Hélène Gilbert

Effect of climatic environment on feed efficiency in swine

Since feed costs comprise about 60 to 70% of the total costs of production, efforts to reduce feed costs is then a major preoccupation for increasing competitiveness of the pig industry. Understanding the factors that affect feed conversion in pigs can enable producer to more effectively combine various inputs in order to achieve a low feeding cost. There are many factors involved in reaching good feed efficiency including genetic, diet, feed, management, housing and environment. Temperature is the single most important environmental factor affecting the global farm feed efficiency. In ad libitum fed animals, changes in metabolic heat production are essential mechanisms to maintain body temperature within a physiologically safe range under cold or heat stress. These adjustments have direct consequences on energy intake and/or maintenance requirements which in turn could reduce energy efficiency as conversion of feed to tissue or other products. However, the low level of performance related to a thermal challenge can also be attributed to a direct effect of ambient temperature (independent of feed intake) on reproductive physiology, health, and energy metabolism. Finally, thermal stress could also be a major cause of pig mortality at birth, during the nursing period or thereafter, and could predispose pigs to mortality or morbidity by other causes (starvation, diseases, etc.). High mortality rates in nursing piglets or in finishing pigs have a significant impact on overall farm feed efficiency. The chapter describes how climatic environment impacts feed efficiency in pigs and reviews solutions that can be used in order to attenuate the effect of environmental temperature on feed efficiency.

Genetic and functional evaluation of MITF as a candidate gene for cutaneous melanoma predisposition in pigs

Cutaneous melanoma arises from transformed melanocytes and is caused mainly by environmental effects such as ultraviolet radiation and to a lesser extent by predisposing genetic variants. Only a few susceptibility genes for cutaneous melanoma have been identified so far in human; therefore, animal models represent a valuable alternative for genetic studies of this disease. In a previous quantitative trait locus (QTL) study, several susceptibility regions were identified in a swine biomedical model, the MeLiM (Melanoblastoma-bearing Libechov minipig) pigs. This article details the fine-mapping of a QTL located on SSC13 (Sus scrofa chromosome 13) through an increase in marker density. New microsatellites were used to confirm the results of the first analysis, and MITF (microphthalmia-associated transcription factor) was selected as a candidate gene for melanoma development. A single-marker association analysis was performed with single-nucleotide polymorphisms (SNPs) spread over the locus, but it did not reveal a significant association with diverse melanoma-related traits. In parallel, MITF alternative transcripts were characterized and their expression was investigated in different porcine tissues. The obtained results showed a complex transcriptional regulation concordant with the one present in other mammals. Notably, the ratio between MITF+ and MITF− isoforms in melanoma samples followed the same pattern as in human tumors, which highlights the adequacy of the MeLiM pig as a model for human melanoma. In conclusion, although MITF does not seem to be the causal gene of the QTL initially observed, we do not exclude a prominent role of its transcription and function in the outbreak and evolution of the tumors observed in pigs.

New susceptibility loci for cutaneous melanoma risk and progression revealed using a porcine model

Despite major advances, it is estimated that a large part of melanoma predisposing genes remains to be discovered. Animal models of spontaneous diseases are valuable tools and experimental crosses can be used to identify and fine-map new susceptibility loci associated with melanoma. We performed a Genome-Wide Association Study (GWAS) of melanoma occurrence and progression (clinical ulceration and presence of metastasis) in a porcine model of spontaneous melanoma, the MeLiM pig. Five loci on chromosomes 2, 5, 7, 8 and 16 showed genome-wide significant associations (p < 5 × 10–6) with either one of these phenotypes. Suggestive associations (p < 5 × 10–5) were also found at 16 additional loci. Moreover, comparison of the porcine results to those reported by human melanoma GWAS indicated shared association signals notably at CDKAL1 and TERT loci but also nearby CCND1, FTO, PLA2G6 and TMEM38B-RAD23B loci. Extensive search of the literature revealed a potential key role of genes at the identified porcine loci in tumor invasion (DST, PLEKHA5, CBY1, LIMK2 and ETV5) and immune response modulation (ETV5, HERC3 and DICER1) of the progression phenotypes. These biological processes are consistent with the clinico-pathological features of MeLiM tumors and can open new routes for future melanoma research in humans.