Reproduction in Domestic Animals

114 NC Friggens, M Bjerring, C Ridder, S Højsgaard and T Larsenwas analysed using the Ridgeway ELISA-kit (RidgewayScience Ltd, Gloucestershire, UK). Milk samples werepipetted, diluted and distributed using a Biomek 2000 Ó(Laboratory Automation Workstation, Beckman Coulter,Fullerton, CA, USA). Milk samples (25 ll, diluted1 + 2 with water) were handled according to themanufacturer’s instructions, however incubation R4was increased to 1 h 30 min. Plates were read using aspectrophotometer ⁄ fluorometer, Fluostar Ó (BMG Labtechnologies,Offenburg, Germany) (575 nm). Analyseswere performed in 96-well plates; two sets of sevenstandards (0–30 ng ⁄ ml), locally made using milk froman ovariectomized cow and ethanolic progesteronesolutions, and two sets of two control samples wereused for every analysis and plate. For the low and highcontrols, the intra assay precision (CV%) was 14.9 and1.4, respectively; the inter-assay precision (CV%) was32.7 and 20.1, respectively; and the average inaccuracy(bias) was +0.82 and )0.60 ng ⁄ ml, respectively.The time series of milk progesterone measurementswas examined for gaps longer than 14 days with noprogesterone values. All data following such gaps wereexcluded. Further, the entire cow-lactation was excludedif there was insufficient data to identify the end of thepostpartum anoestrus period (i.e. the time series did notstart at calving and there were less than five measurementsbefore the cow was detected to have elevatedprogesterone and resumed oestrous cycles). The resultingdata represented information during 578 lactationsfrom 380 cows. The total number of milk progesteronemeasurements was 55 036.Timing of inseminations was based on visualdetection of oestrus backed up by activity meterindications (DeLaval, Tumba, Sweden). Farm staffhad no access to the progesterone data. Visualobservations for oestrus signs were made daily at06:00, 12:00 and 16:00, each period lasted 20 min. Cowsshowing oestrus earlier than 35 days from calving werenot inseminated to that oestrus. All cows wereinseminated to oestrus regardless of other managementfactors such as age, milk yield, and whether the cow wasdesignated for subsequent culling. Inseminations werecarried out the same day for oestruses detected at themorning observation, and the next morning foroestruses detected in the afternoon and evening.The model being testedThe model being tested here has been described in detailby Friggens and Chagunda (2005). Briefly, the model isbased on the cow always being in one of threereproductive states (Status), these are: postpartumanoestrus (Status 0), oestrus cycling (Status 1), andpotentially pregnant (Status 2). In the model thesestatuses are mutually exclusive. The Status the cow wasfound to be in by the previous run of the model is alwaysthe Status at the start of the current run. By default, thecow is assumed to be in Status 0 at calving. The model isdynamic and deterministic, designed to run each time anew trigger input occurs using both the current andprevious values. The main model inputs are a smoothed(extended Kalman filter) progesterone concentrationand slope. Inseminations and pregnancy determinationsare also included as inputs. To make use of other knowneffectors of reproductive performance that are notnecessarily reflected in progesterone concentrations,the model is designed to incorporate a number ofadditional inputs. However, the model is designed tofunction in the absence of these additional inputs(although with some loss of accuracy in some outputs).The model outputs are all reproductive Status specificwith the exception of days to next sample (DNS) whichis calculated in each model run regardless of reproductiveStatus. Days to next sample is an important outputwith respect to the progesterone measurements beingautomated. It is designed to feedback to the samplingsystem so that the frequency of milk sampling (i.e.progesterone measurement) can be varied according tothe predicted likelihood of a future reproductive eventsuch as onset of oestrus cycles. The other model outputsare: risk of prolonged postpartum anoestrus, risk andtype of ovarian cyst (i.e. prolonged luteal or follicularphase), onset of oestrus, likelihood of a potentialinsemination succeeding and likelihood of being pregnant(following oestrus).The shift from Status 0 (postpartum anoestrus) toStatus 1 (oestrus cycling) is caused by two consecutivesmoothed progesterone measurements above the thresholdvalue (LThresh) which is 4 ng ⁄ ml. (If EOD inputsare available these can also provoke this shift). Asdescribed by Friggens and Chagunda (2005), once a cowis in Status 1 the shift to Status 2 is caused by thesmoothed progesterone value decreasing belowLThresh. This shift generates a model-detected indicationof oestrus. If no insemination is recorded in thefollowing 5 days, the cow automatically reverts to Status1. If there is a timely insemination and subsequentprogesterone concentrations increase, then the cowremains in status 2 (potentially pregnant) as long asthe model predicted likelihood of pregnancy remainsabove a pregnancy threshold. Typically, if progesteroneconcentrations decrease, then the model shifts backfrom Status 2 to Status 1.The model tested in the present study contained thefollowing major modification relative to the modeldescribed by Friggens and Chagunda (2005). Visualinspection of the earliest progesterone profiles collectedshowed a number of oestrus-like decreases in progesteronethat did not decrease below LThresh. To dealwith this an additional threshold, HThresh was introduced(6 ng ⁄ ml). This allowed identification of these‘high-progesterone oestruses’ conditional on the maximumprogesterone concentration in the preceding cyclebeing greater than 15 ng ⁄ ml, and the present decreasebeing >10 days since a preceding oestrus.The model tested in the present study also containedthe following minor modifications relative to the modeldescribed by Friggens and Chagunda (2005). The slopeof the progesterone profile is used, for example in thefunction calculating the predicted likelihood of AIsuccess. The slope can have extreme values particularlywith short intervals between measurements, thus anadjusted slope (a sigmoid transformation) was usedinstead. Over the normal range this makes virtually nodifference but it caps the extremes. In Status 2, when thecalculated likelihood of pregnancy (LikePreg) decreasesÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag