Journal: J Anim Sci 1995 73: 198-205.
Abstract: Pregnant cows were fed pine needles (PN, 2 kg.cow-1.d-1) mixed with the diet to determine factors that affect abortion response. In Exp. 1, treatments were used to determine the effects of experimental stress and pelleting of pine needles. Pelleting needles and experimental stress delayed abortion response (P < .01). Stress-induced delay was associated with abnormal patterns of progesterone and cortisol (P < .01). In Exp. 2A and 2B, the role of the corpus luteum (CL) in abortion response to PN consumption was investigated by regressing the CL with prostaglandin F2 alpha. Regression of the CL and PN feeding reduced interval to parturition, but the effect of PN feeding was less when the CL was regressed (PN x CL, P < .01). The progesterone increase in response to experimental stress was decreased by CL regression (P < .01). In Exp. 3, melengestrol acetate (MGA) was fed (0, 2, or 4 mg.cow-1.d-1) in addition to PN. Parturition was blocked more effectively as dose of MGA increased (P = .075), but only parturition was blocked rather than the effects of PN. In Exp. 4, CL regression was blocked by feeding ketoprofen. Ketoprofen delayed response to PN, but the effect was only temporary (P < .01). Our conclusions are that 1) experimental stress delays abortion response to PN by increased concentrations of progesterone, 2) pelleting PN decreases their abortifacient activity, and 3) abortions caused by PN can be blocked by feeding a progestin or a prostaglandin inhibitor, but these compounds do not block the primary abortifacient effects of PN.