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Tips to fine-tune dairy heifer reproductive programs

Fabio Lima Published on 18 July 2014

For a variety of reasons, dairy heifer reproductive performance is not a primary focus on many dairies even though it is critical to future success.

But that shouldn’t be the case on your farm. There are a number of tools, including estrous synchronization and timed-A.I. protocols, that can ensure your heifers are bred on time and are ready to enter the milking herd and help you meet your herd goals.

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Lessons from history

As explained during the 2013 Dairy Cattle Reproductive Council Annual Meeting, these tools have taken a while to fine-tune – estrous synchronization and timed-A.I. programs have had different levels of success for dairy heifers than for lactating cows.

Initially, timed A.I. for dairy heifers was unable to match conception rates obtained when dairy heifers were inseminated after heat detection. Study results ranged from 25.8 percent to 45.5 percent, which is considerably lower than the approximately 60 percent conception rate expected from heat detection.

It’s important to note that these studies were mostly based on implementing an Ovsynch protocol. However, reproductive physiology of dairy heifers is somewhat different than that of lactating cows.

For instance, a larger proportion of heifers have estrous cycles with three waves of follicle development and reduced ovulation to the initial GnRH treatment. These factors can compromise the performance of a seven-day program.

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Timed A.I. became a more viable alternative for heifers when the interval between GnRH and induced luteolysis was reduced to five days and a controlled internal drug release (CIDR) containing progesterone between the first dose of GnRH and the prostaglandin dose (PGF-2) was included.

This protocol has since become known as the “five-day timed-A.I.” program. Conception rates ranged from 53.1 percent to 59.5 percent, paving the way for effective timed-A.I. programs for dairy heifers.

Refining heifer protocols

Additional studies were conducted to refine the five-day timed-A.I. program.

Interestingly, only 23 percent of the heifers in the trials had more than one corpus luteum (CL) five days after the dose of GnRH. This suggests that ovulation to the initial dose of GnRH was probably low and perhaps not critical to improve fertility.

A 2011 study investigated the effect of removing the first GnRH from the protocol. The results revealed no differences in conception rate. However, ovulation at onset of the protocol and the proportion of heifers with increased progesterone concentrations at breeding was increased for heifers that received GnRH.

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It is possible no benefits were observed in response to the GnRH given at the beginning of the protocol because the new CL formed, resulting from follicle turnover in response to the GnRH, may have been too immature to undergo luteolysis in response to the PGF-2.

A follow-up study looked at the combination of GnRH at the start of the five-day timed A.I. to see if two doses of PGF-2 – at day five and day six of the protocol – could improve heifer fertility.

Researchers found this did increase ovulation and the number of heifers with lowered progesterone concentrations at breeding, which ultimately optimized conception rates.

Dollars and sense

Based on these outstanding conception rates, a thorough economic analysis was completed to compare reproductive programs for dairy heifers with timed A.I. and estrous detection.

A computer simulation was used to calculate pregnancy rates, average time to pregnancy, total costs per breeding and cost per pregnancy for the following strategies:

1. 100 percent timed A.I.

2. 100 percent heat detection

3. Timed A.I. for first breeding and heat detection for the remaining services

4. Timed A.I. for first breeding followed by insemination upon heat detection or resynchronized insemination after non-pregnancy diagnosis

The results showed:

  • Timed A.I. for first service lowered the cost per pregnancy versus estrous detection alone. However, benefits were less as estrous detection rates increased (Table 1).
  • Programs with 100 percent timed A.I. were less expensive than programs with exclusive use of insemination at detected estrus if heat detection fell below 70 percent.
  • When additional timed A.I. was incorporated into the breeding program to resynchronize non-pregnant heifers, it further benefited the program with low estrous detection rates. However, for higher estrous detection rates, 70 percent and 80 percent, the benefits were minor or nonexistent.
  • Incorporation of heat detection after one timed A.I. was superior to timed A.I. alone only when heat detection rate was 60 percent or more.
  • Most of the changes in costs per pregnancy were due to the increased feed expense of feeding heifers longer when they did not become pregnant in a timely manner.

Breeding program costs and efficiencies

Therefore, the results indicate that combining timed A.I. for first insemination with heat detection and additional timed A.I. for heifers diagnosed as non-pregnant maximized the economic success of a reproductive program. But that benefit disappeared when estrous detection rates were equal to or greater than 70 percent.

Research recap

Ultimately, programs to synchronize the estrous cycle that result in conception rates of 55 percent to 60 percent are a feasible option for breeding dairy heifers.

Computer simulations indicate that adding timed A.I. to breeding programs is economically beneficial when compared to breeding following detected heats when the heat detection rate is less than 70 percent.

In fact, when detection of estrus in heifers is less than 70 percent, timed A.I. can be economically justifiable as the sole breeding method or as part of a breeding program that relies on A.I. upon heat detection.

You can learn more about heifer synchronization or see the DCRC-created heifer synchronization protocols by visiting the Dairy Cattle Reproduction Council website. PD

Dr. Fabio Lima is a veterinarian with Cornell University’s Department of Population Medicine and Diagnostic Sciences in Ithaca, New York. You can contact him by email.

References omitted due to space but are available upon request. Click here to email an editor.

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