Estrous and litter traits in gilts altered by altrenogest, flushing and pubertal status

Influences of estrous synchronization with altrenogest and flushing on reproductive traits in gilts were evaluated in three experiments on two farms. Crossbred gilts were fed altrenogest or altrenogest and an additional 1.55 kg ground sorghum grain for at least 10 d before breeding (flushing), or served as controls. Additional grain for the flushing treatment was provided to gilts from the eighth day of altrenogest treatment until they were detected in estrus. The combination of altrenogest and flushing (on Farm A) increased (P less than .05) litter size when compared with gilts treated only with altrenogest and controls that received neither altrenogest nor flushing. This response was entirely among gilts inseminated at their pubertal estrus. For pubertal gilts fed altrenogest and the flushing treatment, litter traits were similar to other treated or control gilts inseminated at a postpubertal estrus. No treatment effects on litter size were detected for gilts inseminated at a postpubertal estrus. Gilts on Farm B responded differently, with larger litter sizes (P = .08) for those treated with altrenogest and flushing plus altrenogest than for control gilts. Reasons for farm differences might be unidentified genetic or management factors or different seasons of the year when gilts were treated on Farm B (summer) vs Farm A (fall, winter and spring). Our results indicate a marked potential for increasing litter size in gilts mated at their pubertal estrus because their unstimulated ovulation rate (no altrenogest or flushing) did not challenge adequately the biological capacity of their uteri.     

Scheduled breeding of gilts after estrous synchronization with altrenogest

Fertility of 104 gilts artificially inseminated (AI) at a predetermined time (scheduled AI) after estrous synchronization with altrenogest (15 mg X gilt-1 X d-1 for 18 d) was compared with that of 103 gilts checked for estrus (estrus checked) and inseminated after altrenogest. Scheduled-AI gilts were inseminated once on d 5, 6 and 7 after the last altrenogest feeding (d 0). Estrus-checked gilts were exposed to a boar twice daily at 0830 and 1630 h and inseminated after the second and third estrous detection period following first detected estrus. Percentage of gilts assigned to treatment that farrowed (72.8 vs 67.3%), total pigs farrowed (11 +/- .4 vs 11.3 +/- .4) and pigs born alive (10.1 +/- .4 vs 10.5 +/- .4) were similar for estrus-checked and scheduled-AI gilts, respectively. We conclude that scheduled AI can be used with estrous synchronization for gilts and may have advantages in breeding herd management and the use of AI in swine.     

Effect of birth and fraternal litter size and cross-fostering on growth and reproduction in swine

Twelve hundred fifty-one pigs from six farrowings (FGRP) were classified within a FGRP by their birth litter size (BL- = below average and BL+ = above average), randomly allotted to nursing litter sizes of 6 or 12+ pigs/sow (NL- vs NL+) and reared by their own or foster dams (XF- vs XF+). Pigs were weighed at birth, 21 d and when near 105 kg. A random sample of 40 gilts per FGRP was retained for observation of pubertal age and primipara conception. Twenty-four gilts per FGRP were farrowed and rebred for a second parity. Pigs born in large litters were younger at 105 kg than those born in small litters (189 vs 196 d +/- 1.4); no other differences (P greater than .05) were observed for BL. Pigs reared in larger litters had lower survival rate from birth to weaning (79 vs 86% +/- 1), had slower weight gains to 21 d of age (5.3 vs 6.6 kg +/- .17) and were older at 105 kg (195 vs 190 d +/- 1.4) than those reared in small litters (P less than .04). Cross-fostered pigs were slower gaining to 21 d (5.9 vs 6.1 kg +/- .14) and were older at 105 kg (195 vs 191 d +/- 1.4) than pigs not cross-fostered pigs (P less than .02). Growth beyond 105 kg and pubertal age were unaffected by any factor studied (P greater than .05). Although size of birth litter did not affect (P greater than .05) any reproductive trait, an interaction between litter size and farrowing group was detected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovulation rate and litter size in gilts immunized against androstenedione and 17alpha-hydroxyprogesterone

Two experiments were conducted to evaluate the effects of the immunization of gilts against ovarian steroids on ovulation rate and litter size. In Exp. 1, gilts (n = five gilts/treatment) at 165+/-1.6 d of age were immunized against either carrier (Control), androstenedione, or 17alpha-hydroxyprogesterone. Age at puberty and estrous cycle length averaged 208+/-5.5 (P = 0.67) and 20.3+/-2.8 d (P = 0.41), respectively, and were not affected by treatment. The androstenedione- and 17alpha-hydroxyprogesterone immunized gilts had higher (P < 0.02) ovulation rates than Controls (14.2, 14.2, and 11.4+/-0.8, respectively). Total pigs born (P = 0.66) and pigs born live (P = 0.65) for the androstenedione-treated group were not different from Controls. Gestation length was not different (P = 0.36) between any of the treatments and the Controls (115+/-0.9 d). Procedures used in Exp. 2 were similar to those in Exp. 1, except that only Control (n= 18) and 17alpha-hydroxyprogesterone (n = 16) treatments were included and only litter size at farrowing was measured. Total pigs and pigs born live were higher in the 17a-hydroxyprogesterone-treated gilts than in the Controls (12.6 vs 10.5+/-0.6, P < 0.02; and 11.4 vs 9.2+/-0.6; P < 0.01, respectively). Data from this study indicate that litter size in gilts can be increased by immunization against 17alpha-hydroxyprogesterone.     

Study on the oestrous synchronization in gilts by using progestin altrenogest and hCG: its effect on the follicular development, ovulation time and subsequent reproductive performance.

The aim of this study was to further investigate the effect of using progestin altrenogest and hCG to synchronize the oestrous cycle and its effect on follicular development, ovulation time and subsequent reproductive performance. Thirty crossbred gilts were divided into three groups. Group A (control) received a 5 ml of normal saline for 18 consecutive days by individually top-dressing. Groups B and C gilts received 20 mg (5 ml) of progestin altrenogest for 18 consecutive days by individually top-dressing. On day 3 (72 h) after withdrawal of progestin altrenogest, Group C gilts received hCG (500 IU, im). The follicular development and ovulation time were examined by transabdominal ultrasonography. Subsequent reproductive performances, i.e. number of total born per litter (NTB), number of live born per litter (NBA), number of stillbirth per litter (NSB), average piglet birth weight (ABW), lactation length (LL) and weaning to oestrous interval (WOI), were recorded. None of the gilts in Group A showed oestrus within 10 days after withdrawal of normal saline. Groups B (eight of 10) and C gilts (four of 10) came into oestrus at 5.6 +/- 0.5 and 6.5 +/- 0.6 days after withdrawal of progestin altrenogest, respectively. The ovulation time of Groups B and C gilts took placed at 25.0 +/- 4.7 and 25.0 +/- 5.0 h after standing oestrus, respectively. The pre-ovulatory follicular size (diameter) of Groups B and C gilts was 8.0 +/- 2.0 and 11.0 +/- 3.0 mm, respectively. A tendency of larger litter size (NTB) in Group B gilts was found when compared with Group A gilts. To conclude, using progestin altrenogest alone can be used to synchronize the oestrous cycle in gilts without unenthusiastic effect on the follicular development, ovulation time and subsequent reproductive performances. However, treatment of gilts with hCG at day 3 (72 h) after withdrawal of altrenogest had unenthusiastic effect on oestrus synchronization.     

Effect of altrenogest and Lutalyse on parturition control, plasma progesterone, unconjugated estrogen and 13,14-dihydro-15-keto-prostaglandin F2 alpha in sows

To investigate control of parturition time, 154 sows farrowing 220 litters at three locations were treated with altrenogest and Lutalyse (PG). The four treatment groups were: 1) no treatment (control group); 2) an im injection of 15 mg of PG at 1000 on d 111, 112 or 113 of gestation (d 0 = first day of estrus and gestation); 3) altrenogest (20 mg X sow-1 X d-1) fed twice daily for 4 d starting on d 109, 110 or 111; and 4) altrenogest and an injection of PG at 1000 on the day after the last feeding of altrenogest. Control sows at the University of Delaware (UD), University of Maryland (UM) and USDA, Beltsville Agricultural Research Center (BARC) had mean gestation lengths of 113.5, 114.2 and 115.7 d and live pigs/litter were 10.5, 11.0 and 7.4, respectively. Altrenogest started by d 110 prevented unscheduled early farrowing and increased (P less than .01) gestation length by 1.7 and 1.1 d, respectively, at UD and UM, but had not effect at BARC. The time from PG to parturition was 24.3, 22.6 and 34.4 h, respectively, at UD, UM and BARC. More sows at UD and UM farrowed between 0700 and 1700 on the expected day of parturition after injection of PG (59.3%) than with no PG (20.7%; P less than .05). The high incidence of small litters (less than six pigs) from sows inseminated with frozen semen at BARC resulted in negative correlations of live pigs/litter with gestation length (r = -.533, P = .0001) and with time from PG injection to birth of first pig (r = -.425, P = .017); these correlations were not significant at UD and UM where only natural service was used.(ABSTRACT TRUNCATED AT 250 WORDS)     

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Duration of estrus in relation to reproduction results in pigs on commercial farms.

This research was conducted to determine factors that influence duration of estrus, AI strategy, and reproduction results between and within commercial swine farms that use AI. Data from 15,186 sows and gilts on 55 farms for a period of 6.1+/-4.2 mo per farm were used in this study. The average duration of estrus was 48.4+/-1.0 h, ranging from 31 to 64 h, and was consistent from month to month within a farm (repeatability of 86%). Differences in duration of estrus between farms accounted for 23% of the total variation in duration of estrus. On most farms (n = 45), gilts showed a shorter (P < .05) duration of estrus than sows (40.8+/-1.1 h vs 48.5+/-1.0 h). The duration of first estrus after weaning was longer (P < .0001) compared with that of repeat-breeder sows (50.2+/-1.0 h vs 46.8+/-1.0 h). Duration of estrus decreased (P < .05) when interval from weaning to estrus increased from 4 to 6 d (56.0 +/- 1.2 h vs 45.8 +/-1.2 h). The regression of interval from onset to estrus to first AI and interval from weaning to estrus varied between farms and ranged from -7.4 to +1.3 h/d; four farms had a positive relationship. Farrowing rate decreased (P < .05) from 89.7+/-2.7% to 78.2+/-5.74 when the interval from weaning to estrus increased from 4 to 10 d. The litter size decreased (P < .05) from 11.7 to 10.6 pigs when the interval from weaning to estrus increased from 4 to 7 d. Compared with a single AI, double AI in sows and gilts resulted in a 4.3 and 7.0% higher (P < .05) farrowing rate, respectively. When the first AI was performed after expected ovulation, reproduction results were lower than when AI was performed before or at expected ovulation in sows. Duration of estrus was not related to farrowing rate or litter size in individual pigs. Number of inseminations per estrus, time of AI, and duration of estrus were correlated, which made it difficult to assess which of these factors was primarily related to the farrowing rate or litter size. Knowledge of average duration of estrus on farms and of factors that influence the duration of estrus on commercial farms can help to improve the efficiency of the AI strategy specific for each farm.     

Effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest

We previously reported that ovulation rate, but not pregnancy rate or litter size at d 30 after mating, was enhanced by treatment with P.G. 600 (400 IU of PMSG and 200 IU of hCG, Intervet America, Inc., Millsboro, DE) in gilts fed the orally active progestin, altrenogest (Matrix, Intervet America, Inc.) to synchronize estrus. We hypothesized that in addition to increasing ovulation rate, P.G. 600 may have altered the timing of ovulation. Therefore, mating gilts 12 and 24 h after first detection of estrus, as is common in the swine industry, may not have been the optimal breeding regimen, and as a consequence, pregnancy rate and litter size were not altered. The objective of the present study was to determine the effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest. Randomly cycling, crossbred gilts (5.5 mo old, 117 kg BW, and 14.7 mm of backfat) were fed a diet containing altrenogest (15 mg/d) for 18 d. Twenty-four hours after altrenogest withdrawal, gilts received i.m. injections of P.G. 600 (n = 25) or saline (n = 25). Gilts were checked for estrus at 8-h intervals. After first detection of estrus, transrectal ultrasonography was performed at 8-h intervals to determine the time of ovulation. Gilts were killed 9 to 11 d after the onset of estrus to determine ovulation rate. All gilts displayed estrus by 7 d after treatment with P.G. 600 or saline. Compared with saline, P.G. 600 increased (P = 0.07) ovulation rate (14.8 vs. 17.5, respectively; SE = 1.1). The intervals from injection to estrus (110.9 vs. 98.4; SE = 2.7 h; P < 0.01) and injection to ovulation (141.9 vs. 128.6; SE = 3.2 h; P < 0.01) were greater in gilts treated with saline than in gilts treated with P.G. 600. Duration of estrus (54.4 vs. 53.7; SE = 2.5 h), the estrus-to-ovulation interval (30.2 vs. 31.7; SE = 2.2 h), and the time of ovulation as a percentage of estrus duration (55.8 vs. 57.5; SE = 3.0%) did not differ for the P.G. 600 and saline-injected gilts, respectively. In summary, P.G. 600 advanced the onset of estrus and ovulation following termination of altrenogest treatment and increased ovulation rate; however, treatment of gilts with P.G. 600 had no effect on the timing of ovulation relative to the onset of estrus.     

Efficacy of altrenogest in synchronizing estrus in two swine breeding programs and effects on subsequent reproductive performance of sows.

In two herds that used different breeding and housing schemes, altrenogest (15 mg/d) was fed for 14 d to gilts or 10 d to sows in .45 kg of a diet formulated to meet or exceed their nutrient requirements. In Herd 1 (five breeding seasons per year), 63 of 123 gilts and 40 of 70 sows in seven replications were fed in individual crates to ensure proper intake. In Herd 2 (continuous breeding), 244 of 484 gilts in 20 replications received the treated feed in individual feeding stalls to which animals had free access. Average and median days to estrus were reduced (P less than .01) for treated gilts and sows compared with controls in both herds. Of 29 treated gilts that did not mate or become pregnant, three had cystic follicles, compared to 1 of 14 controls. There were no statistically significant treatment differences in litter size born or number of stillborn pigs in either herd, but farrowing rates of cycling gilts were 8% lower (P less than .05) in Herd 2 for treated gilts than for controls. Overall, altrenogest could be a valuable tool for improving reproductive efficiency by allowing producers to better control the estrous cycle.     

Effect of gilt development diet on the reproductive performance of primiparous sows

The objective of this study was to evaluate the effect of development diet on first-parity reproductive performance across different genetic types of females. Gilts (n = 708) 8 to 15 d of age from five genetic lines were assembled using a segregated early weaning protocol. Genetic types represented industry variation for reproductive capacity and lean growth potential. Sampling procedures were not designed to evaluate performance differences among the genetic lines. When the gilts weighed approximately 20 kg, they were moved from the nursery facilities to a slotted-floor, environmentally controlled facility, and seven to eight animals within a genetic type were penned together. When the gilts weighed approximately 40 kg, they were moved to a modified open-front facility. Nineteen gilts were allotted to each pen (.92 m2 per pig). Gilts were assigned to one of three development diets at 120 d of age. Diet 1 (high energy, 18% CP) and Diet 2 (high energy, 13% CP) were provided for ad libitum consumption to the assigned gilts until they weighed approximately 113 kg. Gilts receiving Diet 3 (23% CP) were fed 1.8 kg/d from 82 kg until they reached 180 d of age (approximately 100 kg). Gilts were fed 2 kg daily of a gestation diet from 180 d to 200 d of age and 2.7 kg daily from 200 d until mating. To stimulate the estrus cycle, gilts were commingled and exposed to vasectomized boars beginning at 180 d of age. Gilts that were in estrus and 210 d of age or older were artificially inseminated with commercial semen. Gilts not detected in estrus within the first 50 d of observation were injected with PG600 and estrus detection continued for 30 additional days. Of the 657 gilts entering breeding pens, 422 farrowed. Bred gilts were distributed to 10 cooperator facilities before farrowing. Mixed model procedures were used to analyze the data. Significant (P < .05) genetic type x gilt development diet interactions were found for number of pigs born, number of pigs born alive, total litter birth weight, and litter birth weight of pigs born alive. Significant interactions consistently involved one genetic line and gilt development Diets 1 and 2. Gilts from this genetic line-diet subclass had poorer farrowing performance (P < .05) than gilts from the same line fed development Diet 3. Only two other significant genetic line x gilt development diet interactions were found. Gilt development diet had little influence on first-parity reproductive performance.     

Long-term, but not short-term, treatment with somatotropin during pregnancy in underfed pigs increases the body size of progeny at birth

Treatment of pigs with porcine ST (pST) in early to mid-pregnancy increases body weight and length of their fetuses by mid-pregnancy, but this increased weight may not persist to birth. We investigated the effects of short- (25 d) and long-term (75 d) treatment with pST, and interactions between long-term pST treatment and crude protein content of diet, in restricted-fed gilts. In both experiments, Large White x Landrace gilts were bred at first estrus to Large White x Duroc boars and allowed to farrow naturally. In the first experiment, gilts were fed 1.8 kg/d of a diet containing 13.5 MJ DE/kg of DM and 15.05% CP (as-fed basis) throughout pregnancy, and were injected daily with 0, 2, or 4 mg pST from d 25 to 50 of pregnancy. Maternal treatment with pST from d 25 to 50 of pregnancy did not affect the number of piglets born per litter or progeny size at birth. In the second experiment, gilts were injected daily with 0 or 2 mg of pST and fed 2.2 kg/d of a diet containing 14.5 MJ DE/kg and either (as-fed basis) 16.6% (0.81% lysine) or 22.2% CP (1.16% lysine) from d 25 to 100 of pregnancy. All gilts were then fed 3.0 kg/d of the lower protein diet from d 100 of pregnancy to farrowing. Treatment with 2 mg pST/d from d 25 to 100 of pregnancy increased live weight of all gilts during the treatment period (P = 0.016), but the change in maternal live weight from d 25 to 100 of pregnancy was only increased (P = 0.001) by pST in gilts fed the higher protein diet. Live weight of gilts 1 d after farrowing was increased by pST treatment (P = 0.007), but was not altered by protein content of diet during pregnancy. In gilts fed the lower protein diet, but not in those fed the higher protein diet, pST treatment decreased maternal backfat depth during treatment (P < 0.020) and 1 d after farrowing (P = 0.002). Treatment with pST during pregnancy did not affect the number of piglets born per litter but independently increased body weight by 11.6% (P < 0.001) and length by 3.4% (P = 0.005) of progeny at birth and decreased (P < 0.01) the negative effect of litter size on body weight at birth. We conclude that in feed-restricted gilts, fetal weight gains in response to 25 d of pST treatment before mid-pregnancy are not maintained to term but that treatment with pST during most of pregnancy increases progeny size at birth and reduces maternal constraint of fetal growth.     

Factors contributing to early embryonic mortality in gilts bred at first estrus

Gilts bred at first (n = 18) and third (n = 18) estrus were assigned in replicates of equal numbers to be slaughtered on d 3, 15 and 30 post-mating to assess fertilization rate, embryonic losses and serum concentrations of estrogen (estradiol-17 beta + estrone) and progesterone. Mean number of ovulations was lower among gilts bred at first vs third estrus (12.2 vs 14.5; P less than .05), with no difference in fertilization rate (100 vs 98%). Embryonic survival was lower (P less than .05) among gilts bred at first vs third estrus on d 15 (78.1 vs 95.4%) and 30 (66.7 vs 89.4%) of gestation. Serum estrogen (pg/ml) and progesterone (ng/ml) levels, although lower in gilts bred at first vs third estrus, were not significantly different at the three stages of gestation studied. The ratio of progesterone to estrogen in gilts bred at first estrus was higher than in those bred at third estrus on d 15 (439 +/- 71 vs 210 +/- 17) and 30 (597 +/- 106 vs 179 +/- 50), but was lower on d 3 (187 +/- 37 vs 444 +/- 123; stage of gestation X estrous period interaction, P less than .05). These data suggest that changes in the ratio of systemic levels of estrogen and progesterone may be related to early embryonic mortality in gilts bred at pubertal estrus.     

Reproductive traits, lactation and foal growth in mares fed altrenogest

Lactating mares were assigned as controls or fed altrenogest (.044 mg.kg body wt-1.d-1) for 15 d after foaling. Mares (n = 6) fed altrenogest were inseminated during the first estrus after treatment and mares (n = 6) in the control group were inseminated during the second postpartum estrus. Ovulation during the estrus in which mares were inseminated occurred 26 +/- 1 d postpartum for treated mares and 36 +/- 1 d postpartum for control mares. The percentage of mares conceiving was not different for control (67%) and alternogest-treated (100%) mares. No differences were observed in tone and size of the uterus or size of the ovulatory follicle between treated and control groups. Uterine cultures and biopsies collected on d 7 and 15 postpartum were similar between treatment and control groups in bacterial populations or endometrial epithelial cell height. Blood was collected on d 7, 11, 15, 19 and 23 postpartum, and concentrations of estradiol-17 beta in serum were determined by radioimmunoassay. Mean concentrations of estradiol-17 beta across days were 10 +/- .8 and 12 +/- .6 pg/ml for control and treated mares, respectively. Concentrations of serum estradiol-17 beta were higher (P less than .05) in treated mares on d 23 postpartum. Daily milk yields, determined by the weigh-suckle-weigh method, and milk composition were similar between treatment groups on each collection day. Altrenogest can be used to predictably delay estrus in the postpartum mare without altering fertility, yield and composition of milk, or foal growth.     

Enhancement of ovulation rate in gilts by increasing dietary energy and administering insulin during follicular growth

Two experiments were conducted to examine influences of dietary energy and insulin on ovulation rate and patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH), glucose, insulin and estradiol in gilts during 6 d before estrus. In Exp. 1, 36 gilts were given altrenogest for 14 d to synchronize estrus. In a factorial arrangement, gilts were fed one of two levels of dietary energy (5,771 or 9,960 kcal metabolizable energy (ME)/d), and given one of two levels of porcine insulin (0 or .1 IU/kg body weight iv every 6 h). Dietary treatments began 4 d before and insulin treatments began 1 d after the last day of altrenogest, respectively, and lasted until 24 h after estrus. Main effect means for number of corpora lutea were 14.0 +/- 1.3 and 17.6 +/- .9 for 5,771 and 9,960 kcal ME (P less than .05), and 14.6 +/- 1.0 and 17.0 +/- .9 for 0 and .1 IU insulin (P less than .05). Number of LH peaks on d 3 was greater for gilts that received 9,960 kcal than 5,771 kcal (3.3 +/- .2 vs 2.7 +/- .2; P less than .05), and for .1 than 0 IU insulin (3.2 +/- .2 vs 2.7 +/- .2; P less than .05). During the first 24 h of sampling, concentrations of LH and FSH were greater (P less than .05) in gilts receiving 9,960 kcal ME plus insulin than for other treatment combinations. Concentrations of estradiol were not affected by treatments. In Exp. 2, two formulations of insulin were evaluated for influence on ovulation rate. All gilts received altrenogest and 9,960 kcal ME/d as in Exp. 1. Then on the first day after altrenogest, seven gilts each received short-acting insulin (as in Exp. 1), long-acting insulin (zinc suspension, 1.0 IU/kg body weight every 18 to 24 h), or served as controls. Ovulation rates were increased (P less than .05) by both insulin preparations (15.6, control; 19.1, short-acting; 18.5, long-acting; SE = 1.2). Concentrations of LH tended to be greater after short-acting insulin, but differences were not significant (P = .13). We conclude that increases in ovulation rate produced by dietary energy and insulin are not necessarily accompanied by changes in gonadotropins or estradiol.     

Effects of a synthetic progestogen, altrenogest, on oestrus synchronisation and fertility in miniature pigs

Groups of six, six and eight miniature gilts, respectively, received 5, 10 or 15 mg/day of altrenogest for 18 days, and the numbers of corpora lutea and residual follicles were counted approximately 14 days after the treatment by an exploratory laparotomy. They were compared with the numbers in a control group of eight gilts which were examined six to eight days after oestrus. The interval between the last dose of altrenogest and the onset of oestrus increased with the dose of altrenogest, and was significantly longer after the treatments with 10 or 15 mg/day than after 5 mg/day (P < 0.01). Significantly more corpora lutea were observed in the gilts receiving 5 or 10 mg/day of altrenogest than in the control gilts (P < 0.1). Groups of six, seven and six miniature gilts that had respectively received 5, 10 or 15 mg/day of altrenogest were artificially inseminated; four, six and five of the gilts in these groups farrowed, and their mean (sd) litter sizes were 5.5 (2.4), 6.8 (1.2) and 5.0 (2.3), respectively. All six of a group of control gilts farrowed and their mean litter size was 5.8 (1.2).     

Case Study: Synchronization of Estrus and Fertility in Gilts Administered P.G. 600® After Treatment with Regu-mate® for 14 or 18 Days

The objective was to determine the effects of duration of progestin exposure prior to gonadotropin treatment on the synchronization of estrus and fertility in gilts. Gilts were fed daily a complete diet containing 15 mg Regu-mate® (Intervet America Inc., Millsboro, DE) for 14 (n = 19) or 18 (n = 18) d. Twenty-four hours after the last feeding of Regu-mate®, all gilts received an i.m. injection of P.G. 600® [400IU pregnant mare serum gonadotropin (PMSG) and 200 IU human chorionic gonadotropin (hCG); Intervet America Inc.]. Gilts were bred artificially 12 and 24 h after first detection of standing estrus. More 18-d (33.3%) than 14-d treated gilts (5.3%) were in estrus on the peak day (d 4.0) after P.G. 600® injection (P=0.02). The percentage of gilts displaying estrus < 7 d after P. G. 600® injection was greater (P=0.06) for the 18-d treatment (88.9%) than for the 14-d treatment (63.2%). Farrowing rate tended to be greater (P=0.17) for gilts exposed to Regu-mate® for 18 d (75%) compared with 14 d (50%). Total pigs born (P=0.43), pigs born live (P=0.63), stillborns (P=0.62), and total litter weight (P=0.52) were similar between groups. The number of mummified fetuses tended to be higher (P=0.11) for gilts in the 18-d treatment group (0.8 ± 0.2) compared with the 14-d treatment group (0.2 ± 0.3). In summary, the precision of estrus synchronization and reproduction was greater in gilts given P.G. 600® after 18 d compared with 14-d Regu-mate® treatment.     

Effect of dietary organic and inorganic selenium on antioxidant status, embryo development, and reproductive performance in hyperovulatory first-parity gilts

This project aimed to determine the effect of Se as inorganic Na-selenite (MSe) or organic Se-yeast (OSe) on antioxidant status, hormonal profile, reproductive performance, and embryo development in first-parity gilts. Forty-nine gilts were allocated to 1 of the 3 dietary treatments starting at first pubertal estrus and lasting up to 30 d after AI: control [CONT: basal diet (Se = 0.2 mg/kg) without added Se; n = 16], MSe (CONT + 0.3 mg/kg of MSe; n = 16), and OSe (CONT + 0.3 mg/kg of OSe; n = 17). Blood was collected from all gilts on the day after each onset of estrus and on d 30 after AI. Blood was also collected daily from d -4 to d +4 of the third onset of estrus (d 0) in 8 CONT, 9 MSe, and 8 OSe cannulated gilts. Gilts had received, after d 14 and 15 of their third estrus, a hormonal challenge to induce super-ovulation. At slaughter, embryos and corpora lutea (CL) were weighed and measured. Blood Se was less (P < 0.01) in CONT than in Se gilts and greater in OSe than in MSe (P < 0.01) from the first estrus until d 30 of gestation. At the same time, blood Se-dependent glutathione peroxidase (GSH-Px) decreased for CONT gilts, whereas it increased for both Se groups. The increase was greater in MSe than in OSe gilts (treatment × time, P = 0.02). Plasma 3,3',5-triiodothyronine and thyroxine concentrations for MSe tended to be less than for OSe gilts (P < 0.06). In cannulated gilts, plasma FSH tended to change among treatments (treatment × time, P = 0.06), and plasma estradiol-17β (E(2)) was less (P = 0.01) for MSe than for OSe. There was no treatment effect on mean litter size or embryonic antioxidant status. The Se content of individual embryos was greater for Se-treated than for CONT gilts (P = 0.03), and Se content of individual embryos and total litter was greater for OSe than for MSe gilts (P < 0.01). The length, weight, and protein content of embryos were greater in OSe than in MSe gilts (P < 0.05). There was no treatment effect on weight, length, Se content, and ferric reducing antioxidant power of CL, but GSH-Px in CL was greater for Se than for CONT gilts (P = 0.02). In summary, the Se status response of gilts to dietary Se was affected by both the quantity and the source of Se dietary supplements. Moreover, the uterine transfer of Se to embryos was improved with OSe as compared with MSe, and this was concomitant with an enhanced development of embryos.     

Influence of norgestomet in combination with gonadotropins on induction of estrus and ovulation in prepubertal gilts.

Our objective was to determine whether priming with the progestogen norgestomet for 9 d would enhance estrual and ovulatory responses of prepubertal gilts to PG600 (400 IU eCG + 200 IU hCG). Gilts (140 to 190 d old) were assigned by litter, age, and weight to one of three treatments: 1) 9 d of norgestomet implant with an injection of PG600 after implant removal on d 9 (N+PG; n = 43); 2) no implant and an injection of PG600 on d 9 (PG; n = 36); or 3) neither implant nor PG600 (control; n = 29). Beginning on d 0, gilts were exposed once daily to a boar and checked until estrus was observed or until d 45 after the start of the experiment. Ovaries were examined for number of corpora lutea (CL) after estrus or at 45 d. Greater proportions of N+PG (63%, P < .05) and PG (69%, P < .01) gilts expressed estrus than did controls (34%), but proportions did not differ between N+PG and PG (P > .10). Among gilts in estrus following treatment with N+PG or PG, 100% showed estrus within 6 d after PG600 injection. For gilts that expressed estrus within 45 d, the average age at estrus was reduced (P < .05) by PG to 172 +/- 2 d compared with 182 +/- 4 d for controls. Average age at estrus did not differ (P > . 10) between PG and N+PG (177 +/- 2 d). Greater proportions of N+PG (82%; P < .001) and PG (65%; P < .001) gilts ovulated than controls (13%), but proportions did not differ between N+PG and PG (P > .10). The number of CL (20 +/- 2) was not affected by treatment and ranged from 2 to 71. There was no increase in ovarian cysts in response to treatment. Results indicated that norgestomet before PG600 did not enhance estrus expression or ovulation compared with PG600 alone, but use of PG600 increased the proportions of gilts that expressed estrus and ovulated compared with controls.     

Effect of unilateral hysterectomy and ovariectomy on puberty, uterine size and embryo development in swine

Eighty crossbred gilts were assigned randomly to treatments: 1) removal of an ovary and ipsilateral uterine horn (UHO) at 130 d of age and removal of the remaining ovary and uterine horn 12 d post-puberty; 2) UHO at 130 d of age, mated and reproductive tracts recovered when slaughtered at 30 d of gestation; 3) UHO 12 d post-puberty, mated and slaughtered at 30 d of gestation and 4) unoperated controls that were mated and slaughtered at 30 d of gestation. Age of puberty was not affected by treatments. Gilts in treatment 1 had a mean ovulation rate at the pubertal estrus comparable to gilts in treatment 3. But, gilts in treatments 2 and 3 had 16% fewer (P less than .01) corpora lutea at 30 d of gestation than control gilts. Length and weight of the remaining uterine horn at 12 d post-puberty for gilts treated at 130 d of age were similar to the averages of gilts left intact. Gilts with one uterine horn had 2.2 fewer live embryos at 30 d of gestation than control gilts (P less than .01). But, the proportion of corpora lutea represented by live embryos did not differ significantly among treatments. Gilts with one uterine horn had 1.1 fewer live embryos (P less than .15) after adjustment for number of corpora lutea, less uterine space occupied by each embryo (P less than .01) and less total placental membrane per embryo (P less than .05) than control gilts.(ABSTRACT TRUNCATED AT 250 WORDS)