A strategy to estimate the rate of recruitment of inflammatory cells during bovine intramammary infection under field management

Abstract

Background: In most infectious diseases, among which bovine mastitis, promptness of the recruitment of inflammatory cells (mainly neutrophils) in inflamed tissues has been shown to be of prime importance in the resolution of the infection. Although this information should aid in designing efficient control strategies, it has never been quantified in field studies.

Methods: Here, a system of ordinary differential equations is proposed that describes the dynamic process of the inflammatory response to mammary pathogens. The system was tested, by principal differential analysis, on 1947 test-day somatic cell counts collected on 756 infected cows, from 50 days before to 50 days after the diagnosis of clinical mastitis. Cell counts were log-transformed before estimating recruitment rates.

Results: Daily rates of cellular recruitment was estimated at 0.052 (st. err. = 0.005) during health. During disease, an additional cellular rate of recruitment was estimated at 0.004 (st. err. = 0.001) per day and per bacteria. These estimates are in agreement with analogous measurements of in vitro neutrophil functions.

Conclusions: Results suggest the method is adequate to estimate one of the components of innate resistance to mammary pathogens at the individual level and in field studies. Extension of the method to estimate components of innate tolerance and limits of the study are discussed.

Keywords: Bovine mastitis; Cell recruitment rate; Ordinary differential equation; Principal differential analysis; Resistance; Tolerance.

Fig. 1

Methodology

Fig. 2

Percentages of the maximum values for y_i (dotted line) and x_i (plain line) simulated for i = 1 to 100 time units since infection and with increasing extra-migration rates when going from scenario ‘a’ to ‘c’

Fig. 3

Means of observed and estimated somatic cell scores for 50 days before to 50 days after clinical mastitis. Standard errors are omitted for clarity of the plot