Serum and saliva immunoglobulin (immunoglobulin G, immunoglobulin A, and immunoglobulin M) dynamics in newborn calves and their association with health status during the first week of life: An exploratory study

Abstract

The transfer of passive immunity is essential to ensure the health and welfare of newborn calves. Although the dynamics of serum Ig concentrations in these animals are well-described, data about saliva Ig are limited. This study aimed to evaluate serum and saliva Ig (i.e., IgG, IgA, and IgM) concentrations during the first week of life in healthy and sick calves. Blood and saliva samples were collected from 20 dairy calves from a dairy farm located in Portugal, at birth (30 min before colostrum intake) and on d 1, 2, and 7 of life. Calves were fed with 3.8 +/- 0.64 L (mean +/- SD) of maternal colostrum (44.7 +/- 16.56 g/L IgG) within 96 +/- 73 min of birth. Calves were examined 2 times daily by the farm staff, and health scores were recorded before sample collection (i.e., d 0, 1, 2, and 7), using a modified version of the Wisconsin calf health scoring system. Based on the health scores, calves were categorized as healthy (HC; n = 11; absence of physical signs of disease, active, and with a positive demeanor during the experimental period) or diarrheic (DC; n = 9; loose or watery feces observed during the experimental period). The Ig and total protein (TP) concentrations in serum and saliva were evaluated with linear mixed models including health status (HC vs. DC), time (d 0, 1, 2, and 7), and the interaction between both as fixed effects. The significance was set as P < 0.05. Except for diarrhea, no other health condition was observed. At birth, all Ig isotypes were present in saliva, with IgA being the most relevant. In serum, IgA and IgG were detected during the entire experimental period, but IgM concentrations were only detectable after d 1. Both serum and saliva Ig concentrations increased after colostrum intake (d 1), although saliva IgG concentration declined on d 2, unlike serum IgG concentration, which only decreased on d 7. All saliva Ig declined from d 1 to 2 but only in the HC group. Saliva Ig concentrations in the DC group did not change from d 1 to 7. A tendency for lower saliva IgA and M concentrations was observed in DC calves compared with HC on d 1. Similarly, DC calves showed a reduced proportion of IgA in saliva relative to serum compared with HC on d 1 and a tendency for higher saliva TP on d 7. In conclusion, calf health status was associated with saliva Ig concentrations during the first week of life, with the calves from the DC group showing lower saliva Ig concentrations before clinical signs were observed.