Small Ruminant Research 52 (2004) 203–209

Predicting the onset of parturition in the goat by determiningprogesterone levels by enzyme immunoassay

Laura A. Singera, M.S.A. Kumara, William Gavinb, Sandra L. Ayresa,∗a Department of Biomedical Sciences, School of Veterinary Medicine, Tufts University, 200 Westboro Road, North Grafton, MA 01536, USA

b GTC Biotherapeutics, 300 Charleton Road, Spencer, MA 01562, USA

Received 30 January 2003; received in revised form 21 May 2003; accepted 3 June 2003

Abstract

There are currently a few methods that can be used to assess the time of impending parturition in the goat, especially ifexact breeding dates are unknown. One indicator of the onset of parturition is a decrease in the doe’s blood progesterone levelapproximately 24–30 h prior to parturition. Laboratory serum/plasma progesterone assays commonly require 24 h or more toobtain results, as well as being expensive. This study was designed to evaluate whether semi-quantitative enzyme immunoassay(EIA) progesterone kits could be used to determine plasma progesterone levels in does during late gestation, and whether acorrelation could be drawn between the test result and the time of parturition. Plasma samples were collected twice daily from16 pregnant does starting on day 143 of pregnancy and ending 1 day following parturition. The plasma progesterone levelsindicated by the three EIA kits were compared to one another and to a radioimmunoassay, and assessed for any relationshipto the actual time of parturition. Test results indicating low plasma progesterone levels (<1.0–2.8 ng/ml) from the StatusPro (Synbiotics), TARGET (Biometallics), and PreMate (Camelot Farms) and tests were found to be correlated 100, 83 and100% with the onset of parturition within 24 h. Test results indicating high plasma progesterone levels (>5.0–7.8 ng/ml) fromthe Status Pro, TARGET, and PreMate tests were found to be correlated 100, 100, and 82.2% with delayed parturition. Theradioimmunoassay results concurred with the progesterone ranges given for Status Pro, TARGET, and PreMate tests in 75.7,58.8 and 53.7% of the cases, respectively. The results of this study indicates that any one of the commercially produced EIAprogesterone tests can be used to predict with a high degree of accuracy the likelihood of parturition occurring within the next24–30 h. These tests are simple to perform and cost effective.© 2003 Elsevier B.V. All rights reserved.

Keywords: Goat; Progesterone; Parturition; RIA; EIA tests

1. Introduction

Predicting the onset of parturition in the doe can bedifficult and unsuccessful particularly when the breed-ing date is unknown. Although signs such as a de-crease in a doe’s rectal temperature or an increase in

∗ Corresponding author. Tel.:+1-508-887-4605;fax: +1-508-839-7091.E-mail address: sandra.ayres@tufts.edu (S.L. Ayres).

her restlessness (Smith and Sherman, 1994) have beenused to indicate a possible impending birth, an accu-rate and reliable method of predicting parturition hasnot been reported.

Goats proceed through the same three stages of par-turition as that observed in other species. Stage I canlast for 2–12 h in goats, and the doe may show signsof discomfort and restlessness during this time. Thecervix begins to relax and light uterine contractionspush the fetus towards the cervix, causing it to dilate.

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204 L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209

Stage II or active labor can last from 1 to 3 h depend-ing on the number of kids and the process is completedwith Stage III, or expulsion of the placenta (Braun,1997a). Assessing the doe’s progress through thesestages can be critical especially during the occurrenceof suspected dystocia. As the cervix remains dilatedfor only 2–3 h, if a kid is not presented within thistime, a condition known as ringwomb, or incompletecervical dilation can ensue (Braun, 1997a). A doe withringwomb has likely progressed through both StagesI and II without successful presentation of a kid, anda Caesarian section may be warranted. Likewise, ifa kid is malpositioned and cannot engage the cervix,Stage II may fail to follow Stage I. There may bequestion as whether or not to perform a Caesariansection in such a situation. If a kid is malpositionedpreventing Stage II from being initiated, other kids inthe uterus may die if surgery is not performed. How-ever, if a Caesarian section is performed too earlybefore a kid is fully developed, the kid may die ofcomplications. If a quick, on-site method was avail-able to evaluate a doe’s delivery status, a more in-formed decision could be made about whether to in-tervene in delivery, to the benefit of both the doe andkid.

One possible method of assessing parturition is bythe measurement of maternal plasma progesteroneconcentration. Maintenance of pregnancy in the goatrequires progesterone secretion from the corpus lu-teum throughout gestation and cessation of lutealfunction is essential for the onset of parturition (Currieet al., 1988). Previous studies have shown a significantdecrease in a doe’s plasma progesterone concentra-tion to occur approximately 24 h prior to parturition(Currie et al., 1988; Currie and Thorburn, 1977; Umoet al., 1976; Thorburn and Schneider, 1972). Althoughradioimmunoassay (RIA) could be used to detect thisdecrease in the progesterone concentration, it must beexecuted in a laboratory and the results are not imme-diately available (Braun et al., 1988). A quick methodthat could be used to determine a doe’s plasma pro-gesterone concentration in the field would be of bene-fit. One such method, an enzyme immunoassay (EIA)test, is available. Semi-quantitative EIA tests havebeen previously evaluated for their ability to predictparturition in the bitch (England and Verstegen, 1996)and cows (Matsas et al., 1992). The EIA tests givequick results, are sensitive to plasma progesterone

concentrations as low as 1.0 ng/ml, are relativelyinexpensive, and can be performed outdoors.

In this study the plasma progesterone levels in theperi-parturient period by RIA and the efficacy of com-mercially available EIA progesterone kits to predictimpending parturition in the goat is excluded.

2. Materials and methods

2.1. Animals

Sixteen goats used in the study were either Alpine×Saanen× Toggenburg does, or crosses thereof, thatwere naturally bred by three bucks. Records ofbreeding dates were kept. The pregnancy status wasdetermined by ultrasound between 5 and 7 weeks ofgestation.

2.1.1. Sample collectionThe 15 ml blood was collected by jugular venipunc-

ture and drawn into EDTA tubes twice daily at7:00 a.m. and 7:00 p.m. Blood collection began onday 143 of pregnancy and continued until 1 day fol-lowing partus. The plasma was separated and dividedinto three aliquots in Corning cryogenic vials andstored at−20◦C freezer.

2.2. Solid phase RIA

A Coat-A-Count Progesterone RIA kit (DiagnosticProducts, Los Angeles, CA) was used to determinethe progesterone concentrations of each of the plasmasamples. The RIA kit had been previously found to besuccessful at measuring caprine plasma progesterone(Epelu-Opio and Madej, 1988). The RIA has a sensi-tivity of 0.03 ng/ml, an interassay coefficient of vari-ation (CV) of 4.7%, and an intra-assay CV of 8.0%,respectively. The 100�l of the calibrator or plasmasamples were placed into the polypropylene proges-terone antibody-coated tubes included with the kit.Each of the samples was measured in duplicate. The1�l [ 125I] progesterone (31,453±770 counts/min) wasdispensed into each of the coated and plain tubes. Alltubes were incubated at 4◦C overnight. The sampleswere decanted and a gamma counter was used to de-termine the counts per minute for each of the samples.

L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209 205

The counts per minute were converted to progesteroneconcentrations by a logit–log transformation.

2.3. EIA tests

For all the EIA tests, the kit instructions were fol-lowed. Plasma samples were used for progesteronedetermination. Plasma separation is fast and conve-nient compared with serum separation.

Each ICG Status Pro Canine Ovulation Timing TestKit (Synbiotics, San Diego, CA) contained material for20 tests. The number of spots visible on the test surfacecorrelated according to the kit literature with proges-terone concentrations as follows: one spot, 7.5 ng/mlor greater; two spots, 2.0–7.0 ng/ml; three spots, lessthan 2.0 ng/ml progesterone.

Each TARGET Rapid Bovine Progesterone Kit(BioMetallics, Princeton, NJ) contained material forsix tests. A standard color comparison was providedwith the kit with the following progesterone con-centrations: white, 5.0 ng/ml or greater; light blue,1.0–5.0 ng/ml; and bright blue, less than 1.0 ng/mlprogesterone.

Each PreMate ovulation timing test kit (CamelotFarms, College Station, TX) contained materials for24 tests. The progesterone concentrations of the highand low standards were not available. The resultswere read as follows: the same color intensity orlighter than the low progesterone standard; or thesame color intensity or darker than the high proges-terone standard; or a color intensity between that ofthe low and high progesterone standards. The plasmaprogesterone concentrations of six of the low pro-gesterone standards and six of the high progesteronestandards were determined by RIA described before.

2.4. Statistical analysis

The progesterone concentrations obtained by RIAwere analyzed using a repeated measure ANOVAand Tukey’s multiple comparisons test to determineif there was a significant drop in progesterone con-centrations 24–30 h prior to parturition (SAS, 1990).The accuracy of the EIA tests at predicting parturi-tion within 24–30 h was determined by dividing thenumber of samples in which a test result was correctin predicting parturition time by the total number ofsamples showing that specific test result. The accu-

racy of the EIA tests in determining progesteroneconcentrations was found by comparing EIA testresults with results obtained by the RIA.

3. Results

The average gestation length for the 16 does was149 days± 3 days (mean± S.D.). One of the 16births was complicated by dystocia due to a breechpresentation requiring assistance, but all other birthsrequired minimal to no assistance. Two of the 16 doesdelivered triplets, six delivered twins, and eight deliv-ered singletons. One doe was excluded from the RIAand EIA test statistical analyses due to an incompletenumber of plasma samples.

3.1. Radioimmunoassay

The RIAs were performed in two separate groups.The standard curve for a total of 138 plasma sampleswas found to bey = 0.244x − 0.567, and ther2 =−0.998. The maximum binding percentage for the as-say was found to be 70.8. The standard curve for a totalof 117 plasma samples from the second set of sevengoats was found to bey = 0.292x − 0.543, and ther2 = −0.998. The maximum binding percentage forthe assay was found to be 72.5. A significant proges-terone concentration decrease (n = 15) was found tooccur 24–30 h prior to delivery (P < 0.01,Fig. 1). Theprogesterone concentration was found to decline anaverage of 4.17± 1.90 ng/ml (n = 15) during the sig-nificant drop. The average progesterone concentrationjust before parturition (range: 0–9 h pre-partum) wasfound to be 1.48±0.69 ng/ml (mean±S.D.; n = 15).

3.2. EIA tests

Progesterone concentrations in a total of 177 plasmasamples were estimated using each of the three EIAtests. The EIA tests were evaluated for their abilityto predict accurately whether or not delivery wouldoccur within a 24–30 h time period from the time atwhich the blood sample was drawn (Table 1). Theprogesterone concentration of the low and high pro-gesterone standards of the PreMate test determinedby RIA were 2.80 ± 0.05 and 7.54 ± 0.36 ng/ml(mean± S.D.), respectively.

206 L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209

0

2

4

6

8

10

12

Days from Delivery

Pro

ges

tero

ne

(ng

/ml)

-4 -3 -2 -1 0 1

*

Fig. 1. The average progesterone concentrations with respect to delivery date were calculated from 15 goats. Blood samples were takenat 7:00 a.m. and 7:00 p.m. daily from day 143 of gestation until the day following delivery. Notice the significant (P < 0.01) drop inprogesterone concentration occurring 1 day prior to delivery (day−1).

Table 1Comparison of three commercial kits to predict parturition timing in the goat

Test kit Progesterone levels as determined by RIA (ng/ml)

High levels Mid-range levels Low levels

Status Pro 7.5 ng/ml or greater: 1 bright spot,100% (55/55) of samples showingthis test result were collected morethan 24 h prior to parturition

2.0–7.0 ng/ml: 2 bright spots, 94.4%(34/36) of samples showing this testresult were collected more than 24 hprior to parturition

Less than 2.0 ng/ml: 2 bright spotsand a faint color in spot #3, 2.0%(13/25) of samples showing thisresult were collected 24 h or lessprior to parturition; 72.0% (18/25)of samples showing this result werecollected 30 h or less prior toparturition. Three bright spots,100% (17/17) of samples showingthis test result were collected 24 hor less prior to parturition

TARGET 5.0 ng/ml or greater: white, 100%(41/41) of samples showing thisresult were collected 24 h or moreprior or parturition

1.0–5.0 ng/ml: light blue, 96.4%(54/56) of samples showing thisresult were collected over 24 h priorto parturition

Less than 1.0 ng/ml: bright blue,83.3% (30/36) of samples showingthis result were collected 24 h orless prior to parturition; 97.2%(35/36) of samples showing thisresult were collected 30 h or lessprior to parturition

PreMate 7.5 ng/ml or greater: lighter or samecolor intensity as high progesteronestandard, 82.2% (89/107) of samplesshowing this result were collectedmore than 24 h prior to parturition

2.8–7.5 ng/ml: color intensitybetween that of the high and lowprogesterone standards, 0.8%(17/24) of samples showing thisresult were collected 24 h or lessprior to parturition; 83.3% (20/24)of samples showing this result werecollected 30 h or less prior toparturition

Less than 2.8 ng/ml: same colorintensity or darker than lowprogesterone standard, 100% (2/2)of the samples showing this resultwere collected 24 h or less prior toparturition

L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209 207

The accuracy of the EIA tests for determiningprogesterone levels when compared to the resultsobtained by the RIA was also calculated. The StatusPro test was found to be 75.7% accurate, the TAR-GET test to be 58.8% accurate, and the PreMate testto be 53.7% accurate in their ability to determinethe progesterone concentration of the samples whencompared to results obtained by the RIA.

The TARGET test results showed that 35 of the 36samples producing a “bright blue” color were collectedwithin 30 h prior to delivery. It is of interest to notethat once a “bright blue” result was obtained for adoe’s plasma sample, all consecutive samples showeda “bright blue” result for all 15 of the 15 does. Theaverage time prior to parturition in which a “brightblue” result first appeared was 16.5±6.5 h pre-partum(mean± S.D.; range: 1–26 h pre-partum).

The Status Pro results showed that 17 of the 17samples producing a result of “three bright spots” werecollected within 30 h prior to delivery. Also, 18 ofthe 25 samples showing a result of “two spots anda faint color on spot #3” were collected within 30 hprior to delivery. All consecutive samples showed a“three spot” or “two spots and a faint color on spot#3” for nine of the 15 does. The average time prior toparturition in which a result of “three spots” or “twospots and a faint color on spot #3” first appeared inplasma samples was 24.8±8.35 h pre-partum (mean±S.D.; range: 9–38 h pre-partum). Excluded from thisaverage were four samples in which a “three spots” or“two spots and a faint color in spot #3” were obtainedfor samples collected over 60 h pre-partum where alaboratory error was suspected.

The PreMate test results showed that two of thetwo samples producing a “color intensity the samecolor or darker than low progesterone standard” werecollected within 30 h prior to delivery. Also, 20 of the24 samples showing a color intensity between thatof the high and low progesterone standards were col-lected within 30 h prior to delivery. All consecutivesamples tested after these results showed a color in-tensity “darker than the high progesterone standard”(either an intensity between that of the high and lowstandards or darker than the low standard) for 10 ofthe 15 does. The average time prior to parturition inwhich a result of a color “darker than the high proges-terone standard” first appeared in the plasma sampleswas 25.3 ± 16.7 h pre-partum (mean± S.D.; range:

4–53 h pre-partum). Excluded from this average wasone sample in which a result of “darker than the highprogesterone standard” was obtained more than 60 hpre-partum and a laboratory error was suspected.

4. Discussion

Although human assistance during kidding in thegoat is not always required (Smith and Sherman,1994), many have found it beneficial to be presentduring parturition. Disease control programs may re-quire immediate removal of kids to reduce exposureto diseases transmitted through colostrum or fecalcontamination of the does’ teats, such as caprinearthritis-encephalitis, mycoplasmosis, and paratuber-culosis (Smith and Sherman, 1994). It may also bebeneficial to assist primiparous or aged does (Smithand Sherman, 1994). Likewise, assistance may beneeded in cases of dystocia. Research goats used inbiotechnology also require careful monitoring duringparturition in order to prevent birthing loss of valuablekids. The current study was performed to determineif an on-site test was available to predict an imminentdelivery.

This study was conducted with the premise that theprogesterone concentration would decrease approx-imately 24 h prior to parturition. The progesteronedrop found in our study resembles those shown inprevious studies that reported progesterone concen-trations decreasing significantly approximately 24 hpre-partum in goats (Currie et al., 1988; Currie andThorburn, 1977; Umo et al., 1976; Thorburn andSchneider, 1972). Our results agree with studiesthat found that progesterone concentrations remainslightly elevated at the onset of parturition and thendecline towards anestrous levels following deliveryin the goat (Rawlings and Ward, 1978; Currie andThorburn, 1977; Thorburn and Schneider, 1972). Pre-vious studies found an average of 3.37± 0.85 ng/mlof progesterone at the onset of parturition (Rawlingsand Ward, 1978), 1.25 ng/ml on the day of parturition(Thorburn and Schneider, 1972), and 0.60 ng/ml for30 min prior to delivery (Currie and Thorburn, 1977).A concentration of 1.48 ± 0.69 ng/ml was recordedto the last sampling prior to potus (0–9 h pre-partum).Rawlings and Ward (1978)found that in the goat ma-ternal progesterone concentrations began to decline

208 L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209

approximately 6 days prior to delivery, whereas in ourstudy, a trend of 2 or 3 days pre-partum was apparent.

The current study was performed to determine ifqualitative tests existed that could accurately detect thesignificant maternal progesterone drop that occurs ap-proximately 24 h pre-partum. In this study, both StatusPro and TARGET were 100% accurate in predictinghigh progesterone levels in plasma samples collectedmore than 24 h prior to delivery, and low progesteronelevels in plasma samples collected within 24 h prior toparturition. Results with the PreMate tests were lessaccurate.

With the TARGET and Status Pro tests able to de-tect the drop in maternal progesterone, we speculatedthat these tests would be useful in a variety of settings.When does show signs that may lead to questioningthe case as a dystocia, predicting the approximatetime of delivery becomes critical to both doe andkid. Determining when to intervene by inducing la-bor, manipulating the kid, or performing a Caesariansection is a frequent question of a goat practitioner.It was found that EIA tests may help minimize errorsin determining when to assist a doe in both distress.If a doe is showing signs of dystocia and a TARGETor Status Pro test is performed on-site obtaining aresult of high progesterone, one would opt not to in-tervene with emergency procedures. Intervening tooearly can have serious consequences, often resultingin non-viable kids from complications such as respi-ratory distress. A doe should not be induced beforeday 144 of gestation for this reason (Braun, 1997b).Therefore, if the breeding date is unknown and anEIA test is performed yielding a high progesteroneresult, again, one would opt not to intervene. Thehigh progesterone results obtained would allow oneto know that parturition was not going to occur withinthe next 24 h, and the veterinarian could look for otherreasons for the doe’s discomfort. EIA tests were alsoused to determine low progesterone concentrationsand identify aborting does in the herd.

Within our facility, we have found that the TARGETtest can be used to eliminate unnecessary pre-partumobservation time preventing husbandry personnel andtechnicians from spending needless overnight hourson “kid-watch”. Consequently, people who are re-quired to be present at kidding could use EIA tests todetermine whether or not overnight observation wasnecessary. The TARGET test is also currently being

used to assess delivery status of does with enlargedabdomens due to hydrops allantois. Prior to the useof the EIA test, kids would die in utero becauseStage II of labor would not occur and clinically noabdominal presses would be observed. Not realizingthat assistance was needed, the kids were often lost.Subsequently, the TARGET test is used to determineif the doe’s progesterone level is high or low. If theprogesterone concentration is found to be low, weintervene with the delivery in these cases and havefound this protocol to be successful.

Compared to progesterone concentrations obtainedby RIA, the EIA kits exhibited relatively low accu-racy at determining progesterone concentrations. Theantibodies employed in the EIA tests are not cali-brated for goat progesterone and this may be a likelycause for their low accuracy at measuring ranges ofprogesterone concentrations. Two previous studiesreported the use of measuring hormones in goats byqualitative studies others than those chosen here. TheOvucheck Mareside (Cambridge Life Sciences, Cam-bridge, England;Braun et al., 1988) and CalfcheckReprostrip and Ovucheck Cowside (Dionysius, 1991)were used as qualitative tests for the characterizationof the goat estrous cycle and for pregnancy diagnosisin the goat, respectively. It would be of interest todetermine if these tests would be a more accurateindicator of progesterone concentrations than the EIAtests used in this study.

Factors that one may want to consider when choos-ing a EIA test include the number of samples thatcan be tested at one time, the type of samples thatcan be used for each test, and the ease of readingthe results. Both the Status Pro and TARGET testsrequire many steps and each step must be timed pre-cisely. Therefore, it would be difficult to test manysamples at one time using either of these tests. ThePreMate test would be the test of choice for testing alarge number of samples at one time, because the testrequires fewer steps and some flexibility in timingthe steps involved. The Status Pro and TARGET testscan be run in less than 20 min, whereas the PreMatetest can take twice that amount of time. If a singlesample is to be run, the Status Pro or TARGET issuggested.

RIA determination of progesterone does not differsignificantly by using either plasma or serum sam-ples. The Status Pro instructions suggested serum use

L.A. Singer et al. / Small Ruminant Research 52 (2004) 203–209 209

only, but plasma samples seemed to work fine in thecurrent study. The PreMate protocol recommendedplasma or serum samples. TARGET allowed the useof a variety of samples, including plasma, serum,milk, or whole blood. Under field conditions, plasmaor serum separator tubes may be used to obtain anappropriate sample for EIA testing.

Readability is also an important considerationwhen choosing an EIA test. TARGET result is easyto interpret for a first time user. The Status Pro test ismore difficult to interpret. A faint color may appearinstead of a bright spot and lead to confusion. Lastly,the PreMate test although easy to perform can berelatively more difficult to interpret.

5. Conclusion

An EIA test may be used as a tool to more accu-rately predict the approximate time of parturitionin the goat. Both the TARGET and Status Pro EIAtests were clinically dependable in their ability topredict that delivery would or would not occur inthe 24 h time period following the sample collection.The EIA tests are economical, costing approximately$ 7.00 per test. It is recommended to incorporatesemi-quantitative estimation of maternal plasma pro-gesterone by EIA along with accurate record keepingand frequent observation of does in determining thetiming of parturition in goats.

Acknowledgements

The authors would like to thank Janine Stuczko,Karen Baldwin, Laura Vaught, Dr. Phyllis Mann ofTufts, and the staff of GTC Biotherapeutics including,Danielle Gaucher, Kathryn Silberman, Amy Rivera,Steve Blash, Nathan Buzzell, Catherine Porter, LizzeAgviar, Shelly Bombard, Christie Lynds, Sheila Don-ahue, and Nate Hawkins. Funding for this project

provided by both an NIH Summer Training Grant andsupport from GTC Biotherapeutics.

References

Braun Jr., W., 1997a. Parturition and dystocia in the goat. In:Youngquist, R.S. (Ed.), Current Therapy in Large AnimalTheriogenology. Saunders, Philadelphia, pp. 521–524.

Braun Jr., W., 1997b. Induced abortion and parturition in the goat.In: Youngquist, R.S. (Ed.), Current Therapy in Large AnimalTheriogenology. Saunders, Philadelphia, pp. 556–558.

Braun, W.F., Solorzano, N.M., Bierschwal, C.J., 1988.Characterization of the caprine estrous cycle using enzymeimmunoassay for the determination of whole blood progesteroneconcentration. Theriogenology 29, 1155–1162.

Currie, W.B., Thorburn, G.D., 1977. Parturition in goats: studieson the interactions between the foetus, placenta, prostaglandinF and progesterone before parturition, at term or at parturitioninduced prematurely by corticotrophin infusion of the foetus.J. Endocrinol. 73, 263–277.

Currie, W.B., Gorewit, R.C., Michel, F.J., 1988. Endocrine changes,with special emphasis on oestradiol-17�, prolactin and oxytocin.J. Reprod. Fert. 82, 299–308.

Dionysius, D., 1991. Pregnancy diagnosis in dairy goats and cowsusing progesterone assay kits. Aust. Vet. J. 68, 14–16.

England, G.C.W., Verstegen, J.P., 1996. Prediction of parturitionin the bitch using semi-quantitative ELISA measurement ofplasma progesterone concentration. Vet. Rec. 139, 496–497.

Epelu-Opio, J., Madej, A., 1988. Direct measurement ofprogesterone in plasma and milk by a simple solid-phaseradioimmunoassay. Vet. Clin. Pathol. 17, 25–28.

Matsas, D.J., Nebel, R.L., Pelzer, K.D., 1992. Evaluation of anon-farm blood progesterone test for predicting the day ofparturition in cattle. Theriogenology 37, 859–868.

Rawlings, N.C., Ward, W.R., 1978. Fetal and maternal endocrinechanges associated with parturition in the goat. Theriogenology9, 109–120.

SAS, 1990. User’s Guide. Statistics Institute, Inc., Cary, NC.Smith, M.C., Sherman, D.M., 1994. Goat Medicine. Lea and

Febiger, Philadelphia, pp. 430–436.Thorburn, G.D., Schneider, W., 1972. The progesterone

concentration in the plasma of the goat during the oestrus cycleand pregnancy. J. Endocrinol. 52, 23–36.

Umo, I., Fitapatrick, R.J., Ward, W.R., 1976. Parturition in the goat:plasma concentrations of prostaglandin F and steroid hormonesand uterine activity during late pregnancy and parturition. J.Endocrinol. 68, 383–389.