THERIOGENOLOGY - STALLION


Fig. 1. Sample March breeding log for the records shown in Table 1. The numbers in front of mare names indicate the order that the mares were bred (for a TB stallion breeding by natural cover when more than 1 mare was bred on a given day). An “O” after a mare’s name indicates that the mare was diagnosed as open following that breeding cycle. A “P” after a mare’s name indicates that the mare was diagnosed as pregnant following that breeding cycle.


Stallion 2 Summary Statistics Book Size


120 (data available for 101 mares)


SPR 68%


PCPR (CPP) 42% (2.4)


to ovulation. Consider reinforcement breeding in an attempt to compensate for what is likely marginal semen quality.


Example Stallion 2


The second example is a 6-year-old Standardbred that stood first season to 120mares (data available for 101); “was a lot of work” but “can we increase book size any- way?” The stallion is collected on a M-W-F-Sat sched- ule, and semen is split evenly to artificially inseminate as many mares as are presented on a given day.


Interpretation


• SPR marginal, PCPR low (CPP high), FCPR low, pregnancy loss normal, breedings per cycle good.


• Breeding over 2 mares per day lowers preg- nancy rate.


• Number of days of sexual rest prior to breeding (0 or 1) was not evaluated as this was a Standardbred on a regular collection schedule.


• PCPR lower in April and May. Probably associ- ated with increase in number of mares per day.


Conclusion


Adding more mares is not recommended since this stallions PCPR decreases when 3 or more mares are bred on a single day. Hypothetically, if the deci- sion is made to add more mares, assume 2.4 cycles per pregnancy. If breedings per cycle doesn’t


AAEP PROCEEDINGS / Vol. 68 / 2022 377


FCPR 46%


Pregnancy Loss Rate 2.2%


Breedings/Cycle 1.2


Stallion 2 PCPR Based on No. of Mares per Day


1 Mare per Day


56%


2 Mares per Day


51%


3 Mares per Day


35%


4+ Mares per Day


26%


Stallion 2 PCPR Based on Month of Breeding Season February


51%


March 45%


April 30%


May 35%


June 49%


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