Relations between sow hormonal concentrations around parturition and immunoglobulin G concentrations in colostrum

Abstract

Session 2 : Endocrine regulation of the mammary gland at different functional stagesInternational audienceLike most farm animals, the piglet is born devoid of systemic humoral immunity and therefore relies on maternal immunoglobulins G (IgG) provided by colostrum. Concentrations of IgG in colostrum are highly variable among sows and factors influencing them are not fully known in pigs. Although passive diffusion between mammary epithelial cells cannot be excluded, the uptake of IgG by mammary glands in pigs could be mediated by a Fc-specific receptor, the neonatal Fc receptor (FcRn), as is the case in ruminants. In cattle, the expression of FcRn could be stimulated by the decrease in progesterone/oestradiol ratio in late pregnancy and then be inhibited by the peripartum peak of prolactin. The aim of the present study was to investigate the relations between hormonal concentrations around parturition and colostral IgG concentrations in primiparous sows. Colostrum samples were collected in 40 Landrace × Large White primiparous sows at the onset of parturition (t0) and 24 h later (t24) and were assayed for IgG concentrations. Colostrum yield was estimated during 24 h starting at the onset of farrowing using piglets’ weight gains. Jugular blood samples were taken on d-8, d-2, d-1 and the day of farrowing (d0) and were assayed for prolactin, progesterone, oestradiol-17β, cortisol, IGF-I, and IgG. Amounts of IgG exported into colostrum in 24 h were estimated (colostrum yield x ([IgG] at t0 + [IgG] at t24)/2). Analyses of correlations and multiple regression were performed. Multiple regression was focussed on a subset of 20 sows because one of the most contributing variables (IgG concentrations in sow plasma) had been measured in 20 sows only. Concentrations of IgG in colostrum (means ± SD) averaged 70.5 ± 23.5 and 13.0 ± 7.4 mg/mL at t0 and t24, respectively. Concentrations of IgG in colostrum at t0 were positively correlated with plasma concentrations of IgG at all times (with IgG on d-1: r = 0.61, P = 0.004) and IGF-I on d0 (r = 0.33, P = 0.041) and were negatively correlated with prolactin on d-2 (r = -0.36, P = 0.031). In the multiple regression analysis, variation in colostral IgG concentrations at t0 were explained by plasma concentrations of IgG on d-1 (36%, P = 0.005), prolactin on d-2 (24%, P = 0.019), and progesterone on d-8 (6%, P = 0.118). Amounts of IgG exported in 24 h averaged 157 ± 55 g and this value was partly explained by plasma concentrations of IgG on d-1 (37%, P = 0.004) and progesterone on d-8 (13%, P = 0.044). In conclusion, IgG concentrations in colostrum at the onset of farrowing are related to IgG concentrations in sow plasma in late pregnancy, as previously reported, and IgG transfer into colostrum could be partly regulated by circulating progesterone in sows