Was factory beef farming (in the USA) the result of
Answer A) The answer is negative, according to
MacDonald, J. M., & McBride, W. D. (2009). The transformation of US livestock agriculture scale, efficiency, and risks. Economic Information Bulletin, (43). USDA.
Although not a historical-statistical account, they write (p. 21, bold my emphasis)
"Two recent reports argue that Federal commodity programs reduce prices for a particular input, purchased feeds, and that those
reductions drive structural change (Pew Commission on Industrial Farm
Animal Production, 2008; Union of Concerned Scientists, 2008).
Specifically, they assert, drawing on Starmer and Wise (2007), that
policy encourages increased production of feedgrains, that the
increased production substantially reduces feedgrain prices, and that
the buyers of purchased feed benefit from lower feed prices. While
producers of homegrown feed have been the direct recipients of
commodity payments, the reports argue that the payments have not been
large enough to offset lower commodity prices, so that commodity
programs have largely benefited large-scale animal feeding operations
at the expense of smaller diversified crop and livestock farms.
However, the size-related differences in production costs that are
summarized in figures 6-8 cannot be attributed to the effects of
commodity programs. In developing cost-of-production estimates, ERS
prices homegrown feed at its market value—that is, the price that
homegrown feed would have drawn as feed in regional feed markets—and
does not attempt to estimate the actual cost of producing the feed. To
the extent that larger operations realize lower feed costs in ERS
estimates, it is because they use less feed per cwt of production and
not because purchased feed costs them less.
But even if commodity policies reduce purchased feed prices, there’s no reason why that should alter the size structure of livestock farms.
No technological barrier prevents small farms from replacing homegrown
feed with purchased feed: if purchased feed prices are lower than the
costs of growing feed, then small livestock operations can simply buy
feed and realize the same savings as large farms. A difference
between the price of purchased feed and the cost of homegrown feed
does not explain why feeders build large rather than small
Answer B) The answer is positive according to
Starmer, E., & Wise, T. A. (2007). Living high on the hog: factory farms, federal policy, and the structural transformation of swine production. Tufts University.
They report the following estimations, among others: The feed costs for Hog represent ~$60\%$ of operating costs of CAFO's. That in the period $1997-2005$ feed subsidies meant that feed was sold at a price $26\%$ below production cost. Hence, the savings in operating costs for CAFO's was around $60 \% \times 26\% \approx 15\%$ (of Costs, not of Revenues). For the top four CAFOs in terms of market share, the authors estimated that this amounted to total cost-savings of $\approx 4.4$ billion USD for the 1997-2005 period.
This paper appears to be an aggregator of previous more detailed studies, so lots of references.