Reproduction in Domestic Animals

116 NC Friggens, M Bjerring, C Ridder, S Højsgaard and T Larsenthresholds were applied. The probabilities had to begreater than 0.95 and the weighted number of observationshad to be greater than 3. The weighted number ofobservations was calculated as:X(absðt tmidpoint Þþ1Þ 1 ;where t is time from the midpoint of the segment for anygiven observation. For observations 7.5, 5, 2.5 and0 days from the midpoint the individual weights were;0.12, 0.17, 0.29 and 1, respectively. The threshold ofthree for the sum of the individual weights correspondsto an observation frequency of two progesterone measurementsper 3 days for evenly spread observations, ora hole of )3 to +3 days from the midpoint in anotherwise complete set of observations.In order to avoid the same oestrus being repeatedlyidentified as the rolling 15-day window moves throughthe progesterone time series, the following filtering ruleswere applied. In addition to p being >0.95, p for thepreceding observation had to be >0.90. Once anobservation was ratified, then subsequent observationsmeeting the above criteria were not accepted as ratifiedunless the probability had decreased to 8 ng ⁄ ml(Mahalanobis distance is scale invariant, i.e. it assessesthe shape of the segment and not the absolute level ofthe segment). The total number of ratified oestruses was679. The shape of the progesterone profile shown inFig. 1 is that which is associated with oestruses thatoccur after a prior period of luteal activity. Oestrusesthat occur in conjunction with the end of the postpartumanoestrus period do not match this profile andhave thus been excluded from the test of the models’ability to detect oestrus.Pregnancy determinationThe ability of the model to identify cows as pregnantfollowing insemination was evaluated in two ways. Bydefinition, the progesterone profile following confirmedoestruses should always be identified by the model as thecow being in Status 2 (pregnant). The proportion ofcases in which this was so was calculated, and anyexceptions were examined. For those inseminations thatdid not result in a confirmed pregnancy (n = 375), thedistribution of time intervals between insemination andmodel detected pregnancy failure (return from Status 2to 1) was examined.Sampling frequencyThe effects of reducing the progesterone measurementfrequency on model performance were evaluated bygenerating new data sets from the original, full, progesteronedata in which a proportion of the originalprogesterone measures were removed. This was done byimposing a minimum interval between consecutiveprogesterone measurements (within each cow-lactationtime-series). For minimum intervals of 1, 2, 3, 4 and5 days, the resulting data sets contained: 42 459, 26 455,16 756, 8713 and 1535 progesterone measurementsrespectively. With each of these reduced data sets, themodel was run and the proportion of ratified oestrusesthat was detected by the model using the original dataset was calculated. In addition, the model was run usingonly those progesterone measurements that it wouldhave requested if it had been running in real-timeaccording to the model output DNS function. This is avariable sampling frequency as described previously(and in Appendix). The total number of progesteronesamples used in this case was 11 957.Results and DiscussionConfirmed oestrusesOut of 121 confirmed oestruses, 104 were associatedwith a model-detected oestrus based on a decrease insmoothed progesterone below 4 ng ⁄ ml. An additional16 of the confirmed oestruses were model-detected onthe basis of the supplementary oestrus detection rulethat smoothed progesterone decreased below 6 ng ⁄ mlhaving previously been >15 ng ⁄ ml. Thus, the model asimplemented detected 99.2% of the confirmed oestruses,whereas the simpler model (4 ng ⁄ ml threshold) resultedin 85.6% of confirmed oestruses being detected.The majority of studies in the literature have used3ng⁄ ml as a threshold for detecting oestrus (Lammingand Bulman 1976). Thus, a discrepancy exists betweenthis definition and the fact that insemination of cowshaving these ‘high progesterone oestruses’ still resultedin conception. A possible explanation for this discrepancycould be related to the smoothing of the progesteroneprofiles. The very nature of smoothing is that it isresistant to extreme values. Indeed, this was one reasonfor using a threshold of 4 rather than 3 ng ⁄ ml in themodel. So, if insufficient low progesterone values areavailable, the smoothed profile may not decrease below4ng⁄ ml even when individual observations are