Poultry represents about 40% of the $3 billion global opportunity that's been created by the elimination of antibiotics in the human food chain.
And so you're talking a $1.2 billion opportunity, where from Fred to that team that I just mentioned, their -- with a quick phone call, they can get to every level at all the major decision-makers around the world, and we are getting interest like never before.
We have 100 million proven, but we have to equal that amount inferred, meaning we don't even bother doing the drilling because we're not going to need it in any of our lifetimes, but mother nature put it there.
We have always a minimum of 40 years reserves in every product line.
And 11 markets really are where we think we have a unique position to go after a large percentage of that $1.2 billion opportunity.
My math is it's between $700 million and $800 million of that $1.2 billion, so maybe two-thirds.
So in our second quarter of fiscal 2021, Oil-Dri delivered another solid quarter of top-line growth with net sales of $74.5 million, growing 5% over net sales during the same quarter in the prior year.
Both our business-to-business products group, which grew 7%, and our retail and wholesale products group, which grew 4%, contributed to this growth, demonstrating that as Dan said, we are achieving success in two of the key areas of our strategic focus, and those are mineral-based animal feed additives and lightweight cat litter.
We are seeing evidence that the focus on our mineral-based strategy in animal health and nutrition products is paying off, with 20% net sales growth during the quarter over the second quarter of the prior year.
Agricultural and horticultural products also had a strong quarter, achieving 10% growth over the same quarter in the prior year, driven primarily by increased sales with existing customers.
And in our fluids purification products, the decrease in sales of our jet fuel purification products that have been adversely impacted by the reductions in air travel due to the global pandemic were more than offset by the growth of our other products as our overall fluids purification products grew 3% in the quarter over the prior year.
And finally, our co-packaged cat litter product, which sits within our business-to-business products portfolio, grew 5% during the second quarter of fiscal 2021.
Now similarly, within our consumer products group, cat litter sales grew 6% over the prior year.
Our second-quarter gross profit of $18.2 million was down $800,000 from the same quarter in the prior year, representing a 4% year-over-year decrease.
Despite the favorable growth in net sales, the quarter was unfavorably impacted by cost increases particularly in the categories of freight, which was up 13% per manufactured ton over the same quarter in the prior year due to domestic trucking supply constraints that resulted in significant increases in transportation costs.
Our packaging costs were also up 13% per manufacturing ton as increased resin pricing resulted in increased costs, particularly in our jugs and pales, and natural gas costs were up 8% per manufactured tons, which we used to operate kilns to dry our clay.
Overall, our cost of goods sold per manufactured ton was up 8% over the same quarter in the prior year, driven, in large part, by these market-based factors that were partially offset by operating cost reductions and efficiencies during the quarter.
Switching to our total selling, general and administrative expenses for the second quarter of $13.9 million, they were $843,000 higher than the prior year, representing a 6% increase.
However, the second quarter of the prior fiscal year included a onetime curtailment gain of $1.3 million related to the freeze of the company's supplemental executive retirement plan, which has since been terminated.
Excluding that $1.3 million onetime gain in the prior year, SG&A was down 3% during the quarter.
However, there was also an underlying shift in costs as corporate expenses, including the impact of the fiscal 2020 onetime gain or excluding the impact of the onetime gain of $1.3 million, decreased from the prior year and SG&A costs to support our business-to-business products, particularly the investments that we're talking about in our animal health and nutrition products, grew 26% or approximately $600,000 over the same quarter of the prior year.
Our second-quarter other income of $1.1 million included an $800,000 gain upon the annual actuarial valuation of our pension plan.
And finally, net income attributed to Oil-Dri for the second quarter of fiscal 2021 was $4.3 million, which represents an 11% decrease from the prior year for the cost and investment reasons we just reviewed.
We ended the quarter with cash and cash equivalents of $31 million and have very little debt, equating to a debt to total capital ratio of only 6%.
During the first six months of fiscal 2021, our accounts receivable increased $3.8 million, reflecting our sales growth and a shift in our customer mix, including an increase of sales to foreign customers who tend to have longer payment terms.
Because of our strong position during the quarter, we also repurchased 33,594 shares of Oil-Dri common stock for $1.2 million at an average price of $36.09 per share.

Summary:
So in our second quarter of fiscal 2021, Oil-Dri delivered another solid quarter of top-line growth with net sales of $74.5 million, growing 5% over net sales during the same quarter in the prior year.