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Among chicken strains, broilers are prone to pulmonary hypertension, whereas Leghorns are not. Relaxations to endothelium-dependent (ACh, A23187) and endothelium-independent [sodium nitroprusside (SNP), papaverine (PPV)] vasodilators were compared in preconstricted pulmonary artery (PA) rings from these chicken strains. ACh (10−7, 10−6, and 10−5 M)- and A23187 (10−6 and 10−5.5 M)-induced relaxations were smaller ( P < 0.05) in broilers than Leghorns. N G-nitro-l-arginine methyl ester (10−3.5 M) caused similar reductions in ACh-induced relaxations in both strains.l-Arginine (10−4 M) enhanced ACh-induced relaxations more in broilers than Leghorns. Relaxations to 10−10–10−6M SNP did not differ between strains, but were greater ( P < 0.05) in broilers than Leghorns at higher concentrations (10−5 and 10−4 M). PPV (10−4 M)- and SNP (10−4 M)-induced maximal relaxations were greater in broilers than in Leghorns (176.2 ± 14.7 vs. 120.9 ± 14.7% and 201.3 ± 7.8 vs. 171.2 ± 10.7%, respectively, P < 0.05). Broiler PA rings appear to have increased intrinsic tone and reduced endothelium-derived nitric oxide activity, both of which may contribute to the susceptibility of broiler chickens to pulmonary hypertension.

An experiment was conducted to determine the change with time in the blood ionized calcium concentration of hens exposed to an acute heat stress. Five hens were surgically fitted with carotid artery cannulae and placed in cages inside a temperature-controlled chamber. Blood samples were drawn before (23 C), during (35 C), and after (23 C), a 3-hr heat-stress exposure. Whole blood ionized calcium, blood gas, plasma pyruvate, and lactate were determined. Respiratory alkalosis developed 1 hr after the start of heat exposure (35 C). Approximately 1 hr later, there was a concomitant decline in blood pH as plasma lactate and pyruvate concentration increased (P less than .05). In addition, the blood ionized calcium level was reduced (P less than .05) by 19% and was negatively correlated (P less than .05) with plasma pyruvate (-.77) and lactate (-.81). These results suggest that changes in acid-base balance during heat stress reduce the blood ionized calcium level, which may in turn limit the availability of calcium for egg shell formation.

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This study was conducted to validate echocardiography in chickens, and to compare cardiac structure and function between broiler and Leghorn chickens. Diameters of the right and left ventricles, and thicknesses of the left ventricular free wall and the interventricular septum were measured echocardiographically in 5- and 7-wk-old chickens from both lines. Images were obtained from minimally restrained, standing birds using a 7.5 MHz probe placed in a parasternal position. End-systolic and end-diastolic echocardiographic measurements were compared with post-mortem measurements of the same variables. Comparisons resulted in correlation coefficients greater than 0.70 between in vivo (echocardiographic) and post-mortem measurements of the same variables, with post-mortem measurements more closely resembling end-diastolic echocardiographic measurements. After being normalized to body weight, post-mortem myocardial thicknesses, aortic and left ventricular diameters, heart weight at 5 wk of age, and left ventricular weight at 7 wk of age were smaller in broiler than in Leghorn chickens. Echocardiographic parameters, including ventricular wall thicknesses, ventricular diameters, and left ventricular fractional shortening, were also smaller in the broiler chicken. Right ventricular fractional shortening did not differ between the chicken lines. These results indicate that echocardiography is a useful noninvasive technique for in vivo evaluation of cardiac structure and function in the chicken, and that broiler chickens have a relatively smaller structural and functional heart than Leghorn chickens.

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SummaryEight Thoroughbred horses were used in a repeated measures, crossover experiment in which horses were fed a fat supplemented and control diet.. On Days 0,7,14,21 and 28, horses performed a standardised exercise test (SET) consisting of three 400 m sprints. Digestion trials were performed over 3 days prior to each SET and muscle biopsies were taken pre-and post SET. Feeding fat had no negative effect (b0.05) on digestion of any diet constituent and digestive adaptation to the fat supplemented diet apparently occurred within 1 week. Pre-exercise muscle glycogen concentrations increased up to Day 14 on both diet treatments. However, when horses were fed the fat supplemented diet pre-SET muscle glycogen concentration increased until Day 21 (P<0.05) at which time it was higher (P<0.05) than when the horses were fed the control diet. This difference was also present at Day 28. Post SET muscle glycogen concentrations were similar (P>0.05) between treatments on all sampling days. In fat supplemented horses, muscle glycogen utilisation during the SET was increased on both treatments to Day 14 (P