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) to equal consideration for DPR and Cow Conception Rate (CCR), 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 from 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.

In the table below are 4 examples of bulls with milking daughters above 1,000 PTAM. It is well understood that it is rare to find a bull above 1,000 PTAM who is positive for DPR and CCR. TAOS is clearly an exception to the rule. Why is this? Simple – cows that produce at higher levels have increased nutrient requirements that take precedence over nutrients required for a proper involution process post-partum, slowing that process, and adding to the required DIMFS to have the uterus prepared to receive a fertilized embryo.

The question that presents itself is how do bulls within a similar range for milk production compare for DPR and CCR, or better put, how do their combined measures for fertility compare when rolled into Holstein’s Fertility Index?  In our example:

CAPTIVATING is losing ground for fertility as he is rapidly adding daughters. He is sliding for both DPR and CCR, and the weighting change in the FI was of no help to CAPTIVATING.

BARCLAY is steady for his fertility values and his updated FI weighting from Holstein has a negligible effect on BARCLAY’s index for fertility.

TAOS is clearly an exception to the rule with his positive values for DPR and CCR. Interestingly, TAOS is lower fertility on his virgin heifers than our three other example sires and therefore the TAOS daughters calve at an older age at first calving than the other three sires.

LIONEL has been ‘King of the Hill for Milk,’ as well as a reigning breed leader for a negative DPR. In contrast to TAOS, LIONEL’s HCR is quite positive, and he is exceptional for EFC which means that LIONEL provides replacements who begin their high production careers at a younger age, saving on their rearing costs compared to their contemporaries. That does compensate for a few days of added DPR...

We applaud the August 2024 HOUSA Fertility Index (FI) Update that removed DPR as the dominant factor, allowing for a clearer expression of the other three factors. It becomes clear that focusing primarily on DPR as a fertility metric will inadvertently reward sires like TAOS who 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 your replacement population. In our example you will notice that the other three sires have a +HCR which translates into a +EFC resulting in daughters genetically designed to present lower rearing costs by starting their production careers early. Hence the CAPTIVATING, BARCLAY and LIONEL daughters all begin their return on investment (ROI) sooner, with a lower investment, getting those initial milk production days in the bank before the TAOS daughters get started.  So, even if it does take a bit longer for the daughters of our three +HCR/EFC sires to become pregnant as cows, they start off money ahead because they calved earlier. Although they will have a higher DIMFS, they become pregnant at a similar date during their initial lactation as the TAOS daughters, who got a later start in their first lactation and at paying their feed bill.

In genetic selection, utilizing the right combination of traits is critical for maximizing progress and profitability. As we saw in the example of the four bulls above, 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.