Microalgae supplementation improves goat milk composition and fatty acid profile: a meta-analysis and meta-regression

Recently, there has been an emphasis on research on sustainable and environmentally friendly agricultural practices. Microalgae are a promising feed that is rich in essential nutrients, and research has been oriented toward their incorporation into ruminant diets. This study aimed to evaluate the inclusion of microalgae in goat diets using a meta-analysis methodology. The data were acquired from 17 peer-reviewed scientific papers. The raw mean difference between the treatment diets supplemented with microalgae and the control diets was evaluated using the random-effects model. Experimental characteristics such as animal breed, days in milk, experimental duration, microalgae species, inclusion levels, and concentrate were used as covariates in meta-regression and subgrouping analyses. Microalgae supplementation did not affect dry matter intake (DMI, $p=0.170$ ) but significantly improved the intake of crude protein (CP, $p<0.001$ ) and neutral detergent fiber (NDF, $p=0.005$ ). The incorporation of microalgae into the goat diet improved all digestibility parameters ( $p<0.01$ ), with an improvement in fermentation parameters, including ruminal pH ( $p=0.010$ ) and propionate ( $p<0.001$ ). Microalgae inclusion in goat diets increased blood glucose levels ( $p<0.001$ ) but did not affect blood antioxidant activity ( $p>0.05$ ). Microalgae supplementation did not affect milk yield ( $p=0.480$ ) but increased the yield of lactose ( $p<0.001$ ), protein ( $p<0.001$ ), and fat ( $p<0.001$ ). Microalgae inclusion in goat diets improves the fatty acid (FA) profile. The milk of goats had significantly decreased C18:0 ( $p=0.001$ ) and C18:1 n-9 ( $p=0.028$ ) and increased C20:5 n-3 ( $p=0.027$ ), C22:6 n-3 (DHA, $p<0.001$ ), polyunsaturated FA (PUFA, $p=0.039$ ), and n-3 ( $p=0.006$ ). Subgroup analysis showed that an inclusion level higher than 30 g per kg DM was advisable to obtain this total improvement. However, even a moderate inclusion level (15-30 g per kg DM) improved the FA profile. The microalgae species Schizochytrium sp. and the Alpine-Greek crossbreed goat breed were covariates that showed interesting results concerning the improvement of DHA and PUFA. In addition, supplementation of goat diets with microalgae could be used as a nutritional approach to enhance milk production and quality.