Feed restriction during the suckling period of ewe Assaf lambs (F0) modifies milk quality and milk exosomal miRNAome of the filial generation (F1)

Feed restriction during the early life of ewe lambs (F0) triggers the transfer of epigenetic marks to the next generation, thus impairing the reproductive performance of F1. However, the effects of this factor on milk production and composition, including its abundance in regulatory miRNA (many of which are contained in exosomes, small vesicles of endocytic origin that play a role in the modulation of immune response of the offspring) has not been tested so far. Therefore, in this study, the replacement ewe lambs (F0) obtained in a previous project (a group of ewes fed milk replacer ad libitum –ADL– vs. a group of ewes restricted –RES– to 62.5 % the intake level of milk replacer during the suckling period) were raised under similar post-weaning conditions and mated to obtain the progeny (F1). The F1 female lambs were also mated to obtain F2. Milk production was recorded during the peak lactation period of F1, and milk samples were obtained for each gland (udder half) separately to measure chemical composition, somatic cell counts (SCC), and bacteria counts. Moreover, exosomes were also isolated from the milk of each gland separately to obtain the miRNAome following a Next Generation Sequencing approach. No significant differences were found in either milk production of F1, chemical composition of milk (fat, protein, lactase), or bacteriology (colony forming units, CFU). However, SCC was reduced significantly in milk samples of F1-RES dairy sheep, whereas the abundance of five miRNAs was also modified. Thus, oar-miR-150, oar-miR-221, oar-miR-23a, oar-miR-27a, oar-miR-376c were all down modulated in F1-RES when compared to F1-ADL. Most of these miRNAs have been found to play a role in biological functions such as development, apoptosis, muscle differentiation, reproduction, or milk production. However, the exosomes extracted from the milk of these sheep (F1-RES) did not affect the production of IL-9 and IL-2 cytokines after in vitro culture with CaCo-2 cells. This study reveals that nutritional programming events such as feed restriction may drive the abundance of not only SCC but also some milk's bioactive components such as miRNAs, although it is not clear if these changes may modulate the immune response at the intestinal level of the offspring.