Genome-wide association studies for the number of piglets born alive and dead in Dongliao black pigs

Litter size (total number born) trait has a great impact on the economic success of pork production. The total number born consists of the number of piglets born alive and dead. To clarify the genetic background of litter size, genome-wide association studies were undertaken in the present study. Samples of DNA were collected and genotyped using the Porcine 50K BeadChip from 723 Dongliao Black sows. Using three different models (BLINK, FarmCPU, and MLM), a total of 155 significant SNPs were discovered, six of which had been reported in previous pig reproduction association studies. We suggest that rs81318434, located in the GLI3 gene, might be the promising candidate affecting litter size trait. Our findings may provide insights for uncovering the genetic mechanisms for the litter size of pigs.

Genome-wide association study of three litter traits in Yorkshire pigs

Litter traits are important in the development of production and economic profits of pigs. The object of this study was to perform genome-wide association studies (GWASs) for the total number born (TNB), number born alive (NBA) and number born healthy (NBH) traits in a Yorkshire population. By mixed model, we conducted GWASs with gcta software, and in total identified 3, 7 and 12 significant SNPs associated with TNB, NBA and NBH respectively: one on Sus scrofa chromosome (SSC) 2 (p = 7.03 × 10^-5 ), one on SSC4 (p = 8.53 × 10^-5 ), two on SSC 6 (p = 9.27 × 10^-5 to 9.64 × 10^-5 ), nine on SSC 8 (p = 1.53 × 10^-5 to 8.52 × 10^-5 ), four on SSC 14 (p = 2.17 × 10^-5 to 6.79 × 10^-5 ), and one on SSC 15 (p = 9.30 × 10^-5 ). We screened for flanking regions ±1 Mb nearby or within the significant SNPs, and found 203 candidate genes, including 53 for TNB, 71 for NBA and 112 for NBH. In conclusion, our findings show the significant SNPs with candidate genes for the TNB, NBA and NBH traits in Yorkshire pigs.

Relationships between litter size, sex ratio and within-litter birth weight variation in a sow herd and consequences on weaning performance

Routine selection for litter size has resulted in an increase in the proportion of lightweight piglets. There is a need to balance prolificacy with litter uniformity to maximize profit. A total of 3,465 piglets from 310 litter records obtained from 2016 until 2019 at the Pig Industry Board research unit, Arcturus, Zimbabwe were used to determine the relationships between litter size, sex ratio, and within-litter birth weight variation in the sow herd and consequences on performance at weaning. The regression procedure of SAS was used to determine the relationships between litter size, sex ratio, and within-litter birth weight variation. The regression procedure was also used to determine the relationships between number born alive, within-litter birth weight variation, and sex ratio, and litter performance traits at weaning. Parity of sow, year, and month of farrowing did not affect sex ratio (P > 0.05). The number born alive and number of piglets born had no relationship with sex ratio (P > 0.05). As the sex ratio increased, percent survival of piglets at weaning also increased linearly (P < 0.05). As the proportion of males in litters increased, within-litter birth weight variation and within-litter weaning weight variation increased reaching maximum as the proportion of males in litters approached 0.5 and then decreased onwards. As the proportion of males in litters approached 1, within-litter birth weight variation and within-litter weaning weight variation reached their least values. In conclusion, within-litter sex ratio does not vary with parity, year, and month of farrowing. Within-litter weight variation is highest in litters with equal number of male and female piglets and lowest in unisex litters. This implies that the production of unisex litters can help to reduce the variation in the weight of pigs at birth, weaning, and marketing which is one of the biggest economic challenges faced by pork producers.

Estimation of genetic parameters for farrowing traits in purebred Landrace and Large White pigs

Genetic parameters were estimated for six reproductive traits related to farrowing events in Landrace and Large White pigs; total number born (TNB), number born alive (NBA), number stillborn (NSB), total litter weight at birth (LWB), mean litter weight at birth (MWB), and gestation length (GL). We analyzed 62,534 farrowing records for 10,637 Landrace dams and 49,817 farrowing records for 8,649 Large White dams. Estimated heritabilities of TNB, NBA, NSB, LWB, MWB, and GL by single‐trait repeatability model analyses were 0.12, 0.12, 0.08, 0.18, 0.19, and 0.29, respectively, in Landrace, and 0.12, 0.10, 0.08, 0.18, 0.16, and 0.34, respectively, in Large White. Genetic correlation between NBA and NSB was unfavorable: 0.20 in Landrace and 0.33 in Large White. Genetic correlations of GL with the other five traits were weak: from −0.18 with NSB to −0.03 with NBA in Landrace, and from −0.22 with NSB to −0.07 with NBA in Large White. LWB had a highly favorable genetic correlation with NBA (0.74 in both breeds), indicating the possibility of using LWB for the genetic improvement of NBA.