This article appeared in The T I A Newsletter, May, 1995.

     Just about everybody agrees that a mare owner should take into account a stallion's conformation when deciding whether to book. But besides avoiding stallions who have crooked legs or are known to sire foals with crooked legs, just what is it that should be taken into account? 
    The answer: The physical match between stallion and mare. 
    That answer doesn't help much, since it doesn't tell how to figure out what's a good match and what isn't. It's an answer worth searching for, because the matching of stallion and mare physical types may be the most important factor of all in the planning of matings. 
    Equix-Pix, a periodical published by Equix Biomechanics of Lexington, Ky., tried to answer the question in an issue a few months ago. The explanation of Equix theories was accompanied by handsome charts using hills and valleys to illustrate compatibility of body types. 
    That was difficult to understand, but an article from Highflyer Journal, published by Highflyer International of Glen Head, N. Y., clarified the message.
    So, by Equix out of Highflyer, here are salient quotes from an article written by Anne Peters, Highflyer Journal editor: 

    "Dr. Mostert [Paul S. Mostert, Ph. D., president of Equix Biomechanics] has introduced the very tangible idea that the reason why some sirelines work together is because the individuals usually are 'neighbors,' in fact close neighbors, on Mostert's Landscape Model. 
    "To put it simply, he proposes that Thoroughbreds come in all shapes and sizes, but that some are more physically alike than others, and those similar animals are considered physical neighbors of sorts. . . . 
    "The crux of Mostert's theory is to manage mating so that the progeny are more predictable in type, and the way to do that is to mate individuals that are closest neighbors on the landscape model. . . . 
    "The more common alternative is to mate individuals that represent extreme physical types. . . . The probability of that mating producing the perfect balance that presumably (but not necessarily) results in a superior racehorse is actually very small. 
    "One is more likely to find that the offspring can fall anywhere within the wide range between the types. . . .In other words, by reducing the range between the parents, you reduce a large number of unpredictable and possibly negative combinations. . . 
    "And here is where pedigree advisors find themselves spinning their wheels most of the time. The mating may look fantastic on paper, but paper doesn't run very fast by itself. The parents have to be a good physical match and balance each other nicely, not extremely, in physical as well as aptitudinal qualities." 

    In other words, for best results, breeders should mate horses of similar, not contrasting, conformation. 
    Almost identical advice is given by respected Kentucky farm manager Joe Taylor in his 1993 book,  Joe Taylor's Complete Guide to Breeding and Raising Racehorses. Here's an excerpt from that book:

    "Your best chance of breeding a good racehorse is to breed type to type. By this, I mean crossing horses of the same basic physical type . . . rather than crossing contrasting types. It seems that predicting the type of foal that will result from a particular mating is most reliable when both parents are decidedly similar. 
    "When parents are dissimilar, the resulting foal is likely to inherit traits which are disproportionate to its size or type." 

        Following that advice from Mostert, Peters, and Taylor is likely to bring better results than making a careful choice of stallion while ignoring the compatibility of physical types. It may limit breeders' choices, but it also may produce better racehorses.