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Selecting for Favorable Genetic Response to Disease Gary Snowder, PhD Research Geneticist USDA, ARS, USMARC Outline Justification Challenges Current research on Genetic Resistance to BRD and IBK Justifications for Genetic Selection Justifications

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selecting for favorable genetic response to disease

Selecting for Favorable Genetic Response to Disease

Gary Snowder, PhD

Research Geneticist

USDA, ARS, USMARC

outline
Outline
  • Justification
  • Challenges
  • Current research on Genetic Resistance to BRD and IBK
justifications
Justifications
  • No new class of antibiotics in over 30 years
  • Emergence of new diseases(BSE, Avian Flu, CWD)
  • Increase in disease transmission(Daszak et al., 2000)
    • Intensive mgmt
    • Wildlife to livestock transmission (Brucellosis, Avian Flu)
  • Therapeutic treatment costs are higher
slide5

Justifications

  • Microbes are antibiotic resistance
  • No available vaccine or antibiotic
  • A variety of pathogens infect the host in a similar manner or pathway.
  • “Organic” labeled product
slide6

Justification

  • Rarely will all animals exhibit clinical symptoms.
  • Cattle breeds differ for disease related traits
      • Tick borne diseases (Wambura et al., 1998)
      • Pinkeye (Snowder et al., 2005a)
      • Bovine respiratory disease (Snowder et al., 2005b)
justifications7
Justifications
  • New consumer expectations
    • Meat free of drug residue
    • Meat animals live a healthy and happy life
slide8

Breeding for societally important traits in pigs1

E. Kanis*,2, K. H. De Greef , A. Hiemstra*,3 and J. A. M. van Arendonk†

*Animal Breeding and Genetics Group, Wageningen University, 6700 AH Wageningen, The Netherlands; and

†Animal Sciences Group, 8200 AB Lelystad, The Netherlands 2

J. Anim. Sci. 2005, 83:948-957

Consumers expect meat animals raised with better welfare, produced in an environmentally friendly manner and,

free of feed “additives”, antibiotics, and vaccines.

slide11

The immune system is highly complex.

Only the nervous system is more complex.

More complex than reproduction, growth, lactation, or feed efficiency.

slide12

Challenges

  • Selection for animals resistant to a particular pathogen may
    • make that pathogen more virulent,
    • make the host more susceptible to another microbe
slide13

Challenges

  • Genetic correlations between production traits and disease resistance are often undesirable
    • Milk yield in dairy cattle has a positive correlation with many disease traits(Simianer et al., 1991; van Dorp et al., 1998)
    • Selection for growth rate in turkeys increased their susceptibility to Newcastle disease(Sacco et al., 1994)
    • Growth rate in mice is genetically associated with over 100 physiologic, metabolic, and microbial susceptible diseases (nih.gov)
    • In beef cattle, these correlations have not been defined.
slide15

Challenges

● Many factors influence disease resistance.

slide16

Challenges

  • Difficult to identify phenotype for disease resistance.
  • False assumption that all healthy animals are disease resistant.
slide17

Challenges

  • Some diseases are caused by a variety of microbes

Calf Pneumonia caused by:

VirusesInfectious Bovine Rhinotracheitis (IBR), Bovine Viral Diarrhea (BVD), Bovine Respiratory Syncytial (BRS), and Parainfluenza 3 (PI3)

Bacteria(Mannheimia haemolytica, Pasteurella multocida, Haemophilus somnus)

Mycoplasmas(Ellis, 2001)

stress pathogens disease
STRESS + PATHOGENS = DISEASE

PATHOGENS + STRESS = DISEASE

slide21

Genetic research of human diseases, especially molecular genetics, is far ahead of livestock research.

highly successful in plants
Highly successful in plants

Corn

Wheat

Oats

Bean

Broccoli

Cabbage

Carrots

Cucumber

Peppers

Tomato

Melon

Squash

Genetically Resistance to:

Fungi

Viruses

Nematodes

Wilt

Blight

Leafspot

Root rot

Sunspot

slide23

Disease Resistance is Heritable

Mastitis .02

Somatic Cell Score .15

Pinkeye .22

Respiratory .11 to .48

infectious bovine keratoconjunctivitis ibk pinkeye
Infectious bovine keratoconjunctivitis (IBK), pinkeye

Introduction

  • Annually affects > 10 million calves in the USA
  • Estimated economic loss > $150 million (Hansen, 2001).
  • 29% of cattle operations reported IBK as an economically important disease (NAHMS, 1998)
slide27

Mar20 Apr19 May19 June18 July18 Aug17 Sept16 Oct16

Incidence of IBK by Date

slide34

Estimates of Heritability

Range 0.00 to 0.28

slide35

Over All Breeds

Low to Moderate heritability

slide38

Crossbred calves from tropically adapted sires had a significantly lower incidence of IBK

bovine respiratory disease
Bovine Respiratory Disease
  • Most common and costly disease of beef cattle, losses $400 - $600 million per year.
  • Commonly causes reduced weight gain from lack of appetite or inability to eat
over all breeds
Over All Breeds

Moderate genetic component to resistance to BRD

slide46

Does heterozygosity

influence BRD?

effect of heterozygosity48
Effect of Heterozygosity
  • Yes, crossbred cattle had significantly lower incidence of BRD compared to purebreds.
additive distressors

Castration

Dehorning

Transport

Diet Change

Additive Distressors

Weaning

Immunity

Challenge

Sick

slide52
Data
  • 18,112 cattle from 9 pure breeds and 3 composites
  • 15 yr feedlot records (1987-2001)
slide53

Incidence of BRD by Year

Range: 5 - 44%; Avg. 17%

days on feed
Days on Feed

Agrees with Loneragan (2001) and Schunicht et al. (2003)

conclusions
Conclusions
  • Research for disease resistance is
    • Highly complex
    • Of significant importance to consumers and product quality
    • Fairly new research area for genetics
  • Genetic variation within and across breeds for some diseases is present
  • A great deal more research must take place