Supplementation of corn dried distillers' grains plus solubles to gestating beef cows fed low-quality forage: II. Impacts on uterine blood flow, circulating estradiol-17β and progesterone, and hepatic steroid metabolizing enzyme activity.

The objective of this study was to investigate the effects of supplementing dried distillers' grains plus solubles (DDGS) during late gestation on uterine blood flow (BF), circulating steroid hormones and hepatic steroid metabolizing enzymes, and calf and placental weights. Multiparous beef cows were randomly divided into a control group (CON; = 15) consuming a diet containing 90% corn stover and 10% corn silage (DM basis) for ad libitum intake and a treatment group (SUP; = 12) consuming the same diet and DDGS (0.3% of BW). Corn silage inclusion was increased to 30% as gestation progressed to meet increasing caloric requirements. Ipsilateral and contralateral uterine BF and cross-sectional area (CSA) of each uterine artery were measured by Doppler ultrasonography on d 180, 216, and 246 of pregnancy. Contralateral BF and CSA increased ( < 0.01) as gestation advanced. Ipsilateral BF and CSA was affected by a treatment × day of gestation interaction ( < 0.05). A main effect of treatment ( = 0.02) and day ( < 0.01) was observed for total BF; BF increased over time and SUP cows had greater BF than CON cows. Circulating concentrations of both progesterone (P4) and estradiol-17β (E2) were affected by an interaction of treatment and day ( < 0.01). Concentrations of circulating E2 steadily increased throughout the study and were greater in CON cows than in SUP cows by d 242. Concentrations of P4 also increased over time; P4 of CON cows was greater than that of SUP cows by d 242. Uridine 5'-diphospho-glucuronosyltransferase (UGT) and cytochrome P450 1A (CYP1A) activity increased with advancing gestation ( < 0.01). There was greater UGT activity ( < 0.05) and a trend for greater CYP1A activity ( = 0.06) in SUP cows than in CON cows. Activity of cytochrome P450 3A was greater ( < 0.01) in SUP cows and decreased ( < 0.05) with advancing gestation. Supplementing DDGS to cows fed low-quality forage during late gestation increased uterine BF but decreased circulating E2 and P4 concentrations and altered hepatic steroid metabolizing enzyme activity. It was anticipated that enzyme activity would reflect circulating hormone levels; however, our data suggests the observed increases in BF are not driven by alterations in hormone concentration. Therefore, further research is warranted to elucidate the underlying mechanisms.