80 ECONOMÍA, DERECHO, HISTORIA

The development of strategies that can improve breeding values is of increasing interest and importance to the livestock industry. Genetic selection is mainly focused on

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production and reproduction traits (the most obvious economically valuable traits) such as growth rate, feed efficiency, lean meat percentage and litter size. Selected traits are

recorded in nucleus herds, multiplier herds and test-stations, and the breeding organisation stores the registrations from all pigs in the nucleus herds. Despite the evidence that sow udder morphology traits play an important role in rearing offspring, increasing milk production and promoting mammary gland health, they have not been included in any selection programme so far except from total teat number. Udder quality represents one of the most important traits in beef production, and in other species udder traits are largely exploited for their relationship with milking ability. This gap in swine may be explained by the lack of interest in the milking ability of the sow, since sow milk is not directly a production outcome but only indirectly seen in piglet growth. Moreover, sow behaviour and udder conformation make the evaluation process more complicated than udder evaluation of cows or sheep. On the other hand, pig genetic selection has focused on cumulative short-term genetic change driven only by market economy. There is much evidence to show that specialised dam line selection has led to undesirable side effects that contribute to increased piglet mortality. In her review, Rydhmer (2000) emphasised the issue that increasing sow prolificacy is no longer a sustainable selection strategy per se and, in order to allow the sow to rear extra piglets by herself, other traits must be included in the genetic criteria. This issue becomes even more urgent when considering the need to improve animal welfare, pig health and reduce environmental impact of the swine production system (Kanis et al., 2005). In light of these

considerations, appropriate animal breeding programs and breeding goals should be considered as an integrative strategy to implement a sustainable production system. This study is one of the first investigations to assess udder quality in sows. The evaluation methodology developed in this project proved to be a functional tool to carry out data collection on a large sample size in order to assess the heritability of these traits. All the evaluated traits had moderate to high heritability, indicating that genetic progress could be made rather quickly. However, such selection would be complicated in commercial practice; this measurement process is physically demanding for the operators and requires time. In the light of this limitation, only some traits should be recorded according with their impact on teat accessibility and considering favourable and unfavourable

correlations within the udder traits, and with economically important reproductive and productive traits.

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The results of this study show a positive genetic correlation between the inter-teat distance and the other traits; this should mean that selection for smaller udder dimension and increased teat number would lead to a diminution of inter-teat distance. Teat length and diameter were negatively correlated with teat functionality, which is easily explained since in the definition of teat functionality given in this thesis there were also teats that remain as a small protuberance. Interestingly, teat non-functionality was positively genetically correlated with the distance from the abdominal mid line. This result suggests that by selecting for a shorter teat distance from the abdominal mid-line the number of non-functional teats will also be reduced.

The ultimate goal of the udder quality selection is to increase nursing activity in all the functional mammary glands. What makes these traits very interesting is their impact on animal welfare, as well as on the farm profit. It has been estimated (BPEX, 2009) that a 5% reduction in total piglet mortality will reduce cost of production by ~3p/kg carcass. Moreover it is estimated that 40 to 50% of sows are culled before their third or fourth parity, a time by which initial replacement costs have not been met, and 20 to 30% of this is due to poor litter performance, related with udder problems. It is therefore reasonable to assume that by improving udder morphology sow culling will also be prevented.

In the light of this consideration, including udder quality traits in the selection program can be considered as worthy of promotion (Olesen et al., 2000). A trait of an animal has an economic value if a level change of that trait results in economic benefit. Kanis et al., (2005) suggested that there are also non-economic reasons to change the level of a trait. By improving teat accessibility, piglet immediate and long term performance will improve, milk production will increase, sow culling will be reduced and the

environmental footprint of pig meat production will decrease. Overall these changes not only produce financial benefit for the enterprise, but will also improve the welfare of both mother and offspring. Considering the impact of udder quality traits on pig production, these traits can be considered both non-economic and economic, accomplishing the needs of modern pig production.

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