The great statistical curmudgeon weighs in with the second part of his book-length assessment of the effects of age on the progeny of broodmares and their foals’ birthrank.
Table 2 summarizes the price data by birth rank, and Table 3 does the same for age of mare.
Table 2 shows the birth rank, the number of foals in each group, the gross sales for those foals, their average price and their maverage (see accompanying sidebar).
First foals were indeed the largest group at 9,348, and the groups decrease regularly from there. I decided to lump 11th-14th foals into one group and 15th+ foals into another group.
The former is about the size of seventh foals. The latter is by far the smallest group in Table 2.
Among the other factors that contribute to the decline of a mare’s foals, the quality of stallions is also a significant contributing element. Typically, a mare is sent to the best stallions she will visit in the first three or four years of her producing life. If she hasn’t produced foals that give her owner encouragement or if she hasn’t produced a stakes winner among this early group, a mare is probably going to be traded on, and her opportunities will diminish. Racehorse Breeding Theories, Chapter 10, page 190.
The quote above sounds perfectly plausible. That is one of the reasons it was decided to use sales foals for this study, because the prices for which they were sold include the perceived value of their sires. The sire is no doubt the most important factor in determining the price of a given sale foal (other important factors being the dam and the foal’s own physical qualities, which are also reflected in their prices). So if the quote above is correct, we would expect to see prices declining as birth ranks (and age of mare) ascend.
The overall average for all 54,000+ foals is $48,659. The highest group is 11th-14th foals at $56,370. The lowest group is first foals at $43,046 (no surprise there). Second-third-fourth foals are below the overall average. Fifth through ninth foals are above the overall average.
As mentioned, 11th-14th foals are the highest group, but tenth and 15th+ foals are below the overall average. The quote above is not exactly confirmed as true. Aside from first and 11th-14th foals, there is very little difference (from $47,811 to $52,859) among any of the other groups. It appears to me that aside from rightfully devaluating first foals, buyers pay very little attention to birth rank (and perhaps rightfully so).
The maverages (see accompanying sidebar for explanation) in Table 1 tell the same story. First foals are lowest at 139. The highest group is 11th-14th foals at 162. The overall maverage for all 54,000+ foals is 150 on the nose. Second and 15th+ foals are below 150. All other groups are above 150.
Table 3 shows a slightly different shape for age of mares. I decided to combine ages three and four into one group (very few threes, Commentator aside), 15-19 into another group, and 20+ into a final group. The highest average belongs to seven at $54,496, the lowest to three-four at $32,906. Five and six are below the overall average, eight through ten are above, 11 is below, 12 is above, 13 is below, 14 is above, and 15-19 and 20+ are below.
Table 3 shows a wider variance and more confusion than Table 2. The maverages agree with averages as to above or below, although they show a bit of a pattern: up to seven and down afterward (only glitch being 13).
If you go by age of mare instead of birth rank, older mares do show a decrease in prices, but it is not a sharp decrease until you reach the last group, 20+ (average of $40,688 and maverage of 141). As will be seen below, that decrease is more than justified by the results for 20+.