母猪低剂量深部输精技术研究

本研究旨在通过优化输精剂量和输精内管插入深度,为低剂量深部输精技术推广应用提供技术参考。实验一,检测12组不同有效精子数（30亿、15亿、7.5亿、5亿）和输精体积（80、60、40 mL）的低剂量猪精液分别保存12、24、48、72 h后的精子活率,30亿/80 mL为对照组,以寻找不影响保存效果和繁殖性能的最低输精剂量;实验二,评价筛选出的低剂量精液深部输精效果,常规输精30亿/80 mL为对照组,每组输精100头,测定母猪的受胎率、分娩率、产仔数等繁殖性能参数;实验三,测量统计大白、长白、二元不同品种和3胎以下、3胎以上不同胎次母猪深部输精内管插入深度。结果表明：与对照组相比,不同有效精子数和体积的精液在保存12、24、48、72 h后相同时间的精子活率无显著差异;10亿/80 mL、7.5亿/80 mL、15亿/40mL和7.5亿/40mL组低剂量精液保存72h后的精子活率低于保存12h(P<0.05);低剂量深部输精组的受胎率和分娩率与对照组无显著性差异;深部输精15亿/80 mL、15亿/40 mL和7.5亿/40 mL组不影响窝均产仔数（P>0.05）,提高了...     

不同有效精子数的深部输精技术对母猪繁殖性能的影响

文章旨在研究低密度猪精液深部输精操作及其应用技术。设计30亿/80 mL、20亿/80 mL、15亿/80 mL、12亿/80mL4个密度等级来进行相同的深部输精操作,探讨不同精液密度深部输精对母猪受孕率、分娩率和产仔数的影响。结果表明:使用相同剂量不同密度的精液进行人工深部输精,对比分析受孕率、分娩率、窝均总仔数、窝均活仔数;受孕率显示密度20亿/80 mL30亿/80 mL15亿/80 mL12亿/80 mL,但每组间差异均不显著;分娩率显示密度15亿/80 mL12亿/80 mL30亿/80 mL20亿/80 mL,但每组间差异均不显著;窝均总仔数显示20亿/80 mL30亿/80 mL15亿/80 mL12亿/80 mL,每组间差异也均不显著;窝均活仔数显示20亿/80 mL30亿/80 mL15亿/80 mL12亿/80 mL,每组间差异也均不显著。综上,15亿～20亿/80 mL剂量实施深部人工授精可以扩大优秀公猪的覆盖率,提高优秀基因的在商品群的价值。     

不同输精方式及输精剂量和次数对母猪繁殖性能的影响研究

为研究不同输精方式和有效精子数及输精剂量、输精次数对母猪繁殖性能的影响,将每周断奶母猪约60多头随机分成2组,即为对照组和试验组。分别进行了不同输精方式和有效精子数及输精剂量、输精次数的试验,每个试验2个重复(连续2周),并对结果进行比较分析。结果表明:深部输精与常规输精方式的受孕率、配种分娩率、窝均总产仔数、初生窝重等指标差异不显著(P>0.05),深部输精窝均产活仔数14.43头,高于常规输精0.61头,但差异不显著(P>0.05);深部输精15亿/60mL组、10亿/40mL组与常规输精22亿/80 mL组受孕率、窝均总产仔数等指标差异不显著(P>0.05);2次深部输精组和3次深部输精组的受孕率和配种分娩率基本持平,差异不显著(P>0.05);窝均总产仔数、窝均产活仔数、初生窝重等指标2次深部输精组略高于3次深部输精组,但差异均不显著(P>0.05)。综上,深部输精可以有效保证母猪的繁殖成绩,并且可以降低输精剂量(15亿/60mL)和输精次数(2次)。     

采用深部输精与常规输精研究不同剂量和有效精子数对经产母猪繁殖力的影响

为探讨不同输精剂量与不同有效精子数对经产母猪繁殖力的影响,使用深部输精和常规输精作为主要配种方式。将发情母猪随机分为2组,A组为深部输精组(n=60),B组为常规输精组(n=60)。对A、B组内母猪分别用不同的输精剂量(Ⅰ:30亿/80 mL、Ⅱ:15亿/80 mL、Ⅲ:15亿/40 mL;n=20)进行输精。结果表明:与常规输精相比,深部输精组的受胎率和分娩率分别为93.33%和88.33%,略高于常规输精组的86.67%和83.33%,但差异不显著(P>0.05);但深部输精可显著提高经产母猪的产仔数和产活仔数,分别提高1.07头和1.15头。无论是深部输精还是常规输精,15亿/80 mL的输精量,均可获得与30亿/80 mL输精量一致的产仔效果,这一结果可以使优秀种公猪的利用率提高1倍,降低了最新国标《GB23238-2009》中对外种猪输精剂量的要求,建议扩大实验并推广使用。     

不同精子密度对母猪繁殖性能的影响

试验选用广东温氏食品集团养猪公司二元杂母猪(长大和大长)300头,随机分为3组,对照组、试验Ⅰ组、试验Ⅱ组各100头,三组均采用三次人工授精,每次输精量均为80mL,对照组母猪输精的精子密度为0.5亿/mL,试验Ⅰ组0.4亿/mL,试验Ⅱ组0.3亿/mL。试验结果表明,三种精子密度对母猪的配种分娩率、窝均总产仔数和窝均产活仔数影响不大,经显著性检验,相互之间差异均不显著(P>0.05),数据上反映试验Ⅰ组的效果最好,公猪精液采用0.4亿/mL的精子密度在大群生产中最适用,经济效益最好。     

暑热季节采用10 cm适度深部输精与常规输精研究不同剂量和有效精子数对丹系大白母猪繁殖性能的影响

为进一步探讨不同输精剂量和不同有效精子数对经产母猪繁殖性能的影响,推广10 cm适度深部输精技术,于暑热季节在罗牛山南吕原种猪场,以10 cm适度深部输精和常规输精作为主要配种方式,进行降低输精剂量和有效精子数的扩大试验。将发情母猪随机分为深部输精组（n=90）和常规输精组（n=90）。对2组母猪分别用不同的输精剂量（30亿/80 mL;15亿/80 mL;15亿/40 mL;n=30）进行输精。结果表明,与常规输精组相比,深部输精组配种后21 d内淘汰率为0,低于常规输精组的4.44%,差异不显著（P〉0.05）;受胎率和分娩率分别为93.33%和87.78%,高于常规输精组的85.56%和83.33%,差异不显著（P〉0.05）;深部输精可提高经产母猪的产活仔数和健仔数,分别提高0.55和0.66头,差异不显著（P〉0.05）。无论是深部输精还是常规输精,降低输精剂量和有效精子数到15亿/40 mL,均可获得与30亿/80 mL输精量一样的产仔效果,这一结果可使优秀种公猪利用率提高1倍,降低了国标《GB23238-2009》中对外种猪输精剂量的要求,建议扩大试验并推广使用。     

家猪染色体13/17易位的发现及表型效应的研究——Ⅱ.家猪染色体13/17易位的表型效应

对13/17易位杂合子猪与同场同期同品种非易位猪的繁殖力、生长发育进行了统计分析.13/17易位杂合子公猪的窝产仔数、初生窝重、20日龄窝重、断奶窝重、窝断奶头数,无论纯繁还是杂交,与非易位猪均无显著性差异(P>0.05).13/17易位杂合子母猪作为杂交母本,其繁殖力与同场同期同品种非易位母猪无显著性差异(P>0.05).在13/17易位杂合子公猪的后裔中,13/17易位杂合子猪的20日龄重、断奶重都与非易位猪差异不显著(P>0.05).13/17易位杂合子公猪6月龄的体高显著高于非易位公猪的体高(P<0.05),但体重、体长和胸围均无显著性差异(P>0.05).13/17易位公猪的女儿与非易位公猪的女儿6月龄的体重与体尺也无显著性差异.本文还提出了对家畜染色体易位的育种措施.     

母猪深部输精技术的临床应用及效果观察

摘要：本文对母猪深部输精技术的临床应用及效果进行观察试验。临床对比试验结果显示,母猪深部输精、常规输精、本交配种的受胎率分别为83.33%、78.13%和82.14%,窝均产仔数分别为11.2头、9.72头和11.04头,表明深部输精的配种受胎率、窝均产仔数显著优于常规输精(P<0.05),与本交配种相当,无显著差异性(P>0.05)。不同输精量对母猪繁殖性能影响的试验结果显示,输精量分别为20 mL/次、40 mL/次、60 mL/次、80 mL/次的配种受胎率分别为75.58%、82.14%、81.48%和82.50%,窝均产仔数分别为8.58头、10.57头、10.82头和10.95头;表明深部输精的理想剂量为40 mL/次(有效精子数为15亿个),与输精量为20 mL/次相比,差异显著(P<0.05),与输精量为60 mL/次、80 mL/次相比,差异不显著(P>0.05)。深部输精技术对母猪子宫内膜炎的影响试验发现,规模养殖场和散养户中母猪子宫炎的发病率分别为2.78%和5.88%;母猪发情率分别为94.44%和89.47%;情期受胎率分别为94.12%和89.47%。由此表明,深部输精造成母猪子宫损伤的概率极低(2%～5%),一般不影响母猪的再次发情和排卵,是成熟的输精技术。     

常规输精与自动仿生输精方式对后备母猪繁殖性能的影响

为研究不同输精方式对后备母猪繁殖性能的影响,并探究自动仿生输精(快配舒)方式下不同输精剂量的输精效果,将待配后备母猪600头,随机分为对照组、试验1组和试验2组,分别进行常规输精80 mL、自动仿生输精60 mL和自动仿生输精80 mL,并对输精后的母猪繁殖性能指标进行比较分析。结果表明,常规输精与自动仿生输精2种不同输精方式下的配种受胎率、配种分娩率、窝均产健仔数、窝均产活仔数、窝均产死胎数、窝均产总仔数、仔猪初生窝重和仔猪初生均重等指标差异不显著(P>0.05),但自动仿生输精(快配舒)能显著提高配种效率,且自动仿生输精方式(快配舒)下,每头母猪使用60 mL精液量的输精效果优于80 mL精液量。     

深部输精技术对大约克夏母猪繁殖性能的影响

本文旨在探讨不同输精技术及输精剂量对大约克夏母猪繁殖性能及仔猪生产性能的影响。通过记录与统计分析2011~2013年间1827头,3~6胎次大约克夏母猪的繁殖性能和仔猪的生产性能。结果表明:与常规输精80ml相比,深部输精80ml提高母猪受胎率和分娩率分别为3.23%和3.31%,产仔猪数提高了0.27头,显著提高断奶窝重4.04kg(P0.05);深部输精技术40ml和80ml输精量相比时,输精量为80ml的受胎率和分娩率分别提高1.97%和1.35%,显著提高总产仔猪数(P0.05)、断奶仔猪数(P0.05)、断奶窝重(P0.05)和哺乳成活率(P0.05),与此同时也显著增加死胎数及木乃伊数(P0.05),但对总活仔猪数和出生窝重影响不显著(P0.05)。综上,与常规输精技术相比深部输精技术能够在减少输精量的同时提高了受胎率、分娩率和断奶窝重,降低了死胎数、断奶仔猪数、哺乳成活率和出生窝重,但对活仔猪数、健仔猪数和木乃伊数无影响。     

Porcine Field Fertility with Two Different Insemination Doses and the Effect of Sperm Morphology

In swine artificial insemination, several dose regimens are applied, ranging from 1.5 x 10(9) to 6.0 x 10(9) spermatozoa per intra-cervical insemination dose. A lower sperm dose is more profitable for artificial insemination centres and offers a more effective use of superior boars. To evaluate fertility, 50 boars were used for a total of 10 773 homospermic first inseminations at a dose of 2 billion spermatozoa. In addition, 96 boars were used at a dose of 3 billion spermatozoa for 34 789 homospermic first inseminations. Fertility was determined by a 60-day non-return rate (NR%) of first inseminations. Litter size was registered by total number of piglets born separately in primiparous and multiparous farrowings. On average, a sow was inseminated 1.5 times. A significant decrease was observed in all three fertility parameters (NR%, litter size of both primiparous and multiparous farrowings) with a dose of 2 billion spermatozoa compared with a dose of 3 billion spermatozoa. The NR% was 75.8% and 84.0% (p < 0.001), the mean litter size of primiparous farrowings 10.1 and 10.7 (p < 0.001) and the mean litter size of multiparous farrowings 11.7 and 12.1 (p < 0.001) for 2 and 3 billion spermatozoa/dose, respectively. The proportion of normal spermatozoa in the sperm morphology analysis correlated significantly with NR% in both insemination regimens: p < 0.001, r = 0.604 and p < 0.05, r = 0.223 for 2 and 3 billion spermatozoa/dose, respectively. These results confirm that quantity can at least partly compensate for poor sperm quality. When the boars with <70% normal spermatozoa in the morphology evaluation were excluded from the data there were no correlation between the sperm morphology and NR%. However, the difference between the NR% and litter size remained statistically significant (p < 0.001) in favour for the bigger insemination dose. In conclusion, a decrease in sperm dose from 3 to 2 billion spermatozoa on commercial farms will severely decrease prolificacy at least under field conditions, where a sow is inseminated an average of 1.5 times/heat, and the semen is typically used within 3 days after collection. We recommend that under commercial circumstances the homospermic semen doses contain no <3 billion spermatozoa/dose.     

Responses to 19 generations of litter size selection in the Nebraska Index line. I. Reproductive responses estimated in pure line and crossbred litters

Our objective was to estimate responses in reproductive traits in the Nebraska Index line (I) after 19 generations of selection for increased litter size. Responses were estimated in dams producing pure line, F1, and three-way cross litters. A total of 850 litters were produced over six year-seasons, including 224 pure line litters, 393 F1 litters produced from I and C females mated with Danbred NA Landrace (L) or Duroc-Hampshire (T) boars, and 233 litters by F1 L x I and L x C females mated with T boars. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. Farrowing rates of lines I (u = 91.0%) and C (u = 92.8%) did not differ. Averaged across all genetic groups, mean number born alive per litter was 10.1 pigs, and number and weight of pigs weaned per litter, both adjusted for number nursed and weaning age of 12 d, were 9.7 pigs and 34.4 kg, respectively. Averaged across mating types, direct genetic effects of I were greater than C (P < 0.05) for total born (3.53 pigs), number born alive (2.53 pigs), number of mummified pigs (0.22 pig), and litter birth weight (2.14 kg). The direct genetic effect of line I was less than C (P < 0.05) for litter weaning weight (-1.88 kg). Interactions of line effects with crossing system were significant (P < 0.05) for total number born, number of stillborn pigs, number weaned, and litter weaning weight. In pure line litters, I exceeded C by 4.18 total pigs and 1.76 stillborn pigs per litter, whereas the estimate of I-C in F1 litters was 2.74 total pigs and 0.78 stillborn pig per litter. The contrast between I and C for number weaned and litter weaning weight in pure litters was 0.32 pig and -0.28 kg, respectively, compared with 0.25 pig and -2.14 kg in F1 litters. Crossbreeding is an effective way to use the enhanced reproductive efficiency of the Index line.     

中草药复方制剂对公猪精液品质和生殖激素的影响

为了研究中草药复方制剂对公猪精液品质和生殖激素的影响,对27头精液品质相近的成年大约克种公猪饲喂不同剂量的中草药复方制剂,测定精液指标和血清生殖激素水平。结果表明:与对照组相比,2%低剂量组(试验Ⅰ组)的采精量、采精持续时间、精子密度,血清中促卵泡刺激素(FSH)、促黄体生成素(LH)和睾酮(T)含量差异显著(P<0.05);与对照组相比,3%高剂量组(试验Ⅱ组)的采精持续时间、精子活力和血液中LH、T含量显著提高,采精量和血液中FSH含量差异极显著(P<0.01);高、低剂量组的精子畸形率与对照组相比均有所降低。说明日粮中添加一定剂量中草药复方制剂可显著提高种公猪的精液品质,促进生殖激素的分泌。     

GPx6在大白猪附睾细胞中的表达及其与繁殖性能的相关性

本试验旨在研究谷胱甘肽过氧化物酶6（glutathione peroxidase 6,GPx6）在大白公猪附睾细胞中的表达和定位,并探究其与公猪繁殖性能的相关性。选取15月龄的公猪和母猪各3头,取睾丸、附睾、前列腺、尿道球腺、精囊腺、卵巢和输卵管,提取蛋白,通过蛋白免疫印迹和免疫组化（IHC）检测组织和细胞中GPx6蛋白的表达和定位;根据评定大白公猪受精能力的数学模型,按照公猪配种胎次≥20胎、3次配种公猪为同一头的标准,筛选并采集符合要求的20头公猪精液,同时,统计相对应的1 279头母猪的生产成绩,计算得到公猪繁殖性能指标（包括窝产总仔数、窝产活仔数、分娩率和繁殖力）。提取精子蛋白和精清蛋白,通过BCA和ELISA检测精子和精清中GPx6蛋白的含量。使用SPSS软件的独立样本t检验及单因素方差分析（one-way ANOVA）,进行差异显著性分析,用双变量Pearson进行相关性分析,P<0.05表示差异或相关显著。结果表明,GPx6蛋白在附睾中高表达,IHC结果显示,GPx6蛋白在附睾的顶细胞、基底细胞、晕细胞、主细胞和精子中表达,在肌样细胞中不表达;精清蛋白中GPx6的含量是精子蛋白的7倍,精液中GPx6蛋白的含量与窝产活仔数、窝产总仔数呈负相关关系。结果提示,GPx6在附睾的顶细胞、基底细胞、晕细胞、主细胞和精子中表达,且其在精液中的含量会影响公猪的繁殖性能,这为GPx6对公猪受精能力影响的研究奠定了理论和试验基础。     

骨桥蛋白在长白公猪生殖细胞中的表达及其与繁殖性能的相关性

本试验旨在研究骨桥蛋白（osteopontin,OPN）在长白公猪生殖细胞中的表达和定位,并探究其与公猪繁殖性能的相关性。试验采集了长白公猪精液和不同阶段（3日龄、3月龄、6月龄和12月龄）的睾丸组织,通过蛋白印迹的方法检测OPN蛋白在精液和不同月龄睾丸中的表达,通过免疫组化的方法对OPN蛋白在公猪睾丸细胞中进行定位;同时,根据配种胎次≥ 20胎,3次配种公猪为同一头的标准,筛选并采集17头长白种公猪精液,统计相对应的1 388头母猪的生产成绩,计算得到公猪繁殖性能指标（包括窝产总仔数、窝产活仔数、分娩率和繁殖力）。低温离心精液分离得到精子和精浆,丙酮法提取精浆蛋白,Lysis buffer方法提取精子蛋白,最后运用BCA和ELISA的方法检测精子和精浆中OPN蛋白的含量,分析OPN蛋白与公猪繁殖性能的相关性。蛋白印迹结果显示,OPN在精子、精浆和各月龄阶段的长白公猪睾丸中均以两种形式表达（67.4和33.7 ku）,且67.4 ku的形式在3月龄公猪睾丸中表达量最高;免疫组化的结果显示,OPN在长白公猪的初级精母细胞、次级精母细胞和精子细胞中表达,在精母细胞、支持细胞和间质细胞中无表达;BCA和ELISA结果显示,精子中的OPN蛋白含量是精浆中的7倍（P<0.05）,精液中的OPN蛋白与公猪窝产活仔数显著正相关（P<0.05）。本试验结果表明,OPN在各阶段的长白公猪睾丸中都有表达,且在精子和精浆中也有表达,这可能与公猪的繁殖性能有关,从而为后期OPN蛋白在公猪受精力的研究奠定基础。     

Effects of Adding Protein Peptide to Diets on Growth Performance and Nutrient Apparent Digestibility of Growing Pigs

The experiment was aimed to study the effects of protein peptide with different pepsin digestibility in vitro (A80,A90) on growth performance,nutrient apparent digestibility of growing pigs. Experiment 1:300 growing pigs of Duroc pig×Landrace pig×Yorkshire pig were selected and randomly divided into 5 groups with 4 repeats pre group and 15 pigs per repeat. The pig of group Ⅰ was fed with basal diet,that of groups Ⅱ to Ⅴ were fed with basal diet with 1%,2%,3%,4% A80 supplement,respectively. The experiment period lasted for 30 d. Experiment 2:240 growing pigs of Duroc pig×Landrace pig×Yorkshire pig were selected and randomly divided into 4 groups with 4 repeats pre group and 15 pigs per repeat. The pig of group Ⅰ was fed with basal diet,that of groups Ⅱ to Ⅳ were fed with basal diet with 1%,2%,3% A90 supplement,respectively. The experiment period lasted for 30 d. The results showed that the average daily gain (ADG),average daily feed intake (ADFI) and feed/gain (F/G) had no significant difference among all groups (P>0.05) in experiment 1. But the ADG had a tendency to reduce with the increase of A80. The DM,CP apparent digestibility of group Ⅱ was significant higher than that of groups Ⅰ,Ⅲ and Ⅴ (P<0.05),and had no significant difference with group Ⅳ(P>0.05). Digestibility of Ca and P showed a tendency to improve with the increase of A80,but there was no regularity. Experiment 2:With the increase does of A90,ADG was increased firstly and then decreased. The ADG of group Ⅲ was significantly higher than that of group Ⅰ(P<0.05),and had no significant difference with other groups (P>0.05).The ADFI of group Ⅲ was significantly higher than that of other groups (P<0.05).DM and CP apparent digestibility showed a tendency to decline with the increase dose of A90.In conclusion,A80 had no significant improvement on growth performance and A90 showed a quadratic improvement to pig's growth performance and the best addition percentage of protein hydrolysate in diet was 2% to 3%.     

The Post‐Cervical Insemination does not Impair the Reproductive Performance of Primiparous Sows

The study evaluated the reproductive performance of primiparous sows submitted to post‐cervical insemination (PCAI) compared with cervical artificial insemination (CAI). Difficulty with catheter introduction, the occurrence of bleeding or semen backflow during insemination, and volume and sperm cell backflow up to 60 min after insemination were also evaluated. Sows were homogenously distributed, according to body weight loss in lactation, lactation length, weaned piglets, weaning‐to‐oestrus interval and total born in previous farrowing, in two treatments: PCAI (n = 165) with 1.5 × 10⁹ sperm cells in 45 ml (2.4 ± 0.04 doses per sow) and CAI (n = 165) with 3 × 10⁹ sperm cells in 90 ml (2.5 ± 0.04 doses per sow). During PCAI, sows were inseminated in the absence of boars. Transabdominal real‐time ultrasonography was performed at oestrus onset, immediately before the first insemination and at 24 h after last insemination. There was no difference (P > 0.05) between treatments in farrowing rate (91.5% × 89.1%) and litter size (12.5 × 11.9 piglets born, respectively for PCAI and CAI sows). Successful passage of the intrauterine catheter in all the inseminations was possible in 86.8% (165/190) of sows initially allocated to PCAI treatment. Difficulty of introducing the catheter in at least one insemination did not affect the reproductive performance of PCAI sows (P > 0.05). Bleeding during insemination did not affect (P > 0.05) the farrowing rate in both treatments, but litter size was reduced in CAI and PCAI sows (P ≤ 0.06). Percentage of spermatozoa present in backflow within 1 h after insemination was greater in CAI than PCAI sows (P < 0.01). More than 85% of primiparous sows can be successfully post‐cervical inseminated with doses containing 1.5 × 10⁹ sperm cells in the absence of the boar during insemination without impairing the reproductive performance.     

太湖猪高产综合技术研究试验

本文系对103头360窝太湖猪的繁殖性能进行系统研究。结果是60头母猪在6个繁殖周期中共繁殖360窝,平均繁殖周期158.33天,年产仔2.31胎。窝产仔16.35头,活仔15.10头,35日龄断奶育成14.44头,窝重83.48公斤。每头母猪年产仔37.69头,年产活仔34.81头,年提供断奶仔猪33.29头。其中窝产仔达到18头以上,出现1胎或连续4胎高产的母猪69头,占试验母猪群66.99％。     

Novel insight into the control of litter size in pigs, using placental efficiency as a selection tool.

Chinese Meishan pigs produce three to five more pigs per litter than less-prolific U.S. or European pig breeds as a result of a markedly decreased placental size and an increased pig weight: placental weight ratio (placental efficiency). We hypothesized that as a result of their intense selection for prolificacy, the Chinese had indirectly selected for a smaller, more efficient placenta in the Meishan breed. The goals of this study were to determine whether 1) significant variation in placental size and efficiency existed within our population of purebred Yorkshire pigs and 2) selection of pigs (boars and gilts) based on clear differences in placental size and efficiency would affect litter size. There was significant (approximately threefold) variation in placental efficiency in our herd of Yorkshire pigs, and marked (approximately twofold) variation existed within individual litters. We then selected pigs (boars and gilts) that had either a higher (A Group) or lower (B Group) than average placental efficiency. Although the birth weights of selected A Group pigs were similar to those of the B Group pigs, they had markedly smaller placentae. Males from each group (A or B) were bred to the females of the same group, and farrowing data were collected from parities 1 and 2. In both parities, A Group females farrowed more live pigs per litter than did B Group females (12.5 +/- .7 vs 9.6 +/- .5, P < .05). Although A Group pigs were on average approximately 20% lighter than B group pigs (1.2 +/- .1 vs 1.5 +/- .1 kg, P < .05), their placentae were approximately 40% lighter (250 +/- 10 vs 347 +/- 15 g, P < .01), resulting in a marked increase in placental efficiency. The results of this study suggest that selection on placental size and efficiency may provide a valuable tool for optimizing litter size in commercially important pig breeds.