2009: Estrus-AI interval and fixed-time AI pregnancy rates in beef cows inseminated with fresh extended or frozen thawed semen


 
Estrus-AI interval and fixed-time AI pregnancy rates in beef cows inseminated with fresh 

extended or frozen thawed semen 
 

T. Wisemana, R. Kasimanickama, J. M. DeJarnetteb, W. D. Whittiera 

aDepartment of Large Animal Clinical Sciences, Virginia-Maryland Regional College of 
Veterinary Medicine, Blacksburg, Virginia 24061, USA 

bSelect Sires Inc., Plain City, OH 43064, USA 
 

We hypothesize that fresh extended semen will improve the AI pregnancy rate compared 
to frozen thawed semen due to its increased longevity in female reproductive tract. The objective 
of this trial was to determine the effect of semen type on fixed-time AI pregnancy rate in relation 
to estrus-AI interval in beef cows synchronized with progesterone based fixed-time artificial 
insemination (AI) protocols. Angus cross beef cows (N=180) were synchronized with CO-
Synch-CIDR protocols for a fixed-time AI. Briefly, cows were synchronized with 100 μg of 
gonadotropin releasing hormone (GnRH) + controlled internal drug release insert (CIDR) on Day 
0, 25 mg of PGF2α and CIDR removal on Day 7 and 100 μg GnRH on Day 10 (67 h from CIDR 
removal) at AI (CO-Synch-CIDR). A subset of cows (N=110) received a Heatwatch pressure 
sensor at CIDR removal to determine the time of estrus. Cows were divided into two groups, 
inseminated at 47h (early) and 67h (late) from CIDR removal with either 3 million cells of fresh 
extended or 20 million cells of frozen thawed semen.  

Results indicated that cows inseminated at 67h had numerically higher fixed time AI 
pregnancy compared to cows inseminated at 47h [44.4% (40/90) vs. 33.3% (30/90); P=0.13]. 
Cows inseminated with frozen thawed semen had similar fixed time AI pregnancy compared to 
fresh extended semen [40.8% (31/76) vs. 37.5% (39/104); P=0.66]. AI-estrus interval was 
divided into three groups < 0 h (AI occurred before estrus), 0 to 16 h and > 16 h (AI occurred 16 
h after estrus). The AI pregnancy outcome for fresh semen for the 3 estrus-AI intervals was 
similar to frozen semen (Figure 1).  
  

 

In conclusion, the fresh semen did not improve the pregnancy rate compared to frozen 
semen in relation to estrus-AI interval. 
 
Keywords: Beef cows, semen type, fresh semen, synchronization, pregnancy rate 

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