Depending on a cattle producer's calving season, breeding may be only a few months away. Will your replacement heifers be ready?
When Elaine Grings asked this question, the Assistant Professor & SDSU Extension Cow/Calf Management & Production Specialist is referring to the heifers' body weight.
"There has been much talk over the years about the proper weight for beef heifers at first breeding, with estimates ranging from about 55 to 65 percent of mature body weight as the target goal," Grings said. "To be able to hit that target, a cattle producer needs to know the average weight of their mature cows."
She explained that on average, mature cow weights seems to have increased by about 12 percent over the last 25 years.
"Be sure you have a reasonable estimate of cow weights for your current herd," she said.
Once the target breeding weight is known, a cattle producer can plan for the average rate of gain needed for heifers between weaning and breeding.
Does it matter when heifers add weight between weaning and breeding?
Over the years, Grings said a number of studies have shown that as long as heifers reach their target weight, the timing of the gain may not be critical.
"Development strategies that take advantage of low cost feeds early in development, followed by feeding heifers to make faster rates of gain in the last 60 to 90 days before breeding have been successful," she said.
At USDA-ARS Miles City, Mont., one group of heifers in an early spring calving herd were raised on pasture with supplemental hay for 130 days after weaning and then moved to drylots where they were fed a diet based on corn silage and barley for 91 days. Gain during the pasture phase averaged 0.6 pounds per day and during the drylot phase heifers gained 2.5 pounds per day (for an average of 1.4 pounds per day). These heifers were compared with another group that was fed a corn silage and hay based diet in the drylot from weaning to breeding and gained an average of 1.5 pounds per day. The number of heifers cycling at the beginning of the breeding season and the proportion pregnant at fall pregnancy check were not different for the two groups.
"In this study, feed costs were similar for the two groups of heifers, but other diets could be formulated that might save on feed costs," she said.
When using a delayed gain strategy, Grings said it is important to have enough time on the high gain diet to ensure that heifers will reach the target weight.
Researchers in Kansas who fed heifers low gain diets that resulted in gains of 0.33 pounds per day followed by 2.7 pounds per day for the last 50 days before breeding for an overall average gain of 1.1 pounds per day observed a decreased number of heifers cycling at the beginning of the breeding season but pregnancy rates were similar to heifers that gained at constant rate of 1.2 pounds per day from weaning to breeding.
Because heifers that conceive earlier in the breeding season will have greater lifetime productivity, this difference in cyclicity at the beginning of the breeding season may be quite important, Grings explained. Aggressive estrus synchronization protocols may help to get heifers bred earlier in the breeding season and these programs may be combined effectively with delayed gain strategies.
"It is important to be realistic about the rate of gain heifers can make during the last few months before breeding. Heifers that were making slow rates of gain may be more efficient in their gains when initially shifted to the higher gain diets. However, this effect will be short-lived and should not be counted on for the entire period of greater gain," she said.
She added that the chance of adverse environmental conditions also needs to be taken into account. Excessive mud in a drylot could cause sufficient performance losses to either cause heifers to miss the target, or wipe out any cost savings that might occur earlier in the development period.
"If your heifers haven't gained as well as you'd like this winter, there is still time to get them ready for the breeding season. Take a good look and evaluate whether you should step up their gains during this last few months before breeding," she said.
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