The basic patterns of thyroid hormones [thyroxine (T4) and 3,3',5-triiodothyronine (T3)] and the T4 and T3 responses induced by thyrotropin releasing hormone (TRH) are reported in captive female barn owls (Tyto alba) during the non-breeding period. The main findings of the study, conducted on a total of 10 owls, are as follow: (1) The thyroid gland of barn owl can be stimulated by the classical TRH stimulation test. (2) T3 response was much more pronounced both under cold (around 10°C) and warm (around 20°C) conditions, whereas T4 response ranged so widely that we could not point out any significant change in it. (3) Basal T3 plasma level was significantly (p = 0.036) higher in birds exposed to cold temperature, and they responded to TRH treatment with a lower plasma T3 elevation than the birds kept in a warm chamber. This pattern, however, cannot be explained by increased food intake, but is in agreement with the fact that enhanced T3 level may account for higher avUCP mRNA expression, which results in higher heat production on the cell level. From the results it is concluded that altering T3 plasma level plays a significant role in cold-induced thermoregulation.
The effect of 10-day zearalenone administration starting 10 days after ovulation was studied in 6 cycling trotter mares in the summer period. After an entire oestrous cycle (Cycle 1), mares were given 7 mg purified zearalenone per os daily (1 mg/ml in ethyl alcohol) beginning on Day 10 of Cycle 2. Toxin exposure was continued until the subsequent ovulation. Luteal function and follicular activity were monitored daily by rectal palpation, ultrasonography and blood sampling for progesterone. During toxin exposure, all animals were in good physical condition. The toxin had no effect on the length of the interovulatory intervals, luteal and follicular phases. It did not influence significantly the plasma progesterone profiles (logistic curve parameters A1 to A6), the follicular activity (growth rate, maximum size of the ovulatory follicles, maximum number and the time of first increase in the number of large follicles) and the uterine oedema. It is concluded that in cyclic mares the methods used in this study could not detect any adverse effect of zearalenone (administered at a low dose similar to natural exposure) on reproduction.
The energy imbalance related predisposition to mastitis was studied in group-fed postpartum dairy cows (n = 333) kept in 4 large-scale units and producing milk of low somatic cell count (SCC). Blood samples were taken on Days 1-3 after calving for assaying some metabolites and hormones related to the negative energy balance (NEB). If mastitis was diagnosed later, aseptic milk samples were taken to identify the pathogens. Considering pathogen types [contagious pathogens: Staphylococcus (S.) aureus, Gram-positive (GP) environmental pathogens, and Gram-negative (GN) environmental pathogens + mastitis with no detectable pathogens (NDP)] separately, stepwise logistic regression was used to analyse the relation between the potential prognostic value of hormones and metabolites and mastitis outbreak. Only the elevated (= 1.00 mmol/l) serum ß-hydroxybutyrate (BHB) levels predisposed the cows to mastitis in the subsequent 4 weeks. This prognostic value of BHB was significant only in GN + NDP mastitis and in cases caused by GP environmental pathogens, but not in S. aureus mastitis (odds ratio: 5.333, 3.600 and 1.333, respectively).
Ketosis was diagnosed in a flock of Merino ewes that conceived from synchronised oestrus in the early autumn period. On day 140 of pregnancy the ewes were sampled for determination of βOH-butyrate (BHB), AST, glucose, non-esterified fatty acids (NEFA), total cholesterol (TCH), insulin, T4, T3, cortisol, IGF-1 and leptin. The results were evaluated according to the number of fetuses born some days later and the presence of hyperketonaemia (BHB: ≥ 1.60 mmol/l). In May, about 3 months after lambing, cyclic ovarian function was induced (Cronolone + eCG), and the ewes were inseminated artificially (AI) 48 h after the removal of gestagen-containing sponge. At the time of AI and 10 days later blood samples were collected again to check the plasma levels of the same constituents as previously (in samples taken at AI), and to monitor the ovarian response by assaying progesterone (in both samples). On day 140 of gestation significantly lower BHB levels were detected in dams with single (n = 41) than in those with twin (n = 57) pregnancies. Hyperketonaemia was found only in ewes bearing twins (n = 27). These animals had higher NEFA and cortisol, and lower TCH, insulin, IGF-1, leptin and T3 levels than their normoketonaemic twin-bearing flock-mates, and those with single pregnancy. The blood glucose concentrations varied within a wide range, and the means of groups did not exhibit any significant differences. The formerly hyperketonaemic individuals were characterised by lower leptin level 3 months after lambing, and they showed a poorer response to the cycle-induction procedure than the others. The non-responders had lower IGF-1 and leptin levels than those ovulated after this treatment. It was concluded that the subclinical form of ovine ketosis is characterised by complex endocrine alterations, reflecting an obvious form of negative energy balance. If attempts to induce cyclic ovarian function outside the breeding season are made soon after lambing, the ovarian response and fertility of these ewes may also be depressed.
Maternal plasma leptin is elevated in ewes during pregnancy. The authors studied whether there was any relation between maternal plasma leptin and insulin concentrations, the number of fetuses and the circulating and faecal levels of gestagens. At the end of the breeding season in January the ovarian activity of Prolific Merino ewes was induced/synchronised with gestagen + eCG treatment. Ewes were inseminated artificially (AI) by laparoscopy. Blood and faecal samples were collected before AI (day 0) and again 41, 81 and 101 days later. The plasma levels of leptin (pL), insulin and progesterone (pP4), and the faecal P4 metabolite (P4-met) content were determined. The day 0 level of pL was significantly higher in pregnant (n = 24) than in non-pregnant ewes (n = 32). By day 41 the pL of pregnant animals had doubled, it showed a further moderate increase on day 81, and decreased slightly thereafter. During pregnancy pP4 and faecal P4-met rose continuously and were positively correlated at all stages. The mean levels of pL and pP4 and the faecal content of P4-met were lower in ewes bearing single (n = 12) than in those with 2 (n = 6) or 3-5 fetuses (n = 6). Analysis of variance demonstrated significant differences according to the number of fetuses in the pL and pP4, but not in P4-met (p = 0.042, 0.044, and 0.051, respectively). Leptin showed positive correlation with insulin before the AI but not during pregnancy. On days 41 and 81 pL showed a slight positive correlation with P4 and P4-met, which decreased slightly by day 101. This study shows that although leptinaemia is affected by the number of fetuses and the level of P4, pregnancy stage is a more important regulator than these additional factors.