In case you're curious, this is a dump of the unit.status.current_soul.unk1 flag - which as posted in the dfhack thread is supposed to be the orientation of the unit
This is from a brand new embark on 40.08, in a world generated in 40.08. The Starter Pack with the addition of a pre-release dfhack, but no other changes. I used the "Ruin Assault" embark which brings a lot of animals, but the script I wrote as well displays foreign ("monster") units as well. I unpaused after embark and let the game run - dwarves idle - until Summer.
This was an interesting embark as even though I had previous embarks where an entire species would not get pregnant - presumably due to a "sterile" male - this one had every species get pregnant even the single female cat and pig, but did have several examples of sterile females alongside fertile ones. 5 of 6 dogs and 4 of 6 turkey hens are fertile.
BIRD_TURKEY(177)[Female] 00010000 8
BIRD_TURKEY(177)[Female] 00000000 0
Pregnant: BIRD_TURKEY(177)[Female] 00100000 4
Pregnant: BIRD_TURKEY(177)[Female] 00100000 4
Pregnant: BIRD_TURKEY(177)[Female] 00100000 4
Pregnant: BIRD_TURKEY(177)[Female] 00100000 4
BIRD_TURKEY(177)[Male] 01001000 18
Pregnant: CAT(158)[Female] 00101000 20
CAT(158)[Male] 00001000 16
DOG(157)[Female] 01000000 2
Pregnant: DOG(157)[Female] 00100000 4
Pregnant: DOG(157)[Female] 00100000 4
Pregnant: DOG(157)[Female] 00110000 12
Pregnant: DOG(157)[Female] 00100000 4
Pregnant: DOG(157)[Female] 00110000 12
DOG(157)[Male] 00001000 16
GIANT_SPARROW(38)[Female] 01000000 2
GIANT_SPARROW(38)[Male] 00010000 8
GIANT_SPARROW(38)[Male] 00001000 16
GIANT_SPARROW(38)[Male] 00001000 16
GIANT_SPARROW(38)[Male] 00001000 16
GIANT_SPARROW(38)[Male] 00000000 0
HORSE(161)[Female] 00100000 4
HORSE(161)[Female] 01000000 2
Pregnant: PIG(164)[Female] 00100000 4
PIG(164)[Male] 00001000 16
Degel Thukkanustuth[Male] 00001000 16
Goden Rithuthir[Female] 00100000 4
Goden Ulabthob[Male] 01001000 18
Rith Sazirluzat[Female] 00100000 4
Thikut Ingiztarem[Female] 00100000 4
Udib Edimalath[Female] 00100000 4
Zasit Arakingiz[Female] 00100000 4
As a further experiment, I set the turkey hens "orientation" that was zero to 4, and the dogs that 2 to 4 and they both got (nearly instantly) pregnant.
So, the problem cause is confirmed, and fixable with dfhack.
I updated the bug report with my findings. I also added justifcation why the inclusion of gay animals may want to be reconsidered if this is intended behavior. Basically, while the inclusion of gay animals would be great from a representational standpoint, making an effecient meat industry would tend to incentivise slaughting gay animals in favor of ones that produce offspring, which is pobably not the message that Toady was going for.
Let's also note that homosexual is not sterile, and even if you could argue behavior differences and resistance to normal breeding (a male animal...maybe..a female, almost certainly not) even then, artificial insemination has been practiced as far back as the 13th century.