BREEDING ▶▶▶
Four good reasons to rethink genetic selection
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?
BY MARCELLO G. MARCHESI, INDEPENDENT INTERNATIONAL CONSULTANT F
Live born Still born Weaned
Total born Prenatal mortality (%)
Pre-weaning mortality (%) Source: Rutherford et al, 2011.
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or decades, average numbers of pigs born alive hov- ered 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, together with 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 commer- cial 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 programs
such as best linear unbiased prediction (BLUP). The rest is his- tory. Nearly all the major genetic companies have made phe- nomenal progress in numbers born alive (see Table 1), and av- erages 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).
1. Pre-weaning mortality Professor George Foxcroft at the University of Alberta has car-
ried out a lot of research into the phenomena of intrauterine growth retardation (IUGR). Pigs that are small at birth remain small at weaning. As a rule of thumb, a pig weighing 100g less than the litter average at weaning will weigh 1 kilo- gramme less at the end of their stay in the grower section. Later the pig will weigh 10–15kg less at the end of the finish- ing period. In an all-in, all-out system, this means either downgraded pigs at the slaughterhouse, or longer times to close out the finisher site. Still, many breeding companies continue to exert selection pressure on numbers born alive. The more far-sighted compa- nies are now looking at selection of “pigs alive on day 5” (LP5). Growing pressure from well-funded and well-informed ani- mal welfare groups is also putting pressure on governments, which sometimes is transformed into legislation. In 2010, the Danish parliament discussed the ethics of rapid genetic pro- gress in numbers born alive, while declaring national figures of 20% pre-weaning mortality. This was followed by a project report by the Danish Centre for Bioethics and Risk Assessment (see Table 1). In the Netherlands, the Partij voor de Dieren (Animal Party),
Table 1 - Ethical and welfare implications of large litter sizes in domestic pigs, Denmark. 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
11.2 11.3 11.5 11.7 11.9 12.1 12.3 12.6 12.9 13.2 13.5 13.6 14 14.2 0.9 1.0 1.0 1.1 1.1 1.2 1.3 1.4 1.5 1.7 1.7 1.7 1.8 1.9 9.9 10 10.2 10.3 10.4 10.5 10.7 10.9 11.1 11.3 11.6 11.7 12.1 12.2 12.1 12.3 12.5 12.8 13 13.3 13.6 14 14.4 14.9 15.2 15.3 15.8 16.1 7.44 8.13 8.00 8.59 8.46 9.02 9.56
10.00 18.18 10.42 11.41 11.18 11.11 11.39 11.8 18.7 18.4 19.53 20 21.05 21.32 22.14 22.92 24.16 23.68 23.53 23.42 24.22
▶PIG PROGRESS | Volume 36, No. 6, 2020
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