SCR: Why are sexed and conventional stud codes critical

Sire fertility is a very important trait when making sire selections and has been shown to vary between individual bulls. A uniform measurement of bull fertility based on field data was constructed more than 30 years ago and evolved into what is now known as Sire Conception Rate (SCR). This trait, while beneficial in theory, continues to have many challenges with correctly comparing conventional breedings between bulls and adjusting for various factors related to fertility. In the past, STgenetics® bulls received SCR evaluations based on sexed breedings which were supposed to be excluded from the SCR evaluation and STgenetics® has since made changes to make sure that our bulls are correctly represented in the SCR evaluation. ST genetics® bulls can now be seen to have an above average SCR overall according to the CDCB evaluations for April 2021.

Sire Conception Rate (SCR) was designed to compare conventional semen conception between bulls, so producers could identify bulls with higher and lower fertility based on field data. SCR is supposed to be used to see how average conception rate in a herd would be affected by utilizing a certain bull. For example, if a herd normally averaged a 35% conception rate and used a bull with 2% SCR, that bull's conception rate in the herd should average 37%. Bull fertility evaluations were first developed in the mid-1980s by Dairy Record Management Systems (ORMS) as the Estimated Relative Conception Rate (ERCR). Based on 70-day Non-Return Rate (NRR) data generated from herds testing through ORMS and AgSource Cooperative, ERCR provided results from herds only in the Midwestern and Eastern United States. In 2006, the Animal Improvement Production Laboratory of USDA (AIPL) took over ERCR calculations from ORMS. While AIPL maintained the original approach of ERCR, they also launched research into improving the reporting of sire fertility. In 2008, with this updated model, the Sire Conception Rate (SCR) was launched. This model expanded on the foundation created by ORMS in ERCR by including only breedings that had confirmation of the outcome such as repeat services, pregnancy checks, abortions, calvings, etc. and replaced NRR. The process also controlled for the age and inbreeding of the bull, the inbreeding of the calf, and the stud that collected the bull. In addition, AgriTech Analytics began contributing data from herds in the Western United States.

 In theory, SCR was meant to compare conventional semen conception between bulls. This was supposed to be controlled by the "sex sorted" stud code. To understand how sex sorted stud codes and conventional stud codes are utilized, we need to look at the origin of these codes. Any bull marketed as Certified Semen Service (CSS) semen must have a National Association of Animal Breeders (NAAB) number. The first part of the number is the Al Units NAAB ID, the second part is the breed of the bull, and the third part is the stud's number for the bull:

If all parts of the data reporting system had worked the way the industry believed they would, conventional semen breedings would only be compared to other conventional semen breedings. Unfortunately, the system did not always perform as envisioned. 
Even though a bull may have more than one NAAB Code, there has to be a "primary" code that ties all the parts of the database together. 
In 2008, when SCR began, the primary NAAB code was always the conventional stud code, and that was the point that data quality issues began for SCR. While a bull may have had both a 151 and a 551 code, the 151 code was primary. Many people were not use to two stud codes, so they would write down or enter the conventional number when using sex sorted semen as that was the number that was familiar from the stud code they saw in stud books and in advertisements. Unfortunately, that was not the only issue. Herd Management Systems (HMS) have a default primary stud code. In many cases, that default is supplied by the creator of the software who uses only the primary number supplied by NAAB, even though NAAB supplies both semen codes. If a producer did not pay close attention, the system would report the primary conventional code even if the correct sex sorted code was entered. This meant that AIPL received incorrect data with no possibility of knowing it was wrong. The result of this was sex sorted semen was being compared to conventional semen for conception in SCR which is in fact comparing apples to oranges. While most studs thought there might be a problem in SCR related to sex sorted semen, none of them marketed bulls only as sex sorted semen, so the impact was diluted. That scenario changed in 2014 when STgenetics® began marketing many bulls in our lineup as sex sorted only. At that time, we had many different codes: 76 from Taurus, 147 from Androgentics, 151 from TWG, 203 the original STgenetics® number, and 513 the TransAmerica Genetics code. As was routine in the industry, all of our bulls' primary stud code was one of those conventional numbers. Of course, they all also had a NAAB sex sorted code as well: 576, 523, 547, 551, 552. 
By early 2015 we knew there was a problem, because bulls who had never had conventional semen released were receiving official SCRs. 
While the sex sorted semen product at that time, Sexed Ultra®, was superior to any previous sex sorted product, it still lagged conventional (that was to change with SexedUltra4M®). None of our code 151 bulls were above O for official SCR. Dairy producers who relied on SC Rs looked at the official SCR and thought that STgenetics® had an issue with semen quality. 
As other studs began to follow STgenetics® lead and market bulls, at least early in their careers, as sex sorted only, they began to experience the same issue. Since 2015, the industry has struggled with this complication. The Council on Dairy Cattle Breeding (CDCB), now responsible for US evaluations, has made changes to the SCR evaluation. However, CDCB still must rely on the stud codes they receive through the system being correct. And, honestly, no one knows today if everything is working properly before CDCB receives the data. (There is still an issue with only one NAAB code per sire being stored in at least some HMS). 

In 2016, STgenetics® made the decision to make all new bulls in our system primary code 551. Our reasoning was that if 551 was the primary stud code, then sex sorted semen usage would automatically be removed from SCR. If someone did use conventional semen, coded 151, and if they entered it correctly, we knew that our bull's conventional semen would be compared with other bulls' conventional semen. Currently, the only other stud that is following the same path using the sex sorted stud code as primary is Semex with code 777. What this means is we know that all STgenetics® bulls that have entered service since 2016, and who have a CDCB SCR, have their conception rate calculated only from conventional to conventional semen; not from a combination of comparing sex sorted to conventional as well as conventional to conventional.
In the table below, we can see the difference in SCRs by stud code from the April 2021 CDCB evaluations. The bar that is circled in pink represents the average SCR for STgenetics bulls coded 551 that have their conventional semen compared only to other conventional semen and the average SCR is 0.514. This is above the average SCR for all bulls with evaluations of 0.001, indicating that STgenetics does not have an issue with semen quality.

When we look at SCR for bulls with a 551 code, this does not indicate that the SCR is comprised of sexed breedings, but rather bulls that have a sex sorted primary code. This is important because the majority of breedings for the 551 code are comprised of conventional breedings from bulls with a primary sex sorted code which means it's a more accurate comparison of SCR between bulls. The other columns that you see on the chart representing other studs' average SCR could have sex sorted semen conception rates included in the official SCR for their bulls. 

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