Rebecca A. Vraspir, Adam F. Summers, Doug O’Hare, Larry D. Rowden, and Rick N. Funston. Summarized by Aaron Berger, Nebraska Extension Educator
Progestin – based estrus synchronization protocols that utilize melengestrol acetate (MGA) or controlled internal drug release (CIDR) devices can be effectively used for synchronizing estrus in heifers. A study conducted by the University of Nebraska – Lincoln compared these two protocols to one another utilizing artificial insemination (AI) along with natural service.
The study involved 1385 yearling heifers. The heifers were randomly assigned to one of two treatments shown in Figure 1 http://go.unl.edu/m3oy (From the 2014 Nebraska Beef Cattle Report “Comparison of Long-term Progestin-Based Synchronization Protocols on Fixed-time AI Pregnancy Rate in Beef Heifers”).
Both groups of heifers were initially bred using a fixed time artificial insemination (FTAI) protocol by 10 AI technicians. Semen from a single bull was used to reduce variation in pregnancy rates due to semen quality. Fixed- time pregnancy rates, natural service pregnancy rates and final pregnancy rates were not signicantly different between the two treatments (See Table 2 http://go.unl.edu/kvrr, from the 2014 Nebraska Beef Cattle Report “Comparison of Long-term Progestin-Based Synchronization Protocols on Fixed-time AI Pregnancy Rate in Beef Heifers”).
SUMMARY
1. The use of an MGA or CIDR estrus synchronization protocol was equally effective when used in a fixed time artificial insemination program.
2. There was no significant difference in natural service (AI clean up) pregnancy rates between the two treatments.
3. Overall final pregnancy rates were not statistically different between the two treatments.
4. An economic analysis showed that the MGA treatment protocol cost approximately $19 less to produce a pregnant heifer than the 14-day CIDR protocol, primarily due to cost differences between the treatments.
When evaluating whether to use an MGA or CIDR estrus synchronization protocol, the advantages and disadvantages of each should be considered.
The following are advantages and disadvantages of using MGA for estrus synchrony as compared to the CIDR protocol:
• MGA must be consumed consistently every day over a 14 day period to be effective. This can be easily accomplished when heifers are being fed a complete ration daily. It is harder when heifers are gazing out and are being fed a supplement containing the MGA.
• MGA requires daily labor for the delivery of the product.
• MGA takes two less trips through the chute than the CIDR protocol.
• MGA costs less for the progestin product per head than a CIDR does.
The following are advantages and disadvantages of using a CIDR for estrus synchrony as compared to the MGA protocol:
• CIDRs can be placed in the heifers and it is known that the heifers are getting the progestin dose needed without daily feeding. This can be an advantage when heifers are grazing and do not need to be fed on a daily basis.
• The daily labor needed for delivery of the progestin in the CIDR protocol is less than when utilizing MGA. Labor is concentrated on the days when the CIDR is placed and removed.
• The CIDR protocol requires two more trips through the chute than the MGA protocol.
• The cost per head is more for the progestin product using a CIDR than it is for MGA.
Producers planning to utilize estrus synchronization and artificially inseminate heifers this spring, should evaluate which of these two estrus synchronization protocols best fit their resources and management. For more information on this study, please see the 2014 Nebraska Beef Cattle Report “Comparison of Long-term Progestin-Based Synchronization Protocols on Fixed time AI Pregnancy Rate in Beef Heifers.” (http://go.unl.edu/574h). For more information on recommended estrus synchronization protocols visit the Resources page at the Applied Reproductive Strategies in Beef Cattle (http://beefrepro.unl.edu/resources.html) website.
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