Orotic acid in guinea pig milk: changes in concentration during lactation.

The orotic acid concentration in guinea pig milk decreased rectilinearly beginning on d 1 through a lactation duration of 21 d. Concentration was 29 micrograms/ml on d 1 and 5 micrograms/ml on d 17. On d 18 to 21 it was less than 1 microgram/ml. The regression equation of orotic acid on day of lactation was: Y(micrograms orotic acid per milliliter milk) equals 32.3 - 1.6X (day of lactation) with a correlation coefficient of .94. Total orotic acid on a daily basis peaked on d 6 at 950 micrograms and declined to less than 5 micrograms by d 21. The rectilinear regression equation from d 6 to 21 was as follows: Y(micrograms orotic acid per milliliter milk) equals -1.64 + .68X (grams of milk production per day) with a correlation coefficient of .97. This may be used as a marker for persistency of lactation.