S. M. Rhind

Endocrine disrupting compounds and farm animals: their properties, actions and routes of exposure

Endocrine disrupting compounds (EDC) comprise a diverse group of compounds of anthropogenic origin, including organochlorine pesticides, alkyl phenols, phthalates, polychlorinated biphenyls (PCB), dioxins and polybrominated diphenyl ethers. EDC are generally present in the environment at low concentrations but they are ubiquitous and persistent and, although environmental concentrations are low, they appear to exert a range of adverse effects on animals of many species, including humans. Their effects include disruption of reproductive function and of the immune system and they can be carcinogenic. Animals may be exposed to relatively high concentrations of EDC because they persist in the environment and when ingested, they may be concentrated in fat tissue and released when the fat is mobilised during pregnancy or lactation, thus exposing, to relatively high concentrations, embryos and neonates. These stages of development are particularly susceptible to EDC effects. Very little is known of EDC body burdens in domestic animal species and particularly in those exposed to unpolluted environments. EDC concentrations in soils and plant material and their rates of ingestion and metabolism have been little studied but it is concluded that there is a potential risk of significant bioaccumulation and of associated effects on the health and reproductive capacity of domestic animals and of humans consuming animal products.

Effects of body condition at calving and feeding level after calving on LH profiles and the duration of the post-partum anoestrous period in beef cows

An experiment was conducted to examine the effects of body condition at calving and feeding level post partum on the duration of the post-partum anoestrous period in beef cows. Forty-seven cows were used in each of 2 years. Cows were fed differentially before calving to achieve two levels of body condition at calving in November and December and were then fed at one of two levels of feeding post partum in a 2 × 2 factorial experiment. At calving, mean body condition scores were 2·85 (F) and 2·23 (T) (P 0·05). At 3 weeks post partum LH pulse frequency was higher in F than in T cows and tended to be higher in H than in L cows. At 6 and 9 weeks post partum LH pulse frequency was higher in H than L cows. LH pulse amplitude was higher in F than T cows at 3 weeks post partum and tended to be higher at 6 weeks post partum. It is concluded that both body condition at calving and feeding level after calving influence the duration of the post-partum anoestrous period with the effect of feeding level being particularly pronounced in thin cows.

Seasonality of meal patterns and hormonal correlates in red deer

Two groups of six adult, castrated, male red deer were housed under natural daylength conditions and at ambient temperature at 57 degrees N and fed ad lib. (AL) or at a fixed rate of 50 g/kg0.75 initial liveweight per day throughout the study (restricted, R). Mean daily intakes of AL animals were higher during periods of long daylength than during short daylength (p < 0.001). The higher rates of food intake during periods of long daylength were a function of greater meal durations (p < 0.001), shorter inter-meal intervals (p < 0.001) and higher (p < 0.001) mean rates of ingestion (g/min). In both groups mean plasma concentrations of prolactin, T3, T4, and insulin-like growth factor 1 (IGF-1) were higher (p < 0.001) during long daylength than short daylength although changes in thyroid hormone profiles were much less marked in AL animals. Insulin and growth hormone (GH) profiles exhibited no consistent seasonal trend. Mean plasma concentrations of T3 were higher in AL than in R animals. Mean plasma IGF-1 concentrations during long days were consistently greater in the AL than R animals. It is concluded that the effects of seasonal changes in daylength on appetite and food intake are expressed through changes in both the duration of daylight periods per se and in underlying seasonal changes in physiology and associated meal patterns and eating rates. It is concluded that the roles of T3, IGF-1, and prolactin in the expression of seasonal changes in appetite should be investigated further and, particularly, their effects on other hormone profiles and liver and gut function.

Effects of levels of food intake and body condition on the sensitivity of the hypothalamus and pituitary to ovarian steroid feedback in ovariectomized ewes

In two experiments involving ovariectomized Scottish Blackface ewes and steroid replacement therapy, the effects of level of food intake and of body condition on hypothalamic and pituitary sensitivity to progesterone and oestradiol feedback were investigated. In experiment 1, groups of 16 ewes in similar levels of body condition were given dried grass pellets ad libitum (mean dry-matter (DM) intake of 2481 (s.e. 71) g per head per day; group H) or 1105 g DM per head per day (group M). In experiment 2, groups of 16 ewes were fed so that they achieved body condition scores of 2·70 (s.e. 0040; group HBC) or 1·67 (s.e. 0·036; group LBC) prior to the start of the experiment. All ewes were then fed to maintain their respective levels of body condition. In both experiments, all ewes were ovariectomized and intravaginal progesterone pessaries and subcutaneous oestradiol implants were inserted; these were designed to induce circulating concentrations of these steroids within the normal range for intact ewes. Approximately 1 week later, blood samples were collected at 15-min intervals for 10 h, and at 10-min intervals for 8 h before and after pessary withdrawal respectively. All samples were assayed for LH and selected samples were assayed for FSH and progesterone. Gonadotropin profiles were also recorded during 2-h periods following injection (i.v.) of 0·25 μg and 5 μg GnRH. When circulating progesterone concentrations were elevated, due to the presence of a progesterone pessary, there was no effect of level of food intake on mean LH or FSH concentrations or mean LH pulse frequency but H ewes had a higher mean LH pulse amplitude than M ewes ( P P P P P P P P P

Accumulation of potentially toxic metals in the liver tissue of sheep grazed on sewage sludge-treated pastures

Concentrations of potentially toxic metals (PTMs) in the livers of pregnant, mature ewes and their 110 day foetuses, and in 6-month old lambs born to other ewes, were determined. The animals had been reared on pastures fertilized for 5 years with either sewage sludge (treated; T) or conventional inorganic fertilizer (control; C). The effects of treatment on patterns of accumulation of PTMs differed with stage of development and with individual PTM. In the liver of lambs, concentrations of Pb were elevated in T compared with C liver ( P P P

Effects of pulsed or continuous infusion of cortisol on immune function in sheep

It was postulated that frequent pulses of cortisol such as might be induced by a repeated or chronic stressor, could induce immune suppression and that the effect would be greater than in animals subjected to less frequent increases. Four groups of nine adult Scottish Blackface ewes were infused for 14 d with saline or hydrocortisone hemisuccinate (cortisol) delivered continuously or in pulses. Plasma concentrations of cortisol were significantly elevated (to between approximately 100 and 1000 nmol/liter; P < 0.001) for about 30 or 75 min after infusion of pulses of hydrocortisone hemisuccinate at intervals of 1 hr (P1) or 6 hr (P6), respectively. In animals continuously infused (CI), they were consistently elevated (P < 0.001), compared with concentrations in control animals infused with saline only (S), to approximately 1000 nmol/liter or more. Antibody production in response to ovalbumin injection was not affected by any of the infusion regimes. At Days 10, 24, and 31 after injection of ovalbumin and initiation of the infusion, rates of multiplication of unstimulated lymphocytes, in vitro, were greater (P < 0.05) in P6 animals than in saline-infused, control animals and this resulted in a reduction in the stimulated lymphocyte response. As a consequence of the increased basal lymphocyte activity, after Day 0, the corrected, stimulated lymphocyte response of P6 animals was consistently below that of controls (P < 0.05 at Day 24). Both mean basal and stimulated lymphocyte activities in CI and P1 animals were similar to those of controls. The gamma interferon (IFN-gamma) response was generally small and not affected by treatment. It is concluded that large, relatively infrequent increases in circulating cortisol concentrations can modify the cell mediated immune response such that the response to a specific antigen challenge is compromised but smaller, more frequent pulses had no effect. Elevated cortisol concentrations per se did not have a significant inhibitory effect on the immune system.

The rôle of cortisol and β-endorphin in the response of the immune system to weaning in lambs

The relationship between weaning stress-induced changes in stress hormone profiles and immune function was investigated in groups of 10 lambs immunized against adrenocorticotrophic hormone (ACTH; treatment A) or fi-endorphin (treatment B) to reduce the circulating concentrations of cortisol and fi-endorphin respectively. Control animals (treatment C) were immunized against a porcine thyroglobulin carrier protein. Application of weaning stress was associated with significantly elevated plasma cortisol concentrations but no significant increase in fi-endorphin concentrations in C lambs. Immunization against ACTH suppressed the post-weaning increase in cortisol concentration. This was associated with a transient reduction in the lymphocyte stimulation response to keyhole limpet haemocyanin (KLH) antigen in the A animals but there was no effect on the antibody response or interferon-y production by antigen stimulated lymphocytes. There were no significant effects of immunization against fi-endorphin on the capacity to mount antibody or cell-mediated immune responses. It is concluded that weaning stress-induced increases in cortisol did not inhibit the immune response. Since cortisol concentrations and the cell mediated immune response at 8 days after immunization were positively associated it is concluded that these indices are not independent measures of stress.

Effects of body condition and estradiol on luteinizing hormone secretion in post-partum beef cows

An experiment was conducted to test the hypothesis that the effect of body fatness on LH pulsatility in post-partum cows is entirely independent of the negative feedback effects of ovarian steroids. Forty beef cows were fed in the last 100 d of gestation so that they achieved either a thin (mean score 1.97) or fat (mean score 2.79) body condition (0 to 5 scale) at calving and were fed after calving to maintain live weight and body condition. At 15 (sd 3.7) d post partum all cows were ovariectomised and half from each body condition score treatment group received a subcutaneous estradiol implant (+EST) while the remainder received no implant (-EST). At weeks 5 and 9 post-partum blood samples were collected via jugular catheter every 20 minutes for 10 hr on two consecutive d and on the third d cows were injected via the jugular vein with 2.5 micrograms GnRH. Blood samples were collected every 15 minutes for 1 hr before and 2 hr after GnRH injection. At 5 and 9 weeks the fatter cows had significantly higher mean LH concentrations, baseline LH concentrations, LH pulse amplitudes and pulse frequencies (P < 0.01). Implantation with estradiol in both fat and thin cows reduced mean LH concentrations, baseline LH concentrations, LH pulse amplitudes and pulse frequencies (P < 0.001). The lack of interaction between body condition and the presence or absence of estradiol implies that the effect of body condition on LH release is independent of ovarian steroid feedback mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)