There are so many papers available. I have used specific primer. Allele score, sample size, primer no is a fact. You can also make a comparison between genotypic and phenotypic. Article Association between microsatellite markers and milk producti...

The association of the genotype to the phenotype will really depend on whether the markers(primers) have been developed from the gene/s or QTL controlling milk production and thats a proper association or else if your sample size is diverse a simple correlation of phenotype and genotype data works but doesn't tell you anything about using that particular marker to select for milk production