Nutrition/forage availability
It is important for you to have the forages available to meet the needs of your lactating cows. The type that you have will be a major factor in deciding if spring or fall calving is better. Warm season grasses tend to be more closely aligned with the needs of spring calvers. Fall calves tend to match up better with the cool season grass varieties.
Weaning and calving rates
Here things tend to get split on which one of the seasons is best, but that is generally for one reason. Fescue toxicity is a likely contributor to lower calving rates here in Texas among cows grazing tall fescues. This seems to show that your forage supply plays an important role in determining which one would be best. I discuss the importance of filling the spring nutrition gap here
The differences in the weaning weights are more affected by climate conditions and/or nutrient availability. Fall-calving cows have a higher nutrient demand when forage quality and supply is going down. The spring ones have the benefit of forage quality rising as their nutrient demands are going up due to being in the later stages of gestation.
Market prices
Both the cattle and feed prices are important factors to consider when deciding which calving season to go with. The availability of forages and other feedstuffs are directly tied to cattle prices when calves are sent to sale. So it is important to find the right balance between cattle and feed market prices.
Labor
As with anything related to cattle production the availability of labor plays a role in which decisions to make. Calving season is one of the most labor intensive times on the ranch so choose wisely. You need to select a season that is in synch with your other responsibilities, whether on or off the ranch. A higher price won’t do you any good if you are just running yourself into the ground.