Impact of lactation length and piglet weaning weight on long-term growth and viability of progeny.

A total of 1,034 pigs produced by breeding PIC sows to 2 different PIC terminal sires were used to create 3 distinct weaning weight populations so that postweaning growth to 125 kg could be studied. The rearing strategies resulted in BW that ranged from 4.1 to 11.5 kg by 20 d of age. Sows and corresponding litters were allocated to 3 treatments: sow reared (SR; n = 367) for 20 d, sow reared for 14 d (14W; n = 330), and sow reared for 2 d (2W; n = 337). Sows were removed from 2W and 14W groups, but progeny remained in the crates and received milk replacer ad libitum (for 18 and 6 d, respectively) until the contemporary SR pigs were weaned at 20 d of age. The SR pigs (6.49 +/- 0.15 kg) weighed 1.01 kg less than 14W pigs (7.5 +/- 0.14 kg) and 2.26 kg less than 2W pigs (8.75 +/- 0.14 kg; P < 0.05). The 14W pigs weighed 1.25 kg less than 2W pigs (P < 0.05). Nursery ADG for the 2W group (547 g/d) was 35 g/d less (P < 0.05) than 14W pigs. The 14W pigs (165 d) required 3 fewer (P < 0.05) days to reach 125 kg of BW compared with SR pigs. The SR and 14W pigs gained BW 24 and 20 g/d faster (P < 0.05) in the postnursery period when compared with 2W pigs. The SR and 2W pigs consumed 0.10 and 0.12 kg/d less (P < 0.05) during this period when compared with 14W pigs (2.32 kg/d). Gain:feed of SR was improved (P < 0.05) when compared with the 14W and 2W pigs over 167 d of age (0.44 vs. 0.42 and 0.42, respectively). Lean percentage was 0.7% greater (P < 0.05) in carcasses from SR pigs (55.0%) compared with carcasses from 2W pigs (54.3%) when adjusted to a constant HCW. A study of the effect of weaning weight on days to 125 kg was limited to SR and 14W groups because maternal deprivation compromised the 2W group postweaning growth. Six weaning-weight groups were defined using a normal distribution: 4.6, 5.5, 6.4, 7.3, 8.2, and 9.5 kg. Pigs weighing 5.5 kg at 20 d of age were able to reach 125 kg 8 d sooner (168.8 d) than those weighing 4.6 kg (176.8 d). There was a linear relationship (P < 0.05) between weaning weight and ADG in the postnursery phase of growth. We conclude that 1) a weaning weight of less than 5.0 kg imposes the greatest marginal loss in production output for a 20-d weaning and 2) lactation length influences long-term growth, composition of growth, and viability of progeny.

Selection for lean growth efficiency in Duroc pigs influences pork quality.

A unique line of Duroc pigs was established by intensive selection for increased lean growth efficiency. The objective of this study was to determine the influence of this selection strategy on fresh pork quality traits. Two lines of Duroc pigs originating from the same foundation herd were evaluated. One line was selected for lean growth efficiency over five generations (Select line), and the other was a contemporary line maintained from the foundation herd (Control line). All pigs in the trial tested negative for the halothane gene. Selection for lean growth efficiency resulted in improved lean gain, carcass lean, increased loin eye area, and less overall carcass fat. The Select line had significantly lower subjective firmness scores in longissimus and significantly greater amounts of moisture and protein lost as measurable drip in longissimus, semimembranosus, and semitendinosus. There were no differences in subjective color scores or in Hunter L, a, and b values between lines. No selection line differences were observed in glycolytic potential or ultimate pH. The longissimus and the semitendinosus exhibited significantly lower early postmortem pH values in Select line pigs. Warner-Bratzler shear values were higher for Select line longissimus chops. Degradation of troponin-T was decreased in the Select line longissimus samples. This result suggests that reduced degradation of myofibrillar proteins may be associated with increased moisture and protein lost during storage. This research points out that elimination of the halothane gene will solve some but not all of the genetically influenced pork quality problems faced by the industry. The Select line of pigs appears to be more prone to producing pork that is soft and exudative, indicating a link between soft and exudative pork and some genetic selection strategies may exist. Therefore, it appears that selection for some economically important traits, such as feed efficiency or increased lean growth in the absence of the halothane gene, may compromise pork quality.

ARPP-16 mRNA is up-regulated in the longissimus muscle of pigs possessing an elevated growth rate.

Selection for increased growth rate in farm and laboratory animals has been used to develop lines with increased body and muscle weights. However, very little is known about the underlying molecular pathways and how their constitutive genes influence this process. In this study, the differential display-reverse transcription PCR (DDRT-PCR) method was employed to identify longissimus muscle genes that are differentially expressed between a line of pigs selected for increased 200-d weight and a randomly selected control line. A 590-bp DDRT-PCR cDNA product was identified and isolated based on its greater abundance in the longissimus muscle of the select line relative to the control line animals. This DDRT-PCR product has 89% identity to the end of the 3'-untranslated region of the bovine 16-kDa cAMP-regulated phosphoprotein (ARPP-16) cDNA sequence. Reverse transcription PCR (RT-PCR) amplification of the porcine homologue of ARPP-16 and subsequent sequencing established that the DDRT-PCR product corresponds to the 3'-end of the porcine ARPP-16 transcript. Semiquantitative RT-PCR verified that ARPP-16 is up-regulated in the select line and determined that the relative expression level of ARPP16 mRNA is approximately fourfold higher (P < .01) in the select than in the control animals. The deduced amino acid sequence of ARPP-16 is highly homologous to the deduced amino acid sequences of bovine, human, and rat ARPP-16, and RT-PCR with ARPP-16-specific PCR primers indicated that this gene is expressed in many different porcine tissues. The porcine homologue of the 19-kDa cAMP-regulated phosphoprotein (ARPP-19) was also amplified by RT-PCR, cloned, and sequenced. The deduced amino acid sequence of ARPP19 differs from ARPP-16 only by the addition of 16 N-terminal amino acids. In all tissues studied, ARPP-19 mRNA was detected by RT-PCR amplification; however, the relative expression level of ARPP-19 mRNA was not differentially expressed between the select and control line animals (P > .05). The fourfold relative increase in ARPP-16 mRNA expression in the select line animals indicates that this gene may play an important role in the molecular pathway(s) that regulate postnatal skeletal muscle growth in the pig.

Heterosis losses resulting from incorrect matings in a three-breed rotational crossbreeding system in pigs.

Losses in individual heterosis were estimated using performance records from 11,700 pigs, 959 litters, and 377 pens of pigs from a three-breed rotational crossbreeding system. Three types of rotational crossbred sows were produced using the Duroc, Landrace, and Yorkshire breeds. Twenty-nine Duroc, 27 Landrace, and 25 Yorkshire boars were mated to 275 sows to produce pigs with theoretical levels of breed heterozygosity of 85.7, 71.4, or 42.9% depending on the genetic composition of the sows and boars. Orthogonal polynomials for unequally spaced levels were used to partition sum of squares for individual heterozygosity into linear and quadratic responses. There was a linear decline in 56-d litter weight (-.222 kg; P < .01) for each 1% decrease in heterozygosity. Responses for pig weight at 56 d (-.02 kg; P < .001) and age at 105 kg (.12 d; P < .001) were linear for each 1% decrease in heterozygosity. Likewise, post-weaning average daily gain ( -.0004 kg/d; P < .05) and feed conversion (-.0001; P < .01) responses were linear for each 1% decrease in heterozygosity. There were linear responses for survival rates of pigs born alive to 21 d (-.089%; P < .01), alive from 21 to 56 d (-.025%; P < .05), alive from 56 d and to 105 kg (-.042%; P < .05), and from birth to 105 kg (excluding stillborn pigs) (-.129%; P < .001) for every 1% decline in heterozygosity from 85.7 to 42.9%, respectively. Quadratic responses were not important for any of the traits examined (P > .05). Decreased productivity, resulting from decreased heterozygosity, can be expected when three-breed rotational crossbred sows are mated to boars from the wrong breed.

Maternal treatment with somatotropin alters embryonic development and early postnatal growth of pigs.

A possible management strategy to alter fetal development and enhance sow productivity and progeny performance was examined by maternal administration of porcine somatotropin during early gestation. Eighteen crossbred gilts were bred naturally to boars of similar genetics, and pregnancy was confirmed between Days 21 and 24 of gestation by ultrasound. All animals were allowed ad libitum consumption of a 16% CP gestation diet through Day 21 of gestation and 3.0 kg/d for the remainder of gestation. Gilts were injected twice daily with 0 (n = 10) or 15 micrograms/kg body weight (BW) (n = 10; total, 30 micrograms/kg BW per d) pituitary-derived porcine somatotropin (pST) during Days 28 to 40 of gestation. Data were collected postmortem during embryonic, neonatal, and market-weight phases. At 41 d of gestation, pST treatment increased embryonic survival (87.9 versus 77.0%; P < 0.05) and embryo crown rump lengths (77.96 versus 65.14 mm; P < 0.01), but embryo weight was not altered (10.15 and 9.03 g; P > 0.10). Pigs from pST-treated gilts had increased (P < 0.01) crown rump lengths at birth (31.5 versus 30.4 cm) and 21 d (50.9 versus 48.4 cm). However, no differences were observed in birth or 21-d weights as a result of pST treatment (P > 0.10). Neonatal carcasses of progeny (20 kg BW) from the pST-treated gilts had heavier semitendinosus muscles (76.1 versus 66.0 g; P < 0.10), larger longissimus muscle cross-sectional area (10.1 versus 8.2 cm2; P < 0.05), longer sides (51.2 versus 47.9 cm; P < 0.001), and decreased 10th rib backfat (6.67 versus 8.64 mm; P < 0.001) compared with those of controls. Carcasses of market-weight progeny (100 kg BW) from pST-treated gilts had larger longissimus muscle cross-sectional area (P < 0.10), heavier trimmed loins (P < 0.10), and longer carcass sides (P < 0.05). Data are supportive of a hypothesis that mechanisms during early embryonic development are sensitive to manipulation through selected management strategies of the sow and that modifications of this strategy may serve as a model for the examination of molecular and cellular events controlling early embryonic growth.

An experimental comparison of equivalent terminal and rotational crossbreeding systems in swine: pig performance.

Eleven thousand forty-nine pigs produced from 934 litters using 262 rotational and F1 crossbred sows were used to study differences in pig weights, survival rates and pen average daily gain, daily feed intake, and feed conversion between pigs from equivalent three-breed rotational and three-breed terminal crossbreeding systems using Duroc, Yorkshire, and Landrace breeds. Pig weights at birth and 21 and 56 d and days to reach 100 kg did not differ (P > .10) between the terminal and rotational crossbreeding systems. However, ultrasound backfat thickness of pigs from the terminal crossbreeding system was .04 cm greater (P < .007) than that of pigs from the rotational crossbreeding system. Survival rate from 56 d to 100 kg was .8% greater (P < .01) for pigs from the terminal crossbreeding system than for those from the rotational crossbreeding system. The crossbreeding system had no effect (P > .10) on survival rate at birth, from birth to 21 d, from 21 to 56 d, or from birth to 100 kg. Differences between the two crossbreeding systems were nonsignificant (P > .20) for pen average daily gain, daily feed intake, and feed conversion. Breed composition of pigs was an important source of variation (P < .01) for pig weights at birth and at 56 d. Similarly, breed composition of the pig also affected ultrasound backfat thickness at 100 kg (P < .01), but not days required to reach 100 kg (P > .10). For survival traits, only survival rate from 56 d to 100 kg was influenced by breed composition of the pig.(ABSTRACT TRUNCATED AT 250 WORDS)

An experimental comparison of equivalent terminal and rotational crossbreeding systems in swine: sow and litter performance.

Two hundred sixty-two rotational and F1 sows were mated to Duroc, Yorkshire, or Landrace boars to study performance differences between equivalent three-breed rotational and three-breed terminal crossbreeding systems. Matings were made to maximize heterosis. The sows were fed either 1.8 or 2.7 kg/d (2.25 and 3.15 kg/d in winter months) during gestation. These matings produced 934 litters to determine the effect of crossbreeding system, breed composition within crossbreeding system, and gestation feeding level on litter sizes and weights, sow weight and backfat thickness at weaning, daily feed intake of the sow during lactation, interval from weaning to estrus, and farrowing rate. Feeding level during gestation was not an important source of variation for any of the traits except litter birth weight and daily feed intake of the sow during lactation. Litter size marketed was .37 pigs/litter greater (P < .05) for the terminal-cross sows than those sows from the rotational crossbreeding system. Litter weights at birth and 56 d were .8 and 6.5 kg heavier (P < .02, .03), respectively, for the terminal crossbreeding system than for the rotational crossbreeding system. Sow weight and backfat thickness at weaning, daily feed intake during lactation, and farrowing rate were not affected (P > .10) by crossbreeding system. Weaning-to-estrus interval was 1.3 d shorter (P < .03) for sows in the terminal crossbreeding system than for those in the rotational system.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlated responses in reproductive and carcass traits to selection for 200-day weight in Landrace pigs.

Correlated responses in reproductive and carcass traits from a line of Landrace pigs selected for increased 200-d weight along with a randomly selected control line were studied in 195 litters (109 select, 86 control) and 285 pigs (132 select, 153 control). Reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weights at birth and at 21 d. Carcass traits studied were carcass length, longissimus area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean growth. Total weighted cumulative selection differential for 200-d weight over six generations was 88.7 kg. The realized heritability for 200-d weight was .26 +/- .08, and the change in 200-d weight was 4.2 +/- 1.3 kg per generation. None of the regression coefficients for reproductive traits differed significantly from zero. Ham weight, belly weight, marbling score, and lean growth increased by .069 +/- .027 kg, .051 +/- .020 kg, .045 +/- .012 points, and .0042 +/- .0007 kg/d, respectively, per generation. Specific gravity decreased by -.00063 +/- .00023 per generation in response to the selection for 200-d weight. The increase in lean growth in the select line was the result of an increased growth rate and not from an improvement in percentage of lean in carcasses from pigs from the select line.

Correlated responses in reproductive and carcass traits to selection for 200-day weight in Duroc swine.

Correlated responses in reproductive and carcass traits from a line of Duroc pigs selected for increased 200-d weight along with a randomly selected control line were studied in 189 litters (116 select, 73 control) and 191 pigs (106 select, 85 control), respectively. Reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle and lean gain per day. Total weighted cumulative selection differential for 200-d weight was 81.7 kg. The realized heritability for 200-d weight was .18 +/- .08, and the change in 200-d weight was 2.5 +/- 1.2 kg per generation. The regression coefficient of litter size born on generation was -.29 +/- .12 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Average backfat thickness, 10th rib backfat thickness, and belly weight increased by .093 +/- .016 cm, .122 +/- .029 cm, and .089 +/- .040 kg, respectively, per generation. Specific gravity, ham weight, shoulder weight, color score, and percentage of muscle decreased -.00086 +/- .00024, -.165 +/- .013 kg, -.104 +/- .011 kg, -.035 +/- .015 points, and -.47 +/- .12%, respectively, per generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlated responses in reproductive and carcass traits to selection for 70-day weight in Landrace swine.

Correlated responses in reproductive and carcass traits were studied in 181 litters and 218 pigs from a line of Landrace pigs selected six generations for increased weight at 70 d of age and a contemporaneous, randomly selected control line. The reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean gain per day. Total weighted cumulative selection differential for 70-d weight was 30.2 kg. The realized heritability for 70-d weight was .13 +/- .06, and the change in 70-d weight was .65 +/- .29 kg per generation. The regression coefficient of litter size at 21 d on generation was .24 +/- .10 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Carcass length, specific gravity, and ham weight decreased (P less than .10) -.075 +/- .036 cm, -.00054 +/- .00027, and -.102 +/- .048 kg, respectively, per generation. Color score and lean gain per day increased .046 +/- .021 points and .0032 +/- .0013 kg/d, respectively, each generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of mass selection for increased weight at two ages on growth rate and carcass composition of Duroc-Landrace pigs.

Duroc boars from a line previously selected over five generations for 200-d weight and those from a randomly selected control line were mated to Landrace sows either from a line previously selected for increased 70-d weight or from a randomly selected pedigree control line. From these matings, 900 pigs were farrowed to examine the effects of crossing lines of pigs mass selected for weight at two ages on growth rate, survival, and carcass composition. A greater (P less than .01) percentage of pigs farrowed survived birth from control-line sows (.974) than from select-line sows (.914). Of those pigs born alive, a greater (P less than .05) percentage of pigs out of control-line sows survived to 21 d (.893) than out of select-line sows (.829). Pigs sired by select-line boars weighed 2.1 kg heavier (P less than .05) at 70 d than pigs sired by control-line boars. Pigs out of select-line sows weighed .11 kg less (P less than .10) at birth and .3 kg less (P less than .10) at 21 d of age but grew .026 kg/d faster (P less than .10) from 70 d to slaughter, weighed 3.9 kg more at 165 d of age (P less than .05), and reached 100 kg 7.0 d sooner (P less than .05) than pigs out of control-line sows. Carcasses from barrows sired by select-line boars had .29 cm more (P less than .10) fat at the 10th-rib than carcasses from barrows sired by control-line boars. Marbling scores were .31 unit greater (P less than .05) and muscle color scores were .25 unit greater (P less than .10) for carcasses from pigs out of select-line sows than for carcasses from pigs out of control-line sows. Selection for increased 70-d weight decreased age at 100 kg without increasing fat deposition. However, survival rates up to 100 kg were reduced. Mass selection for 200-d weight effectively increased 70-d weight, but fat thickness at 100 kg also increased.

Mass selection for increased 200-day weight in a closed line of Landrace pigs.

Mass selection for increased weight at 200 d of age was conducted for six generations in a line of Landrace pigs. In the select line, the heaviest nine boars and 18 gilts were selected from each generation to produce the subsequent generation. A contemporaneous control line was maintained by randomly selecting a son from each sire and a daughter from each dam to attain a line size of five boars and 10 gilts. Inbreeding coefficients averaged .182 and .191 for the select- and control-line pigs and .150 and .162 for the select- and control-line dams, respectively, in the sixth generation. The 200-d weights and ultrasound backfat thickness data were collected from 1,022 pigs of 2,181 pigs farrowed. These pigs were sired by 92 boars and out of 210 sows. The generation interval was 13 mo. Twelve traits were studied: weights at birth and at 21, 35, 70, 154, and 200 d of age; daily gains from birth to 35 d, 35 to 70 d, 70 to 154 d, and 154 to 200 d; ultrasound backfat thickness at 200 d; and ultrasound backfat thickness adjusted for 200-d weight. Total weighted cumulative selection differential for 200-d weight was 88.7 kg. Realized heritability for 200-d weight was .26 +/- .08 with an average response of 4.2 +/- 1.3 kg/generation. Correlated responses resulted in increases for all weights and daily gains evaluated. Although ultrasound backfat thickness at 200 d increased in the select line compared to the control line, it was not altered by selection for 200-d weight when adjusted for 200-d weight.

Mass selection for increased 200-day weight in a closed line of Duroc pigs.

Mass selection for increased weight at 200 d of age was conducted for six generations in a line of Duroc pigs. A randomly selected contemporary control line was maintained. Our objectives were to observe the response in 200-d weight, to measure correlated responses in weights at earlier ages, daily gains and ultrasound backfat thickness and to compare three methods for estimating responses to selection. Inbreeding coefficients averaged .213 and .202 for the select- and control-line pigs and .200 and .173 for the select- and control-line dams in the sixth generation, respectively. A total of 1,866 pigs were farrowed; 200-d weights were collected on 798 of them. These pigs were sired by 89 boars and were out of 193 sows. Twelve traits were studied: weights at birth and at 21, 35, 70, 154 and 200 d of age, daily gains from birth to 35 d, 35 d to 70 d, 70 d to 154 d and 154 d to 200 d, ultrasound backfat thickness at 200 d and ultrasound backfat thickness adjusted for 200-d weight. Three methods for estimating responses to selection gave similar results; therefore, the estimates were averaged. Total weighted cumulative selection differential for 200-d weight was 81.7 kg with a response in 200-d weight of 2.5 +/- 1.2 kg/generation. This response corresponds to a realized heritability for 200-d weight of .18 +/- .08. Increased weight at 200 d was the result of more rapid growth in the 154- to 200-d period, with decreased growth in the period from birth to 35 d. Growth at other periods was not changed significantly. Ultrasound backfat thickness at 200 d increased in the select line compared to the control line, but not when adjusted for 200-d weight.

Mass selection for increased 70-day weight in a closed line of Landrace pigs.

Mass selection for increased weight at 70 d of age was practiced for six generations in a line of Landrace pigs. It was desired to have the next generation sired by the heaviest nine boars and out of the heaviest 27 gilts. A contemporaneous, randomly selected (by pedigree) control line was maintained in which the next generation was sired by five boars and out of 10 gilts. Inbreeding coefficients were .208 and .214 for the selected and control line litters and .177 and .189 for the selected and control line dams in the sixth generation, respectively. A total of 1,906 pigs was farrowed with 70-d weights collected on 1,267 pigs. These pigs were sired by 88 boars and out of 190 gilts. The generation interval was 13 mo. Six traits were studied: birth, 21-d, 35-d and 70-d weights and preweaning (from birth to 35 d) and postweaning (from 35 to 70 d) daily gains. Direct and correlated responses per generation and per weighted cumulative selection differential (WCSD) were estimated. Total WCSD for 70-d weight was 30.3 kg. This corresponds to a standardized WCSD of 6.11 phenotypic standard deviations. The response per generation for 70-d weight was .65 +/- .29 kg. The realized heritability for 70-d weight was .13 +/- .06. Nearly all the increased weight at 70 d was the result of more rapid growth in the postweaning period, with little difference in growth in the preweaning period; birth, 21-d and 35-d weights and preweaning daily gains remained unchanged by selection for 70-d weight.

Comparisons of specific crosses from Duroc-Landrace, Yorkshire-Landrace and Hampshire-Landrace sows managed in two types of gestation systems: pig performance.

Ten thousand one hundred sixty-nine pigs were farrowed in 844 litters that were produced by mating Duroc (D), Yorkshire (Y) and Hampshire (H) boars to Duroc-Landrace (DL), Yorkshire-Landrace (YL) and Hampshire-Landrace (HL) sows to study the effect of sire breed, dam breeding and gestation environment (pasture lots vs confinement stalls) on pig weights, survival rates and feed efficiency. Pigs sired by H boars were .05 kg heavier at birth than Y-sired pigs and .2 kg heavier at 21 d than Y- and D-sired pigs, but they were .6 kg smaller at 56 d. D-sired pigs grew .028 kg/d faster from 56 d to 100 kg and reached 100 kg approximately 5 d sooner than the Y- and the H-sired pigs. At birth, pigs out of DL sows were .21 kg heavier than pigs out of YL sows. Pigs out of HL sows grew .025 and .021 kg/d slower from 56 d to 100 kg compared with pigs out of DL and YL sows, respectively. Sows in the pasture gestation system produced pigs that were .05 kg heavier at birth than pigs out of sows in gestation stalls. Three-breed-cross pigs were .9 kg heavier at 56 d, grew .039 kg/d faster and took 7.9 fewer days to reach 100 kg than backcross pigs. The H sire breed had lower survival rates of pigs at 21 d and to 100 kg of those born alive (P less than .10), compared with pigs sired by D and Y boars. Pigs out of HL dams had the highest survival rates, whereas pigs out of YL sows had the lowest survival rates at birth, 21 d and at 100 kg. Three-breed-cross pigs averaged .025, .028 and .035 greater survival rates at birth, 21 d and 56 d than backcross pigs. Feed efficiency was most desirable in pens of pigs sired by H and D boars compared with pens of pigs sired by Y boars. However, pens of pigs with YL dams were more efficient than pens of pigs with HL dams.

Comparisons of specific crosses from Yorkshire-Landrace, Chester White-Landrace and Chester White-Yorkshire sows.

One hundred thirty Yorkshire-Landrace (YL), Chester White-Landrace (CL) and Chester White-Yorkshire (CY) F1 crossbred sows were mated randomly to Duroc (D), Hampshire (H), Farmers Hybrid 414 (FH414) or Farmers Hybrid 929 (FH929) boars. These matings produced 321 litters and 3,379 pigs, which were used to determine the effect of sire breeding and dam breeding on preweaning and postweaning performance of the pigs and litters. Litter size born alive, litter size at 56 d, litter weight at 56 d and litter weight per day of age to 100 kg were lower in litters sired by H boars than in those sired by D boars. However, sizes and weights of litters sired by D and H boars were not different from those sired by FH414 and FH929 boars. Litter sizes at birth were larger for litters out of CL and CY sows than those out of YL sows, but significant differences were not found for litter sizes at 21 d, 56 d or at marketing. Pigs sired by H boars were heavier at birth than pigs sired by D boars. Pigs sired by H boars did not differ significantly in weights at 21 and 56 d or in postweaning daily gains or days to 100 kg from pigs sired by D boars. Pigs out of CL dams were heavier at birth, 21 d and 56 d of age than pigs out of CY dams, but did not differ significantly in postweaning gains or in days to 100 kg. Pigs sired by D and H boars had less ultrasonic fat than pigs sired by FH414 and FH929 boars. Pigs sired by FH929 boars were leaner than pigs sired by FH414 boars.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of animal density on endocrine development in gilts.

A study was conducted to determine the effect of social crowding on the development of endocrine organs involved in the reproductive process in growing and finishing gilts. One hundred four littermate gilts weighing approximately 30 kg were randomly assigned to treatment groups of either 8 or 16 pigs/pen. Gilts raised in pens of eight were allotted 1.06 m2 per pig from 30 to 65 kg and 1.25 m2 from 65 to 100 kg; whereas, one-half the area was provided for gilts raised in pens of 16. Littermate gilts raised in pens of 8 and 16 were slaughtered on the same day when the average weight of pigs reached 100 kg. At slaughter, the brain, adrenals, pituitary, uterus and ovaries were removed and weighted. The brain was lyophilyzed and reweighed to yield dry brain weight. Gilts raised in the low-density groups had heavier adrenal (P less than .01), pituitary (P less than .08), brain (P less than .11), dry-brain (P less than .02), uterine (P less than .09) and ovarian (P less than .07) tissues. Furthermore, significantly more gilts in the low-density, compared with the high-density groups, had ovulated at slaughter. In a second study, eight littermate gilts raised in pens of 8 or 16 and weighing approximately 100 kg were moved to individual pens and fitted with a jugular vein catheter. Following blood sample collection at 15-min intervals for 2 h, 200 IU of adrenocorticotropin (ACTH) were infused into the cannula. Blood samples were collected at 15-min intervals for an additional 2 h. There were no differences between basal or ACTH-stimulated concentrations of plasma cortisol between treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of pen density during rearing on subsequent reproductive performance in gilts.

A study involving 109 crossbred gilts of Duroc and Landrace breeding that were reared in equal-sized pens with 8 or 16 pigs/pen was initiated to determine the effects of pen density during rearing on subsequent reproductive and maternal performance. Gilts in pens of eight were allowed 1.06 m2/animal from 30 to 65 kg and 1.25 m2/animal from 65 to 100 kg, whereas those in pens of 16 were allowed only one-half as much floor area per animal. Gilts raised in groups of eight farrowed 1.0 more pigs/litter (P less than .05), and .7 more pigs/litter born alive (P = .15), than gilts reared in groups of 16 pigs/pen. There were no pen-density differences in the number of corpora lutea at 30 d of gestation (P = .33) or in litter birth weight (P = .26). After adjusting by covariance for the number of live pigs at the beginning of the lactation period, gilts from the pen density of 16 had more pigs per litter alive (P less than .01) and heavier litter weights (P less than .05) at 21 d postpartum and higher piglet survival rates to 21 d (P less than .02) than gilts that were reared in the low pen-density of eight pigs/pen. Results of this study indicate that pen density during the growing-finishing period may affect subsequent reproductive and maternal performance of gilts.

Comparisons of specific crosses from Duroc, Hampshire and Spot backcross sows.

One hundred 3/4 Duroc-1/4 Landrace (DDL), 3/4 Hampshire-1/4 Landrace (HHL) and 3/4 Spot-1/4 Landrace (SSL) backcross sows were randomly mated to Yorkshire boars to produce a total of 299 litters and 3,271 pigs to determine the effect of dam breeding on preweaning and postweaning performance of the pigs and litters. Litter sizes born and born alive were not significantly different among the three dam breeds studied. However, litter sizes alive at 21 d out of HHL sows were significantly larger than litter sizes out of SSL sows, while the litter sizes out of DDL sows were intermediate to the other two dam breeds. The DDL sows had significantly heavier litters at birth than did SSL sows, but the dam breeds did not differ in the weights of their litters at 21 and 42 d. Pigs out of DDL sows were heaviest at birth but weighed the least at 21 d, while pigs out of SSL sows were heaviest at 21 and 42 d of age. Pigs out of HHL sows weighed the least at birth and at 42 d. There were no significant differences among the dam breeds in the survival rate of their pigs. In the postweaning period, pigs out of HHL sows were the slowest growing and took the most days to reach 100 kg. Feed conversion and average daily feed consumption did not differ significantly among the three dam breeds studied.

Estimates of additive genetic, maternal and specific combining abilities for some litter traits of swine.

Data from 1,234 purebred and crossbred litters were analyzed with a multiple regression procedure to obtain estimates of breed additive, breed maternal, specific combining ability (SCA) and average maternal heterosis effects for the Duroc (D), Hampshire (H), Landrace (L), Spot (S) and Yorkshire (Y) breeds. The traits studied were: number farrowed (NB), litter birth weight (LBWT), average pig birth weight (BWT), litter size at 21 d (N21), litter weight at 21 d (L21WT) and average pig weight at 21 d (WT21). The three traits measured at birth included stillborn pigs. The data were analyzed with a statistical model that included effects of research farm, sow group within year and farm and the regressions of the dependent variables on the D, H, S and Y breed additive genetic and breed maternal effects, deviated from the L breed. The model also included the regressions of the dependent variables on all possible two-breed heterotic combinations (SCA) and on average maternal heterosis. The breed additive and maternal regression coefficients indicated phenotypic effects of substituting D, H, S and Y genes for L genes. The SCA regression coefficients were the phenotypic effects of individual heterosis increasing from 0 to 100% for each two-breed combination. For the breed additive genetic component of the phenotype, the breeds ranked (from largest to smallest effect) H, Y, L, D, S for NB; Y, L, H, S, D for LBWT and Y, H, L, S, D for BWT. At 21 d, the breeds ranked Y, D, L, S, H for N21; Y, L, H, D, S for L21WT and Y, H, L, S, D for WT21.(ABSTRACT TRUNCATED AT 250 WORDS)