The origin of cortisol in the blood of fetal sheep.

The blood clearance rate (BCR) of cortisol was measured in non-pregnant ewes and in pregnant ewes and their intact or bilaterally adrenalectomized fetuses. In pregnant sheep the placental transfer of cortisol in both directions was established. The BCR of cortisol in the non-pregnant sheep was 51.7 +2- 4.9 (S.E.M.) l/h (n = 36) or 1.15 l/h per kg body weight. This was lower than that in the pregnant ewe (97-143 days of gestation) of 76.9 +/- 4.21 l/h (n = 9) or 1.85 l/h per kg. In the intact fetus the BCR was 8.2 +/- 0.26 l/h (n = 10) over the same period of gestation. The percentage of the maternal production rate of cortisol transferred to the fetus was 1.4 +/- 0.11% (n = 9) and the placental transfer from fetus to mother was 19.5 +/- 1.5% (n = 8). The BCR in pregnant ewes bearing bilaterally adrenalectomized fetuses was not significantly different from that of mothers of intact fetuses (58.4 +/- 7.7 l/h; n = 6). The BCR of adrenalectomized fetuses was 8.4 +/- 1.37 l/h (n = 8). The placental transfer of cortisol from mother to fetus was sufficient to account for all the cortisol measured in adrenalectomized fetuses and in intact fetuses of 100-121 days of gestation. However, it accounted for only 37% of the cortisol measured in fetuses of 122-135 days of gestation and 12% or less in fetuses older than 136 days of gestation.

The effects of stress and of ACTH administration in hormone profiles, oestrus and ovulation in pigs.

Hormone concentrations and oestrous cycle patterns were studied in five chronically cannulated gilts. During oestrous cycles that were unaffected by stress, plasma oestrogen concentrations remained at basal luteal phase levels (10 to 30 pg/ml) until plasma progesterone had decreased to less than 2 ng/ml. The pre-oestrus surge of oestrogen ranged from 40 to 80 pg/ml. Plasma corticoid concentrations varied randomly and were not related to oestrogen, progesterone concentrations, or the stage of the oestrous cycle. There was, however, evidence of a positive relationship between elevated corticoid levels and observed stressful events. The stress of surgery or illness acting during the follicular phase of the oestrous cycle delayed the onset of oestrus, and corticoid levels were frequently elevated on these occasions. Elevated plasma corticoid concentrations in response to ACTH treatment were associated with either a change in the timing of or a suppression of the pre-oestrus LH peak. Altering the timing of the LH peak resulted in the formation of large partially luteinized ovarian cysts, while suppressing LH interfered with follicular development and led to small ovarian cysts. These experiments suggest that stress acting via the adrenal gland may play a role in the aetiology of infertility in sows.

Metabolic clearance rate of cortisol in pigs: relationship to adrenal responsiveness.

Experiments were conducted on 12 prepuberal (18- to 20-week-old) Landrace cross Large White gilts to establish if differences in adrenal responsiveness between individuals could be explained by differences in the metabolic clearance rate (MCR) of cortisol. Pigs with the highest (n = 6) and lowest (n = 6) cortisol concentration 60 minutes after challenge with ACTH were selected from a pool of 36 commercial pigs. Tritium-labelled cortisol was infused (17 to 27 ml h-1) continuously for 120 minutes to establish 'steady state' conditions. Blood samples (10 ml) were collected at 90, 100, 110 and 120 minutes. Replicate experiments were performed on some pigs. Classification of individual pigs as high or low adrenal responders to ACTH challenge was confirmed at the end of the clearance rate experiments. The MCR of cortisol in the group classed as low adrenal responders was 59.7 +/- 7.8 litres h-1 or 1.01 litres h-1 kg-1 (n = 7) which was not significantly different from the average MCR in the group classed as high adrenal responders 60.2 +/- 5.9 litres h-1 or 1.19 litres h-1 kg-1 (n = 10). These results suggest that the repeatable differences in adrenal responsiveness to ACTH that exist between individuals within a particular strain of pig depend on differences in the rate of synthesis of cortisol in response to ACTH stimulation, rather than on differences in its rate of metabolism.

Vaccination of boars with a GnRH vaccine (Improvac) eliminates boar taint and increases growth performance.

Peri- and postpubertal boars accumulate substances (e.g., androstenone and skatole) in their fatty tissue that are responsible for boar taint in pork. The objective of this study was to assess the efficacy of a GnRH vaccine, Improvac, in eliminating boar taint. Three hundred male (200 intact boars, 100 barrows) crossbred (Large White x Landrace) pigs were used in a 2 x 3 factorially arranged experiment. The respective factors were sex group (barrows, boars treated with placebo, or boars treated with Improvac) and slaughter age (23 or 26 wk). Vaccines were administered 8 and 4 wk before slaughter. All Improvac-treated pigs exhibited anti-GnRH titers. Testes and bulbo-urethral gland weights in treated pigs were reduced by approximately 50% (P < 0.001) and serum testosterone levels were below 2 ng/mL in the majority of treated boars (94 and 92% across both age groups at 2 and 4 wk, respectively). Boar taint, as assessed by the concentration of androstenone and skatole in s.c. fat, was suppressed to low or undetectable levels in 100% of Improvac-treated boars. No Improvac-treated pigs had significant concentrations of either androstenone (> 1.0 microg/g) or skatole (> 0.20 microg/g). In contrast, 49.5% of placebo-treated controls had significant androstenone and 10.8% had significant skatole levels, resulting in 10% of the control boars with high concentrations of both compounds. The mean concentrations of taint compounds in the Improvac-treated pigs were not significantly different from those in barrows. Improvac-treated boars grew more rapidly (P = 0.051 and < 0.001 for pigs slaughtered at 23 and 26 wk of age, respectively) than control boars over the 4 wk after the secondary vaccination, possibly because of reduced sexual and aggressive activities. Compared with barrows, Improvac-treated boars were leaner and had superior feed conversion efficiency. The vaccine was well tolerated by the pigs, and no observable site reactions could be detected at the time of slaughter. Vaccination of boars with Improvac allows production of heavy boars with improved meat quality through prevention and control of boar taint.

In vitro study of the function of adrenocortical cells from pigs of differing in vivo response to adrenocorticotropin.

A study was conducted to determine whether within-breed differences in adrenocortical response to exogenous adrenocorticotropin (ACTH) might be accounted for by differences in responsiveness of the adrenocortical cells per se. Large White x Landrace male pigs (n = 20) were used; 10 had high adrenocortical response to ACTH administration and 10 had low response. Five high and 5 low responders were euthanatized at 15 weeks of age, and the remaining 5 high and 5 low responders were euthanatized at 21 weeks of age. Adrenal glands were removed and weighed, and adrenocortical cells were dispersed by tryptic digestion and incubated for 2 hours with synthetic ACTH at concentrations ranging from 0.5 to 10,000 pg/ml. Samples were taken at 30-minutes intervals, and cortisol concentration was determined by use of a radioimmunoassay. Results indicate that for pigs of both age groups, high responders had heavier adrenal glands, with higher adrenocortical cell density and higher cell yield than did low responders. Synthetic ACTH had a stimulatory effect on dispersed porcine adrenocortical cells, as indicated by changes in cortisol concentration in vitro. Adrenocortical cells from high responders produced less cortisol, on a per-cell basis, than did those from low responders. However, when corrected for total cell yield, the potential cortisol production by each pair of adrenal glands was significantly (P less than 0.05) higher in the high responders than in the low responders. Thus, high-responding pigs have larger adrenal glands and higher adrenocortical cell density, which may result in higher output of cortisol after ACTH administration or exposure to stressors.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary and adrenocortical responses to corticotropin-releasing factor in pigs.

A study was conducted to determine whether differences in adrenocortical response to exogenous adrenocorticotrophin (ACTH) were an accurate reflection of an animal's perception of and response to stressful stimuli, or whether the pituitary gland might modulate adrenocortical responsiveness. Sixteen Large White x Landrace female pigs, of which 8 had high adrenocortical response to ACTH and the other 8 had low response, were administered IV a bolus of synthetic human corticotropin-releasing factor (hCRF) at dose rates ranging from 0.002 to 2 micrograms/kg of body weight. Blood samples were collected at known times for up to 2 hours after administration of hCRF. Plasma ACTH and cortisol concentrations were measured by radioimmunoassay. Results indicate that hCRF stimulated the pituitary gland of high- and low-responding pigs to secrete ACTH, which in turn stimulated the adrenal cortex to secrete cortisol. Plasma ACTH concentration, before or after hCRF administration, was not significantly different between the high and low responders. However, high-responding pigs had higher cortisol concentration after hCRF administration than did low-responding pigs. Thus, the differences in adrenocortical response to ACTH between the 2 groups of pigs were not attenuated by variation in pituitary response. It is concluded that adrenocortical responsiveness to ACTH is an accurate indicator of the perception of and the response to stress.

Consistent capacity for adrenocortical response to ACTH administration in pigs.

The effect of ACTH administration on plasma cortisol concentrations in purebred and crossbred pigs was investigated. Pigs were given either 25 IU of ACTH or physiologic saline solution IM. Blood samples were collected immediately before and 1 hour after ACTH or saline solution administration. Administration of ACTH resulted in a significant (P less than 0.01) increase in plasma cortisol concentration compared with that resulting from administration of saline solution; mean values after ACTH administration were similar in both breed groups. In contrast, a fivefold range of differences was observed among individual pigs of the same age, sex, and body weight, irrespective of breed group. The type and magnitude of the adrenocortical response was consistent and repeatable in pigs over a 3-month period, suggesting that pigs have a consistent capacity for adrenocortical response to ACTH administration. Development of a dynamic test allowed the high and low responding extremes in a population to be detected. The most suitable dose of synthetic ACTH was established to be 50 IU, and the best time for blood sample collection was 60 minutes after ACTH administration. The classification of individual pigs as high or low responders was repeatable and was not affected by prior short-term exposure to ACTH.

Stress and summer infertility in pigs.

A serious year-round fertility problem on a commercial piggery was investigated. The problem was characterised by a high proportion of non-pregnant sows and gilts which showed a delayed return or failure to return to oestrus after a normal mating to a fertile boar. Several factors were identified that we considered to be placing undue stress on the breeding stock from wearning through mating and early pregnancy. When steps were taken to reduce the influence of these stressors there was a marked improvement in the herd farrowing rate. Across all months this improvement was largely due to a reduction in the number of sows showing delayed return or failure to return to oestrus after mating. There were no concomitant changes in other indices of performance. In conclusion this study has shown that stressful factors other than summer heat stress can cause a syndrome of delayed or failure to return to oestrus, this syndrome is commonly and perhaps wrongly called 'summer or seasonal infertility'. When given the appropriate combination and/or intensity of stressful stimuli, it can be manifest at any time of the year.

The effect of immunization against GnRF on nutrient requirements of male pigs: a review.

In most countries, male pigs are physically castrated soon after birth to reduce the risk of boar taint and to avoid behaviours such as fighting and mounting. However, entire male pigs are more feed efficient and deposit less fat than barrows. In addition, many animal welfare organizations are lobbying for a cessation of castration, with a likelihood that this could lead to inferior pork unless an alternative method is used to control boar taint. An alternative to physical castration is immunization against gonadotrophin releasing factor (GnRF) which allows producers to capitalize on the superior feed efficiency and carcass characteristics of boars without the risk of boar taint. From a physiological perspective, immunized pigs are entire males until shortly after the second dose, typically given 4 to 6 weeks before slaughter. Following full immunization, there is a temporary suppression of testicular function and a hormonal status that resembles that of a barrow. Nutrient requirements will be different in these two phases, before and after full immunization. Given that there have been few published studies comparing the lysine requirements of entire males and barrows in contemporary genotypes, it is useful to use gilt requirements as a benchmark. A series of meta-analyses comparing anti-GnRF immunized boars and physical castrates and use of nutritional models suggest that the lysine requirement of entire males before the second immunization is 5% higher than for gilts, from 25 to 50 kg BW, and by 8% from 50 to 95 kg. Given that the penalty in growth performance for having inadequate dietary lysine is greater in males than in gilts or barrows, it is important to ensure that lysine requirements are met to obtain the maximum benefits of entire male production during this phase. After the second immunization, the lysine requirement of immunized males decreases and may become more like that of barrows. In addition, a consistent effect of full immunization is a marked increase in voluntary feed intake from about 10 days after the second dose. Putting these together, the estimated lysine requirement, expressed in terms of diet composition, falls to 94% of the gilt level. Although general principles can be described now, further research is needed to fully define the lysine requirements of immunized boars. It is important that the temporal pattern of tissue deposition rates and feed intake be explored to be incorporated into models to predict nutrient requirements over the period of rapidly changing metabolism.

Reducing the length of time between slaughter and the secondary gonadotropin-releasing factor immunization improves growth performance and clears boar taint compounds in male finishing pigs.

The objective of this study was to evaluate whether altering the timing of the secondary anti-gonadotropin-releasing factor (GnRF) immunization closer to slaughter in male finishing pigs would reduce the increase in P2 fat depth (6.5 cm from the midline over the last rib), while still limiting the incidence of boar taint. Entire male pigs are immunized against GnRF to reduce the concentration of testicular steroids that in turn limits the incidence of boar taint. Additionally, testicle measurements and color measurements were taken to examine whether they could be used to differentiate nonimmunized entire males from immunized male pigs. A total of 175 Large White × Landrace entire male pigs aged 16 wk (59 kg of BW) were used in a completely randomized design with 5 treatment groups based on the time that pigs received the secondary immunization before slaughter. Pigs were housed in groups of 7 and randomly allocated to 1 of 5 treatments with 5 replicates per treatment. The treatment groups were as follows: no secondary immunization before slaughter, and the secondary immunization given at 2, 3, 4, or 6 wk before slaughter. The P2 fat depth levels were reduced (P = 0.054) with the secondary immunization closer to slaughter (11.7, 11.3, 12.8, 12.6, and 13.7 mm for no secondary immunization, secondary immunization at 2, 3, 4, and 6 wk before slaughter, respectively). Androstenone concentration did not exceed the generally accepted industry sensory threshold of 1.0 µg/g of fat, and both androstenone concentration in the adipose tissue and testosterone concentrations in the blood were suppressed (P < 0.001) in all immunized pigs regardless of timing of the secondary immunization compared with pigs that did not receive the secondary immunization. Skatole concentration of all pigs in the experiment did not exceed the generally accepted industry sensory threshold of 0.2 µg/g. Testes weight was reduced (P < 0.001) with increased time between slaughter and the secondary immunization. Immunized pigs, regardless of time before slaughter, had greater L* (lightness) and b* (yellowness) color of the testicle surface (P < 0.001 and P = 0.020, respectively), and less a* (redness) color compared with entire males (P < 0.001). The study provides further evidence of the efficacy of the anti-GnRF immunization and indicates that the secondary immunization can be moved closer to slaughter, while still limiting the incidence of boar taint. Testicle measurements and color measurements together could provide a method of discrimination between carcasses from immunized entire males clear of boar taint and tainted carcasses.

Clinical biochemical reference ranges for female alpacas (Lama pacos).

1. Serum samples were collected from 352 healthy female alpacas and tested for 17 clinical biochemical analytes. 2. From the total population of alpacas tested, 205 were pregnant, 68 were not pregnant and 79 had an unknown pregnancy status. 3. Reference ranges for the female alpacas were determined for all the biochemical analytes, and compared to ranges reported for llamas, cattle, sheep and goats. 4. The mean values for pregnant and non-pregnant females were compared and any statistically significant differences identified. 5. The biochemical values reported here are suitable as reference ranges for pregnant and non-pregnant female alpacas.

Development of the pituitary-adrenal axis in chronically cannulated ovine fetuses.

In the intact, unstressed ovine fetus, both plasma immunoreactive adrenocorticotrophin (ACTH) and blood cortisol concentrations increased after 121 days gestation. The mean ACTH and cortisol concentrations in intact fetuses of 90-121, 122-135 and 136-144 days gestation were for ACTH 20.4 +/- 3.9 (50) (mean +/- SEM, n), 30.2 +/- 5.6 (26) and 56.0 +/- 6.3 pg/ml (37) respectively, and for cortisol 0.07 +/- 0.01 (24), 0.17 +/- 0.03 (21) and 0.64 +/- 0.13 microgram/100 ml (15), respectively. After 121 days ACTH and cortisol concentrations were correlated positively. Cortisol infused into intact or adrenalectomized fetuses and corticosterone infused into adrenalectomized fetuses suppressed fetal plasma ACTH concentrations. In summary, ACTH and cortisol increase concomitantly after 122 days, so that it is highly probable that ACTH is the trophic stimulus for fetal adrenal maturation. The suppression of ACTH by cortisol and corticosterone suggests that these are the natural feedback regulators. It is proposed that while the mechanism for cortisol feedback may exist early in gestation, it is not until after 121 days that feedback control of ACTH becomes evident and physiologically important.

Regulation of urine osmolality in fetal sheep.

Urine osmolality was measured daily from day of cannulation (80-110 d) until term in six chronically cannulated ovine fetuses. Fetal urine was hypertonic to plasma following surgery, and 24-36 h before parturition. On fifty-five occasions plasma antidiuretic hormone (ADH) concentration was measured concurrently with urine osmolality. When fetal urine osmolality was 154 +/- 45 mosmol/kg water, plasma ADH was 5.6 +/- 2.1 pg/ml (mean +/- S.D.; n = 33) in fetuses less than 120 d gestation. In ten samples from fetuses from 121 d to term urine osmolality was 118 +/- 35 mosmol/kg water when the concurrent plasma ADH concentration was 5.5 +/- 2.1 pg/ml. Urine osmolality greater than 300 mosmol/Kg water was associated with endogenous plasma ADH concentrations of 6.2-9.2 pg/ml in fetuses 86 d until term. However, when exogenous synthetic arginine vasopressin (AVP) was infused into non-stressed fetuses with initial urine osmolalities less than 200 mosmol/Kg water, the minimum plasma ADH concentration that had to be established in order to induce the production of a hypertonic urine was 22.1 pg/ml at gestational ages 95-105 d, 11-1 pg/ml at 110-120 d and 7 pg/ml at 121-130 d. The fetal kidney thus becomes more responsive to infused AVP over the last half of gestation. Under conditions of in utero stress, however, hypertonic urine can be produced at lower endogenous plasma ADH concentrations than required to be established by infusion in non-stressed fetuses, suggesting that urinary concentrating mechanisms independent of ADH are established in these fetuses.

Adrenocortical ACTH receptors in pigs of differing in vivo response to adrenocorticotropin.

1. Adrenocortical membrane protein was isolated from the adrenal glands of 12 Large White x Landrace male pigs, six with high adrenocortical response to adrenocorticotropic hormone (ACTH) and six with low response. 2. The peptide (Phe2, Nle4) ACTH was iodinated by the chloramine-T method and served as the radioligand in receptor binding studies. 3. Only one class of ACTH receptor was detected, with Kd = 2.57 +/- 0.35 x 10(9) M and Bmax = 1.59 +/- 0.06 pmol/mg protein in high responders and Kd = 1.68 +/- 0.18 x 10(-9) M and Bmax = 1.17 +/- 0.11 pmol/mg protein in low responders. 4. The difference in the Bmax between high and low responders was significant (P < 0.05), the difference in Kd was not statistically significant.

Physiological responses to exercise and hypoglycaemia stress in pigs of differing adrenal responsiveness.

1. Twelve Large White x Landrace male pigs, six with high adrenocortical response to ACTH, and six with low response, were subjected to mild and moderate exercise, and then to insulin-induced hypoglycaemia. 2. Plasma ACTH, cortisol, catecholamines and some haematological and plasma biochemical parameters were determined in response to exercise, and glucose and cortisol in response to insulin challenge. 3. High responders had significantly greater increases than low responders in ACTH, cortisol and catecholamines following exercise, and in cortisol following insulin challenge. 4. The results suggest that differences in adrenocortical response to exogenous ACTH are an accurate reflection of the animal's response to stressful stimuli.

The effect of bilateral fetal adrenalectomy on the concentration of ovine placental lactogen in pregnant ewe plasma.

The concentrations of ovine placental lactogen in the plasma of ewes, carrying intact or bilaterally adrenalectomized fetuses, were compared over the last third of gestation. The results were grouped into 10 day periods from 100 days of gestation until term or Caesarean delivery. In ewes carrying intact fetuses, plasma placental lactogen concentrations were 147.8 +/- 64 [5 (21)], 252.5 +/- 137.5 [5 (15)], 341.2 +/- 256.7 [6 (22)], 431.1 +/- 366.2 [6 (20)], 435.1 +/- 314.4 [4 (17)], and 325 +/- 175 [1 (17)] ng/ml in gestational ages 100-109, 110-119, 120-129, 130-139, 140-149 and greater than 150 days respectively (mean +/- SD [number of animals (number of samples)]). In the same age groupings, maternal plasma placental lactogen concentrations in ewes carrying bilaterally adrenalectomized fetuses were 88.5 [1 (2)], 190.4 +/- 55.8 [3 (20)], 204.4 +/- 75.1 [6 (41)], 299.8 +/- 210.5 [5 (18)], 345.5 +/- 24 [2 (12)] and 271.4 +/- 60.3 [1 (3)] ng/ml respectively. There were no significant differences between these values in any age group. The conclusion was that bilateral adrenalectomy of the fetus had no significant effect on the concentration of placental lactogen in maternal plasma.