Dynamics of GHRH in third-ventricle cerebrospinal fluid of cattle: Relationship with serum concentrations of GH and responses to appetite-regulating peptides

Objectives were to (1) characterize the relationship of third-ventricle (IIIV) cerebrospinal fluid (CSF) concentrations of growth hormone–releasing hormone (GHRH) with concentrations of GH in the peripheral circulation; and (2) assess the influence of acute administration of appetite-regulating peptides leptin (anti-orexigenic) and neuropeptide Y (NPY; orexigenic) on the release of GHRH. Six mature beef cows fitted with IIIV and jugular vein cannulae were treated intracerebroventricularly with saline, and leptin (600 μg) and NPY (500 μg) in saline, in a replicated 3 × 3 Latin square design. Third-ventricle CSF and blood were collected 10 min before and continued 220 min after treatments. Mean concentrations of GHRH and frequency of pulses after treatments were 2.2 ± 0.13 ng/mL and 1.2 ± 0.15 pulses/220 min, respectively. These measures were not influenced by treatments. Concentrations of GHRH in CSF were weakly correlated (r = 0.15; P < 0.03) with serum concentrations of GH; however, 58% of the GH pulses were preceded by a pulse of GHRH and 90% of the GHRH pulses occurred within 20 min preceding a pulse of GH. Leptin tended (P < 0.10) to suppress GH area under the curve (AUC) compared to saline. Concomitantly, NPY tended (P < 0.10) to increase GH AUC, which appeared to be a consequence of increased (P < 0.05) pulse amplitude. Infusion of NPY also increased (P < 0.05) AUC of GHRH relative to saline. No differences were detected among treatments in serum concentrations of insulin-like growth factor-I or its AUC. Sampling CSF from the IIIV appears to be a viable procedure for assessing hypothalamic release of GHRH coincident with anterior pituitary gland secretion of GH in cattle. These data also demonstrate the differential responsiveness of the GH axis to appetite-regulating peptides.     

Plasma hormone and metabolite concentrations involved in the somatotropic axis of Japanese Black heifers in association with growth hormone gene polymorphism

Bovine growth hormone (bGH) gene polymorphism of leucine (Leu)-threonine (Thr) (allele A), valine (Val)-Thr (allele B), and Val-methionine (Met) (allele C) at codons 127 and 172 was shown to relate with carcass trait variations in Japanese Black cattle. In this study, 10-mo-old Japanese Black heifers with growth hormone (GH) genotypes AA, AB, BB, AC, BC, and CC (N = 141) were compared for basal GH, insulin-like growth factor-1 (IGF-1), insulin, ghrelin, glucose, and nonesterified fatty acid (NEFA) concentrations. Growth hormone release was also measured as response to growth hormone–releasing hormone (GHRH) (0.4 μg/kg body weight [BW]) using 18 heifers with GH genotypes AA, BB, and CC (n = 6 for each group). The genotype AA heifers showed the greatest BW among genotypes (P < 0.05). Genotype AC, BC, and CC heifers showed greater GH concentrations than genotype AA, AB, or BB heifers, in which genotype CC heifers had the highest concentrations (P < 0.05). However, IGF-1 concentrations did not significantly differ. The genotype AA and BB heifers had a greater GH release at 60 min following GHRH injection than did the genotype CC heifers. The area under the curve (AUC; P < 0.07) and incremental area (IA; P < 0.08) of GH responses to the GHRH challenge tended to be the highest in the genotype AA heifers and the lowest in the genotype CC heifers. In conclusion, GH gene polymorphism altered GH, which may have contributed to differences in BW and carcass traits among genotypes.     

Somatotropin response in vitro to corticosterone and triiodothyronine during chick embryonic development: Involvement of type I and type II glucocorticoid receptors

Corticosterone (CORT) can stimulate growth hormone (GH) secretion on embryonic day (e) 12 in the chicken. However, CORT failed to induce GH secretion on e20 in a single report, suggesting that regulation of GH production changes during embryonic development. Secretion in response to CORT during embryonic development is modulated by the thyroid hormones triiodothyronine (T₃) and thyroxine (T₄). Growth hormone responses on e12 involve both glucocorticoid (GR) and mineralocorticoid receptors (MR); however, involvement of MR has not been evaluated past e12. To further define changes in somatotroph responsiveness to CORT, pituitary cells obtained on e12–e20 were cultured with CORT alone and in combination with T₃ and GH-releasing hormone (GHRH). Growth hormone mRNA levels and protein secretion were quantified by quantitative real-time polymerase chain reaction (qRT-PCR) and radioimmunoassay (RIA), respectively. Corticosterone significantly increased GH mRNA and protein secretion on e12; however, mRNA concentration and protein secretion were unaffected on e20. Contributions of GR and MR in CORT responses were evaluated using GR and MR antagonists. Treatment with a GR-specific antagonist effectively blocked the CORT-induced increase in GH secretion on e12. The same treatment on e20 had no effect on GH secretion. These findings demonstrate that GR is directly involved in glucocorticoid stimulation of GH secretion at the time of somatotroph differentiation but is not regulatory at the end of embryonic development. We conclude that positive somatotroph responses to CORT are lost during chicken embryonic development and that GR is the primary regulator of CORT-induced GH secretion.     

Differential responses in anterior pituitary luteinizing hormone (LH) content and LHβ- and α-subunit MRNA, and plasma concentrations of LH and testosterone, in bulls treated with the LH-releasing hormone agonist deslorelin

Anterior pituitary gland contents of LH and LHß- and α-subunit mRNAs, and circulating concentrations of LH and testosterone, were determined in bulls treated with the LH-releasing hormone (LHRH) agonist deslorelin. Brahman (Bos indicus) bulls (14-month-old) were allocated to two groups and received the following: Control (n = 5), no treatment; Deslorelin (n = 4), four deslorelin implants (approximately 200 μg total deslorelin/day) for 36 d. Plasma concentrations of LH were higher in bulls treated with deslorelin on Day 1, had returned to typical levels by Day 8, and did not differ for control bulls and bulls treated with deslorelin from Day 8 to Day 29. Pituitary content of LH on Day 36 was reduced (P < 0.001) in bulls treated with deslorelin (33 ± 4 ng/mg) compared with control bulls (553 ± 142 ng/mg). Relative pituitary content of LHß-subunit mRNA was also reduced on Day 36 in bulls treated with deslorelin (Control, 0.65 ± 0.10; Deslorelin, 0.22 ± 0.04; P = 0.003). However, α-subunit mRNA relative content did not differ (Control, 0.73 ± 0.15; Deslorelin, 1.06 ± 0.12; P > 0.05). Plasma concentrations of testosterone were increased over the period of the experiment in the bulls treated with deslorelin compared with control bulls. This is the first demonstration of reduced pituitary content of LHß-subunit mRNA and LH, and unaltered content of α-subunit mRNA, in bulls treated with LHRH agonist. This was associated with apparently typical plasma concentrations of LH and elevated plasma testosterone. The anterior pituitary in bulls treated with LHRH agonist, therefore, undergoes classical desensitization and downregulation, but plasma LH and testosterone are not suppressed.     

Reproduction and beyond,kisspeptin in ruminants

Kisspeptin (Kp) is synthesized in the arcuate nucleus and preoptic area of the hypothalamus and is a regulator of gonadotropin releasing hormone in the hypothalamus. In addition, Kp may regulate additional functions such as increased neuropeptide Y gene expression and reduced proopiomelanocortin (POMC) gene expression in sheep. Other studies have found a role for Kp to release growth hormone (GH), prolactin and luteinizing hormone (LH) from cattle, rat and monkey pituitary cells. Intravenous injection of Kp stimulated release LH, GH, prolactin and follicle stimulating hormone in some experiments in cattle and sheep, but other studies have failed to find an effect of peripheral injection of Kp on GH release. Recent studies indicate that Kp can stimulate GH release after intracerebroventricular injection in sheep at doses that do not release GH after intravenous injection. These studies suggest that Kp may have a role in regulation of both reproduction and metabolism in sheep. Since GH plays a role in luteal development, it is tempting to speculate that the ability of Kp to release GH and LH is related to normal control of reproduction.     

Modulation of growth hormone-releasing factor-induced release of growth hormone from bovine pituitary cells

Growth hormone (GH)-releasing factor (GRF) at concentrations of 10−¹² through 10−⁷M for 6 hr linearly increased GH release (b₁ = 10.4 ± .3) from bovine anterior pituitary cells in culture. Maximum release of GH (262% above controls) occurred at 10−⁷M GRF. In contrast, GH release-inhibiting factor (SRIF) at 10−¹² through 10−⁵M had no effect on basal concentrations of GH. In a second experiment, as the proportion of SRIF relative to GRF increased. SRIF suppression of GRF-induced GH release from anterior pituitary cells increased. In a third experiment, anterior pituitary cells cultured in media containing fetal calf serum (FCS) were treated with cortisol (0 or 10 ng/ml media) for 24 hr before exposure to 10−¹³ through 10−⁷M GRF. GRF linearly increased GH secretion (b₁ = 7.4 ± .3) and cortisol augmented this response (b₁ = 10.5 ± .6). However, when cells were cultured in media containing dextran-charcoal treated FCS, cortisol did not alter GRF-induced GH release. Our results demonstrate that GH response of bovine anterior pituitary cells to GRF was modulated negatively by SRIF. However, augmentation of GRF-induced GH release by cortisol was evident only when cells were cultured in media supplemented with untreated FCS.     

Growth hormone excess and the effect of octreotide in cats with diabetes mellitus

In this prospective study 16 cats with diabetes mellitus were examined for concurrent acromegaly by measuring plasma growth hormone (GH) and insulin-like growth factor-I concentrations, and magnetic resonance imaging (MRI) of the pituitary fossa. Additionally, the effects of octreotide administration on the plasma concentrations of glucose, GH, α-melanocyte-stimulating hormone (α-MSH), adrenocorticotrophic hormone (ACTH), and cortisol were measured.Five cats were diagnosed with hypersomatotropism. The pituitary was enlarged in these 5 cats and in 2 other cats. Six cats that required a maximum lente insulin dosage ≥1.5 IU/kg body weight per injection had pituitary enlargement and 5 of these cats had acromegaly. Plasma concentrations of GH, ACTH, and cortisol decreased significantly after single intravenous administration of the somatostatin analogue octreotide in the acromegalic cats. The effect on GH concentrations was more pronounced in some of the acromegalic cats than in others. In the non-acromegalic cats only ACTH concentrations decreased significantly. In both groups plasma glucose concentrations increased slightly but significantly, whereas α-MSH concentrations were not significantly affected.In conclusion, the incidence of hypersomatotropism with concomitant pituitary enlargement appears to be high among diabetic cats with severe insulin resistance. Some of these cats responded to octreotide administration with a pronounced decrease in the plasma GH concentration, which suggests that octreotide administration could be used as a pre-entry test for treatment with somatostatin analogues.     

Pharmacokinetics of doxycycline in sheep after intravenous and oral administration

The pharmacokinetics of doxycycline were investigated in sheep after oral (PO) and intravenous (IV) administration. The IV data were best described using a 2- (n = 5) or 3- (n = 6) compartmental open model. Mean pharmacokinetic parameters obtained using a 2-compartmental model included a volume of distribution at steady-state (V_ss) of 1.759 ± 0.3149 L/kg, a total clearance (Cl) of 3.045 ± 0.5264 mL/kg/min and an elimination half-life (t_1/2β) of 7.027 ± 1.128 h. Comparative values obtained from the 3-compartmental mean values were: V_ss of 1.801 ± 0.3429 L/kg, a Cl of 2.634 ± 0.6376 mL/kg/min and a t_1/2β of 12.11 ± 2.060 h. Mean residence time (MRT_0−∞) was 11.18 ± 3.152 h. After PO administration, the data were best described by a 2-compartment open model. The pharmacokinetic parameter mean values were: maximum plasma concentration (C_max), 2.130 ± 0.950 μg/mL; time to reach C_max (t_max), 3.595 ± 3.348 h, and absorption half-life (t_1/2k01), 36.28 ± 14.57 h. Non-compartmental parameter values were: C_max, 2.182 ± 0.9117 μg/mL; t_max, 3.432 ± 3.307 h; F, 35.77 ± 10.20%, and mean absorption time (MAT_0–∞), 25.55 ± 15.27 h. These results suggest that PO administration of doxycycline could be useful as an antimicrobial drug in sheep.     

Serum profile of metabolites and hormones in obese (Iberian) and lean (Landrace) growing gilts fed balanced or lysine deficient diets

Serum hormones and metabolites of lean and obese gilts were determined. Fifteen Iberian and fifteen Landrace gilts, of approximately 20 kg body weight, were fed isoenergetic (13.6 kJ ME/g DM, semisynthetic diets either with equilibrated amino acid profile at two crude protein (CP) levels (12% (0.81% lysine (Lys)) and 16% CP (1.08% Lys) as-fed basis) or lysine deficient (12% (0.30% Lys) or 16% CP (0.36% Lys) as-fed basis for Iberian and Landrace, respectively). Lysine deficient diets were offered only at the optimal protein level for maximum protein accretion for each breed. Each dietary treatment was assayed in 5 animals. Gilts were allocated in metabolic cages at 21 ± 1.5 °C with free access to water and fed four times daily at 90% ad libitum during 10 days. On day 11th blood samples were taken 5–5.5 h postprandial and serum obtained and frozen at − 20 °C. Growth hormone (GH), insulin like growth factor I (IGF-1), insulin, leptin, glucose, urea, creatinine, cholesterol and triglycerides were determined. Landrace gilts had higher serum glucose (P < 0.05) and creatinine (P < 0.001) than Iberian while no differences (P = 0.122–0.494) were found for the rest of the biochemical variables. Higher serum levels of insulin, IGF-1 and leptin (60, P < 0.05; 79, P < 0.05 and 189%, P < 0.001, respectively) and no differences in GH (P = 0.512) were encountered in Iberian gilts compared to Landrace. Dietary crude protein did not alter the serum hormonal profile (P = 0.110–0.454). Serum cholesterol (total, P < 0.01; HDL, P < 0.05; LDL, P < 0.05) decreased and triglycerides and urea increased (P < 0.05 and P < 0.001, respectively) as dietary crude protein increased. When lysine deficient diets were used, serum glucose decreased (P < 0.05) and urea increased (P < 0.001) compared to equilibrated diets. Serum insulin (P = 0.052), IGF-1 (P < 0.05) and leptin (P = 0.051) concentration decreased when lysine deficient diets were fed to the animals while GH remained unaffected (P = 0.214).These data suggest that Iberian and Landrace growing gilts have distinct hormone and metabolite serum profiles which are altered by a severe dietary lysine deficiency.     

Effects of intermittent suckling on the performance and digestive efficiency of Iberian piglets weaned at 35 days of age

During two consecutive replicates Iberian sows (n = 20) were subjected either to a conventional lactation (C) or intermittent suckling (IS). Piglets in the C treatment had free access to the dam. Piglets on IS treatment were separated from the sow during 6 h on days 29 and 30, 8 h on days 31 and 32, and 10 h on days 33 and 34. Litters on both treatments were weaned at 35 days of age and offered a starter diet until day 60 of age. The apparent digestibility (ApD) of nutrients and gross energy (GE) of the post-weaning diet was measured using Cr₂O₃ as external indigestible marker. Litters on IS tended to increase solid feed intake during the milk restriction (125 ± 12 vs. 70 ± 19 g piglet^− 1 day^− 1; P = 0.08). Feed intake was improved by IS during the second week post-weaning (676 ± 17 vs. 497 ± 12 g piglet^− 1 day^− 1, P < 0.01), but differences were totally offset after the 7th week of age. Differences in average growth rate of litters on C and IS treatments did not attain statistical significance during the period of restriction and in the first week post-weaning. Litters on IS showed increased growth rate during the second week post-weaning (422 ± 31 vs. 289 ± 33 g piglet^− 1 day^− 1; P = 0.01), but slower daily gains from the 3rd week post-weaning to 60 day of age than litters on C treatment (371 ± 14 vs. 432 ± 15 g piglet^− 1 day^− 1; P < 0.05). Nevertheless, neither at weaning nor at 60 days of age average body weight of piglets differed between treatments (7.71 ± 0.31 vs. 7.94 ± 0.30 kg for C and IS, at 35 days of age, 15.62 ± 0.65 vs. 16.20 ± 0.62 kg, at day 60). The apparent digestibility of nutrients of the starter diet offered after weaning remained unaffected by the treatment, except for a trend for higher ApD of GE for the piglets on IS treatment (P = 0.08). ApD for CP and GE was 78.1 ± 0.6 and 78.8 ± 0.3%, respectively. No significant differences in the proportions of total viscera and gastrointestinal tract to empty body weight (EBW) were observed between C and IS piglets at weaning and 60 d of age. In conclusion, the increase in feed intake observed prior and early after weaning as a consequence of intermittent suckling during the last week of 35 d lactation had no effect on nutrient digestibility measured at two weeks after weaning and failed on improving Iberian piglet performance.     

The effect of dietary protein content on calcium and phosphorus retention in the growing Iberian pig

The effects of dietary protein content (DPC) from excessive (192 g/kg DM) to marginally deficient (101 g/kg DM) upon whole-body retention of Ca and P was studied in 25 purebred Iberian pigs growing from 15 to 50 kg BW by means of a comparative slaughter experiment which included a digestibility trial. Ca and P retention related to intake remained unaffected at 0.228 ± 0.0072 and 0.184 ± 0.0052, reaching 3.64 ± 0.119 and 2.00 ± 0.057 g Ca and P per day respectively. Pigs fed on diets containing protein levels in excess of requirements had significantly higher concentrations of Ca and P (P < 0.05) in their bodies (14.41–14.99 and 7.88–8.08 g Ca and P/kg fat-free empty-body gain respectively) than those given adequate or marginally deficient amounts of dietary protein (11.80–12.72 and 6.61–7.01 g Ca and P/kg fat-free empty-body gain respectively). In a second experiment, made with 25 Iberian pigs of 21 kg initial weight, daily intakes of Ca and P to maintain zero retention were determined using five experimental diets in which the concentrations of Ca and P were varied by the addition of graded levels of Ca carbonate and inorganic phosphate to a basal diet balanced in protein-to-energy ratio (131 g CP; 13.8–14.4 MJ ME/kg DM). Growth rate and protein deposition were unaffected by the level of Ca and P in the diet and reached average values of 485 ± 15.4 and 103 ± 1.2 g/d. Increasing the dietary Ca and P levels increased the absolute amounts of Ca and P retained daily from 0.69 to 5.77 and 1.12 to 3.70 g respectively (P < 0.001). Highly significant (P < 0.001) curvilinear regressions were obtained when relating Ca and P absorption or retention (g/d) with Ca and P intake (g/d). From these equations, daily maintenance requirements of 105 and 72 mg/kg BW for Ca and P respectively were obtained. Average total net requirements of Ca and P for the Iberian pig at this stage of growth were estimated to be 5.25 and 3.10 g/d respectively, considerably lower than those reported for conventional and high-performance pig genotypes.     

Effect of supplements during the cold season on the reproductive system in prepubertal Tibetan sheep ewes

We examined the development of the reproductive system in prepubertal Tibetan sheep ewes when fed only oat hay (CON) or supplemented with either lick blocks (BS) or concentrate feed (CS) during the cold season. The average daily gain of the CS ewes was greater than that of the BS ewes (P  < 0.05), which was greater than that of the CON ewes. The same pattern was observed in the number of ovarian follicles (P  < 0.001), that is, CS > BS > CON. Serum concentrations of gonadotropin‐releasing hormone, follicle‐stimulating hormone, luteotrophic hormone, estradiol and progesterone in the CS and BS groups were higher than in the CON group (P  < 0.05). The messenger RNA (mRNA) expression of KiSS‐1, GPR54 (G protein‐coupled receptor 54), ERα (estradiol receptor α) in the hypothalamic anteroventral periventricular area of the CS group were higher than in both the BS and CON groups (P  < 0.05), while the BS group was higher than in the CON group (P  < 0.05). Similar differences among groups were observed for gonadotropin‐releasing hormone receptor mRNA expression in the pituitary, follicle‐stimulating hormone receptor and luteinizing hormone receptor mRNA expression in the ovary. These results indicated that the KiSS1/GPR54 system was more active with nutrition or trace mineral supplementation during the cold season. The system stimulated the hypothalamic–pituitary?gonadal axis and enhanced folliclar development in prepubertal Tibetan sheep ewes. We concluded that energy, protein and trace minerals supplements could improve the reproductive performance of Tibetan sheep on the Qinghai‐Tibetan plateau.     

Suppression of somatotroph function induced by growth hormone treatment in neonatal pigs

The effect of recombinant porcine growth hormone (pGH) treatment on pituitary function was evaluated in young pigs. Piglets received intraperitoneal recombinant pGH implants (0.5 mg/d sustained release) or vehicle implants beginning at 3 d of age. Ten piglets were sacrificed at 4 and 6 wk of age (five piglets/treatment group) for the collection of pituitary glands, blood, and liver tissue. Blood samples also were drawn at 3 and 12 d of age. Serum concentrations of GH, prolactin (PRL), thyroid-stimulating hormone (TSH), insulin-like growth factor-1 (IGF-1) and IGF-2 were evaluated. Levels of IGF-1 and IGF-2 mRNA were determined in liver samples. Treatment with GH increased circulating levels of GH and IGF-1 (P < 0.01), but not PRL, TSH, or IGF-2. Hepatic IGF-1, but not IGF-2, mRNA levels were increased by pGH (P < 0.001). Cultured pituitary cells from each animal were challenged with 0.1, 1, and 10 nM GH-releasing hormone (GHRH); 2 mM 8-Br-cAMP; or 100 nM phorbol myristate acetate. The release of GH from cultured pituitary cells was stimulated by all secretagogues (P < 0.001). The secretion of GH, but not PRL or TSH, in culture was inhibited by previous in vivo GH treatment (P < 0.001). Similarly, cellular GH, but not PRL or TSH, content was lower in the GH-implant group (P = 0.005). Cell cultures from 6-wk-old piglets secreted more GH, but not PRL or TSH, than cultures from 4-wk-old piglets (P < 0.05). Likewise, cellular GH, but not PRL or TSH, content was greatest in cultures from 6-wk-old animals (P = 0.002). Piglet growth was not affected by exogenous GH treatment (P = 0.67). These results demonstrate that exogenous pGH treatment selectively down-regulates somatotroph function in young pigs.     

Growth hormone stimulation of serum insulin concentration in cattle: Nutritional dependency and potential mechanisms

Previous studies on the effect of growth hormone (GH) on serum insulin concentration in cattle had generated seemingly conflicting results, and little was known about the mechanism by which GH affects serum insulin concentration in cattle, if it does. In this study, we determined whether the effect of GH on serum insulin concentration in cattle could be affected by the nutritional levels of the animal and whether GH increased serum insulin concentration in cattle by directly stimulating insulin release or insulin gene expression in the pancreatic islets. Administration of recombinant bovine GH increased serum insulin concentration in nonlactating, nonpregnant beef cows fed a daily concentrate meal in addition to ad libitum hay, but it had no effect in those cows fed hay only. Both GH treatments for 1 and 24 h increased insulin concentrations in cultures of pancreatic islets isolated from growing cattle. Growth hormone treatment for 24 h increased insulin mRNA expression in cultured bovine pancreatic islets. Growth hormone treatment for 16 h increased reporter gene expression directed by a ∼1,500-bp bovine insulin gene promoter in a rat insulin-producing β cell line. Taken together, these results suggest that exogenous GH can increase serum insulin concentration in cattle, but this effect depends on the nutritional levels of fed cattle, and that GH increases serum insulin concentration in cattle by stimulating both insulin release and insulin gene expression in the pancreatic islets.     

Responses to condensed tannins of flowering sulla (Hedysarum coronarium L.) grazed by dairy sheep: Part 1: Effects on feeding behaviour, intake, diet digestibility and performance

The concentration of condensed tannins (CT) in sulla (Hedysarum coronarium L.) is moderate and overall regarded as beneficial. However, the intake of this forage can reduce diet digestibility, particularly during flowering phase. An experiment was run to assess the effect of CT on feeding behaviour, intake, diet digestibility and performance of dairy sheep rotationally grazing sulla at flowering phase. Twenty-four late-lactating sheep were blocked in two homogeneous groups and submitted to the following treatments: i) twice daily drenching with 200 g/day of a 50% w/v water solution of an anti-tannic substance, polyethylene glycol, group PEG; ii) twice daily drenching with 200 g/day of water, group CON (Control group). All the sheep rotationally grazed as a flock two sulla plots from April to June (8 weeks in total). Sward height, herbage mass, botanical and chemical composition of the herbage were measured at the beginning and the end of each grazing period. The feeding behaviour (3 sheep per group) was continuously monitored for 24 h in 6 weeks using the IGER behaviour recorders. Herbage DM intake (DMI), dietary DM digestibility (DMD) and apparent CP digestibility (CPD) were estimated on 8 sheep per group by the n-alkane method. On average, PEG group had longer total grazing (503 ± 12 vs 460 ± 12 min, P < 0.05) and eating time (425 ± 13 vs 391 ± 13 min, P < 0.07) than CON group. Moreover PEG group showed shorter inter-meal intervals (41 ± 3 vs 52 ± 3, min, P < 0.05) and higher number of daily meals than CT-exposed group (24 ± 1 vs 19 ± 1 min, P < 0.01). The herbage DMI was not affected by the treatment whereas DMD (74.60 ± 3.48 vs 58.30 ± 3.01%), and CPD (60.14 ± 4.83 vs 38.21 ± 4.83%) were both increased by PEG administration (P < 0.05) confirming the negative effect of sulla CT on these variables. Milk yield tended to be higher in PEG than CON (1331 ± 45 vs 1205 ± 59 ml, P < 0.11). Milk protein content was similar between groups while milk fat content was higher in CON than PEG ewes (6.61 ± 0.15 vs 6.11 ± 0.15%, P < 0.05), being the reverse true for milk urea (46.04 ± 1.27 vs 53.04 ± 0.76%, P < 0.001). To conclude, this experiment shows that when sulla is grazed at flowering as monoculture, dietary CT can exert negative effects on DM and CP apparent digestibility, in this study partially counterbalanced by a better metabolic utilisation of the nutrients up-taken.     

Effects of photoperiod on the secretion of growth hormone in female goats

The aim of the present study was to clarify the effect of photoperiod on the secretion of growth hormone (GH) in goats. Adult female goats were kept at 20°C with an 8‐h or 16‐h photoperiod, and secretory patterns of GH for 4 h (12.00 to 16.00 hours) were compared. In addition, the goats were kept under a 16‐h photoperiod and orally administered saline (controls) or melatonin, and the effects of melatonin on the secretion of GH were examined. GH was secreted in a pulsatile manner. There were no significant differences in pulse frequency between the 8‐ and 16‐h photoperiods; however, GH pulse amplitude tended to be greater in the group with the 16‐h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16‐h photoperiod (P < 0.05). The GH‐releasing response to GH‐releasing hormone (GHRH) was also significantly greater for the 16‐h photoperiod (P < 0.05). There were no significant differences in GH pulse frequency between the saline‐ and melatonin‐treated groups. However, GH pulse amplitude and mean GH concentrations were significantly greater in the saline‐treated group (P < 0.05). The present results show that a long photoperiod enhances the secretion of GH, and melatonin modifies GH secretion in female goats.     

The supplementary value of different parts of enset (Ensete ventricosum) to sheep fed wheat straw and Desmodium intortum hay

A study which included growth and digestibility experiments was conducted to evaluate the feeding value of a) enset pseudostem, b) enset corm or c) enset mixture (containing equal amounts of pseudostem, corm and enset leaf on a DM basis) as a supplement to a basal diet of wheat straw fed ad libitum and restricted amounts of Desmodium intortum (Desmodium) hay to sheep. During the 71-day growth experiment, 18 one-year-old male sheep of indigenous breed with mean body weight (BW) of 20.2 (± 0.43) kg were randomly assigned to the three treatments. In the digestibility experiment, three male sheep with mean BW of 19.5 (± 1.06) kg were assigned to each treatment. Sheep supplemented with enset mixture consumed more (P < 0.001) wheat straw DM (335 g/day) than those supplemented with pseudostem (295 g/day). No differences were found in total dry matter (DM) and organic matter (OM) intake between diets supplemented with pseudostem, corm and enset mixture. Total nitrogen (N) intake (g/day) was higher (P = 0.0073) in sheep fed the diet with enset mixture (12.2) followed by corm (11.3) and pseudostem (10.7). The apparent digestibility of DM was higher (P < 0.001) in pseudostem (0.53) followed by corm (0.46) and enset mixture (0.41) supplemented sheep. Organic matter, neutral detergent fiber and N digestibility were similar among treatments. The amount of N lost in urine and faeces and the N-retention was similar among treatments. There were no differences in gain/day in sheep fed diets with pseudostem (29.3 g), corm (27.0 g) and enset mixture (36.5 g). It is concluded that supplementation of a wheat straw/Desmodium diet with enset fractions could be used equally at least to maintain body weight during the dry season.     

Ghrelin-stimulation test in the diagnosis of canine pituitary dwarfism

This study investigated whether ghrelin, a potent releaser of growth hormone (GH) secretion, is a valuable tool in the diagnosis of canine pituitary dwarfism. The effect of intravenous administration of ghrelin on the release of GH and other adenohypophyseal hormones was investigated in German shepherd dogs with congenital combined pituitary hormone deficiency and in healthy Beagles. Analysis of the maximal increment (i.e. difference between pre- and maximal post-ghrelin plasma hormone concentration) indicated that the GH response was significantly lower in the dwarf dogs compared with the healthy dogs. In none of the pituitary dwarfs, the ghrelin-induced plasma GH concentration exceeded 5 microg/l at any time. However, this was also true for 3 healthy dogs. In all dogs, ghrelin administration did not affect the plasma concentrations of ACTH, cortisol, TSH, LH and PRL . Thus, while a ghrelin-induced plasma GH concentration above 5 microg/l excludes GH deficiency, false-negative results may occur.     

Comparative pharmacokinetics of an injectable cephalexin suspension in beef cattle

This study describes and compares the pharmacokinetics of a single 7.5 mg/kg dose of cephalexin monohydrate oil-based 20% suspension after its administrations to six cows by the intramuscular (i.m.) and subcutaneous (s.c.) routes, and to five calves by the i.m. route. Significantly (P < 0.05) higher peak plasma concentrations (5.6 ± 0.79 μg/ml versus 3.93 ± 1.24 μg/ml) and lower half-life (1.81 ± 0.56 h versus 4.21 ± 0.82 h) and mean residence time (4.12 ± 1.07 h versus 6.63 ± 0.85 h) were obtained after i.m. administration when compared to the s.c. administration to cows. No differences were found between pharmacokinetic parameters calculated for cows and calves. Cephalexin plasma concentrations remained above 0.5–0.75 μg/ml for 11–14 h and 8–9 h after the s.c. and i.m. administrations, respectively. Thus, route of administration may be an important issue to be considered when calculating dosage schedules for successful treatments and safe withdrawal times for veterinary medicines.