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Milk Caseins Decrease the Binding of the Major Bovine Seminal Plasma Proteins to Sperm and Prevent Lipid Loss from the Sperm Membrane During Sperm Storage¹

Department of Medicine,³ University of Montreal and Guy-Bernier Research Center, Maisonneuve-Rosemont Hospital, Montreal, Québec, Canada H1T 2M4 Centre d'Insémination Artificielle du Québec,⁴ Ste-Hyacinthe, Québec, Canada J2S 7B8 L'Alliance Boviteq Inc.,⁵ Ste-Hyacinthe, Québec, Canada J2T 5H1

ABSTRACT

Milk is used as a medium for sperm preservation. Caseins, the major proteins of milk, appear to be responsible for the protective effect of milk on sperm. Recently, we have shown that egg yolk, which is also widely used to preserve semen, protects sperm functions by preventing the binding to sperm of the major proteins of bull seminal plasma (BSP proteins), thereby preventing BSP protein-mediated stimulation of lipid loss from the sperm membrane. In the present study, we investigated whether milk caseins protect sperm in the same manner as egg yolk. Bovine ejaculates were diluted with skimmed milk permeate (skimmed milk devoid of caseins) or permeate that was supplemented with caseins and stored at 4°C for 4 h. In the semen diluted with permeate, sperm viability and motility decreased in a time-dependent manner. However, in semen diluted with milk or permeate supplemented with caseins, sperm functions were maintained. In addition, lower amounts of the BSP proteins were associated with sperm in semen diluted with milk or permeate supplemented with caseins, as compared to semen diluted with permeate. No milk proteins were detected in the sperm protein extracts. Furthermore, sperm diluted with milk or permeate supplemented with caseins showed 3-fold lower losses of cholesterol and choline phospholipids than sperm diluted with permeate during storage. Thus, milk caseins decreased the binding of BSP proteins to sperm and reduced sperm lipid loss, while maintaining sperm motility and viability during storage. These results support our view that milk caseins prevent the detrimental effects of BSP proteins on the sperm membrane during sperm preservation.

acrosome reaction, gamete biology, male reproductive tract, sperm motility and transport, sperm preservation

¹Supported by a grant from the Natural Science and Engineering Council of Canada.

Correspondence: ²Puttaswamy Manjunath, Centre de Recherche Guy-Bernier, Hôpital Maisonneuve-Rosemont, 5415 boul. l'Assomption, Montréal, Québec, Canada, H1T 2M4. FAX: 514 252 3430; e-mail: puttaswamy.manjunath{at}umontreal.ca

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