They shouldn't. So no, they don't.
False heats are rare in cows or heifers that are already bred. If a heifer does go into heat when pregnant, it only occurs once or twice and that's it. But normally, no, a heifer won't still mate when she's pregnant.
Heifers getting serviced by a bull or through artificial insemination to get pregnant and give birth after 9 months of gestation.
The common rule of thumb is that 10% of heifers born with a twin brother are fertile, leaving only 90% of heifers in a brother-sister twin combination sterile as freemartins or hermaphordites.
Harry Braham's birth name is Henry Nathaniel Braham.
Horace Braham's birth name is Horace Henry Braham.
Philip Braham's birth name is Philip Edward Braham.
Braham Murray's birth name is Braham Sydney Murray.
Rich Braham's birth name is Richard Lee Braham Jr..
Jerseys are one such breed.
Horace Braham is 5' 6".
Lionel Braham is 6' 2".
Rich Braham is 6' 4".