Suckling strategies in the pig: The Göttingen minipig as a model
Introduction
The Göttingen minipig (GMP) is a synthetic breed developed at the University of Göttingen (Germany) artificially selected for small body size, and has gained importance as model animal for studies in human medicine. Minipigs were mainly used in translational research, surgical models, procedural training, and for preclinical toxicological testing of pharmaceuticals (Swindle et al., 2012). Behavioural studies in minipigs mainly focused on behavioural tests suitable for e.g. preclinical toxicity testing (Bode et al., 2010), and on their cognitive abilities (e.g. Moustgaard et al., 2002, Moustgaard et al., 2004). However, much less is known on other aspects of its behaviour. Moreover, to our knowledge the suckling behaviour of minipigs has not even been described, although suckling is considered as a fundamental behavioural trait in mammals, most important for development and survival of the individual. On the other hand the suckling behaviour of commercial pig breeds (CB) has been much more extensively studied (e.g. McBride, 1963; Hemsworth et al., 1976; Puppe and Tuchscherer, 1999; Skok and Škorjanc, 2013, Skok and Škorjanc, 2014a, Skok and Škorjanc, 2014b, Skok and Škorjanc, 2014c), while only one study was published on suckling preferences in wild boar (WB) piglets (Fernandez-Llario and Mateos-Quesada, 2005). In general, these studies showed, that piglets of these two genotypes have diametrically opposite suckling orientation, i.e. to the cranial in CB and the caudal udder in WB. It may be concluded from these observations, that genetic selection in domestic pigs not only caused morphological and reproductive changes, but also differences in suckling behaviour. In particular, in the course of domestication, two features which might crucially affect piglets suckling behaviour have been modified: number of teats and litter size. An average litter size in CB pigs is with about 12 piglets up to three times greater than that of WB (see Fernandez-Llario and Mateos-Quesada, 1998; Fernández-Llario et al., 1999; Gethöffer et al., 2007). Moreover, the litter size in modern high prolific CB sows can be even higher, with litters of 16–20 piglets (see Andersen et al., 2011; Vasdal et al., 2011). However, the number of teats also increased from four teat pairs in the WB (Fernandez-Llario and Mateos-Quesada, 2005) to at least seven teat pairs in CB (up to 17–18 teats in high prolific sows, see Vasdal et al., 2011).
Against this background, the GMP is a highly valuable model for studying the development of suckling behaviour, because its key features are intermediate between that of CB and WB. GMP sows have similar numbers of teats as CB sows, but their litter size is as small as that of WB. Furthermore, although GMP sows have a smaller body size than either CB or WB sows, their body composition and conformation is intermediate, i.e. the GMP has balanced extremity muscularity (Glodek and Oldigs, 1981). The comparative study of suckling behaviour in Göttingen minipigs could, therefore, elucidate how genetic changes in litter size, number of teats, and specific body structure affect suckling behaviour in piglets.
The aims of this study were to collect data on suckling in GMP litters and (1) to characterize suckling behaviour of GMP piglets with regard to the suckling stability (the probability of consecutive sucklings on the same suckling position), suckling ranges (number of teat pairs in the range of the outermost teat pairs that piglets occupied), and piglets' distribution along the udder estimated using the mid-domain effect (MDE) model, i.e. the effect of the geometric constraints (see Colwell and Lees, 2000; Colwell et al., 2004), and (2) to compare their suckling strategies with data from CB and WB. We hypothesized that, (1) differences in key features (e.g., teat number, litter size, body conformation) results in corresponding differences in suckling behaviour, and (2) some ancestral (wild) patterns of suckling behaviour have been maintained in domestic piglets despite selection for increased litter size and teat number.
Section snippets
Materials and methods
This study was carried out according to the European Commission Directive 2010/63/EU (2010) and to the ABS/ASSAB Guidelines for the treatment of animals in behavioural research and teaching.
Suckling stability
Already from the beginning of the lactation period, GMP piglets exhibited relatively high suckling stability, with a 60% probability that the same individual would suckle at the same position in two consecutive sucklings (PSuck approx 0.6). In contrast, it was not before the second week of lactation, following the establishment and stabilization of teat order, that CB piglets attained a similar probability (PSuck=0.55–0.62). Initial suckling stability of CB piglets was only about 0.3 (Fig. 1).
Discussion
Our results showed interesting alterations in suckling behaviour patterns in GMP, compared to CB or WB, with diverse suckling strategies used by the piglets. Furthermore, our observations indicated possible traces of behavioural conservatism in the context of suckling.
In general, during lactation piglets acquire the own suckling territory (teat), wherein each individual piglet tends to suckle permanently on a particular teat, resulting in the formation of a teat order (e.g. McBride, 1963). GMP
Conclusions
The suckling behaviour of the minipigs, which was characterised here for the first time, elucidated some new aspects of the suckling behaviour and its development in the pigs. In general, GMP piglets showed more stable teat order than CB piglets, but their suckling ranges strongly depended on the litter size. Our study, therefore, revealed alterations of suckling behaviour in piglets, wherein GMP showed intermediate suckling strategies (i.e. suckling ranges) compared to the CB and WB. There
Conflict of interests
The authors declare that they have no conflict of interest.
Acknowledgements
We owe special thanks to Otto Schwerdtfeger, the barn manager at the Göttingen minipig breeding station in Relliehausen, for his invaluable help during the research. Without his expertise the observations would not have been done that smoothly and efficiently. Thanks also to the Faculty of Agriculture and Life Sciences at University of Maribor (especially to the Department of Animal Science), for support and financial assistance (P1-0164 Programme Research). First author of this article (JS)
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