Trace elements in milk of guinea pigs during a 20-day lactation

This study was designed to determine patterns of change in milk trace elements over a complete lactation. Guinea pigs were selected because of ease of milking and short lactation duration. Common short-hair albino guinea pigs were milked using a milking apparatus for 4 to 6 h every other day following isolation from their offspring. Forty-eight samples of 4 ml each were analyzed for trace minerals using inductively coupled plasma spectroscopy. Observations represented 14 d scattered over 20 d of lactation. Eight elements with sufficiently high quantities to measure in milk were zinc (4.18 ppm), strontium (1.12), aluminum (.81), boron (.79), iron (.71), copper (.56), barium (.23), and manganese (.019). Regression analyses were used on rectilinear, quadratic, exponential and cubic models. Quadratic functions fit the data best in six elements, whereas in manganese the best model was the rectilinear. Indices of determination (R2) relating to day of lactation varied from R2 = .18 in boron to a high of .62 in strontium. For six elements, concentrations increased as milk volume decreased. The exception was zinc, which decreased in the latter half of lactation.