Uncover the critical variations in dairy cattle genetic assessments for conformation and PTAT between Canada and the USA. What implications do these standards hold for breeding practices?

For breeders aiming to produce the next World Dairy Expo Champion or an EX-97 cow, utilizing the American PTAT or the Canadian Conformation index is not just an option—they are essential tools in your breeding arsenal. While both PTAT and Conformation indices are invaluable, they are not interchangeable. This article will explore the distinctions between Canadian and American genetic evaluations for conformation and PTAT, shedding light on how each system functions and what sets them apart.

The Evolution of Genetic Evaluation Systems in Dairy Cattle: A Tale of Two Nations 

The historical trajectory of genetic evaluation systems in dairy cattle within Canada and the USA signifies an evolution of both countries’ dairy industries. Originally hinging on fundamental pedigree analysis, these systems have dramatically advanced with cutting-edge genetic technology and data analytics. Canada launched its first formal genetic evaluation for dairy cattle in the mid-20th century, focusing on production traits. By the 1970s, Canadian dairy scientists incorporated type traits, utilizing linear classification systems to quantify conformation characteristics. This method allowed breeders to objectively evaluate and select superior dairy cattle based on body and udder traits. 

In parallel, the USA advanced from essential herd records to sophisticated evaluations, incorporating production and type traits by the 1980s. A key milestone was the establishment of Predicted Transmitting Ability (PTAT), revolutionizing how type traits were genetically assessed. PTAT provided a standardized measure allowing breeders to predict genetic merit regarding conformation, facilitating more informed breeding decisions. 

The 1990s and early 2000s marked a crucial phase with genomic evaluations. Canada and the USA swiftly integrated genomic data, increasing accuracy and efficiency. Genomic selection enabled early identification of desirable traits, accelerating genetic progress and enhancing herd quality. Collaborative efforts between Canadian and American dairy geneticists have recently refined methodologies, incorporating advanced statistical models and extensive phenotype databases. 

Today, the genetic evaluation systems in both nations reflect a blend of historical advancements and modern innovations. Conformation and PTAT assessments are entrenched in a framework valuing genetic merit for production, longevity, health, and robustness, ensuring dairy cattle improvement remains responsive to the industry’s evolving demands.

Dairy Cattle Conformation in Canada: An Intricate Evaluation Framework 

Genetic evaluations for dairy cattle conformation in Canada meticulously examine a comprehensive set of traits. Key characteristics like stature, chest width, body depth, angularity, rump angle, and leg traits are assessed to ensure aesthetic appeal and functional efficiency, particularly for durability and productivity.  

Mammary system traits, including udder depth, teat length, and placement, are critical for milking efficiency and udder health. Feet and leg conformation, which is vital for mobility and longevity, is also evaluated.  

In Canada, conformation blends individual traits like udder attachment and teat placement into a single index. Each trait is scored meticulously, providing a detailed evaluation of an animal’s overall conformation. This approach helps breeders make informed decisions, improving dairy cattle’s genetic quality and functional efficiency. Integrating these traits into one index highlights the importance of a balanced dairy cow. Traits such as udder conformation, feet, leg health, and overall robustness work together to enhance performance and longevity in a herd.

The Canadian Dairy Network (CDN) spearheads this complex evaluation process. Utilizing advanced genetic methodologies, the CDN integrates phenotypic data with genetic models to offer accurate breeding values. This scientific approach strengthens the genetic quality of the Canadian dairy herd.  

Supporting organizations, such as Lactanet and Holstein Canada, play crucial roles. Lactanet provides comprehensive herd management services, including conformation assessments. Holstein Canada sets standards and trains classifiers for consistent on-farm evaluations.   These organizations form a network dedicated to enhancing the genetic standards of dairy cattle through diligent conformation evaluations, supporting breeders in informed selection decisions, and maintaining Canada’s reputation for producing world-class dairy cattle.

PTAT and Comprehensive Type Evaluation in the United States: A Framework for Genetic Excellence 

In the United States, dairy cattle conformation evaluation hinges on the Predicted Transmitting Ability for Type (PTAT) and a detailed type evaluation system. Unlike Canada, where conformation is a composite index of individual traits, PTAT in the United States is calculated based on the final classification score about herd mates. PTAT assesses an animal’s genetic potential to pass on type traits to its offspring, focusing on various aspects of physical structure, such as stature, body depth, and udder conformation. Critical traits include:

• Stature: The height of the animal at the shoulders and hips.
• Udder Depth: The distance from the udder floor to the hock affects milk production efficiency.
• Body Depth: The depth of the ribcage, indicating overall body capacity.
• Foot Angle: The angle and structure of the foot influence mobility and longevity.
• Rear Leg Side View: The curvature of the rear legs when viewed from the side.

These traits are meticulously recorded and analyzed for a robust genetic evaluation. Under the USDA, the Council on Dairy Cattle Breeding (CDCB) leads the effort in collecting, analyzing, and sharing genetic and genomic evaluations. Their extensive nationwide database, sourced from dairy farms, provides comprehensive genetic insights. 

Breed-specific organizations like the Holstein Association USA and the American Jersey Cattle Association (AJCA) refine evaluations for specific breeds. They collaborate with the CDCB to ensure accurate and relevant assessments, offer educational resources to breeders, and promote best practices in genetic selection. This collaborative framework ensures that U.S. dairy farmers have access to cutting-edge genetic information, enhancing the genetic merit of dairy herds and advancing dairy cattle breeding nationwide.

Unified Yet Diverse: Genetic Indices Shaping Dairy Excellence in North America 

For decades, significant efforts have been undertaken to harmonize the evaluation of type traits and the classification programs generating the requisite data for genetic evaluations on an international scale. While substantial progress has been achieved, occasional surprises still emerge. These unforeseen developments typically pertain not to production traits but to type and management traits. 

In Canada, Conformation is quantified on a scale where each standard deviation equals five points. Conversely, the United States expresses PTAT in standard deviations. Consequently, a confirmation score of 5 in Canada generally corresponds to a PTAT score of 1 in the U.S. However, assuming a direct equivalence between a PTAT of 1 and a Conformation score of 5 can be misleading. Lactanet in Canada recently conducted an extensive study comparing over 4,000 bulls with daughters and genetic proofs in both countries to elucidate this. The correlation between the TPI and LPI was notably high at 0.93.
Interestingly, the correlation between Canada’s Pro$ and the TPI was even higher, reaching 0.95. As anticipated, production traits demonstrated strong correlations, with Milk at 0.93, Fat at 0.97, and Protein at 0.95, given that production can be measured objectively. However, the variations were more pronounced when evaluating the type of health and management traits.

Type Indexes

The correlation between PTAT in the United States and Conformation in Canada is 0.76. In the United States, the direct contribution of type to the Total Performance Index (TPI) emerges from three primary sources: the PTAT (8%), the udder composite (11%), and the feet & leg composite (6%). In Canada, these components are called Conformation, Mammary System, and Feet & Legs, respectively. A crucial point to understand is that these are composite indices composed of various individual traits within each category, and each nation applies a distinctive formula to weight these traits. Consequently, the differing weightings lead to modestly lower correlations for udders (0.80) and feet & legs (0.65). It’s also essential to recognize that both composites are adjusted in each country to be independent of stature. This adjustment allows for the specific selection of udder or leg improvements without inadvertently promoting increased stature.

Mammary System

Among the mammary system traits, evaluations of Udder Depth (0.95), Teat Length (0.94), Rear Teat Placement (0.90), Fore Teat Placement (0.87), and Fore Attachment (0.93) exhibit remarkable consistency between Canada and the United States. Nevertheless, a divergent perspective emerges with Median Suspensory (0.73), Rear Udder Height (0.78), and Rear Udder Width (0.66), which display significantly lower correlations. This disparity suggests that traits such as rear udder height, rear udder width, and suspensory ligament are appraised with varying degrees of emphasis and interpretation in each country.

Feet and Legs

Feet and legs exhibit a moderate correlation of 0.65 between Canada and the United States. Examining specific traits within this category, the rear leg side view reveals a high correlation of 0.91, indicating substantial similarity between the countries. However, the rear leg rear view (0.76) and foot angle (0.73) diverge more significantly. A noteworthy distinction lies in the traits recorded: while foot angle is commonly observed globally, Canada also measures heel depth. The rationale behind this difference stems from the susceptibility of foot angle to recent hoof trimming, a variable that does not affect heel depth. 

The overarching objective of selecting for superior feet and legs is to mitigate lameness and enhance longevity. In Canada, the mammary system exhibits a 0.25 correlation with herd life, slightly higher than the composite feet and legs score of 0.22. Yet, individual traits within this composite tell a different story. Foot angle shows a negative correlation with longevity at -0.16, whereas heel depth, boasting a positive correlation of +0.20, stands out prominently. This raises a pertinent question: why is heel depth not universally recorded over foot angle? 

Further analysis of specific traits reveals minimal impact on longevity. The rear leg side view holds a correlation of -0.08, the rear leg rear view is 0.03, locomotion is 0.05, and bone quality is a mere -0.01. Given these negligible impacts, particularly bone quality in its current linear measurement, it might be worth exploring its assessment as a medial optimum trait, balancing frailty and coarseness. 

Additionally, Canada uniquely records front legs, correlating with her life at 0.18, second only to heel depth. In the broader context of overall frame traits, stature maintains a high concordance at 0.97 between both countries. In contrast, body depth (0.71) and chest width (expressed as strength in US evaluations, 0.69) have lower correlations, highlighting regional differences in evaluation emphasis.

The Bottom Line

Examining genetic evaluations for dairy cattle conformation and type in Canada and the USA reveals distinctive approaches and converging goals, underlining the importance of tailored yet comprehensive systems. We’ve explored the evolution of genetic frameworks in both nations, highlighting Canada’s detailed evaluations and the USA’s focus on PTAT and holistic type assessment. From composite traits to specific evaluations of mammary systems and feet and legs, each country aims to boost genetic excellence in dairy cattle.  

As these systems continue to adapt to scientific advancements and industry needs, the goal remains to develop a robust, genetically superior dairy cattle population capable of thriving in diverse environments. This endeavor highlights the critical intersection of genetic science, industry priorities, and animal welfare, shaping the future of dairy cattle breeding. While methods may differ, the objective is shared: achieving dairy excellence through rigorous and innovative genetic evaluations that benefit producers, consumers, and cattle. Collaborations and continual improvements ensure  North America stays at the forefront of dairy cattle genetics, leading global dairy production. 

Key Takeaways:

• The genetic evaluation systems for dairy cattle conformation in Canada and the USA have evolved with distinct methodologies, reflecting different priorities and breeding goals.
• Canada emphasizes an intricate evaluation framework that assesses a variety of composite traits, ensuring a comprehensive understanding of a cow’s overall physical attributes.
• In the USA, PTAT (Predicted Transmitting Ability for Type) serves as a crucial metric, further supported by detailed evaluations of specific type traits to drive genetic excellence.
• Both nations utilize genetic indices that consider multiple aspects of conformation, significantly contributing to the genetic advancement and overall quality of dairy cattle.
• Feet and legs, as well as mammary systems, are critical areas of focus in both Canadian and American evaluation systems, reflecting their importance in dairy cattle productivity and longevity.
• The integration of scientific research and technological advancements has been instrumental in refining genetic evaluations, as referenced by numerous studies and scholarly articles.

Summary:

Genetic evaluation systems in dairy cattle in Canada and the USA have evolved through historical advancements and modern innovations. Canada introduced its first formal genetic evaluation in the mid-20th century, focusing on production traits. By the 1970s, Canadian dairy scientists integrated type traits and linear classification systems to quantify conformation characteristics, allowing breeders to objectively evaluate and select superior cattle. The USA advanced from essential herd records to sophisticated evaluations by the 1980s, with the establishment of Predicted Transmitting Ability (PTAT). The 1990s and early 2000s saw a crucial phase with genomic evaluations, integrating genomic data to increase accuracy and efficiency. Today, genetic evaluation systems in both countries value genetic merit for production, longevity, health, and robustness. Supporting organizations like Lactanet and Holstein Canada play crucial roles in enhancing genetic standards and maintaining Canada’s reputation for producing world-class dairy cattle.

Learn more:

• Genomic Selection: Doubling of the Rate of Genetic Gain in the US Dairy Industry
• Deciphering Beef-on-Dairy Mating: The Significance of Mean Breed Performance
• A Comprehensive Guide to Enhanced Genetic Selection