It seems as though we've been stuck in an unforgiving weather cycle for several years throughout much of southern Oklahoma and northern Texas. For the most part, we've had little rainfall from late spring through summer, when most of the year's grass is produced and forage demand is highest. Many people have had to cull livestock, wean calves early, and drought feed. In some cases, prolonged calving intervals and lower weaning weights resulted.
No doubt you have recently read and heard many dissertations on drought management, including adjusting stocking rate to the carrying capacity of dry years, grazing areas with limited water reserves first, identifying a protocol for levels of culling livestock in your herd, and creating early weaning strategies. Despite the precipitation that much of this region received in June, drought management should be an annual consideration for every rancher. With this in mind, it's time to play that same old song again, but now I'll talk about reducing livestock demand during the warm season by looking at herd structure and calving seasons. The table below illustrates the relative differences in grass demand and costs of maintaining a cow unit for a year under four cow-calf management systems. A cow unit includes the grass demand from the cow and her calf (through weaning) and the amount of grass required from her percentage of bulls and replacement heifers. The table assumes one bull per twenty-five cows and an 85 percent pregnancy rate (15 percent culling and replacement rate). In other words, if all the grass on a ranch can be considered a pie, the values in column two are an average piece of the pie that a cow in each system would require.
If you cull open cows after checking for pregnancy and replace them with bred heifers (averaging twenty months old), replacements graze for only four months before calving. If you purchase open heifers and breed them, they graze for nine months before calving. Therefore, the open heifer management system requires 10 percent more grass or hay than the bred heifer system. If you retain replacement heifers and breed them to calve at two years of age, the grass demand is 13 percent more than that in the bred heifer management system because of the additional seven to eight months the heifer is grazing from weaning through breeding. Some people retain their replacements and breed them to calve at three years of age, believing heifers calving at two years of age yield calves with low weaning weights and have a lower rebreeding percentage. The grass demand with this system is 27 percent higher than with the bred heifer system and 13 percent higher than that in calving raised replacements at two years of age.
The fourth column in the table represents the per-cow unit pasture cost of the four management systems. The recent droughts have forced some people to cull livestock. The retained heifer systems require more grass and time to produce a calf. Therefore, they put even more strain on your forage resources during a drought and can make a culling protocol more difficult. I believe some people would rather drought feed than cull animals they've had two or three years, but it is often the most costly measure.
Let's turn to calving seasons. Most of this region's ranches rely on warm-season forages for their livestock, which is normally most abundant during spring and summer. However, the distribution of grass growth throughout the year has shifted recently. On some ranches, the only forage we can depend on lately is early spring cool-season grass. We have had above average crops of ryegrass, spring phase small grain, brome grass, and Texas wintergrass the past few years, which has been the saving grace for ranches in many parts of our service area.
The graph above illustrates the daily forage demand of a cow-calf unit (1,000-pound cow) throughout the year.
Forage demand fluctuates with the physiological stage of the cow and is lowest after weaning and highest before. With a spring calving season, the highest forage demand is from May through September, while a fall season demand peaks from December through April.
The June rain definitely helped, but because of three consecutive dry summers, infestations of grasshoppers, and pretty good small grain production, I have thought about what a difference it would make if we had a fall calving cow herd instead of a spring calving one. The summer forage demand for a spring calving system is 70 to 80 percent higher than that for a fall system, a big difference in terms of grazing pressure on drought stricken grass and the need to cull or drought feed. Calves born in the fall would be weaned and sold by May, so the cows could get by for some time on lower quality forages.
In case you think I've fallen off the deep end, I realize that most of you have predominantly warm season forages, and we have already had signs of getting back to a more normal rainfall pattern. So I am not recommending that everyone move toward a fall calving season, but think about what a dual calving season could mean to you. Calving in the spring and the fall requires that you manage two herds of cattle, but you need fewer bulls and get more use out of them and can market calves twice a year. If you were to structure your herd so that 60 percent of the cows calved in the spring and 40 percent calved in the fall, the forage demand would be more consistent throughout the year. During summer, it would be approximately 20 percent less than that in a spring calving season. Combined with other drought management strategies discussed, this approach could delay your having to reduce livestock numbers or begin drought feeding. If you combine this system with purchasing either bred heifers or open heifers and don't increase stocking rates, you can be better prepared for drought. If there's favorable rainfall, you can sometimes take up the slack with stockers.
These methods can help you adjust your herd structure, letting you weather drought better. Obviously, they won't work for everyone. Thoroughly examine weather patterns and your forage base and livestock before making any changes.