Breeding Intensity versus preg rate in other software
Cycle calculation
All preg rate calculations in the past, including DairyComp305®, use a 21-day cycle based on the calendar dates from the first date on the report. Cycle windows are repeated every 21 d after the initial report date. A simplified criteria highlighting the differences is that DairyComp305® requires an animal to be in the cycle for a minimum of 11 d if not bred, 8d if bred and open, and 4d if bred resulting in a pregnancy. Seemingly the logic for this is you cannot include animals that are open in the calendar period by 1 day, so reasonable cut-offs are necessary. For the first cycle the 8 and 11 day cutoffs would correspond to an expected 72% (8/11) breeding risk and the 4 and 8 day cut-offs correspond with a 50% (4/8) first service conception rate. These criteria are necessary to have a good estimate of the farm pregnancy rate, but provide an artifact in the final output.
Figure 1. Annual preg rate and number of pregnancies included in the preg rate model, calculated by DairyComp305®, every day over a 21-d period. Moderate conception rate, with 60% of breeding done on Thursday, resulted in fluctuations of 1% by day of the week the report is run, Sunday being the greatest. The difference is nearly all attributed to the inclusion or exclusion criteria for first breeding’s, as seen by the number of breeding included in the calculation. The number of pregnancies is highly correlated to the number of pregnant breedings included in the metric (R2=0.51).
Figure 2. Annual preg rate and number of pregnancies included in the preg rate model, calculated by DairyComp305®, every day over a 21-d period. High conception rate, with 90% of breeding done on Thursday, resulted in fluctuations of 3% by day of the week the report is run, Sunday being the greatest. The within week variance is nearly all attributed (R2=0.93) to the inclusion or exclusion criteria for first breeding’s, as seen by the number of breeding included in the calculation. Sunday resulted in the greatest preg rate, Mondays the lowest.
An interpretation of the these charts is that for farms with high first service conception rate and strict protocol adherence in terms of VWP and resynchronization procedure, the variance in pregnancy rate calculated by DairyComp305® is primarily derived from the exclusion criteria of the model. Thus conception rate should be the metric for evaluating reproduction as it does not exclude upwards of 20% of breedings (figure 2, day 10 to day 11 comparison). On farms with good levels of compliance model exclusion criteria does account for half the variability so both should be considered as independent and co-dependent metrics. Farms with natural heat detection by electronic monitor or otherwise and farms with poor protocol compliance the preg rate is the best metric to use in DairyComp305®. For any farm comparison using DairyComp305, it is recommended the report’s start date is always set to the day of the week two days prior to the highest frequency breeding date of the farm.
BoviSync uses a different methodology, whereby the cycle is calculated for each animal based on its history of breedings and VWP. The length of the cycle is allowed to be set by the user, with the suggestion it match the target interbreeding interval (21d for naturally cycling farms and longer for synchronization farms). Doing this is a more complex approach. But, in the opinion of the author, results in a more robust calculation. In simplified terms the cycles are centered around the pattern of breeding to best match that animal’s breeding history. If a 21 d cycle is used, breeding 2 days after the VWP and again 21 d later will result in 2 cycles with 2 breedings in an animal based calculation 350 370 390 410 430 450 470 28.0% 28.5% 29.0% 29.5% 30.0% 30.5% 31.0% 31.5% 32.0% 1 3 5 7 9 11 13 15 17 19 21 Preg Rate Day 59% 1st Service Conception Rate, 90% Th breeding 45%, subsequent conception rate Preg Rate # of Preg (BoviSync). In a calendar system (DairyComp305 and all other calculations to the author’s knowledge) results in 1 cycle and 1 breeding on some of days the report is run and 2 cycles and two breeding on other days. This is the basis for our objection to the calendar approach, the results should not change solely based on the day the report is run. The animal based method is designed to include nearly all the breedings. The model also removes the daily variance due to exclusion criteria because all breedings are included.
Increasing the cycle length can result in better understanding of on-farm trends, and will significantly increase the preg rate for the farm. However, for standardized comparison between farms the same number should be used.
VWP Effects
Another primary point of difference is the use of the VWP. In DairyComp305® a “global” VWP is set for the entire report, where any breeding activity done before the VWP is excluded. In BoviSync, the VWP for every animal is recorded. So if the farm employs different VWP by lactation or there are changes to the VWP, the data is retained on that animal, allowing for a more accurate calculation. Another primary difference is that breedings occurring prior to the VWP are treated as the start of the VWP. The rational for this treatment is that a breeding that occurs before the VWP indicates the recorded VWP for that animal was incorrect and that the breeding date was the true VWP for the animal. This results in nearly all breedings being included in the calculation.
A consequence of this decision is that the preg rate can be over-inflated by having a late VWP and a significant number of breedings occurring before the VWP. This can result in less accurate comparisons between farms. The alternative of excluding all those breeding activities results in inaccurate numbers on the farm and not great comparison between farms either “cherry-picking” animals for insemination or not following the stated VWP. Thus, the reason for the alternative method adoption.
Farms engaged in cherry-picking followed by synchronization, may choose to use a late VWP that matches the synchronization program and animals that are bred are included. The method used by BoviSync results in a more accurate preg rate based on the farm’s actual activity, but will likely be much higher than all other preg rate model calculations.
Abort Effects
The handling of abortions has been an ongoing debate; what animals to consider open and pregnant in the calculation of pregnancy rate when the pregnancy results in an abortion. The best answer to this question depends on the question being asked. For financial considerations, animals that abort at 30 days carried calf and animals that abort at 90 days carried calf do not start a new lactation and are therefore open. For most other questions being asked, 35 days carried calf is a good compromise, and is what is used by DairyComp305®. BoviSync uses 35 days carried calf as the default, but this value is a report setting that can be changed by the user.
Report Detail
Another difference is the reporting methods. Systems using a calendar date can only provide report increments equal to the period of the window used for the calculations. As such, there is poor granularity of data available, 15 cycles per year. BoviSync utilized the animal based cycle model, so the report can be done daily. The resulting reports are of high resolution (Figure 3). However, on farms with weekly breeding, individual day variations should not be considered even though they are displayed.
Figure 3. Breeding intensity chart generated in BoviSync for a one year timeframe. Yellow line indicates the insemination risk, the blue line indicates the conception rate, the red line indicates the pregnancy rate, and the green line indicates the abortion rate (as a percent of pregnancies).
Appendix:
Examples of Calendar Exclusion Criteria in DairyComp305
Animal’s cow card
Command: Bredsum\e for id=8558 == report starts on 9/23-9/27 Pregnant breeding excluded because 10/14 is only in the window for 1-3 days when the 21 day cycle starts on 9/23-9/27.
Command: Bredsum\e for id=8558 == report starts on 9/28-10/14 Pregnant breeding included because 10/14 is only in the window for greater than 4 days when the 21 day cycle starts on 9/28-10/14.
Command: Bredsum\e for id=8558 == reports starts on 9/27, but has VWP of 50 instead of 70 Animal was bred at 76 DIM, so there is a 50-71 DIM cycle, then 71-76, so it is included. This is why VWP changes do not have as big of an impact as one would expect.
Command: Bredsum\e for id=8325 == report starts on 4/27/14
Command: Bredsum\e for id=8325 == report starts on 4/26/14 Breeding occurs 9 days before end of the 4/26 cycle, 1st breeding not counted between 4/19 – 4/26 (inclusive of dates
Here the pregnancy rate calculation uses 360 pregnancy resulting breedings with a 45% conception rate (360/792), but the conception rate calculations use all 497 breedings resulting in pregnancy, resulting in a 49% conception rate.
Blank Lines in Breeding Intensity
There are cases when too many animal have an unknown outcome and a pregnancy risk can not be calculated. Because re-bred animals have a known outcome of open, and pregnancies have to wait to be confirmed, estimating a pregnancy risk on the known results would cause an errantly biased low estimation of pregnancy risk. Generally, this situation is encountered when a high cull rate of the group of animals comprising that line in the report occurs. This is an example of what a breeding intensity table looks like, in this situation. In the 2020-06-24 to 2020-07-14 line, of the 13 animals bred, too many were sold without a result. The overall pregnancy risk skips over that time period to ensure accurate calculations that aren't artificailly biased low by periods of significant culling of bred animals.
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