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T-Snip™: Genetic Test for Fescue Tolerance

What is T-Snip™?

T-Snip™ is a genetic test that uses an animal’s DNA to describe its tolerance to toxic fescue.
DNA from hair, blood, or semen is analyzed based on multiple genetic markers. The DNA results are converted to a T-Snip™ Tolerance Index, which is used to calculate a T-Snip™ Star Rating. Cattle that score 0 to 1 stars are most susceptible to fescue toxicosis; cattle that score 4 to 5 stars are most tolerant to fescue toxicosis.

How has T-Snip™ been validated?

The T-Snip™ test has been VALIDATED using data from over 2,000 head of cattle. A large, 5-year study was carried out to evaluate how T-Snip™ score correlates with tolerance to toxic (endophyte-infected) Kentucky 31 tall fescue. Calf adjusted 205-d weight (weaning weight) was used as an indicator of tolerance in cows. This trait was chosen because it is easy to measure accurately on large numbers of animals in commercial herds. Eight herds were included in the study, and data were collected from 2010 to 2015.

In this study, data were from a total of 1813 cows that weaned 2260 calves (data were collected on some cows across multiple years). All herds were commercial cow herds. Breed or breed cross was recorded for each cow based on the producer’s knowledge of the animal.

Critical points about this study:
  1. Cows were grazing primarily toxic fescue pastures. This is essential to enable fescue toxicosis to be expressed in the study.
  2. ALL cows in the participating herds that weaned a calf were included in the study. Cows were not removed from the study for any other reason.
  3. As required to accurately estimate the differences between highest and lowest scoring animals, the complete range of T-Snip™ scores (0-5 stars) was well represented in the study.
Distribution of T-Snip™ scores in validation study

On average, calves raised by cows with a T-Snip™ score of 4 or 5 were 50 pounds heavier than calves raised by cows with a T-Snip™ score of 0 or 1 (see figure below). Additionally, there was a 10-pound increase in calf weaning weight when cow star score increased from 1 to 2, from 2 to 3, and from 3 to 4 stars. These results are statistically significant.

Relationship between cow T-Snip™ score and weaning weight

Different herds represent different genetic backgrounds that might have influenced the relationship between T-Snip™ score and weaning weight. Thus, data were viewed within each herd (see figure below). The number of cows within herds ranged from 124 to 647. The relationship between cow T-Snip™ score and her calf’s weaning weight was statistically significant within all 8 herds.

Relationship between cow T-Snip™ score and weaning weight, by herd

Data were also evaluated according to breed of dam (see figure below). Breeds were defined based on the owner’s description of the cow; no animals were registered. Once again, weaning weight increased significantly with increasing T-Snip™ score across breeds.

Relationship between cow T-Snip™ score and weaning weight, by breed of dam

Finally, results were evaluated within year of data collection, as changes in environmental conditions across years could have impacted performance of the test. When herds grazing primarily toxic fescue were evaluated, the relationship between weaning weight and T-Snip™ star score was consistent across years (see figure below).

Relationship between cow T-Snip™ score and weaning weight, by year

Collectively, the results of the validation study confirm that cows with higher T-Snip™ scores wean heavier calves, and that this relationship between cow T-Snip™ score and calf weaning weight is intact across multiple genetic backgrounds and across variable environmental conditions as occurs from year to year.

What else does T-Snip™ indicate?

Other research has clarified that T-Snip™ indicates a response to toxicosis, not merely better animal performance. This research can only be conducted when both tolerant and susceptible animals consume both toxic and non-toxic fescue.

In one study, heifers were fed non-toxic and toxic tall fescue (see figure below).

Daily gain of tolerant and susceptible heifers

Tolerant and susceptible heifers performed similarly when they were fed the non-toxic fescue. But on toxic fescue, tolerant heifers had a 41% higher rate of gain than susceptible heifers.

For more information about T-Snip™, contact AgBotanica on the Contact Us tab of this website.

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