In the suite of traits to improve maternal function, good udder structure plays an important role in beef production. Even though milk is not the end product from a beef production system, good udder structure is related to cow longevity and health, as well as calf survival and growth from birth to weaning. 

To characterize udder structure, the American Angus Association has scoring guidelines to help producers evaluate their cow herd. The scores are taken within 24 hours of birth of the calf and can be taken for every calf a cow births. The visual assessment of teat size (TEAT) and udder suspension (UDDR) should be reported on the combined weakest quarter and one person should score all the females within the same management group.

Both scores are on a scale from 1 to 9, where a score of 1 represents a very large and misshapen teat, or a very pendulous udder, while a 9 indicates a very small teat size or a very tight udder. For more information about teat and udder scoring read the Data Dive column in the September 2024 Angus Journal.

For the research and development of the research expected progeny difference (EPD) for teat size and udder suspension, phenotypic records, alongside pedigrees and genotypes are incorporated in the single-step genetic evaluation model. 

There were more than 148,000 records for each TEAT and UDDR scores collected from more than 87,000 individual cows included. The number of records is larger than the number of cows as a cow can have multiple records during her lifetime. 

Overall, both teat and udder scores have an average of 6.6 and range from 1 to 9, representing the entire scoring scale. Table 1 shows the descriptive statistics of the phenotypic data.

Table 1: Descriptive statistics of teat size and udder suspension phenotype records.

For teat size and udder suspension, extremes on either end of the scales are undesirable. Large teats can prevent a calf from suckling and proper intakes of colostrum, and large/pendulous udders can cause problems like mastitis; on the other hand, very small teats can also result in a calf that can’t properly nurse and very tight udders may be associated with low milk production, resulting in poor calf development. 

Modeling and genetic parameters estimation

To estimate heritabilities, genetic correlations and develop a research EPD, the first step is to identify the sources of non-genetic variation that affect a phenotype and develop the statistical model for the traits. For teat size and udder suspension, the contemporary group accounts for environmental and management differences, and the age of the cow is also considered for both traits. 

Both teat size and udder suspension are moderately heritable traits (0.32 and 0.28, respectively). The traits have a genetic correlation of 0.77 which supports modeling them together in a multiple trait model.

Research EPD

The teat size and udder suspension research EPD are expressed in the units of teat and udder scores. These EPDs predict expected differences in teat size and udder suspension scores when comparing progeny of different individuals under similar mating and raised on the same conditions.

Teat Size EPD (TEAT) is expressed in units of teat size score, with a higher EPD indicating smaller teats. The teat size scores range from 9 (very small) to 1 (very large, balloon shaped). Longer, thicker teats inhibit calf suckling which could decrease the intake of colostrum and increase the risk of preweaning mortality.

Udder Suspension EPD (UDDR) is expressed in units of udder suspension score, with a higher EPD indicating tighter udder suspension. The udder suspension scores range from 9 (very tight) to 1 (very pendulous). Weak suspension (low scores) indicates lack of support to the ligament that ties the udder to the cow’s body, allowing the udder to hang low, subjecting the udder to increased chance of injury or other issues. 

While overall smaller teats and tighter udders tend to result in less problems, breeders need to consider making breeding decisions to avoid extremes on either end of the scale. In this context, while higher EPDs would lead to smaller teats and tighter udders over generations, caution is needed not to push the herd towards an undesirable extreme.

Figure 1 shows the EPD distribution of the entire population for teat size and udder suspension. The average EPD for both traits is around 0.52, ranging from -0.6 to 1.51. From largest to smallest there is a range of over two scores, which shows the variation in the population allowing breeders to make selection decisions that fit their breeding programs. 

Fig 1: Teat size and udder suspension EPD distribution.

Conclusion

The current research conducted by the Angus Genetics Inc. (AGI) research team supports the release of research EPDs for teat size and udder suspension. These two new research EPDs will even further expand the American Angus breeder’s toolbox to improve maternal function. Continued data reporting is encouraged as these new EPDs develop and the database expands. The development of the teat and udder research EPDs includes phenotypic data alongside pedigrees and genotypes in the single-step model. 

The teat size and udder suspension research EPDs were released in August 2024, and we will continue to monitor and research these traits until a final production stage release as well as the incorporation into the $Value indexes. 

More information on the development of these research EPDs can be found in the research report online at www.angus.org/ahir/research/teat-udder.