Just to address two points mentioned in this thread (animals not breeding when housed in pairs, and small cows avoiding large bulls); both of these statements are stretches at best, and one is completely incorrect.
In regards to small cows avoiding large bulls, this is quite the opposite actually, particularly with wild animals. Generally only the largest, most dominant, physically imposing bulls will be successfully breeding the cows, and this includes the little 8-10 year old cows conceiving their first pregnancies (which bear in mind, are physically very similar to captive cows around the 5-7 year age mark). This also stands true in captivity and has been proven numerous times (mainly there are significant age differences, but one or two cases are just massive size differences as well), examples being 26 year old Ankhor breeding his 3.5 year old daughter and producing a calf, massive 15000+ pound bull Radza breeding 8 year old Ma Ya Yee and producing a calf, 23 year old Nikolai breeding his 4.5 year old daughter, who is half bornean, to produce a calf, large 14 year old bull Thai breeding 4 year old Omysha and producing a calf, 30+ year old motek breeding his 5 year old daughter and producing a pregnancy, etc...and those are just the ones that produced calves. Lots and lots of young cows will allow the resident mature bull to mount and copulate with them, even if it doesn't result in successful pregnancy. Of course a young cow who has never seen a large bull before might initially be cautious of seeing one for the first time, but even if that's the case, they're usually the first ones to start opening up to them (in cases where the adult cows are scared as well), or come around very quickly (in situations where the older cows are fine with bulls)
Also as for elephants not breeding when housed in pairs, this is utter hogwash, especially without context. Two calves pulled from their mothers at 2 years of age and housed together for the rest of their lives? Sure, there's a chance they might not breed, especially if its a more sensitive male with a more belligerent female; but there's just as much a chance they could become an incredibly prolific breeding pair. Assuming there isn't another more dominant bull suppressing them, and they know what to do, most bulls are more than happy to breed a cycling cow regardless if she is that bulls only other companion or not. Of course if you have a bull raised in a poor social environment he might never figure out how to breed a cow, but regardless if he is housed as part of a pair, or with a whole herd of proven cows, he still won't breed any of them.
Although its not particularly common in this day and age, breeding pairs can be and are successful, for instance Assam and Angele at Budapest who have produced three calves together, and Mac and Zuze at Kobe who have produced 4 calves together. There's a few others where its been a young pair housed with a single older cow, and in those cases you know they older cow hasn't contributed anything, its purely the two youngsters who figured things out on their own.
