- Email: [email protected]
Effect of forty-eight-hour calf removal, once- or twice-daily suckling and Norgestomet on beef cow and calf performance
X. G. CMe,= G. H. Kiracofeand R. R. Schalles Ixqmtmntof~Sciences~Induetry KansasStateUni~ity Manhattan, KS 66506 Remived for publication:Mmeh 5, 7986 July 23, 1986 Accem: ABSTPACJ! Trialswere coxluctedin 1985and 1981to evaluatethe effectsof euckling,48-h czl.lfrx?mWal,~ once-daily eucXLing,twice-daily of epring-calvingcme and their calves NoxCJeemton performance Eighty-&reed73 Polled Herefordand and 42 Simmental-cmxs cdws were utilizedin 1980and 1981,reepectively. cawswere allottedby age,breed,mlvingdate tiwinternutritiontreatmnt tooneof four 1) once-daily sucklefor 24 d sta?Aing11 d beforethe beginm: nirigofthebreedingeeaeon,2) twice-d.ai.lysuckle(sametimeframas -n, 1)I 3) 48-h calf mmoval e&ingim&iatelybeforetbebree&q 4) calves xzTm&ed with cps (cxero~s). one-balfofeech gmxpwae fromlluntil2 dbeforetlxeta?Aofthe ~1~~wi~No~t bmedingeeaeon. Once-tits&x-daily eucklirqimmaeed (XWO.05) the ~~~~_yclirq cu&sebc&nge.etrue thefirst wkafterthe . Pregmmyrateeforthebxeeding seaeonwe?Cehi*er (piO.1)in the once-dailyeuckleand 48-hcelf remval gmupe for ems thathad not exhibitedestrus before the beginning of trmtment. (Ro. 05) the pementageof cows ehming e&rue Noxye&cmetin~ within3 wk afterthe start of treatment within the 48-hcalf-remuval and controlgroups. Milk pmdu&ionwas notaffected (BO.1) byeuckli.rKJtx&m!m~ Calf weight gains duriq euckling treatmentwere greater(RO.05) in controlaM t&&e-daily euckledcalvesthan in 48-h calfremval oronce&ily suckledcalves,Suckling treatmntdidnot affect (PsO.l) adjustedweaning weigbtsof calves or frequencyand durationof su~%iq recorded2 wk afterthe exl of suck&q tree-t. Keywords: beefcattle,calfremval, limitedsuclrling,Noxgeetcmet
Contribution No. 84-1205, Kzinsae Agr. Exp. Sta.,its 66506. a(zllmmtAddress: Dept.of AnimalSci.,ColoradoStateUniv.,Fort b Collins80523. Nom$%&xmet (17acetoxy-11 methyl-19nor-preg-4-ene-3, ao-dione), a syntheticprcgestcgen, wasprovidedby G. D. Searlef Co., Chicago,IL.
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THERIOGENOLOGY
To irqmveproductionin abeefcmqeration, itisnecessaryto achieveayearlycalvingintmzval.To mchthisgoal,cowsmustcycle andbecome pregnant& anaverage of82 dpostpartm. Sucklingcan delaythe onset of estrouscycling in postpartmcam (l-3). Delayed firstpostpartmestrus duet0 sucklingis irdependentofthenutritionalstateof the cow (4). Weaningcalvesbeforetheb&season willshortenthe intemal to fi_rstestrus and increasepregnancyrates (5-8). H~~,duetomanagementconsiderati~,early~ofbeef calves is not awidespreadpractice. Atteqtshave beenmade to eliminatethe effects of suckling withoutcompletely weaningthe calf. Once-dailysuckling frm 30d postparhrmuntilfirstestrusshortenedtheintewdltofirstestrusand conceptionin Em&man X Herefordfirst-calfheifers(9). Once-daily sucklingalsoshortenedtheintemaltofimtestrus inAngus.cmsm didnot shortenthe intemalto conception (10). Also, preventing sucklingfor48 h justbeforethebreeding seasonbyseparatingcalves frcxn cowshastenedthe averageonsetof estrusby 11 d (11). It appears thatvarious systemsused tolimit sucklingcan be advantageousin inducingcycling,but~ccnnparisonsofthese~g~t~~and the subsequent effectsonxnilkpmduction 0fcu.m mkdsucklirqbehavior of calvesis somwhat1iIVited. Failureto shm a beneficial effect of limitedsuckling on pregnancyratesarenthoughcyclingwasstinnilated(lO)maybeduetoalack ofserumprogesteronethatisusudllyabsesvedbeforethefirstpostpar turnestrus (12-14).Norgestmet, administered before weaningcalves, reducedthenumber of shortcyclesand kcreas&wnception ratesat the firstestrus afterweaning (15). RJi?ducing thesuckling stirmiLusand administering progestcgens could have an additiveeffect on iqxoving reproductiveperformance inpostpartumbeefcms. Ihisstudywasdesignedtomeasure the effectof 48-hcalf removal or once- ortwice-daily sucklingon 1) reproductiveperfomanceand inilk production of cows and 2) weightgains and sucklingbehaviorof of cads, C43lW.S. The effectofNoqastcnnetonrepmductiveperforn!ance eitheralone or in conjunctionwith suckling txeatments,also was measured.
lhisexperimentwascorxductedinthespriqandsmmmz of 1980and 1981. In 1980,83 PolledHereford and 29 Simmtal-crces cows were utilized,and in 1981,73 polled Herefordand 42 Sinmkental-cmss ccws Includedwere 28 were utilized. Cmsrarged inagefrom2 to14yr. 2-yr-old first calversard 28 3-yr-old second calvers. &ms calvedfmlate Febnmytoearly May. The herd was kept on native bluestemraqe withapproximtely 3ha per CmPcalf pair. Date of startingtreatmentwasbasedonstartingdateofthebreediragseason, whichwas May 20 in 1980and Way 16 in 1981. The sanks tr&xnentswere appliedtotheherdkmthyears.
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Elepvendaysbeforethe startof the breeding season,ems were allottedbyage,breed, calvingdate and winter nutritiontreatmmt to one of the four following groups. Once-dailysuckle.Calveswereseparatedfm cmsandpemedlld beforethestartofthe b?zedirqs@%son.Forthenext 24 d, ccwswere broughttithe calfpendaily atapproximately hand thecalves wereal&mzdtomrsefor 1 h. Afterallcms hadkeennursed,they werelP&urn&topasture. !lMice-dailysucHe. Thisgnnp, washandledthe sameasome+%iily suckleexceptthat cmswerernrrsed twicedailyat approximatelyO7OO and 1800hours. 2d befOl32 48-h calf removal. ~lvesweresepara~~~ ofthe breedingseasonandreturned theday the breedins seasonstarted.
thestaxt
Ccntmls.Calves remained with cows on range and suckled.ad libitum. ~-halfofthecawsinBadhofthefourgrcrups~~l~with a 6-nqNoq?~tcmt~lant lldbefcre thestartoftheb~season (atthetimeonce- a&twice-daily sucklingwasinitiated) and implants weremrmved9dlater. Ccwswere obeezvedtwice dailyfor signsof estyusbeginning3 wk beforetread so cows cold be classified as cyclingor mncyclingat for estmscontinued thestartof txeatmmt. mice-daily observation through42 dof thebreedjrq season. Testosterone-treated ccmswith chin-ballmar&rswereusedasestrus-detectionaids. Thelengthof thebreediqeeasm was 59 d in 1980 and 63 d in 1981. In 1980,all cowswere bred artificially apprmcimately 12 h after theywemdetected inestrusifthey were inestrusduringthe first13 dofthebreedingseason. mrirq t.h!a next 29 d of the breedingseason, one-halfthewws ineachtreatment~werebredartificidlly~~e otherhalfwere~ tobulls. All cuwswereexposed tolznillsthe reminderofthe breedingseason.In 1981all ems were bred a?ztificiallyduringthefirst42 dofthebe sfzlsonand~tobulls theremaindesofthebreedingseason. Averageage of calvesat the beginnixqof trea&mYCms 45.4+ 1.5 d in 1980 and 39.0+ 1.6 d in 1981. Calves kierefedgrainaMpGirie hayandhadaccesstowaterwhile~~firnntheirdams. Milkproductionwasestimatedbytheweigh-suckle-weigfi~~~ (16) atthe& ofeabmonth frcmAprilth?mugh Augustin1981. For the cows ancl calveswere separatedat 1400h; April~I%IElay measurements, the~~'kFeredll~to~the~at2200h,then~~~ overrli~t.At 0600h the next day, thecalveswereweighed,allcwedto nursetimweighed. Eight-hourmilkyi@ldwasestimatedaspos~ing weightminuspremrsingweight. TM daily8-h estimates were averaged and mltiplied by 3 for an estimateof 24-hmilk production.IXrirqthe SEPTEMBER 1986 VOL. 26 NO. 3
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THERIOGENOLOGY
cows ard calveswere separatedat 0800 J-throughAugust-, h;the calveswere allmedto nursethe cmsat 1800h, then were separatedovernight.At 0600 hthenextday, thecalveswereweighed, allow&to nurse and reweighed. Three daily 12-h estimateswere averagedandthendoubledforan estimateof24-hmilkprcduction.The dailyestimatesweretakenondlternatedaysto~~interferencewith thegrazingpatternoftheccmandcalves. caWhipheightwasrecorded~y1,andcckJsandcdlveswere~ighed atthebeginningofeachmonthfmMaythmugh0ctober. In lateApril 1981 (beforethe treatmentperiod),ems and calves wereo&ervedcmtinuously for a 24-hpericdon pasture,ard incidence and durationof suckling were recorded.Inbuth years,thetotaltime eachcalfsuckledinldinboththeonce-andtwice-dailysucklegroups wasrecordedneartheendofthe sucklingtreatment. Atthesametime, thecontrol groupwas observed continuouslyfor a 24-h period on pasture, and incidence and duration of saxklingwerereco~ Incidenceand durationof sucklingfor allcows also were recorded duringa continuous24-h observationperiodonpasture wkafterthe endofthesucklingtmatment. concepti~datewasdeterminedbyrectdlpdlpationoftheuterus40 to 70 d after artificial insemimtionornatural service. Allcunception dateswzre verifiedby calvingdates. Differencesatmnggrcupsin percentagein estrus and pmgnancy ratesweretestedbyQli~ Intervaltofirstestmsand conception,milkpmonchanges, cm& calfweight changes& diffmcesin incidenceand durationof suckling were analyzed by genezallinearmodelproaedures(17). Thefinalmdelsforeachdeper~+ entvariable measuredincluded independentvariables whichwere significant sources of variation as well assuckl~ treatment. Indepemlentvariables includedin eacbmdel are reported in table footnates. RFSUUSANDDISCUSSIoN One calf each fmn the twiceilaily suckled, 48-h calfmmval, andcontrolgroqe diedeither shortlybefo~~orduring thebreeding seasonin 1980. Dataaboutthese calves ardtheirdamswerenot included. Thepementage ofcows shmingestrus thefirst 3wk afterthe onsetoftreatmntwas greaterinome- (RO.l) ~twice-dailysuckle (PxO.05) groups than in controls(Table 1). Ha--, ~fi=-W3e showingestrusthefirst 3wkof thebreedingseason ardtheintemal fmmcalvingtofizstestmswerenotdifferent. Only25.4%ofthecows were detected in estms during 3 wk of estrus detectionbefore treatment.Innoncyclingcms,thepercentageshowirqestrusthefimt 3 wk afterstartof treatmmt was greaterfor once- (RO.05) and twicedailysuckledems (RO.01) than for con-1 cows (Table2). The percentageshcrwingesWusthefiret3wkofthebreedingseason arKlintervalf?xxn calvingto fir&estrus wexenot diffe.re&almg the folx groups.
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1986 VOL. 26 NO. 3
THERIOGENOLOGY
Table 1.
Effect of forty-eight-hour calf removal oronce-ortiice-daily CWs sucUingo~repmductiveperfozmanceof
suckling
Once daily
IM No. of CCRJS
57
Fercentagesho&qestmsfirst 3wk afzter treatmentonset PercentageshoWqestmsfirst 3 wk of bre.edAq season Interv Fz$z&Lefirst2ld,% a&fzxxmilv~tofirst Freqnancy rate first.42 d, % xzfrate hq ==n, v=llv=Wto conception,d
%
?krice daily
treamt 48-h cdlf rexmval
56
control
55
56
80.7b
83.gc
74.5
64.3
91.2
85.7
85.5
82.1
52.222.6
53.322.6
54.922.6
55.Q2.7
49.1 75.4b 93.0 77.4k3.1
42.9 66.1h 92.9 81.1k3.2
50.9 78.2 90.9 75.123.2
42.9 69.6 82.1 77.753.4
?east-squares mans + SE adjusted for weight:height ratio. bDiffmx?.nt fmn con&l group (RO.10). =Different frtzncontrol group (RO.05). Table 2.
Effect of forty-eight-hour calf remval or once- or Wivly ~~on~~~ive~o~ ofnoncyclingcows SuclCiiRgtrea~t 48-h Twice calf Once daily daily remmal
Item No. of cxxm
44
Percentageshwingestrusfirst 3wkafYze~treatmntonset PercentageshWriragestrusfirst 3 wk of breeding season I"eF=,d fromcalvinqtofirst Pregnancymtefirst21d,% Fregmmyxatefirst42d,% Freqmcyratebreedingseason, Interval.fqmcalvingto conception , d
%
42
40
control 41
75.0c
7a,6d
65.0
51.2
88.6
al.0
80.0
75.6
55.5t3.1
56.e3.3
59.423.3
59.453.4
43.2 68.2 90.ge 77.323.6
47.6 66.7 90.5 74.433.7
47.5 80.0 92.5e 73.723.8
43.9 68.3 78.0 73.qt4.1
a~ were classified as noncycling if they were not detected in es&us bdurirg the 3 wk of estrus detection before treatmnt. L+sst-m means + SE adjusted for weight:height ratio. CDifferent from contrZls (R0.05). dDifferent from controls (R0.01). %ifferent from controls (Ro.10).
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w
THERIOGENOLOGY
rates werenot differentanmg We~m42-d~regnancy thefour gmups,althmgh once-and twice-dailysuckled groups had higher (RO.l) breedingseasonpregnancyrates than did contxols. Breedingseasonpreqarq rate was immased (RO.1) by once-daily suckleand 48-h calf removalinnoncyclingcms. Theintervalfmin calvingtoconceptionwas mtaffectedbysucJcling treaMwhenconsideringeithernoncyclingcmsorallcms. Noryestmetsignificantlyincreasedthe percentageof cows in estrusthefirst3wkafterthestartoftreatmentinbaththe48-hcdlf remval ard controlgmups (Table 3). When Noryestomstcclwswere excluded,morecawsintheonce- andtwice-dailysuckledgroupswere in estrusthefirst3wkafterthestartoftreatmntthaninthe48-hcdlf remvalorcontmlgmxps. Intemalf?mn calvingtofi& estrusarid calvingtoconceptionwerenotdifferentfor sucklingtreatmentgmups givenNorgestmet. Table4. Incidenceanddurationofsucklirqdu.r&q sucklingtreatment andtwoweeksaftersucklingtreatment sucklingtreatlnent Item
Once daily mice daily
No. of cclw-cdlf pairs
IncidencecQring trea=, suckles/24 h Eurationdu@ng treatment, total
1.0
56
55
2.0
Control 56 5.1 + 0.2
21.6+ 1.0
34.8+ 1.1
5.1+ 0.2
4.9 2 0.2
4.8 + 0.2
5.1 + 0.2
47.9+ 2.1
43.62 1.9
46.1t 1.7
48.6+ 2.0
45.8f 2.0
suckling
1nin/24 h Incidencea;ter txeatment, suckles/24 h Cxuationaf$er treamt, total
57
48-hcalf removal
suckling
m&/24 h @luesareleast-squaresmeans+SE. lncidenceanddurationof~~-~duringtreatmentwererecorded~y 26to28bothyears. %cidmce anddurationof su&lingaftertreatmentwererecotiedJune 12 to 16 in 1980and June 12 to 17 in 1981.
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THERIOGENOLOGY
Raritel
(9)
repznzted
that
onoe-daily
suckling
tsl~~rtened
the
inter-
valtofirstestmsandconception inBrahman-cross,2-Yr -oldheifers mrsedorcedaily fmn 21-dpostpartumuntilfirstestrus. Once-daily ~~~alsoshorteneatheintewaltof~testrusin~caws(10) butdiclnotshortentheintemaltocom.mpticm. InoLIrax&G!r~,caws averaged42d pcsQm&mat theb@mirq oflimited suckling. The i&e.mal fmn calvirqto firstestms was 56.8+ 4.1 d for nonimplanted mWm. Zharef0x.q #erewaslittlechanceforsucklirx3treaiment toshW an advantage ininterval fmm calvjq to first estrus or conception.lheadvantageinbreedirqseasonpmgnancy rateforonceatxItwice-dailysuclcledccws inourtrialis similartothatrqmrtedby Stmdemnn et al. (18)for once-dailysuckledAngus~. Vihileonce-andtwice-dailymckledtr&xe&swerezxxm&q, cxmtrolems nurs& an averageof 5.1 f 0.2Cmes/24 h (Table4). The 1~32~~Uoninsu~ing stimulusin ~i~~~e~~~ bethefa~rcausing~cyclingactivitywithin3wkafterstart oftreatment. Sucklingfrequency orduration incontmlanimlshadno effect(DO.05) on interval fm calvirg to estrus or cxmception. SuM~treatithad noeffecton fmquencyorduration of suckling obmrv&2wkaftertrsa~tended. Milkpmduction bsforetreatnmt andchanges inmilk pxoduction inTable 5. SucUing wim=Y, June, YulyandAugustarerepxted txeatmenthadno effecton changein milkp3xx%&ion forany ofthe mnths. ~~~~wi~~~~~~(9)~~ once-dailysucklingarxIsuckl.ingadlibitm. Sucklingtreatmantdid affect(PC0.01) ccalfweightgains during~~y and June (Table5). !IMice-dailysuckled andcontrolcalvssgainednme durirqMay (pericdofsucklingtreatnmt) than did once-dailysuckledor 48-h calfremovalcalv~. Hmever, 48-h calf removalcalveshad thegreatestwsight gai.ndurixqJune. No differences in weightgab duri.rqJuly,ZUgustandSeptm&morinweaniqweightsofcalveswere obsem~~the~~graups. In other sAxdies, once-daily calf weightgainsduring thelimited sucXl*perioa yucMi.ng~ (9,19) but did notaffect weaningweights of calves (9,10, 19). l@mQmmy (19) repoMthatwei*t gainsduringthe1imitedsu&ling pzricdfor calves nursingtwicedaily wsresimilarto cxmtrols,which agmsswithresultsinaurstudy. areshawninTable Changesincoww+htfmr~~Maytzhxmqh~ 5. Ccrwweightchange inMay wasdifferent (F=O.l2) ammg the faur gmq6, with controlshaving greater(PcO.05)weightgains than 48-h calf-removaloronce-dailysuckledems. In Jtme,hmever, controls gainedless (PcO.05) than -ilysucMed aws. The advantagein weightgain fox-the contmlcmis m-the treatm.nt~iaI rraybe becauseofless stressandharxWng arxla morenearly nomalgrazing pattermhmever, b&honce- andtwice-dailysuckledcum seemed to adjusttolimitedsu~ing. Afterapproximtely 4 doftreatment, they grazeda normalamount 0fti.m. Ccwweight gains from Julythmugh septmberwemnotdifferentamngthefourgrcrups.
SEPTEMBER
1986 VOL. 26 NO. 3
THERIOGENOLOGY
Table 5. Effectof sucklingtrea+xtmtonmilkpra%ction, andcowweightchange
calfweightgain
Sucklingtreatment
Item
48-h calf remval
Once daily lWice daily
Milk prcduction (kg/24h)a 28 No. of m 10.3+2.8 Seforeeucklingtlx?a~ _ (lateApril) 2.6+1.0 Changeduriq: May JUne -2.Go.9 -0.4To.7 JOY -0.7zO.6 Ausust Cowbandcalfcweighte, kg No. of cow-calfpairs 57 Cowweight:height,lq/cm 3.7kO.l WY 1) Cowweightbefore 463.4+3.2 treatment (fQY1) Cm weight 50.0+4.9d changeduring: May 26.2T3.7d JUIW? 5.173.9 JW -9.6T5.1 Ausust 6.474.8 S_ Calfweightbefore 70.412.3 treatment (May1) Calfweight gai.ndurirKJ:May 32.5+1.3' JLll-ifZ 26.4+1.3d 42.9T2.9 JOY 18.6Tl.3 Ausust septanber 31.572.1 Calfweaningweight 222.456.1
29 9.eo.7
29
Control
29
9.820.8
9.43.8
1.7+0.9 -1.3To.9 -0.3To.7 -1.60.7
2.9+1.0 -2.4:l.O -0.lTo.a -1.eo.7
2.4tl.O -1.6+0.9 -0.lTO.7 -1.e.6
56 3.620.1
55 3.75.1
56 3.e.1
464.2k3.3
466.3+3.1 -
469.1t3.1
52.2+4.9&
21.aT3.6de 6.1T3.8 -7.3T5.0 ll.lT4.a 72.152.2
4a.7T5.zd 16.6f?.ge 5.e4.0 -4.4+5.2 6.875.1 67.e2.3
5a.3+4.ae 16.g3.5e 6.G3.7 -7.274.8 11.64.7 68.2Z2.1
37.akl.2: 30.e1.3': 36.9+1.2e 27.atl.2 33.1kl.3 30.&l.2e 40.6+2.7 39.822.8 41.dT2.5 2O.Gl.3 18.1+1.3 17.Gl.2 28.2T2.1 28.9T2.1 29.61.9 227.456.0 [email protected] 223.e5.6
43ilkproductionwasestimatedbythewei~-suckle-weightechniqueat the end of each month fmn April thmugh August in 1981. Valuee repo&edare1eaet_scluares means + SE adjusted for cow breed and bweightzheightratio. Cawweights andweightchangesareleast-squares mane +SE adjusted cfor cm breed, ccw age and weighkheight ratio. Calfweights andweightgains are least-equaxsmeans+SE adjusted for calf breed, calf age aM cm age. d,e,fMeansin theeameruwwithoutacommn mperecript differ (R0.05). REFERmcEs
1. Clapp, H. A factor in breeding efficiencyof dairy cattle. Froc. Amer. Sot. ?mim. PJX& -30:259-265 (1937).
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1986 VOL. 26 NO. 3
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2. Wiltbank, J. N. and cook, A. C. The aqarative repmductive pe?zfoxnwlceof nursed c(xJs and m.i.lkKlc!uhYs. J. Anim. Sci. -17:640-648 (1958). 3. Short, R. E., Bellcrws, R. A., Moo&, E. L. andHcwl%d, B.E. Exfecte of suckungand~on bcwine gxs@dxm repx%Ybction. J. Ankn. Sci. -34:70-74 (1972). 4. !@Atemm, Inf%~of rangecws.
R. P., -, E. Y., Wyatt, R. D. &'Ibbzek,R. sucklinginteneity on repmdztive px-fomance of J. Anim. Sci. -47:342-346 (1978).
Effects of early 5. laster, D. B., Gliq, H. A. and Gregory, K. E. weaning on pusreproduction of cfxs. J. Anim. Sci. -36:734-740 (1973). 6. Bellcws, R. A., short, R. E., Uric&, J. 3. and Pahnieh,0. F. Effectsofearlyweaningonpostpartum repmductionofthedrmtard growth of calves born as multiple or single. J. Anink. Sci. -39:589-600 (1974). 7. =r Early weanirq and uxep M., Kiqble, K. G. and Crxah, L. feeding fordrylotcalves. J. Anin!.. Sci. -45 (Suppl.1):47 (1977). 8. ~,K.~~~~, +P. andTuman,E. Effects of Barly fxst-calf heifers mJ' calf and heifer m perfomance. J. Anim. Sci. -53:1193-1197(1981). 9. l?ardel, R. D. Effect of ~~Y~~~~~ andww-calfperfoxlwice offirst calf Bidx0anXHerefordheifers. J. him. Sci. 53:755-757 (1981). 10. Reeves, J. J. arxl Gaskins, C. T. Effsct ofonce-a-daynursingon rebreedingefficiency of beef cows. 3, Anh Sci. -53:889-891 (1981). 11. Leexdster, J. L. and Drake, D. J.
rrmrraloncdlfeo-
Effect of +=w==Y
calf
am3 estrusactivityofp&qarbmbeef
COSJS. J. Anixn.Sci. -47 (Sqpl. 1):144 (1978). 12. lIXanaldson, L. E., Bassett,J. M. ad Thornburn,G. D. I%!xi#Ieral rz&emne~~tionof awedurirqp&erty,oestrous p&zzp7, mgnancy and lactationand the effects of urdemutrition cozxze&mtions. J. oxytodnon pxqeetemne or e=w== Edocrinol. $$599-614 (1970). 13. Cdde, K. G., Ward, H. S., Kiracofe,G. H., I&d&e, R. M. a-d Kittok, R. J. Sho*estrwscyclesardasecciatedeemmpmgestemne levels in beef CICIWS.Thericgenologyg:105-112 (1980). 14. -Y, W. D., XQUmbach, C. C., lsmn, T. G., Koritnik,D. R. and Ni.sweder,G. D. Characterization of hormonal patterns in the l33efccrw~~~~. Y. Aninl. SC& 5&@445-453 (1983).
380
SEPTEMBER 1986 VOL. 26 NO. 3
15.
Ramirez-Godinez, J, A., Kiracofe,G. H., McXee, R, M., SchdLles, R. R. and Kittok,R. J. %ducixq thelnciaence of short estmus reriogenology 2:613-623 cyclesinkefcawswitiIIo~ (1981).
16.
Boggs, D. L., Smith, E, F., schdlles,R. R., Brerrt,B. E., Co=& L. R. and Pruitt‘ R. J. Effech ofmi2kandforagebbIkeoncdlf pe?zfozmanc.e. J. Anim. Sci. -51:550-553 (1980).
statistics. statistiodt~ysissystem 17, SAS. SAS Ufx&sGuide: Institute,Snc., Cay, NC, 1982, pp. 140-199. 18. Studemam, J. A., WilJdnson,S. R. I catdle, A. B., Cicdia, H., Dudzinsky,M. L. ti Williams,D. J. Effect of mce-ddly mddi.nq 0fyGurqAnguscxx#sonth~~~onandcdtf~* J, A&m. Sci. 53 (Sup& I):370 (1981). Inflmof;axdkl*frequencyanJ.b~ 19.. F&m@meq, G. W. tinetxeatmnton themsumptionof cmiriancycles irim kefcattle. Thericgenology-17:551-563(1982).
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Contribution No. 84-1205, Kzinsae Agr. Exp. Sta.,its 66506. a(zllmmtAddress: Dept.of AnimalSci.,ColoradoStateUniv.,Fort b Collins80523. Nom$%&xmet (17acetoxy-11 methyl-19nor-preg-4-ene-3, ao-dione), a syntheticprcgestcgen, wasprovidedby G. D. Searlef Co., Chicago,IL.
SEPTEMBER 1986 VOL. 26 NO. 3
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THERIOGENOLOGY
To irqmveproductionin abeefcmqeration, itisnecessaryto achieveayearlycalvingintmzval.To mchthisgoal,cowsmustcycle andbecome pregnant& anaverage of82 dpostpartm. Sucklingcan delaythe onset of estrouscycling in postpartmcam (l-3). Delayed firstpostpartmestrus duet0 sucklingis irdependentofthenutritionalstateof the cow (4). Weaningcalvesbeforetheb&season willshortenthe intemal to fi_rstestrus and increasepregnancyrates (5-8). H~~,duetomanagementconsiderati~,early~ofbeef calves is not awidespreadpractice. Atteqtshave beenmade to eliminatethe effects of suckling withoutcompletely weaningthe calf. Once-dailysuckling frm 30d postparhrmuntilfirstestrusshortenedtheintewdltofirstestrusand conceptionin Em&man X Herefordfirst-calfheifers(9). Once-daily sucklingalsoshortenedtheintemaltofimtestrus inAngus.cmsm didnot shortenthe intemalto conception (10). Also, preventing sucklingfor48 h justbeforethebreeding seasonbyseparatingcalves frcxn cowshastenedthe averageonsetof estrusby 11 d (11). It appears thatvarious systemsused tolimit sucklingcan be advantageousin inducingcycling,but~ccnnparisonsofthese~g~t~~and the subsequent effectsonxnilkpmduction 0fcu.m mkdsucklirqbehavior of calvesis somwhat1iIVited. Failureto shm a beneficial effect of limitedsuckling on pregnancyratesarenthoughcyclingwasstinnilated(lO)maybeduetoalack ofserumprogesteronethatisusudllyabsesvedbeforethefirstpostpar turnestrus (12-14).Norgestmet, administered before weaningcalves, reducedthenumber of shortcyclesand kcreas&wnception ratesat the firstestrus afterweaning (15). RJi?ducing thesuckling stirmiLusand administering progestcgens could have an additiveeffect on iqxoving reproductiveperformance inpostpartumbeefcms. Ihisstudywasdesignedtomeasure the effectof 48-hcalf removal or once- ortwice-daily sucklingon 1) reproductiveperfomanceand inilk production of cows and 2) weightgains and sucklingbehaviorof of cads, C43lW.S. The effectofNoqastcnnetonrepmductiveperforn!ance eitheralone or in conjunctionwith suckling txeatments,also was measured.
lhisexperimentwascorxductedinthespriqandsmmmz of 1980and 1981. In 1980,83 PolledHereford and 29 Simmtal-crces cows were utilized,and in 1981,73 polled Herefordand 42 Sinmkental-cmss ccws Includedwere 28 were utilized. Cmsrarged inagefrom2 to14yr. 2-yr-old first calversard 28 3-yr-old second calvers. &ms calvedfmlate Febnmytoearly May. The herd was kept on native bluestemraqe withapproximtely 3ha per CmPcalf pair. Date of startingtreatmentwasbasedonstartingdateofthebreediragseason, whichwas May 20 in 1980and Way 16 in 1981. The sanks tr&xnentswere appliedtotheherdkmthyears.
372
SEPTEMBER
1986 VOL. 26 NO. 3
THERIOGENOLOGY
Elepvendaysbeforethe startof the breeding season,ems were allottedbyage,breed, calvingdate and winter nutritiontreatmmt to one of the four following groups. Once-dailysuckle.Calveswereseparatedfm cmsandpemedlld beforethestartofthe b?zedirqs@%son.Forthenext 24 d, ccwswere broughttithe calfpendaily atapproximately hand thecalves wereal&mzdtomrsefor 1 h. Afterallcms hadkeennursed,they werelP&urn&topasture. !lMice-dailysucHe. Thisgnnp, washandledthe sameasome+%iily suckleexceptthat cmswerernrrsed twicedailyat approximatelyO7OO and 1800hours. 2d befOl32 48-h calf removal. ~lvesweresepara~~~ ofthe breedingseasonandreturned theday the breedins seasonstarted.
thestaxt
Ccntmls.Calves remained with cows on range and suckled.ad libitum. ~-halfofthecawsinBadhofthefourgrcrups~~l~with a 6-nqNoq?~tcmt~lant lldbefcre thestartoftheb~season (atthetimeonce- a&twice-daily sucklingwasinitiated) and implants weremrmved9dlater. Ccwswere obeezvedtwice dailyfor signsof estyusbeginning3 wk beforetread so cows cold be classified as cyclingor mncyclingat for estmscontinued thestartof txeatmmt. mice-daily observation through42 dof thebreedjrq season. Testosterone-treated ccmswith chin-ballmar&rswereusedasestrus-detectionaids. Thelengthof thebreediqeeasm was 59 d in 1980 and 63 d in 1981. In 1980,all cowswere bred artificially apprmcimately 12 h after theywemdetected inestrusifthey were inestrusduringthe first13 dofthebreedingseason. mrirq t.h!a next 29 d of the breedingseason, one-halfthewws ineachtreatment~werebredartificidlly~~e otherhalfwere~ tobulls. All cuwswereexposed tolznillsthe reminderofthe breedingseason.In 1981all ems were bred a?ztificiallyduringthefirst42 dofthebe sfzlsonand~tobulls theremaindesofthebreedingseason. Averageage of calvesat the beginnixqof trea&mYCms 45.4+ 1.5 d in 1980 and 39.0+ 1.6 d in 1981. Calves kierefedgrainaMpGirie hayandhadaccesstowaterwhile~~firnntheirdams. Milkproductionwasestimatedbytheweigh-suckle-weigfi~~~ (16) atthe& ofeabmonth frcmAprilth?mugh Augustin1981. For the cows ancl calveswere separatedat 1400h; April~I%IElay measurements, the~~'kFeredll~to~the~at2200h,then~~~ overrli~t.At 0600h the next day, thecalveswereweighed,allcwedto nursetimweighed. Eight-hourmilkyi@ldwasestimatedaspos~ing weightminuspremrsingweight. TM daily8-h estimates were averaged and mltiplied by 3 for an estimateof 24-hmilk production.IXrirqthe SEPTEMBER 1986 VOL. 26 NO. 3
373
THERIOGENOLOGY
cows ard calveswere separatedat 0800 J-throughAugust-, h;the calveswere allmedto nursethe cmsat 1800h, then were separatedovernight.At 0600 hthenextday, thecalveswereweighed, allow&to nurse and reweighed. Three daily 12-h estimateswere averagedandthendoubledforan estimateof24-hmilkprcduction.The dailyestimatesweretakenondlternatedaysto~~interferencewith thegrazingpatternoftheccmandcalves. caWhipheightwasrecorded~y1,andcckJsandcdlveswere~ighed atthebeginningofeachmonthfmMaythmugh0ctober. In lateApril 1981 (beforethe treatmentperiod),ems and calves wereo&ervedcmtinuously for a 24-hpericdon pasture,ard incidence and durationof suckling were recorded.Inbuth years,thetotaltime eachcalfsuckledinldinboththeonce-andtwice-dailysucklegroups wasrecordedneartheendofthe sucklingtreatment. Atthesametime, thecontrol groupwas observed continuouslyfor a 24-h period on pasture, and incidence and duration of saxklingwerereco~ Incidenceand durationof sucklingfor allcows also were recorded duringa continuous24-h observationperiodonpasture wkafterthe endofthesucklingtmatment. concepti~datewasdeterminedbyrectdlpdlpationoftheuterus40 to 70 d after artificial insemimtionornatural service. Allcunception dateswzre verifiedby calvingdates. Differencesatmnggrcupsin percentagein estrus and pmgnancy ratesweretestedbyQli~ Intervaltofirstestmsand conception,milkpmonchanges, cm& calfweight changes& diffmcesin incidenceand durationof suckling were analyzed by genezallinearmodelproaedures(17). Thefinalmdelsforeachdeper~+ entvariable measuredincluded independentvariables whichwere significant sources of variation as well assuckl~ treatment. Indepemlentvariables includedin eacbmdel are reported in table footnates. RFSUUSANDDISCUSSIoN One calf each fmn the twiceilaily suckled, 48-h calfmmval, andcontrolgroqe diedeither shortlybefo~~orduring thebreeding seasonin 1980. Dataaboutthese calves ardtheirdamswerenot included. Thepementage ofcows shmingestrus thefirst 3wk afterthe onsetoftreatmntwas greaterinome- (RO.l) ~twice-dailysuckle (PxO.05) groups than in controls(Table 1). Ha--, ~fi=-W3e showingestrusthefirst 3wkof thebreedingseason ardtheintemal fmmcalvingtofizstestmswerenotdifferent. Only25.4%ofthecows were detected in estms during 3 wk of estrus detectionbefore treatment.Innoncyclingcms,thepercentageshowirqestrusthefimt 3 wk afterstartof treatmmt was greaterfor once- (RO.05) and twicedailysuckledems (RO.01) than for con-1 cows (Table2). The percentageshcrwingesWusthefiret3wkofthebreedingseason arKlintervalf?xxn calvingto fir&estrus wexenot diffe.re&almg the folx groups.
SEPTEMBER
1986 VOL. 26 NO. 3
THERIOGENOLOGY
Table 1.
Effect of forty-eight-hour calf removal oronce-ortiice-daily CWs sucUingo~repmductiveperfozmanceof
suckling
Once daily
IM No. of CCRJS
57
Fercentagesho&qestmsfirst 3wk afzter treatmentonset PercentageshoWqestmsfirst 3 wk of bre.edAq season Interv Fz$z&Lefirst2ld,% a&fzxxmilv~tofirst Freqnancy rate first.42 d, % xzfrate hq ==n, v=llv=Wto conception,d
%
?krice daily
treamt 48-h cdlf rexmval
56
control
55
56
80.7b
83.gc
74.5
64.3
91.2
85.7
85.5
82.1
52.222.6
53.322.6
54.922.6
55.Q2.7
49.1 75.4b 93.0 77.4k3.1
42.9 66.1h 92.9 81.1k3.2
50.9 78.2 90.9 75.123.2
42.9 69.6 82.1 77.753.4
?east-squares mans + SE adjusted for weight:height ratio. bDiffmx?.nt fmn con&l group (RO.10). =Different frtzncontrol group (RO.05). Table 2.
Effect of forty-eight-hour calf remval or once- or Wivly ~~on~~~ive~o~ ofnoncyclingcows SuclCiiRgtrea~t 48-h Twice calf Once daily daily remmal
Item No. of cxxm
44
Percentageshwingestrusfirst 3wkafYze~treatmntonset PercentageshWriragestrusfirst 3 wk of breeding season I"eF=,d fromcalvinqtofirst Pregnancymtefirst21d,% Fregmmyxatefirst42d,% Freqmcyratebreedingseason, Interval.fqmcalvingto conception , d
%
42
40
control 41
75.0c
7a,6d
65.0
51.2
88.6
al.0
80.0
75.6
55.5t3.1
56.e3.3
59.423.3
59.453.4
43.2 68.2 90.ge 77.323.6
47.6 66.7 90.5 74.433.7
47.5 80.0 92.5e 73.723.8
43.9 68.3 78.0 73.qt4.1
a~ were classified as noncycling if they were not detected in es&us bdurirg the 3 wk of estrus detection before treatmnt. L+sst-m means + SE adjusted for weight:height ratio. CDifferent from contrZls (R0.05). dDifferent from controls (R0.01). %ifferent from controls (Ro.10).
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375
w
THERIOGENOLOGY
rates werenot differentanmg We~m42-d~regnancy thefour gmups,althmgh once-and twice-dailysuckled groups had higher (RO.l) breedingseasonpregnancyrates than did contxols. Breedingseasonpreqarq rate was immased (RO.1) by once-daily suckleand 48-h calf removalinnoncyclingcms. Theintervalfmin calvingtoconceptionwas mtaffectedbysucJcling treaMwhenconsideringeithernoncyclingcmsorallcms. Noryestmetsignificantlyincreasedthe percentageof cows in estrusthefirst3wkafterthestartoftreatmentinbaththe48-hcdlf remval ard controlgmups (Table 3). When Noryestomstcclwswere excluded,morecawsintheonce- andtwice-dailysuckledgroupswere in estrusthefirst3wkafterthestartoftreatmntthaninthe48-hcdlf remvalorcontmlgmxps. Intemalf?mn calvingtofi& estrusarid calvingtoconceptionwerenotdifferentfor sucklingtreatmentgmups givenNorgestmet. Table4. Incidenceanddurationofsucklirqdu.r&q sucklingtreatment andtwoweeksaftersucklingtreatment sucklingtreatlnent Item
Once daily mice daily
No. of cclw-cdlf pairs
IncidencecQring trea=, suckles/24 h Eurationdu@ng treatment, total
1.0
56
55
2.0
Control 56 5.1 + 0.2
21.6+ 1.0
34.8+ 1.1
5.1+ 0.2
4.9 2 0.2
4.8 + 0.2
5.1 + 0.2
47.9+ 2.1
43.62 1.9
46.1t 1.7
48.6+ 2.0
45.8f 2.0
suckling
1nin/24 h Incidencea;ter txeatment, suckles/24 h Cxuationaf$er treamt, total
57
48-hcalf removal
suckling
m&/24 h @luesareleast-squaresmeans+SE. lncidenceanddurationof~~-~duringtreatmentwererecorded~y 26to28bothyears. %cidmce anddurationof su&lingaftertreatmentwererecotiedJune 12 to 16 in 1980and June 12 to 17 in 1981.
SEPTEMBER
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THERIOGENOLOGY
Raritel
(9)
repznzted
that
onoe-daily
suckling
tsl~~rtened
the
inter-
valtofirstestmsandconception inBrahman-cross,2-Yr -oldheifers mrsedorcedaily fmn 21-dpostpartumuntilfirstestrus. Once-daily ~~~alsoshorteneatheintewaltof~testrusin~caws(10) butdiclnotshortentheintemaltocom.mpticm. InoLIrax&G!r~,caws averaged42d pcsQm&mat theb@mirq oflimited suckling. The i&e.mal fmn calvirqto firstestms was 56.8+ 4.1 d for nonimplanted mWm. Zharef0x.q #erewaslittlechanceforsucklirx3treaiment toshW an advantage ininterval fmm calvjq to first estrus or conception.lheadvantageinbreedirqseasonpmgnancy rateforonceatxItwice-dailysuclcledccws inourtrialis similartothatrqmrtedby Stmdemnn et al. (18)for once-dailysuckledAngus~. Vihileonce-andtwice-dailymckledtr&xe&swerezxxm&q, cxmtrolems nurs& an averageof 5.1 f 0.2Cmes/24 h (Table4). The 1~32~~Uoninsu~ing stimulusin ~i~~~e~~~ bethefa~rcausing~cyclingactivitywithin3wkafterstart oftreatment. Sucklingfrequency orduration incontmlanimlshadno effect(DO.05) on interval fm calvirg to estrus or cxmception. SuM~treatithad noeffecton fmquencyorduration of suckling obmrv&2wkaftertrsa~tended. Milkpmduction bsforetreatnmt andchanges inmilk pxoduction inTable 5. SucUing wim=Y, June, YulyandAugustarerepxted txeatmenthadno effecton changein milkp3xx%&ion forany ofthe mnths. ~~~~wi~~~~~~(9)~~ once-dailysucklingarxIsuckl.ingadlibitm. Sucklingtreatmantdid affect(PC0.01) ccalfweightgains during~~y and June (Table5). !IMice-dailysuckled andcontrolcalvssgainednme durirqMay (pericdofsucklingtreatnmt) than did once-dailysuckledor 48-h calfremovalcalv~. Hmever, 48-h calf removalcalveshad thegreatestwsight gai.ndurixqJune. No differences in weightgab duri.rqJuly,ZUgustandSeptm&morinweaniqweightsofcalveswere obsem~~the~~graups. In other sAxdies, once-daily calf weightgainsduring thelimited sucXl*perioa yucMi.ng~ (9,19) but did notaffect weaningweights of calves (9,10, 19). l@mQmmy (19) repoMthatwei*t gainsduringthe1imitedsu&ling pzricdfor calves nursingtwicedaily wsresimilarto cxmtrols,which agmsswithresultsinaurstudy. areshawninTable Changesincoww+htfmr~~Maytzhxmqh~ 5. Ccrwweightchange inMay wasdifferent (F=O.l2) ammg the faur gmq6, with controlshaving greater(PcO.05)weightgains than 48-h calf-removaloronce-dailysuckledems. In Jtme,hmever, controls gainedless (PcO.05) than -ilysucMed aws. The advantagein weightgain fox-the contmlcmis m-the treatm.nt~iaI rraybe becauseofless stressandharxWng arxla morenearly nomalgrazing pattermhmever, b&honce- andtwice-dailysuckledcum seemed to adjusttolimitedsu~ing. Afterapproximtely 4 doftreatment, they grazeda normalamount 0fti.m. Ccwweight gains from Julythmugh septmberwemnotdifferentamngthefourgrcrups.
SEPTEMBER
1986 VOL. 26 NO. 3
THERIOGENOLOGY
Table 5. Effectof sucklingtrea+xtmtonmilkpra%ction, andcowweightchange
calfweightgain
Sucklingtreatment
Item
48-h calf remval
Once daily lWice daily
Milk prcduction (kg/24h)a 28 No. of m 10.3+2.8 Seforeeucklingtlx?a~ _ (lateApril) 2.6+1.0 Changeduriq: May JUne -2.Go.9 -0.4To.7 JOY -0.7zO.6 Ausust Cowbandcalfcweighte, kg No. of cow-calfpairs 57 Cowweight:height,lq/cm 3.7kO.l WY 1) Cowweightbefore 463.4+3.2 treatment (fQY1) Cm weight 50.0+4.9d changeduring: May 26.2T3.7d JUIW? 5.173.9 JW -9.6T5.1 Ausust 6.474.8 S_ Calfweightbefore 70.412.3 treatment (May1) Calfweight gai.ndurirKJ:May 32.5+1.3' JLll-ifZ 26.4+1.3d 42.9T2.9 JOY 18.6Tl.3 Ausust septanber 31.572.1 Calfweaningweight 222.456.1
29 9.eo.7
29
Control
29
9.820.8
9.43.8
1.7+0.9 -1.3To.9 -0.3To.7 -1.60.7
2.9+1.0 -2.4:l.O -0.lTo.a -1.eo.7
2.4tl.O -1.6+0.9 -0.lTO.7 -1.e.6
56 3.620.1
55 3.75.1
56 3.e.1
464.2k3.3
466.3+3.1 -
469.1t3.1
52.2+4.9&
21.aT3.6de 6.1T3.8 -7.3T5.0 ll.lT4.a 72.152.2
4a.7T5.zd 16.6f?.ge 5.e4.0 -4.4+5.2 6.875.1 67.e2.3
5a.3+4.ae 16.g3.5e 6.G3.7 -7.274.8 11.64.7 68.2Z2.1
37.akl.2: 30.e1.3': 36.9+1.2e 27.atl.2 33.1kl.3 30.&l.2e 40.6+2.7 39.822.8 41.dT2.5 2O.Gl.3 18.1+1.3 17.Gl.2 28.2T2.1 28.9T2.1 29.61.9 227.456.0 [email protected] 223.e5.6
43ilkproductionwasestimatedbythewei~-suckle-weightechniqueat the end of each month fmn April thmugh August in 1981. Valuee repo&edare1eaet_scluares means + SE adjusted for cow breed and bweightzheightratio. Cawweights andweightchangesareleast-squares mane +SE adjusted cfor cm breed, ccw age and weighkheight ratio. Calfweights andweightgains are least-equaxsmeans+SE adjusted for calf breed, calf age aM cm age. d,e,fMeansin theeameruwwithoutacommn mperecript differ (R0.05). REFERmcEs
1. Clapp, H. A factor in breeding efficiencyof dairy cattle. Froc. Amer. Sot. ?mim. PJX& -30:259-265 (1937).
SEPTEMBER
1986 VOL. 26 NO. 3
379
2. Wiltbank, J. N. and cook, A. C. The aqarative repmductive pe?zfoxnwlceof nursed c(xJs and m.i.lkKlc!uhYs. J. Anim. Sci. -17:640-648 (1958). 3. Short, R. E., Bellcrws, R. A., Moo&, E. L. andHcwl%d, B.E. Exfecte of suckungand~on bcwine gxs@dxm repx%Ybction. J. Ankn. Sci. -34:70-74 (1972). 4. !@Atemm, Inf%~of rangecws.
R. P., -, E. Y., Wyatt, R. D. &'Ibbzek,R. sucklinginteneity on repmdztive px-fomance of J. Anim. Sci. -47:342-346 (1978).
Effects of early 5. laster, D. B., Gliq, H. A. and Gregory, K. E. weaning on pusreproduction of cfxs. J. Anim. Sci. -36:734-740 (1973). 6. Bellcws, R. A., short, R. E., Uric&, J. 3. and Pahnieh,0. F. Effectsofearlyweaningonpostpartum repmductionofthedrmtard growth of calves born as multiple or single. J. Anink. Sci. -39:589-600 (1974). 7. =r Early weanirq and uxep M., Kiqble, K. G. and Crxah, L. feeding fordrylotcalves. J. Anin!.. Sci. -45 (Suppl.1):47 (1977). 8. ~,K.~~~~, +P. andTuman,E. Effects of Barly fxst-calf heifers mJ' calf and heifer m perfomance. J. Anim. Sci. -53:1193-1197(1981). 9. l?ardel, R. D. Effect of ~~Y~~~~~ andww-calfperfoxlwice offirst calf Bidx0anXHerefordheifers. J. him. Sci. 53:755-757 (1981). 10. Reeves, J. J. arxl Gaskins, C. T. Effsct ofonce-a-daynursingon rebreedingefficiency of beef cows. 3, Anh Sci. -53:889-891 (1981). 11. Leexdster, J. L. and Drake, D. J.
rrmrraloncdlfeo-
Effect of +=w==Y
calf
am3 estrusactivityofp&qarbmbeef
COSJS. J. Anixn.Sci. -47 (Sqpl. 1):144 (1978). 12. lIXanaldson, L. E., Bassett,J. M. ad Thornburn,G. D. I%!xi#Ieral rz&emne~~tionof awedurirqp&erty,oestrous p&zzp7, mgnancy and lactationand the effects of urdemutrition cozxze&mtions. J. oxytodnon pxqeetemne or e=w== Edocrinol. $$599-614 (1970). 13. Cdde, K. G., Ward, H. S., Kiracofe,G. H., I&d&e, R. M. a-d Kittok, R. J. Sho*estrwscyclesardasecciatedeemmpmgestemne levels in beef CICIWS.Thericgenologyg:105-112 (1980). 14. -Y, W. D., XQUmbach, C. C., lsmn, T. G., Koritnik,D. R. and Ni.sweder,G. D. Characterization of hormonal patterns in the l33efccrw~~~~. Y. Aninl. SC& 5&@445-453 (1983).
380
SEPTEMBER 1986 VOL. 26 NO. 3
15.
Ramirez-Godinez, J, A., Kiracofe,G. H., McXee, R, M., SchdLles, R. R. and Kittok,R. J. %ducixq thelnciaence of short estmus reriogenology 2:613-623 cyclesinkefcawswitiIIo~ (1981).
16.
Boggs, D. L., Smith, E, F., schdlles,R. R., Brerrt,B. E., Co=& L. R. and Pruitt‘ R. J. Effech ofmi2kandforagebbIkeoncdlf pe?zfozmanc.e. J. Anim. Sci. -51:550-553 (1980).
statistics. statistiodt~ysissystem 17, SAS. SAS Ufx&sGuide: Institute,Snc., Cay, NC, 1982, pp. 140-199. 18. Studemam, J. A., WilJdnson,S. R. I catdle, A. B., Cicdia, H., Dudzinsky,M. L. ti Williams,D. J. Effect of mce-ddly mddi.nq 0fyGurqAnguscxx#sonth~~~onandcdtf~* J, A&m. Sci. 53 (Sup& I):370 (1981). Inflmof;axdkl*frequencyanJ.b~ 19.. F&m@meq, G. W. tinetxeatmnton themsumptionof cmiriancycles irim kefcattle. Thericgenology-17:551-563(1982).
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