Fatty acid profile and health lipid indices in the raw milk of ewes grazing part-time and hemp seed supplementation of lactating ewes

Abstract

This experiment was designed to evaluate the effects of the feeding system (indoor  or part-time grazing) of ewes and dietary supplementation with hemp seed (non-drug varieties of Cannabis sativa L.) on milk production and the composition of milk fatty  acids (FAs). The experimental diets were constituted as a 2 x 2 factorial  arrangement of feeding system (I: indoors and receiving 1400 g dry matter (DM)  grass hay/d or pasture grazing (PG)–4 h/day + 700 g DM grass hay/d), and with or without hemp seed (Hs) supplementation (-Hs = no hemp seed vs. +Hs = 175 g/d hemp seed). All animals received 700 g DM/day of a concentrate for lactation.  Feeding the PG diets increased raw milk production and yields of fat, protein and lactose. Feeding +Hs increased fat-corrected milk, milk fat content and fat yield significantly while the combination of +Hs and PG increased fat-corrected milk and fat yield significantly. Milk protein content was not affected by dietary factors. Feeding the I diets increased the proportion of short-chain FAs (C4:0 - C10:0), at the expense of medium-chain FAs (12 to 17 C units). Feeding +Hs decreased the proportion of short-chain FAs, medium-chain FAs and hypercholesterolaemic FA (sum of C12:0, C14:0, C16:0) and increased the trans-vaccenic acid (C18:1 t11, VA), α-linolenic acid (C18:3 n-3, ALA), conjugated linoleic acid (CLA),  eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations in milk fat significantly. The combination of hemp seed and part-time grazing produced the highest proportion of c9,t11 CLA, t10,c12 CLA and n-3 FA (sum of ALA, EPA, DHA) in milk fat. The polyunsaturated fatty acid (PUFA)/saturated fatty acid (SFA) ratios in the milk from ewes grazing part time were significantly higher, whereas the atherogenicity index (AI), thrombogenic index (TI) and linoleic acid (LA)/ALA ratio were significantly lower compared with the milk of indoor-fed ewes. Supplementing with +Hs has a similar effect of increasing the PUFA/SFA ratio and lowering of the AI, TI and LA/ALA ratio. It was concluded that pasture grazing combined with hemp seed had a synergistic effect on milk production and fat yield without altering the milk protein content in ewes. This combination has favourable effects on milk FA profile from the human consumer’s point of view by increasing the nutritional quality of milk.

Keywords: α-linolenic acid, atherogenicitiy index, Cannabis sativa, c9,t11 CLA, n-6/n-3 FA