ABORTIFACIENT RESPONSE AND PLASMA VASOCONSTRICTIVE ACTIVITY AFTER FEEDING NEEDLES FROM PONDEROSA PINE TREES TO CATTLE AND SHEEP

Consumption of needles from Pinus ponderosa (PN) during late pregnancy causes cattle, but not sheep, to abort. This differential response ma y be caused by differences in ruminal mircoflora or postabsorptive mea tabolism. Pine needles were fed (2 kg . d(-1) or .4 kg . ewe(-1). d(-1 ) mixed with corn silage. In Exp. 1, cows were assigned at 250 d of pr egnancy to feed treatments (T): 1) silage, 2) PN+ silage, or 3) pretre ated with sheep ruminal fluid and fed PN+ silage. Interval to parturit ion was 34.3, 11.3, and 8.3 d for the T1, T2, and T3, respectively (T1 vs T2 + T3, P >.01; T2 vs T3, P>.5). Inoculation with sheep ruminal f luid did not alter activity of the abortifacient agent of PN. In Exp. 2, pregnant and nonpregnant ewes and cows were fed silage or PN mixed with silage, and plasma was analyzed for uterine vasoconstrictive acti vity in an in vitro placentome perfusion bioassay. Consumption of PN d ecreased interval to parturition in cattle (P<.01) but not in sheep (P <.05) in plasma form nonpregnant and pregnant cows and ewes. The PN-fe d ewes had a greater incidence of dead lambs at parturition (0/8 vs 5/ 8 for control vs PN-fed, P<.01). We conclude that pregnancy is not req uired for increased vasoconstrictive activity induced by pine needles, that sheep and cattle do not differ in ruminal metabolism of the abor tifacient compounds in PN, and that species differences are subtle and due to postdigestive differences in response to the abortifacient age nt.