Performance of Holstein Clones in the United States

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Abstract
Phenotypic and genetic performance of US Holstein clones from embryo splitting (ETS) and nuclear transfer (ETN) was documented for yield and fitness traits. Holstein Association USA has registered 2319 ETS and 215 ETN clones. The number of male clones has decreased. Animals selected for cloning were slightly superior genetically to population mean for yield traits. For females, mean superiority of pedigree merit of ETS clones was 186 kg for milk, 9 kg for fat, and 7 kg for protein compared with the population for the same birth year; for ETN clones, superiority to the population was 165, 10, and 8 kg. Advantage in pedigree merit for male clones generally was slightly greater. The small pedigree advantage for female clones of <1 standard deviation above breed mean indicates that selection of animals to clone was not based primarily on yield. Yield deviations were lower for ETS clones than for their full siblings, which indicates a possible impact of the technology on performance. Yields were lower for ETN clones than for their noncloned full siblings, but differences were small and based on small numbers of clones. Milk composition for cloned cows was not different from that for the population. Estimated genetic merit based on daughter yield was more similar for male clone pairs with apparent identical genotype than for clone pairs from the same biotechnology but nonidentical as confirmed by blood typing. For ETS clones with confirmed identical genotypes, identical genetic merit should be assigned.