Animal genetic resources are a valuable input for rural development and research. As a piece of traditional animal agriculture, Creole pigs are an integral part of Colombian heritage, and as such efforts have been taken for their conservation and dissemination (16). Moreover, throughout Latin America, Creole pigs were required to adapt across a range of environments, some of them extreme in terms of temperature and humidity, which, in a context of climate change, makes them a very useful material for the study of the molecular mechanisms underlying stress response (17). Colombian Creole pigs, like other local breeds, are facing extinction because of dramatic decreases in their census due to substitution and extensive intercrossing with improved foreign populations (18). However, there is still a lack of research concerning their genetic characterization, conservation and use. It is known that Creole breeds show an acceptable reproductive performance but slow growth (4,19) which partly can be explained because they are usually produced in family or traditional farms, where feeding and management practices are far from optimal. Moreover, owing to their limited herd size, these farms do not often have at their disposal a boar available (2) or adaptable to their resource-driven production systems (20). Therefore, the key role of the AGROSAVIA germplasm network is to contribute to the genetic characterization of C breeds, while ensuring their conservation and promoting their use through artificial insemination. Assessing semen quality is crucially important to run such a programme. This is what we have done for Colombian Creole boars in light of the latest technologies (7) using the semen of worldwide disseminated breeds as control.
The quantity and quality of semen depends on genetic and environmental factors including the breed (21). In our experiment, VOL was within the normal range (22), but CO was lower than in other studies (23). Results obtained here indicate that C boars produce half the sperm per ejaculate than I boars. Differences observed between C breeds were much lower, but even so SP managed to produce 16% more sperm than ZU. However, the sperm production of C boars was higher than documented in other local breeds, particularly in Mexican Creole (24) and Iberian (25), which accounted for 22.9% to 83.5% of the sperm production of C boars. Results in Fengjing and Meishan Chinese breeds were much more variable, with values from half below (26) to almost three-fold higher (27) than those observed in our study. This fact stresses the difficulty in making comparisons across breeds under different environmental settings, where numerous non-genetic factors may affect the results. In the present experiment, we followed the same experimental protocol in all breeds in order to avoid any potential bias. Innovative tools such as CASA and flow cytometry allows for further interpretation of semen quality. Although CASA outcome should be interpreted multiparametrically (7), it has been shown that MO is positively related to pregnancy rate and litter size (28,29) and the absence of morphology abnormalities to functionality of the seminiferous epithelium and epididymal maturation (30). Values over 70% for MOT, and 80% for NO, are expected and acceptable in healthy boars (31). On average, all breeds meet this requirement, although individually there were one CM boar (78.6%), for MOT, and two CM (76.9% and 78.6%) and four SP boars (from 74.3% to 79.70%), for NO, that had lower values. As compared to I breeds, MOT and NO were only around 5% lower in C boars, which indicates that in Creole breeds quantity rather than quality would limit production of seminal doses. Results reported for MOT (80.4%) and NO (94.5%) in the Mexican Creole Pelón de Yucatán breed point towards the same conclusion24).
Morphological abnormalities as well as velocity and distance traits fall above threshold values (32). Interestingly, CM and SP showed lower values of PMOT than ZU, which also had less abnormal sperm, particularly relative to SP. Mitochondrial membrane potential was on the high side of reported values, which ranged from 66.9% to 93.5% (33,34). The ΔΨmHigh expresses the capacity of the mitochondria to produce the energy needed by the axonemal dynein system to fuel sperm motility (33). The sperm membrane integrity has shown a closer relationship to litter size than traditionally estimated sperm motility (35). Thus, ΔΨmHigh has been associated to functionally intact mitochondria and ultimately to MOT (36), PMOT (37) and litter size (35). In fact, spermatozoa with ΔΨmLow are less able for acrosome reaction and in the ability to fertilize (38). We did not detect a clear distribution pattern of ΔΨmHigh across breeds, although both mitochondrial membrane and acrosome integrity were higher in I breeds. However, the within breed correlation of ΔΨmHigh with membrane mitochondrial and acrosome integrity were positive (ranging from 0.25, for acrosome integrity in SP, to 0.93, for membrane integrity in ZU) as well as with MOT (ranging from 0.14 for CM to 0.88 in SP). The more variable behaviour of these parameters among Creole breeds could be explained by a combination of historical differences, unequal past influences of foreign breeds, nucleus foundational effects and genetic drift associated to limited population size (39). To avoid additional sampling variability, C boars were sampled from all available lineages within each breed.
Boar semen traits are important indicators for predicting boar fertility and hence their importance in artificial insemination. Widespread use of refrigerated semen for artificial insemination has benefitted commercial pig units from higher genetic gains at lower economic costs. However, so far Colombian Creole pigs are only produced under natural mating, thereby limiting their use. The development of an artificial insemination programme for Creole pigs would favour dissemination and therefore conservation. A programme like this requires setting the scale capacity and conditions under which seminal doses should be prepared and stored. Seminal doses with poor motility and morphology are the main screening criteria for diagnosis of infertility and subfertility in boars (40). These two features, although show a lower profile in Colombian Creole breeds than in international breeds, are still within the acceptable range. However, the reproductive efficiency of a boar is also given by the ability to produce a large amount of sperm. In this study, C pigs produced between 58.2 and 67.5 billion sperm cells, which results in a potential production capacity of 17–18 doses of 3 x 109 normal and motile sperm, around 10-fold less than in I boars. Thus, sperm dosage must take into account the lower performance of Creole boars in terms of the number of viable sperm by ejaculate. There is no need to differentiate between Colombian Creole breeds since all three produce a similar amount of motile sperm per ejaculate. The greater capacity of SP to produce sperm is offset by the greater sperm quality of ZU pigs.