Effect of rearing cross-fostered piglets in litters of differing size relative to sow functional teat number on preweaning growth and mortality

Litter sizes of commercial sows have increased considerably over recent decades, and often exceed the number of functional teats on the sow. The objective of this study was to evaluate the effect of litter size after cross-fostering relative to sow functional teat number on piglet preweaning growth and mortality. A total of 39 litters (561 piglets) were used in a randomized complete block design; blocking factors were farrowing day and sow parity, body condition score, and functional teat number. Three Litter Size treatments were compared (relative to sow functional teat number): Decreased (two piglets less); Control (same number of piglets); Increased (two piglets more). Piglets were randomly allotted to treatment at 24 h after birth to form litters of the appropriate size, with similar mean and CV of birth weight within block. Weaning weights (WW) were collected at 19.5 ± 0.50 d of age; preweaning mortality (PWM) was recorded. Litter sizes were between 11 and 17 piglets, depending on block and treatment. The Decreased treatment had lower (P ≤ 0.05) PWM than the Increased (7.7% and 17.9%, respectively); the Control was intermediate (11.5%) and not different (P > 0.05) from the other treatments. The rate of decline in litter size from birth to weaning was greater (P ≤ 0.05) for the Increased than the Decreased treatment (−0.16 vs. −0.05 piglets per day), with the Control (−0.09 piglets per day) being intermediate and different (P ≤ 0.05) to the other two treatments. Litter sizes at weaning were greater (P ≤ 0.05) for the Increased than the Decreased treatment (13.3 and 11.3, respectively); the Control treatment was intermediate (12.6) and not different (P > 0.05) to the other treatments. The log odds of PWM increased with the decreasing birth weight, at a similar rate (P > 0.05) for all Litter Size treatments. However, the intercept was greater (P ≤ 0.05) for the Increased compared with the Decreased treatment; the Control was intermediate and different (P > 0.05) to the other two treatments. Mean WW tended (P = 0.07) to be greater for the Decreased (6.17 kg) compared to the Control and Increased treatments (5.86 and 5.84 kg, respectively). In conclusion, increasing litter size after cross-fostering relative to the number of functional teats of the sow increased piglet PWM, and tended to decrease WW.

Genome-Wide Association Study for Body Length, Body Height, and Total Teat Number in Large White Pigs

Body length, body height, and total teat number are economically important traits in pig breeding, as these traits are usually associated with the growth, reproductivity, and longevity potential of piglets. Here, we report a genetic analysis of these traits using a population comprising 2,068 Large White pigs. A genotyping-by-sequencing (GBS) approach was used to provide high-density genome-wide SNP discovery and genotyping. Univariate and bivariate animal models were used to estimate heritability and genetic correlations. The results showed that heritability estimates for body length, body height, and total teat number were 0.25 ± 0.04, 0.11 ± 0.03, and 0.22 ± 0.04, respectively. The genetic correlation between body length and body height exhibited a strongly positive correlation (0.63 ± 0.15), while a positive but low genetic correlation was observed between total teat number and body length. Furthermore, we used two different genome-wide association study (GWAS) approaches: single-locus GWAS and weighted single-step GWAS (WssGWAS), to identify candidate genes for these traits. Single-locus GWAS detected 76, 13, and 29 significant single-nucleotide polymorphisms (SNPs) associated with body length, body height, and total teat number. Notably, the most significant SNP (S17_15781294), which is located 20 kb downstream of the BMP2 gene, explained 9.09% of the genetic variance for body length traits, and it also explained 9.57% of the genetic variance for body height traits. In addition, another significant SNP (S7_97595973), which is located in the ABCD4 gene, explained 8.92% of the genetic variance for total teat number traits. GWAS results for these traits identified some candidate genomic regions, such as SSC6: 14.96–15.02 Mb, SSC7: 97.18–98.18 Mb, SSC14: 128.29–131.15 Mb, SSC17: 15.39–17.27 Mb, and SSC17: 22.04–24.15 Mb, providing a starting point for further inheritance research. Most quantitative trait loci were detected by single-locus GWAS and WssGWAS. These findings reveal the complexity of the genetic mechanism of the three traits and provide guidance for subsequent genetic improvement through genome selection.

PSI-10 The Relationship Between Litter Size and Functional Teat Number at Farrowing on Litter Size at Weaning

Sow functional teat number (FTEAT) is positively associated with piglet preweaning survival and litter throughput. The objective was to estimate the value of FTEAT in relationship to litter size to optimize the number of pigs weaned. Number of pigs born alive (NBA) and total teat number (TTEAT) were counted at farrowing on 836 multiparous purebred sows between March and September, 2020. Teats were evaluated by trained staff at farrowing and considered functional based on visual appraisal of teat morphology. Litter size at weaning (LSW) was recorded after a 26.5 d lactation length (LL). Sow was the experimental unit and all data were analyzed as a function of the biological sow. Number born alive was categorized by quartile: Q1 ≤ 10 NBA (n=185; µ=8.2); Q2 = 11 to 12 NBA (n=194; µ=11.6); Q3 = 13 to 14 NBA (n=238; µ=13.5); Q4 ≥ 15 NBA (n=219; µ=16.3). Data were analyzed in PROC GLM of SAS with farm, breed, and NBA quartile as categorical effects and LL and FTEAT as linear terms. The interaction of NBA quartile and FTEAT was also included. Mean TTEAT, FTEAT, LSW and preweaning survival were 15.4, 14.5, 11.3 and 89.4%, respectively. As a linear term, a one teat increase in FTEAT improved (P< 0.01) LSW by 0.3±0.1 pigs. Yet the value of an additional functional teat increased with increasing NBA. A one teat increase in FTEAT improved (P< 0.01) LSW in Q1, Q2, Q3, and Q4 by 0.12, 0.27, 0.33, and 0.38 pigs, respectively. The analysis demonstrates the impact of FTEAT on sow performance increases with increasing litter size, and highlights the importance of functional teats to optimize litter throughput and maximize the genetic potential of a maternal line.

92 Effect of Rearing Cross-fostered Piglets in Litters of Differing Within-litter Birth Weight Variation on Pre-weaning Growth and Mortality

Cross-fostering of piglets is a common commercial practice, however, there is limited information on optimum methods. The objective of this study was to evaluate the effects of within-litter birth weight variation after cross-fostering on piglet pre-weaning mortality (PWM) and growth. A RCBD was used with 47 blocks of 6 litters (total 282 litters/3,948 piglets); blocking factors were farrowing day, sow parity, body condition score, and functional teat number. Piglets were allotted at 24 h after birth according to Birth Weight Category (BWC) [L (< 1.0 kg), M (1.0 to 1.5 kg), or H (1.5 to 2.0 kg)] to 6 Litter Composition (LC) treatments with 14 piglets/litter: Uniform (14 L, M or H); Mixed L+M (7 L, 7 M); Mixed M+H (7 M, 7 H); Mixed L+M+H (3 L, 6 M, 5 H). Piglets were weaned at 18.7 ± 0.64 d and PWM was recorded. Piglet birth and weaning weights were analyzed using PROC MIXED of SAS; PWM were analyzed using PROC GLIMMIX of SAS; models included BWC, LC, the interaction, and sow within block. There were LC by BWC interactions (P < 0.05) for PWM and weaning weights. For L piglets, there was no effect (P > 0.05) of LC on PWM (22.8, 26.7, and 28.4% for Uniform, Mixed L+M, and Mixed L+M+H treatments, respectively). For H piglets, PWM was lower (P < 0.05) in Mixed L+M+H compared to Uniform or Mixed M+H litters (1.7, 9.6, and 5.8%, respectively). For M piglets, PWM was lower (P < 0.05) in Mixed L+M than Uniform or Mixed M+H litters (7.1, 12.2, and 14.6%, respectively); Mixed L+M+H were intermediate (10.0%; P > 0.05). Weaning weights generally followed a similar but opposite pattern for all BWC. In conclusion, increasing the average weight of littermates generally decreased weaning weights and increased PWM within each BWC.

PSIII-1 Effect of Rearing Cross-fostered Piglets in Litters of Differing Size Relative to Sow Functional Teat Number on Pre-weaning Growth and Mortality

Litter sizes of commercial sows have increased recently, often resulting in the number of piglets exceeding the sow functional teat number. The objective of this study was to determine the effects of litter size after cross-fostering on piglet pre-weaning mortality (PWM) and growth. A RCBD was used with 13 blocks of 3 litters (total 39 litters/561 piglets); blocking factors were farrowing day, sow parity, body condition score, and functional teat number. Three Litter Size treatments (LS) relative to sow functional teat number were compared: Under (2 piglets below); Equal (same number of piglets); Over (2 piglets above). Piglets were weighed 24 h after birth and allotted to LS to create litters with similar gender ratio and average and CV of birth weight. Weaning was at 19.5 ± 0.50 d, weights and PWM were recorded. Piglet weight data were analyzed using PROC MIXED of SAS; PWM data were analyzed using PROC GLIMMIX of SAS. Models included LS and sow within block. Litter sizes averaged 12.1, 14.1, and 16.1 for the Under, Equal, and Over treatments, respectively (P ≤ 0.05). The Under treatment tended (P = 0.07) to have greater weaning weights compared to the Equal and Over treatments (Table 1). The Under treatment had lower (P ≤ 0.05) PWM than the Over treatment, with the Equal treatment being intermediate and not different to the other 2 (P > 0.05; Table 1). In conclusion, reducing litter size after cross-fostering to two piglets below the number of functional teats of the sow decreased PWM and tended to increase weaning weights.

57 The Impact of Functional Teat Number on Piglet Survival and Sow Efficiency

Pre-weaning mortalities have become a pressing issue in modern swine production. Litter size at birth has greatly increased through direct genetic selection. Unfortunately, little emphasis was placed on improving functional teat number, resulting in a nutrient access shortage. Therefore, a total of 750 sows consisting of three genetic lines in a commercial barn in Nebraska, USA, were used to evaluate the impact of functional teat number on piglet survival. Teat traits recorded at farrowing included total teat number (TT), functional teat number (FT), and non-functional teat number (NFT); with population means of 14.84 (1.21), 14.55 (1.30), and 0.28 (0.56), respectively. Production traits recorded included total number born (TNB), wean number (WN), total pre-weaning mortality (PWM), and post-cross foster mortality (CFPWM). The lm function within RStudio was used to estimate regressions, with parity and piglets placed (PP) used as covariates for WN and CFPWM, and parity, PP, and TNB for PWM. One additional FT increased WN (P < 0.01; 0.33), and reduced PWM (P < 0.01; -3.04%) and reduced CFPWM (P < 0.01; -3.71%). A subset of 274 sows were used to determine the effects of increasing functional teats on sow and piglet efficiency. Additional traits recorded included sow average daily feed intake (ADFI), backfat loss (BF) and average piglet weaning weight (WW). Parity, ADFI, backfat-entry, and WN were used as covariates for BF; parity, backfat-entry, and WN for ADFI; and parity, PP, ADFI, and WN were used for estimating WW. Regression estimates showed that an additional functional teat had no significant impact (P > 0.05) on ADFI, BF, or WW. Taken together, these results suggest that improving functional teat number does not impact ADFI or BF for sows and does not influence average piglet weaning weight, but it does decrease PWM resulting in more pigs weaned per litter.

87 Effect of Number of Source Litters Used to Create Cross-fostered Litters on Piglet Pre-weaning Mortality and Weaning Weight

Sow litter sizes have increased over recent decades, increasing the need for cross-fostering. The objective of this study was to determine the effect of the number of source litters used to create cross-fostered litters on piglet pre-weaning mortality (PWM) and weaning weight. A RCBD was used with 26 blocks of 5 litters (total 130 litters/1820 piglets), all litters consisted of 14 piglets. Blocking factors were farrowing day, sow parity, body condition score, and functional teat number, and the average and CV of piglet birth weight. Five cross-fostering treatments were compared: 0%, 1 source (all piglets remaining on the birth sow); 100%, 1 source (all piglets moved from birth to a different sow); 100%, 6+ sources (piglets from ≥ 6 birth sows used to form a litter on a different sow); 50%, 2 sources (7 piglets remaining with birth sow, 7 from one other sow); 50%, 4+ sources (7 piglets remaining with the birth sow, 7 from ≥ 3 other sows). The single-source litters were selected from those with > 14 piglets at birth, with excess piglets removed. For other treatments, piglets were selected to meet blocking factors. Piglets were weighed 24 h after birth and at weaning (19.5 ± 0.50 d); all PWM was recorded. Weight data were analyzed using PROC MIXED of SAS; PWM data were analyzed using PROC GLIMMIX of SAS. Models included Treatment and sow within block. There was no effect (P > 0.05) of treatment on weaning weights. Pre-weaning mortality was greater (P < 0.05) for the 0%, 1 source compared to the 50%, 2 source treatment, with the others being intermediate and generally not statistically different (Table 1). In conclusion, cross-fostering and/or mixing litters had no effect on weaning weights, but pre-weaning mortality was highest for the non-fostered treatment.

Revealing New Candidate Genes for Teat Number Relevant Traits in Duroc Pigs Using Genome-Wide Association Studies

The number of teats is related to the nursing ability of sows. In the present study, we conducted genome-wide association studies (GWAS) for traits related to teat number in Duroc pig population. Two mixed models, one for counted and another for binary phenotypic traits, were employed to analyze seven traits: the right (RTN), left (LTN), and total (TTN) teat numbers; maximum teat number on a side (MAX); left minus right side teat number (LR); the absolute value of LR (ALR); and the presence of symmetry between left and right teat numbers (SLR). We identified 11, 1, 4, 13, and 9 significant SNPs associated with traits RTN, LTN, MAX, TTN, and SLR, respectively. One significant SNP (MARC0038565) was found to be simultaneous associated with RTN, LTN, MAX and TTN. Two annotated genes (VRTN and SYNDIG1L) were located in genomic region around this SNP. Three significant SNPs were shown to be associated with TTN, RTN and MAX traits. Seven significant SNPs were simultaneously detected in two traits of TTN and RTN. Other two SNPs were only identified in TTN. These 13 SNPs were clustered in the genomic region between 96.10—98.09 Mb on chromosome 7. Moreover, nine significant SNPs were shown to be significantly associated with SLR. In total, four and 22 SNPs surpassed genome-wide significance and suggestive significance levels, respectively. Among candidate genes annotated, eight genes have documented association with the teat number relevant traits. Out of them, DPF3 genes on Sus scrofa chromosome (SSC) 7 and the NRP1 gene on SSC 10 were new candidate genes identified in this study. Our findings demonstrate the genetic mechanism of teat number relevant traits and provide a reference to further improve reproductive performances in practical pig breeding programs.

Effect of within-litter birth weight variation after cross-fostering on piglet pre-weaning growth and mortality

Cross-fostering is commonly used in commercial swine production to equalize litter sizes and/or adjust piglet birth weights within litters. However, there is limited published information on optimum cross-fostering procedures. This study evaluated effects of within-litter birth weight variation after cross-fostering (using litters of 14 piglets) on piglet pre-weaning mortality (PWM) and weaning weight (WW). A RCBD was used (blocking factors were day of farrowing and sow parity, body condition score, and functional teat number) with an incomplete factorial arrangement of the following two treatments: 1) Birth Weight Category (BWC): Light (< 1.0 kg), Medium (1.0 to 1.5 kg), or Heavy (1.5 to 2.0 kg); 2) Litter Composition: Uniform, all piglets in the litter of the same BWC [UNIFORM LIGHT (14 Light piglets); UNIFORM MEDIUM (14 Medium piglets); UNIFORM HEAVY (14 Heavy piglets)]; Mixed, piglets in the litter of two or more BWC [L+M (7 Light and 7 Medium piglets); M+H (7 Medium and 7 Heavy piglets); L+M+H (3 Light, 6 Medium, and 5 Heavy piglets)]. Piglets were weighed at 24 h after birth and randomly allotted to Litter Composition treatment from within BWC; all piglets were cross-fostered. There were 47 blocks of 6 litters (total 282 litters and 3,948 piglets). Weaning weights were collected at 18.7 ± 0.64 d of age; all PWM was recorded. Individual piglet WW and PWM data were analyzed using PROC MIXED and PROC GLIMMIX of SAS, respectively; models included fixed effects of BWC, Litter Composition, and the interaction, and random effects of sow within block. There were Litter Composition by BWC interactions (P ≤ 0.05) for WW and PWM. Within each BWC, WW generally increased and PWM generally decreased as littermate weight decreased. For example, WW were greatest (P ≤ 0.05) for Light piglets in UNIFORM LIGHT litters, for Medium piglets in L+M litters, and for Heavy piglets in L+M+H litters. Pre-weaning mortality was lowest (P ≤ 0.05) for Medium piglets in L+M litters, and for Heavy piglets in L+M+H litters; however, Litter Composition had no effect (P > 0.05) on PWM of Light piglets. In conclusion, increasing the average birth weight of littermates after cross-fostering generally decreased WW and increased PWM for piglets of all birth weight categories. This implies that the optimum approach to cross-fostering that maximizes piglet pre-weaning growth and survival is likely to vary depending on the birth weight distribution of the population.

The Association of an SNP in the EXOC4 Gene and Reproductive Traits Suggests Its Use as a Breeding Marker in Pigs

In mammals, the exocyst complex component 4 (EXOC4) gene has often been reported to be involved in vesicle transport. The SNP rs81471943 (C/T) is located in the intron of porcine EXOC4, while six quantitative trait loci (QTL) within 5–10 Mb around EXOC4 are associated with ovary weight, teat number, total offspring born alive, and corpus luteum number. However, the molecular mechanisms between EXOC4 and the reproductive performance of pigs remains to be elucidated. In this study, rs81471943 was genotyped from a total of 994 Duroc sows, and the genotype and allele frequency of SNP rs81471943 (C/T) were statistically analyzed. Then, the associations between SNP rs81471943 and four reproductive traits, including number of piglets born alive (NBA), litter weight at birth (LWB), number of piglets weaned (NW), and litter weight at weaning (LWW), were determined. Sanger sequencing and PCR restriction fragment length polymorphism (PCR-RFLP) were utilized to identify the rs81471943 genotype. We found that the genotype frequency of CC was significantly higher than that of CT and TT, and CC was the most frequent genotype for NBA, LWB, NW, and LWW. Moreover, 5′-deletion and luciferase assays identified a positive transcription regulatory element in the EXOC4 promoter. After exploring the EXOC4 promoter, SNP −1781G/A linked with SNP rs81471943 (C/T) were identified by analysis of the transcription activity of the haplotypes, and SNP −1781 G/A may influence the potential binding of P53, E26 transformation specific sequence -like 1 transcription factor (ELK1), and myeloid zinc finger 1 (MZF1). These findings provide useful information for identifying a molecular marker of EXOC4-assisted selection in pig breeding.