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Monday, February 25, 2002
FULL TEXT PAPER
Synchronization of Estrus in Heifers with MGA and PGF2a
by Darrel J. Kesler
TAKE HOME MESSAGES
- Reproductive management of dairy heifers is given a low priority. Ironically, heifers are far easier to settle than their counterpart, the lactating cow. Estrus synchronization programs are available to permit breeding of the heifers with AI that require minimal cost and labor.
- The administration of melengesterol acetate for 14 days following by an injection of PGF2a 17-19 days later results in a short window of highly fertile estrus.
Dairy heifers are often bred via natural service because they are not prioritized. However, heifers generally have high fertility and synchronization procedures are available. Syncro-Mate B7 was available; however, it is currently off the market. Although Ovsync has been effectively used in dairy cows, it is not effective and should not be used in dairy heifers.
MGA AND PGF2aα
MGA, melengesterol acetate, effectively suppresses estrus and is approved by FDA for estrus suppression in heifers. Although the estrus subsequent to long term, ~14 days or more, MGA treatment is synchronized, fertility is subnormal. This is because follicles persist and the viability of the oocytes is compromised. The follicles, however, will ovulate and subsequently develop into a normal corpora lutea. Therefore, several years ago researchers developed the strategy that the synchronized corpora lutea could be lysed with PGF2a and ensuing estrus would be synchronized and fertile. Several studies have been conducted using this strategy and substantial research has demonstrated that it is a highly effective way to synchronize estrus in heifers. This research was primarily done in beef heifers and the beef industry quickly adopted the procedure and continues to use it today. Therefore, it has passed the tests of time and applicability on the farm. The procedure is as effective in dairy heifers and involves the following steps.
- Daily feeding of MGA7 at a rate of 0.5 mg per head per day for 14 days.
- A waiting interval of 17-19 days before administering PGF2α (25 mg Lutalyse7 or 500 μg of Estrumate7)-the 19 day interval yields a narrower window of estrus.
- Breed upon the estrus detection 1-7 days after the injection of PGF2a
We are conducting a study on various methods of breeding: at estrus, at estrus and at 72 hours for heifers not exhibiting estrus, and at 60 hours along with an injection of GnRH.
- MGA7 is supplied as a supplement. Each pound of supplement contains 200 mg of MGA mixed primarily with soybean hulls. The supplement should be mixed with ground corn so that each heifer receives one pound containing 0.5 mg of MGA per day. Label instructions are available to help with calculations.
- Insure that your heifers are familiar with eating out of the same bunk every day. Beware of aggressive or docile heifers. Group feeding assumes that each heifer will receive an equal amount of feed; however, select heifers can destroy that assumption.
- Insure that the MGA supplement is mixed thoroughly with the ground corn. Also, clean your mixing facility to insure that traces of MGA are not within the next batch of feed.
- Feed the MGA daily for 14 days. Do not skip any days and provide the feed in the morning each day.
- Administer PGF2a, either 5 cc of Lutalyse7 or 2 cc of Estrumate7, 17 to 19 days after the last day of MGA feeding. The first day after MGA feeding is equal to day 1. Most research is based on an interval of 17 days; however, more recent research demonstrates that a 19 day interval will result in a higher synchrony. Do not administer before day 17 as our research demonstrates that synchrony and fertility will be compromised.
- Short term administration of MGA will not cause weight gain or fattening of dairy heifers.
- This procedure is most effective in heifers that are exhibiting estrous cycles. Therefore, feed heifers to an age and weight that insures that most are exhibiting estrous cycles before administering MGA and PGF2a.
- Breeding at a predetermined time after PGF2a has been done successfully; however, higher pregnancy rates will be obtained if heifers are bred upon the detection of estrus. The predetermined time we successfully used was 72 hours after PGF2a. I would recommend estrus detection, but if heifers are not observed in estrus by 72 hours you may want to inseminate them. If they subsequently exhibit estrus, they should be inseminated again. This assumes that semen cost is reasonable; however, if expensive semen is used then only heifers displaying estrus should be inseminated.
- This procedure requires significant lead time and planning. The time from the first day of MGA feeding to the injection of PGF2a is over a month.
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