Since you're Canadian, there is a product produced by Vetrepharm called a CIDR. It is a pessiary which when used in conjunction with injections gives a very reliable onset of estrus for mass inseminations.
Other methods are MGA in the feed then removing the hormone (don't recommend it, can wreck fertility), timed injections of prostaglandins (estrumate or lutalyse generally, pretty good, different regimens...) and even pulling the calf for a day to bring them in heat (there are much better methods, but this is the cheapest...)
Hope this helps! V
