N.Y. Comp. Codes R. & Regs. tit. 9 § 4081.3
To qualify as having been bred back in New York, a mare, after foaling in New York State, shall remain in New York for a minimum of 90 consecutive days after arrival. During such applicable period, such mare shall be booked exclusively to and serviced exclusively by a registered New York sire. Should such mare fail to be so certified as in foal during such period, it may be taken from the State after that minimum 90-consecutive-day period and be deemed "bred back" provided it is not serviced by a nonregistered New York sire thereafter in the year. Should such mare die or otherwise become medically unfit for breeding during or after foaling, it shall be considered "bred back" if such mare had been booked for service to a registered New York stallion in such year and, if alive, was not serviced by a nonregistered New York sire thereafter during such year or the following year.
N.Y. Comp. Codes R. & Regs. Tit. 9 § 4081.3