The effect of willow fodder feeding on immune cell populations in the blood and milk of late-lactating dairy goats

In a previous study, we showed that access to willow fodder decreased somatic cell counts (SCC) in the milk of local Mamber goats grazing in brushland at the end of lactation. To test whether the consumption of willow affects the cells of the immune system, Alpine crossbred dairy goats grazing in the same environment were either offered free access to freshly cut willow fodder (W, n = 24) or not (C, n = 24) for 2 weeks. The willow fodder contained 7.5 g/kg DM of salicin. The other major secondary compounds were catechin, myricitrin, hyperin and chlorogenic acid (2.2, 2.6, 1.0 and 0.75 g/kg DM, respectively). Udder health status was determined before the experiment, and each of the two groups included five (W) or six (C) goats defined as infected, as established by microbial cfu in milk, and 19 (W) or 18 (C) non-infected goats. Goats ingested, on average, 600 g of DM from willow (25% of food intake), resulting in minor changes in dietary quality compared to the controls, as established by faecal near-IR spectrometry. Throughout the 2 weeks of experiment, differences between groups in dietary CP contents were minor and affected neither by infection nor by access to willow; the dietary percentage of neutral detergent fibre (NDF) decreased in C and increased in W; dietary acid detergent fibre (ADF) increased; and the dietary tannin contents decreased for both treatments. However, milking performance and milk quality attributes in both W and C goats were similar. Initial SCC and milk neutrophil (cluster of differentiation (CD)18⁺ and porcine granulocyte (PG)68) cell counts were higher in infected than in non-infected goats; counts decreased significantly in W but not in C uninfected goats. The percentage of CD8⁺ T-cells increased in all C goats, while in the W group, a significant increase was found only for infected goats. The consumption of willow mitigated an increase in CD8⁺ in blood and triggered an increase in CD8⁺ in milk, suggesting an immune-regulatory effect independent of udder status. To our knowledge, this is the first report of a direct nutraceutical effect of fodder ingestion on the immune status of goats.