In August 2024, Holstein Association USA (HAUSA) released an updated Fertility Index with the official genetic evaluations. The revision was recommended by Holstein Association USA’s Genetic Advancement Committee and recently approved by the HAUSA Board of Directors. 

The Fertility Index combines several reproductive components into one overall index including: ability to conceive as a maiden heifer, ability to conceive as a lactating cow, and a cow's overall ability to start cycling after calving, show heat, conceive, and maintain a pregnancy. 

The current formula for Fertility Index (FI) is: 

FI August 2024 = (0.4 x Daughter Preg Rate) + (0.4 x Cow Conception Rate) + (0.1 x Heifer Conception Rate) + (0.1 x Early First Calving) 

Which was updated from the previous FI of: 

(0.7 x Daughter Preg Rate) + (0.1 x Cow Conception Rate) + (0.1 x Heifer Conception Rate) + (0.1 x Early First Calving) 

Holstein’s update shifted the dominant weighting for Daughter Pregnancy Rate (DPR) (when she becomes pregnant) to equal consideration for DPR and Cow Conception Rate (CCR) (her ability to become pregnant), while continuing a 0.1 weighting for Heifer Conception Rate (HCR) and a 0.1 weighting for Early First Calving (EFC). 

So, why an increase in the weighting for CCR and a reduction in weighting for DPR? 

Submission/Heat Detection Rate is the primary difference between Daughter Preg Rate and Cow Conception Rate. In other words, the timeliness of estrus and its detection, and action taken upon such detection, is key in determining the rate of pregnancy success, pending the success of a cow’s rate of conception, followed by uterine acceptance of the fertilized embryo via adhesion of the fertilized embryo to the uterine wall. 

However, with the usage of protocols to manage the time of ovulation, Submission/Heat Detection Rates are not always naturally occurring events in many dairy herds. Timed Artificial Insemination (TAI) protocols aligned with preset voluntary waiting periods have clouded the data received for use in genetic projections. Groups of animals are scheduled for ovulation on a preset schedule, not left to their own naturally occurring estrus cycles. These interventions impact the variances in Days In Milk at First Service (DIMFS). For example, timed first services can artificially delay pregnancies in cows who were not yet ready to receive a fertilized embryo and now must wait until the next 21-day estrus cycle to become pregnant, when they may have naturally been ready to receive a fertilized embryo on a day between the scheduled first breeding and the following 21-day estrus cycle. 

Whatever ‘noise’ that Timed AI may have contributed to challenges with DPR as a dominant metric for fertility may become a non-issue over time as such protocols are being challenged in many markets around the world. While some of the tools for timing insemination may fade away, the growing influence of cow monitoring systems, that are clearly enhancing our ability to capture Submission/ Heat Detection rates, are not going away. Improving Heat Detection will aid our pregnancy rates with cow conceptions from increased natural estrus detections. Therefore, the move by HOUSA to place equal weighting on CCR and DPR in FI, makes FI today’s ‘Go-To’ fertility metric for improving genetic profiles for fertility. 

The August 2024 HOUSA Fertility Index (FI) update is a good move for the industry, allowing for greater expression of all the factors impacting fertility. It is clear that focusing primarily on DPR as a fertility metric will inadvertently reward sires that may carry a negative HCR. That trend will then translate into heifers who freshen for the first time at an older age, gradually adding rearing costs to a replacement population. Therefore, the new index better estimates the impact of the combined fertility traits, and therefore a better estimate of overall lifetime profitability as it relates to animal fertility. 

In genetic selection, utilizing the right combination of traits is critical for maximizing progress and profitability.  Singular focus on DPR can result in missing other opportunities. Additionally, with electronic heat detection methods we can more easily identify animals in natural heat, where an increased focus on CCR will bring greater benefit. Therefore, the change in the Fertility Index formula is the right approach to improve our ability to identify and create animals who will maximize profitability through elevated fertility in the management systems of today and the future.