Influence of environmental temperature on PGF(2alpha)-induced nest building in female pigs

Domestic pigs build a maternal nest in the day preceding parturition. We have shown that prostaglandin F(2alpha) (PGF(2alpha)) induces nest building behaviour in non-pregnant pigs. The aim of this experiment was to examine the effects of different environmental temperatures on PGF(2alpha)-induced nest building. Data were collected from 9 Large White (LW) and 10 Large Black (LB) 8-9-month-old nulliparous sows (gilts). The pigs were housed in social groups between experiments and tested individually in pens (1.8mx1.8m) containing straw, within an environmentally controlled chamber. Pigs were habituated to the testing pens (maintained at 17 degrees C) and tested once at each of three temperatures (low, 5 degrees C; moderate, 17 degrees C; high, 30 degrees C). During testing the temperature of the chamber was adjusted at 09.00h and had reached set point by10.00h. The pigs were injected intramuscularly with 3ml saline at 10.30h and 0.1mg/kg PGF(2alpha) (Lutalyse, Upjohn) at 11.30h. Behaviour was scored for 1h after treatment with saline and 1h after treatment with PGF(2alpha) using one/zero sampling from video recordings. Nest building behaviour (rooting, pawing and gathering straw) was induced by PGF(2alpha) at all temperatures in both LW and LB breeds. There was a significant increase in rooting behaviours with decreasing temperature. No significant effects of temperature were found on the scores for gather or paw. The pigs spent more time lying down at the high compared to the low temperature after both saline and PGF(2alpha) treatment. Other behaviours unrelated to nest building but induced by PGF(2alpha), such as scratching, were unaffected by temperature. The results show that the nest building behaviour of non-pregnant pigs can be induced by exogenous PGF(2alpha) treatment, and that some, but not all, aspects of PGF(2alpha)-induced nest building (rooting but not pawing or gathering) are altered by environmental temperature.     

Effects of prostaglandin F2alpha treatment on the behavior of pseudopregnant pigs in an extensive environment

In seminatural environments, prepartum sows leave the herd and construct a maternal nest (a dug out hollow lined with vegetation) prior to the birth of their piglets. The endocrine drives motivating this behavior are not understood, but may involve prostaglandin (PG) F2alpha. This study examined the effect of PGF2alpha treatment on the behavior of pseudopregnant gifts housed in a large enclosure. Pseudopregnancy was induced using 5 mg/ml estradiol valerate/day im from days 11 to 15 of the estrous cycle (first day of estrus = day 0). The gifts' behavior was recorded on a control day, during which no treatment was given, and a test day (= 45.9 +/- 0.42 days of pseudopregnancy) when gilts received either 15 mg PGF2alpha (dinoprost: Lutalyse, Upjohn, Crawley, UK, n = 11) or 0.9% saline (n = 10) im at 11.00 h. PGF2alpha-treated gilts traveled further and were more frequently >10 m from the nearest pig than saline-treated animals. In the hour following injection, PGF2alpha-treated animals also showed increased frequencies of rooting and pawing the ground and stood for longer than saline-treated animals. However, gathering and carrying nest materials were not increased. These results suggest that PGF2alpha, given as a single dose to extensively housed gilts, initiated many, but not all, of the behaviors characteristic of prepartum nest building. The dose and duration of PGF2alpha treatment may have limited the observed behaviors. In addition, environmental feedback is likely to affect the degree to which some nest building behaviors are expressed.     

Effects of prostaglandin F2alpha treatment of pseudopregnant pigs on nest building and interactions with newborn piglets

Previous studies showed that prostaglandin (PG)F2alpha treatment stimulated nest building behaviors in prepartum and pseudopregnant pigs. This experiment studied behaviors of PGF2alpha-treated pseudopregnant nulliparous pigs (gilts) exposed to newborn piglets. Penned pseudopregnant gilts (days 46-53) were injected with either 10 mg PGF2alpha (n = 8) or saline (n = 8) im, and behavior was recorded for 2 h (period A). Between 2 and 6 h (period B), gilts were given two male piglets (< 12 h old) and a novelty object (house brick) and recordings continued. During period A, PGF2alpha animals showed greater frequencies of standing, pawing, rooting, lifting, and carrying straw (indices of nest building) and scratching than saline treated animals. During period B, one PGF2alpha- and two saline-treated gilts attacked piglets, which were removed from the pen and the gilts excluded from further analysis. There were no treatment differences in period B in gilt posture, nest building behavior, or interactions with piglets or novelty object, except for a reduced frequency to trap piglets beneath their bodies and an increased frequency to attempt to escape from the pen in PGF2alpha-treated animals. Piglet position relative to the gilts' head and udder was unaffected by treatment. Gilts in both groups approached and nosed piglets more within the first 30 min of period B than subsequently. PGF2alpha-induced nest building had only a weak impact upon subsequent interactions between gilts and piglets, suggesting that mechanisms controlling porcine nest building and maternal behavior in this model were not directly linked.     

Effects of oestrogen supplementation and space restriction on PGF2alpha-induced nest-building in pseudopregnant gilts.

This study examined the role of oestrogen supplementation on PGF2alpha-induced nest-building in pseudopregnant gilts. Oestradiol valerate (5 mg/day) injections were given on Days 11-15 of the oestrous cycle to induce pseudopregnancy. A further series of injections of either oestradiol valerate (5 mg/day) or vehicle were given on days 44-46 of pseudopregnancy to reflect more closely the hormone profile seen in pregnancy. Nest-building was induced by a single intramuscular injection of 15 mg of PGF2alpha (Lutalyse) on Day 47 of pseudopregnancy. The gilts were housed in pens (2.8 x 1.7 m) containing straw in experiment 1 or chronically confined in crates (0.6 x 1.7 m) that did not contain straw on days 44-48 of pseudopregnancy for experiment 2. Oestrogen supplemented gilts had significantly higher concentrations of circulating 17beta-oestradiol on day 47 of pseudopregnancy but there were no significant differences between treatments for circulating levels of prolactin, progesterone, cortisol or oxytocin, or for any behavioural measure in either experiment. These results indicate that there is no direct effect of supplementing already pseudopregnant gilts with oestradiol valerate on PGF2alpha-induced nest-building. The results also show that the pre-partum environment has a pronounced effect on nest-building behaviours and that non-pregnant pigs might be a useful model for pre-partum nest-building in this species.     

Effect of oxytocin on concentration of PGF2 alpha in the uterine lumen and subsequent endometrial responsiveness to oxytocin in pigs

The aim of this study was to determine the effect of oxytocin on PGF2 alpha secretion into the uterine lumen of pigs and subsequent endometrial responsiveness to oxytocin in vitro. Cyclic, pregnant and oestradiol-induced pseudopregnant gilts were injected i.v. with vehicle or 20 iu oxytocin 10 min before hysterectomy on day 16 after oestrus. Concentrations of PGF2 alpha and 13,14-dihydro-15-keto PGF2 alpha (PGFM) were significantly increased in uterine flushings collected at hysterectomy (P < 0.05) in pregnant oxytocin-injected gilts. Concentrations of PGF2 alpha and PGFM were greater (P < 0.001) in pregnant than in pseudopregnant and cyclic gilts, and greater (P < 0.01) in pseudopregnant than in cyclic gilts. The ratio of PGFM:PGF2 alpha tended to be greater in cyclic (P < 0.06) and pseudopregnant gilts (P < 0.1) than in pregnant gilts. At 85 +/- 5 min after oxytocin injection, endometrium from each gilt was incubated for 3 h for determination of phosphoinositide hydrolysis and PGF2 alpha secretion in response to treatment with 0 or 100 nmol oxytocin l-1. Endometrial phosphoinositide hydrolysis in response to 100 nmol oxytocin l-1 in vitro was greater (P < 0.05) in cyclic oxytocin-injected gilts than in cyclic vehicle-injected gilts. Treatment with oxytocin in vitro did not stimulate phosphoinositide hydrolysis significantly in vehicle- or oxytocin-injected pregnant gilts or pseudopregnant gilts. Endometrial PGF2 alpha secretion increased after treatment with 100 nmol oxytocin l-1 in vitro in cyclic vehicle-injected (P < 0.01), cyclic oxytocin-injected (P < 0.01), pregnant vehicle-injected (P = 0.06), pseudopregnant vehicle-injected (P < 0.05) and pseudopregnant oxytocin-injected (P < 0.05) gilts, but not in pregnant oxytocin-injected gilts. The increase in PGF2 alpha in pseudopregnant oxytocin-injected gilts was less (P < 0.05) than that in cyclic oxytocin-injected gilts. These results indicate that oxytocin increases the concentration of PGF2 alpha and PGFM in the uterine lumen during pregnancy and may upregulate endometrial responsiveness to oxytocin during late dioestrus in pigs, but does not have the latter effect during early pregnancy or oestradiol-induced pseudopregnancy.     

Estrogen-induced pseudopregnancy in gilts: Its use in estrus synchronization and subsequent influence on litter response

The effectiveness of using estrogen-induced pseudopregnancy followed by PGF(2alpha) (Lutalyse) treatment to synchronize estrus in gilts and the subsequent effect of pseudopregnancy on litter parameters was examined in two experiments. Experiment 1 consisted of a control (n = 49) group and a pseudopregnant (n = 49) group. Pseudopregnant gilts received PGF(2alpha) between Days 25 and 38 and were bred at the ensuing estrus. Ninety-two percent of the gilts responded to PGF(2alpha) and exhibited estrus in 4.9 +/- 0.2 (Least Square Mean +/- SEM) days. Duration of estrus was longer in pseudopregnant compared to control gilts (2.8 vs 1.7 d, P<0.001). Experiment 2 consisted of a control (n = 24) group and a pseudopregnant (n = 24) group. All pseudopregnant gilts received PGF(2alpha) on Day 38 and 79% responded with a mean onset of estrus at 5.2 +/- 0.2 d. As in Experiment 1, duration of estrus was longer in gilts from the pseudopregnant group (2.2 vs 1.7 d, P<0.005). The percentage of farrowing was similar for both groups in both experiments, and no differences existed in the number of pigs born and those alive at 21 d post partum. Litters from gilts in the pseudopregnant groups were heavier at birth than those in the control group (Experiment 1, 17.21 vs 15.25 kg, P<0.01; Experiment 2, 15.31 vs 13.55 kg, P<0.02) and at 21 d (Experiment 1, 60.81 vs 56.79 kg, P<0.01; Experiment 2, 51.89 vs 46.96 kg, P<0.02). Survival rate at 21 d was higher in offspring from pseudopregnant gilts in both experiments (Experiment 1, 85.3% vs 78.2%, Experiment 2, 91.4% vs 81.2%).     

Changes in corpus luteum content of prostaglandin F2 alpha and E in the adult pseudopregnant rat

Conflicting reports exist regarding the source of luteolytic PGF2 alpha in the rat ovary. To assess the quantities of different PGs, measurements of PGF2 alpha, PGE and PGB were performed by radioimmunoassay in the adult pseudopregnant rat ovary throughout the luteal lifespan. Ovaries of 84 rats were separated by dissection into two compartments, corpora lutea of pseudopregnancy and remainder of ovary. Tissue samples were homogenized and prostaglandins extracted and determined by radioimmunoassay. During the mid-luteal and late-luteal phases, levels of PGs were significantly higher in the corpora lutea of pseudopregnancy than in the remainder of ovary. An increase of PGF2 alpha-content in the corpus luteum was registered with peak-levels of 53.9 +/- 8.5 (mean +/- SEM, N = 18) ng/g tissue wet weight at day 13 of pseudopregnancy. PGE-levels reached peak-values at day 11 of pseudopregnancy (271.6 +/- 28.4 ng/g w w, mean +/- SEM, N = 12). PGB-levels were below detection limits in all compartments for all ages studied. The present study demonstrates increased availability of PGF2 alpha in the corpus luteum during the luteolytic period, and points toward either increased luteal synthesis or luteal binding of PGF2 alpha during the luteolytic period.     

The effects of branches on prepartum nest building in gilts with access to straw

Sows farrowing in a semi-natural environment terminate nest building 1-7 h prior to parturition after having built a nest for which a variety of materials are used. No nest-building behaviour occurs during parturition and the sows remain lying in the nest throughout most of the farrowing. In contrast, many intensively housed sows are restless during farrowing. To investigate whether gilts housed indoors would use branches for nest building and whether access to branches would affect the termination of nest building and parturient behaviour, we studied gilts housed individually in pens designed to stimulate natural nest building. The control group (n=21) had unlimited access to straw and the experimental group (n=21) had unlimited access to straw and branches. During nest building all the gilts used straw and all the experimental gilts also used branches. In the experimental group the interval from termination of nest building to birth of the first piglet (BFP) was significantly longer than in the control group (132 versus 58 min, P=0.04). In the experimental group, nest-building behaviour was also performed by fewer individuals during the interval from BFP until 2 h after than in the control group (38% versus 71% of the gilts, P=0.03). Gilts that performed nest building during this interval carried out more postural changes (P<0.001) and spent less time in lateral recumbency (P=0.001) than gilts which did not perform nest building. On average, gilts that performed nest building behaviour after BFP (n=26) spent 54% of the first 2 h of parturition in lateral recumbency and carried out 16 postural changes. Gilts that did not perform nest building behaviour during this interval (n=16) spent 85% of the time in lateral recumbency and carried out five postural changes. In 10 gilts that were selected randomly from the experimental group nest building was studied in more detail. In these gilts nest building peaked between 17 and 6 h prepartum. There was no difference in amount of behaviour directed towards straw and amount of behaviour directed towards branches.The results indicate that the termination of nest building in sows is under environmental feedback control. When only straw was provided the nests did not have much of a lasting structure. However, when gilts had access to straw and branches more structured and functional nests could be built. These nests may have been more effective in reducing the motivation for nest building prior to the onset of parturition.     

In vivo levels of prostaglandin F2 alpha, E2 and prostacyclin in the corpus luteum of pregnant and pseudopregnant rats

Prostaglandin F2 alpha (PGF2 alpha) is a well-known luteolytic factor in the rat corpus luteum. To investigate a possible luteal origin of PGF2 alpha, measurements of this prostaglandin were performed in different luteal tissues in vivo. Prostaglandin E2 (PGE2) and the stable metabolite of prostacyclin, 6-keto-PGF1 alpha, were assayed simultaneously. Corpora lutea of different ages from 57 pregnant and pseudopregnant rats (mated with sterile males) were rapidly excised, dissected in 0 degree C indomethacin solution, homogenized, and extracted for prostaglandins with solid-phase extraction cartridges. Prostaglandins were determined by radioimmunoassay. Plasma levels of progesterone and 20 alpha-dihydroprogesterone were also monitored. In the adult pseudopregnant rat model, luteolysis occurs at Day 13 +/- 1, and maximal levels of all three prostaglandins were detected on Day 13 of pseudopregnancy: 0.40 +/- 0.02, 2.6 +/- 0.29, and 1.76 +/- 0.24 pmol/mg protein (mean +/- SEM, n=7) for PGF2 alpha, PGE2, and 6-keto-PGF1 alpha respectively. In pregnant rats, on the corresponding day, levels were considerably lower: 0.15 +/- 0.02, 0.90 +/- 0.13, and 0.50 +/- 0.06 pmol/mg protein (mean +/- SEM, n=9, p less than 0.0001), respectively. Luteal levels in pregnant rats showed a continuous decline on Days 13 and 19 for all prostaglandins measured, whereas in pseudopregnant rats an increment of PGF2 alpha was noted between Days 7 and 13 and remained high on Day 19. PGE2 closely followed levels of PGF2 alpha, but at a 5- to 10-fold higher level. The coefficient of correlation between PGF2 alpha and PGE2 in the luteal compartment of both models was 0.87 (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Anabolic action of insulin on skin wound protein is augmented by exogenous amino acids

We investigated the contribution of neutrophils to prostaglandin (PG)F(2 alpha)-induced luteolysis and the role of reactive oxygen species (ROS) as potential mediators of neutrophil accumulation in regressing corpora lutea of superovulated rats. On day 8 of pseudopregnancy, subcutaneous injection of PGF(2 alpha) (500 microg) significantly increased rhodamine 6G-labeled leukocyte adhesion in luteal venules, as observed by intravital microscopy. Neutrophil accumulation was confirmed by significantly increased myeloperoxidase (MPO) activity. Pretreatment with anti-leukocyte antibody (CD18-directed monoclonal antibody, WT-3) significantly inhibited the PGF(2 alpha)-induced increases in adherent leukocytes and MPO activity. Anti-leukocyte antibody also maintained serum progesterone concentrations. Pretreatment with oxygen free radical scavengers, superoxide dismutase (50,000 U/kg) and catalase (90,000 U/kg), also attenuated these PGF(2 alpha)-induced alterations. Corpora lutea preloaded with dichlorodihydrofluorescein diacetate succinimidyl ester, a fluorescent indicator for determining intracellular ROS generation, exhibited an increase in fluorescence after PGF(2 alpha) treatment. These findings suggest that leukocyte-endothelium interactions mediated by ROS generation are important in PGF(2 alpha)-induced luteolysis in rats.     

Effects of hysterectomy and uterine decidualization on in vivo levels of prostaglandins in the corpus luteum of adult pseudopregnant rats

A possible role of the uterus in regulating content of luteal prostaglandins (PGs) was investigated. Pseudopregnancy was induced in adult virgin female rats by mating them with vasectomized male rats. On Day 5 of pseudopregnancy, decidualization of the uterus was induced or hysterectomy was performed. As controls, intact pseudopregnant animals with a luteal phase of 13 +/- 1 days were used. Measurements of in vivo tissue levels of PGF2 alpha, PGE2, and 6-keto-PGF1 alpha were performed by RIA after homogenization and extraction procedures in CL of pseudopregnancy and remainder of ovaries on Days 5, 13, and 19. Serum levels of progesterone and 20 alpha-dihydroprogesterone were determined by RIA. In hysterectomized animals, PGF2 alpha levels increased 2.5-fold in corpora lutea on Day 13 compared with levels on Day 5 of pseudopregnancy, but were still lower than in control rats undergoing functional luteolysis on Day 13. Decidual-tissue-bearing rats exhibited low levels of PGF2 alpha on Day 13 of pseudopregnancy. On Day 19, when luteolysis had occurred in decidual-tissue-bearing and hysterectomized rats, as judged by plasma levels of progestins, luteal content of PGF2 alpha was elevated to a similar level as that in control animals undergoing functional luteolysis on Day 13. When data pooled from control, decidual-tissue-bearing and hysterectomized rats were analyzed, a highly significant inverse correlation (r = -0.72, n = 46, p less than 0.001) between luteal PGF2 alpha content and ratio of plasma progestins was found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis of prostaglandin F2 alpha, E2 and prostacyclin in isolated corpora lutea of adult pseudopregnant rats throughout the luteal life-span.

The ability of de novo biosynthesis of prostaglandins (PGs) in individual whole corpora lutea (CL) obtained from sterile-mated adult pseudopregnant rats on different days of the luteal phase and the post-luteolytic period was evaluated. Production of PGs, progesterone and 20 alpha-dihydroprogesterone were determined after in vitro incubation of CL extirpated from Day 2 to Day 19 after mating. A time-relationship with increased accumulation of PGs in the medium was demonstrated from 18 s to 5 h, with large increments during the first 30 min. Basal accumulation of PGs in the incubation medium was highest for 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) greater than PGE2 greater than PGF2 alpha greater than thromboxane B2 (TXB2) and basal accumulation of PGF2 alpha and PGE2 measured in the medium was maximal on Day 10-11 of pseudopregnancy, concomitantly with a decline in secretion of progesterone. Addition of arachidonic acid (AA) dose-dependently increased synthesis of PGs, with absolute amounts of PGE2 greater than 6-keto-PGF1 alpha greater than PGF2 alpha greater than TXB2 and addition of 14 microM indomethacin markedly inhibited accumulation of all PGs measured. Luteinizing hormone (LH, 10 micrograms/ml) stimulated progesterone secretion on all days during pseudopregnancy, but not on the post-luteolytic Day 19. LH increased PGF2 alpha, PGE2 and 6-keto-PGF1 alpha secretion on Day 13 of pseudopregnancy by 76%, 91% and 28%, respectively, but not on the other days tested. Furthermore, stimulation of PG-synthesis by addition of AA abrogated the LH-induced progesterone accumulation markedly, but only on Day 13 of pseudopregnancy. Epinephrine (5 micrograms/ml) increased production of progesterone and also PGs, but only on Day 2 of pseudopregnancy, whereas oxytocin (100 mIU/ml) was found to be without effect on progesterone as well as PG secretion on all days tested. The results of the present study demonstrates the independent ability of the rat CL to synthesize PGG/PGH2-derived prostaglandins, including the putative luteolysin PGF2 alpha. Secondly, we demonstrate that LH and AA-induced increases in PGF2 alpha and PGE2 production during the luteolytic period, may be an autocrine or paracrine mechanism involved in luteolysis.     

Acute stimulatory effects of prostaglandin F2 alpha on serum progesterone concentrations in pregnant and pseudopregnant pigs.

The objective of this study was to investigate whether PGF2 alpha, administered to pregnant and pseudopregnant gilts in vivo, would cause an acute increase in serum progesterone concentrations prior to luteolysis. Pregnant (n = 9) and pseudopregnant (n = 4) gilts were fitted with a jugular vein cannula on day 40, were treated with 3 ml vehicle (control) i.m. on day 42 and with 15 mg PGF2 alpha on day 45. Blood samples were collected at frequent (5 and 15 min) intervals from 1 h before until 1 h after control and PGF2 alpha injections, at 15 min intervals for 4 h, and then at 5, 6, 9, 21, 33, 45 and 57 h post injection. Progesterone was measured by radioimmunoassay (RIA) in all samples. Porcine LH was measured by RIA in samples collected frequently in the 1 h pre- and 1 h post-injection periods. Serum progesterone concentrations were unchanged in both pregnant and pseudopregnant animals in response to control injection on day 42. However, in both pregnant and pseudopregnant gilts, PGF2 alpha injection on day 45 resulted in an acute increase (approximately 75-80% above pre-treatment levels; p less than 0.05) in serum progesterone lasting approximately 1 h, followed by a return to pre-treatment levels by 2 h, and then a decline to 1 ng/ml or less by 45-57 h (pregnant) or 21-57 h (pseudopregnant), associated with luteolysis. Serum LH concentrations were unchanged between 1 h pre- and post-treatment periods in response to either control or PGF2 alpha-treatment, in both pregnant and pseuodpregnant gilts. These results indicate that PGF2 alpha-injection produces a rapid and transient increase in serum progesterone concentrations which may result from a rapid and direct stimulatory action of PGF2 alpha on porcine luteal cell progesterone synthesis/secretion in vivo.     

Effect of straw on the behaviour of growing pigs

The effects of straw on the behaviour of young growing pigs were studied in two experiments. In Experiment 1, groups of three pigs, aged about 7 weeks, were housed in raised decks with or without straw bedding. Time-lapse video recording showed no major differences between treatments in the amount or daily pattern of overall activity and feeding. Detailed observations showed that bedding reduced the incidence of rooting and chewing on pen-mates, but had little effect on other social activities such as mounting and aggressive biting. Experiment 2 compared groups of eight growing pigs aged about 10 weeks, housed in floor pens with or without a small amount of straw provided daily in a rack. Pigs with straw concentrated more of their daily activity into the period when straw was fresh, but the total amount of overall activity and time spent feeding were not affected. Rooting and chewing of pen-mates were the only social activities reduced by the provision of fresh straw. In these studies, where straw was not required to compensate for deficiencies such as low temperatures or hunger, the one major function of straw was to provide a stimulus and outlet for rooting and chewing, with a resulting reduction in such activities directed at pen-mates.     

Maternal behavior in pigs

When sows kept under commercial conditions were put into crates in the early 1960s, the neuro-endocrine regulation of the maternal behavior in these domestic animals was disputed. Thus, the study of sow maternal behavior intensified and today a significant body of knowledge has accumulated to support the hormonal regulation of sow maternal behavior. The onset of nest building is associated with a periparturient decline in progesterone, an increase in prolactin and a major rise in plasma concentrations of PGF2alpha the day before parturition. Some nest building behaviors, such as pawing and gathering straw, have been found to correlate with changes in the levels of progesterone, prolactin and somatostatin. The duration of the birth process correlates negatively with peripheral oxytocin levels. During lactation, the stimuli from the piglets affect the release of several hormones which not only regulate the let down of milk but also sow metabolism and mammary milk production. The sow's nursing behavior ensures an even distribution of milk to her piglets. The piglets suckling behavior, in turn, is mainly a way to communicate their individual nutritional needs.     

Effect of decidual tissue on the uterine production of prostaglandins in pseudopregnant rats.

The concentration of prostaglandin F (PGF) in uterine vein plasma of non-traumatized pseudopregnant rats and pseudopregnant rats with deciduomata were not significantly different from each other at any of the times of pseudopregnancy studied (Days 7, 10 and 12). There was a significant increase in PGF levels on Day 10 in both groups of pseudopregnant animals (P less than 0-05) compared to the Day 4 values, and PGE values were significantly greater on Day 10 in the decidual tissue-bearing rats (P less than 0-01). A slight but not significant elevation in PGE concentration was observed on Days 7 and 12 in rats with deciduomata, but there was no significant difference in the control rats on Days 4, 7, 10 or 12. The results indicate that the prolongation of pseudopregnancy in rats with deciduomata is not due to a decreased production of uterine PGs and lend support to the recent suggestion of a luteotrophic effect of decidual tissue in the rat.     

The effect of long or chopped straw on pig behaviour

In the EU, pigs must have permanent access to manipulable materials such as straw, rope, wood, etc. Long straw can fulfil this function, but can increase labour requirements for cleaning pens, and result in problems with blocked slatted floors and slurry systems. Chopped straw might be more practical, but what is the effect on pigs’ behaviour of using chopped straw instead of long straw? Commercial pigs in 1/3 slatted, 2/3 solid pens of 15 pigs were provided with either 100 g/pig per day of long straw (20 pens) or of chopped straw (19 pens). Behavioural observations were made of three focal pigs per pen (one from each of small, medium and large weight tertiles) for one full day between 0600 and 2300 h at each of ~40 and ~80 kg. The time spent rooting/investigating overall (709 s/pig per hour at 40 kg to 533 s/pig per hour at 80 kg), or directed to the straw/solid floor (497 s/pig per hour at 40 kg to 343 s/pig per hour at 80 kg), was not affected by straw length but reduced with age. Time spent investigating other pigs (83 s/pig per hour at 40 kg), the slatted floor (57 s/pig per hour) or pen fixtures (21 s/pig per hour) was not affected by age or straw length. Aggressive behaviour was infrequent, but lasted about twice as long in pens with chopped straw (2.3 s/pig per hour at 40 kg) compared with pens with long straw (1.0 s/pig per hour at 40 kg, P=0.060). There were no significant effects of straw length on tail or ear lesions, but shoulders were significantly more likely to have minor scratches with chopped straw (P=0.031), which may reflect the higher levels of aggression. Smaller pigs showed more rooting/investigatory behaviour, and in particular directed towards the straw/solid floor and the slatted floor than their larger pen-mates. Females exhibited more straw and pen fixture-directed behaviour than males. There were no effects of pig size or sex on behaviour directed towards other pigs. In summary, pigs spent similar amounts of time interacting with straw/solid floor when long and chopped straw were provided, and most aspects of pig-directed behaviour and injuries were not affected by straw length. There was an increase in pigs with minor shoulder lesions with chopped straw, perhaps because of increased aggression. The use of chopped straw as an enrichment material for pigs warrants further investigation in larger and more detailed studies.     

A Test of the Effect of Male Song on Female Nesting Behaviour in the Serin (Serinus serinus): a Field Playback Experiment

It is well established, through laboratory experiments, that male song in birds can stimulate female reproductive activity, affecting their behaviour and physiology, such as follicular growth, nest building and egg‐laying. However no clear demonstration has yet been provided that this effect works under natural conditions. Previous work in natural populations of serins showed that female nest‐building behaviour correlated with male singing time. Furthermore male serin song peaked exactly in the day that rapid follicular growth was estimated to start in females, suggesting that in this species song may also serve to stimulate the female's reproductive development. Direct causal evidence, however, was lacking. We conducted field playback experiments to investigate how song can influence female nesting activity during nest building. Our results show that females who listened daily to playbacks of serin songs, during the nest‐building stage, spent more time nest building than females that were not exposed to additional songs. Moreover, the singing behaviour of the mated males was not affected by the playbacks, suggesting that the song playback treatment had a direct positive effect on female nesting behaviour.     

Studies on the mechanism of action of prostaglandin F2 alpha induced luteolysis in rats

The effects of prostaglandin F2 alpha (PGF2 alpha) administration on the utilization of low density lipoprotein (LDL) and progesterone secretion were examined in dispersed luteal cells from rat ovaries. Immature rats were rendered pseudopregnant with administration of pregnant mare serum gonadotropin and human chorionic gonadotropin. Animals were sacrificed at different times after PGF2 alpha (5 mg/kg) or vehicle administration on day-5 of pseudopregnancy. Administration of PGF2 alpha in vivo decreased human chorionic gonadotropin (hCG) binding to luteal cell membranes in vitro but enhanced binding of LDL. Utilization of labelled cholesterol for steroid synthesis from reconstituted LDL [(3H)-CL-LDL] by dispersed luteal cells was enhanced following PGF2 alpha administration. This suggests that the LDL pathway is not suppressed during prostaglandin induced luteolysis. Progesterone and total progestin secretion in response to N6-2'-0-Dibutyryladenosine 3'5'-cyclic monophosphate (cAMP) was decreased at 2, 4 and 24 hours following PGF2 alpha administration demonstrating a post-cAMP defect in steroidogenesis. Addition of the hydroxylated sterols, 20 or 25-OH cholesterol as substrate stimulated progesterone secretion in vehicle treated rats in a dose dependent fashion with 20-OH cholesterol being more potent. Progesterone secretion in response to stimulation with luteinizing hormone (LH) and cAMP from vehicle treated rats was less than that observed with 20 or 25-OH cholesterol, indicating that endogenous substrate may be a limiting factor in steroid synthesis. The maximal capacity of luteal tissue to produce progestins following PGF2 alpha administration was determined with 20-OH cholesterol as the substrate. The results suggest that the post-cAMP defect at 4 hours following PGF2 alpha administration may be due to failure of the cells to mobilize endogenous cholesterol. However at 24 hours following PGF2 alpha administration the decreased ability of luteal cells to convert cholesterol to pregnenolone may contribute to decreased progesterone synthesis.     

Effects of PGE1 or PGE2 on luteal function in pseudopregnant rats

Effects of PGE1 or PGE2 on luteal function were studied in 163 pseudopregnant rats. PGE1 (10, 100, or 300 micrograms) given intrauterine every 6 hr did not shorten pseudopregnancy (P greater than 0.05), however, the same doses of PGE2 given intrauterine every 6 hr advanced luteolysis (P less than 0.05). PGE1 (100 or 300 micrograms) given every 4 hr intramuscular maintained levels of progesterone in peripheral blood above controls (P less than 0.05) while 100 or 300 micrograms of PGE2 hastened the decline in progesterone (P less than 0.05). The antiluteolytic effect of PGE1 was not via an inhibition of PGF secretion (P greater than 0.05) by the uterus or by induction of ovulation in treated animals. Moreover, PGE1 (100, 200, or 500 micrograms) given intramuscular every 4 hr from day 4 of pseudopregnancy until the next proestrus delayed luteal regression around 3 days (P less than 0.05). PGE2 at doses of 100, 200, or 500 micrograms every 4 hr given intramuscular consistently shortened pseudopregnancy (P less than 0.05). Lower doses were without effect (P greater than 0.05). Based on the above data it is concluded that PGE2 is consistently luteolytic whereas PGE1 is not luteolytic in pseudopregnant rats and that PGE1 may be an antiluteolysin.