The Cow-Calf Manager

Livestock Update, May 2007

Dr. John B. Hall, Extension Animal Scientist, Beef, VA Tech and
Dr. Dee Whittier, DVM, Extension Veterinarian, VA Tech.

New CIDR Based Synchronization System Gives Another Fixed Time AI Option

Last year we reported on a Fixed Time AI system (CO-Synch+CIDR) that has become widely recommended in the industry for AI breeding of postpartum cows on a single day. (See October 2006 Cow Calf Manager - http://www.ext.vt.edu/news/periodicals/livestock/aps-06_10/aps-367.html ).  Our work in Virginia indicates this program results in pregnancy rates of 55 % to 65% to fixed-time AI (FTAI).  In field studies in Missouri, the CO-Synch+CIDR system averaged 65% pregnancy rate in over 3000 cows in 35 herds.  The range in their studies was 57% to 72% AI pregnancy rate.  It should be noted that all herds were well managed with cows in good body condition.
Recently, we have been investigating another system in cooperation with Dr. Mike Day at The Ohio State University and Dr. Ramanathan Kasimanickam from the VA-MD College of Veterinary Medicine.  The new system (Figure 1) only keeps the CIDR in place for 5 days and delays AI until 72 hours after CIDR removal.  This allows for a long phase of follicular development that may increase oocyte (egg) quality and AI success.

Results with CO-Synch+ 5 day CIDR in Virginia
The results with this system are extremely promising.  Before we go any further, it should be noted that this is still considered an experimental system.  We are planning large scale field studies with this program to gather more data over a large range of environments and management conditions.  Producers interested in this system should be aware that it is considered a promising experimental system and is not currently recommended by the Beef Reproduction Task Force. 

The experiment led by Drs. Day and Kasimanickam investigated the need for two doses of prostaglandin F2a (PG).  The study was conducted in 830 cows from 6 VA Dept. of Corrections herds.  The key results were:

• Two doses of PG (one at CIDR removal and another one 8 to 12 hours later) were needed for highest pregnancy rates.
• CO-Synch+ 5 day CIDR with 2 doses of PG resulted in an average FTAI pregnancy rate of 69.5 %
• The range in FTAI pregnancy rates across locations was 63.8% to 75.2%.

Clean-up bulls need to be monitored carefully
The study also reinforced the need to monitor clean-up bulls during the breeding season.  At all locations, bulls had passed a full pre-breeding exam.  However, the percentage of cows open after AI that became pregnant to the clean-up bull varied from 35.1 % to 88.5 % (Table 1).

Table 1.  Effect of location on percentage of cows not pregnant to AI that became pregnant to natural service

Adapted from Kasimanickam et al., 2007

The causes of decreased pregnancy rates at two locations appear to be related to libido, penile deviations, or failure to find cows in estrus.  The bull’s libido and ability to seek and breed cows cannot be determined in a standard breeding soundness exam.  Bulls need to be observed carefully especially during the first 5 days after introduction to the herd.  Producers need to observe bulls mounting and successfully breeding cows in order to insure success with natural mating.

Another key management strategy is to observe cows for estrus during the mid-point of the breeding season.  If too many cows appear to be in heat, then producers need to identify the possible cause and correct the problem.  Causes include bull failure, cow body condition, cow age, and heat stress.

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