Four good reasons to rethink genetic selection

摘要

Genetic selection has caused an ever-growing increase in the number of pigs born alive. However, other important factors in pig production have become overlooked - this article lists four of them. Could it be time for a fundamental rethink?For decades, average numbers of pigs born alive hovered around the 10.5 mark. Selection for prolificacy was not considered worthwhile, as the heritability values (h2) were considered too low (8-10%). Then French research in the 1960s and 1970s started looking at identifying subpopulations that demonstrated much higher than average numbers of pigs born alive and breeding up from these populations to create a "hyperprolific"line. In the late 1980s a consortium of four British breeding companies, togetherwith the Animal Breeding Research Organisation at the Roslin Institute in Edinburgh, Scotland, imported a group of Meishan pigs from China which were very prolific and also very fat. Meishan genes found their way into some commercial hybrids in the 1990s.In the mid-1990s, genetic selection was revolutionised with the better understanding of pig DNA and the identification of the genes responsible for prolificacy. Traditional phenotypic, quantitative selection was now complemented with genomic selection based on the sequencing of the nucleotides. All of this was made possible by giant steps in number-crunching-capacity with more effective computing power and programssuch as best linear unbiased prediction (BLUP). The rest is history. Nearly all the major genetic companies have made phenomenal progress in numbers born alive (see Table I), and averages of 14-16 born alive are frequently seen on commercial farms. As average numbers born alive has increased, so the average birth weight has declined. There are many small, unviable pigs being born (below 800 grammes).