Estimation of genetic parameters for reproductive traits in connectedness groups of Duroc,Landrace and Yorkshire pigs in China

The objective of this study was to estimate group- and breed-specific genetic parameters for reproductive traits in Chinese Duroc, Landrace, and Yorkshire populations. Records for reproductive traits between April 1998 and December 2017 from 92 nucleus pig breeding farms, which were involved in the China Swine Genetic Improvement Program, were analysed. Due to weak genetic connectedness across all farms, connectedness groups consisting of related farms were used. Three, two and four connectedness groups for Duroc, Landrace and Yorkshire were firstly established according to the genetic connectedness rating among farms. For each connectedness group a five-trait animal model was implemented, and via restricted maximum likelihood procedure the genetic parameters were estimated for five reproductive traits i.e., total number born (TNB), number born alive (NBA), litter weight at farrowing (LWF), farrowing interval (FI) and age at first farrowing (AFF). The average of heritabilities among connectedness groups ranged from .01 (for FI in Yorkshire) to .30 (for AFF in Duroc). Estimates of repeatability for litter traits ranged from .14 to .20 and were consistent for each breed, and for FI, the estimates varied from .01 to .11 across breeds and groups. The estimated genetic correlations among litter traits (i.e., TNB, NBA and LWF) were all significantly high (>.56) and similar across breeds. Averaged genetic correlations over three breeds were −.25, −.27, −.18, −.04, −.10, −.02, and .28 for FI-TNB, FI-NBA, FI-LWF, AFF-TNB, AFF-NBA, AFF-LWF and FI-AFF, respectively. The standard errors of the estimates were all very low (<0.01) in most situations. Results from this study suggest that selection based on TNB which is currently used in dam line selection index can improve NBA and LWF simultaneously. However, care should be taken on FI and AFF as they are both greatly influenced by non-genetic factors such as management and measurement.     

Selection potential of different prolificacy traits in the finnish landrace and large white populations

Heritabilities and genetic correlations for different prolificacy traits were estimated to assess possibilities of selection for high number of piglets weaned. Three litter-size traits: total number of piglets born (TNB), number of piglets born alive (NBA), number of piglets weaned (NW); four piglet survival traits: number of stillborn piglets (NSB), percent of stillborn piglets (NSB%), piglet mortality between birth and weaning (PM), percent of dead piglets during suckling (PM%); and three traits measuring time intervals: age at first farrowing (AFF), first farrowing interval (FFI), and gestation length (GL) were analysed. The Finnish national litter recording scheme provided data on the first parity litters of 11 329 Landrace and 8 362 Large White pigs born between 1986 and 2000. The heritabilitiy estimates were moderate for AFF and GL (0.24–0.37), and low for all the other traits (0.03–0.11). The genetic correlations between TNB and PM (0.68 in Landrace and 0.43 in Large White) and between NBA and PM (0.64 in Landrace and 0.31 in Large White) suggest that selection only for high TNB or NBA will lead to increased PM. The results showed further that GL will increase indirectly if the selection pressure is for low PM (r _g =?0.050 in Landrace and ?0.43 in Large White.     

Genetic associations of sow longevity with age at first farrowing, number of piglets weaned, and wean to insemination interval in the Finnish Landrace swine population

The objective of the study was to estimate genetic parameters for length of productive life (LPL), and determine its genetic correlation with age at first farrowing (AFF), number of piglets weaned at first farrowing (NW), and first wean-to-insemination interval (W2I) in the Finnish Landrace swine population. Data from the Finnish national litter recording scheme were utilized to estimate the genetics of LPL, and genetic associations between LPL, AFF, NW, and W2I. Data from the Finnish Landrace sow records were utilized from farms that farrowed more than 20 gilts annually from 2000 through 2005. The data set included information from 11,222 sows, all of which had AFF and NW information available. The sows producing the records evaluated were daughters of 1,267 sires, and there were 3,684 animals in the pedigree when all of the sires were traced back to founder animals. All data were obtained from FABA Breeding (Vantaa, Finland). Multivariate Bayesian analysis of Gaussian, right censored Gaussian, and categorical traits was utilized to estimate (co)variance parameters of LPL, AFF, NW, and W2I of the sow. From these traits, AFF and NW were treated as Gaussian, LPL as right-censored Gaussian, and W2I as categorical traits. Estimated posterior means of heritabilities were 0.22, 0.16, 0.09, and 0.08 for LPL, AFF, NW, and W2I, respectively. A relatively large proportion of variance due to farm-year interaction was observed (posterior means of f(2) ranged between 0.03 and 0.26). The LPL was moderately genetically correlated with NW and AFF (posterior means were -0.20 and 0.36, respectively), whereas no clear association was found between W2I and LPL. Favorable genetic correlations between AFF and W2I and between NW and W2I were also observed. Additionally, an unfavorable genetic correlation between AFF and NW was observed in the present data set. Because LPL is genetically associated with other economically important prolificacy traits, it should be included in a multiple trait swine breeding value estimation system.     

Genetic relationships of body composition, serum leptin, and age at puberty in gilts

Leptin produced by adipocytes acts through leptin receptors in the hypothalamus to control appetite and food intake and thus communicates information about degree of fatness. It is thought that a degree of body fat is required for initiation of puberty and maintenance of reproductive function in mammals. The objective of this study was to determine whether polymorphisms in the leptin (LEP), leptin receptor (LEPR), paired box 5 (PAX5), aldo-keto reductase (AKR), and pro-opiomelanocortin (POMC) genes were associated with age, leptin concentration, backfat as an indicator of body condition, or BW at puberty in 3 lines of gilts and to characterize genetic relationships among these traits. The first 2 lines, born in 2001, were formed by crossing maternal White Cross (Yorkshire x Maternal Landrace) gilts to Duroc (n = 210) or (lean) Landrace (n = 207) boars. The remaining line (n = 507), born in 2002, was formed by crossing progeny of the Duroc- and Landrace-sired lines. At first estrus, age, BW (BWP), and backfat (BFP) at puberty were recorded and blood was collected for leptin assays. Nine SNP were detected in candidate genes/regions: 1 in LEP, 3 in LEPR, 1 in PAX5, 2 in AKR, and 2 in POMC. Animals were genotyped for each of the SNP; genotypes were validated using GenoProb. The association model included fixed effects of farrowing group, covariates of SNP genotypic probabilities (from GenoProb), and random additive polygenic effects to account for genetic similarities between animals not explained by SNP. Variance components for polygenic effects and error were estimated using MTDFREML. Leptin concentrations were logarithmically transformed for data analysis. All 4 traits were moderately to highly heritable (0.38 to 0.48). Age and leptin at puberty had a significant (P < 0.01) genetic correlation at -0.63 +/- 0.097, and the genetic correlation between BWP and age at puberty was 0.65 +/- 0.083 (P < 0.01). Significant additive associations (a; P < 0.05) were detected at PAX5 for age at puberty (a = 3.2 d) and for BFP (a = 0.61 mm). One SNP in LEPR was associated with leptin concentration (a = 0.31 log units; P < 0.05). The associations from PAX5 correspond to a QTL peak for age at puberty detected on SSC1. Although not necessarily the causative mutation, this result implies that a QTL that can decrease age at puberty without increasing BFP and BWP at puberty may exist in this region in commercial pigs.     

Effects of pre- and postpubertal feeding on production traits at first and second estrus in gilts

The effects of feeding level on body weight (BW), lifetime growth rate, backfat thickness (BF), fatness (BF/BW) and ovulation rate at first (puberty) and second estrus were examined in 145 gilts. From 47.2 kg until puberty, gilts were fed 2.0 kg/d (L) or had ad libitum access to feed (H). From puberty to second estrus, the feed allowance of one-half of the L gilts was increased to 2.8 kg/d. Flush-feeding only normalized ovulation rate (OR) to that observed in gilts with ad libitum access to feed. At puberty, a quadratic negative relationship between lifetime growth rate and age indicated that age at puberty was minimum at a growth rate of less than or equal to .60 kg/d. Thereafter, age at puberty became independent of, or possibly positively related to, lifetime growth rate. Gilts with higher lifetime growth rate also were heavier and fatter at puberty. It was concluded that puberty may have been attained when a certain BF or fatness was achieved, because growth rate of restricted-fed gilts and quickly growing gilts with ad libitum access to feed may have been associated with reduced fat deposition. Hence, maximizing growth rate in replacement gilts does not hasten the attainment of puberty. Growth rate may be manipulated by feed restriction, in order to attain a target BW at boar stimulation (approximately 90 kg), which would coincide with a minimum age (approximately 155 d) and BW at puberty (approximately 97 kg). Nutritional flushing during the first estrous cycle then could be used to normalize OR at mating at second estrus of gilts that were restricted-fed when prepubertal.     

Genetic parameter estimates among scale activity score and farrowing disposition with reproductive traits in swine

The primary objective of this study was to determine if certain behavior traits were genetically correlated with reproduction. If 1 or both of the behavior traits were found to be correlated, a secondary objective was to determine if the behavior traits could be useful in selecting for more productive females. A scale activity score taken at 5 mo of age and a farrowing disposition score taken at farrowing were selected as the behavioral traits. Scale activity score ranged from 1 to 5 and farrowing disposition ranged from 1 to 3. Reproductive traits included age at puberty, number born alive, number born dead, litter birth weight, average piglet birth weight, number weaned, litter weaning weight, average weaning weight, wean-to-estrus interval, ovulation rate including gilts, and postweaning ovulation rate. Genetic correlations between scale activity score and reproduction ranged from -0.79 to 0.61. Three of the correlations, number born alive (P < 0.01), average piglet birth weight (P < 0.001), and wean-to-estrus interval (P = 0.014), were statistically significant but included both favorable and antagonistic correlations. In contrast, all but 1 of the farrowing disposition correlations was favorable and ranged from -0.66 to 0.67. Although only the correlation with litter birth weight was significant (P = 0.018), the consistent favorable direction of all farrowing disposition correlations, except average weaning weight, shows a potential for inclusion of farrowing disposition into a selection program.     

Genetic parameter estimates for reproductive traits of male and female littermate swine

Reproductive traits of purebred and crossbred pigs produced in a four-breed diallel mating system using the Duroc, Landrace, Spotted and Yorkshire breeds were collected for five consecutive farrowing seasons (two farrowing seasons/year) beginning in fall 1976. Paternal half-sib heritabilities and genetic correlations for testicular traits (120 boars from 36 sires), serum testosterone (TE) and luteinizing hormone (LH) concentrations before and after treatment with gonadotropin releasing hormone (GnRH; 131 boars from 37 sires) and breeding performance traits (151 boars from 38 sires) were estimated. Heritability estimates were generally small to moderate except for sperm/gram testis (SGT), LH concentrations before (LHO) and at 3 h (LH3) after treatment with GnRH (.73 +/- .48, .61 +/- .46 and 1.19 +/- .45, respectively). A large positive genetic correlation was found for LHO with LH3 (.94 +/- .39), while a negative relationship existed for LH3 with TE concentrations at 3 h after GnRH injection. The genetic correlation between a boar's average first service conception rate and average conception rate also was significant (.82 +/- .54). Genetic correlations among littermate traits would suggest that selection for decreased age at puberty in gilts could cause an increase in LH concentrations in boar offspring, before and after GnRH injection, and may also have adverse effects on their ability to settle females. Selection for increased weight at puberty of gilts could cause TE concentrations of boar offspring to increase while having little effect on their breeding performance.     

Long-term effects of boron supplementation on reproductive characteristics and bone mechanical properties in gilts

An experiment was conducted to determine long-term effects of dietary boron (B) on reproductive and bone characteristics in gilts. Weanling gilts (n = 50) were allotted to 10 pens based on weaning weight and litter origin. Pens were randomly assigned to receive one of two dietary treatments that consisted of a basal diet low in B (control) and the basal diet supplemented with 5 mg of B/kg diet as sodium borate. Gilts remained on their respective experimental diets throughout the nursery phase, growing-finishing phase, sexual maturity, breeding, gestation, and lactation. The day of first observed standing estrus was defined as puberty, and each pubertal gilt was bred via AI at the second observed standing estrus. Eight randomly selected gilts per treatment were slaughtered at d 35 of gestation for the assessment of embryonic and reproductive characteristics, bone characteristics, and tissue B concentrations. The remaining pregnant gilts (control, n = 11; 5 mg supplemental B/kg diet, n = 10) farrowed, and litter characteristics at farrowing and weaning were determined. Age at puberty was not affected (P = 0.72) by B, and neither were the number of corpora lutea on the ovaries (P = 0.44) or the total number of embryos (P = 0.95) at d 35 of gestation. Boron supplementation increased (P = 0.05) pig weaning weight and tended (P = 0.11) to increase pig birth weight; however, no other litter characteristics were affected (P > 0.12) by B. Extrinsic and intrinsic strength measures of bone were increased (P < 0.09) by B. Fat-free bone ash percentage and bone mineral concentrations were not affected (P > or = 0.19) by dietary B. Supplemental B increased (P < or = 0.06) the B concentrations of the muscle, liver, and reproductive tissues. Serum osteocalcin concentrations tended (P = 0.13) to be increased by dietary B, which may be related to increased bone turnover in B-supplemented gilts. Results indicate that B may have beneficial effects upon reproductive and bone characteristics.     

Effect of age and physical or fence-line boar exposure on estrus and ovulation response in prepubertal gilts administered PG600

Boar exposure has been used for estrus induction of prepubertal gilts, but has limited effect on estrus synchronization within 7 d of introduction. In contrast, PG600 (400 IU of PMSG and 200 IU of hCG; Intervet, Millsboro, DE) is effective for induction of synchronized estrus, but the response is often variable. It is unknown whether boar exposure before PG600 administration might improve the efficiency of estrus induction of prepubertal gilts. In Exp. 1, physical or fence-line boar contact for 19 d was evaluated for inducing puberty in gilts before administration of i.m. PG600. Exp. 2 investigated whether 4-d boar exposure and gilt age influenced response to PG600. In Exp. 1, 150-d-old prepubertal gilts were randomly allotted to receive fence-line (n = 27, FBE) or physical (n = 29, PBE) boar exposure. Gilts were provided exposure to a mature boar for 30 min daily. All gilts received PG600 at 169 d of age. Estrous detection continued for 20 d after injection. In Exp. 2, prepubertal gilts were allotted by age group (160 or 180 d) to receive no boar exposure (NBE) or 4 d of fence-line boar exposure (BE) for 30 min daily before receiving PG600 either i.m. or s.c. Following PG600 administration, detection for estrus occurred twice-daily using fence-line boar exposure for 7 d. Results of Exp. 1 indicated no differences between FBE and PBE on estrus (77%), age at puberty (170 d), interval from PG600 to estrus (4 d), gilts ovulating (67%), or ovulation rate (12 corpora lutea, CL). Results from Exp. 2 indicated no effect of age group on estrus (55%) and days from PG600 to estrus (4 d). A greater (P < 0.05) proportion of BE gilts expressed estrus (65 vs. 47%), had a shorter (P < 0.05) interval from PG600 to estrus (3.6 vs. 4.3 d), and had decreased (P < 0.05) age at estrus (174 vs. 189 d) compared with NBE. Ovulation rate was greater (P < 0.05) in the BE group for the 180-d-old gilts (12.7 vs. 11.9 CL) compared with the NBE group. However, age group had no effect on ovulation (77%) or ovulation rate (12 CL). Collectively, these results indicate that physical boar contact may not be necessary when used in conjunction with PG600 to induce early puberty. The administration of PG600 to 180-d-old gilts in conjunction with 4 d prior fence-line boar exposure may improve induction of estrus, ovulation, and decrease age at puberty.     

氯前列醇钠、产前背膘厚及便秘对后备母猪同期分娩效果的影响

试验旨在研究氯前列醇钠、产前背膘厚、便秘对后备母猪同期分娩集中度和生产性能的影响,并进一步探讨母猪同期分娩的最优方案。选取后备母猪共295头,根据妊娠期110 d时P2点处的背膘厚,随机分为3组：对照组（CON组：0.9%生理盐水）、低剂量氯前列醇钠组（LPG组：0.1 mg氯前列醇钠）、高剂量氯前列醇钠组（HPG组：0.2 mg氯前列醇钠）,于妊娠期114 d进行阴户部注射诱导分娩。结果表明,与对照组相比,高、低剂量氯前列醇钠均可显著缩短母猪从注射到分娩的时间间隔（P<0.05）,且两试验组间差异不显著（P>0.05）。但是,LPG组后备母猪在注射氯前列醇钠后48 h内的分娩率高达95%,并且白天分娩率达75.7%。此外,LPG组后备母猪的产仔间隔也显著短于CON组（P<0.05）。同时本研究发现,背膘厚在16~20 mm范围内的后备母猪从注射到分娩的时间间隔显著短于背膘厚≤15 mm的后备母猪（P<0.05）;便秘指数0~1.0组后备母猪的产程和产仔间隔均显著大于便秘指数1.1~2.0组及2.1~3.0组的后备母猪（P<0.05）。进一步回归分析发现,母猪背膘厚分别与产程、总产仔数、活仔数存在极显著线性相关（P<0.01）,母猪便秘指数分别与产程、产仔间隔、总产仔数、活仔数存在极显著线性相关（P<0.01）。综上所述,在妊娠期114 d对后备母猪阴户部注射0.1 mg氯前列醇钠诱导分娩,不仅可显著加快母猪分娩的进程,而且还可大大节约药物成本。此外,母猪产前背膘厚和便秘均会影响母猪同期分娩的效果,应使母猪分娩前保持最佳的背膘厚（16~20 mm）,且避免母猪便秘,方可保证同期分娩的顺利实施。     

Serum profiles of progesterone, LH, FSH and prolactin immediately preceding induced puberty in gilts

Two experiments were conducted to determine if the secretory patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) and serum concentrations of progesterone change immediately preceding induced puberty in gilts. To help predict when prepubertal gilts would attain puberty, gilts were induced into puberty by relocation from confinement housing to an outdoor lot and exposure to mature boars. In Exp. 1, 17 prepubertal gilts were bled on two successive days from 0800 to 1200 h before relocation and boar exposure and until the second day of estrus or for 8 d in gilts that failed to exhibit estrus. Blood samples were collected from indwelling cannulas at 20-min intervals for 4 h. In Exp. 2, blood samples were collected from 20 prepubertal gilts at 20-min intervals from 0800 to 1200 h and from 2000 to 2400 h until the second day of estrus or for 6 d if the gilt failed to exhibit estrus. In each experiment, 11 gilts exhibited pubertal estrus 3 to 6 d after relocation and boar exposure. When the frequency of LH spikes in each gilt was normalized to the day of her preovulatory surge of LH (d 0), a decline in the frequency of LH secretory spikes was observed as gilts approached puberty. However, neither the average magnitude of LH spikes nor mean LH concentrations were different among these days. Mean serum concentrations, frequency of spikes or average magnitude of secretory spikes of FSH or PRL did not change on the days preceding the preovulatory peak of LH.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of premating feed intake on the reproductive performance of gilts.

In an attempt to improve the reproductive performance of gilts mated at puberty, 70 Yorkshire x Landrace gilts were allocated at 120 d of age and 60 kg body weight to one of two treatments. Restricted gilts were fed 2.0 kg d-1 of a diet formulated to provide 18% crude protein and 14.5 MJ DE kg-1 from selection until mated at their first estrus (n = 35). Flushed gilts were fed 2.0 kg d-1 of the same diet from 120 to 150 d of age, but then had their feed intake increased to 3.5 kg d-1 until mated at their first estrus (n = 35). An additional group of gilts (control fed; n = 33) were fed 3.0 kg d-1 from selection until they were bred at their third estrus in order to investigate the influence of feed restriction on the onset of puberty. During gestation all gilts were fed 1.8 to 2.2 kg d-1 of a 16.8% crude protein diet having 13.7 MJ DE kg-1. Control fed gilts were younger (p less than 0.05) at puberty (150 d) than restricted (165 d) or flushed gilts (165 d). There was no difference in subsequent litter size between the restricted and flushed gilts (7.7 and 8.0, respectively). It is concluded that the institution of a flushing nutritional regime in the prepubertal period will not enhance piglet production from gilts mated at puberty.     

Effects of feeding schedule on body condition, aggressiveness, and reproductive failure in group-housed sows

A total of 208 sows and 288 gilts (PIC line C29) were used to determine the influence of feeding frequency (2 vs. 6 times/d, floor fed) on performance and welfare measurements on a commercial sow farm. Treatments consisted of feeding similar amounts of feed to each sow (2.5 kg) or gilt (2.05 kg) over 2 (0700 and 1530) or 6 times daily (0700, 0730, 0800, 1530, 1600, and 1630). There were 8 sows or 12 gilts in each pen. Gilts and sows were moved to pens 1 to 4 d after breeding. In sows, there were no differences (P > 0.10) in ADG, backfat change, or variation in BW. There was a trend (P < 0.08) for sows fed twice daily to farrow more total pigs born, but number born alive or other reproductive performance traits were not different (P > 0.10) among treatments. Sows fed 6 times per day had increased vocalization during the morning (P < 0.07) and afternoon (P < 0.01) feeding periods compared with sows fed twice daily. Sows fed twice daily had more skin (P < 0.01) and vulva (P < 0.04) lesions as well as a small increase in feet and leg (P < 0.01) and hoof (P < 0.02) problems. In this commercial facility, the standard management protocol required moving gilts to a different gestation facility on d 42. On d 42, two pens of gilts with similar breeding dates and treatment were combined and moved to another facility with larger pens until farrowing. Gilts fed 6 times daily had a tendency for greater ADG (P < 0.07) from d 0 to 42 and a tendency for greater (P < 0.09) backfat on d 42. After movement to the larger groups from d 42 to farrowing, ADG was similar (P > 0.10) for gilts fed 2 or 6 times daily. Gilts fed twice daily had lower BW variation at d 42 (P < 0.04) and tended to at farrowing (P < 0.10). In gilts, there were no differences (P > 0.10) for reproductive performance, skin and vulva lesions, and feet and leg scores. In conclusion, there were few growth, farrowing, or aggression differences among gilts fed 2 or 6 times daily. This suggests that either feeding method is suitable for group-housed gilts. Among sows, feeding frequency resulted in few growth or farrowing performance differences. Feeding 6 times daily resulted in a small but significant reduction in skin and vulva lesions and structural problem scores while increasing vocalization. Increasing the feeding frequency from 2 to 6 times daily does not appear to have a negative or positive impact on performance or welfare of group-housed gilts and sows.     

Effects of adrenalectomy and glucocorticoids on puberty in gilts reared in confinement

The effect of adrenal function and flumethasone (FM, a synthetic glucocorticoid) on induction of puberty in crossbred gilts raised in confinement was examined in two experiments. In Exp. 1, gilts were adrenalectomized (Adx) or subjected to sham adrenalectomy (Sham) between 140 and 160 d of age. Twenty days later indwelling jugular catheters were implanted in Adx, Sham and another group of intact gilts designated as Controls, and the gilts were moved from confinement to outdoor pens and checked daily for estrus with a mature boar. Fewer (P less than .05) Adx (1/11) than Sham (9/14) gilts showed estrus and ovulated by 205 d of age. Response of Control gilts (6/14) was not different from the other groups. Although Adx gilts received 40 mg cortisone acetate and 10 mg deoxycorticosterone acetate daily throughout the experiment, mean plasma glucocorticoids were lower (P less than .05) in Adx (24 +/- 4.7 ng/ml) than in either Sham (47 +/- 8.1 ng/ml) or Control (44 +/- 6.1 ng/ml) gilts. Experiment 2 was conducted to determine whether FM given to Adx gilts immediately after surgery could have inhibited estrus and ovulation. Intact gilts received a total of 27.5 (FM1) or 17.5 (FM2) mg FM over 4 d between 150 and 160 d of age before relocation and boar exposure 20 d later. Control gilts received no injections. Nine of 13 FM-treated but none of the Control gilts showed estrus. It is concluded from these results that the adrenal glands may facilitate the onset of puberty in gilts through increases in glucocorticoid production, but that this is not required for puberty to occur.     

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of lean growth rate on puberty attainment in gilts

Two hundred sixteen prepubertal Genex Manor hybrid F1 gilts were used to determine the impact of lean growth rate on sexual development of gilts. This study was composed of two experiments (Exp. 1 and Exp. 2). In Exp. 1, at approximately 96 d of age and 54 kg weight, gilts were allocated with respect to growth rate and litter origin to one of two dietary treatments: 1) a diet formulated to maximize lean growth potential (LP; n = 84) or 2) a diet formulated to produce a lower lean growth rate (LL; n = 84). In Exp. 2, at approximately 88 d of age and 50 kg weight, gilts were allocated with respect to growth rate and litter origin to one of two dietary treatments: 1) a diet formulated to maximize lean growth potential (LP; n = 24) or 2) a diet formulated to restrict lean growth further than was achieved in LL in Exp. 1 (RL; n = 24). All gilts were fed treatment diets for ad libitum consumption and housed in groups of six. Weight, backfat depth and loin depth, and feed intake were measured weekly. Starting at 135 d of age, gilts received 20 min of direct daily exposure to a boar as a pen group for pubertal stimulation. Puberty attainment was determined as the day gilts first exhibited the standing reflex in response to contact with a boar. At pubertal estrus, body weight, backfat depth, and loin depths were recorded. Diet affected (P < or = 0.05) estimated fat-free lean gain (LP, 424 vs LL, 347 g/d, Exp. 1; LP, 397 vs RL, 376 g/d, Exp. 2) during the growth period (start to stimulation). However, age at puberty was not affected by diet (LP, 157.3 vs LL, 157.6, Exp. 1; LP, 166.7 vs RL, 167.3, Exp. 2) or overall lean growth at stimulation (P > or = 0.05 in both experiments), confirming that innate variability in sexual development of commercial genotypes, rather than growth performance, determines onset of sexual maturity. A negative correlation between age at puberty and growth rate from 50 kg until puberty (P < or = 0.05) (LP, r = -0.40, LL, r = -0.36, Exp. 1; LP, r = -0.64, RL, r = -0.48, Exp. 2) was a consequence of reduced lean tissue growth during the stimulation period in later-maturing gilts.     

Reproductive performance in gilts through their first two parities

Fertility data were collected for 766 gilts from 12 breeding and commercial herds. The age at first breeding was 244.5 days and at first farrowing 363.2 days. The litter size was 9.91 piglets born (9.16 live). The farrowing rate at the first service was 87.8%. The total farrowing rate was 95.5% of the mated gilts and 88.4% of all the gilts. 9.8% were repeat breeders. 2.6% of the once mated gilts never returned to oestrus and still did not farrow. The culling rate was 11.6%. The major reason for culling was delayed puberty/anoestrus (7.7%). Of the 565 gilts having a first litter 85.3% were mated after weaning. The age at second farrowing was 541.7 days. The litter size was 10.9 piglets born (10.3 live). The farrowing rate after first service was 83.0%. The total farrowing rate of the 482 sows was 92.9% and of the 565 weaned sows 79.3%. 12.2% were repeat breeders. 4.8% of the sows once mated never returned to oestrus and still did not farrow. The culling rate was 20.7%. Culling because of anoestrus was 4.4%. The month of birth significantly influenced the number of gilts culled because of anoestrus, the age at first breeding and at first and second farrowing. The season also influenced the interval from weaning to service, the percentage of sows served within 7 days of weaning and culled because of anoestrus. No correlation between a high ultrasonic index and lowered fertility was found. The age at first breeding was 1.12 days younger per unit higher ultra-sonic index.     

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.     

The effect of confinement on days to puberty in gilts

In the late fall and winter of 1982 to 1983, 112 crossbred gilts were used in a factorially arranged experiment to determine the effect of confinement on the age at which a gilt reaches first estrus (puberty). Two environments (confinement and non-confinement) and three ages at movement to non-confinement (100, 140, and 180 d) were studied. No differences were detected (P greater than .05) between confinement and non-confinement in the proportions of gilts reaching puberty by 210 d of age. Gilts were older at puberty (P less than .05) in confinement than in non-confinement (192.0 vs 187.7 d) and had a longer interval (P less than .05) from first boar contact to first estrus (12.1 vs 7.8 d). Age at puberty (192.1 vs 187.0 vs 190.5 d) and the proportion reaching puberty (56.4 vs 45.7 vs 65.8%) were not different (P greater than .05) between age-of-movement groups. However, a higher (P less than .05) proportion of the non-confinement gilts reached puberty within 10 d after the beginning of boar exposure than confinement (44.6 vs 26.8%). Moving gilts from confinement to non-confinement (pasture) at 180 d appeared to be the most effective method tested for inducing puberty in gilts.