| Much effort has been devoted to the increase of litter size in swine due to its impact on productive and economic efficiency. Different selection strategies have been investigated the improvement of litter size. Ovulation rate and uterine capacity can be implemented rephrasing two of the physiological components of litter size which will not be effective in making large improvements in litter size. As is known to all, American Iowa research team introduced the placental efficiency into Chinese Meishan pigs greater prolificacy, they hypothesized that placental efficiency as a result of their intense selection for prolificacy. Wilson, in 1999, found that selection on placental size and efficiency may provide a valuable tool for optimizing litter size in commercially important pig breeds. The results of Wilson’s research showed that the higher placental efficiency, namely its higher litter size, low conversely. Our country also in this area studied a lot, the results confirmed that within a certain range, the higher placental efficiency, the higher litter size. Variety, tire time also have certain influence on its litter size, the sow, as an important means of production of pig farms, the sow body condition level directly affects the health and welfare of the sows, reproduction and life, etc, if the sow in the breeding of it can maintain the best in his life and stable level of body condition, will help to improving the reproductive performance, increasing production efficiency, optimizing selection strategy, reduce mortality. Many studies have shown that the sow body condition of different physiological stages has much effect on the reproductive performance, back fat thickness as an important index reflecting the sow body condition, for its easy measuring, are often used in the production practice. This test aim at researching the Landrace and Yorkshire×Landrace hybrid sows placental efficiency and the relationship between litter size, and back fat thickness effects on reproductive performance, and then from the molecular to investigate the relationship between the placental function and fat metabolism gene expression, clarify the sow body condition affect placental function and efficiency of the placenta to provide experiment basis. This test is divided into three parts:1 Study on Using Placental Efficiency Select Reproductive Performance in PigThis study was to explore the different varieties of sows placental efficiency and the relationship between reproductive performances. Model for the Landrace, total 63 head, and the Yorkshire×Landrace hybrid, total 50 head, measured the Landrace and the Yorkshire×Landrace hybrid litter weight, the placenta weight, different varieties of sow to calculate the placental efficiency can be divided into high (> 5.5), (4.5-5.5), low (< 4.5) in three groups. At the same time record the sow after birth nest litter size, litter number born alive, dead fetus number. The results showed that the Yorkshire×Landrace hybrid sows litter size and litter born alive were significantly higher than that of Landrace sows (P< 0.05), while the placental efficiency difference was not significant. Placental efficiency has a huge significant effect on different varieties sows litter size alive and placental weight(P<0.01); Otherwise, litter size and litter weight have a significant difference (P< 0.05). Different variety sows have no significant difference on reproductive performance. The results showed us:different variety sows, placental efficiency has no significant difference. Placental efficiency has a great significant difference on reproductive performance. Interactions between varieties and placental efficiency and had no significant effect on reproductive performance.2. Fat Mass:Effects on Reproductive Performance of Pregnant SowsIn the first chapter the sow Placental efficiency with litter size effect based on the research of choice, In this study, we determined the effects of fat mass in pregnant sows on litter live size, birth litter weight, placental efficiency, and weaning litter weight. A total of 98 gestational sows from YorkshirexLandrace hybrid were grouped into high back fat thickness (21 to 27 mm), medium back fat thickness (16 to 20 mm) and low back fat thickness (10 to 15 mm), respectively, according to the measurement of back skin fold thickness before delivery. The litter live size, birth litter weight, placental weight and weaning weight at 21 d were measured after childbearing. Also, placental efficiency was calculated by the ratio of birth weight to placental weight. We found that litter live size in medium back fat thickness sows was significantly increased compared with that in low and high back fat thickness sows (P<0.05). Furthermore, the increase of back fat thickness in pregnant sows significantly reduced birth litter weight and placental efficiency (P<0.05). However, weaning litter weight was not significantly influenced by adipose deposition in pregnancy. Taken together, these data demonstrate that adequate fat mass during pregnancy can promote litter live size, birth litter weight and placental efficiency in sows, so improving thinner and fatter mass condition through nutritional regulation is particularly important.3. The Relationship between the Sows Placental Efficiency and Its Lipid metabolism genesThis chapter builds on the previous two chapters research, the Landrace sows and the YorkshirexLandrace hybrid sows grouped in order to the placental efficiency and back fat thickness. Back fat group (20-27mm), back fat moderate group (17-19mm), back fat thin group (10-16mm); placental efficiency high group (> 5.5), moderate group (4.5 to 5.5),low group (<4.5), for (Sterol regulatory element binding protein-1, SREBP-1c; Fatty acid syntheses, FAS; Acetyl-CoA carboxylase, ACC; relative expression of peroxisome proliferator-activated receptors gamma, PPARy) and lipoprotein lipase (Lipoprotein Lipase, LPL) were determined to compare different back fat thickness sows fat metabolism gene expression levels and their differences; different placental efficiency sow their differences in fat metabolism gene expression results showed that:Landrace sow back fat group of SREBP-lc relative expression levels were significantly higher than the thin back fat group and moderate group (P<0.05); other genes was not significant Landrace sows, placental efficiency low group, ACC, FAS expression was significantly higher in the moderate group of placental efficiency (P<0.05); between groups, SREBP-lc expression levels were significantly difference (P<0.05), whereas the expression of LPL and PPARy was no significant difference. The Yorkshirex landrace hybrid placental efficiency moderate group,Expression of ACC was significantly higher than the efficiency of the placental efficiency low group, LPL expression level of placental efficiency high group was significantly higher than the placental efficiency low group (P<0.05). While fat metabolism associated with PPARy, SREBP-lc relative expression levels had no significant difference. |
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