Thirty-two lactating Boer goats (35.2 ± 1.4 kg body weight) were grouped into control and three treatment groups in completely randomised design. In treatment groups, supplementation was done as a mixture of 5 g Chlorella vulgaris + 4.5 mg of supplemental Cu/kg diet from CuSO4 (Alg5 treatment), 10 g C. vulgaris + 9 mg of supplemental Cu/kg diet (Alg10 treatment), or a mixture of 15 g C. vulgaris + 13.5 mg of supplemental Cu/kg diet (Alg15 treatment). Treatments did not affect feed intake; however, Alg10 treatment increased (P<0.001) nutrient digestibility. Treatments did not affect ruminal pH, ammonia-N, butyrate; however, the Alg10 treatment increased (P<0.01) ruminal total volatile fatty acids, propionate and acetate concentrations. Without affecting other blood measurements, the Alg10 treatment quadratically increased (P<0.001) serum glucose and Cu. The Alg10 treatments increased (P<0.001) daily milk production and the concentration of fat, and enhanced milk (feed) efficiency. The Alg10 treatment decreased (P<0.05) milk saturated fatty acids and the atherogenic index, and increased the proportions of total conjugated linoleic acids, C18:1n9t, odd fatty acids and total unsaturated fatty acids compared with the control treatment. Present study concluded that inclusion of a mixture of 10 g C. vulgaris + 9 mg Cu/kg diet in the diet of lactating Boer goats enhanced nutrient digestibility, ruminal fermentation, milk production, feed efficiency as well as milk nutritive value. Increasing the dose of the mixture to 15 g C. vulgaris + 13.5 mg Cu/kg diet is not recommended in the diet of lactating Boer goats.
