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• Colostral lactoferrin is absorbed into the newborn calf's blood. Concentrations of lactoferrin found in the blood are dependent upon the concentration of lactoferrin in the colostrum fed, the amount of colostrum fed, and the time after feeding of the colostrum.
• Absorbed lactoferrin is rapidly cleared from the calf's blood. However, the transiently elevated blood levels of lactoferrin achieved in the newborn calf might be sufficient to affect development of immune function in the calf.

INTRODUCTION

The value of colostral immunoglobulins for the newborn calf is well established. Absorption of colostral IgG in the calf's intestine occurs by a nonspecific mechanism which also results in absorption of other potentially bioactive macromolecules. One such bioactive factor found in colostrum and which could have a variety of effects on the newborn calf is lactoferrin (Lf). Lactoferrin is an iron-binding protein found in many external secretions of the body including milk. Lactoferrin is generally considered to be an iron scavenger rather than an iron-transport protein. Lactoferrin has antimicrobial properties against a variety of organisms. In addition, several roles in inflammation and the immune system have been ascribed to Lf including regulation of myelopoesis, control of hypersideremia (binding of systemic iron released into the blood during inflammation), inhibition of antibody synthesis, enhancement of neutrophil function, regulation of leukocyte cytotoxic activity, and regulation of lymphocyte proliferation.

Lactoferrin contained in colostrum may have a protective effect in the neonatal calf's intestine by encouraging development of beneficial intestinal microflora and inhibiting growth of pathogenic bacteria. Colostral Lf also may be absorbed into the calf's blood along with other macromolecules prior to gut closure. Consumption of large amounts of colostral Lf and subsequent intestinal absorption might affect the development of the calf's immune system. It is necessary to determine the extent and nature of absorption of Lf by the newborn calf before further studies can be conducted to determine if the absorbed Lf has an effect on the neonate. The objective of this study was to characterize the absorption of Lf into the calf's blood after feeding colostrum.

METHODS

Seventeen Holstein bull calves were sequentially assigned to three treatment groups as they were born. Calves in group A (n = 6) were fed pooled colostrum from second and third milkings of postpartum cows which contained Lf at 0.58 mg/ml and IgG1 at 32.9 mg/ml. Two liters of colostrum were fed both at 0 and 12 h. Calves in groups B (n = 6) and C (n = 6) were fed pooled colostrum from the first milking of postpartum cows in which Lf concentration was 0.73 mg/ml and IgG1 concentration was 60.1 mg/ml. Calves in group B received 2 L of colostrum both at 0 and 12 h and calves in group C received 4 L of colostrum at 0 h and 2 L at 12 h. In all cases colostrum was fed within 3 h after birth. Blood samples were collected from calves at 0, 4, 8, 12, 24, and 48 h after the first feeding. Blood samples were allowed to clot and then were centrifuged and serum collected. Serum was assayed for Lf with an enzyme linked immunosorbant assay (ELISA). Concentrations of IgG1 were determined by radial immunodiffusion (RID) and have been reported previously in the Illinois Dairy Report (Morin, D.E., G.C. McCoy, and W.L. Hurley. 1996. Colostrum management affects immunoglobulin absorption in newborn calves).

RESULTS

The concentration of calf serum Lf for all calves at birth (within 3 h of birth and before the first feeding of colostrum) was 1.09 µg/ml ± 0.22. The time course of changes in concentrations of Lf in calf serum is summarized in Table 1. Increasing total consumption of colostral Lf at the first feeding after birth resulted in increased peak serum Lf concentration (Table 1). Similarly, serum concentrations of IgG1 attained in a calf's blood are dependent upon colostral IgG1 concentrations and amount of colostrum fed (see Morin et al., 1996). Increasing the volume of colostrum consumed shortly after birth resulted in a longer time to the peak serum Lf concentration (Table 1). Feeding of additional Lf at 12 hours after the first feeding did not further increase serum Lf concentrations. In contrast, absorption of IgG1 occurs beyond 12 hours so that there is continuing benefit from providing a second colostrum feeding 12 hours after the first feeding. Concentrations of IgG1 generally peak at about 24 hours when two colostrum feedings are provided (Morin et al., 1996). The colostral Lf absorbed apparently is cleared rapidly from the blood, while absorbed IgG1 has a much longer half life in the calf's blood. The system for clearing Lf from the blood may become active only about 12 hours after birth or after the first feeding. Mean concentration of Lf for all calves at 48 h after the first feeding was 3.18 ± 0.17 µg/ml. This compares to the concentration of Lf in older calves (1to 3 weeks after birth) of 1.06 ± 0.29 µg/ml.

CONCLUSIONS

Results from this study indicate that colostral Lf is being absorbed from the intestine and that the increased serum Lf is not the result of a transitory release of endogenous Lf into the calf's blood. The results suggest that Lf clearance from the blood of the calf is increased within about 12 hours after the first feeding. A specific clearance rate of Lf could not be accurately estimated from these data. In contrast, clearance of absorbed IgG1 from the calf's serum occurs slowly and elevated concentrations of colostral-derived IgG1 are present for a number of weeks after birth.

Concentrations of serum Lf in calves at about 8 to 12 hours after the first feeding can be over 10 fold higher than concentrations a number of days to weeks later, depending upon the amount of Lf consumed in the first feeding. These peak Lf concentrations may be more similar to concentrations found in human diseases where Lf is released into the blood by leukocytes. Regardless of the source, Lf in the blood is rapidly cleared. The primary tissue of Lf clearance in other species is the liver. In addition, some Lf may be excreted in the urine. Less is known about Lf clearance in the newborn calf.

Bactericidal activity of Lf typically is achieved only at concentrations of 500 µg/ml or higher. However, in vitro studies of Lf demonstrate effects on leukocytes in the 1 to 20 µg/ml range. Whether the transitory high concentrations of Lf achieved in the calf's blood would result in a bioactive effect on the calf's developing immune system remains to be demonstrated. Further investigation is required to characterize the dynamics of lactoferrin absorption and clearance by the calf and the potential bioactive effects of absorbed Lf on the calf.

Table 1. Serum concentrations of lactoferrin in calves after feeding colostrum.

^a Mean ± standard error of the mean.

^b Total lactoferrin feed at 0 hr.

^c Time after first feeding.