PINE NEEDLE ABORTION IN CATTLE - EFFECTS OF DIET VARIABLES ON CONSUMPTION OF PINE NEEDLES AND PARTURITION RESPONSE

Cows that consume needles from Pinus ponderosa (PN) abort, but little is known about variables that affect consumption or response. These ex periments were conducted to test the effects of several variables on p ine needle-induced abortion. Cows were placed on experiment at 250 d o f pregnancy and were either given ad libitum (AL) access to PN separat e from other feed sources or the PN were ground and fed (2 kg.cow-1.d- 1) mixed with the diet. In Exp. 1, cows were assigned to a 2 x 2 facto rial experiment with adequate (AP) vs high-protein (HP) diets and no s traw vs AL straw (S). All cows ate PN and aborted, and there were no e ffects (P > .5) on interval to parturition (IP). Consumption of PN (kg /d) was increased by HP (P < .1). In Exp. 2, cows were assigned to fiv e treatments to test the effects on response to PN of magnesium supple mentation, weathering the PN, and using silage rather than hay as the basal diet. Consumption of PN shortened IP (P < .01), but magnesium, w eathering PN, and silage-based diets did not decrease the response to PN (P > .5). In Exp. 3, cows were assigned to five treatments to test the effects of aging needles after they were ground, feeding bentonite , and feeding a complete mineral supplement. Pine needles decreased IP (P < .01), and the effects of PN were greater when PN were aged or be ntonite or minerals were added (all P < .05). IN Exp. 4, cows were ass igned to six treatments to test the effects of controlled vs AL access to feed, and within AL access to feed, whether protein level of the d iet or salt-sulfur blocks affected response. Feeding PN reduced IP, an d effects were greater when PN were mixed with the diet than when they were available for AL access (P < .01). There were no effects (P > .2 ) of protein level or salt-sulfur blocks. In Exp. 5, cows were assigne d to five treatments to test the effects of limit feeding vs AL availa bility of the basal diet and basal diets of hay vs corn silage. Access to PN decreased IP only when the basal diet was hay (P < .01), becaus e silage-fed cows did not eat PN. Our conclusions are that 1) feeding high levels of protein increased PN consumption but not abortion rate, 2) weathered or aged needles had activity similar to or greater than that of dried needles, 3) feeding corn silage prevented cows from eati ng pine needles, and 4) none of the other diet variables prevented con sumption of PN or response to PN.