An attempt was made to determine the efFect of corticosteroid on intestinal absorption and subsequent endogenous synthesis of immunoglobulins by the newborn calf. This was carried out by measuring changes in the serum concentration of IgGj, IgG2, IgM and IgA at intervals after birth in a total of 14 calves, 11 of which were born of corticosteroid-treated cows and the remainder from untreated cows. Calves were each fed 2 1 of a large volume of mixed colostrum in the first 6 hours after birth.The results indicate that corticosteroid treatment of cows induced early parturition and inhibited intestinal absorption of immunoglobulin. For the treated calves the efficiency of absorption for each immunoglobulin was half that for the untreated calves (P < 0-01). The time of onset of endogenous production of IgGj, IgGa and IgM was similar in treated and untreated calves, but the increase in serum IgA concentrations was delayed in treated calves.The practical implications of these findings are discussed.

Summary. The significance of local effects associated with mammary involution on transfer of immunojilolmlin and especially on the selective transfer of IgGî nto mammary secretion of cows approaching parturition has been determined. This wa.s carried out by nieasurinfj the chanycs in the eoncentration of I(iG,, IjiC,. IgM and IgA in .serum and manunary .secretion of 5 cows in whicli two mammary glands were milked continuously (twice daily) during the period preceding parturition, while the other two glands were allowed to undergo normal involution.In the secretion of nnniilked glands of all eows there was a sul>stantial increase in the concentrati{)n of IgC, as cows approached parturition. In contrast, the increases in the concentration ol IgG, and in the selective index for IgGj of milked glands were either \irtiially non-existent (1 cow) or generally reduced in magnitude and delayed in time of onset (4 cows), It is clear from the results that continued milking of a mammary gland throughout pregnancy tends to maintain milk production in the milked gland and at the same time reduces the mas.si\e selective transfer of IfiO, into secretion of that gland.INTRODUCTION.

Summary Involution of the mammary gland was initiated by stopping milking in 8 cows in the eighth to tenth month of lactation, in 4 ewes which had been lactating less than 7 weeks and in a further 6 ewes lactating more than 12 weeks. In all animals the concentrations of immunoglobulins in the mammary secretion—IgG1, IgC2, IgA and IgM—increased as involution progressed. In the cows and in those ewes in early lactation there was a transitory increase in selective transfer of IgG1 during the initial phase of involution. Subsequently, the glandular epithelium completely lost its ability to selectively transfer IgG1, and the results indicated that the loss of structural integrity of the epithelium characteristic of advanced involution allowed a ready equilibration of proteins between the secretion and interstitial fluid. There was no suggestion of a transitory increase in selective transfer of IgC1 in those ewes involuted late in lactation.

Summary.The effect of corticostLToid-induced parturition on transfer of immunoglobulin into mammary secretion of cows has been studied. Seven nonlactating cows in late gestation were injected intramuscularly with a long-actinj; synthetic glucocorticoid and the concentrations of IgG, and IRC, were followed in l)!()od serum and nianiniary secretion which were collected before and after parturition.Within 1 week of injection the udder became distended with secretion identical in appearance to mature milk. In contrast to the situation in normal cows approaching parturition, l>oth the concentration of IgGj in secretion and the selective index of IgG, decreased after the glucocorticoid injection. A feature of the results was the absence in treated cows of the characteristic decrease in serum concentration of IgG, just before parturition.It is concluded that glucocorticoid treatment of cows in late pregnancy results in a decreased availability of colostral imnmnoglobulin to the newborn calf.