Genetic Load Expressed as Fetal Death in Cattle

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Abstract
The outcomes of 1404 inseminations from matings of known inbreeding coefficients and blood types were used in an attempt to estimate the mutational and incompatibility components of the genetic load in dairy cattle. Inbreeding of the zygote and dam, and homozygosity for blood group factors had a significant deleterious effect on embryonic mortality. The effect of maternal-fetal incompatibility due to isoimmune antibodies had a significant effect on fetal mortality also. However, the method of measuring incompatibility provided only a crude estimate. A new index of inbreeding, "11" devised by Slatis (1961) to measure lethals, was used, but the correlation between "11" and F was very high. For this reason it was impossible to divide the genetic load into lethal and detrimental components. The mutational load affecting embryonic and fetal death was estimated to be 0.862 [plus or minus] 0.233 and 0.407 [plus or minus] 0.243 respectively, and the B/A ratios were 1.75 and 1.88 respectively, suggesting that most embryonic and fetal deaths are not due to genes maintained by recurrent mutation.