ISO 13366-1:2008

Overview

ISO 13366-1:2008 - Milk - Enumeration of somatic cells - Part 1: Microscopic method (Reference method) defines a laboratory microscopic reference method for counting somatic cells in raw and chemically preserved milk. It is intended primarily for cows’ milk (with specified prerequisites) and is used to prepare standard test samples and determine reference values needed to calibrate mechanized and automated somatic cell–counting systems.

Key topics and technical requirements

• Principle: a measured milk volume is spread as a smear on a slide, stained, and somatic cells are counted under a microscope; counts in a defined area are multiplied by a working factor to give cells per millilitre.
• Reagents: specified dye solutions (Modified Newman‑Lampert stain; ethidium bromide stain and buffer) and Phosphate Buffer Solution (PBS). Document includes safety warnings for hazardous reagents (e.g., tetrachloroethane, ethidium bromide).
• Apparatus: routine laboratory equipment plus a microscope (500×–1 000×; fluorescence attachment required when using ethidium bromide), a 0.01 ml microsyringe (±2 %), certified micrometer and premarked slides (area ≈ 1 cm2).
• Sampling & sample handling: store samples at 4 °C ± 2 °C and analyse within 6 h. If preserved, recommended preservatives and maximum concentrations are given (e.g., boric acid ≤ 0.6 g/100 ml, bronopol ≤ 0.05 g/100 ml, potassium dichromate ≤ 0.1 g/100 ml) and preserved samples may be stored up to 6 days at 4 °C ± 2 °C.
• Procedure: preparation of smears, staining (options provided), counting methods (rectangular/circular shapes and field strategies), calculations and expression of results.
• Quality and performance: sections on precision (repeatability and reproducibility) and requirements for preparing standard test samples for calibration.

Practical applications and users

• Dairy laboratories performing official somatic cell counts (SCC) and establishing reference results.
• Instrument manufacturers and calibration labs using the method to generate reference values for validating and calibrating automated/fluoro‑opto‑electronic counters.
• Quality assurance/processing teams in milk processors and dairy cooperatives monitoring udder health and milk quality.
• Regulatory and standards bodies needing a traceable reference method for compliance or inter-laboratory comparisons.

Related standards

• ISO 13366-2 - Guidance on operation of fluoro‑opto‑electronic counters (complements Part 1).
• ISO 707|IDF 50 - Recommended sampling methods for milk (referenced for representative sampling).

This standard is essential where accurate, traceable somatic cell count (SCC) reference values are required for milk quality control, instrument calibration and regulatory testing.