Performance of dairy cattle clones and evaluation of their milk composition.

Genetic and phenotypic performance of U.S. Holstein embryo-split and nuclear-transfer clones was documented for yield and fitness traits. For cows, mean genetic superiority based on pedigree was 186 kg of milk, 9 kg of fat, and 7 kg of protein for embryo-split clones and 165, 10, and 8 kg, respectively, for nuclear-transfer clones compared with the population for the same birth year; pedigree advantage for male clones generally was slightly greater. Estimates of genetic merit that considered a clone's own performance as well as pedigree merit were slightly lower for embryo-split cows than for their full siblings for yield but not for milk composition (fat and protein percentages), mastitis resistance (somatic cell score), longevity (productive life), or cow fertility (daughter pregnancy rate); no corresponding genetic differences were found for nuclear-transfer cows or for cloned bulls regardless of clone type. For bulls, estimated genetic merit based on daughter yield was more similar for clone pairs with apparent identical genotype than for pairs from the same biotechnology but nonidentical as confirmed by blood typing. Yield deviations were lower for clones than for their full siblings. Milk composition (total solids, fat, fatty acid profile, lactose, and protein) also was compared for nuclear-transfer clones (Brown Swiss, Holstein, and Holstein-Jersey cross) with non-cloned cows and literature values; no differences were found for gross chemical composition of milk. No obvious differences were evident between cloned and non-cloned animals or for the milk that they produced.