A sex difference in the cortisol response to tail docking and ACTH develops between 1 and 8 weeks of age in lambs.

It is important to understand factors that may influence responses to stress, as these factors may also influence vulnerability to pathologies that can develop when stress responses are excessive or prolonged. It is clear that, in adults, the sex of an individual can influence the cortisol response to stress in a stressor specific manner. Nevertheless, the stage of development at which these sex differences emerge is unknown. We tested the hypothesis that there are sex differences in the cortisol response to tail docking and ACTH in lambs of 1 and 8 weeks of age. We also established cortisol responses in males when tail docking was imposed alone and in combination with castration at these ages. In experiment 1, 1 and 8 week old male and female lambs were subjected to sham handling, tail docking or, in males, a combination of tail docking and castration. In experiment 2, we administered ACTH (1.0 IU/kg) to male and female lambs at 1 and 8 weeks of age. There were significant cortisol responses to all treatments at both ages. Sex differences in the cortisol responses to tail docking and ACTH developed between 1 and 8 weeks of age, with females having greater responses than males. The data suggest that the mechanism for the sex difference in response to tail docking may involve the adrenal glands. At both ages, in males, the cortisol response to the combined treatment of tail docking and castration was significantly greater than that for tail docking alone.

Enhanced transdermal delivery of sex hormones in swine with a novel topical aerosol.

This study investigated the enhanced transdermal delivery of testosterone (Tes) and estradiol (E2) in swine in vivo with novel metered-dose topical aerosols containing the penetration enhancer padimate O (PadO) and predicted the dose deliverable in humans from the calculated drug flux across the skin. Weanling swine were catheterized and castrated under general anaesthesia and used as a conscious hypogonadal model. Tes and E2 (with and without PadO) were applied once, and venous blood samples were taken over 24 h. Tes and E2 plasma levels were determined by radioimmunoassay. After daily topical dosing of Tes for 6 days, the plasma Tes levels were determined and the transdermal flux was calculated by correcting the pseudo steady-state plasma concentration versus time profile with the clearance of an iv dose within the same swine. After a single application of the E2 aerosol over 30 cm2, or the Tes aerosol over 180 cm2, the mean AUC0-24 h when PadO was included in the spray was 14.1- and 2.0-fold greater than control, respectively (p < 0.03). After the sixth application of the Tes spray with PadO, the mean flux (+/-SE, n = 4) across swine skin in vivo was 2.12 +/- 0.35 microg/cm2.h, which gave a predicted flux in humans of 0.95 microg/cm2.h. From these data the expected plasma levels of Tes in hypogonadal men would compare well with the normal diurnal Tes profile in healthy men. These novel topical aerosols are capable of enhanced transdermal delivery of sex hormones in vivo, and they have the potential to deliver clinically relevant doses to humans.

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance.

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25-28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P < 0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P < 0.01) and 87% for CW sows (P > 0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P < 0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P > 0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.

Feed intake affects metabolic clearance rate of progesterone in sheep.

To study the inverse relationship between feed level and concentrations of peripheral plasma progesterone, 36 ovariectomised ewes were fed rations at levels calculated to maintain liveweight (M). On the seventh day, the ewes were given an intravenous infusion of progesterone and the metabolic clearance rate (MCR) was calculated. The ewes were then randomly allotted to receive either 1/2M, M or 2M rations for seven days at which time the infusion and blood sampling schedules were repeated. The mean (SE) MCR of infused progesterone in ovariectomised ewes fed either 1/2M, M or 2M rations for seven days was 7.1 (0.59), 9.9 (1.64 and 13.0 (1.19) litre h-1 kg-1 of liveweight, respectively. Differences in MCR of progesterone between ewes fed 1/2M and 2M rations were significant (P < 0.05). The inverse relationship between level of feed intake and plasma progesterone concentration was attributed to differences in clearance rate of progesterone rather than to changes in the entry rate of the hormone into the blood.

Liver blood flow and metabolic clearance rate of progesterone in sheep.

To study the effects of feeding on concentrations of peripheral plasma progesterone, ovariectomised ewes, given exogenous progesterone, were fed 750 g of chopped lucerne hay at either 09.00 (group A, n = 5) or at 15.00 (group B, n = 5) or were fed ad libitum regularly through the experimental period (group C, n = 5). Peripheral blood samples were taken from each ewe at 09.00, 11.00, 15.00, 17.00 and 23.00. In ewes of groups A and B, mean plasma progesterone concentrations declined significantly (P < 0.05) after feeding. Mean progesterone concentrations of group C ewes remained low and were significantly different (P < 0.05) from the pre-feeding values of group A and B ewes. These results showed that the metabolic clearance rate of progesterone changed with the act of feeding. In a second experiment, portal, hepatic and mesenteric vein cannulae were placed in ovariectomised ewes (n = 17). They were then fed a ration calculated to maintain liveweight for seven days (M ration). The ewes were then infused with progesterone into a jugular vein and with p-amino hippuric acid into a mesenteric vein. Ewes were then allotted to receive either half M or twice M rations for seven days after which the infusions and blood sampling procedures were repeated. The mean rate of blood flow in the portal vein was directly related to the level of feed offered when ewes received either 1/2M, M or 2M rations. The liver and gut region removed a mean of 96 per cent of the progesterone entering these tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Human leukemia inhibitory factor improves the viability of cultured ovine embryos.

Embryos were collected from ewes on Day 6 after estrus (Day 0 = estrus), placed in M2 culture medium, and assigned to 1 of 4 treatment groups. Some embryos were transferred to recipient ewes on Day 6 of their estrous cycle either in pairs (group 1) or singularly (group 2) within 3 h of collection. The remaining embryos were individually cultured for 48 h in an atmosphere of 5% CO2 in humidified air in either synthetic oviduct fluid (SOF) medium (group 3) or SOF containing 1,000 U/ml of recombinant human leukemia inhibitory factor (hLIF) (SOF + hLIF: group 4). These embryos were then transferred to recipient ewes on Day 8 of their estrous cycle. The addition of hLIF to culture medium significantly improved the development of the embryos compared with control embryos prior to transfer (blastocysts hatching from the zona pellucida: group 3 = 16% vs. group 4 = 64%, p less than 0.05; those degenerative: group 3 = 27% vs. group 4 = 9%, p less than 0.05) and the subsequent pregnancy rates of the recipient ewes, receiving a single embryo, at Day 70 of pregnancy (group 3 = 16% vs. group 4 = 50%, p less than 0.05). The pregnancy rate of ewes given embryos cultured for 48 h in SOF + hLIF prior to transfer (50%; group 4) was similar to the group 2 ewes receiving a single embryo soon after collection (52%), but the pregnancy rate for both groups was significantly lower than that for the group 1 ewes receiving two embryos soon after collection (89%: 53% twins, 36% singles; p less than 0.05).

Nutrition-progesterone interactions during early pregnancy in sheep.

A series of studies was undertaken to determine the relationship between level of feed intake during early pregnancy, concentrations of peripheral progesterone and embryo survival in sheep. Ewes fed twice maintenance (2M) rations after joining had a pregnancy rate of 48%. Ewes fed 2M rations and given exogenous progesterone between 8 and 14 days after mating had a pregnancy rate of 76%. Ewes fed rations calculated to maintain live weight (maintenance, M) or fed restricted rations during this same time had pregnancy rates ranging from 60 to 68%, with no beneficial effect of progesterone supplement. Concentrations of peripheral plasma progesterone on Day 12 after mating were inversely related to the level of feed intake; this relationship reflected an increase in the metabolic clearance rate of progesterone with increased feed intake (1/2M, M and 2M) without concomitant changes in the entry rate of the hormone. Injection of epostane, an inhibitor of the enzyme 3 beta-hydroxysteroid dehydrogenase, caused 'windows' of progesterone reduction for 48-h periods over Days 9-13 after mating. The sheep embryo was sensitive to low peripheral plasma progesterone concentrations only on Days 11 and 12 after mating. Blood flow rates in the portal vein of ewes fed either 1/2M, M or 2M rations for 7 days were directly related to the level of feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Overfeeding during early pregnancy reduces peripheral progesterone concentration and pregnancy rate in sheep.

The 330 Merino ewes used in the study were placed with rams at a synchronized oestrus and, on Days 2-14 after mating, the ewes were placed in a feed lot and fed daily a low, medium or high ration (25%, 100% or 200% of maintenance respectively). Progesterone supplement was given to some ewes on Days 8-14 after mating by using a device containing 340 mg progesterone. Blood samples were taken from all ewes on Day 12 for measurement of plasma progesterone concentrations. On Day 14 after mating all ewes were returned to pasture. Pregnancy rate was determined by returns to oestrus and was later confirmed using ultrasound. There was a decline in the peripheral progesterone concentrations with increasing ration. The pregnancy rate in ewes fed a high ration was significantly reduced when compared with those of ewes fed a medium or low ration (48% vs 68 and 67% respectively; P less than 0.05). In ewes fed the high ration exogenous progesterone increased the pregnancy rate from 48 to 76% (P less than 0.01). Progesterone treatment did not influence pregnancy rates in ewes fed medium or low rations. The number of fetuses per ewe pregnant was not influenced by level of nutrition or progesterone treatment.

Evidence for maternal control of blastocyst growth after asynchronous transfer of embryos to the uterus of the ewe.

The fate of embryos transferred asynchronously in the ewe was investigated when the functional life of the corpus luteum was prolonged by both hemi-hysterectomy and by the presence of a second synchronously transferred embryo. The development of asynchronously transferred embryos was assessed at progressively later stages after transfer. Prolongation of luteal function did not enable asynchronously transferred embryos to persist. Embryos from Day 4 donors were found to be retarded in their rate of development when placed in 'younger' Day 1 or 2 uteri and appeared unable to develop beyond the early blastocyst stage. Conversely, embryos from Day 4 donors placed in 'older' Day 6 or 7 uteri showed accelerated growth and development which was maintained until the uterus reached Day 12. Thereafter further growth of the asynchronously transferred embryos was retarded, although synchronously transferred embryos then entered the phase of rapid blastodermic vesicle elongation. Asynchronously transferred embryos disappeared from the uterus when the ewe entered pro-oestrus. The experiments demonstrate the existence of an active relationship between the embryo and the maternal environment during mid-cycle and an apparent lack of association between embryo size, growth rate and physiological maturation.

Nutrition of the ewe and embryo growth during early pregnancy.

Mature Merino ewes (n = 228) were fed rations at levels of either 5, 10, 15, 20, 30 or 40 g/kg daily from day 1 until day 35 after mating. Embryos were then removed from single ovulating ewes and, after being weighed and measured, were dissected and embryo liver weights were obtained. Plasma samples were taken from all ewes on days 5, 10, 15, 20, 27 and 35 after mating and later analysed for glucose concentrations. During the 35-day treatment period, mean liveweight changes of ewes ranged from -6.9 to 5.5 kg in groups receiving the lowest and highest levels of nutrition respectively. Although there were no significant differences in the percentages of ewes pregnant at day 35 the weight and size of embryos, including embryo liver weight, varied with the level of nutrition. Mean wet weights (+/- s.e.m.) of embryos from ewes receiving rations at the rate of 10 g/kg daily and those receiving 30 g/kg daily were 1.67 +/- 0.04 g and 1.91 +/- 0.04 g respectively (difference significant at P less than 0.01). Plasma glucose concentrations of the ewes increased with increasing level of ration and decreased with time.

Content of LH, FSH, and growth hormone in the pituitaries of pregnant and anestrous sheep.

The total content of LH, FSH, and growth hormone was measured in pituitaries from anestrous ewes and from ewes at known stages of pregnancy. LH content was lower in the pregnant ewes than in the anestrous group. Compared with the anestrous group, a significant drop in mean LH content was seen by days 40-50 of pregnancy (894 vs 350 mug, P less than 0.001), and it reached its lowest value by 120-135 days of pregnancy (43 mug, P less than 0.001). In sheep 148 days of pregnant, mean LH content was higher than in the latter group (155 mug). The correlation coefficient between the stage of gestation and the LH content was 0.63 (P less than 0.01). There was no significant change in mean FSH content in ewes up to 135 days pregnant (range 1196-1550 mug) compared with anestrous ewes (1023 mug). In the group 148 days pregnant (531 mug), a significant decrease was seen compared with ewes at other stages of pregnancy (P less than 0.05). Stage of gestation and FSH content were poorly correlated (r = 0.07). No significant differences in growth hormone content were seen in any of the groups. The results suggest that the progressive reduction in LH response to synthetic GnRH which has been reported for pregnant sheep may be due to selective inhibition of LH biosynthesis.

Wastage of ova in young Merino ewes.

Eight sub-flocks each of 48 to 51 Merino ewes were mated for 18 days with 1 ram to each subflock. Four of the sub-flocks were of non-parous 1.5-year-old ewes and the other 4 were of parous 2.5-year-old ewes. Fertilisation rates for the subflocks of 1.5-year-old ewes varied from 83 to 94%, and the sub-flocks of 2.5-year-old ewes ranged from 81 to 94%. By day 29 post coitum 42% and 56% of 1.5-year-old ewes in sub-flocks 1 and 2 respectively were no longer pregnant. Embryonic mortality was low in other sub-flocks of 1.5- and 2.5-year-old ewes. Virtually all embryonic death occurred after day 12 post coitum. The sporadic occurrence of high ova wastage in maiden 1.5-year-old ewes in this experiment and in others is discussed in relation to the short duration of oestrus in young ewes and the great variation in service activity of rams.