Direct estimation of urine estrone conjugate for a rapid pregnancy diagnosis in sows

A rapid and direct radioimmunoassay of urine estrone conjugate (E₁C) was developed. Urine samples were taken from Large White sows by inserting sponges in the vagina which were expelled during micturition. Analysis of samples collected daily from 13 sows between 2 and 40 days after service showed that high urine E₁C levels occurred between day 20 and 30 after insemination in pregnant sows; maximum concentrations were observed on day 25 (79.4 ± 11.7 ng/ml, $\text{X}\text{± s.e.m.}$). In this period E₁C levels never exceeded 1 ng/ml in nonpregnant sows. A single urine sample was then taken from 84 sows, 25 days after insemination, to check the accuracy of E₁C estimation as a test for early pregnancy diagnosis. Seventy-six of the examined animals were correctly diagnosed, giving an overall accuracy of 90.4%. No relationship was found between litter size and urine E₁C levels.     

Detection of early pregnancy factor in swine: A need for dialogue

The rosette inhibition test, which has been used to detect early pregnancy factor (EPF) and other immunosuppressive factors in the serum of pregnant mice, women, and sheep, was adapted for use in swine. Since the initial methods described for use of the assay were cumbersome and time consuming, our first efforts were to simplify the technique. Substitution of microtiter plates for test tubes and treatment of sheep erythrocytes with AET to increase numbers and stability of the rosettes were successful. Although consistently higher rosette inhibition titers were obtained after incubation of lymphocytes in the serum of pregnant sows compared to controls, the variability in numbers of rosettes obtained on a day to day basis and the cumbersome nature of the test have impeded progress in firmly establishing the presence of EPF in pregnant swine and demonstrating the homology between it and the EPF reported in other species.     

Early pregnancy diagnosis in swine by direct radioimmunoassay for progesterone in blood spotted on filter paper.

A direct radioimmunoassay method for the measurement of progesterone in blood dried on filter paper has been developed for the early pregnancy diagnosis in sows, as well as for monitoring progesterone levels during the oestrous cycle.Pregnancy diagnosis was performed with 95 sows on Days 17-22 after artificial insemination (AI). The cut-off value for pregnancy diagnosis of 7.5 ng/ml was calculated (mean+/-2S.D.) from the progesterone concentrations measured on the same days from non-inseminated animals. There were 85 cases considered pregnant on the basis of progesterone concentration, leaving 10 animals non-pregnant. The accuracy for the positive cases was 98.8%. Two of the 10 sows considered as negative subsequently farrowed, giving an accuracy of 80%. The overall accuracy of the method was 96.8%.The blood-spot assay may be a useful tool for early pregnancy diagnosis in swine, with respect to sampling, simplicity, speed and accuracy.     

Evaluation of false ultrasonographic pregnancy diagnoses in sows by measuring the concentration of unconjugated estrogens in feces

On Days 26, 28, and 30 after AI, ultrasonographic pregnancy diagnoses were performed on 207 gilts and sows by using a 3.5 MHz linear-array transducer. Fecal samples were taken from the rectum after each ultrasonographic examination, and the concentrations of unconjugated estrogens in selected samples (n = 73) were measured by RIA. Fecal unconjugated estrogen concentration of 11.7 ng/g feces or higher was indicative of pregnancy. The overall sensitivity and specificity of the ultrasonographic test was 99% for farrowing sows and 73.1% for nonfarrowing sows. With one exception, sows with a false negative diagnosis by ultrasonography on Day 26 were correctly diagnosed pregnant by elevated fecal unconjugated estrogens or repeated ultrasonographic examinations on Days 28 or 30. Return to estrus around the sampling period may cause false positive results in the unconjugated estrogen assay, while early embryonic mortality can result in false positive diagnoses in both the ultrasonographic test and estrogen assay. Although there was a positive correlation between the concentrations of unconjugated estrogens in the feces and litter size at farrowing in the selected sows, it seems very unlikely that fecal estrogens can provide an accurate tool for predicting litter size.     

Effect of feeding level on progesterone concentration in early pregnant multiparous sows

The effect of three feeding regimens on progesterone level was tested during early pregnancy in multiparous sows. A total of eighteen sows in their eighth parity (8.1 +/- 2.8, mean +/- S.D.) were used. During lactation the sows were fed to appetite and after weaning they received 4 kg (52 MJ) a commercial feed per day. Following ovulation, sows were allocated to one of three treatment groups and fed 2 kg/day (low feeding, LLL) or 4 kg/day (high feeding, HHH) throughout the trial or 2 kg/day for 11 days, 4 kg/day for 10 days, and 2 kg/day for the remaining days of the study (modified feeding, LHL). Blood for progesterone and cortisol analyses was collected daily throughout the study, and for luteinizing hormone (LH) assay for 12 h at 15 min intervals on days 14 and 21 of pregnancy. An adrenocorticotropic hormone (ACTH) challenge test was performed on all sows day 28 of pregnancy. Dietary treatment did not significantly affect hormonal parameters. However, progesterone concentration tended to be lower (P = 0.08) in the HHH group than in the LLL group. In the LHL group venous progesterone concentration seemed to fluctuate. No effects of feeding were observed on progesterone concentration in allantoic fluid on day 35 of pregnancy. Venous cortisol level was significantly higher (P < 0.05) during proestrus and oestrus in all groups and there was no significant difference between groups in response to ACTH challenge. The mean amplitude of LH pulses decreased significantly (P < 0.01) from days 14 to 21 of pregnancy in all groups. In addition, an interaction was found between feeding level and baseline LH concentration and also between feeding level and mean LH concentration. Embryonic recovery was highest in the LLL (69%), lowest in the HHH (45%) and moderate in the LHL (55%) group. Neither high feeding nor modified feeding provided any benefits for reproductive performance in multiparous sows. A low feeding regimen thus appears optimal for multiparous sows in early pregnancy at least with the management regime described.     

Comparison of three different farrowing systems: skin lesions and behaviour of sows with special regard to nursing behaviour in a group housing system for lactating sows

While group housing (GH) is mandatory in the European Union for the greater part of pregnancy, single housing in farrowing crates (FCs) during lactation that restrict sows in most of their natural behaviour patterns is still practised on a large scale. Research is urgently needed to develop alternative farrowing systems that improve sows’ welfare. Therefore, sows in three different farrowing systems – pens with FC, loose housing (LH) pens and GH for six sows – were compared regarding the level of skin injuries and their active and resting behaviour. A skin injury score was assessed for 15 body parts of 102 sows in six batches on 3 days (days 1, 14 and 34). In total, the active and resting behaviour of 77 sows in six batches was examined on 3 days (days 18, 25 and 32) between 0700 h and 1900 h by means of a scan sampling method. The suckling behaviour and the level of cross-suckling were analysed in GH by means of direct observation in four batches during three 4-h sampling periods (days 17, 24 and 31). No significant differences were found in total skin injuries when the sows entered the systems (day 1), but GH sows showed significantly higher total skin injuries compared to FC and LH sows in the middle (day 14) and at the end (day 34) of the lactation period. A significant difference between FC and LH sows was never seen. Differences were found for the proportion of different body postures between the three systems. The odds for lying in lateral recumbency versus standing and sitting versus standing were significantly higher for FC and LH sows compared to GH sows. Additionally, sows were significantly more likely to be standing as opposed to lying in lateral recumbency as the lactation period progressed. Cross-suckling was a frequent behaviour in GH, seen in 35.0% of all successful suckling bouts. However, only an average of 0.56 piglets per successful suckling bout was observed cross-suckling, suggesting only a few piglets were engaged in cross-suckling. In conclusion, the skin injury score was only moderately increased in GH compared to FC and LH and comparable to pregnant group-housed sows, both free farrowing systems seemed to be an environmental enrichment for lactating sows and good management cannot prevent the occurrence of cross-suckling in a GH system, but can probably reduce it.     

Ontogeny of the opioidergic regulation of LH and prolactin secretion in lactating sows. II: Interaction between suckling and morphine administration

Administration of morphine to ten suckled and nine zero-weaned (piglets removed immediately after farrowing) sows was used to investigate the apparent absence of opioid regulation of LH and prolactin secretion in early lactation. Blood samples were collected at 10 min intervals at 24-30, 48-54, 72-78 h post partum, and for a 12 h period from 08:00 to 20:00 on day 10 after farrowing. Morphine (0.1 mg kg-1) was administered as three i.v. bolus injections at intervals of 1 h during the last 3 h of each of the 6 h sampling periods, and at 6, 7 and 8 h after the beginning of sampling on day 10. There were significant (P < 0.001) group (zero-weaned versus suckled), time and morphine effects on LH secretion. Plasma LH concentrations increased (P < 0.001) within 48 h of farrowing in zero-weaned sows. Long-term trends of an increase in mean plasma LH in the sampling periods before treatment were attenuated in both groups by morphine treatment. Morphine also significantly inhibited (P < 0.05) prolactin secretion in suckled sows. In zero-weaned sows, plasma prolactin was already low at the start of sampling and did not change with time or in response to morphine treatment. Therefore, the inability to demonstrate an opioidergic involvement in the suckling-induced inhibition of LH secretion during the early post-partum period in sows is not due to a lack of opioid receptors. Furthermore, in suckled sows, morphine is stimulatory to systems that have an inhibitory effect on prolactin secretion.     

Urinary excretion of collagen degradation markers by sows during postpartum uterine involution

Incomplete uterine involution is the putative cause of the increased embryo mortality and reproductive failure often exhibited by sows that lactate for less than 21 days. Since such short lactation lengths are common in American swine production, an effective technique to monitor the postpartum involution process and test this hypothesis might be valuable. Rapid and extensive catabolism of uterine collagen is essential for normal postpartum involution. The objective of this study was to characterize postpartum excretion of two biochemical markers of collagen degradation. In experiment I, urine samples were collected from five sows every other day from the day before parturition (day -1), through a 21-day lactation, to day 8 postweaning. The collagen crosslinks hydroxylysyl pyridinoline (HP), which is present in many tissues, and lysyl pyridinoline (LP), which is primarily concentrated in bone, were assayed by both ELISA and HPLC. Urinary levels of both free (ELISA) and total (HPLC) HP and LP increased (P < 0.001) approximately two-fold during lactation. The mean molar ratio of total HP:LP increased (P < 0.001) from 6.6 +/- 1.6 at day 1 to a maximum of 10.2 +/- 1.5 at day 7 postpartum and averaged 9.1 +/- 0.3 for the entire sampling period. These data are consistent with a postpartum increase of soft tissue collagen catabolism since bone has a low HP:LP ratio of 4 and soft tissues like the uterus have a high HP:LP ratio of >/=20 because they contain only trace amounts of LP. Since HPLC (total) and ELISA (free) crosslinks estimates were highly correlated (r = 0.85-0.91, P < 0.001) in experiment I, only the less technical ELISA technique was used in experiment II. Urine samples were collected from 21 sows every third day from day 1 to 19 of lactation. Sows from this second group exhibited one of four distinct crosslinks excretion patterns: peak on day 1 (n = 3), peak on day 7 (n = 4), peak on day 10, 13 or 16 (n = 7), or no peak (n = 7). This variation of postpartum crosslinks excretion among sows was not related to parity, body weight, lactation body weight change, litter size, or litter birth weight. Overall, data from experiments I and II indicate that urinary HP does increase postpartum in a pattern temporally consistent with uterine involution. However, significant variation among sows in the magnitude and timing of peak HP excretion was evident.     

Relationship between estrone sulfate in plasma and litter size at farrowing for sows and gilts

A positive association (P < 0.01) was detected between estrone sulfate (ES) concentrations in maternal plasma at Day 30 of pregnancy and litter size at parturition in swine. This relationship was best described by a fifth order regression equation (R(2) = 0.5) which indicated that as ES increased from 1 to 7.5 ng/ml on Day 30, litter size increased from 0 (nonpregnant) to 18 piglets farrowed. Day of sampling (P < 0.02), month (P < 0.04) and parity (P < 0.08) were major sources of variation in the model. This indicated that effects of environmental factors such as heat stress, which influence conception rate and embryonic survival, are reflected in changes in maternal ES. Also, larger litter size associated with parous sows is reflected in increased ES in maternal plasma. We conclude that measurement of ES early in gestation may be useful in reproductive management to identify nonpregnant gilts and sows as well as those with small litters.     

Oestrone Sulphate Measurements for the Prediction of Small or Large Litters in Pigs

Serum from 88 pregnant sows and gilts was sampled 24 and 28 days after their first insemination or mating day. The oestrone sulphate (E1S) concentration in the samples was assessed with a commercially available radioimmunoassay kit modified for use with swine serum. The first aim was to test whether it was possible to predict litters of total number <10 piglets at term. The second aim was to compare the use of day 24 or day 28 samples, or of both, in this prediction.     

Hormonal profiles and embryo survival of sows subjected to induced stress during days 13 and 14 of pregnancy

Group housing of sows during the mating and gestation period has become the overall common management practice in Sweden. Loose housing is probably less stressful for the animals because it allows them more opportunities to behave naturally, but mixing unfamiliar sows does create a stressful situation due to aggressive interactions, which can lead to food deprivation. The objective of the present study was to investigate and compare the effects of stress in form of food deprivation and ACTH administration at days 13 and 14 of pregnancy (day 1, first day of standing oestrus) in sows. The hormonal secretion of the sows and foetal survival by day 30 of pregnancy was, therefore, studied in 17 crossbred multiparous sows. The sows were randomly allocated into three different groups: one control (C-) group; one food deprived (FD-) group, which was deprived of food from the morning of day 13 of pregnancy until the evening meal on day 14; and a third group (A-), which was given intravenous injections of synthetic ACTH (Synachten Depot), at a dose of 0.01 mg/kg body weight every sixth hour from 6 a.m. on day 13 until 6 a.m. on day 15 of pregnancy. All sows were slaughtered at 30 +/- 2 day of pregnancy and the genital tracts recovered. Total number of corpora lutea (CL), total number of viable or nonviable embryos and foetal survival rates were determined. Samples from the peripheral blood circulation were collected four times a day from day 12 until slaughter, except during days 13-15 when blood was collected every second hour. The blood samples were analysed for cortisol, progesterone, oestrone, prostaglandin F(2alpha)-metabolite, oestrone-sulphate, insulin, free fatty acids and triglycerides. FD-sows had increased levels of cortisol, free fatty acids and progesterone, as well as a lowered level of insulin in the peripheral blood plasma, while A-group sows had increased levels of both cortisol and insulin compared with the C-group. Treatment with ACTH seemed to cause a 2-day delay in the increase of oestrone, from day 19, as seen in the FD- and C-group, to day 21 of pregnancy. At the time of slaughter, there were no significant differences among groups in terms of total number of foetuses and foetal survival rate. The results of the present study suggest a capacity of the sow to compensate for the influence of induced moderate stress at the time of pregnancy when maternal recognition occurs.     

Returns to service after mating and removal of sows for reproductive reasons from commercial swine farms

We studied the records of 30 herds with an average inventory of 11,705 sows, 25,719 farrowings and 25,040 daily feed intake logs. Production events were recorded by producers using the PigCHAMP production information system. Of 21,505 matings, 7.2% of sows subsequently returned to estrus after service. The proportionate rates of intervals from service to the subsequent post service event were 0 to 17 d, 2.1%; 18 to 25 d, 27.9%; 26 to 37 d, 13.8%; 38 to 46 d, 15.8%; 47 to 108 d, 30.4%; and >108 d, 10.0%. Sows returned to service after mating were categorized into groups that either regularly or irregularly returned to service after mating. Of a total inventory of 19,076 sows, 10.0% were removed following weaning for reproductive reasons. The reasons for removal included those of anestrus (25.2%), failure to conceive (37.0%), failure to farrow (15.0%), not pregnant (1.4%), negative pregnancy check (14.0%), and abortion (7.4%). The last 5 types of post weaning reproductive failure were grouped into the category of did not farrow. Categorical additive models and comparisons using contrasts were used to analyze the influence of risk factors on reproductive failure. Parity 1 sows had a higher proportion (P < 0.01) of returns to service and a greater proportion of sows remaining anestrous post weaning relative to Parity 3 sows. The proportion of sows that did not farrow was higher (P < 0.01) in Parities 9 and 10 than in Parity 3. More sows were removed for anestrus during the spring (P < 0.01) and summer (P = 0.06) than during the winter. All categories of lactation length had similar rates of reproductive failure except for the lactation length 1 to 7 d, which had a higher (P < 0.05) proportion of reproductive failure. Lower lactational feed intake was associated with an increased risk of occurrence of each reproductive failure category. The odds ratios of lactation feed intake in logistic regression analyses were 0.84, 0.89, 0.82 and 0.88 for regularly and irregularly returned to service, anestrus, and did not farrow groups, respectively. This means, for example, that a sow was 0.88 times less likely to have an occurrence of not farrowing for each 1 kg increase in average daily feed intake during lactation. Our results indicate that lower and higher parities, spring and summer seasons, a lactation length of less than 8 d and lower feed intake during lactation affect the occurrence of return to service after mating and of herd removal for reproductive reasons.     

Use of ultrasound scanning in swine for detection of pregnancy and some pathological conditions

The adaptation of ultrasound scanning to the diagnosis of pregnancy and other physiological conditions in swine was examined. The scanner was equipped with a 3.5-MHz transducer. The probe was placed against the skin in the area of the abdominal flank of a standing sow and moved between the first and third posterior teats. The 2,257 sows were all presumed to be pregnant and underwent a single echography examination between 18 and 90 d post-insemination. For pregnant sows, the accuracy rate of diagnosis averaged 98.7 %. The majority of errors were made between 18 and 21 d of pregnancy in sows which subsequently gave birth to fewer than five piglets. This technique allowed us to detect only 54 % of non-pregnant sows. Nevertheless, a high accuracy rate was obtained when examination was performed within 7 d before the return of estrus (80 %). Conditions at the time of the examination were also an important factor. Ultrasound scanning opened up possibilities for observing other conditions such as cystic ovaries and metritis.     

Acute-phase protein profile during gestation and diestrous: proposal for an early pregnancy test in bitches

Early pregnancy diagnosis in bitches has special relevance for adequate medical assistance to assure normal gestation, diagnosis of abortion or embryonic resorption, undesirable pregnancy interruption and dog owners wishing to assure medical assistance during parturition and to program participation of females in dog shows. The aim of this study was to verify acute-phase protein profile variation as a consequence of generalized inflammatory reaction due to embryonic endometrial invasion and use alterations as a method for early pregnancy diagnosis. Also the relationship between hormonal status and acute-phase proteins concentrations was assessed. Weekly serum samples were collected from 20 non-pregnant (NP) bitches and 20 pregnant females (P) to determine levels of fibrinogen, haptoglobin, ceruloplasmin, seromucoid, glycoprotein, alpha(2) globulin, progesterone and estradiol-17beta. No correlation was found between the implantation sites formed (number of pups born) and the hepatic stimulus for the acute-phase protein production. The conclusions are that acute-phase proteins can be used as an early pregnancy test for bitches from the 3rd week of gestation (14th-21st day post LH peak) for haptoglobin assay (values above 112.42 mg/dl of HbCN binding capacity), from the 4th to the 6th week (21st-42nd day post LH peak) for ceruloplasmin (values above 12.76+/-5.29 U/l), from the 4th week (21st-28th day post LH peak) for glycoprotein (values above 13.67%) and from the 4th week of gestation (21st-28th day post LH peak) for alpha(2) globulin (values above 0.61 g/dl). Fibrinogen and seromucoid increased in the P group from the 5th to the 6th week, respectively, thus not being suitable as parameters for an early pregnancy diagnosis. Relationship between ceruloplasmin and estradiol-17beta and seromucoid and progesterone were verified. For the acute-phase protein test it is important to verify bitches' healthy condition and to assure the precise mating dates to avoid false-positive and -negative results, respectively.     

Pregnancy diagnosis in sows: direct ELISA for estrone in feces and its prospects for an on-farm test, in comparison to ultrasonography

The usefulness of fecal estrone (E1) measurement as a tool for pregnancy diagnosis was investigated. Concentrations of E1 were measured in feces from pregnant and nonpregnant sows by a direct ELISA without extraction. Highly significant differences in E1 concentrations were found in feces from nonpregnant and pregnant sows (P = 0.016 to < 0.001). Pregnancy diagnosis on Days 26 to 32 after insemination, based both on fecal E1 concentrations as measured by ELISA and ultrasonography using a 5.0 MHz linear-array transducer, was performed in a group of 496 gilts and sows. The fecal E1 test had a sensitivity (correct diagnosis of pregnancy) of 96.5% and a specificity (correct diagnosis of nonpregnancy) of 93.6%, using 3.65 ng E1/g feces as a cut-off value. For ultrasonographic pregnancy diagnosis the test sensitivity and specificity were 99.3 and 92.5%, respectively. Although an increase of fecal E1 concentrations was noticed for increasing litter sizes, the results indicated that these concentrations could not be used to predict litter size. It is concluded that the distribution of fecal E1 concentrations in both nonpregnant and pregnant sows offers a suitable basis for the development of a simple, sow-side pregnancy test.     

Association of Fusarium mycotoxicosis with failure in applying an induction of parturition program with PGF2alpha and oxytocin in sows

This trial was conducted in a farrow-to-finish pig unit from November 1999 to February 2000. Since November 1998 an induction-of-parturition program was applied in gilts and sows with PGF2alpha (2 mL Dinolytic, i.m.) 113 d post service, followed by oxytocin (1 mL Intertocine-S, i.m.) 24 h later. This program resulted in a high proportion of animals farrowing within the working hours of the day. At mid December 1999 splay-legs and edematous swelling and reddening of the vulva started to be observed in newborn piglets. A concurrent decline of parameters related to parturition also was noticed. Mycotoxicological analyses of the feeds revealed a co-occurring contamination with deoxynivalenol and zearalenone. For a 4-week period, sows were divided into two groups: (a) an induction-of-parturition and (b) a non-induction-of-parturition group. Significant differences were found between the two groups relating to prevalence of dystocia (<.05) and pregnancy duration (<.05). Moreover, it was found that prevalence of splay-legs and swelling of the vulva were highly correlated (<.05) with reduction of percentage of sows farrowing within the working day and increase of pre-weaning mortality. It was concluded that such an induction-of-parturition program should be avoided during a Fusarium mycotoxicosis.     

Timing of lactational oestrus in intermittent suckling regimes: consequences for sow fertility

Three intermittent suckling (IS) regimes were evaluated for their effects on lactational oestrus and subsequent fertility. Control sows were weaned (CW; n = 38) at d 26 ± 2 of lactation. In IS19-7D (n=40) and IS19-14D (n=42) sows, IS started at d 19 ± 1 of lactation and sows were weaned 7 or 14 d later. In IS26-7D (n=41), IS started at d 26 ± 1 of lactation and sows were weaned 7d later. During IS, sows were separated from their piglets for 10h/day. Oestrus detection was performed twice daily without a boar and ovulation was confirmed by ultrasound once a week. In IS19-7D, IS19-14D and IS26-7D, respectively, 50%, 64% and 61% of the sows showed oestrus and ovulation during IS (P>0.05), and, of the remaining sows, 100%, 93%, and 69% showed oestrus in the first week after weaning. In CW sows, 95% showed oestrus in the first week after weaning. Parity 1 sows were considerably less likely than older parities (23% vs. 68%) to show oestrus in lactation. Pregnancy rate of the first post partum oestrus (during lactation or after weaning) was 89% (CW), 92% (IS19-7D), 80% (IS19-14D) and 77% (IS26-7D) (P>0.05) and subsequent litter size was 14.5 ± 0.5, 14.5 ± 0.6, 15.3 ± 0.5 and 15.2 ± 0.8, respectively (P>0.05). Sows mated during lactation had similar pregnancy rate and litter size to those mated after weaning. Hence, ongoing lactation for the first 2-9 d of pregnancy did not negatively affect fertility. A total of 50-64% of IS sows showed lactational oestrus, regardless of the stage of lactation. Pregnancy rates and litter size were similar to control sows, and were not affected by stage of lactation at mating.     

Luteolytic potencin in a novel prostaglandin analogue

Estrus induction in cycling sows with exogenous prostaglandin is hindered by the extended refractory period and resistance of swine to the luteolytic action of PG's. The luteolytic potency of a novel PGF_2α analogue, Schering ZK 71677, was assessed at four different dosages in chronically cannulated cycling swine. Dosages totalling 1, 1.5, 3 and 10 mg of ZK 71677 were split into two injections given intramuscularly on day 13 of the estrous cycle. Onset of behavioural estrus and serum levels of progesterone and PGF metabolite were monitored. The three lowest doses did not advance estrus but did cause a transitory decline in serum progesterone concentration on day 13. The 10 mg level advanced estrus in three of four sows although the overall mean cycle length did not differ from pretreatment cycles (18.5 ± 1.3 vs 21.3 ± 0.6 days). Progesterone values droppd steadily in all four sows in the 10 mg treatment group. No level of ZK 71677 affected serum levels of PGF metabolite. The highest level tested of PGF_2α analogue ZK 71677 elicited an uninterrupted decline in serum progesterone concentrations but was inconsistent in its ability to promote early onset of behavioural estrus in swine.     

Control of oestrus in primiparous sows

The weaning to service records were analysed for 69 primiparous sows in the University College herd. More large white sows had returned to service within 7 days of weaning than crossbreds (O<0.05). However, there was no significant difference in the mean interval from weaning to heat in Large White or crossbred animals (10.5 vs 13.3 days). Sows with a weaning to service interval of less than 12 days had an average litter size of 10.3 piglets compared with 10.9 piglets when the interval was greater than 12 days. In attempts to gain control over the interval from weaning to oestrus 63 primiparous sows were allocated to either control or 20 mg allyl trenbolone per head per day for either 3 or 7 days starting on the day of weaning. Following a 7-day allyl trenbolone regime, no sow showed signs of oestrus prior to day 6 post-withdrawal, but 82% of sows were in oestrus 6–8 days post treatment, compared with 17% of controls. Results indicate that oestrus can be synchronized in about 80% of treated animals in the period of 3–8 days post-treatment. Pregnancy rates and average litter sizes were 82.9, 88.2, 88.9 and 10.5, 10.7 and 11.0 for the three treatments, respectively.     

Follicular Development in Lactating,Post Weaning and Anoestrous Primiparous Sows

The ovarian follicular system was studied in 4 lactating sows (6 or 8 weeks lactation period), 4 post weaning sows (2 or 4 days after weaning) and 5 post weaning anoestrous sows (22 days after weaning) by macroscopical and microscopical examinations. Blood sampling was performed daily in the post weaning anoestrous sows. The results showed that none of the sows had ovulated during lactation and after weaning. Only small and medium sized follicles were present in the ovaries of the sows. The blood levels of oestradiol-17β and progesterone were low throughout the post weaning period in the anoestrous sows. Microscopical examination showed that all sows had more normal than atretic follicles. In the lactating sows all follicles were below 5 mm in size, the majority being small (1.00–2.99 mm in diameter). The post weaning sows had follicles up to 5.00–5.99 mm and 23–24% of the follicles were medium sized (3.00–5.99 mm in diameter). The post weaning anoestrous sows had no follicles above 5 mm in diameter but many normal medium sized follicles.