Mineral Nutrition
Net sales of $105.6 million for the six months ended December 31, 2020, decreased $2.7 million, or 3%, driven by lower average selling prices, partially offset by increased unit volumes. The decline in average selling prices is correlated with the movement of the underlying raw material costs.
Performance Products
Net sales of $31.1 million for the six months ended December 31, 2020, increased $1.3 million, or 4%, driven by increased volumes of copper-based products, partially offset by lower sales of personal care product ingredients.
Gross profit
Gross profit of $132.4 million for the six months ended December 31, 2020, increased $5.6 million, or 4%, as compared to the six months ended December 31, 2019. Gross margin increased 160 basis points to 33.0% of net sales for the six months ended December 31, 2020, as compared to 31.4% for the six months ended December 31, 2019. The six months ended December 31, 2019, included $0.3 million of acquisition-related cost of goods sold.
Animal Health gross profit increased $3.8 million, driven by increased volumes of nutritional specialty and vaccine products, favorable product mix and favorable production costs, primarily related to foreign currency movements. Mineral Nutrition gross profit decreased $0.1 million, as declines in average selling prices were mostly offset by favorable raw material costs and product mix. Performance Products gross profit increased $1.7 million driven by higher volume coupled with decreases in raw material and production costs.
Selling, general and administrative expenses
Selling, general and administrative expenses (“SG&A”) of $96.8 million for the six months ended December 31, 2020, decreased $0.2 million, or less than 1%, as compared to the six months ended December 31, 2019. SG&A for the six months ended December 31, 2019, included $0.4 million of restructuring costs, $0.5 million of acquisition-related transaction costs and $0.2 million of other acquisition-related costs. Excluding these costs, SG&A increased $0.9 million, or 1%.
Animal Health SG&A decreased $0.8 million primarily due to the favorable effects of foreign currency exchange and decreased marketing and sales team travel costs driven by COVID-19 safety concerns and limitations, partially offset by increased professional fees to support the continued use of carbadox. Mineral Nutrition SG&A was comparable to the prior year and Performance Products SG&A decreased $0.1 million. Corporate expenses increased $1.9 million, driven by increased costs for business development initiatives, professional fees and information technology. The restructuring costs, acquisition-related transaction costs and other acquisition-related costs resulted in a net $1.1 million decrease to SG&A.
Interest expense, net
Interest expense, net of $6.0 million for the six months ended December 31, 2020, decreased $0.8 million, or 11%, as compared to the six months ended December 31, 2019. Interest expense decreased due to favorable variable interest rates, partially offset by higher levels of debt outstanding and lower interest income from short-term investments.
Foreign currency (gains) losses, net
Foreign currency gains, net for the six months ended December 31, 2020, were $3.0 million, as compared to net losses of $2.5 million for the six months ended December 31, 2019. Foreign currency gains primarily arose from intercompany balances, driven by the movement of the Mexican, South African and Turkish currencies relative to the U.S. dollar.
Provision for income taxes
The provision for income taxes was $7.5 million and $6.1 million for the six months ended December 31, 2020 and 2019, respectively. The effective income tax rate was 22.9% and 29.6% for the six months ended December 31, 2020 and 2019, respectively. The provision for income taxes during the six months ended December 31, 2020, included (i) a $1.5 million benefit for the years