Effect of somatic cell count on milk fat and protein in different parities and stages of lactation in Holstein cows | Vpliv števila somatskih celic na odstotek maščobe in beljakovin v mleku holštajnskih krav v različnih zaporednih laktacijah in v različnih stadijih laktacije

anglais. The objective of this study was to investigate the effect of somatic cell score (SCS) on milk fat and protein in different parities and stages of lactation in Iranian Holstein cows. Records between June 2003 and January 2014 from 208,478 cows in lactations one to nine in 845 herds, comprising 2,456,303 monthly test-day (TD) records were used. The MIXED procedure of the SAS software with repeated measurements was used. The fixed effects of the model were herd, year-season of calving, month of TD, weeks of lactation, previous dry period length and somatic cell score (SCS) and covariate was calving age. Lactations were divided into six stages and analyses were performed within each stage. Also, different lactations were analyzed separately. Increase of SCS led to increase of milk fat and protein percentage and the increase of milk fat and protein associated with SCS was higher in early stages of lactation relative to later stages of lactation. Also, increase of milk fat and protein associated with SCS was higher in the first lactation rather than later lactations and decreased with increase of parity.

slovène. Namen te raziskave je bil proučiti učinek števila somatskih celic (SCS) na vsebnost mlečne maščobe in beljakovin v različnih laktacijah in v različnih fazah laktacije pri iranskih kravah holštajnske pasme. Uporablili smo podatke za 208.478 krav v prvi do deveti laktaciji iz 845 čred, ki so vsebovali 2.456.303 zapisov za mesečni testni dan (TD). Analiza je bila opravljena s proceduro MIXED s ponovljenimi meritvami v programskem paketu SAS. Fiksni vplivi v modelu so bili čreda, leto-sezona telitve, mesec testnega dneva, teden laktacije, trajanje predhodne presušitve in število somatskih celic ter starost ob telitvi kot kovariabla. Laktacije smo razdelili v šest obdobij in opravili analize znotraj vsakega obdobja. Analize so bile opravljene ločeno po laktacijah. Povečanje števila somatskih celic je vodilo do povečanja odstotka maščob in beljakovin, ki je bilo večje v zgodnjih obdobjih laktacije v primerjavi s kasnejšimi. Povečanje vsebnosti maščob in beljakovin je bilo tudi večje v prvi laktaciji kot v kasnejših laktacijah in je upadalo z zaporedno laktacijo.