title: Effect of shortening or omitting the dry period of Holstein-Friesian cows on casein composition of milk.
abstract: The aim of this study was to evaluate the effect of shortening or omitting the dry period of dairy cows on milk casein composition. For this study, we analyzed milk samples of 90 cows with a dry period of 0, 30, or 60d and either a glucogenic or a lipogenic ration in early lactation. Milk was sampled at 6 and 2wk prepartum and at 2, 6, and 12wk postpartum. Milk was analyzed for casein (CN) composition by capillary zone electrophoresis, and isoforms of κ-CN were measured by reversed phase-HPLC. Shortening the dry period from 60 to 30d reduced the αS1-CN fraction by 3.8% and increased the αS2-CN fraction by 5.5%. In milk from cows with a 0-d dry period, the glycosylated κ-CN fraction in late lactation increased from 8 to 12% between 6 and 2wk prepartum. After calving, the glycosylated κ-CN fraction in milk was higher for cows with a 0-d dry period (6.7%) compared with cows with a 60-d dry period (5.2%). The glycosylated κ-CN fraction at 2wk postpartum was negatively correlated with milk yield, suggesting that glycosylation was related to reduced productivity of mammary epithelial cells. In early lactation, the β-CN fraction was reduced in milk of cows with a 0-d dry period. A lowered β-CN fraction was associated with high somatic cell count and greater parity, indicating that it was the result of proteolytic activity. In conclusion, casein composition changes that result from shortening the dry period from 60 to 30d are not expected to affect processing characteristics of milk. Applying a 0-d dry period may affect processability of milk because of a higher glycosylated κ-CN fraction, and possibly because of higher proteolytic activity compared with a 60-d dry period.
authors.affiliation: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, PO Box 7024, 750 07 Uppsala, Sweden; Dairy Science and Technology, FQD, Wageningen University, PO Box 8129, 6700 EV, Wageningen, the Netherlands.
authors.forename: Ruben
authors.initials: R
authors.lastname: de Vries
authors.affiliation: Adaptation Physiology Group, Department of Animal Science, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands.
authors.forename: Ariëtte
authors.initials: A
authors.lastname: van Knegsel
authors.affiliation: Department of Food Science, Swedish University of Agricultural Sciences, PO Box 7051, 750 07 Uppsala, Sweden.
authors.forename: Monika
authors.initials: M
authors.lastname: Johansson
authors.affiliation: Dairy Sweden, Ideon Science Park, SE-223 70 Lund, Sweden.
authors.forename: Helena
authors.initials: H
authors.lastname: Lindmark-Månsson
authors.affiliation: Dairy Science and Technology, FQD, Wageningen University, PO Box 8129, 6700 EV, Wageningen, the Netherlands.
authors.forename: Toon
authors.initials: T
authors.lastname: van Hooijdonk
authors.affiliation: Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, PO Box 7024, 750 07 Uppsala, Sweden.
authors.forename: Kjell
authors.initials: K
authors.lastname: Holtenius
authors.affiliation: Dairy Science and Technology, FQD, Wageningen University, PO Box 8129, 6700 EV, Wageningen, the Netherlands. Electronic address: kasper.hettinga@wur.nl.
authors.forename: Kasper
authors.initials: K
authors.lastname: Hettinga
mesh_terms: D000818:Animals; D002364:Caseins / Q000032:analysis*; D002417:Cattle / Q000502:physiology*; D005260:Female; D006031:Glycosylation; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry*; D010298:Parity; D049590:Postpartum Period; D011247:Pregnancy; D013997:Time Factors
chemical_list: D002364:Caseins
keywords: capillary electrophoresis; dry period; milk casein; reverse phase-HPLC; κ-casein glycosylation