A study of bovine salivary proteins

Abstract

This physiological genetics approach to the study of the bovine salivary proteins was designed to: (a) Test the hypothesis that the salivary proteins, other than mucoprotein, might be related to, or involved in determining an animal’s susceptibility to bloat. (b) Gain some knowledge on the nature of the proteins in bovine saliva. This study paralleled the breeding programme selecting animals for high (HS) and low (LS) susceptibility to bloat. Two groups of adult cows, classified as HS or LS by field gradings (Group 1 and Group 2), and three groups of HS and LS progeny (1973, 1974 and 1975 animals), were studied. Part I of this project involved studying saliva flow, total protein, and the eleven protein bands separated by polyacrylamide gel electrophoresis (PAGE) from saliva samples (collected from the mouth of cows), in relation to bloat grade or susceptibility. Consistent results from these studies indicated that protein bands 4 and 6 were positively related to bloat susceptibility, and saliva flow and band 7 were negatively related to susceptibility. Band 7 was also negatively related to individual cow variance and positively related to saliva flow. It was demonstrated that a cow’s saliva flow could be markedly stimulated by the oral administration of acetic acid and this stimulation also increased the proportion and concentration of band 7. The time since a cow last had access to feed which did not induce bloat, made very little difference to the parameters measured in saliva. However, in a series of Pasture Type Trials, where saliva samples were collected from animals directly after coming off grass or ‘bloat potent’ clover pasture, the level of band 4 was increased (shown as an environmental correlation between bloat grade and band 4). Band 6 showed a positive phenotypic correlation with bloat grade and a positive environmental correlation with saliva flow, while band 7 showed a positive correlation with protein. Changes in bloat grade and the salivary parameters with age were followed in the 1973, 1974 and 1975 animals. Results from studies in Part Two, indicated that immunoglobulins were present in saliva and a semi-purified protein fraction, band 1-2-3 complex, when run on SDS-electrophoresis was composed of subunits corresponding in molecular weight to those of IgG and secretory-IgA. Comparisons between saliva collected from the mandibular gland, mouth and oesophagus indicated that band 1 was secreted by the mandibular gland. Band 6 was shown to contain two proteins one of which cross-reacted with anti-albumin serum, had the same electrophoretic mobility and molecular weight as serum albumin. Band 7, 8 and 9 were statistically related and this relationship was demonstrated chemically by incubating saliva or semi-purified proteins, band 7-8-9 complex, with neuraminidase. The molecular weight of this complex was 65 300 (2 800 SEM) and appeared to be composed of three subunits with molecular weights of 26 000, 22 500 and 17 500. Band 7 and 8 appeared to be secreted by the mandibular glands. Other studies included, screening for enzymic activity, SDS-electrophoretic studies to determine the range of proteins present, screening for cationic proteins, and electrophoretic and immunoelectrophoretic comparisons of mouth saliva with secretions from the mandibular, nasal, and nasolabial glands using whole saliva antiserum. It was concluded that protein bands 4, 6 and 7 and saliva flow were related to bloat susceptibility and that further work investigating the biological significance of these relationships was warranted.