Dr. Larry Bramlage had this to say (see red circled paragraph) at one of the Jockey Club Round Table Conferences about the decline in the number of starts in US racehorses of the present era versus those from the 1950s:
Was his math correct? I jotted some numbers from the Jockey Club fact book on a napkin to check his ratios. In 2007, the US foal crop numbered 34,341 foals. In 2011, four years later, there were 49,794 races in the US, while the average number of starts per runner that year was 6.20 and average field size was 8.04.
In contrast, in 1951 the foal crop was 8,944. In 1955, four years later (to be consistent), there were 31,757 races. The average number of starts per runner was 11.10 and average field size was 9.06. Based on these numbers, there were 3.8 times the number of foals in 2007 than in 1951, but there were only 1.6 times the number of races in 2011 than in 1955. This, then, must account for at least some of the drop in the average number of starts per year, 11.10 versus 6.20, that we see, as Dr. Bramlage hypothesized, right? Drugs (Lasix, plus illegal substances such as EPO), management (trainer statistics, speed fig guidelines, veterinary opinions), breeding (larger books, less variety of bloodlines), racetracks (varied surfaces, less variety of distances) and travel (increased shipping/vanning to races) are some other contributors as well, no doubt.