When women take estrogen, we may reduce our risk of ovarian cancer, but we increase our risk of several others, including cervical and breast, not to mention increase our risk of blood clots and disrupt our 'good' bacteria levels which makes us more susceptible to fungal infections. Of course pregnancy is dangerous too and some girls suffer from PCOS etc so it's all about weighing up the risks in light of the circumstances. Anyway, I'm not sure what I would do if I had a female bitch - in regards to whether I would desex or not that is. The female reproductive system and hormone fluctuations are so much more complicated than those of the males and every study I've seen says the benefits and risks from desexing are much closer than with males. Just pick and choose which conditions are of greater concern I guess. I'm starting to think I'd agree with you and desex later in life - 18months +.
What I have read though has made me quite sure that I will never willingly desex a male dog. I've seen enough to feel confident they can be trained easily enough to not display any unwanted behaviours stemming from being entire and with the exception of removing the risk of testicular cancer (which is both rare and quite treatable because it takes so long to spread from the testicles), I have yet to find any articles that detail benefits. There are lots of articles out there based on dogs of different breeds, I will link some more to you if you like. This was just one I came across the other day that was particularly well funded because it was potentially going to help people through assistance dogs. I found an interesting one years ago when I was deciding what to do with Sammy that was comparing dogs in Scandinavian countries where desexing is put in the same category as tail docking and ear cropping etc to those in England where almost all were desexed. I'll try find that one again for you if you like, because that one included lots of breeds. Kelpies are a relatively healthy breed, compared to say GR or GSD (much larger gene pool etc) so I imagine the risk of everything is probably lower, but potentially still increased by desexing. I haven't seen Kelpies specifically mentioned in any studies unfortunately.
My dog spent a year living in a house with another entire male, wasn't even my dog. I hear of plenty of fights breaking out between desexed dogs as well so I'm not entirely convinced that desexing really lowers your risk too much there. Sammy does get attacked by other dogs on occasion, but they are almost exclusively desexed males. I am often told it's normal behaviour for desexed males to feel uncomfortable around entire males. Anyway,, there are no studies to show that desexing benefits a dog from a health or behavioural standpoint - only unsubstantiated claims. I just find these studies interesting and I thought maybe others would too. My dog is a huge part of my life and I want to be informed when it comes to making decisions that can't be undone; I imagine I'm not the only one. What anyone decides to do with that information is their prerogative, only they know all their own circumstances.