Relationship between litters per sow per year sire breeding values and sire progeny means for farrowing rate, removal parity and lifetime born alive.

The objective of this study was to determine the relationship between individual sire estimated breeding values (EBV) for litters/sow/year (LSY) and sire progeny means for farrowing rate (FR), removal parity and lifetime born alive (LTBA). Genetic parameters and breeding values were estimated using ASREML. The heritability estimate for LSY was 0.11. When all sires with 10 or more daughters with records were included in the analysis, Spearman rank correlations between the sire's LSY EBV and the sires' daughter means for FR, removal parity and LTBA were 0.49, 0.23 and 0.25 (p < 0.01). The sire EBV for LSY was favourably correlated with sires' daughter means for all three traits. This provides evidence that selecting sires with high EBV for LSY could improve herd FR, removal parity and LTBA. By including LSY as part of the selection criterion, the LTBA may be indirectly improved. The positive genetic correlation between LTBA and LSY may be a result of the improved longevity of sows with greater LSY compared with sows with lower LSY. The relationships between LSY and FR, removal parity and LTBA are strongly supported by the correlations between the sire progeny means for each trait and the sire LSY EBV.

Evaluation of growth, deposition of back fat, and loin muscle for purebred Berkshire pigs housed in bedded hoop buildings.

This study was conducted to evaluate the accretion of BW, back fat, and loin muscle from purebred Berkshire pigs raised in bedded hoop barns in Iowa. The growth of a total of 144 purebred Berkshire pigs (18 barrows and 18 gilts per trial) was evaluated from 4 trials (2 winter and 2 summer trials). Pigs were fed ad libitum utilizing a 5-phase standard corn-soybean meal feeding program that met or exceeded NRC nutrient requirements. Pigs were housed in bedded hoop barns (unheated) to approximate common niche market requirements. At 21-d intervals, pigs were serially weighed, and ultrasonic back fat depth and loin muscle area (LMA) measurements were taken. Live BW measurements began at the trial initiation at approximately 18 to 32 kg, but ultrasonic scans for 10th-rib back fat depth and LMA began at between 36 and 45 kg until market weight of about 122 ± 2.5 kg. The rate (µ) of live body growth (weight) and ultrasonic back fat depth were influenced ( < 0.01) by trial and sex, with no significant interactions between trial and sex. Both live BW and back fat deposition were significantly greater in trial 1 than all other trials (2, 3, and 4). The rate of accretion and maximum growth of LMA depth were not affected ( > 0.05) by trial and sex. Overall, barrows averaged 31 mm of back fat at 125 kg, whereas gilts had an average of about 23 mm at 121 kg of market weight. Results suggest that because of the sex differences in growth and back fat deposition between Berkshire barrows and gilts, it may be important to formulate their diets differently in commercial pork production systems.

Genetic correlations between lean growth and litter traits in U.S. Yorkshire, Duroc, Hampshire, and Landrace pigs.

The objective of this study was to estimate breed-specific genetic correlations between lean growth and litter traits for four U.S. swine breeds. Records for lean growth and litter traits on Yorkshire, Duroc, Hampshire, and Landrace pigs collected between 1990 and April 2000 in herds on the National Swine Registry Swine Testing and Genetic Evaluation System were analyzed. A bivariate animal model and restricted maximum likelihood procedures were used to estimate genetic and environmental correlations between lean growth rate, days to 113.5 kg, backfat, and loin muscle area with litter traits of number born alive, litter weight at 21 d, and number weaned. Most genetic correlation estimates between lean growth and litter traits were small in magnitude and consistent across breeds. Backfat had the largest within-breed genetic correlations with number born alive (0.18 to 0.20) and litter weight at 21 d (-0.27 to -0.30). Estimates of genetic correlations between lean growth traits and number weaned were very small. Estimates of the environmental correlations between lean growth and litter traits also were very small for all traits and for all four breeds. Results indicate that selection for lean growth traits could have a long-term effect on litter traits. Including lean growth traits in a maternal-line evaluation using a multiple-trait model could increase the accuracy of the genetic evaluation for litter traits.

A comparison of an 8- versus 16-hour photoperiod during lactation on suckling frequency of the baby pig and maternal performance of the sow.

Seventeen crossbred sows were used in a lactation trial to compare the effects of a 16-h photoperiod with an 8-h photoperiod from d 107 of gestation to weaning at 28 d postpartum. Crossbred sows were used to compare the effects of 16-h (n = 8) and 8-h (n = 9) photoperiods on litter and maternal performance traits. Females were moved into two identical farrowing rooms under either 16- or 8-h photoperiods on d 107 of pregnancy, litters were equalized across treatments at birth and the treatments terminated at weaning on d 28 postpartum. Traits evaluated included litter size at birth and weaning, 21-d pig and litter weights, milk yields and composition on d 15, litter survival rates, suckling frequency for a 24-h period on d 13 and percentage of sows returning to estrus and days to estrus after weaning. Pigs exposed to 16 h light nursed more often (P less than .05) than pigs exposed to 8 h light over a 24-h period. This advantage was greatest during the 4-h periods of 1200 to 2000, 0000 to 0400 and 0800 to 1200 h. This difference is perhaps an explanation of why litters exposed to 16 h light weaned more (P less than .05) pigs/litter with heavier (P less than .01) 21-d litter weights. Nonsignificant advantages were also seen in milk yield and litter survival percentage. In addition, sows exposed to 16 h light had higher (P less than .05) total solids content of their milk.

Restricted maximum likelihood estimation of variance components from field data for number of pigs born alive.

Variance components for number of pigs born alive (NBA) were estimated from sow productivity field records collected by purebred breed associations. Data sets analyzed were as follows: Hampshire (n = 13,537), Landrace (n = 10,822), and Spotted (n = 3,949). Variance components for service sire, sire of sow, dam of sow, and residual effects on NBA (adjusted for parity) were estimated. The single-trait model included relationships between service sires, sires of sows, and dams of sows. The model was implemented using an expectation maximization (EM) REML algorithm. A sparse-matrix solver was also used. Heritability estimates for NBA were .13, .13, and .12 for Hampshire, Spotted, and Landrace, respectively. Estimates of maternal genetic (co)variances (m2) expressed as a proportion of the phenotypic variance were .05, .01, and .03 for Hampshire, Spotted, and Landrace, respectively. Results indicated that service sires account for 1 to 2% of the total variation for NBA. Genetic effects influencing NBA seem to be small in these data sets, but selection for increased NBA should be effective.

Development of an animal model for across-herd genetic evaluation of number born alive in swine.

An animal model and computer software were developed to conduct across-herd genetic evaluations using data from producers participating in the Sow Productivity Index program of the American Yorkshire Club. The final data set consisted of 61,596 litter records from 1986 to early 1990. The animal model included fixed contemporary group effects and random additive direct, service sire, permanent environmental, and residual effects. Additive genetic relationships among animals were included. A separate relationship matrix for service sires and their sires was also included. A data set similar to the Yorkshire field data was simulated to use in testing the animal model. The simulated data set consisted of 40 herds, each with 120 reproducing dams and either four or five sires. Six generations of simulated data were produced, resulting in 20,605 litter records. These records were then evaluated using the animal model for number of pigs born alive. Finally, correlations between the true breeding values from the simulation and the predicted breeding values were computed. The correlation between the 918 true and predicted sire breeding values was considerably lower for the animal model without a service sire effect than when it was included (.53 vs .74, respectively). However, the difference was cut in half (.66 vs .77) when only sires with greater than five daughter records were included. The high accuracy of the animal model with a random service sire effect indicates that the proposed model adequately accounts for the variation found in records for number of pigs born alive.

Genetic parameters and trends for lean growth rate and its comvonents in U.S. Yorkshire, Duroc, Hampshire, and Landrace pigs.

Records on 361,300 Yorkshire, 154,833 Duroc, 99,311 Hampshire, and 71,097 Landrace pigs collected between 1985 and April of 2000 in herds on the National Swine Registry Swine Testing and Genetic Evaluation System were analyzed. Animal model and REML procedures were used to estimate random effects of animal genetic, common litter, maternal genetic, and the covariances between animal and maternal for lean growth rate (LGR), days to 113.5 kg (DAYS), backfat adjusted to 113.5 kg (BF), and loin eye area adjusted to 113.5 kg (LEA). Fixed effects of contemporary group and sex were also in the statistical model. Based on the single-trait model, estimates of heritabilities were 0.44, 0.44, 0.46, and 0.39 for LGR; 0.35, 0.40, 0.44, and 0.40 for DAYS; 0.48, 0.48, 0.49, and 0.48 for BF; and 0.33, 0.32, 0.35, and 0.31 for LEA in the Yorkshire, Duroc, Hampshire, and Landrace breeds, respectively. Estimates of maternal genetic effects were low and ranged from 0.01 to 0.05 for all traits across breeds. Estimates of common litter effects ranged from 0.07 to 0.16. A bivariate analysis was used to estimate the genetic correlations between lean growth traits. Average genetic correlations over four breeds were -0.83, -0.37, 0.44, -0.07, 0.08, and -0.37 for LGR with DAYS, BF, and LEA, DAYS with BF and LEA, and BF with LEA, respectively. Average genetic trends were 2.35 g/yr, -0.40 d/yr, -0.39 mm/yr, and 0.37 cm2/yr for LGR, DAYS, BF, and LEA, respectively. Results indicate that selection based on LGR can improve leanness and growth rate simultaneously and can be a useful biological selection criterion.

Genetic parameters and trends for litter traits in U.S. Yorkshire, Duroc, Hampshire, and Landrace pigs.

Records on 251,296 Yorkshire, 75,262 Duroc, 83,338 Hampshire, and 53,234 Landrace litters born between 1984 and April of 1999 in herds on the National Swine Registry Swine Testing and Genetic Evaluation System were analyzed. Animal model and restricted maximum likelihood procedures were used to estimate variances of animal genetic (a), maternal genetic (m), permanent environmental, and service sire, and the covariances between a and m for number born alive (NBA), litter weight at 21 d (L21WT), and number weaned (NW). Fixed effects of contemporary groups were included in the analysis. Based on a single-trait model, estimates of heritabilities were 0.10, 0.09, 0.08, and 0.08 for NBA; 0.08, 0.07, 0.08, and 0.09 for L21WT; and 0.05, 0.07, 0.05, and 0.05 for NW in the Yorkshire, Duroc, Hampshire, and Landrace breeds, respectively. Estimates of maternal genetic effects were low and ranged from 0.00 to 0.02 for all traits and all breeds. Estimates of permanent environmental effects ranged from 0.03 to 0.08. Estimates of service sire effects ranged from 0.02 to 0.05. A bivariate analysis was used to estimate the genetic correlations among traits. Average genetic correlations over the four breeds were 0.13, 0.15, and 0.71 for NBA with L21WT, NBA with NW, and L21WT with NW, respectively. Average genetic trends were 0.018 pigs/yr, 0.114 kg/yr, and 0.004 pigs/yr for NBA, L21WT, and NW, respectively. Although estimates of heritabilities for litter traits were low and similar across breeds, genetic variances for litter traits were sufficiently large to indicate that litter traits could be improved through selection. This study presents the first set of breed-specific estimates of genetic parameters available from large numbers of field records. It provides information for use in national genetic evaluations.

Genetic parameter estimates from joint evaluation of purebreds and crossbreds in swine using the crossbred model.

Records on lifetime daily gain and backfat from two purebred lines A (n = 6,022), B (n = 24,170), and their reciprocal crosses C (n = 6,135) were used to estimate genetic parameters using within-line and terminal-cross models. The models that were fitted included fixed (contemporary group and sex), random additive A and(or) random additive B, random dominance, and random litter effects. Model for purebreds included only one additive effect, whereas the model for crossbreds included two additive effects. End weight was included as a covariable for backfat. Heritability estimates for lifetime daily gain were 0.26, 0.28, and 0.23 with within-line models for lines A, B, and C, respectively, and 0.26, 0.30, and 0.27 with the crossbred model, respectively. Heritability estimates for backfat were 0.52, 0.35, and 0.29 with within-line models for lines A, B, and C, respectively, and 0.51, 0.38, and 0.29 with the crossbred model, respectively. The genetic correlations between purebreds and crossbreds (r(pc)) for lifetime daily gain were 0.99 (A-C) and 0.62 (B-C); for backfat the correlations were 0.32 (A-C) and 0.70 (B-C). The amount of dominance variance from the crossbred model expressed as a proportion of phenotypic variance for lifetime daily gain was 0.39, 0.16, and 0.29 for lines A, B, and C respectively. Dominance variance for backfat was estimated as 0. A joint evaluation of purebreds and crossbreds would be most efficient with the crossbred model. The dominance variation should be accounted for lifetime daily gain.

Genetic parameters for pork carcass components.

Data from 456 homozygous halothane normal purebred Yorkshire, Duroc, and Other-breed pigs from two national progeny testing and genetic evaluation programs were utilized to estimate genetic parameters for carcass components in pigs. Carcass components were cut and weighed according to Institutional Meat Purchase Specifications. Primal cut weights evaluated included 401 Ham (HAM), 410 Loin (LOIN), 405 Picnic shoulder (PIC), 406 Boston Butt (BB), and 409 Belly (BELLY). Individual muscle weights included the inside (INS), outside (OUT), and knuckle (KNU) muscles of the ham, the longissimus dorsi (LD) and psoas major (TEND) of the loin, and the boneless components of both the Boston Butt (BBUTT) and picnic (BPIC). Muscle weights from each primal were summed to yield a boneless subprimal weight (BHAM, BLOIN, BSHLDR), and all boneless subprimals were summed to yield total primal boneless lean (LEAN). Heritability estimates for HAM, LOIN, and BELLY were 0.57, 0.51, and 0.51, respectively. Heritability estimates for BB and PIC were 0.09 and 0.21, respectively. Heritability estimates for the boneless components of each primal were higher than those for the intact primals. Genetic correlations for HAM, LOIN, and PIC with loin muscle area (LMA) were 0.53, 0.78, and 0.70, respectively, and-0.62, -0.51, and -0.60, respectively, with 10th rib off-midline backfat (BF10). Boneless subprimal components were highly correlated with LEAN. Gilts had heavier weights (P < 0.01) than barrows for all boneless subprimals, individual muscles, LEAN, and for all primal cuts except BELLY. Gilts also had less BF10 and more LMA (P < 0.01) than barrows. Duroc pigs had a heavier (P < 0.01) weight for HAM and PIC when compared to Yorkshires. Yorkshire pigs had more (P < 0.01) LOIN weight than did the Durocs. Results suggest primal, boneless subprimal, and individual muscle weights in pigs should respond favorably to selection.

Joint evaluation of purebreds and crossbreds in swine.

Data from two purebred swine lines A (n = 6,022) and B (n = 24,170), and their reciprocal, cross C (n = 6,135), were used to examine gains in reliability of combined purebred and crossbred evaluation over conventional within-line evaluations using crossbred and pureline models. Random effects in the pureline model included additive, parental dominance, and litter. In the crossbred model, effects were as in the pureline model except traits of each line were treated as separate traits and two additive effects were present. The approximate model was the same as the pureline except it was used for all lines disregarding breed differences. The traits in the evaluation were lifetime daily gain (LDG) and backfat. When separate line evaluations were replaced by evaluations with crossbreds, mean reliabilities of predicted breeding values increased by 2 to 9% for purebreds and by 21 to 72% for crossbreds. Rank correlations between these breeding values were > 0.99 for purebreds but 0.85 to 0.87 for crossbreds. Rank correlations between predicted breeding values obtained from crossbred and approximate models were 0.98 to 0.99 for purebreds and 0.96 to 0.98 for crossbreds. When the number of crossbreds was small in comparison to purebreds, the increase in reliability by using the crossbred data and the crossbred model as opposed to purebred models was small for purebreds but large for crossbreds. The approximate model provided very similar rankings to the crossbred model for purebreds but rankings were less consistent for crossbreds.

Evaluation of strategies for selection for lean growth rate in pigs.

Lean growth rate (LGR) in pigs is a nonlinear biological function of growth rate and lean quantity. According to animal breeding theory, genetic progress for LGR is maximized with selection on a linear index of its component traits, but selection on direct EBV for LGR is also common. In this study, the performance of five criteria for selection on estimated LGR in pigs was evaluated through simulation over five generations: linear indexes of multiple-trait EBV of component traits with or without updating index weights in each generation; a nonlinear index of multiple-trait EBV of component traits; and direct selection on EBV for LGR from a single-trait model or a multiple-trait model that included LGR and component traits. The nonlinear index yielded the highest response in LGR in Generation 5, but the linear index with updating performed almost as well. Not updating weights for the linear index reduced response in LGR by 1.1% in Generation 5 (P < 0.05). Direct selection on single-trait EBV for LGR yielded the lowest responses in Generation 5. Direct selection on EBV for LGR from a multiple-trait animal model yielded a 3.1% greater response in LGR in Generation 5 than direct selection on EBV for LGR based on a single-trait animal model (P < 0.05), but yielded a 1.9% lower response than the nonlinear index. Although differences in response in LGR were limited, alternative selection criteria resulted in substantially different responses in component traits. Linear index selection for LGR placed more emphasis on lean quantity, whereas direct selection for LGR emphasized growth rate. Based on the relative changes in the responses in LGR, selection for estimated LGR based on a nonlinear index or a linear index with updating is recommended for use in the swine industry.

Estimation of dominance variance in purebred Yorkshire swine.

We used 179,485 Yorkshire reproductive and 239,354 Yorkshire growth records to estimate additive and dominance variances by Method Fraktur R. Estimates were obtained for number born alive (NBA), 21-d litter weight (LWT), days to 104.5 kg (DAYS), and backfat at 104.5 kg (BF). The single-trait models for NBA and LWT included the fixed effects of contemporary group and regression on inbreeding percentage and the random effects mate within contemporary group, animal permanent environment, animal additive, and parental dominance. The single-trait models for DAYS and BF included the fixed effects of contemporary group, sex, and regression on inbreeding percentage and the random effects litter of birth, dam permanent environment, animal additive, and parental dominance. Final estimates were obtained from six samples for each trait. Regression coefficients for 10% inbreeding were found to be -.23 for NBA, -.52 kg for LWT, 2.1 d for DAYS, and 0 mm for BF. Estimates of additive and dominance variances expressed as a percentage of phenotypic variances were, respectively, 8.8 +/- .5 and 2.2 +/- .7 for NBA, 8.1 +/- 1.1 and 6.3 +/- .9 for LWT, 33.2 +/- .4 and 10.3 +/- 1.5 for DAYS, and 43.6 +/- .9 and 4.8 +/- .7 for BF. The ratio of dominance to additive variances ranged from .78 to .11.

Effect of level, source and duration of feeding of supplemental energy in sow diets of metabolic and hormonal traits related to energy utilization in the baby pig.

In each of two trials, 30 sows were assigned to six energy-supplemented diets for 5 (trial 1) or 35 d (trial 2) before farrowing, and the effects on sow milk and pig survival characteristics were examined. Treatments consisted of 1.6 kg/d of a basal diet plus .09, .18 or .27 kg of animal fat/d or .20, .39 or .58 kg of cornstarch/d. Two pigs were killed at birth after blood samples were taken and before suckling. Two pigs per litter were fasted to 24 h and two to 48 h of age. Blood glucose was increased (P less than .05) at birth in pigs from sows fed fat in the 35-d feeding, whereas blood glucose was not different in pigs in the short-term feeding of diets Beta-hydroxybutyrate was highest in blood from pigs in the fat-fed groups after a 48-h fast, which was an indication of increased fat metabolism. Beta-hydroxybutyrate was also higher (P less than .05) after a 24 h fast in livers of pigs from sows fed the highest level of fat in both trials than in livers of pigs from sows fed the same level of cornstarch. There were also treatment differences (P less than .05) in liver glycogen content, oxidation of palmitate to CO2, oxidation of glucose to CO2, number of pigs born dead, birth weight and colostrum total lipids and energy content. No treatment-related differences in levels of FFA, triiodothyronine, thyroxine or glucagon in blood of the offspring were observed.

A comparison of methods for ranking boars from different central test stations.

Data were received from 24 test stations on 3,999 boars tested in fall 1984 and spring 1985. In an effort to increase the connectedness between stations, one reference sire was selected to produce sons (reference boars) through artificial insemination to be tested in the different stations. Fifty-two reference boars were placed across 17 of the test stations. The performance traits analyzed were average daily gain (ADG) and backfat adjusted to 105 kg (ABF). The methods used to rank boars were: 1) individual record (ADG, ABF), 2) individual record deviated from the contemporary group mean, and 3/4) individual record plus performance of relatives (including/excluding reference boars) using expected progeny differences (EPD) estimated from a reduced animal model (RAM) statistical procedure. Ranks of boars using these four methods of genetic evaluation were compared using Spearman rank correlation methodology. The ranks of the boars changed significantly as the complexity of analysis increased for both ADG and ABF. Rank correlations between individual record and contemporary group deviations for ADG and BF were .47 and .20, respectively. Rank correlations between contemporary group deviations and RAM estimates of EPD for ADG and ABF were .53 and .41, respectively. These were significantly different from 1.0. However, there was no significant difference between rankings based on EPD including vs excluding the reference boars. The importance of rank changes coupled with the increased accuracy of these more complex evaluation methods strongly suggest that best linear unbiased predictors of genetic value be utilized in comparing boars in central test stations.

Breed-specific adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine.

Number born alive (NBA) and litter weaning weight (LWT) can be influenced by many factors, including environment, parity, age at farrowing, lactation length, and genetic merit as well as number of pigs after transfer (NAT) and weaning age (WNAGE) for LWT. The objectives of this study were to estimate adjustment factors for NBA and LWT using all effects in the model and to refine parity effects by including age of the sow in parity 1 (P1) and parity 2 (P2). The models used included fixed effects of contemporary groups and parity/age class, random direct genetic and permanent environment effects, as well as the fixed effects of NAT and WNAGE for LWT. A large effect due to age of the sow at breeding within P1 and P2 was found and new adjustments were found to differ from previous studies. In the Yorkshire population, for example, the average P1 adjustment was 1.0 pig in this study, compared to the current .69; however, this ranges from 1.46 for the youngest P1 females to .57 for the oldest. Similarly, in P2 the average adjustment was found to be .50, with an adjustment of .99 for the youngest P2 and 0 for the oldest. Also, age of dam was found to contribute variation to P1 litter records for LWT. A residual analysis showed nonsignificant differences (P > .60) across the age classes after using the new adjustments; however, significant differences (P < .01) remained after using the current adjustments.

Estimation of direct and maternal heritability and genetic correlation for backfat and growth rate in swine using data from centrally tested Yorkshire boars.

The purpose of this study was to estimate components of variance and covariance for backfat and growth rate in swine tested in central test stations in the United States. Data were collected from 26 central boar test stations from 1984 through 1990. The traits analyzed were backfat adjusted to a 104.5-kg basis and ADG adjusted to a 36-kg on-test weight. Records from 7,951 purebred Yorkshire boars were analyzed. Contemporary groups were defined as boars of a breed that were tested and sold as a common group in a test station. Variance components were estimated using a pseudo-expectation method with a multiple-trait, sire-maternal grandsire model. Direct heritabilities for backfat and ADG were estimated to be .56 and .24, respectively. Direct maternal effects were significant for both backfat and ADG; they accounted for 11 and 23% of the variance, respectively. The additive genetic correlation between backfat and ADG was approximately zero. Within this population of centrally tested Yorkshire boars, heritability seems to be high for backfat and moderate for ADG, with a significant maternal effect on each trait.

Serum concentrations of pituitary and adrenal hormones in female pigs exposed to two photoperiods.

Serum concentrations of pituitary and adrenal hormones were determined in lactating sows and ovariectomized (OVX) gilts exposed to 8 h (8L:16D) or 16 h of light (16L:8D). In addition serum prolactin (PRL) concentrations were determined after a thyrotropin releasing hormone (TRH) challenge. At 103 +/- 2 d of gestation or 3 wk after ovariectomy of nulliparous gilts on d 7 to 9 of the estrous cycle (d - 10), blood samples were collected from jugular vein cannulae at 30-min intervals for 8 h beginning at 0800 h. Immediately after the last sample, 13 sows and five OVX gilts were assigned to 8L:16D and 14 sows and five OVX gilts were assigned to 16L:8D/d and placed in two identical chambers in the farrowing house. Blood sampling was repeated on d 7, 14 and 21 of lactation in the sows and on d 7, 14, 21 and 28 in the OVX gilts. In Exp. 1, serum cortisol (C) concentrations were similar for sows exposed to 8L:16D (n = 7) and 16L:8D (n = 6) treatments, whereas in Exp. 2, serum C concentrations for sows exposed to 8L:16D (n = 6) were lower than those exposed to 16L:8D (n = 6) on d 7, 14 and 21. Photoperiod failed to influence serum concentrations of PRL, luteinizing hormone (LH) and growth hormone in the lactating sows or PRL in the OVX gilts. Photoperiod also failed to affect mean basal serum concentrations, peak height and peak frequency for PRL and LH in the lactating sows or for PRL in the OVX gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

The National Pork Producers Council Maternal Line National Genetic Evaluation Program: a comparison of six maternal genetic lines for female productivity measures over four parities.

Litter (n = 8,424) and female performance records were collected in two breed-to-wean production units in order to evaluate genetic line differences for sow longevity and maternal performance over four parities. Lines evaluated were American Diamond Genetics, Danbred North America, Dekalb-Monsanto DK44, Dekalb-Monsanto GPK347, Newsham Hybrids, and National Swine Registry. Females within a line were derived from a minimum of 65 sires, 197 dams (three dams per sire), and a maximum of three daughters per dam, except in the GPK347, which were produced using semen from 12 Nebraska Index boars mated with Dekalb-Monsanto Line 34 females. All lines expressed 100% maternal heterosis. Mixed model statistical procedures were used with fixed effects including genetic line, parity, production unit, and two-way interactions. Random effects included a contemporary week of production and female for repeated records. Lactation length (average 15 d) was included as a linear covariate where appropriate. In total, 3,599 females entered as early-weaned pigs, 3,283 entered the breeding herd, 2,592 farrowed at least a single litter, and 1,656 and completed four parities. Line (P < 0.001) and parity (P < 0.001) effects were observed for virtually all traits measured. Ranges of genetic line differences averaged across parities were 1.76 pigs for total born, 1.45 pigs born alive, and 0.31 stillborn pigs per litter. Ranges of line differences in total and live litter weight were 1.4 and 1.3 kg, respectively. Ranges among lines, within Parities 1 through 4, for litter size at weaning were 0.56, 1.08, 0.91, and 0.64 pigs per litter, respectively. Line differences for weight (33.8 kg) and backfat depth (6.4 mm) at farrowing, lactation feed intake (8.7 kg), weight loss (5.0 kg), and backfat loss (0.87 mm) were observed. Extended wean-to-estrus interval was related to variation in weight, feed intake, and backfat loss in all lines except the GPK347. The GPK347 females farrowed and weaned the largest number of pigs, ate less feed in lactation, and lost more backfat and weight during lactation, yet they had the largest litters and the shortest wean-to-estrus intervals. Line x parity interactions existed for many traits due to small rank changes, but in general, the high- and low-ranked lines did not change. Genetic line differences in reproductive efficiency through four parities exist and must be recognized when choosing a female line.

Evaluation of procedures to predict fat-free lean in swine carcasses.

The objectives were to develop equations for predicting fat-free lean in swine carcasses and to estimate the prediction bias that was due to genetic group, sex, and dietary lysine level. Barrows and gilts (n = 1,024) from four projects conducted by the National Pork Board were evaluated by six procedures, and their carcass fat-free lean was determined. Pigs of 16 genetic groups were fed within weight groups one of four dietary regimens that differed by 0.45% in lysine content and slaughtered at weights between 89 and 163 kg. Variables in equations included carcass weight and measures of backfat depth and LM. Fat-free lean was predicted from measures of fat and muscle depth measured with the Fat-O-Meater (FOM), Automated Ultrasonic System (AUS), and Ultrafom (UFOM) instruments, carcass 10th-rib backfat and LM area (C10R), carcass last-rib backfat (CLR), and live animal scan of backfat depth and LM area with an Aloka 500 instrument (SCAN). Equations for C10R (residual standard deviation, RSD = 2.93 kg) and SCAN (RSD = 3.06 kg) were the most precise. The RSD for AUS, FOM, and UFOM equations were 3.46, 3.57, and 3.62 kg, respectively. The least precise equation was CLR, for which the RSD was 4.04 kg. All procedures produced biased predictions for some genetic groups (P < 0.01). Fat-free lean tended to be overestimated in fatter groups and underestimated in leaner ones. The CLR, FOM, and AUS procedures overestimated fat-free lean in barrows and underestimated it in gilts (P < 0.01), but other procedures were not biased by sex. Bias due to dietary lysine level was assessed for the C10R, CLR, FOM, and SCAN procedures, and fat-free lean in pigs fed the lowlysine dietary regimen was overestimated by CLR, FOM, and SCAN (P < 0.05). Positive regressions of residuals (measured fat-free lean minus predicted fat-free lean) on measured fat-free lean were found for each procedure, ranging from 0.204+/-0.013 kg/kg for C10R to 0.605+/-0.049 kg/kg for UFOM, indicating that all procedures overestimated fat-free lean in fat pigs and underestimated it in lean pigs. The pigs evaluated represent the range of variation in pigs delivered to packing plants, and thus the prediction equations should have broad application within the industry. Buying systems that base fat-free lean predictions on measures of carcass fat depth and muscle depth or area will overvalue fat pigs and undervalue lean pigs.