INTRODUCTION The selection of a calving season could well be one of the most important economic decisions made on a ranch. Changes in calving season and weaning date can cause or require many other changes in a cow-calf production system. Therefore, a systems approach should be used wherein every variable that one can think of should be considered to get the best estimate of the overall effect. The economic rewards of selecting the best calving season can make the analysis worthwhile. CONSIDERATIONS The first consideration in selecting or changing a calving season is the effect on profitability. Since so many things can change simultaneously when a calving season is changed, it is difficult to assess the complete effect of the change without looking at the effect of the coincidental changes. Some, but not all, of the factors deserving consideration follow: Climatic and resource constraints. Feed quantity and quality available before, during and after the calving season and the availability of protection and stock water at the place and time chosen can eliminate several choices or result in additional expenditures to compensate. Competing enterprise constraints. Sometimes work required in another enterprise such as crop production or work on a sheep herd or brood mare enterprise may make it difficult or impossible to calve at certain seasons. However , you should be careful not to let a few dollars in the small enterprise deprive you of big dollars in the large enterprise. Potential change in winter feed costs. This is, perhaps, the biggest and most important question of all. It can have huge economic consequences and the following questions deserve a lot of attention: 1) Can you save hay costs? Many producers have significantly reduced hay production and feeding by using some of the marginal hay land for grazing. Others have completely eliminated haying by using the hay ground for grazing and buying any supplemental hay needs. It is important to know what your own hay costs. It will usually surprise you. It is important to know what happens to carrying capacity when you convert from hay to pasture. Your guesses on this will probably not be very good until you find some research data or talk to someone who has already made a similar change. 2) How much will you have to add to supplement cost to compensate for protein that was provided by the hay? Research in Nebraska indicates that the addition to protein when switching from hay feeding to winter grazing may be less than most people think. 3) Can you eliminate haying equipment? Sometimes the elimination of haying equipment and the purchasing of reduced hay needs will result in carrying capacity for more cows and elimination of some fixed costs and thus a compounded reduction in cost per cow. Potential changes in non-feed costs. It is good to consider the changes that might come about in labor for range and pasture management, cattle care and machine care and maintenance when changing a calving date. Change in carrying capacity. Carrying capacity changes are difficult to estimate without some experience on you own ranch. My experience leads me to expect a little reduction when you switch from haying to grazing until your grazing and pasture management gets good. However, if you buy all your hay needs, that will result in an increase in carrying capacity that is easy to calculate. Change in weaning date. Weaning dates may or may not change depending on marketing objectives, calf-quality grazing that may or may not be available, cost of winter pasture vs. calf feed, etc. In Nebraska we have not changed the weaning date as we have moved the calving date from March to April. We have subirrigated meadows to wean on. They would not support pairs very long, but calves only can stay quite awhile. We like to wean the calf directly on the meadows (fence-line wean) and use the meadow aftergrowth before it freezes down. This will allow the calf to perform about the same as if still nursing, and the cow will now begin to gain weight on hill pasture. In our case this reduces winter feed costs. On a ranch in Wyoming we changed from March to June calving and didn t wean the calves until February or March. In this case we didn t have quality aftergrowth for the calf in the fall, and we did have inexpensive desert winter range. By caking the cow a little extra to allow for lactation and the calf consuming direct, we could carry the pair at a very low cost. After weaning we had to feed the calf for about one month before going back to range and then irrigated pasture until August or September. The irrigated pasture was previously poor hay ground. Sale dates, weights and prices. After changes in winter feed costs, these marketing factors require the most careful analysis. You must look at your own situation while considering the previously named factors and list feasible sale dates. Should you sell bawling calves, preconditioned and weaned calves, warmed-up calves or yearlings? Then you need to project weights and prices for these calves. Don Adams, Dick Clark and others at the University of Nebraska have done some work on this. Selecting a new calving season may result in the loss of old options, but new options nearly always appear. Marketing opportunities lost and gained. At our Nebraska Ranch we have thought that May calving would probably be better than April. However, we have a market for our later calving cows that we might not have cows for if we calved later. We sell cows for May calving and cows for June and July calving. These cows go to herds for terminal crossing. Because of this marketing opportunity we have decided to stay with the April calving. Range management. A change of calving season presents range management challenges and opportunities. If you move in the direction of more winter grazing, it becomes easier to remove less feed during the growing season and create more options for the management of time and timing of grazings and recovery. Summer calving in rotational grazing or on some BLM or Forest Service in common permits presents some unique problems that need solution before hand. People benefits and problems. Can you and your co-workers get excited about this, or do you get depressed? The people that I see who are convinced they made a right choice have been very careful in their decision-making. The outcomes of the decision match their lifestyle desires, values and profit objectives. If your team can't get excited about a change, don't do it. CONCLUSION From personal experience I know that a change in calving season can, but won t always, make a huge difference in ranch profit. There are still lots of unanswered questions regarding weight per day of age at various market endpoints and cow rebreeding rates for different calving dates. I think if you will carefully consider the above named factors, you will make a reasonably good decision. My own preference is for later calving than is typical. However, I hope I have convinced very few of you because I would like to be one of only a few calving and marketing when we do.