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♦ What Would Another 5% Be Worth?
♦ What Would Another 5% Be Worth?

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Sarah Thorson, Beef Marketing & Education Manager, Genex

In October 2011, GENEX was working on a project at Four G's Ranch in Republic, Missouri, using GenChoice™ semen. Using the HeatWatch® Estrus Detection System, they were breeding cows that had been synchronized using the 7-day CO-Synch + CIDR program. At timed A.I. (TAI) the cows were all given an injection of GnRH and bred using GenChoice male-sorted semen. It was also noted if the cow had exhibited estrus based on the HeatWAtch system. Cows were then rebred approximately 20 hours later using GenChoice female-sorted semen. Dr. Scott Poock, Assistant Extension Professor at the University of Missouri, performed fetal sexing via ultrasound at approximately 70 days post A.I. What they found surprised them. A very high percentage of the cows that had not shown heat at TAI, and had been bred at TAI using male-sorted semen and then with female-sorted semen 20 hours later were found to be pregnant, and carrying heifer calves! This led GENEX to the hypothesis that the cows which hadn't shown heat at TAI (and GnRH) just needed a little more time to boost pregnancy rates.

The Science
This hypothesis fits in very well with the science of the hormones of the estrous cycle. GnRH has been shown to cause ovulation 28 to 30 hours following injection. Sperm cells need to be in the reproductive tract approximately eight hours to undergo capacitation before they are capable of fertilizing the freshly ovulated egg. Delayed breeding of females that are not in heat at the time of GnRH injection helps to properly align the viable life of the ovum and sperm following insemination.

Although the original hypothesis was formed using sexed semen, two groups of researchers decided to see if it fit with the use of conventional semen.

The Results in Heifers
Jordan Thomas and Dr. David Patterson, from the University of Missouri, designed a trial to test the theory, which Jordan called Split-Time Artificial Insemination. Jordan synchronized 931 heifers across three locations using the 14-day CIDR-PG protocol.

The heifers were assigned to one of two treatments. The heifers in the first group were inseminated at 66 hours post PG injection regardless of estrus expression. Estrus expression was determined using ESTROTECT™ patches that were applied at the time of PG injection on day 30. Estrus was defined as removal of >50% of the rub-off coating.

In the second treatment group, heifers expressing estrus prior to GnRH administration at 66 hours received A.I. concurrent with GnRH. Heifers failing to express estrus prior to GnRH administration were A.I. bred 20 hours after GnRH.

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In treatment one, heifers that exhibited estrus had a 52% A.I. pregnancy rate, heifers not exhibiting estrus at TAI had a 34% A.I. pregnancy rate. In treatment two, heifers exhibiting estrus and A.I. bred at 66 hours had a 56% A.I. pregnancy rate, heifers that were not in estrus that underwent delayed breeding at 20 hours post GnRH had a 49% A.I. pregnancy rate. There was a 15% pregnancy rate advantage among non-estrous heifers across the two treatment groups. Overall pregnancy rates across both heifers exhibiting estrus and not exhibiting estrus were improved by the split-time breeding at 46% vs. 54% (see Table 1).

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The research indicates that when using the 14-day CIDR-PG protocol, producers can attain higher heifer pregnancy rates by delaying insemination of non-estrous heifers through a Split-Time A.I. approach.

What About Cows?
Jordan also identified 951 cows across nine locations to study the effects of Split-Time Artificial Insemination in mature cows. He set his experiment up similarly to the heifer trial except he used the 7-Day CO-Synch + CIDR protocol.

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In treatment one, cows that exhibited estrus had a 65% A.I. pregnancy rate, cows not exhibiting estrus at TAI had a 45% A.I. pregnancy rate. In treatment two, cows exhibiting estrus and were A.I. bred at 60 to 66 hours had a 63% A.I. pregnancy rate. Cows that were not in estrus, that underwent delayed breeding at 20 hours post GnRH, had a 50% A.I. pregnancy rate.

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The researchers saw a numeric advantage to delayed TAI for cows, however, not a statistical advantage. In addition, they did not observe an increase to overall pregnancy rates between the two protocols. Jordan Thomas explained that generally, the difference between two pregnancy rates must have a P value less than .05 to be considered statistically significant. Therefore, although there may appear to be a numeric advantage in delaying insemination of non-estrous cows, the data set does not offer a statistically significant improvement over a conventional Fixed-Time A.I. approach. At this time the University of Missouri is not recommending the use of Split-Time Artificial Insemination in cows.

Matthew Markwood and Dr. Jack Whittier from Colorado State University also wanted to study the effects of delayed breeding on mature cows. In the spring of 2013 they identified 1101 mature beef cows at five ranches in Colorado, Wyoming and Nebraska and synchronized them using a variation of the 7-Day CO-Synch + CIDR Protocol. Instead of TAI occurring at 60 to 66 hours and delayed breeding at 20 hours as it had in the University of Missouri trial, they performed TAI at 58 hours and delayed breeding at 18 hours for those not in heat.

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Once again the researchers used ESTROTECT patches as a way to evaluate if the cow was in heat at 58 hours post CIDR removal. The cows were broken into four subgroups; half of all cows both with patches rubbed off at 58 hours post CIDR removal and not rubbed off were inseminated. The remaining half of both subgroups was inseminated 18 hours later at 76 hours post CIDR removal.

Delayed TAI in cows that had not shown heat based on the ESTROTECT patch at 58 hours post CIDR removal resulted in a 6.1% numeric improvement to pregnancy rates (45.6% vs. 51.7%) compared to those inseminated at 58 hours.

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While the data from Colorado State University showed a numeric advantage to delayed breeding in mature cows, it doo, did not show a statistical advantage. However, Dr. Whittier's group intends to further study the positive trend they observed with their protocol. More research is needed in cows to fine tune the protocol and find if a true statistical advantage does exist. Dr. Whittier points out that a 5% potential increase in pregnancy rates in non-estrus cows (2 to 3% overall increase) is worth some level of risk, and given that the downside risk is low, may be a management strategy many producers will consider this A.I. season.

Dr. Whittier also noted that while pregnancy rates may be improved by using a delayed breeding strategy in mature cows, there are some other management considerations to be made because of the suckling calves. Dr. Whittier suggests that calves be separated from the cows when cows are worked through the chute for GnRH injection at 58 hours and then placed with the cows that were inseminated at that time. This allows for the second group of cows that are to be A.I. bred at 76 hours to be held separately until A.I. without the need to re-sort their calves.

ESTROTECT patches do add some additional upfront costs, and delayed breeding causes need for some additional time and labor. However, the chance to increase conception rate on the first day of the breeding season can more than make up for expenses in the form of more A.I. calves and a heavier, more uniform calf crop!

Sources
Thomas, J.M. 2013. Split-time artificial insemination: delayed insemination of non-estrous beef cows and heifers to optimize fertility in fixed-time artificial insemination protocols. MS Thesis. Univ. of Missouri, Columbia.
Whittier, J. and Markwood, M. 2013. Increasing timed-A.I. pregnancy rate in beef cows by delaying insemination in cows not showing heat by 58 hours after CIDR removal when using the 7-day CO-Synch + CIDR protocol.


January 2014


 
 
 
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