Can Agro-Industrial By-Products Rich in Polyphenols be Advantageously Used in the Feeding and Nutrition of Dairy Small Ruminants?

Abstract

Recently, the interest in industrial by-products produced at the local level in Mediterranean areas, resulting from fruit and vegetable processes, has increased because of their considerable amounts of bioactive compounds, including polyphenols. In this review, we analyze the most recent scientific results concerning the use of agro-industrial by-products, naturally rich in polyphenols (BPRP), in the diets of small dairy ruminants. Effects on milk production, milk and rumen liquor fatty acid profile, metabolic parameters, and methane production are reviewed. The feed intake and digestibility coefficients were generally depressed by BPRP, even though they were not always reflected in the milk yield. The main observed positive effects of BPRP were on quality of the milk's FA profile, antioxidant activity in milk and blood, a reduction of rumen ammonia, and, consequently, a reduction of milk and blood urea. The expected beneficial effects of dietary polyphenols in small ruminants were not always observed because of their complex and variable matrices. However, owing to the large quantities of these products available at low prices, the use of BPRB in small ruminant nutrition offers a convenient solution to the valorization of residues arising from agricultural activities, reducing feed costs for farmers and conferring added value to dairy products at the local level, in a sustainable way.

Keywords: antioxidant; biohydrogenation; by-products; fatty acids; methane; polyphenols; small ruminants.

Figure 1

Main classes of polyphenols: flavonoids, non-flavonoids, and tannins.

Figure 2

Relationship between total phenol content of by-products naturally rich in polyphenols (BPRP) (expressed in g/kg DM) and dry matter intake (DMI, expressed in kg/d) in sheep (◊) and goats (●) (goats: [40,93,94,107]; sheep: [16,17,90,91]).

Figure 3

Effect of total polyphenol (TP) concentration in the diet on sheep (dark grey) and goat (light grey) milk yield calculated as a percentage of the increase or decrease compared to the control group; * indicates a significant difference (p < 0.05) compared with the control group.

Figure 4

Causal loop diagram of the beneficial role of the use of agro-industrial byproducts in the food chain. Arrows indicates causality, whereas polarity signs, + and -, indicate positive and negative correlation, respectively. B indicates balancing system loops.