The effect of the SCD genotype on litter size and weight at weaning

Genetic markers associated with meat quality may have adverse effects on reproduction performance, as shown for a variant in the leptin receptor (LEPR) gene. There is a single nucleotide polymorphism (SNP) in the stearoylCoA desaturase (SCD) gene that influences the monounsaturated fatty acid content of pork. Here, we investigate single and combined effects of the SCD (rs80912566 T>C) and LEPR (rs709596309 C>T) SNP on litter size and weaning weight. A total of 1,246 sows of known genotype for SCD (732 of which were also genotyped for LEPR) were monitored for age at farrowing, number of piglets born, born alive and weaned, and litter weight at weaning during two years. The effects of these SNP and of a variant in the diacylglycerol O-acyltransferase 2 (DGAT2) gene on milk fat content and fatty acid composition were also analysed in 99 primiparous sows. No adverse effects of the SCD SNP on overall reproductive performance were observed. However, in primiparous sows, we found that the SCD-T allele, the one that increases the monounsaturated fatty acid content, influenced negatively the weight of piglets at weaning (the piglets from SCD-TT sows weighted 126 g less at weaning than those from SCD-CT sows), especially in combination with the LEPR-TT genotype (the piglets from SCD-TT/LEPRTT sows weighted 277 g less at weaning than piglets from SCD-C-/LEPR-C- sows). In contrast to SCD, the negative effect of the LEPR-TT sows on the piglets weaning weight was maintained in all parities (piglets from LEPR-TT sows were on average 126 g lighter than LEPR-C- sows). The unfavourable effect of the SCD-T allele on the litter weight of primiparous sows could be due to lower body reserves at first farrowing (SCD-TT pigs had 0.62 mm less backfat thickness at 205 d than SCD-CT pigs) together with larger litters at birth (the SCD-TT sows had 0.32 more piglets born alive per litter than the SCD-CT sows). The milk of primiparous sows with the SCD-T allele showed higher desaturation indices (i.e. higher monounsaturated to saturated fatty acid ratios), but lower fat content. No relevant effects of the DGAT2 SNP on milk traits were found. In conclusion, the SCD SNP does not impact overall reproductive performance in pigs, but cautious management of SCD-TT gilts is recommended.