Influence of nitrogen and sulfur intake on bovine uterine pH throughout the luteal phase.
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Previous research has reported that diets high in protein and sulfur decreased uterine pH in cattle. The objective of this study was to determine the effect of high N and high S intake on uterine pH. Holstein (n = 15) and Angus-cross (n = 5) heifers (337.5 8.4 kg of BW) were randomly assigned to 1 of 4 diets: control (CON; 13.4% CP and 0.17% S); high nitrogen (HN; CON plus urea supplement); high sulfur (HS; CON plus calcium sulfate); or both high nitrogen and sulfur (HNS). Diets were individually fed at 2.6% of BW on a DM basis using Calan gates and estrus was synchronized to occur on d 13 (d 0 = start of dietary treatment). Blood samples were collected on d -2 and daily (d 1 to 28) at 1400 h to determine concentrations of plasma urea nitrogen (PUN), sulfate (d 1, 4, 8, 12, 16, 20, 24, and 28), and progesterone. Uterine pH was measured on d 16, 20, 24, and 28 (d 3, 7, 11, and 15 of the estrous cycle). There was a treatment, time, and treatment by time interaction (P < 0.01) on concentrations of PUN. There was an effect of treatment (P < 0.01) on concentrations of sulfate, with concentrations being increased in HS compared with CON, HN, and HNS (P < 0.01), and HNS increased compared with CON (P < 0.01) and HN (P < 0.01). Uterine pH was increased in HN and HNS compared with CON (P < 0.02), whereas HS was not different from any treatment (P > 0.11). There was no effect of time (P = 0.26) or treatment by time interaction (P = 0.71) on uterine pH. In summary, uterine pH was increased in HN and HNS compared with CON, whereas HS was intermediate and was associated with increased concentrations of PUN.