Effect of a supplement rich in linolenic acid added to the diet of mares on fatty acid composition of mammary secretions and the acquisition of passive immunity in the foal

Due to the structure of the placenta in the horse (epitheliochorial) and the as yet un-activated immune system of the foal at birth, the transfer of maternal immunoglobulin G (IgG) is essential in the protection of the young foal until its own immune system develops. The fluidity of intestinal cell membranes may affect the transfer of IgG by receptor mediated endocytosis. In the present experiment we studied the effect of the addition of supplements rich in either alpha-linolenic acid or oleic acid to the diet of the mares starting 1.5 months before foaling and for 1 month after foaling on the passive transfer of IgG and the fatty acid composition of mammary secretions and plasma of foals. Twenty-six mares were allocated to one of two treatment groups (L : linseed supplement, no. = 13 and R: rapeseed supplement, no. = 13) according to date of foaling and live weight to produce two homogeneous groups. Mammary secretions were collected to measure IgG and fatty acid composition. Jugular blood samples were taken from the foals at time 0, 12 h, 24 h, 48 h, 1 week, 2 weeks, 3 weeks and 4 weeks after foaling to measure the concentration of IgG. A subsample of foals was used to measure the IgG absorption coefficient and the plasma fatty acid compositon. There was no effect of dietary treatment on the length of gestation, the production and transfer of IgG. Group L mares produced mammary secretions which were richer in C18 : 3 and poorer in C18 : 1 than group R mares (P < 0.001). Contrary to expectations the C18 : 3 content of blood from foals at birth from both dietary treatments was very low and there was no difference between dietary groups. The percentage of C18 : 3 and C18 : 2 in fatty acids increased in foal blood only after sucking had occurred, with a difference between dietary groups (L > R). In addition, the percentages of C20 : 3 and C20 : 4 were higher in the foals at birth than 48 h later (P < 0.001) and at birth they were highest in the R group compared with the L group foals (P < 0.05 and P < 0.10, respectively). In conclusion, the attempt to increase the supply of C18 : 3 during gestation to foals and to improve the transfer of IgG post partum did not appear to succeed, perhaps because the foal uses C22 : 6 (produced from C18 : 3) for brain growth.