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Managing pregnant heifers: Monitor, monitor, monitor!

Terry Batchelder for Progressive Dairyman Published on 31 December 2018

After the time and attention that has been invested in raising and breeding heifers, it can be easy to transition heifers to the pregnant pen and put them on autopilot until calving. However, there are some critical things that need to be monitored during this time period to ensure we are on target to meet dairy goals, and that those goals align to being a profitable dairy farm.

Monitor the amount

It’s fairly common knowledge that replacement heifers account for 15 to 20 percent of a dairy’s total cost. However, that number is completely dependent upon the number of replacement heifers being raised. Today, many dairies have lost focus on how many heifers they need to raise, and we are seeing a glut of excess heifers like never before.



More and more dairies are starting to realize that it’s to their financial detriment to house and feed more heifers than they actually need, and are beginning to tightly monitor this number to improve efficiencies.

If you’re not closely monitoring the total number of heifers you’re raising against the number you actually need, then use this article as a starting point.

Table 1 details how many replacements are needed to maintain herd size, based on age at first calving (AFC) and cull rate.

Age at first calving

It’s important to factor these variables in because they determine what age animals enter the milking herd and the turnover rate.


As you can see, a herd that is calving at 21 months with a cull rate of 30 percent will only need to raise 58 heifers for every 100 cows. However, a herd calving at 24 months with a cull rate of 40 percent will need 88 heifers for every 100 cows.

For either scenario, raising more heifers than actually needed is likely resulting in a ripple of consequences. From the risks and management challenges of overcrowding, to the increase in unnecessary feeding costs that ultimately result in reduced cash flow.

While raising excess heifers might have made sense in the past, it is not the economic reality of today. When everyone is raising excess heifers, there is no market for them. By sticking with the amount of replacements you actually need, you can put more focus on raising a better quality replacement animal.

Monitor growth

Pregnant heifers still need to maintain a fairly aggressive growth schedule to ensure they are on track to attain 95 percent of mature bodyweight (MBW) in the two to three weeks pre-calving. We often focus on 85 percent MBW post-calving.

However, in order for us to meet this number, we need to ensure she’s at 95 percent MBW prior to calving as a portion of her bodyweight is directly associated with the bodyweight of the calf and fetal fluids. The rate of growth is also directly associated with the MBW of cows on your farm, not the industry average or your neighbor’s farm.

Table 2 shows the average daily gain (ADG) needed at each key growth phase to achieve two distinctively different bodyweight targets – one with a MBW of 1,450 pounds and the other at 1,650 pounds.


mature bodyweight

By actively monitoring growth, you can keep heifers on pace to achieve MBW targets and catch an issue before it becomes a major problem. However, if you realize your pregnant heifers are not on track to attain 95 percent MBW pre-calving because they came into the pen too small, there is very little, if anything, that can be done to make up for a lost opportunity.

For instance, a heifer that was bred at 800 pounds, but should have been bred at 950 pounds, needs to achieve a weight of 1,562 pounds pre-calving. She now only has 280 days to make up the growth. This would require an average daily gain of 2.72 pounds per day (1,562 pounds - 800 pounds = 762 pounds of bodyweight gain required/280 days = 2.72 pounds), which is impossible to achieve while still maintaining proper body condition.

Seventy-five percent of heifer growth – not just weight gain, but frame and structural growth – happens during the first 12 months of life. Once she becomes pregnant, we are past that physiological development, and she begins to partition nutrients differently. Thus, less nutrients become available for structural growth.

When dairies try to add growth at this stage, animals often become overconditioned and pay the consequences at calving. We see heifers short in stature, but with excess body condition. The birth canal now has more fat and less structural room; thus, we see increased issues at calving time and potentially metabolic issues as well. The challenges then continue into milk production.

If you realize your pregnant heifers are not on track to achieve 95 percent MBW pre-calving, the best thing to do is reassess the calf and heifer pre-breeding program immediately to ensure heifers are 55 percent of the MBW of your third-lactation cows at the time of breeding. Using your own herd data to set the target for MBW is key to having a profitable goal.

If you bred them at the right size, then keeping them on target should be fairly easy if you routinely monitor them. Adjust the diet as needed for seasonal and environmental challenges to consistently meet their nutrition requirements.

Monitor the business model

The heifer business model is a critical component of the dairy business model. As with all business models, there has to be a clear understanding of profitability. Unfortunately, there seems to be a “disconnect” at this time between the business model or goal versus the biological needs of the animal to maintain the proper type and rate of growth.

Table 3 shows data from three farms we’ve worked with. As you can see, all three farms were aiming for AFC to be between 20 and 22 months.

Average age at first fresh

The data also showed the lifetime milk production on all these farms was greater for the animals that entered at 23 to 25 months.

Farm 1 came closest to accomplishing the proper growth on heifers that calved between the ages of 20 to 22 months, while Farm 3 had the greatest “disconnect” between the business model and heifer growth performance. It’s likely that the heifers on Farm 1 had a chance to achieve better structural growth through a more aggressive feeding program.

Imagine how well these herds would have been doing if 80 percent of their heifers were entering during the farm’s most profitable age group. If you haven’t looked at this data for your own operation, now is the time to reevaluate your entire heifer business model. Discover the most profitable AFC for your dairy and the actual amount of replacement animals you need to be raising. Then put a disciplined plan in place to raise them for the most profitable outcome.

The best dairies we work with have a clearly defined heifer business model that coincides with the biological growth and performance of the heifer. They also implement a disciplined monitoring and decision-making system to ensure animals are on the proper growth performance track that ensures the greatest potential for future milk production.

They know what the most profitable AFC is for their herd, and they align growth goals, management, diets and facilities to attain the most profitable outcome. If a heifer “looks” ready to breed, they take the time to check her growth measurements and age, and follow the management plan.

They do not breed her if the data doesn’t indicate she’s ready, even if she shows signs of heat. Having weight scales, corrals and record systems in place to accurately determine trends for the heifer program is key to lifetime performance.  end mark

Terry Batchelder is a dairy technical specialist with Cargill Animal Nutrition. Email Terry Batchelder.