Effect of Somatic Cell Count on Milk Yield in Different Parities and Stages of Lactation in Holstein Cows of Iran

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1 ORIGINAL SCIENTIFIC PAPER 55 Effect of Somtic Cell Count on Milk Yield in Different Prities nd Stges of Lcttion in Holstein Cows of Irn Arsh CHEGINI Nvid GHAVI HOSSEIN-ZADEH ( ) Hossein HOSSEINI-MOGHADAM Abdol Ahd SHADPARVAR Summry The objective of this study ws to investigte the reltionship between somtic cell score (SCS) nd milk yield in different stges of lcttion for cows in different prities. Records between June 2003 nd Jnury 2014 from 209,781 cows in lcttions one to nine in 845 herds, comprising 2,500,407 monthly test-dy (TD) records extrcted from the niml breeding center, were used. The MIXED procedure of SAS softwre ws used to investigte the effect of SCS on milk yield in different stges of lcttion. Defined model considered herd, yer-seson of clving, month of TD, weeks in lcttion nd previous dry period length s fixed effects nd clving ge nd SCS s covrite. Lcttions were divided into six stges nd nlyses were performed within ech stge. Also, different lcttions were nlyzed seprtely. The mount of dily milk yield loss ssocited with incresed SCS ws higher with incresed number of prity nd lso lter in lcttion (especilly fter pek in week nine). The regression coefficient for milk yield on SCS ws to in different stges of lcttion in first prity cows, while tht ws between to in third lcttion cows. Key words somtic cell score, clving ge, dry period length, regression coefficient, stge of lcttion Deprtment of Animl Science, Fculty of Agriculturl Sciences, University of Guiln, P.O.Box: , Rsht, Irn e-mil: nhosseinzdeh@guiln.c.ir, nvid.hosseinzdeh@gmil.com Received: My 6, 2016 Accepted: July 5, 2016 Agriculture Conspectus Scientificus. Vol. 81 (2016) No. 1 (55-60)

2 56 Arsh CHEGINI, Nvid GHAVI HOSSEIN-ZADEH, Hossein HOSSEINI-MOGHADAM, Abdol Ahd SHADPARVAR Introduction Diry cttle breeding policies re minly focused on milk production trits in Irn. Although these trits re of primry economic importnce, functionl trits such s udder helth nd productive life re of greter interest to producers to improve the herd profitbility. Mstitis is one of the mjor diseses in diry cows nd leds to economic losses, minly rising from discrded milk, reduced milk production nd qulity, nd incresed helth cre costs in diry cows (Wellenberg et l., 2002). Selecting for incresed resistnce to mstitis cn be done directly or indirectly. Direct selection needs the dignosis of the infection nd indirect selection corresponds to use of indictor trits or criterion relted to mstitis. Among the mesures, the most frequently used to detect mstitis re milk somtic cell count (SCC) (Shook nd Schutz, 1993; Mrode nd Swnson, 1996) nd hd been used to estimte the reduction in milk yield ssocited with mstitis (Ali nd Shook, 1980; Ruberts nd Shook, 1982; Rjčevič et l., 2003). A good estimte of milk yield reduction due to increse in SCC cn be n incentive for breeding specilists to consider the detrimentl effect of disese nd to estblish pproprite selection progrms with blnced weights for mstitis. With some exceptions (Dürr et l., 2008; Hgnestm-Nielsen et l., 2009), most estimtes of milk yield losses ssocited with SCS hve been derived from lcttion verges. Miller et l. (2004) reported decrese in 305-dy milk yield of 54.6 kg nd 61.4 kg per somtic cell score unit increse on the first test-dy for the first nd second prities, respectively. In review by Hortet nd Seegers (1998), the estimted lcttion milk loss ws found to vry between 0 nd 9.5% cross prities for cows developing clinicl mstitis. The mount of milk losses ssocited with mstitis is depended on when in lcttion the cow is disesed (Lucey et l., 1986; Rjl-Schultz et l., 1999; Hgnestm et l., 2007). Since mstitis nd SCS re highly correlted, in order to obtin ccurte estimtes stge of lcttion should be tken into considertion when studying ssocition between milk yield nd SCS. Therefore, the objective of this study ws to investigte the reltionship between somtic cell count nd milk yield per prity nd stge of lcttion in Holstein cows of Irn. Mteril nd methods Records between June 2003 nd Jnury 2014 from 209,781 cows in lcttion one to nine in 845 herds, comprising 2,500,407 monthly test-dy (TD) records extrcted from the niml breeding center of Irn, Krj, were included in dtset. Cows were kept in intensive production systems nd fed mnully throughout the yer with lflf hy, corn silge nd whet strw s forges nd mixture of brley grin, corn grin, soyben mel, whole cottonseed, cottonseed mel, cnol mel, whet brn, corn gluten nd beet pulp nd vitmin nd minerl premix s concentrte. In most of herds, cows were housed in covered brns with concrete floors nd free stlls nd, in herds with medium to lrge sizes, were grouped regrding to the stge of lcttion, production nd pregnncy sttus. The dtset file included niml ID, herd, clving dte, prity, clving ge, test-dy milk nd somtic cell count, test-dtes, nd dtes of drying off. Records between dys 5 to 305 DIM were included. Dily milk yields less thn 8 kg were deleted, becuse these represent recording error or sick cow. Only nimls with five or more test-dy records were included. Somtic cell count ws trnsformed to SCS. Number nd percent of dt in different SCS clsses in different lcttions re shown in Tble 1. Clving ge ws clculted s dte of clving minus dte of birth. Also, dry period length ws clculted s the dte of present clving subtrcted from dte of pervious dry off. Months of clving were grouped into four sesons: April through June (seson 1 = spring), July through September (seson 2 = summer), October through December (seson 3 = fll), nd Jnury through Mrch (seson 4 = winter). Only herds with three milking times per 24 h were included. According to study by Hgnestm-Nielsen et l. (2009) tht reported dividing lcttion to six stges resulted in better model fit, lcttions were divided into six stges (wk 1 to 2, 3 to 8, 9 to 16, 17 to 24, 25 to 32, nd 33 to 44) nd nlyses were performed within ech stge. Also, dry period length of cows ws grouped into 14 clsses: 0-10 (clss 1), (clss 2), (clss 3), (clss 4), (clss 5), (clss 6), (clss 7), (clss 8), (clss 9), (clss 10), (clss 11), (clss 12), (clss 13) nd > 130 (clss 14). Weeks in lcttion were divided into 19 clsses (records collected within the first 8 weeks of lcttion were grouped into weekly intervls, records from week 9 to 16 were grouped into 2-weeks periods, nd records tken lter thn 17 weeks fter clving were grouped into 4-weeks periods). The MIXED procedure of SAS softwre (SAS Inst., 2002) ws used to investigte the effect of SCS on milk yield in different stges of lcttion with the following model: Tble 1. Number (percent) of test-dy records in different SCS s clss in different lcttions SCS 1 st lcttion 2 nd lcttion 3 rd lcttion 4 th lcttion (13.72) (9.12) (6.84) (5.15) (26.64) (17.11) (13.66) (10.60) (22.63) (20.12) (17.61) (14.49) (14.24) (17.70) (17.36) (16.21) (9.40) (14.31) (15.87) (16.63) (5.86) (9.77) (12.27) (14.41) (3.74) (6.12) (8.33) (10.91) (2.15) (3.41) (4.74) (6.73) (1.09) 9793 (1.65) 9743 (2.31) (3.37) (0.53) 4115 (0.69) 4241 (1.01) 8404 (1.50) 7: 1,131,000-2,262,000, 8: 2,263,000-4,525,000, 9: 4,526,000-nd bove.

3 Effect of Somtic Cell Count on Milk Yield in Different Prities nd Stges of Lcttion in Holstein Cows of Irn 57 TD milk yield = niml number + herd + yer-seson of clving + month of TD + clving ge + weeks in lcttion + previous dry period length + SCS. Fixed effects were: herd, yer-seson of clving, month of TD, weeks in lcttion, previous dry period length nd SCS, nd covrite ws clving ge. Animl number ws considered s subject nd the type of structure ws defined for n utoregressive model. The subject defines the vrible on which repeted mesurements were tken nd utoregressive model ssumes tht with greter distnce between periods, correltions re smller. Also, REG procedure ws used to quntify mount of milk loss per ech increse in SCS within ech stge. Results Averge of dily milk yield nd dys in milk in first, second, third nd fourth lcttion cows were kg, kg, kg nd kg, nd dys, dys, dys nd dys, respectively. Also, men of SCS in first, second, third nd fourth lcttion cows were 2.325, 2.965, nd Tble 1 shows the number of records in different SCS s clsses in different lcttions. Milk yield losses ssocited with SCS's in different stges of lcttion in lcttion 1 to 4 re shown in Tbles 2 to 5. There ws reduction in dily milk yield with increse of SCS in ll lcttions, nd prity nd stge of lcttion ffected the mount of reduction. For primiprous cows the rnge of dily milk yield devition ws from kg for n SCS of 0 to kg for n SCS of 9 in comprison with SCS of 3 in week 1. At the end of the lcttion (week 33-44), however, the rnge of dily milk yield devition for primiprous cows ws from kg for n SCS of 0 to kg for n SCS of 9 in comprison with SCS of 2. For 4 lcttion cows the rnge of dily milk yield devition ws from kg for n SCS of 0 to kg for n SCS of 9 in comprison with SCS of 3 in week 1. At the end of the lcttion (week 33-44), however, the rnge of dily milk yield devition for these cows ws from kg for n SCS of 0 to kg for n SCS of 9 in comprison with SCS of 2. Also, regression coefficients of milk yield on SCS in different stges of lcttion, bsed on test-dy records, in first, second, third nd fourth lcttions re shown in Tble 6. The increse in SCS leds to decrese in milk yield tht ws higher in lter prts of lcttion reltive to erly lcttion. The regression coefficients of Tble 2. Milk yield losses ssocited with different SCS's in different stges of lcttion in first lcttion cows (expressed s devition in comprison with milk yield t SCS of 3 in first week of lcttion nd SCS of 2 in rest of lcttion; 890,708 test-dy records for 120,149 nimls from 759 herds with 43 levels for YS of clving) SCS Week in lcttion ns b b b ns b ns c b : 1,131,000-2,262,000, 8: 2,263,000-4,525,000, 9: 4,526,000-nd bove.,b,c,d : p < 0.001, p < 0.01, p < 0.05, p < 0.1, respectively; ns : non-significnt. Tble 2. Milk yield losses ssocited with different SCS's in different stges of lcttion in second lcttion cows (expressed s devition in comprison with milk yield t SCS of 3 in first week of lcttion nd SCS of 2 in rest of lcttion; 595,469 test-dy records for 79,755 nimls from 638 herds with 43 levels for YS of clving) SCS Week in lcttion ns c b ns b : 1,131,000-2,262,000, 8: 2,263,000-4,525,000, 9: 4,526,000-nd bove.,b,c,d : p < 0.001, p < 0.01, p < 0.05, p < 0.1, respectively; ns : non-significnt.

4 58 Arsh CHEGINI, Nvid GHAVI HOSSEIN-ZADEH, Hossein HOSSEINI-MOGHADAM, Abdol Ahd SHADPARVAR Tble 4. Milk yield losses ssocited with different SCS's in different stges of lcttion in third lcttion cows (expressed s devition in comprison with milk yield t SCS of 3 in first week of lcttion nd SCS of 2 in rest of lcttion; 436,209 test-dy records for 57,963 nimls from 617 herds with 43 levels for YS of clving) SCS Week in lcttion b ns ns ns d b ns c b b c : 1,131,000-2,262,000, 8: 2,263,000-4,525,000, 9: 4,526,000-nd bove.,b,c,d : p < 0.001, p < 0.01, p < 0.05, p < 0.1, respectively; ns : non-significnt. Tble 5. Milk yield losses ssocited with different SCS's in different stges of lcttion in fourth lcttion cows (expressed s devition in comprison with milk yield t SCS of 3 in first week of lcttion nd SCS of 2 in rest of lcttion; 578,021 test-dy records for 53,321 nimls from 610 herds with 43 levels for YS of clving) SCS Week in lcttion ns d b ns c ns c b c b : 1,131,000-2,262,000, 8: 2,263,000-4,525,000, 9: 4,526,000-nd bove.,b,c,d : p < 0.001, p < 0.01, p < 0.05, p < 0.1, respectively; ns : non-significnt. Tble 6. Liner regression coefficients of milk yield on SCS in different stges of lcttion in different lcttion cows, bsed on test-dy records Prity Week in lcttion st prity cows nd prity cows rd prity cows th prity cows All vlues were significnt t p < milk yield on SCS rnged from to for primiprous cows nd from to for multiprous cows. Discussion Multiprous cows hd higher SCS. It hs been shown tht prity hs significnt effect on SCC (Olde Riekerink et l., 2007; Chegini, 2010) nd multiprous cows hve higher SCC. Milk yield devition ssocited with SCS s ws from kg to kg for primiprous cows nd from kg to kg for multiprous cows. The corresponding figures estimted by Jones et l. (1983) were from 0.73 kg to kg for first lcttion cows nd from 1.77 kg to kg for lter lcttions. Hile- Mrim et l. (2001) conducted study to estimte genetic nd environmentl correltions between test-dy yield trits nd SCC using rndom sire model. They reported higher bsolute vlues for genetic nd environmentl correltion between milk yield nd SCC in lter stges of lcttion reltive to erlier stges of lcttion. Hortet et l. (1999) suggested tht udder infection cn

5 Effect of Somtic Cell Count on Milk Yield in Different Prities nd Stges of Lcttion in Holstein Cows of Irn 59 cuse permnent grndulr dmge nd this is responsible for higher milk reduction in lte lcttion. By discrding dt of lcttions preceding by lcttion ffected by mstitis, Hgnestm- Nielsen et l. (2009) performed n experiment tht could test the ccurcy of this hypothesis. Their results showed tht clinicl mstitis in previous lcttion could not ffect milk yield in lter lcttions. It seems tht high SCC cn ccelerte the degenertion of milk secretory cells nd the ctbolic process. Tble 6 shows liner regression coefficients of milk yield on SCS in different stges of lcttion in different lcttion cows. Multiprous cows hd higher milk loss with incresed SCS. This result is in ccordnce with the results of previous studies (Kennedy et l., 1982; Jones et l., 1983; Hortet et l., 1999; Normn et l., 1999; de los Cmpos et l., 2006; Hgnestm et l., 2007; Dürr et l., 2008; Rekik et l., 2008; Hgnestm-Nielsen et l., 2009). The reports of phenotypic correltion between milk yield nd SCC rnged from for first prity cows to for lter prity cows (Kennedy et l., 1982; Normn et l., 1999). In cse of dilution effect, using structurl equtions nd considering the recursive effect of SCS on milk yield, de los Cmpos et l. (2006) mentioned tht the negtive effect of disese on milk yield creted the negtive phenotypic correltion between SCS nd milk yield nd tht dilution effect would not be n importnt cuse of this phenotypic correltion. It hd been demonstrted tht first lcttion cows hve higher persistency (Weller et l., 1987; Gengler, 1996; Chegini, 2010). This is becuse of higher bility of their udder tissues to recover nd regenerte secreting cells nd better consequence of mmmry cell deth nd regenertion in dvntge of regenertion. Therefore, it cn be concluded tht with incresing number of lcttion the effect of SCC would be intensified on the rte of secretory cells degenertion nd multiprous cows with lower rtes suffer more. Investigting on the reltionship between milk yield nd SCC, Chegini (2010) found negtive genetic correltion between milk persistency nd different mesures of SCC (rnged from to -0.42). Also, Hile-Mrim et l. (2003) reported negtive genetic correltion (-0.29) between men of nturl logrithm of SCC with milk persistency. Contrry to the results of Hgnestm-Nielsen et l. (2009), the wekest ssocition between SCS nd dily milk yield ws found in lcttion week 1 to 2 in ll lcttions. Since men of SCC in erly lcttion is high (most of cows hve high SCC in this period), it cn be concluded tht increse of SCC erly in lcttion is n intrinsic phenomenon nd plys protective role reltive to increse of SCC in lter prts of lcttion. The effect of SCC on milk yield is different from the effect of mstitis on milk yield. Estimting the regression coefficient of milk yield on SCS, Hgnestm-Nielsen et l. (2009) reported tht multiprous cows with mstitis event in previous lcttion experienced less severe milk loss in present lcttion. However, since there ws no record for mstitis, we could not include the effect of this disese in the model. Conclusion Cows in third lcttion hd the highest dily milk yield nd cows in first lcttion hd the lowest SCS. In ll lcttions, there ws reduction in dily milk yield with increse of SCS, nd prity nd stge of lcttion ffected the mount of reduction. Reduction in milk yield ssocited with increse of SCS ws higher with increse of prity nd stge of lcttion. 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