There are several reasons why:
1) Bovines would go extinct if cows were not producing calves all the time
2) Cows do not live forever, so they need to produce offspring to keep carrying on their genetics to the next generation.
3) The only way to get good quality beef is to slaughter calves from cows that have been raised to a slaughter age between 18 and 24 months.
4) Cows cannot continue to produce milk if they do not have a calf once a year. In order to produce milk, a cow must give birth to a calf.
5) It's a natural thing for cows to do, just like in all animals in this big ol' world (including humans). It's all a part of the Life and Death cycle.
Yes. Cows cannot reproduce with other cows in order to produce young. They need to have a bull in with them in order to have a good chance of getting bred and giving birth to a calf over 9 months later.
Not all do. A lot of cows are better off without unnecessary human interference than with it, especially beef cows that are meant to be giving birth and looking after their calves on their own. With dairy cows, well that can be a different matter, especially with those dad-gummed Holsteins. It's not uncommon to have to assist calving out a Holstein cow or heifer, though a dairy producer tries to minimize this by breeding them to low birth-weight bulls like Jerseys to their Holstein heifers.
Cows are not plants, they are animals, which are capable of growing in any and all seasons.
Yes.
Some do, most don't. It always depends on when they're bred that will coincide to when they will calve. Some cows may calve on a New Moon, some may calve when the moon is at it's first or last quarter, or some may calve in between any of these times.
Yes.
VERY rarely. Cows will only calve once a year.
Kinda. If you are referring to their rear ends, yes. But, cows calve out of their vaginas, not their anuses.
#1. Ease of calving. You would want to keep cows who have a history of being able to calve without help as opposed to those who always need help during calving. #2. Size of calves and viability. You would want to keep cows that generally calve larger calves, as well as those who rarely loose calves due to small birth size or general weakness of newborn calves. Over time your herd will become generally more robust.
This all depends on your herd size, how long your calving season is, and the fertility of your cows and bulls. Some people will calve their cows 365 days a year, whereas others will have all of their cows calve within a time frame of 45 to 60 days, no matter if you have a herd of 50 cows or 1000. The better fertility you have in your cowherd, the shorter your calving season will be.
You should start calving season by March 16.
Yes, though the differences aren't all that significant.
Plenty. "Cow have calf" is not a proper sentence, it's referred to as an "incomplete sentence." To form a proper sentence using these words give you something like this:"A cow will have a calf.""A cow is going to have a calf.""The cow will have a calf.""The cow is going to have a calf."And so on and so forth.
The majority (at least 60 to 70% ) of all cows in North America get bred between summer and fall. The rest of the cows get bred winter or spring, or any other time a bull or a producer wants to catch them to calve.