Genetic Improvement of Dairy Cattle Health

1. Genetic Improvement of Dairy Cattle Health

2. Overview Response to selection using field-recorded traits is efficient and well-documented. Herd owners are interested in healthy, longer-lived cows. Genetic variability exists for health traits of economic interest.

3. Overview Statistical and computational tools for genetic evaluation exist. Data processing routines can be developed. However, data needed for routine evaluations are limited.

4. Why select for improved health? Longer-lived (more profitable) cows. Decreased cost of production. Reduced herd turnover. Improved animal welfare. Genetic gains are cumulative!

5. Desirable Properties of Health Traits Reasonably large genetic variability or heritability. Significant economic value. Reasonable cost of measurement and recording. Consistent methods for measurement and recording. (Shook, 1989)

6. Challenges Low heritabilities for some traits. Unfavorable correlations with milk, fat, and protein yield. Affected animals have a low frequency of occurrence. Diagnoses may be uncertain. Data are not collected in a national database.

7. Heritabilities and Correlations of Composite Health Traits (Lyons, Freeman, and Kuck, 1991)

8. Genetic Correlations Between Composite Health and Yield Traits (Lyons, Freeman, and Kuck, 1991)

9. Genetic Tools Currently Available Calving Ease: Easier calving, less dystocia, fewer stillbirths (h2=0.022). Daughter Pregnancy Rate: Improved female fertility (h2=0.040). Productive Life: Longer working life (h2=0.085). Somatic Cell Score: Improved resistance to mastitis (h2=0.100).

10. Holstein Daughter Pregnancy Rate (%)

11. Holstein Productive Life (mos)

12. Format 6 The USDA Animal Improvement Programs Laboratory has drafted a data exchange format to collect health data. It includes standard health codes. The objective is to collect data for research. The goal is to facilitate selection for healthier cows.

13. Format 6 Records Format 6 records include Animal and herd identification Up to 20 health event segments Cow records begin with a calving and end with disposal or the next calving. Heifer records begin at birth and end at first calving.

14. Health Event Segment Health event code Health event date Health event detail (optional)

15. Standard Health Event Codes Currently, no health event codes are used uniformly in dairy records systems. Standard codes have been developed based on frequency of occurrence in field data and consultation with veterinarians.

16. Health Event Codes Cystic ovary Diarrhea/scours Digestive problem/off feed Displaced abomasum Downer cow Dystocia Johne’s disease (clinical) Ketosis/acetonemia Lameness Mastitis (clinical) Metritis Milk fever/hypocalcemia Nervous system problem Other reproductive problem Respiratory problem Retained placenta Stillbirth Teat injury Udder edema

17. Most Frequent Health Events in DRMS Data

18. Management Events Three management traits are also in Format 6 Body condition score Milking speed Temperament The format can accommodate new traits e.g. Locomotion score

19. Optional Health Event Detail Details of problems of high economic impact (e.g. clinical mastitis) There is one mastitis event code. Organism and quarter may be reported. Other codes may also use this field Dystocia: scores of 1 to 5. BCS: scores of 1.00 to 5.00.

20. Research Needs Data quality edits Individual versus composite traits Environmental factors affecting records Relationships among traits Variance components estimation Genetic evaluation models

21. Summary Format 6 provides the framework for a national health database. Selection for improved health is possible and desirable. Selection complements advances in management and veterinary care.