Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2001
Publication Date: 6/1/2001
Citation: SHORT, R., GRINGS, E.E., MACNEIL, M.D. A MODEL FOR DETERMINING RISK OF PINE NEEDLE ABORTION IN CATTLE CALVING AT DIFFERENT TIMES OF THE YEAR. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2001. v. 52. p. 174-176. Interpretive Summary: Cow-calf producers in areas with Ponderosa pine trees are at risk of production loses due to pine needle induced abortions. The level of risk is determined by a combination of the risk of cows eating pine needles and the risk of an effect once pine needles are eaten. Little can be done to alter the risk of an effect once needles are eaten, but producers can minimize risk of consumption by changing season of calving. Calving in summer or fall will have little risk of pine needle abortion. For producers in areas with similar cold temperature profiles as at Miles City, MT, risk of abortions is highest for cows calving from January 15 through May 1. Locations with a lower risk of cold temperature will have a lower risk of abortions and a shorter time period where calving season has a high risk.
Technical Abstract: Abortions in cattle caused by consumption of needles from Ponderosa pine trees (PN) are a significant risk in the Western United States. This risk is determined by a combination of the risks of consumption of PN and of an effect once PN are consumed. Risk of abortions once PN have been consumed is affected by amount consumed and stage of pregnancy. We assumed that low temperature is one of the primary risk factors affecting consumption. Previous data on risks associated with stage of pregnancy were used to determine the regression of day of gestation when PN are eaten on the probability (PD) of abortions. This regression was: PD = -88 + .74 d with 0 PD being from 0 to 120 d and 1.0 PD being from 255 d through calving. A 107-year data set (1893 to 2000) for Miles City, MT, was obtained from the National Weather Service to determine the probability of temperatures being </= -10 deg C (PT). Daily PT were averaged for bimonthly (1st and 15th) intervals and were 0 from April 15 through Oct. 15 and then were .05, .19, .33, .45, .55, .56, .59, .49, .39, .19, and .07 from Nov. 1 through April 1. Cows were simulated to calve at 24 bimonthly intervals (1st and 15th). Daily PT were multiplied by the PD curve of an abortion and summed across days to obtain a cumulated relative risk (CRR) by calving date. CRR was 1 for cows calving Nov. 1 and 4, 9, 15, 23, 31, 39, 42, 45, 43, 39, 33, 27, 20, 15, 10, 6, 4, 2, 1, 0, 0, 0, and 0 for each of the 23 subsequent bimonthly periods. CRR was high for cows calving from Jan. 15 through May 1 with maximal risk on March 1. We conclude that date of calving may be used as a tool to decrease risk of PN induced abortions in cattle with minimal risk occurring for cows calving from June 1 through Dec. 15.