Post-weaning Estrus Research Articles

PSIII-13 Putative metabolites for sow lifetime opportunity and production traits

Abstract Identifying females with favorable lifetime born alive (opportunity) and weaned (wn; production) traits requires extended observation. Estimate of lifetime (4 parities) difference in the economic margin over genetic cost between a high producing female (48 pigs weaned; wn) and a low producing female (31 wn) is approximately $1,000. Determining metabolic compounds present from females with favorable or unfavorable longevity traits may provide profiles that could be assessed in younger females prior to entry within the breeding system to indicate their potential productivity. Females within the USMARC breeding system were retained through four parities then harvested between 12 to 15 d following their post-weaning estrus. Liver, skeletal muscle, and subcutaneous adipose tissues were collected and stored at -80° C for later analyses. Females were categorically identified by the level of opportunity (born alive; ba) and production (wn) over their lifetime. Females with consistent opportunity and production traits at each parity were categorized as high (H; 61 ba), medium (M; 50 ba), or low (L; 39 ba) opportunity and H (50 wn), M (42 wn), or L (34 wn) production resulting in six categories (HH, HL, MH, ML, LH, LL). Tissue extracts were subjected to positive mode UPLC-MS and numerous features were detected. Using Progenesis Q software features were annotated and those with a fold-change ≥ 2.0 and P < 0.05 by category were then tested using a mixed model in SAS to determine LS Mean differences of raw abundances among the six categories. Of those compounds tested in SAS, a significance threshold was set at P < 0.01 as a false discovery adjustment. Within liver 877 compounds were analyzed with 152 yielding a significant (P < 0.01) categorical effect. Of those, 43 compounds predominantly identified either HH or LL from other categories. Within skeletal muscle 359 compounds were subjected to mixed models, 221 compounds had significance for a category effect, and 105 compounds were predominantly different for HH or LL from all other categories. Within adipose tissue, 406 compounds were submitted to mixed model testing, 186 compounds had a categorical effect with 44 compounds predominantly different for HH or LL categories. Annotation of these compounds suggest differences in metabolites associated with, but not limited to, bacteria by-products (pradmicin, adifolin, lactobacillic acid), alkyloids, sapogenins, amino acids (lysine, tyrosine), minerals (calcium, copper), lipids (sphingomyelin), and fatty acids (mono-, di-, tri-acylglycerol). Future confirmation and evaluation of these metabolites in young pre-breeding females will need to be done. Establishing a metabolic profile panel that could discern young pre-breeding gilts with a likelihood of becoming a LL female will improve economic productivity and animal welfare concerns.

Developing a Sow Vulva Volume Estimation Pipeline Based on LiDAR Imagery and Deep Learning

Highlights An artificial intelligence-enabled imagery data processing pipeline. Sow vulva swelling can be quantified using imagery automatically. Biological signs of sow estrus are quantified. Abstract. Accurate and timely estrus detection is one of the critical factors for improving the conception rate of sows in swine reproduction. Estrus detection in the current industry relies on experienced breeding technicians using the back pressure test method, which is time-consuming, labor-intensive, and subjective. This study aimed to develop an image-processing pipeline that could predict the onset of estrus by monitoring the variation of the vulva volume of sows. A robotic imaging system consisting of a LiDAR camera was used to collect depth and infrared (IR) images of sows multiple times per hour. The developed image processing pipeline consisted of a deep learning model (MobileNet) to exclude images with defective postures (e.g., excreting posture, vulva region not showing) for vulva detection. The selected images were further processed to (1) segment sow vulva regions (3-dimensional surface) using a U-Net model, (2) exclude incorrectly segmented 3D vulva surfaces using a MobileNet model, and (3) calculate the vulva volume using the segmented 3D vulva surface. Results show that all three models achieved high test accuracy of 94.8% (MobileNet 1), 96.7% (U-Net), and 100% (MobileNet 2). The vulva volume was calculated using the developed pipeline for all the test sows. Daily average vulva volume showed a noticeable increase in all sows at 0-1 day prior to the onset of estrus. This study concluded that the developed image processing pipeline could automatically detect vulva swelling, which may be used as a biological sign indicating the onset of post-weaning estrus in sows. Keywords: 3D camera, Digital agriculture, Estrus detection, Robotic imaging system, Swine reproduction.

Isomaltooligosaccharide and Bacillus regulate the duration of farrowing and weaning-estrous interval in sows during the perinatal period by changing the gut microbiota of sows.

This study investigated the effects of isomaltooligosaccharide (IMO) and Bacillus in perinatal diets on the duration of farrowing and post-weaning estrus, serum reproductive hormone concentrations, and gut microbiota and its metabolites of sows. Multiparous sows (n = 130) were fed diets without IMO (control, CON group), or diets containing only IMO (IMO group), IMO and Bacillus subtilis (IMOS group), IMO and Bacillus licheniformis (IMOL group), and IMO and B. subtilis and B. licheniformis (IMOSL group), respectively. The results indicate that the duration of farrowing and post-weaning estrus was shorter in sows in the IMOS, IMOL, and IMOSL groups, and the weaning-estrous interval was lower in sows in the IMOL greoup. In addition, the lowest fecal score was observed in the IMOL group during d 106 to 112 of gestation. Sows in most of the treatment groups had a higher concentration of serum prolactin and prostaglandin at farrowing, but a lower serum concentration of estradiol, oxytocin, and progesterone on d 18 of lactation than sows in the CON group. The treatment groups had a higher abundance of Candidatus Methanoplasma and Bacillus and a lower abundance of Escherichia-Shigella in their feces at farrowing. Furthermore, the treatment groups had higher concentrations of total short-chain fatty acids (SCFA) in feces at farrowing and a higher concentration of branched fatty acids in feces on d 18 of lactation. Furthermore, the abundance of Bacillus in feces was positively correlated with serum prostaglandin concentrations and fecal total SCFA of sows at farrowing, but was negatively correlated with the duration of farrowing. Overall, dietary IMO and Bacillus supplementation affected the concentration of serum reproductive hormones and the duration of farrowing and post-weaning estrus, and the gut microbiota is a key factor.

Complete sleep and local field potential analysis regarding estrus cycle, pregnancy, postpartum and post-weaning periods and homeostatic sleep regulation in female rats

Sleep and local field potential (LFP) characteristics were addressed during the reproductive cycle in female rats using long-term (60–70 days) recordings. Changes in homeostatic sleep regulation was tested by sleep deprivation (SDep). The effect of mother-pup separation on sleep was also investigated during the postpartum (PP) period. First half of the pregnancy and early PP period showed increased wakefulness (W) and higher arousal indicated by elevated beta and gamma activity. Slow wave sleep (SWS) recovery was suppressed while REM sleep replacement was complete after SDep in the PP period. Pup separation decreased maternal W during early-, but increased during middle PP while did not affect during late PP. More W, less SWS, higher light phase beta activity but lower gamma activity was seen during the post-weaning estrus cycle compared to the virgin one. Maternal sleep can be governed by the fetuses/pups needs and their presence, which elevate W of mothers. Complete REM sleep- and incomplete SWS replacement after SDep in the PP period may reflect the necessity of maternal REM sleep for the offspring while SWS increase may compete with W essential for maternal care. Maternal experience may cause sleep and LFP changes in the post-weaning estrus cycle.

Principles and Clinical Uses of Real-Time Ultrasonography in Female Swine Reproduction.

Simply SummaryReal-time ultrasonography (RTU) has become an essential diagnostic value when assessing female swine reproduction in either individual or groups of animals. Diagnostic application of RTU is applied throughout most stages of production, including gilt development, breeding, gestation and farrowing. Along with its most common use in on-farm assessment of pregnancy status, RTU is also used to troubleshoot disruptions in reproductive performance such as delayed puberty, prolonged wean-to-estrus interval, absence of post-weaning estrus, decreased conception and farrowing rates, vulval discharge, peripartum and puerperal disorders. This review aims to provide an overview on principles and clinical uses of RTU in female reproduction on commercial swine farms.Within the past 30 years, through ongoing technology and portability developments, real-time (b-mode) ultrasonography (RTU) has increasingly become a valuable diagnostic tool in assessing the female reproductive tract in swine. Initially applied in swine production to visually determine pregnancy status, RTU use has expanded to include assessment of the peri-pubertal and mature non-pregnant females as well. Transabdominal and transrectal modalities to visualizing the reproductive tract in swine have been reported with the transabdominal approach more common due to the fact of its ease of accessibility, animal/personnel safety, and reduced time to perform. Adjustable frequency transducers are preferred as they allow optimization of image quality at various depths. If a single transducer frequency must be selected, a 5 MHz probe provides the best versatility for visualizing the reproductive tract in swine. Other basic requirements for ultrasound equipment which will be used on commercial swine farms include being light weight and easy to handle, readily cleanable and disinfectable, long battery-life, and good durability. When using RTU for pregnancy determination, diagnosis is based upon a combination of the animal’s breeding records, the presence of embryonic fluid, and, depending upon gestational stage, fetal structures. If RTU is used as a diagnostic tool in assessing reproductive problems in an individual or a group of animals, sonographic evaluation of both the uterus and ovaries is performed. Tissues are delineated and assessed based upon their echogenicity, echotexture, and size. Uses of RTU in clinical practice may include assessment of delayed puberty, prolonged wean-to-estrus interval, absence of post-weaning estrus, herd disruptions in conception and farrowing rates, vulval discharge, peripartum and puerperal disorders. This review aims to provide an overview on principles and clinical uses of RTU with respect to application to address female reproductive performance issues in commercial swine operations.

Supplementation of Milky Flavors Improves the Reproductive Performance and Gut Function Using Sow Model.

This study was conducted to evaluate the effect of flavors on reproductive performance of sows and we also studied its effect on gut barrier function. Forty-eight Landrace × Yarkshire sows were randomly allotted and fed a basal diet added 0%, 0.05% or 0.10% flavor feed, respectively from parturition to day 28 of weaning. The results showed that supplementation of 0.05% or 0.10% flavors increased average daily feed intake (ADFI) of sows and average daily gain (ADG) of piglets, decreased the weight losses of sows, increased the survival ratio of weaning piglets (P < 0.05), especially shorten the post-weaning estrus interval significantly (P < 0.05). Supplementation of flavor additives tend to reduce the weight losses of sows and raise the survival ratio of piglet weaned (P > 0.05). Moreover, addition of flavors in diets reduced the intestinal permeability and enhanced digestibility of dry matter, crude protein, and energy (P < 0.05). Flavors supplementation significantly increased the level of gonadotropin releasing hormne (GnRH) of serum in sows after weaning. In conclusion, the results suggested that supplementation of dietary flavors could improve digestibility of nutrients and the reproductive performance of sows as well as the gut barrier function.

Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance

Excessive mobilization of body reserves during lactation delays the return to reproductive function in weaned primiparous sows. This study tested the hypothesis that supplementing the lactation diets of first-parity sows with ractopamine hydrochloride would reduce maternal weight loss and improve subsequent reproductive performance. Gestating gilts were allocated to one of two treatment groups (n=30 sows/treatment), with one group fed a standard lactation diet (2.5g/Mcal LYS: DE) throughout lactation (CTRL), whereas the treatment group received the standard lactation diet supplemented with 10mg/kg ractopamine hydrochloride (RAC) from d 1 to 13 of lactation and 20mg/kg RAC from d 14 of lactation until artificial insemination (AI). Weaning occurred on d 21 of lactation, with AI occurring at the first post-weaning estrus. Compared to CTRL, RAC supplementation decreased (P<0.05) liveweight loss between d 13 and 20 of lactation (4.3±0.90 versus 1.3±0.96kg), and tended to increase (P=0.06) the number of second litter piglets born alive (9.5±0.52 versus 8.1±0.74). Treatment (RAC versus CTRL) reduced milk protein levels on d 13 and 20 of lactation (P<0.05), and piglet weight gain between d 13 and 20 of lactation (260±0.01 versus 310±0.01g/day, P<0.01). In conclusion, it is evident that dietary RAC altered milk composition and stimulated conservation of maternal body reserves during the third week of lactation, resulting in a beneficial effect on subsequent reproductive performance.

Current strategies for reproductive management of gilts and sows in North America.

Many advances in genetic selection, nutrition, housing and disease control have been incorporated into modern pork production since the 1950s resulting in highly prolific females and practices and technologies, which significantly increased efficiency of reproduction in the breeding herd. The objective of this manuscript is to review the literature and current industry practices employed for reproductive management. In particular the authors focus on assisted reproduction technologies and their application for enhanced productivity. Modern maternal line genotypes have lower appetites and exceptional lean growth potential compared to females of 20 yr ago. Thus, nutrient requirements and management techniques and technologies, which affect gilt development and sow longevity, require continuous updating. Failure to detect estrus accurately has the greatest impact on farrowing rate and litter size. Yet, even accurate estrus detection will not compensate for the variability in the interval between onset of estrus and actual time of ovulation. However, administration of GnRH analogs in weaned sows and in gilts after withdrawal of altrenogest do overcome this variability and thereby synchronize ovulation, which makes fixed-time AI practical. Seasonal infertility, mediated by temperature and photoperiod, is a persistent problem. Training workers in the art of stockmanship is of increasing importance as consumers become more interested in humane animal care. Altrenogest, is used to synchronize the estrous cycle of gilts, to prolong gestation for 2–3 d to synchronize farrowing and to postpone post-weaning estrus. P.G. 600® is used for induction of estrus in pre-pubertal gilts and as a treatment to overcome seasonal anestrous. Sperm cell numbers/dose of semen is significantly less for post cervical AI than for cervical AI. Real-time ultrasonography is used to determine pregnancy during wk 3–5. PGF2α effectively induces farrowing when administered within two d of normal gestation length. Ovulation synchronization, single fixed-time AI and induced parturition may lead to farrowing synchronization, which facilitates supervision and reduces stillbirths and piglet mortality. Attendance and assistance at farrowing is important especially to ensure adequate colostrum consumption by piglets immediately after birth. New performance terminologies are presented.

POSTWEANING ESTRUS REACTION of sows after the treat MeNT with eCG IN WARM AND COOL SEASONS

POSTWEANING ESTRUS REACTION of sows after the treat MeNT with eCG IN WARM AND COOL SEASONS

Macroenvironment effects on oocytes and embryos in swine

As in other domestic mammals, the interaction between genotype and environment in swine has profound effects on the ultimate phenotype of the individual born. Interactions within the litter in utero add an additional level of complexity in a litter-bearing species like the pig. Nutritional manipulations during the preovulatory period affect the maturity of the follicle and enclosed oocyte, and the metabolic and endocrine mechanisms potentially mediating these effects have been described. Extensive research on lactational catabolism in the first parity sow has established an association between the development of immature follicles and oocytes, and the reduced fertility of these sows when bred at the first postweaning estrus. This negative impact of lactational catabolism appears to be exaggerated in contemporary dam-lines by a minimal delay between weaning and first estrus, further limiting the maturity of the follicle and oocyte at the time of ovulation. Metabolic programming may induce gender-specific loss of embryos by Day 30 and affects embryonic development directly, without significant effects on placental size. In contrast, inadvertent crowding of embryos in utero, particularly evident in a sub-population of mature sows with high ovulation rates and moderate to high embryonic survival to Day 30, significantly limits placental development of crowded litters. However, even at Day 30, moderate crowding in utero also appears to affect myogenesis in the embryo in a gender-specific manner. In the absence of compensatory placental growth after Day 30, classic measures of IUGR are evident in surviving fetuses at Day 90 and at term.

19 LOW-DOSE DEEP INTRAUTERINE INSEMINATION IN SOWS UNDER CONDITIONS: INCIDENCE OF UNILATERAL FERTILIZATIONS

A new procedure for nonsurgical deep intrauterine insemination (DUI) in non-sedated sows has recently been reported (Martinez et al. 2002 Reproduction 123, 163–170). In comparison to traditional artificial insemination (AI), using this procedure, a 20-fold reduction in the number of spermatozoa inseminated can be used without a decrease in fertility when hormonally treated post-weaning estrous sows are used. The aim of the present study was to evaluate the effectiveness of DUI under field conditions. In Experiment 1, crossbred sows (2–6 parity) were weaned at 20.75 ± 0.06 days. Estrous detection was performed once per day, beginning 3 days after weaning. Sows with a weaning to estrus interval of 4–5 days were selected to be inseminated. A total of 190 sows were inseminated at 12, 24, and 36 h after onset of estrus using one of the following two regimes: (1) DUI with 150 × 106 fresh spermatozoa in 5 mL of BTS (n = 95) and (2) Traditional AI with 3 × 109 fresh spermatozoa in 100 mL of BTS (n = 95) prepared from the same semen samples used for the DUI group. Farrowing rates (FR) and litter sizes (LTS; mean ± SEM) from both groups were compared using chi-squared test and ANOVA, respectively. There was no significant difference in the FR between groups (83.2 and 86.3% for DUI and AI groups, respectively). However, a decrease (P &lt; 0.001) in the LTS was observed in sows inseminated by the DUI procedure (9.8 ± 0.29 and 10.9 ± 0.17, respectively). In Experiment 2, seventy one natural post-weaning estrus sows were used. Fifty-five sows were DUI inseminated three times with 150 (n = 17), 300 (n = 19), or 600 (n = 19) × 106 spermatozoa in 5, 10, or 20 mL of BTS, respectively. The remaining sows (n = 16) were traditionally inseminated. On Day 6 after estrus, sows were subjected to laparotomy and the tips of both uterine horns were flushed in order to evaluate pregnancy rate (PR: percentage of sows with at least 4 viable embryos) and fertilization rate (ratio of viable embryos to the total number of embryos and oocytes). PR was similar in all the groups, ranging from 84.2% (DUI 300 × 106 spermatozoa group) to 94.7% (DUI 600 × 106 spermatozoa group). Fertilization rate and the percentage of bilateral fertilization after DUI with 600 × 106 spermatozoa did not differ from those of the AI group (97.8 and 100% vs. 98.4 and 100%, respectively), but a significant decrease in both parameters (P &lt; 0.05; chi-square test) was observed in sows inseminated with 300 (94.3 and 87.5%) or 150 (84.4 and 66.7%) × 106 spermatozoa. In conclusion, DUI with 150 × 106 spermatozoa offers similar FR but a lower LTS in sows with natural estrus in comparison with those parameters obtained when traditional AI is used. The lower litter size could be related to the low percentage of bilateral fertilization observed in that group. This work was supported by CDTI 020003.

Early-weaned sows: altrenogest therapy, estrus, ovulation, and reproductive performance

Early weaning is a technique used to increase swine health status, and may cause consequences in reproductive performance of sows. An experiment was performed to evaluate these effects in a herd of sows, with weaning at 9 or 10 days post-farrowing, located in west of Minas Gerais, Brazil. Large-White sows ( n=102), with three or four previous parturitions were randomly allocated to three treatment groups: T1: artificial insemination (AI) at first post-weaning estrus of the sows; T2: AI at second post-weaning estrus, T3: AI at first estrus, after an administration of a daily individual dose of 20 mg of altrenogest from 5 to 8 days post-weaning. The duration of the first post-weaning estrus did not differ among treatment groups; however, the second estrus of the T2 group was of shorter duration relative to the other treatment groups ( P≤0.035). Ovulation occurred earlier at the second estrus of the T2 group, compared with the T1 and T3 groups ( P≤0.027), being similar to that at the first estrus of T2 group ( P=0.177). The relationship of the timing between ovulation and estrus was similar among treatment groups ( P≥0.221). There was no difference in farrowing rate among treatment groups ( P≥0.313). The T2 group produced a mean of 2.5 more piglets per litter ( P=0.002). In conclusion, the use of altrenogest did not increase the reproductive performance of early-weaned sows.

Reproductive endocrinology and postweaning performance in the multiparous sow: Part 2. Influence of nursing behavior

The reason for variation in postweaning reproductive performance among multiparous sows is to a large extent unknown. In the present study, the influence of nursing behavior was explored. Blood samples were collected during lactation and after weaning from 18 multiparous sows for cortisol, LH, estradiol-17β (E2), and progesterone analysis. Sow and piglet behavior was videotaped. The sows were fed according to litter size and slaughtered after the second postweaning estrus. The sows were divided into two groups based on average values for the different behavioral parameters. Sows with a long average nursing duration (long group) had lower average and basal LH levels on Day 14 and 21 of lactation as compared to the sows having a short average nursing duration (short group). In the long group, concentrations of E2 were lower the day after weaning, but on Day 15 and 21 of lactation no differences were noted between the two groups. Postweaning performance seemed impaired in the long group, though, differences were not significant. The sows in the long group were heavier and tended to lose less weight during lactation. To conclude, nursing duration seems to influence the extent to which reproductive functions are inhibited during lactation.

Lack of an effect of prostaglandin injection at estrus onset on the time of ovulation and on reproductive performance in weaned sows

We evaluated the effects of a PGF2alpha analogue on time of ovulation and reproductive performance in multiparous Camborough sows (n=47). At onset of first post-weaning estrus, sows received either an intravulval injection of 3.75 mg of prostaglandin analogue (PGF) or, served as a non-injected control (CON). Beginning 24 h after the onset of estrus, transcutaneous ultrasonography was carried out every six h to determine time of ovulation. At 36, 54, and 72 h after the onset of estrus, blood samples were taken for progesterone analysis. Weaning-to-estrus (WEI), duration of estrus, ovulation rate and number of live embryos at d 28 of gestation were recorded. Treatment had no effect (P > 0.05) on any parameters measured. Duration of estrus classified as less or greater than the overall mean also had no effect (P > 0.05) on any of the parameters measured. Results indicate that treatment did not advance ovulation nor did it improve reproductive performance in sows. Overall, a negative correlation of WEI with the ovulation rate (P = 0.0005, r = −0.54) was established.

Adaptations of glucose metabolism in multiparous sows: effects of pregnancy and feeding level.

This experiment was undertaken to determine whether pregnancy affects glucose metabolism and insulin sensitivity in sows fed at different levels. Four replicates of six multiparous Large White sows were involved. In each replicate, four sows were inseminated on the first postweaning estrus (pregnant group) and the two remaining were kept nonpregnant. Half of the sows of each group were fed 2.5 kg/d (low level) and the others 4 kg/d (high level) of the same standard pregnancy diet. Jugular catheters were implanted 2 to 3 d after estrus. Plasma concentrations of glucose, insulin, and FFA were determined before and during the 4 h following the morning meal at 10, 30, 59, 87, 93, 101, and 110 d of gestation and at equivalent periods for the nonpregnant sows. Intravenous glucose tolerance tests were performed at 33, 71, 85, 96, and 108 d by i.v. injection of 0.5 g glucose/kg BW. Compared with the glycemia before the meal, all the sows showed hyperglycemia 30 min after the initiation of the meal and hypoglycemia thereafter, with a minimum reached at approximately 75 min. Insulinemia increased from 20 min after food access, reached a maximum at 40 min, and returned to the basal level after 180 min. The higher feeding level increased plasma insulin and lowered plasma glucose levels. Glycemia and insulinemia profiles changed from 87 d onward in the pregnant sows. The peak of glucose induced by the meal was higher, and the subsequent period of hypoglycemia almost disappeared. The area under the insulin curve was unchanged, but insulin secretion was delayed. The glucose tolerance tests showed that between d 85 and 108 the half-life of injected glucose increased and insulin secretion was delayed in the pregnant sows. Compared to the following stages, plasma FFA were high before and after the meal at 10 d, which most likely was a residual effect from the previous gestation/lactation cycle. They were lower from 30 to 101 d in the pregnant and nonpregnant sows. At 110 d, fasting FFA were high again in the pregnant sows only, very likely in relation to the preparation for lactation. This experiment showed that insulin sensitivity decreases after 85 d of pregnancy in multiparous sows.

Effect of zearalenone on days 7 to 10 post-mating on blastocyst development and endometrial morphology in sows.

First litter sows in naturally occurring post-weaning estrus were hand mated to proven boars and were fed a diet supplemented with zearalenone, an estrogenic mycotoxin (1 mg zearalenone/kg body weight), or a control diet on days 7 through 10 after mating. Embryos (blastocysts) and endometrial biopsies were collected from control and treated sows on days 9, 11, and 13 after mating. All blastocysts harvested on day 9 were spherical; treatment of sows with zearalenone had no effect on blastocyst development. Blastocysts collected from treated sows on day 11 were in stages of elongation comparable to those of blastocysts from control sows but had mild degenerative changes in the embryonic disks, characterized by slightly retarded development and an increase in the number of necrotic cells. Blastocysts collected from treated sows on day 13 were in an advanced stage of degeneration, characterized by circumferential constrictive division, fragmentation, and degeneration and disorganization of the embryonic disk. Feeding zearalenone to pregnant sows had no effect on the normal decrease in height of the endometrial luminal epithelium on days 9 through 13 after mating and no effect on morphologic appearance of secretory vesicles in the endometrial glandular epithelium. The dosage scheme of zearalenone used in this study did not cause any morphologic changes in the endometrium that could be associated with hyperestrogenism.

THE INFLUENCE OF FEEDING LEVEL DURING LACTATION AND GESTATION ON THE ENDOCRINE STATUS AND REPRODUCTIVE PERFORMANCE OF SECOND PARITY SOWS

During their second lactation, 123 second-parity Yorkshire × Landrace sows were fed either 6 kg or 3 kg d−1 of a barley-soybean meal diet formulated to provide 12.5 MJ DE kg−1 and 16% crude protein (approximately 90 and 45% of National Research Council (NRC 1988) requirements). From 48 h after the onset of the post-weaning estrus, sows from each lactation feed treatment were allocated equally to receive the same diet at 3.6 kg or 1.8 kg d−1 (approximately 160 and 80% of NRC (1988) requirements), until slaughtered at 25 d of gestation. On days 4, 8, 12 and 16 of gestation, eight sows from each of the four feed level combinations were blood sampled at 15-min intervals for 4 h. Additionally, a further eight sows were sampled once on each of the above days. The lower plane of feeding during lactation resulted in a greater body weight and backfat loss (26.6 vs. 13.8 kg and 6.5 vs. 3.6 mm, respectively; P &lt; 0.01 for both), an increased incidence of anestrus (21 vs. 8%; P &lt; 0.05) and a longer and more variable interval to estrus (8.9 ± 0.4 vs. 6.0 ± 0.2 d; P &lt; 0.01) than higher level feeding. There was no effect of lactation feeding level on ovulation rate (17.6 ± 0.3 vs. 17.7 ± 0.4 for sows having the higher and lower feed intakes, respectively). There was a main effect of lactation (P &lt; 0.01), but not gestation, feeding level and an interaction between lactation and gestation feeding level (P &lt; 0.02), on number of embryos and percent embryo survival. Embryo numbers and survival were reduced following lower plane feeding during lactation but were lowest following lower plane feeding during both lactation and gestation. There was no effect of sampling day on plasma LH concentrations but plasma LH was lower (P &lt; 0.01) in sows on lower plane feeding during both lactation and gestation. The present data confirm an adverse effect of low plane feeding during lactation on subsequent sow reproductive performance and suggest that a reduction in plasma LH concentrations may be involved. These data fail to confirm any adverse effect on embryo survival of high plane feeding during the first 25 d of gestation. Key words: Sow, feed intake, LH, progesterone, reproduction

Relationship between body fat and postweaning interval to estrus in primiparous sows.

Twenty-two primiparous Yorkshire sows were used to determine whether a minimal threshold of body fat exists below which the return to estrus is delayed. A second objective was to examine the relationship between body fat and interval from weaning to estrus in restricted-fed sows. During lactation (28 d), sows received 7, 9, 11 or 13 Mcal of ME daily to produce a range of sow body fatness at weaning. Intake of all dietary essentials except ME was similar for all sows. Litter size was adjusted to 10 pigs for all sows by d 3 postpartum. Each day from weaning to estrus, sows received 110 kcal ME per kg metabolic body weight plus 1,359 kcal ME per sow. Body fat was estimated at weaning and at first postweaning estrus by deuterium oxide dilution. Last rib backfat depth was determined ultrasonically 24 h postpartum and at weaning. Irrespective of dietary ME intake, percentage body fat at weaning (R2 = .24; P less than .05) and first postweaning estrus (R2 = .03; P greater than .50) accounted for only a small portion of variation in interval from weaning to estrus. Likewise, loss of backfat depth during lactation was not an accurate predictor of interval from weaning to estrus (R2 = .24; P less than .05). The low coefficients of determination (less than .25) suggest that body fat is a minor controller of postweaning interval to estrus. In contrast, dietary ME intake during lactation accounted for the largest portion of the variation (R2; = .48; P less than .01) in postweaning interval to estrus. We conclude that timing of postweaning estrus in primiparous sows is not dependent on a minimal threshold of body fat. Furthermore, effects of lactational ME intake on the postweaning interval to estrus are more pronounced than the effects of body fat.

Study of follicular development and heredity of morphological types of ovaries in prepuberal gilts.

Two different morphological types of ovaries ("grape" and "other" types) previously described by microscopic examination were studied on 107 live gilts. The ovarian type and distribution of macroscopic follicles during the prepuberal period were determined at 140, 160 and 180 d of age by laparoscopic examination. The incidence of grape-type (GT) ovaries was higher (P less than .05) at 140 d of age (50.5%) than at 160 d (38.3%) or 180 d (35.5%). At maturity (d 19 of the first postweaning estrus), 37.7% of the ovaries were classified as GT. The proportion of gilts that maintained their initial type (at 140 d of age) at 160 d, 180 d and at maturity was higher (P less than .05) for the gilts having the other-type (OT) ovaries (49% and 25% for OT and GT, respectively). The mean number of small follicles (1 to 3 mm in diameter) was higher (P less than .05) for the OT ovaries at 140 d (71.5 vs 18.0), at 160 d (79.3 vs 26.2) and at 180 d (77.0 vs 32.8). The number of follicles of 4 to 5 mm was higher (P less than .05) for GT ovaries at 140 d (16.4 vs 4.8), at 160 d (20.9 vs 4.8) and at 180 d of age (21.4 vs 5.7). The large follicles (greater than or equal to 6 mm) were more numerous for the GT at 140 d (7.0 vs .3), at 160 d (5.7 vs .5) and at 180 d (4.4 vs .6). No statistical difference was observed at maturity in the distribution of follicles between the two types.(ABSTRACT TRUNCATED AT 250 WORDS)

EFFECT OF LACTATION FEED INTAKE AND GONADOTROPHIN-RELEASING HORMONE ON THE REPRODUCTIVE PERFORMANCE OF SOWS

Twenty-four first parity and 48 multiparity crossbred sows (Yorkshire × Landrace) were used in a 2 × 2 factorial design involving high (H) or low (L) lactation feed intakes and the intramuscular injection, or not, of 50 μg of gonadotrophin-releasing hormone (GnRH) at the onset of the first postweaning estrus. All sows were weighed at farrowing and weaning. The H feed intake entailed feeding sows at levels of 10, 13, and 14% of each sow's immediate postfarrowing metabolic weight during weeks 1, 2, and 3–4 of lactation, respectively. Low-fed sows received 50% of the H feed level. The diet contained 12.5 MJ DE kg−1 and 16% crude protein. Between weaning and mating, and following mating, all sows were fed 2.25 kg daily of the lactation diet. After weaning, sows were exposed to a boar twice daily to facilitate estrus detection. GnRH was administered at the onset of standing heat. All sows were slaughtered 25 d after mating at which time the reproductive tracts were removed and examined to determine the number of ovulations and the number of viable embryos. Low-level feeding resulted in an extension of the remating interval (5.9 ± 0.3 vs. 4.5 ± 0.2 d; P &lt; 0.05), an increased incidence of anestrus (16.7 vs. 3.6%; P &gt; 0.1) and a reduction in pregnancy rates (69.7 vs. 81.6%; P &gt; 0.1). Interactions were noted between lactation feeding level and GnRH injection (P &lt; 0.05) and between parity and GnRH injection (P &lt; 0.05) for number of viable embryos. The data obtained suggest that both low level of feeding during lactation and a young age are associated with decreased embryo numbers, but this situation is alleviated by the administration of GnRH. Key words: Sows, feed intake, estrus, GnRH