Mastitis Resistance Selection: Now a Reality!

Mastitis – it’s a real game changer in terms of profitability at the farm level! It can turn a good cow into a poor one very quickly! In 2013, over 20% of cows removed by involuntary culling from Canadian dairy herds left due to problems with mastitis and/or high somatic cell count. Over the past several decades since somatic cell testing became a routine service offered by milk recording agencies across the country, great progress has been realized. Although herd management is very important for maintaining low levels of somatic cell count, genetic selection should also be used to improve mastitis resistance. Effective August 2014, Canadian Dairy Network (CDN) will publish official genetic evaluations for Mastitis Resistance, which combines both clinical and sub-clinical mastitis into a single genetic selection index.

Health Data

Following a coordinated industry effort involving CDN, milk recording agencies, breed associations, A.I. organizations and various veterinarian groups, a national system for collecting health events was implemented in 2007. Since that time, approximately 40% of all herds enrolled on milk recording are voluntarily recording the incidence of eight key diseases and reporting this data to their milk recording agency (or their DSA veterinarian in Quebec). This accumulation of data has led to the calculation of genetic evaluations for clinical mastitis.

Clinical Mastitis and Somatic Cell Count

Somatic cell count (SCC) is a measure of sub-clinical mastitis that is easy to assess by laboratory analysis of each cow’s milk sample on test day. Due to the ease of recording this trait and its relative importance for herd and cow management, milk recording has offered somatic cell testing for decades as part of its portfolio of services. Now, with the additional collection of herd health events related to clinical mastitis, producers will have a tool to select directly for resistance to clinical mastitis as well as sub-clinical mastitis. Table 1 provides correlations among Holstein sire proofs for the various traits related to mastitis that CDN will be evaluating in the Holstein, Ayrshire and Jersey breeds.


Mastitis Resistance is an overall index that equally combines evaluations for three other traits, namely Clinical Mastitis in first lactation cows, Clinical Mastitis for cows in later lactations and Somatic Cell Score evaluated across the first three lactations. The heritability of Mastitis Resistance is estimated at 12%, indicating that genetic selection is possible. Official sire proofs for Mastitis Resistance have a desirable correlation of 79% with current proofs for Somatic Cell Score as well as correlations of 85% and 90% respectively, for clinical mastitis in first versus later lactations. Of particular interest as well is the fact that Somatic Cell Score, as a measure of sub-clinical mastitis, has only a moderate desirable association with clinical mastitis in first and later lactations (44% and 58% respectively).

Figure 1 provides a visual representation of the association between sire proofs for Somatic Cell Score and the new Mastitis Resistance index, expressed as Relative Breeding Values with an average of 100 and 95% of bulls ranging between 115 (best) to 85 (worst). As suggested by the strong desirable correlation of 79%, the plot shows that many bulls already known to be good for low somatic cell counts in their daughters are also good for overall selection of Mastitis Resistance, including clinical mastitis. In fact, of those bulls that were at least one standard deviation better than average for Somatic Cell Score (i.e.: rating of 2.77 or lower), 98% of them are above breed average for Mastitis Resistance. Among those that were simply better than breed average for Somatic Cell Score (i.e.: below 3.00), 78% have a rating higher than the breed average of 100 for Mastitis Resistance. In other words, these bulls were better than average for Somatic Cell Score but below average for Mastitis Resistance. The availability of the new Mastitis Resistance evaluations allows for the improvement of both sub-clinical and clinical mastitis simultaneously.


Interpretation of Mastitis Resistance

To assist producers in understanding the expected response achievable in their herd when considering sire proofs for Mastitis Resistance, Table 2 provides a “translation” in terms of average daughter performance for both clinical mastitis and somatic cell count throughout the first three lactations.

When used in a typical herd with average herd management, an average bull with a rating of 100 for Mastitis Resistance is expected to produce daughters that will have somatic cell counts averaging 178,000, 226,000 and 292,000 in each of the first three lactations, respectively. In addition, 92% of the daughters in first lactation are not expected to have clinical mastitis and this percentage decreases slightly to 88% for later lactations. Bulls that are better than breed average receive a Mastitis Resistance evaluation higher than 100 and are expected to produce daughters that are less susceptible to having both sub-clinical and clinical mastitis, as shown in Table 2.



The August 2014 arrival of official genetic evaluations for Mastitis Resistance for the Holstein, Ayrshire and Jersey breeds provides dairy producers with an advanced tool for genetic selection against mastitis, simultaneously for both sub-clinical and clinical. Due to the larger number of progeny proven sires with an official Mastitis Resistance, the Holstein breed will also benefit from the calculation by CDN of genomic evaluations for this important trait. The publication of Mastitis Resistance will not replace the availability of genetic evaluations for Somatic Cell Score but dairy producers should move towards using this new index when making selection decisions to reduce the overall incidence of mastitis in their herd.

Authors: Brian Van Doormaal and Lynsay Beavers
Date: June 2014

Nutrition Research


Nutrition Research– by Maria Kalergis, PhD, RD, CDE
National Program Manager, Nutrition Scientific Affairs Dairy Farmers of Canada

With seven new projects underway and 33 completed in the first Dairy Research Cluster, a lot of information is being transferred to health professionals on the benefits of dairy products in the Canadian diet.

The new research activities were launched on January 1st 2014. The objectives are to better understand the link between dairy foods, nutrition, health and wellness in order to improve the health of Canadians, reduce health care costs and to contribute to the economic development of the dairy sector. Obesity, cardiovascular diseases, type 2 diabetes and osteoporosis continue to be global health burdens that are associated with substantial health care costs thus need to be urgently addressed. Emerging scientific evidence indicates a beneficial role for milk products in reducing the risk of these conditions as well as associated health care costs. 

Seven Projects to Benefit the Health of Canadians

  1. The following is a list of the new projects launched under the Dairy Research Cluster (2013-2018)
  2. Integrated research program on dairy, dairy fat and cardiovascular health
  3. The effect of milk products and novel milk products on satiety, food intake and metabolic control (glycemia) in early and late adulthood
  4. Dairy nutrition and risk of diabetes in vulnerable populations: a novel biomarkers-based approach
  5. Beneficial effects of milk and fermented dairy products on intestinal and adipose tissue inflammation, and obesity-linked cardiometabolic diseases
  6. Association between dietary intakes and cardiovascular risk of Canadians using the Canadian Health Measures Survey cycles 1+2
  7. Role of high dairy diet on bone health outcomes in pregnant women and their offspring in early life (Bone BHIP): A randomized clinical trial
  8. FAMILY (FAmily MILk product two Year) dose-response study to enhance bone health

Nutrition Research Results and Knowledge Transfer

Dairy Farmers of Canada’s nutrition team is hosting a nutrition symposium in four cities across Canada. This year’s theme is focused on dietary guidelines and will address hot topics such as fat, sugar and salt in the diet, by examining the scientific evidence to date and the implications on dietary guidelines in Canada and throughout the world. 

The symposium will be held in:

  • Vancouver on November 17
  • Toronto on November 19 (live webcast in English)
  • Montreal on November 20 (live webcast in French)
  • Moncton on November 21

Live webcasts will be available on for those who cannot attend in person. Complete information (including registration forms) will be available on the website in October.

For more information, subscribe to the Nutrition newsletter online at:

Research investments in Organic Dairy projects announced

Research investments in Organic Dairy projects announced

Dairy farmers keep proudly innovating in dairy and investing in research that will help to improve practices on farms across the country. Recently, the Minister of Agriculture and Agri-Food Gerry Ritz announced an $8 million investment in the Organic Science Cluster (2013-2018), adding its investment to multiple industry partners’ contributions of $2.7 million. Dairy Farmers of Canada is a proud partner in this new Organic Cluster with an investment of $185,000 over five years in four projects.

The Organic Agriculture Centre of Canada at the University of Dalhousie will be administering the Cluster and oversee the implementation of 37 projects at 36 research institutions across Canada, including universities, Agriculture and Agri-Food Canada research stations, and others.

The dairy projects include :


  1. The development of sustainable alternative sources of bedding for dairy cows

Principal Investigator: Renée Bergeron, University of Guelph, Alfred Campus

 General objective: The study aims to investigate the use of switchgrass in two forms (deep-bedded chopped switchgrass or “switchgrass-lime” mattress) as sustainable, alternative bedding sources for dairy cows that also enhance cow welfare.


  1. Effect of exercise and stall modifications on cow comfort and performance in tie-stall farms

 Principal Investigator: Elsa Vasseur, University of Guelph, Alfred Campus


General objective: The present study aims to investigate, on 20 commercial tie-stall farms in Ontario and Quebec, how modifications of stall configuration may improve cow comfort and productivity, and whether cows provided with exercise will respond differently to stall improvements.


  1. Evaluating alternative therapies for the treatment of clinical mastitis on organic dairies

 Principal Investigators: David Francoz and Simon Dufour (Université de Montréal)

General objective: The general objective of the study is to identify, evaluate, and promulgate an alternative multi-pronged approach for the treatment of clinical mastitis (CM) in dairy cows. This research objective would directly answer the need for the development of an alternative approach for mastitis treatment on organic dairies, which was identified as an important priority at the 2012 Canadian Organic Science Conference.


4. Bioactive products from plants and control of internal and external parasites in large ruminants

Principal Investigator: Dr. Simon Lachance, University of Guelph – Campus d’Alfred

General objective: Develop new methods and products for the control of external and internal parasites with the use of natural repellents and bioactive components from plants.


The project summaries can be found at: