Ch Morazé, Bourgeois conquérants, París, 1957.

The outcomes of the preliminary study pointed out which were the more feasible traits to record, the more convenient days to record the traits in order to reduce the variability of the measurements, the ideal posture to evaluate the sow in the farrowing crate to limit measurements errors, and the most appropriate devices to optimize data collection time

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and repeatability. The evaluation methodology for udder morphology traits developed in this research (Chapter 3) offered a repeatable and feasible measurement tool.

Another important observation that emerged was the extent of anatomical differences in udder morphology traits between sows. The investigation presented in Chapter 4

highlighted some causes of variation in udder morphology traits such as breed type, parity number and teat pair position. Meidam sows had shorter and more uniform teats

compared to Large White x Landrace. Meidam sows are a cross-breed of Large White and the Chinese Meishan. The latter tends to have higher teat numbers (Meishan average: 17 teats; Meidam average: 16.2 teats) and it is well known for its high prolificacy, but also for its poor growth and body composition (high backfat thickness percentage) (Bazer and First, 1983; Haley et al., 1995). Meishan sows have also received great interest for their good temperament, which has been associated with a higher offspring survival rate (Van der Steen and De Groot, 1992), and heavier piglets at weaning (Edwards, 2002). The outcomes originating from this thesis add knowledge on the nursing ability of the Meidam, with better udder traits in respect to the distance between the teat and the abdominal midline and the teat length. However, the inter-teat distance within the same row and the teat diameter were not different between the two breeds which were studied and other factors have been pointed out to affect udder size. In accordance with Vasdal et

al. (2012), who noted that teat access was reduced in old sows compared with younger

ones, sow udder morphology traits of both breeds were affected by parity number. At the population level, increased sow parity number was associated with increased teat

dimensions, but surprisingly not with a larger teat distance from the abdominal mid line. However, comparing udder morphology of the same sow at consecutives parities showed that the distance between teat and abdominal mid line does increase with increasing parity number. Hyperprolific sows have become larger and their body size grows greatly with each lactation compared to sows of almost 30 years ago (O'Connell et al., 2007;

Moustsen et al., 2011). The comparison of phenotypic traits of the same animal at consecutives parities showed that around a quarter of the variation in the measurements was explained by sow identity, much more than by parity group. This outcome adds information on the udder evaluation methodology suggesting that one standardised measurement in the life cycle of the sow might be adequate to describe the phenotypic trait.

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Moreover anatomical differences have been shown within sow. Mammary glands are not uniform; the glands located in the most cranial part of the body are more compact than the glands located in the caudal part (Kim et al., 2000). The measurements of both studied breeds revealed that the udder could be separated in three sectors: anterior (the two most cranial mammary gland pairs) and posterior (the two most caudal pairs) with teats of small length and diameter, shorter distance from the abdominal midline and longer inter- teat distance within the same row; and a middle section with larger length and diameter of teats, closer to each other and more distant from the abdominal mid line. However, the majority of variance in udder morphology traits could not be accounted for and it was not clear which were the causes of variation of the distance from the abdominal mid-line. Kim et al. (2000) suggested that a bigger size of the middle portion of the udder after farrowing indicates that, during gestation, growth rate of mammary gland tissue differs between anatomical locations.

Phenotypic correlations between udder morphology traits and production and reproduction performance of the sow extended the knowledge about this variation (Chapter 7). Heavier litters at birth were correlated with a larger udder dimension,

measured as inter-teat distance within the same row, teat distance from the abdominal mid line and udder development score. Moreover, litter size at birth was positively correlated with larger udder dimensions. This could be explained by the evidence that litter size at birth is associated with milk production (Auldist et al., 1998; Kim et al., 2001; Nielsen et

al., 2001; Vadmand et al., 2015). In their review, Quesnel et al. (2012) suggested that, as

milk yield depends on the number of milk-producing cells present in the gland at the onset of lactation, colostrum production should follow the same process. In our study also, colostrum IgG concentration was positively correlated with the total born number and litter weight at birth. Ogawa et al. (2014) noted that higher colostrum yield tends to contain more IgG. Another recent study confirms the positive relationship between litter size and weight at birth and colostrum production (Vadmand et al., 2015). In contrast, in the study of Quesnel (2011), colostrum yield did not increase as a result of a higher litter size whereas it did increase with piglet birth weight (Devillers et al., 2007; Quesnel, 2011). Altogether, the results from the literature and the evidence arising from this work suggest that colostrum IgG concentration is positively associated with colostrum yield. Ogawa et al. (2014) found that IgG concentration was associated with the teat location on the udder. This result supports previous findings on the relationship between daily body

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weight gain of piglets and teat order (Kim et al. 2000; Skok et al. 2007). Kim et al. (2000) did not find any difference in body weight of piglets that suckled either anterior or middle teats. In our study, colostrum was collected from all teats and no relationship was found of mean Ig concentration with litter performance (size and weight) at ten days. A possible explanation for this might be that during our experiment a great number of cross fostering took place and many data were missing during this process. The literature also indicates ambiguous results about the relationship between teat position and

immunoglobulin content: anterior (Rooke et al., 1998; Wu et al., 2010), posterior (Klobasa et al., 1987) and middle regions (Tuchscherer et al., 2006) have all been reported to be richer in IgG concentration. In contrast, there is a strong consensus that neonatal teat preference seems to be driven by colostrum outflow (Fraser, 1976; Fraser, 1977; Jeppesen, 1981; Fraser, 1984; King et al., 1997; Skok et al., 2007). However, another important driver that needs to be considered is that anterior mammary glands are more appealing, since they offer more protection, are closer to the mother’s head and piglets are attracted by maternal odour and grunting (Jeppesen, 1981; Castren et al., 1989; Kasanen and Algers, 2002; Skok and Škorjanc, 2013). In the light of these considerations it could be hypothesised that this favourable position is attained by the more vital and strong piglets that then deliver a greater stimulation of their gland, in turn making it more productive. However, Kim et al.(2000) and Skok et al. (2013) did not find a correlation between birth weight and teat position. This was also the case for the outcomes of our research. To support the hypothesis that piglet teat preference for anterior teats results from their attractiveness, Nielsen et al. (2001) found that mammary glands of primiparous sows did not differ in milk yield, as measured by piglet growth rate. This assumption could also hold true for colostrum yield, as suggested by Quesnel et al. (2012) from the relationship between milk-producing cells and milk yield. However, in the multiparous sows, growth rate was higher in the piglets suckling the front teats than in the piglets suckling the rear teats. Kornblum et al. (1993) found similar results for milk yield in first and later parity sows. Farmer et al. (2012) discovered that mammary glands that have not been used in a previous lactation have decreased productivity in a subsequent lactation. Altogether, these evidence suggest that mammary gland productivity and size are correlated to the stimulation of piglets influencing the production in the subsequent lactation (King et al., 1997). This assumption gives an explanation about the differences in udder morphology traits and body weight of piglets that suckled from anterior teat in multiparous sows.

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