Effect of altrenogest‐treatment of mares in late gestation on adrenocortical function,blood count and plasma electrolytes in their foals

Reasons for performing study: Mares with compromised pregnancies are often treated with altrenogest to prevent abortion. However, there is only limited information about effects on the foal when altrenogest treatment is continued during final maturation of the fetus. Objectives: To determine effects of altrenogest treatment during late gestation in mares on maturity, haematology changes, adrenocortical function and serum electrolytes in their newborn foals. Methods: Six mares were treated with altrenogest (0.088 mg/kg bwt) once daily from Day 280 of pregnancy until foaling and 7 mares served as controls. Results: Foals born to altrenogest‐treated mares had a significantly lower neutrophil/lymphocyte ratio on the first day after birth than control foals (P<0.05). Basal plasma cortisol concentrations immediately after birth were higher in foals of altrenogest‐treated mares than in control foals (P<0.05). Cortisol release in response to exogenous adrenocorticotropic hormone (ACTH) ‐ except for higher values 15 min after ACTH injection in foals of altrenogest‐treated mares on Day 1 ‐ revealed no differences in adrenocortical function between the groups of foals. Plasma potassium concentration in foals from altrenogest‐treated mares compared to control foals was significantly lower immediately after birth (P<0.05) and plasma ionised calcium concentration was significantly lower 3 h after birth (P = 0.01). Conclusions and potential relevance: Altrenogest treatment of pregnant mares prolonged labour had no major effects on adrenocortical function in foals. A reduced neutrophil/ lymphocyte ratio in these foals may suggest either immunomodulatory effects of altrenogest or dysmaturity of the foals.     

Colic and diaphragmatic hernias in neonatal foals

Colic in neonatal foals is common and unusual causes of colic are not rare. The case reported in this issue by Tapio et al. (2012 ) is a good example of an unusual cause of neonatal colic which presents both a diagnostic challenge and unusual consequences. Gastrointestinal disease, especially colic, ranks as one of the most common reasons why foals require veterinary attention during their first week of life, beyond the initial post natal examination. Foals with colic present a special diagnostic challenge, especially to the practitioner who might not have extensive experience in neonatal medicine. With the often rapid progression of neonatal diseases it is important to make a rapid and accurate assessment.     

The effect of omeprazole paste on intragastric pH in clinically ill neonatal foals

REASON FOR PERFORMING STUDY: Administration of omeprazole paste per os to healthy neonatal foals has been shown to effectively increase intragastric pH, but has not been evaluated in sick neonatal foals. OBJECTIVES: To determine the effect of orally administered omeprazole paste on intragastric pH in clinically ill neonatal foals requiring nasogastric intubation. METHODS: Intragastric pH was measured continuously for 24 h using an indwelling electrode and continuous data recording system in hospitalised neonatal foals age < or =2 days. Intragastric pH was measured for 12 h prior to (pretreatment period) and 12 h following (post treatment period) treatment with omeprazole paste (4 mg/kg bwt per os). All foals displayed periods of acidity (pH <4) prior to treatment. Statistical analysis compared pre- and post treatment mean and median intragastric pH, and percentage of time below pH 4. RESULTS: Eight foals were evaluated age 1-3 days, a gestational age of at least 320 days or reported to be full term. The mean (3.19 +/- 1.50 vs. 6.20 +/- 0.93) and median (4.6 +/- 1.7 vs. 6.86 +/- 0.89) pH were significantly higher and the percentage of time below pH 4 (32.25 vs. 1.1%) was significantly lower in the post treatment compared to the pretreatment period. CONCLUSION: Omeprazole paste effectively increases intragastric pH in clinically ill neonatal foals after one dose at 4 mg/kg bwt orally.     

Effect of dietary restriction on body condition,composition and welfare of overweight and obese pony mares

Reasons for performing study: Increased prevalence of obesity among UK horses and ponies demands evidence‐based advice to promote weight loss. Hypothesis: Restriction of dry matter intake (DMI) to 1% of body mass (BM, 6% of predicted maintenance digestible energy [DE] requirements) would promote weight loss without compromise to health. Methods: Five mature (mean ± s.e. 10 ± 2 years), overweight/obese pony mares (BM, 257 ± 20 kg: body condition score [BCS] 6.8/9 ± 0.5) were studied over 12 weeks. Animals were individually housed. Daily provision of a chaff‐based, complete diet (measured DE, 8.5 MJ/kg DM) was restricted to 1% of actual BM as DMI daily. BCS, girth measurements and ultrasound‐derived measures of subcutaneous fat depth overlying the gluteal region and 12th intercostal space (rib‐eye) were recorded weekly. Body fat content was estimated at the beginning and end of the study by deuterium oxide dilution methods. Clinical biochemistry was monitored weekly. Behaviour was observed (24 h, 3/5 ponies) on 3 occasions. Results: BM decreased by 4.3 ± 1.1% during the first week and thereafter by 0.7 ± 0.1% of BM at end of Week 1 each week. BCS remained constant. Heart and belly girths, rump width and subcutaneous fat depth at rib‐eye decreased significantly with time and BM. Fat comprised 45 ± 19% of BM loss. Fatter animals lost relatively more fat. With decreased feeding activity, time spent in ‘play’ and rest increased by 36 ± 11% and 438 ± 95%, respectively. Conclusions: This plane of nutrition resulted in an overall rate of weight loss of 1% of outset BM weekly. BCS was not a useful index of early weight loss but heart and belly girths and subcutaneous rib‐eye fat were identified as alternative markers. Potential relevance: This study provides an evidence‐base for the management of weight loss in obese animals, especially those for which exercise may be contra‐indicated.     

Assessment of body fat in the pony: part I. Relationships between the anatomical distribution of adipose tissue, body composition and body condition

Reasons for performing study: Evaluation of equine body fat content is important for nutritional and clinical purposes. However, our understanding of total body fat and its regional distribution in the body is sparse. Currently, body fat evaluation relies on the subjective assessment of body condition score (BCS), which has never been validated against ‘gold standard’ chemical analysis or dissection measurements in ponies. Objectives: To define the relationships between subjective (BCS), objective (morphometric) indices of body fat and ‘gold standard’ measurements of actual body composition. Hypotheses: BCS and morphometry offer valid, noninvasive methods for determination of body fat in equids. Methods: Seven mature (mean ± s.e. 13 ± 3 years, 212 ± 14 kg, BCS 1.25–7/9), Welsh Mountain pony mares, destined for euthanasia (for nonresearch purposes), were used. For all ponies, body mass (BM), BCS and various morphometric measurements were recorded. Following euthanasia, all ponies were systematically dissected. Discrete white adipose tissue (WAT) depots were independently described. Gross, body chemical composition was determined by proximate analyses. Results: Total somatic soft tissues increased linearly (r²= 1.00), whereas body WAT content (1–26% live BM) increased exponentially (r²= 0.96), with BCS. WAT was equally distributed between internal and external sites in all animals irrespective of BCS. Nuchal fat was a poor predictor of total WAT (r²= 0.66). Periorbital WAT did not alter with BCS (r²= 0.01). Heart girth:withers height and ultrasonic retroperitoneal fat depth were closely associated with total, chemically‐extracted lipid which comprised 1–29% live BM (r²= 0.91 and 0.88, respectively). Conclusions and potential relevance: The exponential relationship between BCS and total body WAT/lipid suggests that BCS is unlikely to be a sensitive index of body fat for animals in moderate‐obese states. Morphometric measurements (body girths and retroperitonel fat depth) may be useful to augment subjective BCS systems.     

Air sampling in the breathing zone of neonatal foals for prediction of subclinical Rhodococcus equi infection

Reasons for performing the study: Disease caused by Rhodococcus equi is a significant burden to the horse breeding industry worldwide. Early detection of rhodococcal pneumonia, albeit important to minimise treatment costs, is difficult because of the insidious nature of the disease and the lack of definitive diagnostic tests. Objectives: To investigate air sampling from the breathing zone of neonatal foals as a predictor of subsequent rhodococcal pneumonia. Methods: Air samples were collected from the breathing zone of 53 neonatal foals (age ≤10 days) and again at the time of routine ultrasonographic screening for R. equi pneumonia (age 1–2 months). Results: Pneumonia was diagnosed ultrasonographically in 23% of foals. Virulent R. equi was detected in air from the breathing zone of 19% of neonatal foals and 45% of foals at age 1–2 months. There was no association between virulent R. equi in the breathing zone of foals and the subsequent ultrasonographic diagnosis of rhodococcal pneumonia. The median concentration of virulent R. equi in the breathing zone of both neonates (0 [range 0–4] colony‐forming units [cfu]/250 l) and older foals (0 [range 0–3] cfu/250 l) was not significantly different from that in background air samples (0 [range 0–6] cfu/250 l). There was no difference in the concentration of virulent R. equi in the breathing zone of older foals that were diagnosed with rhodococcal pneumonia or clinically normal foals. Conclusion: Detection of virulent R. equi in air from the breathing zone was not a positive predictor of rhodococcal pneumonia in foals up to age ≤2 months. Potential relevance: Selective culture of air samples from the breathing zone of young foals is not better at diagnosing rhodococcal pneumonia than early ultrasonographic screening. However, culture of air samples from the breathing zone of older foals remains a useful herd‐based epidemiological tool.     

Agreement between point-of-care glucometry, blood gas and laboratory-based measurement of glucose in an equine neonatal intensive care unit

Objective: To test the agreement between 3 common methods of glucose measurement in a population of critically ill foals presenting to a neonatal intensive care unit. Design: Prospective clinical study. Setting: University large animal hospital neonatal intensive care unit. Animals: Sequentially admitted critically ill neonatal foals <30 days of age. Interventions: Venous blood obtained from a jugular vein was used for determination of blood glucose concentration using point‐of‐care (POC) glucometry (GLU), a laboratory chemistry technique (CHEM) and a multi‐electrode blood gas analyzer (BG). Paired data were compared using Lin's concordance correlation, Pearson's correlation and robust regression. Bias and limits of agreement were investigated using the technique of Bland and Altman. Measurements and main results: Concordance was significant for all comparisons and was strongest for CHEM‐BG while weakest for GLU‐BG. Pearson's correlation was excellent for all comparisons: CHEM‐BG, 0.98; GLU‐BG, 0.94; GLU‐CHEM, 0.96. All comparisons had significant robust regression coefficients: CHEM‐BG, 0.99; GLU‐BG, 0.80; GLU‐CHEM, 0.79. For Bland–Altman analysis, mean differences (mean±SD, 95% limits of agreement) were: GLU‐BG (?33±18 mg/dL, ?68.6 to 1.5); GLU‐CHEM (?20±16 mg/dL, ?51.0 to 10.9); CHEM‐BG (13±11 mg/dL, ?8.7 to 34.7). Conclusions: This study demonstrates that glucometry has less than ideal agreement with a laboratory standard and another POC test, blood gas analysis. These differences may be clinically important and decisions regarding management of glucose concentrations in critically ill foals should be made with these differences in mind.     

Pharmacokinetics and physiologic/behavioral effects of buprenorphine administered sublingually and intravenously to neonatal foals

Buprenorphine is absorbed following sublingual administration, which would be a low‐stress delivery route in foals. However, the pharmacokinetics/pharmacodynamics are not described in foals. Six healthy foals <21 days of age participated in a blinded, randomized, 3‐period, 5‐sequence, 3‐treatment crossover prospective study. Foals received 0.01–0.02 mg/kg buprenorphine administered SL or IV with an equivalent volume of saline administered by the opposite route. Blood was collected from the cephalic vein for pharmacokinetic analysis. Physiologic parameters (HR, RR, body temperature, GI sounds), locomotion (pedometer), and behavioral data (activity level, nursing time, response to humans) were recorded. Plasma concentration of buprenorphine exceeded a presumed analgesic level (0.6 ng/ml) in five foals in the IV group and one in the SL group but only for a very brief time. Pharmacokinetic analysis following IV administration demonstrated a short elimination half‐life (t_1/2β 1.95 ± 0.7 hr), large volume of distribution (6.46 ± 1.54 L/kg), and a high total clearance (55.83 ± 23.75 ml/kg/min), which differs from adult horses. Following SL administration, maximum concentrations reached were 0.61 ± 0.11 ng/ml and bioavailability was 25.1% ± 10.9%. In both groups, there were minor statistical differences in HR, RR, body temperature, locomotion, and time spent nursing. However, these differences were clinically insignificant in this single dose study, and excitement, sedation, or colic did not occur.     

Epiphyseal cartilage canal blood supply to the distal femur of foals

REASONS FOR PERFORMING STUDY: The developmental pattern of the cartilage canal blood supply to epiphyseal growth cartilage has been linked to osteochondrosis (OC) in the tarsus of foals. This pattern has not yet been described in the distal femur, another site frequently affected by OC. OBJECTIVE: To describe the developmental pattern of the blood supply to the distal femoral epiphyseal growth cartilage in 8 Standardbred foals age 0-7 weeks. METHODS: One foal was sacrificed weekly from birth to age 7 weeks (n=8) to undergo a barium perfusion procedure to demonstrate vessels within cartilage canals of one hindlimb. The distal end of the femur was cleared in methyl salicylate and perfused vessels were studied in the intact bones. Each distal femur was then sawed into 5 mm thick slabs in the transverse plane, and the slabs decalcified and radiographed. Finally, the lateral trochlear ridge was separated from each slab and examined histologically. RESULTS: The cartilage canal blood supply regressed with increasing age, but several regions remained vascularised in the oldest foal at age 7 weeks. Vessels arose from perichondrial and subchondral arterial sources, and coursed perpendicular or parallel to the ossification front. The midsection of parallel vessels became incorporated into the ossification front during growth. Anastomoses formed and vessels within the distal portion of canals with an original perichondrial source shifted to use subchondral vessels as their arterial source. Both parallel and perpendicular vessels therefore traversed the ossification front to enter cartilage canals. No histological lesions were observed in sections from any of the foals. CONCLUSION: The same anatomical feature (traversing the ossification front to enter cartilage canals) reported to render vessels vulnerable to failure in the tarsus was also present in the distal femur of foals. POTENTIAL RELEVANCE: OC may occur by the same pathogenetic mechanism in the distal femur as in the tarsus of foals.     

Effects of dietary fish oil and alpha-tocopherol supplementation on selected blood parameters and fatty acid profiles in mares and their foals

The effects of fish oil (40 ml/day) supplementation, with or without synthetic all-rac-alpha-tocopherol-acetate (2,500 IU/day), during the last 65 days before expected parturition were investigated in 15 adult mares (553 ± 24 kg BW) and their foals. Mares were assigned to one of three diets: control (n = 5), control plus fish oil and alpha-tocopherol (n = 4; FO + AT) or control with just fish oil (n = 6; FO). Blood samples were obtained from the mares before a 15-day dietary adaptation period (T1) and from mares and foals the first (T2) and fifth (T3) days post-partum. Colostrum was collected at T2 and milk at T3. Routine haematological, biochemical and alpha-tocopherol analyses were undertaken on all blood samples. Fatty acid concentrations were determined in the foal serum and alpha-tocopherol concentrations measured in the milk and colostrum. Diet had no effect on haematology or biochemistry in the mares. Alpha-tocopherol concentrations were significantly higher at T2 & T3 in the FO + AT mares. Foal WBCs were higher in FO (11.33 ± 2.59 × 10⁹/l), comparing to FO + AT and control groups (9.18 ± 1.24 × 10⁹/l and 7.26 ± 1.03 × 10⁹/l, respectively), at T3 (p < .05). There was no significant effect of the fish oil supplementation on the foal's serum fatty acid profile. In the FO + AT group, both colostrum and milk alpha-tocopherol concentrations (2.56 ± 0.36 and 1.36 ± 0.22 µg/ml, respectively) were higher compared than those of the FO group (1.33 ± 0.39 and 0.72 ± 0.31 µg/ml, respectively; p < .05). Additional 2,500 IU/day of synthetic alpha-tocopherol in the last 65 days of pregnancy increased alpha-tocopherol concentrations in colostrum and milk and the foal's serum. 40 ml/day fish oil, however, did not significantly increase serum eicosapentaenoic acid and docosahexaenoic acid concentrations in the foals.