Thursday's outcome was the largest on record for the period since 1964, maintaining a string of quarterly record highs dating back to March 2016.
Still, analysts viewed the data as neutral for Chicago Mercantile Exchange lean hog futures on Friday because the results were close to expectations.
Analysts attributed the herd expansion to improved producer profits, affordable feed and the need for more supplies to accommodate at least two new packing plants scheduled to come on line later this year.
A record number of baby piglets that survived during the quarter helped farmers to be more efficient and boosted herd sizes.
USDA's report showed the U.S. hog herd as of June 1 at 103.0 percent of the year-ago level or 71.650 million head.
The result topped analysts' average forecasts and was the most for the quarter since USDA began compiling data for the period in 1964.
Analysts, on average, had expected 71.597 million head, or 103.3 percent of the year-earlier herd.
The U.S. breeding herd was 102.0 percent of the year-ago level, at 6.069 million head, up from 5.979 million last year.
The average trade forecast was 6.069 million, or 101.5 percent of the previous year.
The June 1 supply of market-ready hogs for sale to packers was 104.0 percent of a year earlier, at 65.581 million head, up from 63.302 million last year. Analysts, on average, had estimated a 3.5 percent rise, or 65.490 million.
Allendale Inc chief strategist Rich Nelson called the record hog herd size "shocking," but said it would have no effect on the market. Industry observers for several months had expected record production and most of the results came in line with expectations, he added.
The industry will monitor whether two new hog plants will be operational by September to handle the massive supplies ahead, said Nelson.
"Any delays in the start of the two plants will be clearly taken as bad news by the industry," he added.
Bob Brown, an independent market analyst in Edmond, Oklahoma, agreed that the "numbers came in pretty much as expected - nothing outlandish."
Nearby CME hog futures will likely follow prices for market-ready, or cash, hogs and not focus on trading months further out associated with Thursday's report, said Brown. (Editing by Richard Chang). BY THEOPOLIS WATERS.