Veterinary Wisdom

Burning money

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The other day, a few of our doctors were discussing heifer pregnancy rates. A top-notch client had recently posted a 57% pregnancy rate. This is an annual pregnancy rate, not a conception rate, and it represents the highest replacement heifer pregnancy rate we have seen in the history of our practice. This farm’s high pregnancy rate is achieved through a conception rate of 70% and a service rate of 81%. This is a big deal, but why?

There are two obvious reasons: cost and performance. Cost because feeding, housing and caring for replacement animals is expensive. Indeed, for many farms, net herd replacement cost is their second-largest expense.

There are no advantages to feeding, housing and caring for heifers for even one day more than whatever age at first calving is optimal for your dairy. If the total cost is $3 per day, for example, extending the age at first calving for 30 days costs $90 per head. If you calve 500 heifers per year, that is an unnecessary loss of $45,000 annually.

Increasing the pregnancy rate means more animals calve at or near the optimum age. A pregnancy rate of 57% means that about 57% of your heifers will calve in a range of age of just 21 days, and 82% will freshen within a range of 42 days, or two cycles. 

Herds in our veterinary practice have an average annual heifer pregnancy rate of 29%. This means, on average, 29% of heifers will calve within a 21-day age range, and 50% will calve within two cycles.

The cost of this inefficiency to our practice’s farms varies. For example, farms that use a predominantly timed A.I. system for first breeding will have very few animals calving in too young, with nearly all the animals that do not calve within an optimal window being too old. Most of the excess cost to those farms comes from feeding, housing and caring for them for extra days.

For farms that rely on heat detection for the first insemination, the losses may add up differently. Farms typically adjust the voluntary waiting period based on the average age at calving. Herds that use mostly heat detection will have more equal amounts of heifers that get pregnant too young and too old in contrast to the timed A.I. herds where the outliers are almost always too old.

So, while heat detection herds do incur the cost of excess days, they also suffer decreased performance on roughly the same number of animals because they calve too young. Calving too young means less milk production. There is at least some evidence that milk production never recovers for these animals, meaning they will produce below their potential for every lactation. Thus, the herd will produce below its potential as well. These herds suffer from excess costs and decreased performance.

The herds in our practice achieve an average heifer pregnancy rate of 29% by having a conception rate of 53% and a service rate of 55%. These same herds average an adult cow pregnancy rate of 31%, and they do this with a conception rate of 47% and a service rate of 67%. Even though the average herd uses much more sexed semen in heifers than cows, they achieve a higher conception rate in heifers versus cows but a lower pregnancy rate because of poor service rates. There is no acceptable reason why heifers should have a service rate less than adult cows, especially 12 percentage points lower.

This is a good news-bad news situation. Yes, the bad news is that heifer pregnancy rates are lower because of poor service rates. The good news is that poor service rates are simple to fix.

For example, heifers typically respond well to prostaglandin injections, and expecting more than 75% to be bred following one injection is not at all unreasonable. Plus, prostaglandin is cheap; the cost of one injection is usually about the cost of one-half extra day of raising. Veterinarians can design effective breeding protocols using prostaglandins or other drugs. Activity systems also work well on heifers and can be a great aid to increasing service rates.

So, why do so many herds tolerate low heifer service rates?

First, some just do not see the urgency. Heifers may not get moved to the breeding pen on time, and/or farmers may wait for a certain number of days beyond the voluntary waiting period before administering any injections.

Second, some send their animals to custom raisers, and they may be unwilling to demand better reproductive performance.

Third, a few probably feel there is an advantage to waiting for a natural heat. There is no science available to suggest that a non-induced heat leads to better fertility than an induced heat, and there is plenty of scientific evidence that some induced heats lead to better fertility. Thus, waiting for a natural heat is just burning money.

Fourth, a few herds may have poor heifer growth rates and may have many animals that simply are not big enough to breed when they reach the voluntary waiting period.

What can we do?

Increase heifer service rates. If our clients achieved the same service rate for heifers as cows, their average heifer pregnancy rate would be around 36%, which is not bad. However, if they matched our top herd’s rate of 81%, the pregnancy rate would be closer to 45%, which is great. This should not be difficult to accomplish.

Jim Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at [email protected].

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