The influence of colostral leukocytes on the immune system of the neonatal calf. IV. Effects on bactericidity,...

The influence of colostral leukocytes on the bactericidity of whole blood of calves against a strain of E. coli and on the activities of haemolytic complement and interferon-alpha (the antiviral activity of sera resisting an acidic treatment at pH 2 for 6 h) in the serum was investigated during a period of 4 weeks using 4 experimental groups. The calves received either complete colostrum (COL+, n = 16), cell-depleted colostrum (COL-, n = 16), cell-supplemented milk substitute (MS+, n = 7) or pure milk substitute (MS-, n = 6) during their first three days of life. The bactericidity of whole blood of the COL+ group was significantly higher on the second and third days of life while the activity of haemolytic complement was lower after the first week as compared to the COL- group. No interferon-alpha was detectable in the sera of both COL groups. The bactericidity of the MS groups was significantly lower than that of the COL groups after the first day of life. It was significantly lower in the MS+ group after one week of life while the activity of haemolytic complement was higher than that of the MS- group. Three out of 5 MS- and only one out of 7 MS+ calves had low titres of interferon-alpha in their sera on the third day. Three out of 6 MS- calves died and 5 out of 7 MS+ animals. The mean day of death was 4.0 in the MS- and 8.4 in the MS+ group. Based on the in vitro results of this and the previous three communications it can be concluded that leukocytes which are an integral part of normal bovine colostrum, influence immunological reactions of the calf and that they may enhance its defence against infection. Colostral leukocytes in the absence of humoral components of the colostrum are not able to prevent fatal losses in the calves due to natural infection, although their influence on immune responses of the calves was detectable in vitro.