Lazyacre
Good advice on this board. Let me add my 2 cents worth from the perspective of a life long cattleman and 18 years experience as a risk manager and insurance agent. My advice to friends and clients has always been to purchase insurance for those losses that will seriously impair your financial well being and self-insure the smaller risks that will not ruin you financially. That being said, only you can determine what level of risk tolerance is acceptable to you.
As mentioned by others, there are different types and levels of coverage available. Very broad mortality insurance is quite pricey and is mostly used for high valued registered breeding stock.
For most commercial cattle, adequate coverage for your herd can usually be added to a farm & ranch policy for a modest premium. This coverage will generally cover losses due to specifically named causes of loss such as lightning, fire, flood, injury during transit, and theft, but not from sickness or natural death. Some policies will also cover farm equipment, feed, hay and farm buildings such as barns. Generally the premium is based upon the total dollar amount you have chosen. This premium can be reduced by choosing a higher deductible ( the part you self-insure). For coverage like this, I reccomend you choose the highest deductible that you would be comfortable paying from you pocket in the event of a loss. As far is the total dollar limit, I would suggest you follow the advice of an agent who is experienced in insuring farm risks. Some policies have clauses will only pay a pro-rated amount of your loss, if your total dollar limit is lower than a certain percentage of the total value of your cattle, equipment, etc. Some policies do not have these potential got ya's. That is why is is crucial to have an agent that is extremely familiar with this type of coverage. After a loss is not the time to find out you do not have adequate coverage.
Also, make sure you have Farm Liability Insurance. This is coverage that pays for damages done to others when your cow get in the road and causes a car accident or your tractor is involved in an accident. This also pays for legal defense (lawyer$$) costs involving covered accidents. Don't skimp on low liability limits. Higher limits cost very little more. I would never reccomend less than $250,000 liability limits.
Sorry for the length of this post. Too complex for a shorter answer.
Regards
Brock