Effects of Ingestion of Ponderosa Pine Needles

Consumption of Ponderosa pine needles by late-pregnant beef cows results in the premature delivery of a viable calf. We have demonstrated the presence of a factor(s1 in plasma from cows fed pine needles that specifically increased uterine arterial tone (i.e., decreased arterial diameter) in vitro. This study was designed to investigate changes in uterine blood flow and steroid secretioduptake by the gravid uterus of cows fed pine needles to induce premature parturition. Sixteen beef cows were laparotomized on d 240 of gestation, and an electromagnetic bloodflow probe was placed around the uterine artery supplying the gravid horn. Cows were randomly assigned on d 250 of gestation to a control (n = 8; 8.2 kg/d of alfalfa hay) or pine needle (n = 8; 2.7 kg/d of pine needles + 5.5 kg/d of alfalfa hay) diet. Uterine blood flow was monitored, and systemic blood [uterine arterial and[orl jugular venous) and uterine venous blood samples were collected daily between 0630 and 0800, just before feeding. Five of eight cows fed pine needles calved prematurely (average day of gestation = 260.2 f .61 compared with cows fed the control diet, which calved on 287.6 * 3.4 d of gestation. Uterine blood flow in the control cows remained constant from d 250 through the day of parturition. In contrast, uterine blood flow of cows fed pine needles that calved early decreased progressively ( P e .Ol ) , declining to 25.2% of its original value by the day of parturition. Cows fed the pine needle-diet and cows fed the control diet exhibited similar declines in progesterone concentrations in systemic blood and uterine venous blood during the last 4 d of pregnancy. Although estrone and estradiol-17P both increased during the last 9 d preceding parturition in both cows fed the control diet and those fed the pine needle diet, cows fed pine needles exhibited reduced (P e .OO21 concentrations of both estrogens in both systemic and uterine venous blood. We conclude that consumption of pine needles progressively reduces uterine blood flow to the gravid horn and that this reduction induces the onset of a premature parturition as evidenced by normal prepartum changes in steroid secretion.