Abstract
The objective of this study was to determine whether peroxisome proliferator-activated receptor y (PPARγ) is involved in the regulation of weaning to estrus of primiparous sows. Twelve sows composed of 6 groups of 2 full-sibs in a similar age (325.2 d), body weight (BW; 152.4 kg) and backfat thickness (BFT; 27.0 mm) at start of lactation, were allocated to accept 31 MJ (restricted group, R-group) or 53 MJ (control group, C-group) DE/d treatment, respectively. The experimental results indicated that the low energy intake resulted in excessive losses of BW and BFT during lactation in R-group sows, which may be related to decrease of serum 15-deoxy-Δ 12,14 -prostaglandin J 2 (15d-PGJ 2 ), a ligand of PPARγ. The obvious peak and the frequency of LH, FSH and estradiol (E 2 ) were only observed in C-group sows. Except for E 2 at d 1 and 2, serum FSH, LH and E 2 concentrations in R-group were lower than those in C-group sows after weaning. However, the serum progesterone (P 4 ) level in R-group sows was always more than that in C-group. The expression abundances of PPARγ and GnRH receptor (GnRH-R) in pituitary, FSH receptor (FSH-R), LH receptor (LH-R), estrogen receptor (ES-R) and aromatase in ovary of anestrous sows were lower than those of estrous sows. Neither the BFT nor the BW was associated with the mRNA abundance of PPARγ in hypothalamus during lactation. Expressions of PPARγ in pituitary and ovary were affected evidently by the BFT changes and only by the loss of BW of sows during and after lactation. Furthermore, PPARγ mRNA level in ovary was significantly related to the expression abundances of GnRH-R, FSH-R, ES-R and aromatase, and GnRH-R was obviously associated with PPARγ expression in pituitary. However, PPARγ expression in hypothalamus likely has no effects on these genes expression and no obvious difference for all sows. Not serum E 2 or P 4 alone but the ratios of E 2 to P 4 and 15d-PGJ 2 to P 4 , and serum FSH and LH were evidently related to PPARγ expression in pituitary and ovary. It is concluded that PPARγ is associated with body conditions, reproduction hormones and their receptor expression, which affected the functions of pituitary and ovary and ultimately the estrus after weaning of primiparous sows.
Highlights
The MLC Pig Year Book 1995 (MLC, 1995) analyses the reasons for culling sows in UK and shows that the major reason for 18% of all sow disposals is mainly reproductive failure
The results of linear regression analysis showed that the mRNA levels of peroxisome proliferator-activated receptor γ (PPARγ) in ovary is significantly related to the expression abundances of GnRH receptor (GnRH-R), FSH receptor (FSH-R), estrogen receptor (ES-R) and Arom, and only GnRH-R was obviously associated with PPARγ expression in pituitary (Table 4)
Start to the reproductive cycle
Summary
The MLC Pig Year Book 1995 (MLC, 1995) analyses the reasons for culling sows in UK and shows that the major reason for 18% of all sow disposals is mainly reproductive failure. With a confined intensive raising system and more modernizing managing strategy, reproductive failures commonly occur and maybe get more and more serious on pig farms. One of the major reproductive problems that a Anestrus is the state of ovarian acyclicity, reflected by complete sexual inactivity without exhibition of estrus (Wright and Malmo, 1992). Several factors may affect the prolonged return to estrus following weaning (Meredith, 1984; Gourdine et al, 2006), but the factor of most concern to many nutritionists and producers is the nutritional and metabolic status of the sow at weaning, such as excessive losses of weight and body tissue stores during lactation.
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