (1992), Jansa Perez et al. (1994), Martin et al. (2002) F : more than 10 transcripts (exon skipping) G : exon 4 skipped E : insertion of 457 bp in exon 19 O1 : exons 13 to 19 deleted

  10. Cell biology • First observations of epithelial cells : abnormal vacuoles in FF and OO individuals • Reduced expression of s1-cas alters the normal intra-cellular transport of caseins • Indirect effect on fat synthesis and fatty acid composition in goat milk ? • Chanat et al. (1999)

  11. EFFECTS ON:dairy performances, properties of products • s1- Casein polymorphism

  12. Dairy performances (1) Barbieri et al., 1995; (2) Mahé et al. (1993)

  13. Residual heritability of protein content • Performance = environment + genetic effects Polygenic model : Y = m + G + e h2G PC = 0.6 Mixed genetic model : Y = m + (C + g ) + e h2g PC = 0.3 Barbieri et al. (1995)

  14. Nutritional value of milks Fevrier et al. (2000)

  15. Milk properties and cheese processing • AA EE FF . • Total N (g/l) 34.4 30.3 28.2 • Protein (g/l) 31.8 27.6 25.5 • Casein (g/l) 26.7 22.8 20.7 • Casein/total N (%) 77.8 75.2 73.5 • Casein/protein (%) 84.2 82.6 81.2 • Fat content (g/l) 33.5 31.8 29.2 • Rennet coagulation (mm/min) 3.56 2.68 2.85 • Curd firmness (mm) 50.4 40.5 37.3 • Cheese yield 21.9 20.2 18.8 • Vassal et al. (1994)

  16. Sensorial scores of cheese – Notes from 1 to 5 Delacroix et al., 1996

  17. Sensorial properties • Subjective notes of Aroma, Taste, Flavor… • Interaction with texture • Molecules : fatty acids (4Me-C8, 4Et-C8, …) • Influence of lactation stage, feeding, cheese processing, fat content … • Indirect and unexplained effect of the s1-cas polymorphism on fat content and lipolysis/lipase activity of milk ? • Delacroix and Lamberet (2000)

  18. A structural gene is not a good candidateVariable level of expression associated with the variable structureVariability also exists in other loci of the casein cluster Relative high frequency of defective alleles of s1-cas in goat populationsExperimental results suggest that s1-cas is at least a good marker of the whole cluster effectAlso, s1-cas polymorphism would have impact on the normal synthesis/transport of mammary epithelial cells • s1- Casein model - Limitations

  19. LIMITED USE IN SELECTION • s1- Casein polymorphism

  20. Selection objectivesFavorable effects on goat performances, nutritional value, cheese yieldBut unfavorable (small) effects on flavorSo, ignore the intrinsic value of ‘strong’ genotypes and keep the traditional goals : protein yield, protein content • s1- casein use in selection - Objections

  21. Selection methodsInterest of the major gene for improvement of protein content and protein yield ? : low h2 ? h2 of PC=0.6 ; h2 of PY=0.3 unavailable phenotypes ? routine measurement of PY and PC recessive alleles ? additive gene action at the casein locusMoreover : unfavorable consequences on long term selection (Gibson, 1994) ? • s1- casein use in selection - Objections

  22. Dams of bucks Standard selection Planned matings Sires of bucks Standard selection • Selection scheme - Open nucleus based on A.I. Bucks born Paternity tests (DNA) Sanitary control Semen production and quality Bucks put into progeny test 40 daus/buck; > 20herds Select best bucks (standard selection)

  23. Selection scheme - efficiency • MILK FAT PROT • (kg) (g/kg) (g/kg) • 1995 Nucleus herds vs. • other recorded herds +81 +1.0 +0.6 • AI daus vs. NM daus +89 +1.1 +0.4 • (INRA Bourges; 1995) • Genetic trends +90 +1.0 +1.0 • 10 years

  24. Selection scheme - Inefficiency • Alpine Saanen • Casein n % n % • Genotype kept kept • AA 41 42 - - • AF 89 26 27 41 • FF 54 2 69 29 • ALL 184 23 96 32 • The casein genotype works as a partial and early predictor of progeny test (Manfredi et al.; 1995)

  25. Undergo mendelian sampling ? Sire AF Dam AF AA buck : 50% kept AF buck : 25 % kept FF buck : culled Control mendelian sampling : planned mating and within family selection

  26. Do not alter standard EBV (keep BLUP selection)Use s1-genotypes to avoid putting into progeny test homozygous ‘weak’ bucks by :negative assortative mating among selected parents within full-sibs selection of AI males at birthKeep costs low :dams genotype by electrophoresis of milk male genotype by PCR (blood samples : for casein genotype and mandatory paternity DNA test) • Selection scheme - Changes in 1996

  27. Dams of bucks Standard selection Planned mating Sires of bucks Standard selection • Selection schemes – Changes in 1996 Bucks born Casein genotype Paternity tests (DNA) Sanitary control Semen production and quality Bucks put into progeny test 40 daus/buck; > 20herds Select best bucks (standard selection)

  28. Practical problems encountered :Lack of maternal genotypes (about 30 % of dam genotypes known)Availability of male genotype before selection decisions are taken at the AI center • Selection scheme - Changes in 1996

  29. Genotype frequencies of AI males – Alpine breed

  30. Genotype frequencies of AI males - Saanen breed

  31. Conclusions • GAS may be useful for sex-limited traits (even for traits with high h2) • GAS limited to planned mating and within full-sib selection is yielding a slow increase of favorable genotype frequencies of AI males

  32. Conclusions • Possible improvements of GAS : • estimate unknown genotype probabilities from known genotypes, pedigree and performances • use a combined index (polygenes + s1 cas) for across family selection, with some control on polygenic variability and consanguinity • With GAS, selection objectives and biological components of genetic gain need a more precise description than in the past

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