Summary and Implications
The objective was to examine the relationship between circulating blood or plasma urea nitrogen concentrations (BPUNC) and reproductive efficiency in beef heifers and suckled beef cows. Data from nulliparous heifers (n = 284) as well as primiparous (n = 241) and multiparous (n = 806) beef cows were compiled across 15 experiments. A single blood sample collected from each female during estrous or ovulation synchronization was analyzed for BPUNC. Only females that were maintained on the same nutritional management scheme (pasture or coproduct-based drylot ration) for at least 1 week prior to synchronization though the first 21 days of the breeding season were included in the analysis. Based on the data, when cattle are allowed to adapt to a nutritional management scheme prior to breeding and maintained on that diet through the first 21 days of the breeding season, BPUNC is not negatively associated with first-service pregnancy rates. Instead, a positive relationship was observed
Iowa State University
Gunn, Patrick J.; Lundberg, Allie L.; Cushman, Robert A.; Freetly, Harvey C.; Amundson, Olivia L.; Walker, Julie A.; and Perry, George A.
"Effect of Circulating Blood or Plasma Urea Nitrogen Concentrations on Reproductive Efficiency in Beef Heifers and Cows,"
Animal Industry Report:
AS 662, ASL R3066.
Available at: http://lib.dr.iastate.edu/ans_air/vol662/iss1/27