Effect of forage to concentrate ratio and fat supplementation on milk composition in dairy sheep: A meta-analysis

The milk fat content and fatty acid profile in sheep milk can vary considerably and can be manipulated through diet. The aim of this study was to analyse the effect of forage concentration ratio and fat supplementation in diet on milk yield production, fat, protein, lactose and conjugated linoleic acid (CLA) content in dairy sheep using a meta-analytical approach. The sources of heterogeneity of dependent variables were explored using a meta-regression analysis. Compared to sheep fed high-concentrate diets (HC; concentrate content 40% DM), those fed high-forage diets (HF; forage content >40% DM) had 0.087 L/d lower milk yield (P = 0.001) and 0.065 g/100g milk lactose content (P = 0.02). However, fat content and CLA concentrations were greater in dairy sheep fed HF (0.32 g/100g and 2.28 mg/g, respectively). The addition of fat to sheep diets had a positive effect on fat (0.22 g/100g; P = 0.005) and CLA concentrations (0.78 mg/g; P = 0.001) in milk, but protein concentration was reduced (-0.20 g/100g; P < 0.001). In conclusion, the low concentrate rations induce a significant increase of fat and CLA content in milk, likely associated with the alterations of rumen functions, including biohydrogenation processes governing saturation level of fatty acids and CLA synthesis promotes by concentrate-based rations. Finally, the inclusion of fat in the sheep dairy rations produces an increase in milk yield and fat and CLA content, which may improve the milk quality in terms of human health.