Trophyhill - per your question regarding what makes a BULL attractive to a COW...
A lot depends on age structure and sex ratio of the herd you're interested in, and what stage of her "choice" you're talking about when a COW is settling on a BULL.
If you're talking about approaching/staying within a harem - in general - a cow will "choose" the bull that:
1) ACTS the most dominant within the area; and
2) Provides the greatest level of "protection" while allowing the maximum amount of "freedom" and "peace" on a daily basis.
While there's also the habitat component to it, that's a bit more complicated and a bigger discussion - BUT - those two things are what attract a cow to a bull INITIALLY. There used to be those (Val Geist and others) that thought the size and symmetry of antlers also played into a cow's "choice", but I think when you compare typical antlers with non-typical antlers, behavior wins every time; the cow will choose substance over looks.
In some areas, a small 5x5 may provide the highest degree of protection from harassment from other bulls. In other areas, older age-class animals, and larger antlered animals may be the bulls that offer the greatest level of protection. COWS WANT TO BE LEFT ALONE!!! ...they'll initially gravitate to those bulls that will ENSURE that to the greatest extent. I used the word "ACTS" most dominant, because in some populations, the ACTUAL dominant bulls (often older age-class bulls) don't participate in rounding up/keeping harems. They stay in the "shadows" so-to-speak, and don't show up until there's a cow ready to breed - like others on here have said. If a bull like that isn't willing to provide a cow the protection from harassment she seeks, she'll settle on the next-best option.
Sometimes the bulls that cows are attracted to are vocal and aggressive. Sometimes they're more the type that "run and hide" at the first sign of a fight. ...here, the personality of the COW can play into her choosing a bull that fits her personality the best.
What attracts the cow to a bull when its time to BREED is pretty straight forward: she will choose the biggest, strongest, most dominant bull she has at her disposal at the TIME she's ready to breed. Cows won't CHOOSE to miss an estrous cycle just to hold out for a better bull; their first priority is to BREED, then its to "breed with the best." So...if a small 5x5 is the one that provides her the protection she needs day-to-day, and he's the one there when she cycles in - his hard work typically gets to pay off. If, however, she starts to cycle in, and an older age-class, bigger, more dominant bull walks in (or is close enough for her to run out and rendezvous with) - sorry, Charlie!!!!
In areas with diverse age structures, typically the more dominant animals hold the most cows, with subordinate bulls playing the "satellite" roll. In areas with skewed age structures (many OTC areas where the bull population is typically 3.5 years of age or less), you can find cows in one of two types of harems: small harems with a "smaller" bull, with multiple harems all scattered across the landscape, or in GIANT harems all concentrated around one older - typically very aggressive - bull. These groups/this type of bull can sometimes be the HARDEST to kill!!!!!
Roe Hunting Resources