The Interaction Of Blood Urea Nitrogen And Semen Type In A Fixed Time AI Program In Angus Cross Beef Cows–A Pilot Study

Abstract

Cows fed excess dietary protein had increased blood urea (BUN), altered uterine fluid composition, decreased uterine pH, and reduced fertility. The objective of the study was to examine the effect of BUN concentrations at the day of breeding on the fixed time artificial insemination (AI) pregnancy rate in Angus cross beef cows inseminated with fresh extended or frozen thawed semen. Angus cross beef cows (N=266) from seven locations were synchronized with a CO-Synch + CIDR protocol for fixed time AI. Cows were inseminated with either fresh extended (3 million sperm, Caprogen® extender) or frozen thawed semen (20 million sperm; egg yolk extender) from two AI sires. On the day of AI, blood samples were collected for BUN analysis. In the study population, there were 165 cows with  18 mg/dL (mean 11.6) and 101 cows with > 18 mg/dL (mean 23.2) BUN concentrations. Accounting for significant variables such as AI sire (P<0.001) and semen type by BUN level interaction (P<0.05) in the model, there were no differences in the fixed time AI pregnancy between BUN groups (P>0.05). However, the fixed time AI pregnancy rate was different between fresh and frozen semen, 61.1% and 52.4%, respectively (P<0.05). The AI pregnancy rates were significantly different between sires 1 and 2, 66.7% and 44.0%, respectively (P<0.05). A semen type by BUN concentration interaction for AI pregnancy was recorded. No AI sire by BUN concentration or AI sire by semen type interactions were recorded. There was a quadratic relationship observed for locations’ mean BUN concentrations with locations’ mean AI pregnancy rates. Lower and higher mean location BUN concentrations had reduced AI pregnancy. Cows with >18% mg/dL BUN concentrations inseminated with fresh semen had a 61.2% AI pregnancy rate. Our findings suggest that the negative effect of increased BUN concentrations may be overcome by utilizing fresh semen extended in an extender with catalase (Caprogen®) in a fixed time AI programs.