Replacement heifers are your future cow herd and contribute yearly to the advancement of your genetics along with a significant impact on profitability. Genetics, nutritional development, health programs and breeding management will ultimately define your cow herd. Get them right and they will provide you years of successful returns to your cow-calf operation. Fall short in one or two areas and you will negatively impact profitability that can take years to correct. For spring calving cow herds, replacement heifers should have already achieved puberty or will do so, soon. Their nutrition program has a big influence on achieving cyclicity and preparedness for breeding.
Heifers should reach approximately 55 to 65% of their mature cow weight by the time they are bred around 13 to 14 months of age. This translates to daily gains of around 1.5 lb. per day or more from weaning tot breeding. It’s important to know what your mature cows weigh on average since these guidelines use a percent of their weight as a target for your development program. Let’s look at a herd with mature cows that average 1,300 pounds and you use the 65% rule of thumb to make sure first calf heifers reach approximately 845 pounds at breeding. If those heifers weaned off in the fall at 525 pounds they would need to gain 320 pounds over 7 months, or 1.5 pounds per day. For most herds these guidelines arrive at very acceptable breeding results given the nutrition inputs that are required to achieve them. There are a number of ways to get heifers to their target weights but progress needs to be monitored closely starting at weaning and continuing right up to breeding.
More recent research that originated from work out of Nebraska has looked at herds where they have moved the breeding target weight of replacement heifers down to 55% of mature cow weight. That would mean, from the example above, that herds with a 1,300 pound mature cow size would produce replacement heifers that are ready for first breeding at approximately 715 pounds rather than 845 pounds, or 130 pounds lighter compared to 65% of mature cow weight. The logical reason for managing to a lighter body weight at first breeding is to help decrease nutritional inputs. These inputs would be over the winter period and usually when supplemental nutrition is a requirement to achieve targeted gains. Bred heifers managed this way are targeted to make highly efficient gains while on pasture over the summer, rather than putting weight on during the winter with supplemental feeds. It also reduces the temptation to overfeed young females that can actually impair their ability to become pregnant even though they are cycling and develop deposits of udder fat that can impair long-term milk production. As you can see, too much is not desirable and we all know that coming up short leaves you disappointed with late breeders and possibly lower pregnancy rates.
There are cow-herd producers that use this lower percentage of mature body weight guideline for their replacement heifer program very successfully, but one needs to pay attention to make sure overall reproductive rates do not suffer. If you have been managing to the higher end of the range and want to make a change, consider moving down incrementally rather than taking an abrupt step down all in one year. Puberty is closely associated with breed, age and weight. Make sure you are accounting for these factors when managing your herd to a lighter replacement heifer target weight. Heifers born early in the calving season are simply older when selecting replacements. Use genetic selection in bulls that will sire heifers that reach puberty at a younger age. Don’t forget the impact that nutrition has on reaching your target body weight.
Overall, make sure you have some extra heifers in your replacement heifer group that will provide you with the right amount of females needed to maintain your herd size and match your forage base. If everything goes right you may have some surplus females to sell. If you hit a few bumps along the road you should still then have adequate numbers to maintain your cow herd. Have a nutrition program that includes meeting growing heifer protein needs as well as vitamin and mineral requirements. The addition of a well-fortified supplement including an Iono-phore like Bovatec® or Rumensin® can help heifers reach weight gains needed to initiate and maintain reproductive processes.
Look up your local CRYSTALYX® dealer for help designing a program that is right for your heifers and your feeding program. There are a number of supplements like the CRYSTALYX® Breed-Up® products, Replacement Heifer™ or Iono-Lyx® B-300 that will help you keep your young females on track for a successful breeding season and a profitable future.
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Rumensin® is a registered trademark of Elanco Animal Health