By Harly Durbin, Ph.D. student, and Jared Decker, Associate Professor, University of Missouri Animal Sciences.
Editor’s note: Harly Durbin and advisor, Dr. Jared Decker, were recipients of the Walton-Berry Graduate Student Support Grant from the American SimmentalSimbrah Foundation. This grant, started by Jim Berry in honor of Dr. Robert Walton’s dedication to animal breeding, supports the professional development, success, and experiences of young animal scientists by providing support for graduate study.
Savvy business leaders know how important it is to identify and hire the right employees. Your staff needs to be a good fit for the job. The same can be said for your cow herd. Even within the same breed, performance varies between individuals across different environments. Some of this variation is due to interactions between genetics and the environment. This is common knowledge for producers but it can still be difficult to quantify, especially when purchasing genetics from a different region. One tool producers in heat-stressed environments and producers grazing toxic endophyte-infected (hot) fescue can use to easily evaluate their “employees” is early summer hair shedding scoring.
Background and How-to
Early summer hair shedding is an adaptive trait and an indicator of tolerance to heat stress and fescue toxicosis. Australian researchers developed the hair shedding scoring system in 1960 (Turner & Schleger, 1960:). Similar systems were independently developed by others, such as University of Missouri (MU) livestock extension specialist Eldon Cole at the Southwest Research Center in Mt. Vernon, Missouri. Observers realized later-shedding cattle tended to have depressed growth and decreased reproductive success. Cattle are scored on a 1 to 5 scale with a 1 being completely slick (100% shed off), 2 being 75% shed off, 3 being 50% shed off, 4 being 25% shed off, and 5 being a complete winter coat (0% shed off). It’s easy to distinguish a 1 from a 5, but the scores in between can be more difficult. As a general rule, cattle tend to shed hair from front to back and top to bottom. So, a 4 will usually have shed only on her neck. Similarly, a 2 usually has winter coat remaining only on her belly and lower hindquarters; however, there is some variability in the order of shedding from individual to individual. We recommend producers score their herd between late April and mid-June depending on the climate in their region. Hair shedding scoring is most useful when variability within the herd is highest; for producers in the South that tends to be early May.
The cost of compensating for employees that are a poor fit for the job is a drain on profitability. Hair coat removal via shearing or flame application has been suggested as one way to combat heat stress. Additionally, producers grazing hot fescue can renovate affected pastures; however, these solutions can be costly and time-consuming. A sustainable option is to address the problem from the animal side by selecting well-adapted cattle that will work for you and pay their keep. When used with other management best practices, hair shedding scoring is an easy-to-adopt evaluation tool with a high return on investment.
As part of a broader effort to identify cattle well-suited to their environment, producers enrolled in the Mizzou Hair Shedding Project collected over 12,000 hair shedding scores in 2016 and 2017, with 2018 and 2019 scores forthcoming. These scores came from approximately 8,000 crossbred and purebred cattle, including 1,800 head of registered Simmental (Figure 1). Most of these cattle have been DNA tested to identify DNA markers associated with heat tolerance and fescue toxicosis tolerance. This data is being used to create a hair shedding score EPD for the evaluation of adaptation to heat and fescue toxicosis. A hair shedding score EPD would provide producers grazing toxic fescue and producers in heat-stressed environments a way to gauge the potential of bulls and females from other regions to succeed in their herd. Preliminary estimates of hair shedding score heritability range from 0.38 to 0.45, which is higher than most weaning weight heritability estimates. This means that approximately 40% of the variability in hair shedding score is due to genetic variation and that genetic progress can be made by culling cattle with high hair shedding scores.
Although the goal of the Mizzou Hair Shedding Project is to understand the genetic basis of early summer hair shedding, hair shedding scoring is a useful selection tool even in the absence of DNA testing. Using 2016 and 2017 Simmental weaning weight data for dams enrolled in the Mizzou Hair Shedding Project and raw hair scores (no DNA data incorporated), we find an approximately 12-pound increase in weaning weight each unit decrease in hair shedding score (Figure 2).
This means that in our data, dams with a hair shedding score of 1 weaned 48 more pounds of calf on average than dams with a hair shedding score of 5. The trend is similar in Mizzou Hair Shedding Project Red Angus data and is consistent with other estimates of the relationship between hair shedding score and weaning weight in heat-stressed and toxic fescue-stressed environments (Gray et al., 20110). However, more rapid genetic improvement will always be made with the use of genetic predictions and EPDs. Preliminary genomic EPDs generated using 2016 and 2017 hair shedding scores and DNA data also show a clear relationship with cow performance. Using all available weaning weight data for calves weaned by Simmental dams in the Mizzou Hair Shedding Project, we find an approximately 14-pound average increase in calf weaning weight with every point decrease in hair shedding EPD (i.e., dams with better hair shedding scores tend to wean heavier calves than those with worse hair shedding scores). One caution to keep in mind for these results is that almost all of the Simmental cattle in the Mizzou Hair Shedding Project originate from heat-stressed or toxic fescue-stressed environments. Therefore, these results may not be representative of hair shedding trends in all regions of the United States.
This past spring, about 5,000 new cattle were enrolled in the Mizzou Hair Shedding Project. Most of these cattle come from the Fescue Belt and the Gulf Coast, expanding our power to detect DNA variants associated with heat tolerance and fescue toxicosis tolerance. As previously mentioned, the Mizzou Hair Shedding Project is part of a broader effort by MU researchers to match genetics to the environment. This research will be used to identify genes involved in early summer hair shedding and to help us interpret our other gene-by-environment interaction research. We will also create a genomic EPD for hair shedding to help farmers and ranchers find the right cows for the job.
- Written by ASA
- Category: Industry News
- Created: 05 March 2019