The Broodmare Influence

 Traditionally horse breeders look to the stallion for pedigree lines to produce the superior performance offspring with the desired characteristics of speed conformation and health. But the lineage of mares plays an equally important role not only in the genetic quality of the foal but potentially in the breeders selection for fillies or colts. In addition a mares maternal heritage influences the length of gestation.
At the Graf Lehndorff Institute for Equine Science a joint research institution of the Vetmeduni Vienna and the Brandenburg State Stud in Germany researcher Juliane Kuhl investigated the degree to which the maternal lineage family lines influences gestation length and foal characteristics.

When I started my work at the Brandenburg State Stud in 2009 part of my duty was to supervise parturition in the mares says Kuhl. As horse breeders may well know gestation length in mares is highly variable and early signs of impending parturition can be subtle impeding accurate prediction of foaling. However the experienced staff at the stud often told me something like Oh this is a Pmare. She will probably take more time until foaling. Or the other way round Mon Plaisir belonging to the Mmare lineage will probably come earlier with the foal. And often they were right. On the other hand every morning when the stud director would be looking at the mares and the newborn foals I got to hear Again a filly. You have to produce more colts. I wanted to know more and started to look at the breeding data of these mares.
Working with a team of researchers Kuhl found that the length of gestation varied significantly between the different lineages. In addition certain family lines will produce more fillies than colts.
As breeders know the gestation period for horses ranges from 335 to 345 days and sometimes more widely from 320 to 360 days. Some maternal lines will average 10 days longer than other family lines. The researchers also noted in their study that the gestation length for male foals tended to be longer than for female foals which added to the complex variation between the mare families in the focus broodmare group.
In general when you want to investigate genetic effects on a trait influenced by a variety of factors which in the horse is gestation length as well as foal sex ratio environmental factors have to be reduced to a minimum to be as constant as possible