Automated monitoring of urination events from grazing cattle

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Misselbrook, T. H., Fleming, H. R., Camp, V., Umstatter, C., Duthie, C-A.,

Nicholl, L. and Waterhouse, T. 2016. Automated monitoring of urination

events from grazing cattle. Agriculture, Ecosystems & Environment. 230

(16 August), pp. 191-198.

The publisher's version can be accessed at:

• https://dx.doi.org/10.1016/j.agee.2016.06.006

The output can be accessed at:

https://repository.rothamsted.ac.uk/item/8v244/automated-monitoring-of-urination-events-from-grazing-cattle

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© 18 June 2016, CC-BY terms apply

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Misselbrook, T., Fleming, H., Camp, V., Umstatter, C., Duthie, C-A.,

Nicoll, L. and Waterhouse, T. (2016) Automated monitoring of

urination events from grazing cattle. Agriculture, Ecosystems and

Environment, 230, pp.191-198. ISSN 0167-8809.

© 2016 The Authors. Published by Elsevier B.V.

This is an open access article under the CC BY license

(http://creativecommons.org/licenses/by/4.0/).

http://hdl.handle.net/11262/11056

http://dx.doi.org/10.1016/j.agee.2016.06.006

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Automated

monitoring

of

urination

events

from

grazing

cattle

T. Misselbrook

a,

*

,

H. Fleming

a

,

V. Camp

a

,

C. Umstatter

b

,

C.-A.

Duthie

b

,

L. Nicoll

b

,

T. Waterhouse

b

a_Rothamsted_Research,_North_Wyke,_Okehampton,_Devon_EX20_2SB,_UK

b_SRUC,_Future_Farming_Systems,_West_Mains_Road,_Edinburgh,_EH9_3JG_Scotland,_UK

ARTICLE INFO

Articlehistory:

Received10April2016

Receivedinrevisedform3June2016 Accepted4June2016

Availableonlinexxx

Keywords:

Urinesensor Nitrogen Ammoniaemission Spatialdistribution

ABSTRACT

Urinepatchesdepositedbygrazingcattlerepresent‘hot-spots’ofveryhighnitrogen(N)loadingfrom whichenvironmentallyimportantlossesofNmayoccur(ammoniaandnitrousoxideemissions,nitrate leaching).InformationonthequantitiesofNdepositedtograzedpasturesasurine,thespatialand temporal distributionofurine patchesandhowthesemay be influencedbypasturemanagement practicesislimited.Theobjectivesofthisstudyweretoassessthepotentialofrecentlydevelopedurine sensorsforprovidingdataonurinationbehaviourbygrazingcattleandrelatethistomeasurementsof ammoniaemissionsfromthegrazedpaddocks.Atotalofsixtrialswereconductedacrosstwosites;two ona1hapaddockatEasterBushnearEdinburghusingbeefcattle(c.630kgliveweight)andfourona 0.5hapaddockatNorthWykeinDevonusingin-calfdairyheifers(c.450kgliveweight).Laboratory calibrationswereconductedtoprovidesensor-specificfunctionsforurinevolumeandNconcentration. The quantityand qualityof data from theurine sensors improvedwith successive trials through modificationstothemethodofattachmenttothecow.Thenumberofurinationeventsperanimalper daywasgreaterforthedairyheifers,withameanvalueof11.6(se0.70)comparedwith7.6(se0.76)for thebeefcattle.Volumeperurinationevent(mean1.8,range0.4–6.4L)andurineNconcentration(range 0.6–31.5gL 1_, _excluding _outliers) _were _similar _for _the _two _groups _of _cattle. _Ammonia _emission measurementswereunsuccessfulinmostofthetrials.Theurinesensorshavepotentialtoprovideuseful informationonurineNdepositionbygrazingcattlebutsuggestedimprovementsincludingmakingthe sensorslighter,designingabettermethodofattachmenttothecowandincluding amorereliable locationsensor.

ã2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).

1.Introduction

Cattleurinecontainssigniﬁcantquantitiesofnitrogen(N),with concentrationstypicallyintherange2–20gL 1(Whitehead, 1995), mostlyinaverylabileform(Bristowetal.,1992).Therelatively smallareacoveredbyaurinepatchfromcattlegrazingatpasture thereforeresultsinveryhighNloadingratestothesoil,exceeding thecapacityofthegrasstofullyutiliseit.Urinepatchestherefore represent‘hot-spots’fromwhichlossesofNmayoccurthrough ammonia volatilisation, nitrate leaching and nitrous oxide emissions(Allenetal.,1996;DiandCameron,2007;Jarvisetal., 1989;Laubachetal.,2013)withpotentiallydamagingimpactson theenvironment(Gallowayetal.,2003).

TheNcontentandspatialandtemporaldistributionofurine patchesareimportantfactorsaffectingthesepotentiallossesand

maybeinfluencedbycattlediet,grazingmanagement, environ-mentandseason.OurabilitytomodelNlossesandutilisationin grazed pasture systems and tooptimise management practices requires good information on cattle urination behaviour. In particular,model representationoftheurine patch,withahigh Nloadingtoasmallspatialareaisimportantratherthanassuming anevendistributionofgrazingNreturnsacrossthewholegrazed paddock(e.g.Hutchingsetal.,2007).Non-linearitybetweenNloss andNloadingtoaurinepatch(Ledgard,2001)meanthatscaling upbasedonestimatesofaveragevaluesforurinepatchNloading maydiffersubstantiallyfromthatwhichtakesintoaccountthe variationinNconcentrationandvolumeperurinationeventand thepossibilityofurinepatchoverlap(Lietal.,2012).Additionally, it maybe important to represent the spatial distributionof N returnsinurineinrelationtovariationinsoiland environment parameters (e.g.wetness,compaction,slope).However,todate, there havebeen few publisheddataonurination behaviourby grazingcattleasfieldobservationsaredifficulttomake.Thosethat * Correspondingauthor.

E-mailaddress:tom.misselbrook@rothamsted.ac.uk(T. Misselbrook).

http://dx.doi.org/10.1016/j.agee.2016.06.006

0167-8809/ã2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/). Agriculture,EcosystemsandEnvironment230(2016)191–198

ContentslistsavailableatScienceDirect

Agriculture,

Ecosystems

and

Environment

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havebeenmadesuggestthaturinepatchdistributionandoverall spatialextentcanbe inﬂuencedby factorsincludingfence line positions,watertankpositions,ﬁeldslopesandpreferrednight restingareas(Auerswaldetal.,2010;Augustineetal.,2013;White etal.,2001).

Betteridge et al. (2010) described an automated urination sensorwhich,whenusedinconjunctionwithaGPSunit,couldgive information on thetiming and location of urination events by grazingcattleorsheep.Theyshowedthaturinepatchdistribution wasverynon-uniformforsheepandcattlegrazingonhillpastures inNewZealand.FurtherdevelopmentofthesensorbyBetteridge etal.(2013)enabledmeasurementofurinevolumeandNcontent foreachurinationeventandreportedthatfrequencydistribution patternsofurinaryNconcentrationcouldhavealargeeffecton modelledNleachingloss.Thesensorsalsohadthepotential to recordlocationofurinationevents,usingZigBeecommunication (www.zigbee.org) by triangulation with ﬁxed location ZigBee referencenodesaroundthegrazedpaddock.

Theobjectiveofourstudywastoassessthepotentialofthe urine sensorstoprovide detailed spatialand temporal data on urination behaviour and urine N content for grazing cattle. A secondary objective was to determine the proportion of the urinaryNexcretedbythegrazingcattlethatwassubsequentlylost totheatmosphereviaammoniavolatilisation.

2.Materialsandmethods

2.1.Urinesensors

Purposely designed urine sensors (AgResearch, Palmerston North,NewZealand)wereusedinthetrials.Theurinesensorwas attachedtothecowbygluingoverthevulva,suchthatallurine

flowedthroughthesensor,andwassupportedbyattachmentto thecowsback. Development ofthe methodofattachment and supportcontinuedthroughoutthetrialsfromaninitialconfi gura-tionwherebyVelcrostrapsweregluedtothecow’sback(Fig. 1a)to afinalversionwheretheweightofthesensorwasbettersupported byaharnesswornbythecow.Lateralmovementofthesensorwas minimised by supporting straps fixed to the lower end and a shroud was fitted to minimiserisk of contamination by faecal material(Fig.1b).

Urineﬂowthroughthesensorinitiatedsensorfunctioningand providedatime-stampfortheurinationevent.Theurineﬂowed through a funnel within the sensor from which the majority drainedawaytothegroundwhileasmallsubsample(10–20mL) wasretainedinthebottomofthechamber.Urinevolumefora givenurinationeventwasdeterminedbyrecordingthepressure head of urine (recorded every two seconds while urine was

flowing)inthesensorfunnelforthedurationittakestodrainaway. Thearea under thepressuretime curve was related to urine volume. Urinary N concentration was determined from the refractiveindexreadingintheresidual10–20mLofurineinthe sensor.Thisresidualurinewastotallydisplacedbyfreshurineat thenexturinationevent;retentionofthissmallvolumeofurinein thechamberminimisedthelikelihoodofamineralfilmformingon therefractiveindexsensorwindow.Urinesensorsalsoincludeda ZigBeesystemforlocationofthesensorforeachurinationevent relative to fixed position nodes located around the grazed paddocks.

TheRothamstedResearchandSRUCEthicalReviewCommittees andassociatedprofessionalveterinarianwereinvolvedthroughout thisstudyandweresatisﬁedthat theproceduresand materials useddidnotadverselyaffectthecattle,withnosigniﬁcantskin damagearoundthe vulvaareafromgluing andremoval ofthe sensors and no impact on cattle behaviour. There were some problemsintheearliertrialswiththeanimalsbeingawareofthe

sensorbecauseoflateralmovemente.g.whilewalkingandthisled to some instances of animal bucking and sensor detachment. However,asthemethodofattachmentwasimproved,particularly through the use of lateral supports to minimise any lateral movementofthesensor(Fig.1b),thiswasnolongeraproblemand fromvisualobservations animals veryquickly resumednormal behaviouraftersensorattachment.

Calibrationfunctionswere derivedfor each urine sensorfor volumeandNconcentrationusingcattleurinecollectedfromdairy cows duringmilking ata local dairy farm. Volumecalibrations wereperformedbypouringvolumesofbetween1and4L,in0.5L graduations,throughthesensorandrelatingurinevolumetothe integral of the pressuretime curve. Nitrogen concentration calibrations were performed using cattle urine of known N concentrationatfourdifferentdilutionsandrelatingN concentra-tiontotherefractiveindexreading.

2.2.Trialsites

TwograzingtrialswereconductedinSeptemberandOctober 2012 using 14 beef cows (Charolais cross, Limousin cross and Aberdeen Angus cross, average live weight 630kg) on a 1ha paddockatEasterBush,nearEdinburgh,Scotland,andafurther fourtrialsconductedfromJulytoSeptember2013usingbetween7 and12in-calfdairyheifers(Holstein-Friesian,averageliveweight 450kg) ona 0.5ha paddockat North Wyke in Devon,England (Table1).Bothsiteswerepermanentpasture,withtotalfertiliserN

Fig. 1.Attachmentofurinesensortothecow:A,showinginitialconfigurationusing Velcrostrapsgluedtocow;B,finalconfigurationusingaharnesswithtopandside strapstosupportsensorweightandminimiselateralmovement.GPScollaralso shownonthebeefcowinA.

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applicationsof140and160kgha 1_to_Easter_Bush_and_North_Wyke

(appliedastwosplitsinMarchandMayof90and50kgha 1_at

EasterBushand100and60kgha 1atNorthWyke),respectively, duringtherelevantyear.Immediatelypriortograzing,eitherallor asub-setofthecattlewereﬁttedwithurinesensors,whichwere thenremoved3–5dayslater.AttheEasterBushsite,cattlewere alsoﬁttedwithGPStrackingcollars(AgTrex,BlueSkyTelemetry, Aberfeldy, UK), which gave positional information at a 1-min resolution.

2.3.Ammoniaemissionmeasurements

Ammoniaemissionsfromtheplotduringthegrazingperiod were measured using a backward Lagrangian stochastic (bLS) modellingapproach(Fleschetal.,2007),basedonmeasurements of ammonia concentration at ﬁxed points around the grazed paddocks and of wind statistics using a sonic anemometer (Windmaster, Gill Instruments Ltd, Hampshire, UK). Ammonia concentrationsweremeasuredusingtwoenhancedperformance LosGatos EconomicalAmmonia Analysers (Los Gatos Research, California,USA)and,attheNorthWykesiteusingALPHApassive samplers(Tangetal.,2001; Walkeretal., 2014)atlocationsas shown in Fig. 2. The Los Gatos analysers were sampling at approximately1-minintervalsataheightof1.4maboveground through15mPTFEtubingwithheat-tracetoprevent condensa-tion.TheALPHAsamplerswereusedintriplicateateachofthefour samplinglocationsshowninFig.2b,mountedat1.5mheightand werechangedevery24h.Thesoftware‘Windtrax’(ThunderBeach Scientiﬁc, NovaScotia, Canada) wasused toestimate ammonia

emission rates, using either 20min average concentration and windstatisticsor,fortheALPHAsamplerderivedconcentrations using24haverageconcentration,windspeedandwinddirection data.TheuseoflongersamplingintervalswiththebLSapproach has beenpreviously veriﬁed (Sanzet al., 2010; Sommer et al., 2005).

3.Results

3.1.Urinesensorcalibrationandperformance

TypicalcalibrationcurvesforurinevolumeandNconcentration aregiveninFig.3.Forurinevolume,verygoodregressionﬁtswere obtained(r2_>_0.97_in_all_cases)_and_the_slope_of_the_ﬁ_tted_line_varied

between11.3and16.5forthedifferentsensors.Goodcalibration functionswerealsoobtainedforurineNconcentration(r2>0.99) withregressionslopevaluesvaryingbetween0.109and0.116.

Datawerenotusedfromanysensorsthatonremovalfromthe cowwerefoundtobeblockedorpartiallyblockedbyfaecesor fromanythat werenotcapturingtheentiretyof urineflow(as identifiedthroughfieldobservations).Theproportionofsensors providingreliabledataimprovedinthelaterexperiments,asthe methodofsensorattachmenttothecowwasimproved.Thus,the numberofsensorsremainingattachedproperlyforperiodsof1 dayorlongeralsoimproved(Table2).

Onefeatureoftheurine sensorswhichdidnotfunctionwell wasthelocationrecording,withnoreliabledatabeingrecorded. Theonlylocationdatainrelationtourineeventswasthatobtained usingtheGPScollarsattheEasterBushsite.The1-mininterval

Table1

DetailsofthegrazingexperimentsatEasterBush(EB)andNorthWyke(NW).

Expt. Site No.cattle No.withurinesensors Startofgrazing Urinesensorremoval Endofammoniaemissionmeasurement

1 EB 14 7 03/09/201219:00 06/09/201214:00 07/09/201209:00

2 EB 14 9 01/10/201211:00 05/10/201210:00 05/10/201211:00

3 NW 7 7 01/07/201316:00 05/07/201308:45 11/07/201314:00

4 NW 8 8 05/08/201312:00 09/08/201309:00 15/08/201309:15

5 NW 12 7 02/09/201312:40 06/09/201309:00 12/09/201309:15

6 NW 12 6 24/09/201311:15 27/09/201314:00 03/10/201311:25

Fig.2.Trialsites:Site1,EasterBush–1hapermanentpasturewithammoniaconcentrationsamplinglocations(LosGatosanalysers)atAandB.Site2,NorthWyke–0.5ha permanentpasturewithLosGatosammoniaanalyserammoniaconcentrationsamplinglocationsatAandCandALPHApassiveammoniasamplersatA–D.Prevailingwind directionforbothsiteswasSW.

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locationswithinthepaddockoverasingle24hperiodofthefour cattlefor which sufficient urine sensordata wererecordedare showninFig.4(opencircles,individualanimalsnotidenti_fied).In thisperiod,thecattleshowedadistinctpreferencefortheSWpart ofthepaddock,particularlyalongthefencelines(notshown).The gatetothepaddockwasintheWcornerandtherewasahedge along the SW boundary, an area which the animals used particularly forresting at night time. Urination events arealso shownin Fig.4,differentiatedby daytimeevents(filled yellow circles)andnighttimeevents(filledbluecircles).Whilethereare insufficientdatatodrawstrongconclusions,thenighttimeevents mostlyoccurredattheSWend of thefield,wheretheanimals predominantlyrestedatnight,whereasdaytimeeventsweremore distributedaccordingtotheanimalpresenceacrossthepaddock.

3.2.Urinationbehaviour

Atotalof119and559individualurinationeventswererecorded forthebeefanddairycattle,respectively,withanaveragenumber of urination events per animal per day of 7.6 (n=9, standard error=0.76)forthebeefcattleand11.6(n=24,se=0.70)forthe dairy heifers. The frequency distributions in urine volume, N concentrationandNloadingperurinationeventweresimilarin shapeforthebeefanddairycattle(Fig.5).Fourhighvaluesfor dairyheiferurineNconcentration(>35gNL 1)wereconsideredto beoutliers,possiblyasaresultofcontaminationofthecellwindow throughwhichtherefractiveindexmeasurementtakesplace,and were excluded from the analysis. Mean values were similar betweenthecattletypes,withrespectivemeanvolumesof1.75 (se0.05)and1.80(se0.08)Lperurinationevent,meanurineN concentrationsof14.4(se0.33)and13.1(se0.26)gL 1_and_mean_N

loadingof25.6(se1.39)and22.0(se0.66)gperurinationeventfor thebeefanddairycattle,respectively.Withthegreaternumberof urination events per day, the urine N excretion was therefore

greaterforthedairyheifersthanthebeefcattle,withrespective valuesof255and194gNperanimalperday.

Therewas obviousdiurnal variation in the urine volume,N concentration and N loadingper urination event for the dairy heifers(Fig.6),withmaximumvolumepereventintheearlyhours ofthemorningandminimumatmidnight,andminimumurineN concentrationinthemiddleoftheday.Thispatternwasconsistent acrossallfourtrialsattheNorth Wykesite (experiments3–6). Therewereinsufﬁcientdatafromthebeefcattletrialstoevaluate diurnalvariation.

3.3.Ammoniaemissions

Foralltrials,thedatafromtheLosGatosEconomicalAmmonia Analysers were insufﬁciently robust to be used. Despite initial calibration of both instruments against a standard, there was signiﬁcantdriftintherecordedvaluesforsubsequentcalibration checks between instruments that was of a similar(or greater) order ofmagnitude tothe expecteddifferencesin upwind and downwind concentrations. The emissions from the grazed paddocks were therefore below the limit of detection for the LosGatosinstrumentsusedinthisway.

UsingtheALPHAsamplerswitha24hexposuretimewasalso generally insufficient to be able to reliably measure ammonia emissions from the grazed paddocks. For two of the trials (experiments5and6),therewasnosignificantdifferencebetween theamountofammoniacollectedontheexposedALPHAsamplers andthatontheunexposedblanksamplers.Forexperiments3and 4,exposedsamplerconcentrationswereabovethoseoftheblanks andemissionestimatescouldbemadeusingthebLSmodelling approach.Averagemeasuredfluxeswere0.11and0.57kgha 1_d 1

NH3-Nforexperiments3and4,respectively,whichrepresented

8.6and33.5%oftheestimatedurineNdepositiontothepastures during the grazing period. However, these results are not

Fig.3.Urinevolume(A)andNconcentration(B)calibrationcurvesforoneoftheurinesensorsusedinthestudy.

Table2

Urinesensorperformance.

Expt. No.sensorsgivingreliabledata Durationofdatarecording(h) No.ofsensorsgivingdataformorethan

Average Minimum Maximum 24h 48h

1 4 39 34 47 4 0

2 5 59 21 92 4 2

3 5 38 14 87 3 1

4 6 53 25 94 6 2

5 7 59 20 82 6 5

6 5 56 38 72 5 3

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consideredreliableandfurtherresearchisrequiredtogathervalid ammoniaemissiondatausingthismethod.

4.Discussion

The urine sensors have enabled us to collect data in an automated wayfrom a large number of urination events from grazingcattleacrossmultipleanimalsonmultipleoccasions.This wouldhavebeenextremelydifﬁcult,ifnotimpossible,toachieve throughmanualsamplingandobservation. Thesensorsusedin thisstudy,asdesignedbyAgResearch(Betteridgeetal.,2013)were aconsiderableimprovementonthosedescribedbyBetteridgeetal. (2010)inthattheymeasurevolumeandNconcentrationforeach urinationeventinadditiontotiming.Unlikethesensorsusedby Betteridgeetal.(2010),which wereattachedtotheanimalsby insertionintothevagina,thoseusedbyBetteridgeetal.(2013)and in this study were non-invasive. However, potential effects on animalwelfaremuststillbetakenintoconsideration,hencethe inclusion the Rothamsted Research and SRUC ethical review committeesandassociatedveterinarians.

Inter-animal and temporal variation in urination behaviour (amounts,location)andNconcentrationrequirethesamplingof sufﬁcient animals and occasionstoprovide representativedata and,asdiscussedabove,theurinesensorshavethepotentialto provide this. However, improvements to sensor design and functioningcouldbemadetoincreasethereliabilityandquality ofdatacaptured.Asnotedabove,themethodofsensorattachment was improved throughout the study resulting in increased durationofmonitoring.Thiscouldbefurtherreﬁnedtoincrease theproportion ofsensors remainingattachedfor threedays or longer.Reducingsensorweight(currentlyc.1.3kg)mayalsohelp withthis.TheZigBeesystemforlocationrecordingdidnotwork successfullyinanyofthetrials,possiblybecauseofthepresenceof the cattle interfering with the signals between sensors and reference nodes, sofor spatial information the sensors should becombinedwiththeuseofGPSdevices,ideallyco-locatedwith thesensors(GPScollarswillgivelocationdisplacedfromtheurine patchbyapproximately2mbutwithanunknownorientation).

Theurinationfrequency,volumeandNcontentdataobserved in this study comparewell with literaturevalues. Selbie et al.

Fig.4.Mapshowing1-minintervalsforanimallocations(opencircles)anddayandnighttimeurinationevents(yellowandbluecircles,respectively)for4monitoredgrazing beefcattleovera24hperiodattheEasterBushsite.(Forinterpretationofthereferencestocolorinthisﬁgurelegend,thereaderisreferredtothewebversionofthisarticle.)

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(2015),inareviewofavailable literature,notedthatdailyurine volumeand frequencyvariedwidely. Theyreportedanaverage frequencyofurinationof10–12eventsperdayforcattle(range 5–18withinindividualstudies),similartothatof8–12eventsper day reported by Whitehead (1995). The average volume per urinationeventwasreportedas2.1Lfordairycattleand1.2Lfor beef cattle but within individual studies was in the range `0.9–20.5Lacrossallcattle(Selbieetal.,2015).Meancattleurine Nconcentrationforcattlewasgivenintherangeof2–20gL 1by Whitehead(1995).Themeta-analysisperformedbySelbieetal. (2015)gave meanvaluesof 6.9and 7.2gL 1_for _dairy_and _beef

cattle,respectively,grazingapredominantlygrassdiet,somewhat lowerthanourmeanvaluesfromthepresentstudy.MeandailyN excretioninurinefromthepresentstudyof194and255gforbeef anddairy cattle,respectively,is attheupperend of theranges givenbyWhitehead(1995)of80_–240and80_–320gd 1_for_dairy

cowsandsteers,respectively.Dennisetal.(2011)andOudshoorn etal.(2008)reporturinationfrequenciesforgrazingdairycowsof 8.6 and6.2 eventsper day,respectively,while Orretal.(2012) reportsavalueforbeefcattle(meanliveweightof570kg)grazinga moderatelyimprovedswardof7.0eventsperday.Orretal.(2012) reportedalowermeanvolumeperurination eventof0.8L and urineNconcentrationof10.8gL 1_._Betteridge_et_al.₍₂₀₁₃₎_reported

ameanvolumepereventof2.1L,witharange0.3–7.8Lforgrazing non-lactating dairy cows and mean urine N concentration of 9.5gL 1_(range_1.2_–_24.7_g_L 1_).

Betteridgeetal.(2013)alsoreportedacleardiurnalpatternto theNloadingperurinepatch(mean18.1gNperurinationevent), asfoundinthisstudy(Fig.6),withvaluesduringthenightbeing greaterthanthoseduringthedaytimeanddiscusstheimportance ofthiswithrespecttothespatialdistributionoftheurinepatches. The higher N loading of the night-time patches have greater potentialfornitrateleachingandgaseousNlosses,whichmaybe furtherexacerbatedifregularnight-timecampingareasareused whicharerelativelysmallincomparisonwithday-timeroaming/ grazingresultingingreaterprobabilityofurinepatchoverlap.The reasonforthegreaterNloadingatnightisnotclear,butmaybe related to the diurnal pattern of intake by the cattle (no observationsmade),withurineNconcentrationincreasingfrom the morning to evening (Fig. 6). Additionally, there was some evidenceofurinationfrequencybeinglowerovernight(datanot shown),presumablyasthecattlewerelessactive,andvolumeper urinationwasgreatestduringthe0–4hperiodoftheday(Fig.6). Ammoniaemissionsmeasuredfromindividualurinepatches, e.g.usingdynamic chambers,mayaccountforupto30%ofthe urine N deposited (Lockyer and Whitehead,1990; Misselbrook et al.,2014).However,aproportionof thisemissionwillbe re-depositedtothepastureverylocaltotheurinepatch,soemissions measuredattheﬁeldlevelusingmicrometeorologicaltechniques will generally give lower emission estimates (Asman, 1998). Misselbrooket al.(2015)derived anemissionfactor fortheUK inventoryofammoniaemissionsfromagricultureof6%ofurine returnsatgrazingbeingvolatilisedasNH3-Nbasedonanumberof

ﬁeldstudiesusingmicrometeorologicalmeasurementtechniques (including Bussink, 1994; Jarvis et al., 1989) with individual emissions reported in the range 0–10% of urine N deposited. Laubachetal.(2013),alsousingmicrometeorologicaltechniques, reportedhigheremissionsfroma grazing trialinNew Zealand, withanemissionfactorof25%ofurineNwhichisapproachingthe uppervaluemeasuredinourstudy(althoughashasbeennoted above,emissionresultsfromthepresentstudyarenotconsidered reliable).

5.Conclusions

Theurinesensorsasusedinthisstudyprovidedanautomated meansofmonitoringurinationeventsfromgrazingcattlealthough improvementstosensorattachmentandlocationmonitoringare needed.Atotalof678urinationeventswererecordedthroughout thestudyacrossthebeefanddairycattle.Frequencyofurination wasgreaterforthedairyheifersthanthebeefcattleat11.6and7.6 eventsperday,respectively.Meanurinevolume,Nconcentration and N loadingperurination eventweresimilar acrossthe two cattletypeswithrangesof0.4–6.4L,0.6–34.4gNL 1_and_0.3_–₁₁₄_g,

respectively. There was clear diurnal variation in urine N concentration and hence N loading per urination event. Mean dailyurineNexcretionwas225and194gfordairyandbeefcattle, respectively. Themethodsusedtomeasureammoniaemissions providedunreliabledata.Furtherworkisneededtogathervalid ammoniaemissiondatausingthesemethods.

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0-4h 4-8h 8-12h 12-16h 16-20h 20-24h

Vol u m e p e r e v e n t ( L) 0 2 4 6 8 10 12 14 16 18

0-4h 4-8h 8-12h 12-16h 16-20h 20-24h

Ur in e N c o n ce n tr a o n ( g L -1) 0 5 10 15 20 25 30 35 40

0-4h 4-8h 8-12h 12-16h 16-20h 20-24h

N loa d in g ( g N pe r ur in a o n e v e n t)

Fig.6.Diurnalvariationinvolume,NconcentrationandNloadingperurination eventfordairyheifers.Errorbarsindicate1standarderrorofthemeanvalue.

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Acknowledgements

TheauthorsgratefullyacknowledgetheUniversityofEdinburgh farmmanagerforallowingaccesstotheEasterBushstudyﬁeldand to SRUC technical staff in the management of the livestock throughoutthetrial.Valuableassistancewasalsoprovidedbythe NorthWykefarmstaffand ﬁeldsupportteam.Fundingfor this studywasprovidedbytheUKGovernmentthroughDefraproject AC0116.RothamstedResearchissponsoredbytheBiotechnology andBiologicalSciencesResearchCouncil.

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