Factors associated with the concentration of immunoglobulin G in the colostrum of dairy cows

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1 Animl (213), 7:11, pp & The Animl Consortium 213 doi:1.117/s niml Fctors ssocited with the concentrtion of immunogloulin G in the colostrum of diry cows M. Conneely 1,2, D. P. Berry 1, R. Syers 1, J. P. Murphy 1, I. Lorenz 2, M. L. Doherty 2 nd E. Kennedy 1-1 Animl & Grsslnd Reserch nd Innovtion Centre, Tegsc, Mooreprk, Fermoy, Co. Cork, Irelnd; 2 School of Veterinry Medicine, University College Dulin, Dulin 4, Irelnd (Received 24 Septemer 212; Accepted 1 June 213; First pulished online 6 August 213) Trnsfer of sufficient immunogloulin G (IgG) to the neontl clf vi colostrum is vitl to provide the clf with immunologicl protection nd resistnce ginst disese. The ojective of the present study ws to determine the fctors ssocited with oth colostrl IgG concentrtion nd colostrl weight in Irish diry cows. Fresh colostrum smples were collected from 74 diry cows of vrying reed nd prity from four Irish reserch frms etween Jnury nd Decemer 211; colostrl weight ws recorded nd the IgG concentrtion ws determined using n ELISA method. The men IgG concentrtion in the colostrum ws 112 g/l (s.d g/l) nd rnged from 13 to 256 g/l. In totl, 96% of the smples in this study contined.5 g/l IgG, which is considered to e indictive of high-qulity colostrum. Men colostrl weight ws 6.7 kg (s.d kg) with rnge of.1 to 24 kg. Fctors ssocited with oth colostrl IgG concentrtion nd colostrl weight were determined using fixed effects multiple regression model. Prity, time intervl from clving to next milking, month of clving, colostrl weight nd herd were ll independently ssocited with IgG concentrtion. IgG concentrtion decresed ( P,.1) y 1.7 (s.e. 5.6) g/l per kg increse in the colostrl weight. Older prity cows, cows tht hd shorter time intervl from clving to milking, nd cows tht clved erlier in spring or in the utumn produced colostrum with higher IgG concentrtion. Prity ( P,.1), time intervl from clving to milking ( P,.1), weight of the clf t irth ( P,.5), colostrl IgG concentrtion ( P,.1) nd herd were ll independently ssocited with colostrl weight t the first milking. Younger prity cows, cows milked erlier post-clving, nd cows with lighter clves produced less colostrum. In generl, colostrum qulity of cows in this study ws higher thn in mny previous studies; possile resons include use of reltively low-yielding cow type tht produces low weight of colostrum, short clving to colostrum collection intervl nd grss-sed nutritionl mngement. The results of this study indicte tht colostrl IgG concentrtion cn e mximised y reducing the time intervl etween clving nd collection of colostrum. Keywords: colostrum, diry, cow, milk, immunogloulins Implictions The ojective of the present study ws to determine the fctors ssocited with oth colostrl qulity nd colostrl weight in diry cows in psture-sed system. The results provide useful informtion to frmers to enle them to mximise the efficiency of their colostrum mngement progrmmes nd improve clf helth. Frmers should collect colostrum from cows s soon s possile fter clving, e wre tht if lrge quntity of colostrum is produced it is likely to e of lower qulity, nd tht cows clving lte in spring my hve reduced colostrum qulity. In this study, there ws no requirement to discrd colostrum from heifers ecuse of inferior qulity. - E-mil: Emer.Kennedy@tegsc.ie Introduction Colostrum is the first milk secreted fter prturition (Prk nd Jcoson, 1993) nd contins mny sustnces tht re importnt to the helth of the neonte including immunogloulins, cytokines, nutritionl elements nd growth fctors (McGuirk nd Collins, 24). Immunogloulins re plsm proteins, produced y lymphocytes in the mmmlin loodstrem in response to foreign ntigens, which ply crucil role in the immune mechnism to defend the ody from pthogenic orgnisms nd provide resistnce to disese (Prk nd Jcoson, 1993). Five clsses of immunogloulins exist: IgM, IgG, IgA, IgD nd IgE (Butler, 1969). Immunogloulin G (IgG), which comprises 85% to 9% of the totl immunogloulins present in ovine colostrum (Lrson et l., 198), is trnsferred from the lood cross the mmmry epithelium, 1824

2 Colostrum qulity ccumulting in the mmmry glnd efore prturition. Although colostrum contins wide spectrum of other importnt components, the reltionship etween IgG concentrtions nd clf helth is est understood; thus, the concentrtion of IgG in colostrum is considered the hllmrk for evluting colostrum qulity (Godden, 28). Good-qulity ovine colostrum is defined s colostrum tht hs n IgG concentrtion of.5 g/l (McGuirk nd Collins, 24). In 211, the reported officil ntionl clf mortlity rte in Irelnd ws 4.6% (clves ded in the first 12 months of life excluding stillirths: AIM Sttistics Report, 211). This compres unfvourly with mortlity rtes reported for other Europen countries; Gulliksen et l. (29) reported lower mortlity rte of 3.7% for clves in the sme ge group in Norwy. Presently, there is lck of pulished dt on the colostrum qulity of Irish diry cows, nd s such it is not known whether production of colostrum with low IgG concentrtion my e contriutory fctor to the high clf mortlity rte in Irelnd. Ensuring tht the neontl clf receives sufficient high-qulity colostrum s soon s possile fter irth is widely recognised s eing crucil to the niml s helth nd well-eing. The mny unfvourle consequences of insufficient sorption of IgG y the neontl clf (e.g. incresed risk of disese nd deth, slower growth rtes nd reduction in long-term productivity) re well documented (Roison et l., 1988; DeNise et l., 1989). Indequte sorption of immunogloulins y the clf my occur for mny resons such s timing of the first feeding (Besser et l., 1985) nd volume of the feeding (Stott et l., 1979).However,the fctor of most criticl importnce is the concentrtion of IgG in colostrum (Pritchett et l., 1991). Although much reserch hs een conducted on the fctors ssocited with colostrum qulity in cows, including prity (Pritchett et l., 1991; Gulliksen et l., 28; Kehoe et l., 211), reed (Muller nd Ellinger, 1981), length of the dry period (Pritchett et l., 1991), time intervl from clving to milking (Lom et l., 1978; Moore et l., 25; Morin et l., 21) nd volume of colostrum produced (Kruse, 197; Pritchett et l., 1991), few studies hve exmined the fctors ssocited with the colostrum qulity of cows in sesonl, grss-sed systems such s those tht exist in Irelnd. Moreover, only limited numer of studies hve ttempted to quntify the reltionship etween colostrl IgG concentrtion nd colostrl weight (Pritchett et l., 1991; Guy et l., 1994; Bumrucker et l., 21). The ojective of this study ws to determine the fctors ssocited with colostrl IgG concentrtion nd colostrl weight of the first milking post-clving in Irish diry cows. Results from this study will provide vlule informtion to enle frmers to mximise the efficiency of their colostrum mngement progrmmes nd ultimtely improve clf helth. Mteril nd methods The study ws conducted from 15 Jnury to 7 Decemer 211 on four Tegsc reserch frms, nmely Mooreprk, Curtin s, Kilworth nd Bllydgue, ll locted in County Cork, in southern Irelnd (ltitude 5289, longitude 8816 ). Study popultion Fresh colostrum smples (1 ml) were collected from 74 diry cows, which clved etween the months of Jnury nd April (n 5 642), or etween the months of Septemer nd Decemer (n 5 62). These nimls consisted of 455 Holstein Friesin, 5 Jersey, 81 Jersey 3 Holstein Friesin crossreeds, 28 Norwegin Red, 4 Norwegin Red 3 Holstein Friesin crossreeds nd seven Montellirde, with the remining 43 cows eing vriety of Holstein crossreeds. In totl there were 25 first prity nimls nd 157, 139, 98 nd 15 cows in their second, third, fourth nd fifth or greter prity, respectively. Cow mngement Dry cow mngement. All spring-clving cows were mnged similrly efore nd during colostrum smple collection. Cows were dried off when producing,8 kg milk dily or within 6 dys of clving. Spring-clving cows were housed in cuicle shed, where they remined until they were turned out to grss directly post-clving. The dry cow diet consisted of d liitum silge (71% dry mtter digestiility (DMD)), 2 kg of rley strw nd 1 to 2 kg of dry cow concentrte per cow depending on cow ody condition score (BCS) t drying off. Minerl supplementtion commenced 2 months efore clving using powder mixed through the silge t rte of 1 g/cow per dy (Multitrce Pre-clver, Inform Nutrition Irelnd). All utumn-clving cows were retined t psture during the dry period with the mjority clving outdoors. Once clved, they joined the lctting herd ut were mintined on grzed psture diet. The diet of the utumn-clving cows during the dry period consisted of grzed grss nd they hd ccess to minerl lick to meet their pre-clving minerl requirements while t psture. The helthcre progrmme for ll cows included prophylctic tretment for gstrointestinl roundworms nd liver fluke, s well s routine vccintion ginst leptospirosis, ovine virl dirrhoe, slmonellosis nd rotvirus. Mngement t clving. Lte-gesttion spring-clving cows nd heifers were housed in lrge group pens of,2, while utumn-clving cows were retined t psture in two groups (,3 per group) depending upon prturition dte. When prturition ecme imminent, cows were moved into individul clving pens, where ll clvings were ttended nd oserved y competent nd trined personnel. Clves were removed from the dm immeditely (efore they were stnding) so tht no suckling occurred. Informtion recorded t clving included dte nd time of irth, sex of clf, weight nd reed of clf, whether the clf ws orn live or stillorn, presenttion of the clf (norml, posterior, reech, leg ck, hed ck, etc.) nd degree of clving difficulty on 1 to 5 scle (1 5 no ssistnce, 5 5 veterinry intervention). Other informtion ville 1825

3 Conneely, Berry, Syers, Murphy, Lorenz, Doherty nd Kennedy included time intervl from clving to susequent milking, cow ody weight mesured up to 14 dys post-clving nd BCS (scle 1 to 5; Edmonson et l., 1989) mesured within 14 dys of clving, length of preceding dry period (pluripre only), reed frction, degree of heterosis nd recomintion nd cow economic reeding index (EBI; Berry et l., 27). The EBI is single figure profit index imed t identifying the most profitle nimls for reeding diry herd replcements, which comprises informtion on six su-indexes relted to profitle milk production: milk production, fertility, clving performnce, eef crcss, mintennce nd helth. Colostrum smpling nd nlysis Cows were individully milked t the next scheduled herd milking time following clving (83 or 153 h) y mchine into steel churn nd the weight of the colostrum ws recorded. The entire quntity of colostrum otined ws gitted to ensure its constituents were evenly distriuted; 1 ml smple ws tken into 12 ml polypropylene ottle (SGR Scientific Ltd, Swords, Co. Dulin, Irelnd) nd ws frozen immeditely t 228C. The frozen colostrum ws thwed t room temperture, susmple of the collected colostrum ws centrifuged t 35 3 g for 3 min, the surfce ft ws removed nd the superntnt ws collected nd refrozen t 228C until nlysis. The colostrum smples were thwed t room temperture the dy efore lortory nlysis. IgG concentrtion of the smples ws determined y the ELISA method (Bovine IgG ELISA Kit Ct. No. 81, Alph Dignostic Interntionl, Sn Antonio, TX, USA). Smples were ssyed in duplicte, with n interssy CV of.15. The concentrtion of IgG in smples ws clculted from stndrd reference curve contining known concentrtions of IgG. Any smple tht resulted in n IgG concentrtion tht fell outside the rnge of the stndrd reference curve ws retested fter further dilution ccording to the test recommendtions. Dt editing Cows were ctegorised ccording to the month of clving. One hundred nd twenty three cows clved in Jnury, 338 clved in Ferury, 128 in Mrch nd 52 in April nd 1 in My, 2 in August, 28 in Septemer, 21 in Octoer, 9 in Novemer nd 2 in Decemer. For the purposes of the sttisticl nlysis in this study, the one cow tht clved in My ws ssumed to hve clved in April, the two cows tht clved in August were ssumed to hve clved in Septemer nd the two cows tht clved in Decemer were ssumed to hve clved in Novemer. The time of dy of clving ws ctegorised s: clved etween the hours of 6 nd 12 h (n 5 181), 12 nd 18 h (n 5 155), 18 nd h (n 5 184) nd nd 6 h (n 5 164); time of dy of clving ws unville for 2 nimls nd these were treted s seprte ctegory. The time intervl from clving to first milking ws ctegorised s: milked within 3 h of clving (n 5 173), etween 3 nd 6 h (n 5 143), 6 nd 9 h (n 5 118), etween 9 nd 12 h (n 5 111), etween 12 nd 15 h (n 5 49), etween 15 nd 18 h (n 5 55) nd etween 18 nd 21 h post-clving (n 5 21). Cows for which no record of time of clving ws ville (n 5 34) were treted s seprte ctegory. The length of the dry period ws ctegorised s,8 weeks (n 5 41), 8 to 16 weeks (n 5 384), 16 to 24 weeks (n 5 41) nd.24 weeks (n 5 33); primipre were treted s seprte ctegory. The degree of clving difficulty ws ctegorised s: (1) no ssistnce given to cow during clving (n 5 621), (2) mnul ssistnce given without use of clving id (n 5 47), (3) mnul ssistnce given with use of clving id (n 5 22) nd (4) clving time prolonged nd/or veterinry ssistnce required (n 5 14). Cows tht gve irth to clf of,2 kg (n 5 9), 2 to 3 kg (n 5 145), 31 to 4 kg (n 5 338), 41 to 5 kg (n 5 163) nd.5 kg (n 5 8) were treted s seprte ctegories; records of weight of the clf t irth were unville for 41 cows nd these were treted s seprte ctegory. Cow BCS (scle 1 to 5), mesured up to 14 dys post-clving, ws ctegorised s: <2.75 (n 5 55), 3(n 5 135), 3.25 (n 5 231) nd >3.5 (n 5 11). Cow BCS records were unville for 182 nimls nd these were treted s seprte ctegory (i.e. missing ). Cow ody weight mesured up to 14 dys following clving ws ctegorised s: <4 kg (n 5 6), 41 to 45 kg (n 5 111), 451 to 5 kg (n 5 132), 51 to 55 kg (n 5 11), 551 to 6 kg (n 5 99) nd >61 kg (n 5 17). Cow ody weight records were unville for 94 nimls nd these were treted s seprte ctegory. Concentrte fed in the first 35 dys of the previous lcttion ws ctegorised s <4 kg (n 5 46), 41 to 6 kg (n 5 19), 61 to 8 kg (n 5 21) nd >8 kg (n 5 52); records of concentrte fed in the first 35 dys of the previous lcttion were unville for 26 nimls (including primipre) nd these were treted s seprte ctegory. Cows were ctegorised ccording to their EBI s:,h6 (n 5 33), h61 to h9 (n 5 72), h91 to h12 (n 5 163), h121 to h15 (n 5 213), nd.h15 (n 5 94); EBI dt were unville for 129 nimls nd these were treted s seprte ctegory. Milk production in the first 35 dys of the previous lcttion ws ctegorised s:,35 kg (n 5 19), 351 to 4 kg (n 5 28), 41 to 45 kg (n 5 78), 451 to 5 kg (n 5 73), 51 to 55 kg (n 5 94), 551 to 6 kg (n 5 99), 61 to 65 kg (n 5 51) nd.65 kg of milk produced (n 5 56); primipre were treted s seprte ctegory. Sttisticl nlysis Both colostrl IgG nd colostrl weight were normlly distriuted. Fctors ssocited with colostrum IgG concentrtion nd weight were determined using fixed effects multiple regression model in PROC GLM in SAS (Version 9.1, SAS Institute Inc., Cry, NC, USA). A numer of vriles were first tested for ssocition with IgG nd colostrl weight in series of univrite nlyses. Month of clving, time of dy of clving, time intervl from clving to milking, prity, dry period length, degree of clving difficulty, sex of the clf, whether the clf ws orn live or stillorn, weight of the clf t irth, cow BCS mesured up to 14 dys following clving, cow ody weight 1826

4 Colostrum qulity mesured up to 14 dys following clving, the quntity of concentrte fed in the first 35 dys of the previous lcttion, EBI of cow, milk production in first 35 dys of previous lcttion nd herd were ll considered s ctegoricl vriles. Heterosis nd recomintion loss coefficient s well s proportion of the reed Holstein, Jersey, Friesin, Montellirde, Norwegin Red or other, ech treted s seprte effects, were considered s continuous vriles. Furthermore, IgG concentrtion of colostrum ws included s n independent vrile when the dependent vrile ws colostrl weight. Weight of colostrum ws included s n independent vrile when the dependent vrile ws IgG concentrtion. All vriles ssocited (P,.5) with the dependent vrile in the univrite nlyses were included in multiple regression model. Non-significnt vriles (P..5) were sequentilly removed using ckwrd elimintion. Once ll remining independent vriles were ssocited (P,.5) with the dependent vrile, the removed vriles were once gin tested for significnce with the significnt vriles forced into the multiple regression model. Interctions etween ll significnt vriles were exmined; none were found to e significnt. Lest squres mens were compred. Genetic nd residul vrinces were estimted for oth IgG concentrtion nd colostrl weight using liner mixed niml model in ASREML (Gilmour et l., 29). Fixed effects included in the model were determined from the fixed effects model nlysis with the exception of colostrl weight, which ws not considered for inclusion in the model. Animl ws included s rndom effect in the mixed model with the pedigree of ech niml trced ck t lest four genertions, where ville. Results Colostrl IgG concentrtion The concentrtion of colostrl IgG vried gretly mong nimls, with men of 112 g/l (s.d g/l) nd rnge of 13 g/l to 256 g/l (Figure 1); the coefficient of vrition ws 46%. In totl, 96% of smples contined.5 g/l of IgG, which is used s the threshold to define colostrum s eing of high qulity (McGuirk nd Collins, 24). Prity (P,.1), time intervl from clving to next milking (P,.1), month of clving (P,.5), colostrl weight (P,.1) nd herd (P,.5) were ll independently ssocited with IgG concentrtion in the multiple regression model. There ws generl trend for colostrl IgG to increse with prity (Figure 2). First (97 g/l) nd second (99 g/l) lcttion cows produced colostrum with lower IgG concentrtion thn cows in their third nd fifth lcttion. Colostrl IgG ws negtively ssocited (P,.1) with time intervl from clving to milking. In generl, colostrum hrvested lter thn 9 h post-clving hd lower IgG concentrtion thn colostrum hrvested efore this time (Figure 3). Colostrum with the gretest men IgG concentrtion (124 g/l) ws produced y cows tht were milked etween 3 nd 6 h post-clving, lthough there ws no difference etween Percent IgG Figure 1 Distriution of immunogloulin G (IgG; g/l) in colostrum smples from 74 Irish diry cows. IgG (g/l) c Prity Figure 2 Lest squres mens for colostrl immunogloulin G (IgG) concentrtion (g/l) for different prities. Error rs represent one stndrd error ech side of the lest squre men.,,c Mens with different superscripts differ. IgG (g/l) to 3 3 to 6 6 to 9 colostrum hrvested 3 to 6 h post-clving nd colostrum hrvested 3 h erlier or 3 h lter. Cows milked etween 18 nd 21 h post-clving hd the lowest IgG concentrtion (93 g/l), lthough this ws not different to tht of colostrum hrvested fter 9 h. Cows tht clved in April produced colostrum with lower IgG concentrtion (87 g/l) thn cows clving in the erlier spring 9 to to 15 c 15 to to 21 Time intervl from clving to milking (hours) Figure 3 Lest squres mens for colostrl immunogloulin G (IgG) concentrtion (g/l) y time intervl from clving to milking in hours. Error rs represent one stndrd error ech side of the lest squre men.,,c Mens with different superscripts differ. 1827

5 Conneely, Berry, Syers, Murphy, Lorenz, Doherty nd Kennedy IgG (g/l) Jn Fe Mrch April/My Month of clving Aug/Sep Oct/Nov/Dec Figure 4 Lest squres mens for colostrl immunogloulin G (IgG) concentrtion (g/l) y month of clving. Error rs represent one stndrd error ech side of the lest squre men.,,c Mens with different superscripts differ. Colostrl weight (kg) to 3 3 to 6 6 to 9 9 to to to to 21 Time intervl from clving to milking (hours) Figure 6 Lest squres mens for colostrl weight (kg) y time intervl from clving to milking. Error rs represent one stndrd error ech side of the lest squre men.,,c Mens with different superscripts differ. c c c Colostrl weight (kg) c c Prity Figure 5 Lest squres mens for colostrl weight (kg) y prity. Error rs represent one stndrd error ech side of the lest squre men.,,c Mens with different superscripts differ. c Colostrl weight (kg) < > 5 Clf weight ctegory (kg) Figure 7 Lest squres mens for colostrl weight (kg) y clf weight ctegory. Error rs represent one stndrd error ech side of the lest squre men., Mens with different superscripts differ. months or in the utumn months (Figure 4). Concentrtion ws negtively ssocited (P,.1) with colostrl weight, decresing linerly y 1.7 g/l (s.e. 5.6) per kg increse in colostrl weight. The heritility of IgG concentrtion ws.1 (s.e. 5.7). The genetic stndrd devition for IgG concentrtion ws 16. g/l suggesting coefficient of genetic vrition of 14.3%. Colostrl weight Men colostrl weight t the milking immeditely postclving ws 6.7 kg (s.d kg) with rnge of.1 to 24 kg. Prity (P,.1), time intervl from clving to milking (P,.1), weight of the clf t irth (P,.5), colostrl IgG concentrtion (P,.1) nd herd (P,.1) were ll independently ssocited with colostrl weight t the first milking in the multiple regression model. Colostrl weight t the first milking ws positively ssocited (P,.1) with prity (Figure 5). First lcttion nimls produced the lowest yield of colostrum (5.3 kg). The highest yield, from third lcttion cows (7.9 kg), while not different for cows entering their second or fourth lcttion, ws higher thn tht for cows entering their first nd fifth lcttion. Colostrl weight t first milking incresed (P,.1) with time intervl from clving to first milking (Figure 6). Cows milked 12 h post-clving nd therefter, yielded more colostrum thn cows milked efore this time. There ws no difference mong the lest squres mens of nimls milked efore 12 h; nor ws there difference mong the lest squre mens of nimls milked fter 12 h. The highest yield of colostrum (8.2, s.e. 5.7 kg) ws from cows milked for the first time etween 18 nd 21 h post-clving, nd the lowest yield (6.3, s.e. 5.4 kg) ws from cows milked etween 3 nd 6 h post-clving. Colostrl weight t the first milking ws positively ssocited (P,.5) with weight of the clf t irth (Figure 7) with difference of 2.1 kg colostrl weight etween the lightest (,2 kg) nd heviest (.5 kg) clves. The weight of colostrum t the first milking decresed linerly (P,.1) y 7 g (s.e. 5 2 g) per g/l increse in IgG concentrtion. The heritility of colostrl weight ws.21 (s.e. 5.8). The genetic stndrd devition of colostrl weight ws 1.49 kg indicting coefficient of genetic vrition of 22.3%. Discussion Ensuring tht the neontl clf ingests nd sors criticl mss of IgG from colostrum is necessry for it to cquire immunity (McGuirk nd Collins, 24) nd is estlished s eing crucil to its future helth nd productivity (Kruse, 197; Roison et l., 1988; DeNise et l., 1989). The ovine 1828

6 Colostrum qulity plcent does not llow the trnsfer of immunogloulins from the dm to the clf while in utero nd so the neworn clf must sor criticl mss of IgG from colostrum efore cesstion of intestinl trnsport occurs t 24 to 36 h of ge to cquire immunity ginst the pthogenic orgnisms it will encounter s soon s it is orn (Wever et l., 2). As mny studies evluting colostrl IgG concentrtion nd weight hve een undertken within non-psture-sed systems of production (Morin et l., 21; Kehoe et l., 211), it is unknown whether low concentrtion of IgG in colostrum could e fctor contriuting to the reltively high clf mortlity rte in Irelnd. The ojective of this study, therefore, ws to quntify the colostrl IgG concentrtion nd weight of Irish diry cows in psture-sed system nd determine the ssocited fctors. Colostrl qulity The colostrum of the cows in this study ws, in generl, of good qulity. In totl, lmost 96% of the colostrum smples in this study contined. 5g/l IgG, which is considered to e n indiction of high-qulity colostrum (McGuirk nd Collins, 24). Fifty-four percent of smples contined >1 g/l IgG. The existence of heritle genetic vrition for IgG reported in this study, lthough lower thn the heritility of.41 reported y Gilert et l. (1988) in the colostrum of US Hereford, Angus nd Simmentl cows, nonetheless suggests tht reeding for improved IgG levels in colostrum is indeed fesile. The rnge of IgG concentrtion (13 to 256 g/l) ws similr to the rnges reported in other studies; Bumrucker et l. (21) reported vlues of 9 to 166 g/l in US study of 214 cows while concentrtions of 2 to 235 g/l were reported in Norwegin study (Gulliksen et l., 28). This wide rnge in colostrl IgG concentrtion demonstrtes the enormous vrition tht exists etween individul cows. The men IgG concentrtion of smples in the present study ( g/l; men6s.d.) ws higher thn tht of some previous studies (Pritchett et l., 1991; Bumrucker et l., 21; Morrill et l., 212), ut similr to tht of others. Kehoe et l. (211) reported men colostrl IgG concentrtion of 96 g/l (s.d g/l) in 54 Holstein cows in Pennsylvni, United Sttes Americ, while Rivero et l. (212) in study of 157 Holstein Friesins in Southern Chile lso reported high men IgG concentrtion of 93 g/l (s.d g/l). Bielmnn et l. (21) lso reported high men concentrtion of 94 g/l in study of 288 Holstein diry cows in Ontrio, Cnd. It is importnt to er in mind tht these studies hve quntified colostrl IgG using different lortory nlysis techniques; some hve used rdil immunodiffusion (Kehoe et l., 211; Rivero et l., 212) while others hve used ELISA (Bumrucker et l., 21; Nowk et l., 212). Furthermore, differences in smple preprtion etween studies lso exist. Bumrucker et l. (21) removed the colostrl ft efore nlysis ut Morrill et l. (212) did not. These differences in lortory methods present difficulties when ttempting to mke true comprisons of colostrl IgG concentrtions cross studies s vrition in IgG concentrtions mesured my e prtly ttriutle to the method used. While it hs een estlished tht removl of colostrl ft efore RID nlysis cn led to n overestimtion of IgG concentrtion (Fleenor nd Stott, 1981), the uthors of the present pper hve found tht there is currently no cler consensus on whether ft should e removed efore nlysis y ELISA. In order to further vlidte the ELISA results otined in the present study, 2 colostrum smples were retested using the sme kit in different lortory (Enfer Group, M7 Business Prk, Newhll, Ns, Co. Kildre, Irelnd). The results otined were eqully s high s those otined in the initil nlysis. Moreover, 2 colostrum smples were retested using different ELISA kit (Bethyl Lortories Inc., Montgomery, TX, USA); on this occsion the results otined were higher thn those otined in the initil nlysis. It is possile tht the high men IgG concentrtion of colostrum reported in this study my e result of overestimtion y the ELISA kit itself. Potentil is in the estimte of totl men IgG concentrtion does not ffect the results of the fixed effects nlysis. Possile resons for the reltively high men IgG concentrtion of colostrum in the present study include short clving to colostrum collection intervl (Morin et l., 21), good grss-sed nutritionl mngement, nd the use of reltively low-yielding cow type tht produces low weight of colostrum. The verge totl lcttion milk yield for the cows in the present study ws 5256 kg, considerly lower thn yields reported in previous studies; Pritchett et l. (1991) reported men totl lcttion milk yield of 979 kg. Short clving to colostrum collection intervl ws considered to e n importnt fctor contriuting to high colostrum qulity in the study y Kehoe et l. (211), in which colostrum ws collected within 2 to 6 h of clving, nd in the study y Rivero et l. (212), in which colostrum ws collected in the 1st hour fter clving. In the present study, while there ws wide rnge in the time intervl from clving to colostrum collection (shortest time intervl from clving to milking ws 1 h, the longest ws 21 h), 61% of the smples were collected within 9 h of clving, which my hve contriuted to the high colostrum qulity. Colostrl weight The inverse reltionships reported in the present study etween colostrl weight nd IgG concentrtion corroortes previous studies (Pritchett et l., 1991; Guy et l., 1994) nd is possily due to dilution effect. Guy et l. (1994) reported n increse in lctogenic ctivity tht ws concurrent with decresed IgG concentrtion in colostrl secretion, the timing nd mgnitude of which indicte tht colostrl IgG concentrtion is determined y the reltive quntity of the non-igg constituents of colostrum. IgG is ctively trnsported from the serum of the dm cross the mmmry epithelil rrier y specific receptors to ccumulte in the mmmry glnd efore prturition (Lrson et l., 198). Incresed secretion of lctose occurs nd egins to incorporte more wter, which increses colostrum volume nd hs diluting effect on IgG concentrtion (Bumrucker et l., 21). 1829

7 Conneely, Berry, Syers, Murphy, Lorenz, Doherty nd Kennedy Time intervl etween clving to milking In greement with previous interntionl studies (Lom et l., 1978; Stru nd Mttheus, 1978; Moore et l., 25; Morin et l., 21), colostrum IgG concentrtion ws negtively ssocited with the intervl from clving to colostrum collection. Corroorting the results from Stru nd Mttheus (1978), the present study filed to identify significnt difference in IgG concentrtion for cows milked up to 9 h post-clving, lthough IgG decresed therefter. Lom et l. (1978) reported tht immunogloulin content ws reduced to 8%, 7% nd 4%, respectively y 6, 12 nd 24 h postprtum, compred with immunogloulin content in colostrum milked immeditely postprtum. In the present study, IgG concentrtion of colostrum collected etween 9 nd 12 h postprtum ws reduced to 86% compred with tht of colostrum collected in the first 3 h postprtum, while IgG concentrtion of colostrum collected etween 18 nd 21 h postprtum ws reduced to 77%. A more recent study (Morin et l., 21) reported decrese in colostrl IgG concentrtion of 3.7% per hour post-clving. In the present study, colostrl IgG concentrtion decresed y 1.1% per hour post-clving. Furthermore, the ility of the neontl clf to sor IgG from colostrum declines progressively fter 6 h of ge (Besser et l., 1985) nd thus colostrum should e collected from the dm nd fed to the neworn clf s soon s possile fter irth. This ensures colostrum of the highest possile IgG concentrtion is eing fed, nd lso ensures mximum sorption of IgG y the neonte. Cows tht were milked lter still produced colostrum with lower concentrtion of IgG even fter djustment ws mde for weight of colostrum (i.e. the fct tht cow milked long time post-clving hd low colostrum IgG concentrtion ws not simply due to the fct tht she ws more likely to hve hd higher colostrl weight). As such, while post-prturient secretion y the mmmry glnds of fluid with much lower IgG concentrtion thn tht of colostrum contriutes to lower colostrl IgG with incresed time from clving to milking (Morin et l., 21), the present study does not support the view tht dilution lone is responsile. Moore et l. (25) lso disputed the dilution hypothesis; reporting tht while colostrum collected 6, 1 nd 14 h fter clving from 13 Holstein cows hd significntly lower IgG concentrtions thn colostrum collected 2 h fter clving, there ws no significnt increse in the weight of the colostrum produced t these times. For this reson they concluded tht the oserved decrese in colostrl IgG concentrtion ws not due to dilution effects nd suggested tht perhps colostrl immunogloulins diffuse pssively into the cow s systemic circultion. Further reserch is required to elucidte the exct mechnism. Prity The lower men IgG concentrtion in younger cows is consistent with previous studies (Kruse, 197; Muller nd Ellinger, 1981; Pritchett et l., 1991). The immunogloulins of ovine serum trnsferred into colostrum crry wide rry of ntiody properties ginst multitude of ntigens to which the cow hs een exposed (Lrson et l., 198); older cows re likely to e exposed to greter numer of pthogenic ntigens in their lifetime, which is the likely explntion for the increse in colostrl IgG with incresing prity. Incresed milk yield of older cows is not contriutory fctor here since milk yield ws included in the multiple regression model. Selmn et l. (1971) previously recommended discrding colostrum from first lcttion heifers, ut the results of this study do not support this. The men IgG concentrtion of colostrum for heifers in this study ws lmost twice tht considered to e the threshold for goodqulity colostrum (5 g/l), nd only 1% of the colostrum smples otined from heifers were elow tht threshold. Therefore, on the sis of our findings, we would dvise Irish frmers to disregrd ny previous recommendtions to utomticlly discrd colostrum from first lcttion heifers, s it my e of high qulity. The lower colostrl weight recorded in first lcttion heifers in the present study is in contrst to some previous studies (Kehoe et l., 211), which reported no significnt ssocition etween prity nd colostrum volumes produced. However, results from the present study re nonetheless consistent with others (Kruse, 197). The lower quntity of colostrum produced y this group of nimls is not surprising, given tht the totl milk yield of first lcttion heifers throughout the entire lcttion is less thn tht of cows in lter lcttions (Horn et l., 25). Month of clving Fctors relting to cow helth nd nutrition my underlie the ssocition oserved in the present study etween month of clving nd colostrl IgG concentrtion. Cows tht clved in lte spring in sesonl clving herd were likely to hve hd reduced fertility, which prevented n erly return to cyclicity nd estlishment of pregnncy erly in the previous reeding seson. Suclinicl helth issues my hve een contriutory fctor to oth reduced fertility nd lower colostrl IgG concentrtions in these cows; however, no helth dt were ville to confirm or refute this. There is insufficient reserch t present exmining the reltionship etween cow helth sttus nd IgG concentrtion of colostrum ut this is n re tht wrrnts further investigtion. In generl, the cows tht clved in April hd longer dry period thn cows clved erlier. Forty-seven percent of the nimls tht clved in April (25 out of 47 for whom there re dry period records) hd dry period length,16 weeks, compred with 88% of cows clving in other months of the yer. Cows with long dry periods re predisposed to ecoming excessively ft (Morrow, 1976) nd this ppers to hve een thecsewiththeaprilclvingcows;44%hdbcstclving ove the trget of 3.25 (Roche et l., 29) compred with 17% of cows clving in the other months of the yer. Over-conditioning of the diry cow t clving hs negtive consequences for her immune system (Mullign nd Doherty, 28); this my hve een fctor in the lower colostrl IgG concentrtions in the April clving cows. 183

8 Colostrum qulity The diet during the dry period of the utumn-clving cows in this study consisted of grzed grss, which hd higher CP (229 g/kg, s.d ) nd DMD (871 g/kg, s.d ) thn the grss silge diet of the spring-clving cows (14 g/kg, s.d , 716 g/kg, s.d ; protein nd DMD, respectively). The nutritionl superiority of grzed grss reltive to grss silge hs een long estlished (Myne nd Lidlw, 1995) nd this my hve contriuted to the high qulity of colostrum of these utumn clving cows in prticulr nd of cows in this study in generl. Similrly, Gulliksen et l. (28) reported tht cows clving during the months following the psture seson produced colostrum of higher qulity compred with cows clving during other sesons. While some studies to dte hve shown tht IgG concentrtion of colostrum is not ffected y preprtum mternl nutrition, in terms of protein nd energy requirements (Blech et l., 1981; Hough et l., 199; Nowk et l., 212), further reserch is required to elucidte the complex reltionship etween nutrition nd colostrum qulity. Clf irth weight Lrger cows re expected to hve lrger (i.e. hevier) clves ecuse of the moderte heritility of niml size (Berry et l., 24). Lrger cows, on verge, lso hve greter lcttion yields (Berry et l., 24), which lso suggests greter colostrum yield. This is the likely reson for the greter colostrum yields in cows tht hd hevier clves t irth. Conclusion The results from this study show tht in generl the colostrum qulity (112 g/l IgG) of cows from well-mnged moderteyielding Irish diry herds of mixed reed is high. Older prity cows, cows tht were milked erlier post-clving, cows tht produced smller quntity of colostrum nd cows tht clved erlier in spring or in utumn produced colostrum with higher IgG concentrtion. Trnsfer of sufficient IgG to the neontl clf vi high-qulity colostrum is of criticl importnce to optimise clf helth. Reducing the time intervl etween clving nd collection of colostrum is the most prcticl mens y which the frmer cn mximise colostrl IgG concentrtion. Acknowledgements The uthors wish to thnk Mrgret Murry, Tegsc, Grnge for lortory ssistnce nd lso Fergl Coughln nd the frm stff t Tegsc, Mooreprk for their ssistnce during the study. References Animl identifiction nd movement sttistics report 211. Deprtment of Agriculture, Fisheries nd Food. Retrieved My 12, 212, from gov.ie/medi/migrtion/nimlhelthwelfre/nimlidentifictionndmovement/ AimBovineStts9512.pdf Bumrucker CR, Burkett AM, Mgliro-Mcrin AL nd Dechow CD 21. Colostrogenesis: mss trnsfer of immunogloulin G 1 into colostrum. 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