Effect of birth litter size, birth parity number, growth rate, backfat thickness and age at first mating of gilts on their reproductive performance as sows

The present study was performed to evaluate retrospectively the influence of birth litter size, birth parity number, performance test parameters (growth rate from birth to 100kg body weight and backfat thickness at 100kg body weight) and age at first mating (AFM) of gilts on their reproductive performance as sows. Traits analysed included remating rate in gilts (RRG), litter size, weaning-to-first-service interval (WSI), remating rate in sows and farrowing rate (FR). Data were collected from 11 Swedish Landrace (L) and 8 Swedish Yorkshire (Y) nucleus herds and included 20712 farrowing records from sow parities 1-5. Sows that farrowed for the first time during 1993-1997, having complete records of performance test and AFM, were followed up to investigate their subsequent reproductive performance until their last farrowing in 1999. Analysis of variance and multiple regression were applied to continuous data. Logistic regression was applied to categorical data. The analyses were based on the same animals and the records were split into six groups of females, i.e. gilts, primiparous sows, and sows in parities 2-5, respectively. Each additional piglet in the litter in which the gilt was born was associated with an increase of her own litter size of between 0.07 and 0.1 piglets per litter (P<0.001). Gilts born from sow parity 1 had a longer WSI as primiparous sows compared with gilts born from sow parity 4 (0.3 days; P<0.05) or parity 5 (0.4 days; P<0.01). Gilts with a higher growth rate of up to 100kg body weight had a larger litter size (all parities 1-5; P<0.05), shorter WSI (all parities 1-5; P<0.05) and higher FR (parities 2 and 5; P<0.05) than gilts with a lower growth rate. Gilts with a high backfat thickness at 100kg body weight had a shorter WSI as primiparous sows (P<0.001) compared with low backfat gilts, and 0.1 piglets per litter more as second parity sows (P<0.01). A 10 day increase in AFM resulted in an increase in litter size of about 0.1 piglet for primiparous sows (P<0.001) and a decrease (P<0.05) for sow parities 4 and 5.     

Factors influencing age at first mating in purebred Swedish Landrace and Swedish Yorkshire gilts

The aim of the present study was to retrospectively analyze causes of the variation in age at first mating in Swedish Landrace (L) and Swedish Yorkshire (Y) gilts. Production traits including growth rate from birth to 100kg body weight and backfat thickness at 100kg body weight were also studied. Data analyzed were obtained from 11 L and 11 Y nucleus herds and included gilts born during a 5-year-period from October 1993 until September 1998. The complete data set included information on 14,761 gilts (6997 L and 7764 Y). Traits analyzed included age of gilt at first mating, growth rate and backfat thickness. Seven statistical models were used for analyzing the data. Factors included were gilt breed, birth month, parity number and size of the litter in which the gilt was born as well as their interactions. Compared with Y gilts, L gilts grew faster (571 versus 556 g/day; P<0.001), had a thinner backfat (11.9 versus 12. 3mm; P<0.001) at 100kg body weight and were 12 days younger at first mating (237 versus 249 days; P<0.001). Birth month significantly (P<0.001) influenced age at first mating, growth rate and backfat thickness. Gilts born from smaller litters were mated at younger age than gilts born from larger litters even when age at first mating was adjusted for the effect of growth rate and backfat thickness. Growth rate of the gilts decreased when 'birth litter size' increased. Gilts born from primiparous sows grew slower, had a thinner backfat at 100kg body weight and were older at first mating compared with gilts born from multiparous sows. Gilts with a higher growth rate were younger at first mating than those with a lower growth rate. Gilts with a thicker backfat at 100kg body weight were mated earlier than the thin ones. However, the effect of growth rate on age at first mating was more pronounced in the gilts with a thinner backfat rather than the ones with a thicker backfat.     

Detection of quantitative trait loci for reproduction and production traits in Large White and French Landrace pig populations (Open Access publication)

A genome-wide scan was performed in Large White and French Landrace pig populations in order to identify QTL affecting reproduction and production traits. The experiment was based on a granddaughter design, including five Large White and three French Landrace half-sib families identified in the French porcine national database. A total of 239 animals (166 sons and 73 daughters of the eight male founders) distributed in eight families were genotyped for 144 microsatellite markers. The design included 51 262 animals recorded for production traits, and 53 205 litter size records were considered. Three production and three reproduction traits were analysed: average backfat thickness (US_M) and live weight (LWGT) at the end of the on-farm test, age of candidates adjusted at 100 kg live weight, total number of piglets born per litter, and numbers of stillborn (STILLp) and born alive (LIVp) piglets per litter. Ten QTL with medium to large effects were detected at a chromosome-wide significance level of 5% affecting traits US_M (on SSC2, SSC3 and SSC17), LWGT (on SSC4), STILLp (on SSC6, SSC11 and SSC14) and LIVp (on SSC7, SSC16 and SSC18). The number of heterozygous male founders varied from 1 to 3 depending on the QTL.     

Influence of major histocompatibility complex on reproduction and production traits in swine

The effects of the swine lymphocyte antigen (SLA) system on different performance traits were investigated in Swiss pig breeds. Litter size and piglet weight at birth and at weaning were considered and in gilts the average daily weight gain, backfat and muscle thickness as well as percentage valuable cuts were measured. These data were analysed with least squares procedures. Although the effect of SLA on these traits was very small, a few haplotypes seemed to have some influence. Sows of the Large White breed carrying H12 had a significant smaller and those with H24 had a bigger litter size at weaning. Some mating studies were performed to investigate the effects of SLA homozygosity. The obtained results suggest that this has a negative effect on the litter size, especially when H19 in the Large White breed and H7 in Landrace are involved.     

Whole-genome analysis for backfat thickness in a tropically adapted, composite cattle breed from Brazil

Backfat thickness affects the preservation of the beef carcass after slaughter and confers organoleptic characteristics assessed by the consumer. One of the breeding goals for Canchim, a tropically adapted breed, is to comprehensively increase fat thickness. Our goals were to identify genomic regions associated with backfat in Canchim populations and validate the association of single nucleotide polymorphisms (SNPs) overlapping previously identified QTL regions known to affect fat deposition. Fifteen animals with lower and 15 animals with higher residues for backfat, according to a linear model using the SAS GLM procedure, were selected from a population of 1171 animals and genotyped using the BovineSNP50 BeadChip. Initial analysis revealed more than 100 SNPs that discriminated the tails of phenotypic distribution. One extended region of association included the centromeric region of chromosome (Chr) 14. Because this region overlapped with QTL from previous reports, we developed SNP assays to interrogate two linkage disequilibrium blocks, one in the centromeric region and another in the middle region of Chr 14 to confirm the association. The analysis validated the presence of specific haplotypes affecting fat thickness.     

Influence of some sow characteristics on within-litter variation of piglet birth weight

Within-litter variation of piglet birth weight (BW0) is associated with an increased piglet mortality and a high variability in pig weight at weaning and weight or age at slaughter. Data collected in two experimental herds were used to quantify within-litter variability in BW0 and to assess the influence of factors mainly related to the sow. Within 24 h after birth, piglets born alive were individually weighed and stillborn piglets were collectively (first data set) or individually (second data set) weighed. The first data set was restricted to litters with no or only one stillborn piglet (3338 litters). It was used to assess the influence of genetic selection on BW0 variation by comparing litter characteristics before (1994 to 1996) and after (2001 to 2004) the development of hyperprolific sows in this herd. The second data set included all litters (n = 1596) from sows born between 2000 and 2004. For each litter, mean BW0 (mBW0) and its coefficient of variation (CVBW0) were calculated. Then, variance analyses were performed to test the influence of litter size, parity, year of sow birth and season at conception. Prolificacy improvement was associated with an increased CVBW0 in litters from pure Large White (LW) and Landrace × Large White (LR × LW) crossbred sows. The CVBW0 averaged 21% and was significantly influenced by litter size and parity. It increased from 15% to 24% when litter size varied from less than 10 piglets to more than 15 piglets. The proportion of small piglets (i.e. weighing less than 1 kg) increased concomitantly. The CVBW0 was not repeatable from a parity to the following. It was lowest for first and second parities (20%) and thereafter increased progressively. The CVBW0 was positively related to sow's backfat thickness gain during gestation. Taking into account litter size, parity, year of sow birth and season at conception explained 20% of BW0 variation. Thus, major part of heterogeneity is due to other factors, presumably including embryo genotype, on the one hand, and factors that influence embryo and foetus development, such as epigenetic factors, on the other hand.     

Influence of the halothane gene (HAL) on pork quality in two commercial crossbreeds

We evaluated the effect of the halothane (HAL) gene on the quality of pork in domestic pigs. Half-carcasses from two different commercial pig (Sus domestica) crossbreeds were analyzed, 46 of which were homozygous dominant (HAL(NN)) and 69 of which were heterozygous (HAL(Nn)) for the halothane gene. The measures included backfat thickness, lean meat percentage, carcass weight, pH 24 h after slaughtering, color, and drip loss; DNA was extracted from the haunch muscle. Swine with the HAL(Nn) genotype had less backfat thickness and higher lean meat percentages than swine with the HAL(NN) genotype. Yet, swine with the HAL(Nn) genotype had lower quality meat than those with the HAL(NN) swine. The pH at 24 h was lower in HAL(Nn) swine. The meat color was paler in HAL(Nn) animals, the drip loss was greater in those animals bearing the n allele, and the amount of intramuscular fat was not related to the halothane genotype. We conclude that bearers of the recessive allele of the halothane gene produce more meat, but with quality parameters that are inferior to those sought by consumers and industry.     

Interval mapping of carcass and meat quality traits in a divergent swine cross.

An autosomal scan of the swine genome with 119 polymorphic microsatellite (ms) markers and data from 116 F2 barrows of the University of Illinois Meishan x Yorkshire Swine Resource Families identified genomic regions with effects on variance in carcass composition and meat quality at nominal significance (p-value <0.05). Marker intervals on chromosomes 1, 6, 7, 8 and 12 (SSC1, SSC6, SSC7, SSC8, SSC12) with phenotypic effects on carcass length, 10th rib backfat thickness, average backfat thickness, leaf fat, loin eye area and intramuscular fat content confirm QTL effects identified previously based on genome wide significance (p-value <0.05). Several marker intervals included nominally significant (p-value <0.05) dominance effects on leaf fat, 10th rib backfat thickness, loin eye area, muscle pH and intramuscular fat content.     

Effects of age on slaughter performance and meat quality of Binlangjang male buffalo

Twelve representative buffalo were selected from 22 suckling calves, 41 weaned calves, 57 reserve bulls and 20 adult bulls for slaughter. The study aims to assess the effect of age on dressing percentage, meat percentage and carcass meat yield and physico-chemical properties of longissimus dorsi and biceps femoris, and to evaluate the correlation between live weight and marbling, backfat thickness, rib eye area. The results showed that the slaughter performance and meat quality of Binlangjang male buffalo showed an obvious change with age. The dressing percentage decreased from 54.93% to 51.22% with the increase of age, while meat percentage and carcass meat yield increased gradually with age, which were 34.58–38.59%, 62.95–75.34%; Marbling, backfat thickness and rib eye area increased with age, and there was significant difference between the situation before 3 months and after 12 months of age (P < 0.05). The moisture content was maximum at birth, which then gradually decreased, but the difference was insignificant (P > 0.05). The levels of fat, protein, cholesterol and inosine acid were significantly different before 3 months of age from those after 12 months (P < 0.05). Cholesterol content was negatively correlated with age, the minimum was 80.25 mg/100 g; Inosine acid content increased with age, reaching 133.11 mg/100 g. Marbling, backfat thickness, rib eye area had a high correlation with live weight, with correlation coefficients respectively at 0.9096, 0.9291, 0.9551. Based on the prediction model of live weight, Buffaloes was suitable for slaughtering for superior slaughter performance and meat quality after 24 months of age.     

Design and statistical methods in studies using animal models of development

Experiments involving neonates should follow the same basic principles as most other experiments. They should be unbiased, be powerful, have a good range of applicability, not be excessively complex, and be statistically analyzable to show the range of uncertainty in the conclusions. However, investigation of growth and development in neonatal multiparous animals poses special problems associated with the choice of "experimental unit" and differences between litters: the "litter effect." Two main types of experiments are described, with recommendations regarding their design and statistical analysis: First, the "between litter design" is used when females or whole litters are assigned to a treatment group. In this case the litter, rather than the individuals within a litter, is the experimental unit and should be the unit for the statistical analysis. Measurements made on individual neonatal animals need to be combined within each litter. Counting each neonate as a separate observation may lead to incorrect conclusions. The number of observations for each outcome ("n") is based on the number of treated females or whole litters. Where litter sizes vary, it may be necessary to use a weighted statistical analysis because means based on more observations are more reliable than those based on a few observations. Second, the more powerful "within-litter design" is used when neonates can be individually assigned to treatment groups so that individuals within a litter can have different treatments. In this case, the individual neonate is the experimental unit, and "n" is based on the number of individual pups, not on the number of whole litters. However, variation in litter size means that it may be difficult to perform balanced experiments with equal numbers of animals in each treatment group within each litter. This increases the complexity of the statistical analysis. A numerical example using a general linear model analysis of variance is provided in the Appendix. The use of isogenic strains should be considered in neonatal research. These strains are like immortal clones of genetically identical individuals (i.e., they are uniform, stable, and repeatable), and their use should result in more powerful experiments. Inbred females mated to males of a different inbred strain will produce F1 hybrid offspring that will be uniform, vigorous, and genetically identical. Different strains may develop at different rates and respond differently to experimental treatments.     

Phenotypic and genetic parameters compared during repeated measures of longissimus muscle area and subcutaneous fat thickness in Nelore cattle

Real-time ultrasound is currently used for in vivo carcass evaluation of beef cattle. We estimated heritability and repeatability coefficients for ultrasound-measured carcass traits in Nelore cattle. We measured longissimus muscle area, backfat thickness, and rump fat thickness in male and female animals ranging in age from 10 to 26 months. The variance components were estimated by single-trait analysis using the derivative-free restricted maximum likelihood method, under an animal model. The complete data file included 3077 records of 1172 animals born between 2003 and 2008. Two analyses were performed using a repeatability model: a) all records of longissimus muscle area, backfat thickness, and rump fat thickness of animals aged 10 to 26 months, and b) considering two age periods (11 to 17 and 18 to 24 months). The heritability estimates ranged from 0.33 to 0.46 for longissimus muscle area, from 0.20 to 0.26 for backfat, and from 0.26 to 0.29 for rump fat, demonstrating that direct selection for these traits can provide genetic gain. The repeatability estimates were moderate, ranging from 0.42 to 0.73. The highest repeatability estimates were obtained for longissimus muscle area in both the first (0.70) and second (0.73) analyses. The repeatability estimates suggest that ultrasound measures are precise; higher precision was obtained for longissimus muscle area than for subcutaneous fat thickness. The latter could be obtained during periods of greater feed availability to increase precision.     

Allelic variation in the erythropoietin receptor gene is associated with uterine capacity and litter size in swine

A single nucleotide polymorphism (SNP; C vs. T) that creates an extra GATA-1 site (T allele) in intron 4 of the swine erythropoietin receptor (EPOR) gene was discovered and a genotyping assay for this SNP was developed. A total of 402 gilts from lines selected either at random (control), for ovulation rate (OR) or for uterine capacity (UC) for 11 generations were unilaterally hysterectomized-ovariectomized (UHO) at 160 days of age, mated at approximately 250 days of age and slaughtered at 105 days of pregnancy. Blood samples and spleens were collected from each foetus and the numbers of corpora lutea (CL) and live foetuses, the weights of each foetus and placenta, and each foetal haematocrit were recorded. In addition, intact gilts from the OR line or from a Yorkshire, Landrace, Duroc, crossbred line (BX) were mated and farrowed. At farrowing, the numbers of fully formed and live piglets were recorded for each litter. Genomic DNA was isolated for both the UHO and intact gilts, from foetuses from the UHO gilts that were heterozygous for the EPOR SNP, and from the boars from the BX line and were then used to determine EPOR SNP genotypes. Only CC and CT gilts were observed in the control, OR and UC selected lines. Presence of the EPOR T allele was associated (P < 0.05) with increased UC in these gilts. The number of heterozygous and homozygous foetuses did not differ within UHO litters, or did EPOR genotype influence foetal haematocrit. In intact gilts from the OR line, litter size was significantly associated (P < 0.05) with EPOR SNP genotype. Finally, results from intact gilts of the BX line, in which both the gilt and the boar genotypes were known, allowed an analysis to determine the effect of the gilt and/or the foetal genotype on litter size. This analysis indicated that the predicted foetal genotype (with gilt genotype as covariate) was associated with litter size (an increase of 2.6 +/- 1.0 piglets born alive predicted for homozygous T litters compared with homozygous C litters, P < 0.01) whereas the effect of the gilt genotype (adjusted for foetal genotype) on litter size was not significant. These results indicate that the EPOR SNP is associated with UC and litter size in two distinct populations and could be useful in increasing litter size in swine that are not limited in OR.     

Effect of dietary fat or starch supply during gestation and/or lactation on the performance of sows, piglets' survival and on the performance of progeny after weaning

Two trials were carried out to compare the effects of fat or starch inclusion in sow's diet on sow and litter performance. In each trial, sows were assigned to one of two treatments. In trial 1, the sows were fed diets containing either soybean oil (5%, treatment GL5) or cornstarch (11.3%, GL0) from day 35 of gestation to weaning. Daily net energy and nutrient allowance were equalised during gestation. In trial 2, the same treatments were applied only after farrowing (treatments L5 and L0, respectively). Within each trial, a batch of piglets was studied until slaughter. In trial 1, adipose cell development and total lipid content were determined on some pigs at weaning (n = 6/treatment) and at slaughter in dorsal subcutaneous adipose tissue (n = 13/group at least) and in muscle (n = 46/group at least). Piglets' birth weight was not affected by treatment in trial 1. Survival rates at birth and after 24 h of life were higher in treatment GL5 (4.0% v. 7.5% stillborn piglets in GL0 treatment, P < 0.05; 8.7% v. 12.6% of piglets alive at 24 h of age died in treatment GL0, P = 0.06). Subsequently, overall survival rate until weaning was higher in treatment GL5 (81.4% v. 75.7% of total born piglets, P = 0.03), but litter size at weaning was not significantly affected (11.3). Litter growth rate before weaning was increased when a fat-enriched diet was provided during gestation and lactation (+140 g/day per litter; P < 0.01) and to a lower extent when provided only after farrowing (+90 g/day; P < 0.05). Energy supply through fat did not decrease the mobilisation of the sow's body reserve and backfat thickness loss was even higher with treatment GL5 (P < 0.05). After weaning, pigs' average daily gain, feed : gain ratio and carcass lean content were not affected by the energy source supplied before and/or after farrowing. At weaning, the number of adipose cells in the dorsal subcutaneous adipose tissue and in the Longissimus dorsi muscle was higher in the GL5 pigs. Muscle lipid content at weaning did not differ between treatments, but it was higher at slaughter, around 110 kg, in the GL5 pigs (3.46% v. 2.58%, P < 0.001).     

Quantitative trait loci (QTL) analysis in a Meishan x Göttingen cross population

In order to locate the genetic regions in the swine genome that are responsible for economically important traits, a resource population has been constructed by mating two female Meishan pigs with a male Göttingen miniature pig. In subsequent generations, 265 F2 offspring were produced from two F1 males and 19 F1 females. The F2 offspring were scored for eight traits including growth rate, teat number, vertebra number and backfat thickness, and genotyped for 318 genetic markers spanning the swine genome. Least‐square analysis revealed quantitative trait loci (QTL) effects for vertebra number on chromosomes 1 and 2; for teat number on chromosomes 1 and 7; for birth weight on chromosome 1; for average daily gain between 4 and 13 weeks of age on chromosomes 9 and 10; for backfat thickness on chromosome 7; and for backskin thickness on chromosome 3.     

Generation and sequence characterization of a normalized cDNA library from swine ovarian follicles

Ovulation rate is a major factor determining litter size in swine and is, therefore, a trait of economic importance to the pork industry. The dynamics of follicle development, which in turn are dictated by a balance between follicle recruitment, maturation, selection, and atresia, are a major determining factor of ovulation rate. The role of several genes expressed in the ovaries during these processes has been described, but studies utilizing large-scale genomic approaches have yet to be conducted to examine gene expression in this tissue more globally. We have developed a normalized cDNA library from swine ovarian follicles in various stages of development, ranging from 2.0 to 10.0 mm in diameter, collected from gilts from divergent genetic lines selected for high and low ovulation rates, during the 7 initial days of the follicular phase of the estrous cycle. EST sequences were obtained from 5231 distinct clones derived from this library. In total, 3479 unique sequence clusters were obtained, of which 2661 singletons (76.5%) were observed. BLASTN searches with the primary sequences from the clusters obtained resulted in 1037 sequences not matching (E <1.0(-06) any of the sequences in the nt database (29.8% novelty rate). This resource will facilitate the use of cDNA microarrays in functional genomics studies aiming at unraveling the genetic and physiological mechanisms underlying follicle maturation and ovulation rate in swine.     

Energy Metabolism During Late Gestation and Lactation in Muciparous Sows in Relation to Backfat Thickness and the Interval from Weaning to First Oestrus

Ten crossbred, fourth or fifth parity sows were divided into 2 groups - high (H) and low (L) - according to their backfat thickness 9 days before parturition. Body weight, backfat thickness and litter weight were recorded repeatedly during a 5 week lactation period. The length of the interval from weaning to first oestrus was also noted. All sows were fed a commercial diet (11.9 MJ/kg, 14.5% crude protein). During gestation, daily food intake was 2.2 kg/sow, while during lactation it was 3.0 kg/sow plus 0.4 kg/piglet. Blood samples were drawn on day 9 before parturition and on days 2,7,14 and 21 of lactation. The samples were analysed to determine concentrations of glucose, urea nitrogen, creatinine, triglycerides, free fatty acids and beta-hydroxybutyric acid. In both groups, concentrations of free fatty acids and urea nitrogen were low on day 9 before parturition while those of triglycerides were high, indicating anabolism regardless of backfat thickness. During the first week of lactation, concentrations of free fatty acids increased in the H-group but not in the L-group, and concentrations of urea nitrogen were higher in the H-group. These differences, together with the greater loss of weight observed in the H-group, indicate that catabolism of maternal fat and protein depots was more pronounced in the Η-group than in the L-group during this time. On day 14 of lactation, both groups showed equally low concentrations of free fatty acids, decreasing creatinine concentrations and stable triglyceride and urea nitrogen concentrations. Furthermore, weight loss during the second and third weeks of lactation was low in both groups. These facts, taken together, indicate that the catabolic rate was decreasing in both groups during this period. No differences in return to oestrus interval were noted between the groups. The present study indicates that under a restricted feeding regime the catabolic rate during the first week of lactation is higher in sows with higher backfat thickness in late gestation. As lactation progresses, a more balanced metabolism is achieved regardless of backfat thickness, which may tend to reduce differences in return to oestrous interval.     

Exogenous steroid effects on litter size and early embryonic survival in swine

These studies confirm the efficacy of 12.5 mug estrone and 25 mg progesterone, administered on Days 16 and 17 of pregnancy, on increased litter size in swine. Substitution of estradiol (with ten-fold greater biological activity) for estrone in this regimen eliminated the positive effect on litter size and estradiol given alone at dosages of 3.1 and 6.3 mug were without effect. However, when estradiol was given in combination with progesterone (25 mg) at a dosage equivalent to 10% the effective estrone dosage (1.25 mug), a 22.6% increase in total pigs born per litter over controls was observed. Estrone alone at dosages of 6.25 and 12.5 mug did not alter litter size. At a dosage of 18.75 mug, an 8.7% decrease in total pigs born was noted. The amniotic fluid from sows treated for ten days with 12.5 mug estrone and 25 mg progesterone near the time of implantation, had significantly higher protein concentration, pH and osmolality.     

Some Factors Influencing Pregnancy Rate and Subsequent Litter Size in Primiparous Sows

The pregnancy rate and the subsequent litter size were studied in 332 Swedish Yorkshire primiparous sows, fed according to a commercial Swedish feeding regime during lactation. The sows were weighed and backfat depth was recorded at the first farrowing, at weaning, and at mating. Oestrous detection was performed once daily after weaning, and the interval from weaning to first oestrus (IWO) was recorded. Blood samples for determination of plasma progesterone were drawn regularly after the first weaning. Statistical analyses were only performed on sows with an IWO of 3-8 days. Of these 206 sows were mated on their first (OE1 sows) and 87 sows on their second (87 OE2 sows) oestrus after weaning. The pregnancy rate was 85.4% for OE1 sows and 75.9% for OE2 sows (p=0.048). There was no significant difference in pregnancy rate between OE1 sows with an IWO of 3-5 days and OE1 sows with an interval of 6-8 days. OE2 sows with an IWO of 6-8 days, on the other hand, had a significantly lower pregnancy rate compared with OE2 sows with an interval of 3-5 days. The pregnancy rate in sows that lost more than 30 kg during the first lactation period did not differ from that of sows losing less than 30 kg. In sows with a first litter size of more than 9 piglets alive at birth, the pregnancy rate decreases significantly if mating is delayed until the second oestrus after weaning. OE2 sows had a significantly larger second litter size at birth than OE1 sows (+ 2.0). The litter size at six weeks did not, on the other hand, differ significantly (+ 0.4). There was a positive correlation between the IWO and 2nd litter size, although significant only for OE1 sows between the IWO and litter size alive at birth. In the OE1 group, sows losing 20 kg or less during lactation had significantly larger second litters at birth than the sows losing 21-30 kg, but not significantly larger than the sows losing more than 30 kg. One piglet more, at birth, in the first litter resulted in 0.25 piglet more in the second litter. For sows with a large first litter there was a low probability of also having a large second litter.     

应用VCE4.0估计长白猪生长性状的遗传参数

应用PEST和VCE4.0对温氏长白猪的主要生长性状进行了遗传分析。利用温氏水台原种猪场1998～2002年的6344头长白猪生长性能测定记录,运用多性状动物模型REML方法估计主要生长性状的遗传参数。估计遗传力的变化范围为0.207～0.493,性状达30kg体重日龄（AGE30）、达100kg体重日龄（AGE100）、30～100kg平均日增重（ADG）和100kg体重活体背膘厚（FAT）的估计遗传力分别是0.207、0.396、0.304和0.493;FAT/ADG、FAT/AGE100、ADG/AGE100、ADG/AGE30和AGE30/AGE100的各自遗传相关为-0.343、0.180、-0.941、-0.48和0.745;它们的表型相关分别为-0.139、0.138、-0.829、-0.026 和 0.565;AGE30、AGE100、ADG和FAT的窝效应估计结果分别为0.194、0.156、0.157和0.043。     

The effect of sperm number on fertility in blue fox vixens (Alopex lagopus ) artificially inseminated with frozen silver fox (Vulpes vulpes ) semen

During the breeding seasons of 1989 and 1990, a total of 617 blue fox vixens aged 1 to 6 years (mean +/- SEM, 2.6 +/- 0.1) were inseminated with frozen silver fox semen with either 150 million (n = 213, 1989 + 1990), 100 million (n=172, 1990), 75 million (n = 119, 1989) or 37.5 million (n = 113, 1989) spermatozoa per insemination. Two intrauterine inseminations, each with an insemination volume of 1.0 ml, were performed at 24-hour intervals on the first and second days after maximum vaginal electrical resistance was measured. Conception rates were 87% (186 of 213) with 150 million spermatozoa per insemination, 85% (146 of 172) with 100 million, 77% (91 of 119) with 75 million and 68% (77 of 113) with 37.5 million. The mean numbers of cubs per litter +/- SEM for the four groups were 7.6 +/- 0.2 (168 registered litters), 7.5 +/- 0.3 (115 litters), 6.4 +/- 0.4 (86 litters) and 6.4 +/- 0.4 (75 litters). A negative effect on both the conception rate and mean litter size at whelping was observed with decreasing sperm numbers (conception rate percentage: p = 0.0001, Chi-square, litter size: p = 0.02, Kruskal-Wallis Test). Only the two larger numbers of spermatozoa gave litter sizes comparable to those obtained by artificial insemination (AI) with fresh semen.