Association between elevated plasma urea nitrogen and elevated ammonia concentration in follicular fluid of preovulatory follicles in early lactation dairy cows

Two experiments were conducted to study the relationship of blood plasma urea nitrogen (PUN) concentrations with NH3, urea nitrogen, K, Mg, P, Ca, and Na concentrations in fluid of preovulatory follicles (experiment 1) and the relationships of PUN concentration and stage of estrus cycle with ammonia and urea nitrogen concentrations in uterine fluids (experiment 2) in early lactation dairy cows. Mean PUN levels were used to distribute cows into two groups: cows with PUN ≥ 20 mg/dl (HPUN), and cows with PUN \u3c 20 mg/dl (LPUN). In experiment 1, blood and follicular fluids from preovulatory follicles of 38 early lactation dairy cows were collected on the day of estrus (day 0) 4 h after feed was offered. Follicular fluid NH3 was higher (P \u3c 0.01) in HPUN cows (339.0 μmol/L ± 72.2) compared to LPUN cows (93.9 μmol/L ± 13.1). Follicular fluid urea N was higher (P \u3c 0.001) in HPUN cows (22.4 mg/dl ± 0.4) compared to LPUN cows (17.0 mg/dl ± 0.3). PUN and follicular fluid urea N were correlated (r2 = 0.86) within cows. In experiment 2, blood and uterine fluids were collected from 30 cows on day 0 and on day 7. Uterine fluid NH3 was higher (P = 0.05) in HPUN cows (1562 μmol/L ± 202) than in LPUN cows (1082 μmol/L ± 202) on day 7, but not on day 0. Uterine fluid urea N was higher (P \u3c 0.001) in HPUN cows than in LPUN cows on day 0 (26.9 mg/dl ± 1.3 and 20.4 mg/dl ± 0.7) and day 7 (26.5 mg/dl ± 1.1 and 21.4 mg/dl ± 1.1). There was a correlation (r2 = 0.17) between PUN and uterine fluid urea N within cows. The results of this study indicate that high PUN concentrations were associated with elevated NH3 and urea N concentrations in the preovulatory follicular fluids on the day of estrus and in the uterine fluid during the luteal phase of the estrous cycle in early lactation dairy cows. Elevated NH3 or urea N concentrations in the reproductive fluids may contribute to reproductive inefficiency in dairy cows with elevated plasma urea nitrogen due to embryo toxicity