Insulin and growth hormone responses to glucose infusion in mature and first-lactation dairy cows

Five mature Holstein cows and 6 first-lactation Holstein cows were administered 100 mg of glucose/kg of body weight, IV, over a 20-minute period on postpartum day 30. A series (preinfusion, glucose infusion, and postinfusion) of blood samples was collected at -15, -10, -5, 5, 10, 15, 20, 30, 45, 60, 75, 90, 105, and 120 minutes from the start of the infusion. Serum was obtained and was assayed for glucose, immunoreactive insulin (IRI), growth hormone (GH), and free fatty acid concentrations. Baseline glucose and free fatty acid concentrations were similar in cattle of both groups throughout the sample collection period. Both groups of cattle disposed of the infused glucose in a similar manner. The first-lactation cows secreted significantly (P less than 0.0001) more IRI to utilize the glucose load than did the mature cows, 71 +/- 13 microU/ml vs 38 +/- 7 microU/ml, respectively (mean +/- SEM). Preinfusion and glucose infusion GH concentrations were similar in cattle of both groups. In the postinfusion period, GH values were significantly (P less than 0.0002) higher in the first-lactation cows (8.7 +/- 1.8 ng/ml) than in the mature cows (5.8 +/- 1.6 ng/ml). Compared with that in the mature cows, the higher IRI concentration required by the first-lactation cows to utilize approximately the same glucose load suggested that first-lactation cows were insulin resistant. The increased insulin response to increased glucose concentration may be one reason first-lactation cows produce less milk than do mature cows. Other factors, such as variation in the ability of the mammary gland to synthesize milk cannot be excluded.     

Prevalence and risk factors for medical events following exercise at Australian Greyhound race meetings

Aim

A prospective, observational study to determine the prevalence of post‐exercise conditions at Australian Greyhound race meetings and to assess association with race performance and other environmental, race‐ and dog‐related factors was undertaken.

Methods

A total of 4020 starters were observed (2813 Greyhounds, 1009 trainers, 536 races, 52 race meets, 48 race dates and 11 race tracks) following a race. The presence of diaphragmatic flutter (DF), ataxia, seizure, collapse or sudden death was recorded. Risk factors were screened by univariable logistic regression prior to multivariable backward stepwise model building.

Results

In this study, 962 starters (n = 768 dogs) had DF (23.9%), 16 starters were ataxic (0.4%) and there were no observed cases of collapse, seizure or sudden death. Race track location, increasing race distance, race grade based on increasing 1st place prize value, lower (earlier) race number at the meeting, age, a previous observation of DF at the last start, females, colour (white) and better finishing position were all associated with an increased risk of a Greyhound being observed with DF. However, when logistic regression assessing the random effect of dog was performed, the presence of previous DF was not significant. In this cohort, DF was common following strenuous exercise in Greyhounds and on its own does not appear to result in reduced performance or distress to the animal.

Conclusion

The incidence of ataxia was low and collapse, seizure and sudden death were not observed. However, even though uncommon, ataxia has welfare concerns for racing Greyhounds that warrants further investigation.     

Effect of desmopressin on plasma factor VIII and von Willebrand factor concentrations in Greyhounds

Objective To determine the effect of 1-Deamino-8-D-argi-nine vasopressin on plasma concentrations of von Willebrand factor and factor VIII in Greyhound blood donors, and to compare the response of 1-Deamino-8-D-arginine vaso-pressin injection on plasma concentrations of von Willebrand factor between groups with different resting plasma concentrations of von Willebrand factor.
Animals Fifteen Greyhound blood donors were used. Dogs were grouped into three categories depending on their von Willebrand factor concentrations.
Procedure Desmopressin was administered subcuta-neously at 1 mg/kg to all dogs. Plasma von Willebrand factor and factor VIII concentrations were measured before and 10, 20, 30, 45, 60, 90 and 120 min after desmopressin injection.
Results The von Willebrand factor and factor VIII concentrations in all dogs increased significantly and remained higher than base-line throughout the 2 h period.
Conclusion Desmopressin is useful in increasing von Willebrand factor concentrations in Greyhound blood donors, including those with low resting concentrations.     

von Willebrand's disease in Scottish Terriers in Australia

SUMMARY Over a 5-year period (1988–92), von Willebrand factor antigen (vWf:Ag) assays were performed on plasma samples from 207 Scottish Terriers. Based on these tests, 47 dogs (23%) had vWf:Ag concentrations < 50 canine units (CU)/dL and were classified as heterozygous carriers of the von Willebrand's disease (vWD) gene, while 9 (4%) had concentrations below the sensitivity of the assays and were classified as homozygous. There was thus an overall prevalence of 27% for the vWD gene in the Scottish Terriers tested. The homozygous dogs (median age 0.6 years at diagnosis) consisted of 7 males and 2 females. Eight of these had haemorrhage attributable to the disease, mostly spontaneous and from the oral mucosa. Other signs included haemorrhage induced by trauma or surgery, easy bruising and epistaxis. Many haemorrhagic episodes were severe enough to warrant therapeutic intervention and there was a single fatality. Pedigree analysis, possible in 7 of the dogs, revealed that each was the progeny of a mating between dogs with vWf:Ag concentrations < 50 CU/dL, which supported an autosomal recessive mode of inheritance. A single heterozygous carrier suffered haemorrhage after surgery that, in contrast to the homozygotes, was mild and did not require therapy. The data indicate that vWD is a significant problem in Scottish Terriers in Australia. Accordingly, we recommend that steps be taken to reduce the prevalence of the disease and thereby the number of clinically affected dogs, such as the establishment of a national testing scheme to determine the vWD status of all breeding dogs.     

Effect of fasting and dexamethasone on binding characteristics of canine erythrocyte insulin receptors

Insulin binding characteristics of canine erythrocyte insulin receptors were studied before and after a 72-hour fast, and one and three days following glucocorticoid (dexamethasone) administration. The 72-hour fast tended to increase maximum insulin binding, but no significant differences were found. The administration of dexamethasone resulted in an increased maximum binding of insulin to its receptors which, at day 1, was due to an increase in receptor concentration, and at day 3, to an increased insulin binding affinity of the receptor. These data suggest that the erythrocyte insulin receptor may be useful in clinical and experimental studies in the dog.     

Skin concentrations of thromboxane synthetase inhibitor after topical application with bioelastic membrane

Elevated thromboxane levels are associated with a number of disease states, including dermal pressure ulcers. When dazmegrel was orally administered to greyhound dogs wearing leg casts, it resulted in a sparring effect on the skin areas of potential pressure ulcer development. The objective of this research was to determine if bioelastic matrices could provide controlled release of thromboxane A2 synthetase inhibitor (dazmegrel) at tissue concentrations sufficient for inhibition of thromboxane synthesis. The animal used for these studies was the greyhound, which has thin skin, angular conformation, limited body fat and is predisposed to pressure ulcers similar to those occurring in humans. In vivo skin penetration studies showed that epidermal exposure to bioelastic thromboxane synthetase inhibitor (TSI) matrix resulted in local tissue concentrations of TSI sufficient for thromboxane synthetase inhibition. There were no significant differences between dazmegrel in the skin layers (epidermis, dermis and subcutaneous layers) on 1, 7 and 14-day exposures.     

Increased expression of MAIL, a cytokine-associated nuclear protein, in the prodromal stage of black walnut-induced laminitis

REASONS FOR PERFORMING STUDY: The mediators and signalling cascades important in the initiation of laminitis remain unclear. We therefore wanted to explore the genes and overall signalling mechanisms that play an important role in the developmental stage of laminitis. OBJECTIVE: To use a broad genomic screening technique to identify novel genes that are differentially regulated in the equine lamellae during the developmental period of laminitis. METHODS: Differential mRNA display (DRD) was performed to discover regulated genes, and real-time quantitative polymerase chain reaction (RT-qPCR) was then used to evaluate lamellar mRNA levels of a regulated gene (MAIL) and mediators related to that gene (IL-1beta and IL-6) in control horses (n = 5) and horses administered black walnut extract (BWE; n = 5). RESULTS: Using DRD, MAIL was identified as a regulated gene. RT-qPCR indicated a 4-fold increase in expression of the MAIL mRNA in BWE lamellae compared to controls. A 30-fold increase in IL-1beta, and a 160-fold difference in IL-6 mRNA expression was present in BWE lamellae. Differences in MAIL, IL-1beta and IL-6 mRNA expression were statistically significant between groups (P < 0.05). CONCLUSIONS AND POTENTIAL RELEVANCE: The data strongly support a role for inflammatory cytokines in the developmental stages of laminitis, possibly inducing the vascular and metabolic alterations reported to occur in the affected digit. These results potentially support the use of anti-inflammatory drugs in horses at risk of laminitis, and warrant further investigation of the link between systemic disease processes associated with laminitis and the reported digital inflammation.     

Seasonal changes in plasma adrenocorticotropic hormone and α-melanocyte-stimulating hormone in response to thyrotropin-releasing hormone in normal, aged horses

Background: Results of diagnostic tests for equine pituitary pars intermedia dysfunction (PPID), including endogenous ACTH concentration and the overnight dexamethasone suppression test (DST), are affected by season. New and potentially more sensitive diagnostic tests for equine PPID, such as thyrotropin‐releasing hormone (TRH)‐stimulated ACTH response, have been developed, but have had limited evaluation of seasonality. Objective: Our purpose was to evaluate seasonal changes in plasma ACTH and alpha‐melanocyte‐stimulating hormone (α‐MSH) responses to TRH administration. Animals: Nine, healthy, aged horses with normal DST results. Methods: Synthetic TRH (1 mg) was administered IV. Plasma ACTH and α‐MSH concentrations were measured at 0, 5, 10, 15, 20, 25, 30, 45, 60, and 180 minutes. Testing was performed in February, July, August, September, October, and November. Mean TRH‐stimulated ACTH and α‐MSH concentrations were compared across months and time by repeated measures analysis of variance. Significance was set at the P < .05 level. Results: Concentrations of ACTH and α‐MSH significantly increased after TRH administration. Endogenous and TRH‐stimulated ACTH and α‐MSH concentrations were significantly different across months with higher concentrations in the summer and fall compared with February. Conclusions and Clinical Importance: Plasma ACTH and α‐MSH responses to TRH administration experience seasonal variation, with TRH‐stimulated ACTH and α‐MSH concentrations increasing from summer through fall. These results support previous evidence of a seasonal influence on the equine pituitary‐adrenal axis. More research is warranted with a larger number of horses to determine if seasonal reference ranges for TRH stimulation testing need to be defined.