Changes in N-acetyl-beta-D-glucosaminidase activities in relation to other milk components throughout normal lactation in the guinea pig

Changes in milk production, NAGase activities, Na, Cl, K, lactose, total N, and fat were followed throughout normal lactation in 26 healthy guinea pigs. Appropriate microassays were used and all determinations were performed on the same small skim milk sample (microhematocrit tube). A very sensitive and rapid spectrofluorimetric determination of NAGase in 10-microliters skim milk samples was evaluated. Four days after parturition, daily milk production reached a maximum of about 20 ml. Thereafter milk yield decreased progressively to about 7 ml on d 15. During the entire course of lactation, a progressive increase in NAGase, total N, fat, Na, and Cl was observed. However, K and lactose decreased. Highly significant positive correlations between NAGase and Na, Cl, fat, and total N were evident, whereas correlations were negative between NAGase and K, lactose, and milk production. These changes can be explained on basis of alterations that occur at the level of the blood-milk barrier. The short lactation period of the guinea pig, the easy handling and milking practices, together with the available sensitive micromethods can lead to the establishment of a convenient guinea pig mastitis model.