Leaving Genetics to the Geneticist and Differences Between USA “Genotypes”
Roger G. Campbell
The performance of different genetic lines or genotypes is the product of both their designer (“The Geneticist”) and the environment in which they are asked to express their genetic potential.
There are plenty of examples of genotype X environment interactions for traits ranging from reproduction to carcass fatness. For example, genotypes, which appear lean under commercial production systems often, get fat when grown in systems which promote greater feed intake. Examples of the latter are new buildings, high health situations and alternative housing systems such as hoops or ecoshelters.
Similarly there are many examples within the USA industry of genotypes or pigs from different breeding companies, which are lean, but have relatively poor feed efficiency and growth rate. Conversely, there are pigs from other companies, which are relatively “fat” but have excellent feed efficiency and growth. These differences obviously reflect selection pressures by geneticists for traits thought to be of the greatest economic value. In this paper I have attempted to demonstrate how including the geneticist in a team including members who understand the biology of pigs and the business environment will result in “better” and more consistent or stable genetic programs.
Leaving Genetics to be Geneticist
Profitability in the pig production business requires improvements in all traits, which affect both price and costs. Consequently geneticists and genetic companies need to understand the drivers of profit, how these might differ between customers and how the biology and business of pig production interact to affect profitability.
Geneticists are generally limited in their knowledge of production and biology and consequently should (and do) work in a team if genetic/selection programs are to be more successful and more stable than they have been in the past. Geneticists are able to change almost any trait but often do not understand the consequences of the change on other traits or if the change has really altered the basic mechanisms controlling growth or reproduction.
The basic mechanisms controlling growth rate, feed efficiency and carcass composition are well understood at the tissue, metabolic and even hormonal and gene levels. We know that it is possible to improve growth rate, feed efficiency and carcass lean simultaneously. However, this rarely occurs in genetic selection programs firstly because improvements in apparent lean based on fat thickness and loin depth doesn’t necessarily reflect real changes in protein deposition capacity or in the partitioning of energy between fat, protein and maintenance.
Consequently, feed efficiency may improve or get worse depending on the extent maintenance energy requirement is altered. Growth rate my remain static or decline. Carcass lean content and/or feed intake and feed efficiency are not necessarily related in the different genetic lines available in the USA. Indeed, in some of the more “advanced” or more profitable genetic lines feed intake and feed efficiency are positively correlated.
These differences and the possible reasons for them are discussed using as examples, animals from different genetic companies in the USA. The animals are the product of their selection program and if the underlying changes in metabolism were better understood further improvement should be more certain and more reliable. Alternatively if the biology of the pig was better understood by geneticist’s selection decisions and outcomes would likely improve.
For these reasons geneticists need to work in teams with production specialists and biologists that fully understand the basic mechanisms underlying growth performance, carcass lean, meat quality and/or reproduction.
Differences Between Genetics
The protein deposition curves for two lines of female pigs are shown in Figure 1. The consequent differences in growth performances and carcass fat level for pigs grown to a common age are given in Table 1.
The protein deposition curves suggest Line 2 pigs have been selected for growth rate and feed efficiency whilst greater selection pressure has been placed on “lean” in Line 1. The pig has achieved the latter by reducing feed intake during later development. We also know that Line 1 females have a higher energy requirement for maintenance than Line 2 which again reflects selection pressure for lean. On the other hand it is unlikely that the geneticist was aware that his selection program had altered maintenance requirements.
At constant weight pigs from Line 1 would be leaner than Line 2 but would grow slower and have a higher feed: gain. At constant age pigs from Line 2 would be heavier, slightly fatter and have a similar overall feed efficiency but be more profitable than those from Line 1. Similar differences exist between sexes within genotypes/lines and in reproduction. Providing the differences are known and understood management can be adjusted to maximize returns. However, if genetic decisions were based more on the biology of growth (or reproduction) than the outcomes of these (traits) genetic gains are likely to be enhanced and the value of the product to producers improved.
Figure 1. Protein Deposition curves for female pigs for two US “genotypes”
Table 1. The performance of female pigs of two US “genotypes”