Effects of oestrous synchronization with altrenogest in gilts on endometrial and embryonic characteristics

The use of altrenogest (ALT) supplementation for oestrous synchronization improves subsequent reproductive performance of gilts and sows. However, the causes of this improvement in reproductive performance after ALT treatment are not fully/clearly understood. The objective of this study was to evaluate the effects of ALT supplementation for oestrous synchronization in gilts on the endometrial glands and embryonic development characteristics at 28 days of pregnancy. Pregnant gilts were divided into two experimental treatments: Control (did not receive ALT; n = 9 gilts) and ALT (ALT feeding at 20 mg/day for 18 days; n = 9 gilts). At 28 days of pregnancy, six gilts from each treatment were slaughtered, and reproductive tracts were immediately evaluated. There was no statistical difference (P > 0.05) between treatments regarding ovulation rate, number of embryos, number of vital embryos and number of non-vital embryos. Embryo weight, length and embryonic vesicle weight were lower in ALT treatment compared with Control (P < 0.01), and it was lower in the cervical uterine region compared with apex uterine region, respectively (P < 0.05). Higher values of gland duct area, gland duct perimeter, percentage of the glandular area and total endometrial area were observed in ALT treatment compared with Control (P < 0.05). The use of ALT during 18 days for oestrous synchronization in gilts increased the gland duct area, perimeter and total endometrial area but did not increase the embryo number and embryo size at day 28 of pregnancy.     

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg⁻¹ of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1⁻¹. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l⁻¹ (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.     

The effects of PG600 and boar exposure on oestrus detection and potential litter size following mating at either the induced (pubertal) or second oestrus

Within gilt pools, incidences of delayed puberty attainment, failure to exhibit regular oestrous cycles and low first litter size are often high. Boar exposure is an effective method of accelerating puberty; however, the timing of gilt response can vary greatly. Although, PG600 (400 IU of PMSG and 200 IU of hCG; Intervet) can induce a rapid and synchronous ovulatory response, thus providing an alternative to boar contact, the quality of the response is often variable. This study compared the effect of PG600, either alone (NBC) or in conjunction with boar exposure (BC), on puberty attainment and maintenance of oestrous cyclicity. The effects of first mating these gilts at the hormonally induced (pubertal) or second oestrus on ovulation rate and early embryo survival were also studied. Eighty Large White cross terminal (Duroc) line gilts were used in this study. The study was conducted in two blocks, with 10 gilts allocated to each of the four treatments in each block. Gilts were artificially inseminated at the allocated oestrus, with the reproductive tracts collected at 26.5+/-0.29 days after first mating (mean+/-S.E.M.), and the number of corpora lutea and viable embryos recorded. Mean days-to-puberty was significantly reduced (P<0.05) when gilts received both PG600 and boar exposure as opposed to PG600 alone (5.7+/-0.15 versus 6.9+/-0.37 days; P<0.01). The proportion of gilts exhibiting an ovulatory response to PG600 was similar for the BC and NBC treatment groups (0.88 and 0.84); however, the proportion of gilts exhibiting visible signs of oestrus in response to PG600 was significantly higher for the BC compared to the NBC treatment groups (0.81 versus 0.49; P<0.05). Boar contact resulted in a numerical, but not significant, increase in the proportion of gilts exhibited a second oestrus (1.00 versus 0.76). There was no significant effect of boar contact on ovulation rate, embryo number or survival. Although ovulation rate was unaffected by oestrus at mating, embryo number was significantly increased (P<0.05) following mating at the second compared to the first oestrus (11.2+/-0.96 versus 7.8+/-1.17). In conclusion, the current data indicate that the timing of puberty attainment and oestrus detection are significantly improved when PG600 treated gilts receive full boar contact. Further, it is evident that mating gilts at their second as opposed to the hormonally induced oestrus significantly increases embryo number at day 26 post-mating.     

Evidence that Meishan and Large-White hybrid preovulatory follicles may differentially affect oocyte in vitro maturation and fertilization

Two experiments were carried out to test the hypothesis that follicles recovered from Meishan animals may provide a more favourable environment for oocyte maturation in vitro than follicles recovered from Large-White hybrid animals. In Experiment 1, all follicles ≥4 mm were recovered from six Meishan and seven Large-White hybrid gilts in the late follicular phase and healthy oocyte cumulus complexes recovered. Cumulus oocyte complexes were randomly divided into two groups, and each group cultured for 27 or 34 h (62 and 64; 56 and 56 for Meishan and Large-White hybrid, respectively) in defined medium in the presence of either of the two largest follicle shells per animal. Subsequent examination of oocyte nuclear maturation showed that although maturation did not differ significantly between the breeds after 27 h, more (P<0.01) Meishan oocytes co-cultured with Meishan follicles developed to metaphase II stage than Large-White hybrid oocytes co-cultured with Large-White hybrid follicles after 34 h. The next eight largest follicles per animal were cultured for 34 h to produce conditioned media. In Experiment 2, oocytes recovered from the slaughterhouse were matured for 46 h in the presence of conditioned media from Meishan (612 oocytes) or Large-White hybrid (731 oocytes) follicles, or in fresh medium in the presence of a follicle shell from slaughterhouse ovaries. Oocytes were then inseminated and 12 h later examined for penetration and male pronuclear formation. A higher (P<0.05) percentage of oocytes cultured in Meishan follicle conditioned medium underwent sperm penetration and male pronuclear formation than oocytes cultured in conditioned media from Large-White hybrid animals. Concentrations of oestradiol and progesterone in the conditioned media did not differ between the breeds (P>0.1). In conclusion, these results suggest that (1) Meishan oocytes have advanced maturational capacity when cultured with Meishan preovulatory follicle shells and (2) differences in follicle maturation in the Meishan compared to the Large-White hybrid pig may result in an improved ability of the follicles, via conditioned media, to support oocyte maturation and fertilization in vitro.     

Supplemental progesterone during early pregnancy exerts divergent responses on embryonic characteristics in sows and gilts

Progesterone (P4) plays a key role in pregnancy establishment and maintenance; during early pregnancy, P4 stimulates the production and release of uterine secretions necessary for conceptus growth prior to implantation; therefore, exogenous P4 supplementation may improve embryo development. This study evaluated the effects of supplementation during early pregnancy with long-acting injectable progesterone or altrenogest on embryonic characteristics of sows and gilts. Thus, a total of 32 sows and 16 gilts were used. On day 6 of pregnancy sows and gilts were allocated to one of the following groups: non-supplemented; supplemented with 20 mg of altrenogest, orally, from days 6 to 12 of pregnancy; supplemented with 2.15 mg/kg of long-acting injectable progesterone on day 6 of pregnancy. Animals were killed on day 28 of pregnancy, and ovulation rate, embryo survival, embryo weight, crown-to-rump length, uterine glandular epithelium and endometrial vascularization were assessed. Treatments had no effect on pregnancy rate, embryo survival or endometrial vascular density (P > 0.05). Non-supplemented gilts presented larger and heavier embryos compared to gilts from supplemented groups (P < 0.05). Sows in the altrenogest group presented larger and heavier embryos compared to non-supplemented sows and sows supplemented with long-acting injectable progesterone. In conclusion, supplementation of sows and gilts with progestagen from day 6 of pregnancy can be used as a means to improve embryo survival without deleterious effects.     

Estrus synchronization affects WNT signaling in the porcine reproductive tract and embryos

The purpose of the study was to investigate an effect of estrus synchronization with prostaglandin (PG) F_2α and PMSG/hCG on WNT4, WNT5A, WNT7A, β-catenin (CTNNB1) and E-cadherin (CDH1) gene expression. The weight of the uterus, morphometrical parameters of the endometrium and the number of CL were recorded. The analysis of estradiol (E₂), prostaglandin (PG) F_2α and E₂ content in the uterine luminal flushings (ULFs) and progesterone (P₄) level in the blood serum were conducted. RNA was isolated from endometrial, luteal and embryonic tissue of pregnant non-synchronized (Control; n = 15) and pregnant synchronized (PGF_2α/PMSG/hCG; n = 15) pigs. Whereas there was no change in uterine weight, differences in height of endometrial surface and glandular epithelium were found. However, height of the endometrium, number of the glands and capillaries were unaffected. The total number of the CLs was higher (P < 0.05) in animals treated with PGF_2α/PMSG/hCG. The amount of E₂ and P₄ was lower (P < 0.05, P < 0.001, respectively) in pregnant gilts administrated with PGF_2α/PMSG/hCG. The concentration of PGF_2α in ULFs was not affected by hormonal management, while PGE₂ was higher (P < 0.01) in hormonally in comparison to non-hormonally treated pigs. The content of WNT4 mRNA in conceptuses increased on particular Days studied in Control and PGF_2α/PMSG/hCG administered animals. WNT7A and CTNNB1 were affected by PGF_2α/PMSG/hCG treatment in both conceptuses (P < 0.001, P < 0.05) and endometrial tissue (P < 0.001, P < 0.01). The PGF_2α/PMSG/hCG treatment resulted in elevated expression of WNT4 (P < 0.001) and CTNNB1 (P < 0.05) in luteal tissue in comparison to the Control gilts. Moreover, luteal amount of WNT5A mRNA was higher in PGF_2α/PMSG/hCG animals in comparison to the Control group (P < 0.05). Presented data show that exogenous hormones administration can affect gene expression in the porcine reproductive tract and embryo.     

Estrus synchronization affects WNT signaling in the porcine reproductive tract and embryos

The purpose of the study was to investigate an effect of estrus synchronization with prostaglandin (PG) F_2α and PMSG/hCG on WNT4, WNT5A, WNT7A, β-catenin (CTNNB1) and E-cadherin (CDH1) gene expression. The weight of the uterus, morphometrical parameters of the endometrium and the number of CL were recorded. The analysis of estradiol (E₂), prostaglandin (PG) F_2α and E₂ content in the uterine luminal flushings (ULFs) and progesterone (P₄) level in the blood serum were conducted. RNA was isolated from endometrial, luteal and embryonic tissue of pregnant non-synchronized (Control; n = 15) and pregnant synchronized (PGF_2α/PMSG/hCG; n = 15) pigs. Whereas there was no change in uterine weight, differences in height of endometrial surface and glandular epithelium were found. However, height of the endometrium, number of the glands and capillaries were unaffected. The total number of the CLs was higher (P < 0.05) in animals treated with PGF_2α/PMSG/hCG. The amount of E₂ and P₄ was lower (P < 0.05, P < 0.001, respectively) in pregnant gilts administrated with PGF_2α/PMSG/hCG. The concentration of PGF_2α in ULFs was not affected by hormonal management, while PGE₂ was higher (P < 0.01) in hormonally in comparison to non-hormonally treated pigs. The content of WNT4 mRNA in conceptuses increased on particular Days studied in Control and PGF_2α/PMSG/hCG administered animals. WNT7A and CTNNB1 were affected by PGF_2α/PMSG/hCG treatment in both conceptuses (P < 0.001, P < 0.05) and endometrial tissue (P < 0.001, P < 0.01). The PGF_2α/PMSG/hCG treatment resulted in elevated expression of WNT4 (P < 0.001) and CTNNB1 (P < 0.05) in luteal tissue in comparison to the Control gilts. Moreover, luteal amount of WNT5A mRNA was higher in PGF_2α/PMSG/hCG animals in comparison to the Control group (P < 0.05). Presented data show that exogenous hormones administration can affect gene expression in the porcine reproductive tract and embryo.     

Effects of dietary menhaden oil on growth and reproduction in gilts farrowed by sows that consumed diets containing menhaden oil during gestation and lactation

In sows, n-3 fatty acids increase litter sizes, however, effects on gilt reproductive development have not been adequately studied. Moreover, not determined are effects of feeding n-3 fatty acids to sows on reproduction in offspring. The objective here was to determine effects of 4% dietary menhaden oil on growth and puberty in gilts farrowed by sows fed menhaden oil. Sows (n = 44) were assigned to: (1) control gestation and lactation diets, or (2) diets including menhaden oil. For primiparous sows only, total litter size and born alive were greater (P < 0.05) in females fed menhaden oil. Conversely, pigs from primiparous controls were heavier (P < 0.05) than pigs from primiparous sows fed menhaden oil (parity by diet interactions, P < 0.01). Diet did not affect (P > 0.20) other sow and litter characteristics. At weaning, 84 gilts from control- or menhaden oil sows were placed three gilts per pen and provided control diets or diets containing menhaden oil. Nursery and grow-finish feed intake and feed efficiency were similar (P > 0.21) for gilts from the different sows and weight gain was similar (P > 0.24) for gilts fed control or menhaden diets. Gilts fed menhaden oil tended to eat less in the nursery (1.18±0.08 kg v. 0.98±0.08 kg; P = 0.09) and overall (1.83±0.04 kg v. 1.72±0.04 kg; P = 0.06). Thus, overall feed to gain was greater (2.52±0.03 v. 2.33±0.03; P < 0.01) and nursery (2.12±0.04 v. 1.80±0.04; P = 0.10) and grow-finish (3.07±0.19 v. 2.58±0.19; P = 0.08) feed to gain tended to be greater, for control gilts. Age at puberty was greater (P = 0.02) for gilts from menhaden oil-fed sows (205.1±3.2 days) compared to gilts from controls (193.9±3.2 days) and tended to be greater (P = 0.09), for controls (203.5±3.2 days) compared to gilts fed menhaden oil (195.5±3.2 days). A tendency existed (P = 0.09) for greater follicular fluid in gilts fed menhaden oil, however, ovulation rate and ovarian, luteal and uterine weights were not affected by sow diet, gilt diet or the interaction (P > 0.23). Feeding gilts menhaden oil enhanced feed efficiency and hastened puberty onset. Gilts from sows consuming menhaden oil exhibited delayed puberty and retaining females from sows fed this feedstuff may be ill advised.     

Effects of composition and density of the group on the performance,behaviour and age at puberty in swine

Two hundred and eighteen cross-bred pigs (Duroc × Hampshire × Landrace × Yorkshire) were assigned to a 3 × 2 factorial experiment; the factors being composition of the group and density. The composition of the group factor consisted of pigs not reaggregated (NR), re-aggregated below the median body weight (RBMW), and re-aggregated above the median body weight (RAMW) at the time of transfer to the finishing pens. The density factor consisted of groups of 6 or 12 pigs/pen. Two trials with 2 replications of each trial were conducted. Twenty-six gilts from Trial I were used to determine their age and ovulation rate at the pubertal oestrus. During the nursery phase, composition of the group had no effect (P>0.05) on average daily feed intake (ADFI) or feed efficiency (F/G). Pigs in the NR and RAMW groups had a similar (P>0.05) average daily gain (ADG), whereas, those pigs in the RBMW group gained (P<0.05) at a slower rate. Pigs housed in groups of 6 had a higher (P<0.05) ADFI, had similar (P>0.05) ADG and poorer (P<0.05) F/G than those housed in groups of 12. During the finishing phase, composition of the group had no effect (P>0.05) on ADFI, ADG or F/G. Pigs housed in groups of 6 had a greater (P<0.05) ADFI and ADG, but similar (P<0.05) F/G compared to those housed in groups of 12. Correlation coefficients between the various behaviours and the performance variables suggested that the more active pens of pigs gained less per day and were less efficient. Gilts housed in the NR groups of 6 were younger (P<0.05) at puberty than gilts in the other groups of 6 or 12. Also, gilts housed in the RBMW groups of 6 were younger (P<0.05) at puberty than those housed in the RAMW groups of 6, whereas those housed in the RBMW groups of 12 were older (P<0.05) at puberty than those housed in the RAMW groups of 12. Ovulation rate was not affected (P>0.05) by composition of the group, density or their interaction. In summary, composition and density of the group affected the performance of pigs and was correlated to some of the behavioural measurements. The most noticeable effect was that these same factors caused a delay in the onset of puberty in gilts.     

Synchronization of oestrus in gilts with altrenogest: effects on ovulation rate and foetal survival

Previous studies have shown that use of altrenogest resulted in a high rate of fertility and increased litter size compared with controls under conditions of practical pig production. The present study was designed to evaluate whether ovulation rate and/or foetal survival were increased by altrenogest using crossbred gilts derived from one herd (n = 227) and introduced in the same piggery over 12 months. Each gilt was allocated to a treated group (n = 103) receiving an individual daily dose of 20 mg of altrenogest for 18 days in its feed or a control group (n = 124) after puberty had been diagnosed, (197 ± 1 day; mean ± SEM). They were inseminated (double AI) at the second induced or natural oestrus. Pregnancy was diagnosed by ultrasonography at Days 22 and 42 post-insemination in the absence of return to oestrus. Pregnant gilts were slaughtered at 48 ± 3 days of pregnancy following the second examination. The number of living and dead foetuses were recorded before uterine contents (foetuses and placentae) were weighed and the number of corpora lutea (CL) per ovary counted.Precise synchronization of oestrus was observed after the end of the progestogen administration, with 93% of the gilts in oestrus by Days 5 to 7. For the controls, the interval from first to second oestrus ranged from 17 to 25 days in 93% of the control gilts. The pregnancy rate was 89.3% for treated gilts and 77.4% for controls (P < 0.05). The ovulation rate was increased by the treatment (15.4 ± 0.3 vs 14.6 ± 0.3; mean ± SEM, P < 0.02). Although the altrenogest group had more foetuses (11.1 vs 10.6), this difference was not significant (P > 0.14). The percent of foetal survival was similar in both groups (64.9%; P > 0.27). The foetal and placental weights differed only between dams and increased with stage of gestation. The increase in litter size through feeding altrenogest was associated with an increased ovulation rate.     

Effect of progesterone supplementation in the first week post conception on embryo survival in beef heifers

Progesterone is essential for establishment and maintenance of pregnancy in mammals. The objective of this study was to examine the effect of elevating progesterone during the different physiological stages of early embryo development on embryo survival. Estrus was synchronized in cross-bred beef heifers (n = 197, ∼2-years old) and they were inseminated 12-18 h after estrus onset (=Day 0). Inseminated heifers were randomly assigned to 1 of 3 treatments: (1) Control, n = 69; (2) progesterone supplementation using a Controlled Internal Drug Release Device (CIDR) from Day 3 to 6.5, n = 64; or (3) progesterone supplementation using a CIDR from Day 4.5 to 8, n = 64. Body condition (BCS) and locomotion scores (scale of 1-5) were recorded for all animals. Animals with a locomotion score ≥4 (very lame) were excluded. Embryo survival rate was determined at slaughter on Day 25. Conceptus length and weight were recorded and the corpus luteum (CL) of all pregnant animals was dissected and weighed. Supplementation with exogenous progesterone increased (P < 0.05) peripheral progesterone concentrations, but did not affect embryo survival rate compared with controls. Mean CL weight, conceptus length and conceptus weight were not different between treatments. There was a positive relationship (P < 0.04) between the increase in progesterone concentrations from Days 3 to 6.5 and embryo survival rate in treated heifers and a similar trend existed between the increase from Days 4.5 to 8 (P < 0.06). There was also a positive relationship (P < 0.05) between the progesterone concentration on Day 6.5 and the embryo survival rate in treated heifers. A direct correlation was seen between locomotion score and embryo survival rate, with higher (P < 0.05) early embryo survival rates in heifers with a lower locomotion score. In conclusion, supplementation with progesterone at different stages of early embryo development increased peripheral progesterone concentration and resulted in a positive association between changes in progesterone concentration during the early luteal phase and embryo survival rate. Supplementation with progesterone had no effect on either CL weight or conceptus size in pregnant animals. Lameness had a significant negative effect on early embryo survival.     

Attainment of puberty in female pigs: Influence of boar stimulation

The object of the present study was to investigate whether the presence of a boar is of importance for the age at puberty and the expression of external heat symptoms in female pigs. Altogether 60 crossbred gilts were purchased at an age of 12 weeks and grouped, three or four per pen, in three separate barns (treatment groups A, B and C). Treatment group A: Boars were kept in adjacent pens to the gilts during the whole period. One vasectomized boar was penned with the gilts daily for 20 min during the experimental period, which started at a mean age of 142 days. Treatment group B: Boars were kept in adjacent pens to the gilts during the whole period. Treatment group C: No boars were kept in the barn at any time.The study was performed six times. Daily heat control was carried out during the experimental period, which was terminated when the gilts had passed at least two oestrous cycles. Blood samples for progesterone analysis were taken once a week. Laparoscopy was performed in all gilts after their first observed heat. The gilts were slaughtered after their third or fourth heat. The effects of treatment group were estimated by the method of least squares analysis.All gilts except one showed external heat symptoms at regular intervals during the experimental period. A few gilts did not stand for the boar at each oestrous period, regardless of oestrous number. Gilts belonging to group A showed their first oestrus on average 20 days earlier than gilts in group B and 35 days earlier than gilts in group C. These differences were highly significant (P < 0.001). The stimulatory effect of the boar on the age at puberty varied between the six experimental groups and the interaction between treatment and experimental groups was significant (P < 0.01).     

The Correlation of Reproduction-Related Gene Expression with Germ Cell Number in DM and PLL Gilts

In this study, the ovarian germ cell number was counted in 3-week-old Duroc × Meishan (DM, n=30) and PIC × (Landrace × Large White) (PLL, n=53) gilts, and the mRNA expression levels of four reproduction-related genes were investigated by quantitative RT-PCR. Correlation of germ cell number with the expression level of these genes was analyzed. Results showed that the germ cell number of DM was significantly higher than that of PLL gilts (P<0.01), although there was no significant difference between the ovarian weight of DM and PLL gilts (P=0.269). No significant correlation existed between germ cell number and ovarian weight in the two gilt groups (R=0.335, P=0.07; R=0.119, P=0.398, respectively). A significant correlation was found between the germ cell number and expression level of ESR and IGF1R mRNA in DM gilts (R=0.648, P<0.05; R=0.757, P<0.01, respectively), but the correlation between the germ cell number and expression level of FSHR and INHBA mRNA did not reach statistical significance. Significant correlation was found between the germ cell number and the expression level of ESR, FSHR, and IGF1R mRNA in PLL gilts (R=0.435, P<0.01; R=0.438, P<0.01; R=0.292, P<0.05, respectively), but not with INHBA mRNA in PLL gilts.     

Treatment with progesterone affects follicular steroidogenesis in anoestrous ewes

Ovaries were recovered from two groups (n=6/group) of anoestrous Romney Marsh ewes, one group of which had been treated with progesterone implants prior to slaughter. A comparison was made between the maturational characteristics of the follicles > 2 mm diameter recovered from both groups and some significant differences were noted. In particular, the large follicles (> 4 mm diameter) recovered from the progesterone-treated ewes had a significantly (P<0.01) reduced capacity to secrete oestradiol, but enhanced (P<0.01) ability to bind hCG when compared to follicles recovered from control ewes. There were also differences in the relationships between follicular characteristics in the two groups of animals including a significant (P <0.05) correlation between follicular fluid progesterone and hCG binding to theca tissue in large follicles from progesterone-treated animals which did not exist in the control animals. Conversely, in the control animals a significant (P<0.05) relationship existed between oestradiol production and hCG binding to granulosa cells, but there was no such relationship in the follicles from progesterone-treated ewes. These results demonstrate that the treatment of ewes with progesterone during the anoestrous period clearly affects oestradiol synthesis and hCG binding and thus modifies follicular development.     

The effects of immunization against gonadotropin-releasing hormone on growth performance,reproductive activity and carcass traits of heavy weight gilts

Heavy weight gilts commonly show signs of oestrus during the late finishing phase, which results in a period of reduced feed intake and growth rate. Immunization against gonadotropin-releasing hormone (GnRH) (IM, immunocastration) was developed for finishing boars and recently extrapolated to females. Immunocastration acts by suppressing reproductive activity and improving the growth potential. The objective of this study was to evaluate the effects of IM on growth performance, reproductive activity and carcass characteristics of late finishing gilts. Seventy-two gilts (63.49 ± 0.39 kg) were either injected with saline (Intact) or immunized against GnRH (Immunized). The study consisted of three experimental periods: between the first to second immunization (V1 to V2, 15 to 19 weeks of age), from the second immunization to the beginning of daily boar exposure (DBE) (V2 to DBE, 19 to 21 weeks of age) and from the beginning of DBE to slaughter (S) (DBE to S, 21 to 25 weeks of age). Immunized gilts showed an overall increase (from 15 to 25 weeks) of 3.90 kg (P < 0.05) of live weight, 56 g (P < 0.05) of average daily gain (ADG) and 250 g (P < 0.001) of average daily feed intake (ADFI). Immunized gilts had a greater ADFI (+240 g, P < 0.05) and worse feed conversion ratio (+0.26, P < 0.05) from 19 (V2) to 21 weeks of age (before DBE). Furthermore, those females had higher feed intake (+410 g; P < 0.001) plus greater daily weight gain (+92 g; P < 0.05) from V2 to S, and from DBE to S (+470 g of ADFI, P < 0.001; +129 g of ADG, P < 0.01, respectively). Immunocastration had no effect on backfat thickness, lean meat percentage and weight, cold carcass yield or loin depth (P > 0.05). Immunized gilts showed 4.4% increased cold carcass weight (P < 0.01) and 10.6% greater gross flank weight (P < 0.001). Immunization against GnRH did not influence shoulder, collar, loin, belly or ham weights. Nor did it influence belly fat thickness, or meat, skin plus fat and bones yields of cold ham (P > 0.05). Immunocastration reduced ovarian and uterine weights by 82% (P < 0.001) and 93% (P < 0.001), respectively, and suppressed oestrus manifestation in all gilts in the immunized group (P < 0.001). These results indicate that immunization against GnRH is a promising tool for stimulating growth performance with no detrimental effects on carcass quality of heavy weight finishing gilts, by means of oestrus suppression.     

Effect of estrus induction on prostaglandin content and prostaglandin synthesis enzyme expression in the uterus of early pregnant pigs

Prostaglandins (PGs) play a pivotal role in maternal recognition of pregnancy and implantation in pigs. In the present study, PGE₂, PGF_2α, and PGFM (PGF_2α metabolite) content, as well as PGE₂ synthase (mPGES-1) and PGF_2α synthase (PGFS) expression was investigated in early pregnant gilts with natural (n = 21) and PMSG/hCG-stimulated (n = 19) estrus. Endometrial tissue samples, uterine luminal flushings (ULFs), and blood serum were collected on days 10-11, 12, and 15 after insemination. Additionally, day 15 conceptuses were collected for mPGES-1 and PGFS protein expression. Effect of estrus induction was observed on day 15 of pregnancy, when the content of PGE₂ in the uterine lumen was fourfold lower in gonadotropin-stimulated gilts in comparison to controls (P < 0.001). Decreased PGE₂ content in ULFs of gonadotropin-treated pigs was preceded by lower endometrial mPGES-1 gene expression in hormonally-stimulated animals in comparison to control gilts (P < 0.01). On the other hand, estrus induction with PMSG/hCG resulted in higher PGE₂ accumulation in the endometrial tissue on day 15 of pregnancy (P < 0.01). Furthermore, PGF_2α content in the endometrium and PGFM levels in blood serum were lower in gonadotropin-treated gilts, especially on day 12 after insemination when compared to control gilts (P < 0.01). Finally, PGFS expression in day 15 conceptuses was decreased in animals with hormonally-induced estrus. We conclude that PMSG/hCG stimulation of prepubertal gilts to induce estrus results in changes of PG production and secretion during early pregnancy, which, in turn, may affect conceptus development, implantation, and the course of pregnancy.     

Maternal backfat depth in gestating sows has a greater influence on offspring growth and carcass lean yield than maternal feed allocation during gestation

A commercial pig spends nearly half of its life in utero and its nutrition during this time can influence birth weight and postnatal growth. We hypothesised that postnatal growth is increased in pigs raised by sows with a high backfat depth and high level of energy intake during gestation compared with sows with a low backfat depth and low level of energy intake during gestation. This was tested in a 2×3 factorial design experiment with 2 factors for gilt backfat depth (Thin and Fat) and 3 factors for gestation feed allowance (Restricted, Control and High). Between d 25 and d 90 of gestation, Thin gilts (n=68; 12±0.6 mm P2 backfat) and Fat gilts (n=72; 19±0.6 mm P2 backfat) were randomly allocated, as individuals, to a gestation diet (6.19 g/kg lysine, 13.0 MJ DE/kg) at the following feed allowances: 1.8 kg/day (Restricted); 2.5 kg/day (Control) and 3.5 kg/day (High). For the remainder of gestation and during lactation all gilts were treated similarly. At weaning (day 28), 155 piglets were sacrificed and 272 were individually housed and followed through to slaughter (day 158). At day 80 of gestation, fasted Thin Restricted gilts had lower serum IGF-1 concentrations than Thin High or Thin Control fed gilts (P<0.001). Pigs born from Fat gilts had greater backfat depths (P<0.05), a lower lean meat yield (P<0.05) and were heavier (P<0.05) at slaughter than pigs born from Thin gilts. Gilt gestation feed allowance had only transitory effects on average daily gain and feed conversion efficiency and had no effect on pig weight at slaughter (P>0.05) or lean meat yield (P>0.05). In conclusion, gilts with a backfat depth of ~19 mm at insemination produced pigs that were heavier and fatter at ~158 days of age than those born from gilts with ~12 mm backfat depth at insemination. Maternal body condition during gestation had a more predominant influence on growth parameters of the offspring, such as weight at slaughter and backfat depth, than did feed level during gestation.     

Dietary energy source and feeding levels during the rearing period affect ovarian follicular development and oocyte maturation in gilts

Fifty-four Landrace × Yorkshire gilts (59.0 ± 4.2 kg and 147 ± 3 d old) were used to examine the effects of dietary energy source (starch or mixed fat) at high [112.5% of energy requirements recommended by NRC (1998)], normal (100%), and low (87.5%) energy feeding levels on ovarian follicular development and oocyte maturation. Forty-seven estrus gilts were slaughtered at Day 19 after the second estrus; oocytes were recovered from follicles >4 mm in diameter, and matured in vitro for 44 h. Gilts fed high-energy diets had more follicles >4 mm (mean, 25.8 vs. 19.1, P < 0.05) and more oocytes that reached metaphase II (80.3 vs. 64.0%, P < 0.05) than those fed the low-energy diet. Furthermore, gilts fed starch-rich diets had enhanced oocyte nuclear maturation relative to those fed fat-rich diets (75.4 vs. 68.0%, P < 0.05). Compared to the lower-energy feeding groups, high-energy feeding groups had higher (P < 0.05) blood concentrations of postprandial insulin (1562.4 vs. 990.0 ng/4 h), IGF-I (321.2 vs. 256.9 ng/mL), and LH pulses (2.7 vs. 1.4 pulses/6 h). Follicular fluid concentrations of IGF-I (198.5 vs. 143.1 ng/mL) and estradiol (152.6 vs. 124.8 ng/mL) were higher (P < 0.05) in the high-energy group than in the normal group. Compared with gilts fed the high-energy diet supplemented with fat, gilts fed the high-energy diet supplemented with starch had a tendency (P < 0.10) towards increased IGF-I concentration in both blood and follicular fluid, and improved oocyte nuclear maturation during culture in vitro. We inferred that starch-rich, high-energy diets during rearing may improve ovarian follicular development and oocyte maturation in replacement gilts.     

Consequences of different dietary energy sources during follicular development on subsequent fertility of cyclic gilts

The objective of the present study was to investigate the effects of dietary-induced insulin enhancement during the late luteal phase on subsequent fertility of gilts. Fifty-two littermate cyclic gilts were subjected to dietary treatments where two energy sources were tested: corn starch (T1) and soybean oil (T2). The experimental diets were supposed to provide similar amounts of dietary energy, but from different sources. Gilts were fed ad libitum, starting day 8 of the estrous cycle, until the next standing heat. Blood sampling was performed in a subgroup of 20 gilts on days 14 and 21 of the cycle for analyses of glucose and insulin, and after ovulation detection until 18 h after ovulation for progesterone. All gilts were slaughtered on day 28 of pregnancy and the reproductive tracts recovered for further analysis. T1 gilts showed higher postprandial insulin peak on days 14 and 21 and lower glucose levels 4 h after feeding on day 14 (P<0.05), however, there were no treatment effects on plasma progesterone concentrations. Dietary energy sources did not affect average daily feed intake, body weight and backfat on day 28 of pregnancy. Estrous cycle length, estrus duration and time of ovulation were not affected by previous nutritional treatments either. T1 gilts showed higher ovulation rates, number of embryos, embryo weight and placental weight (P<0.05). There were no treatment effects on pregnancy rate, embryo survival rate and volume of amniotic fluid. A positive correlation between progesterone concentration 18 h after ovulation and ovulation rate was observed (r=0.75; P<0.01). These results suggest that it is possible to manipulate dietary insulin response in cyclic gilts and, thus, improve reproductive efficiency when feeding starch as the main energy source during the late luteal and follicular phases of the cycle.     

Exogenous genistein in late gestation: effects on fetal development and sow and piglet performance

Due to their functional similarity to estradiol, phytoestrogens could prove to be beneficial in late gestating sows. The goal of this study was to determine the impact of providing the phytoestrogen genistein during late pregnancy on the performance of sows and their litters. In total, 56 gilts were equally divided into the two following groups on day 90 of gestation: (1) controls (CTL); and (2) two daily i.m. injections of 220 mg of genistein (GEN). Treatments were carried out until farrowing. Jugular blood samples were collected from 16 gilts/treatment on days 89 and 110 of gestation, and on days 3 and 21 of lactation. Milk samples were also obtained from those sows on day 3 of lactation. A male piglet from 16 CTL and 15 GEN litters was slaughtered at 24 h postpartum and a blood sample was obtained. The liver, heart and visceral organs were weighed and the semitendinosus (ST) muscle was collected and carcass composition was determined. The treatment increased (P<0.05) the concentrations of genistein and daidzein in the plasma of gilts on day 110 of gestation and of genistein in the plasma of piglets at 24 h postpartum. It also increased IGF1 concentrations in gilts at the end of the treatment period (P<0.05). Genistein had no impact (P>0.1) on weight or backfat loss of sows during lactation, milk composition or weights of piglets. The pre-weaning mortality rate of piglets was very low (<7%), yet the odds ratio comparing CTL with GEN sows indicated almost twice as many chances of pre-weaning deaths occurring in litters from CTL than GEN sows. Weights of the piglet carcasses were similar for both treatments, as well as weights of the various organs and of the ST muscle (P>0.1). However, carcasses from GEN litters contained more fat than those from CTL litters (9.63% v. 8.34%, P<0.05). None of the biochemical properties of the ST muscle differed between groups (P>0.1). In conclusion, injecting gilts with 440 mg/day of genistein in late gestation increased IGF1 concentrations in gilts and carcass fat in neonatal piglets, but had minimal effect on muscle development of piglets at birth and on the performance of lactating sows and their litters.