Indirect myosin immunocytochemistry for the identification of fibre types in equine skeletal muscle.

The histochemical ATPase method for muscle fibre typing was first described by Brooke and Kaiser in 1970. However, problems have been found with the subdivision of type II fibres using this technique. To determine whether indirect myosin immunocytochemistry using anti-slow (5-4D), anti-fast (1A10) and anti-fast red (5-2B) monoclonal antibodies with cross reactivity for type I, II and IIa fibres, respectively, in a number of species, could identify three fibre types in equine skeletal muscle, data on fibre type composition and fibre size obtained using the two different techniques were compared. Results indicate that different myosin heavy chains can coexist in single equine muscle fibres. Type I and type II fibres were identified by immunocytochemistry, but subdivision of type II fibres was not possible. Although the percentage of type I and type II fibres was not significantly different for the two techniques, a few fibres reacted with both the 1A10 and 5-4D antibodies.     

Sequential feeding of whole wheat to growing broiler chickens

1. Four broiler feeding trials were performed to examine the suitability of a whole wheat sequential feeding regimen for commercial broiler production. The sequential feeding programme gave a continuous cycle of ad libitum access to only whole wheat followed by the same time of access to only a pelleted diet. The pelleted diet provided a concentration of nutrients to balance that provided by the whole wheat. This was called a balancer diet.

2. The first trial used 144 cage‐reared broilers from 28 to 49 d of age. Four different times of access (4, 8, 12 and 24 h) to the two alternate foods were compared. A whole wheat choice‐feeding treatment and a complete single diet treatment were also compared. Whole wheat accounted for over 40% of the broilers’ total food intakes when they were given the sequential feeding treatments of 8 h or greater. The whole wheat intakes of the birds given the 4 h sequential feeding and the choice‐feeding were only 20 and 5% respectively. There was a non linear relationship between the weight gains of the broilers and the length of the sequential feeding period (P< 0.01). The growth rates of the broilers given sequential feeding were lowest (P< 0.05) in the 4‐h feeding periods but highest (P< 0.05) in the 8‐h periods. Weight gains decreased (P< 0.01) linearly as the sequential feeding periods were increased above 8 h.

3. A second trial, using 144 cage‐reared broilers, examined the effect of different balancer compositions or different wheat varieties in 8‐h sequential feeding. The broilers selected more whole wheat in their diet when they were given balancers with increased cereal contents. However, these broilers did not eat enough whole wheat to compensate for the reduced cereal content of the balancers and their overall diets had lower energy: protein ratios. The two different wheat samples did not result in any differences (P> 0.05) in the proportion of whole wheat selected by the broilers.

4. A third trial compared the diet selections, weight gains, food intakes and water excretions of 72 cage‐reared broilers given whole wheat feeding regimens. The growth rates of the broilers given a loose mix of whole wheat and a pelleted balancer diet were similar (P> 0.05) to broilers given a complete single diet. The growth rates of these two groups were 7% greater (P< 0.05) than broilers given choice‐feeding or 8‐h sequential feeding. There were no differences (P> 0.05) in the total amounts of water excreted among the 4 treatments.

5. The fourth trial used 828 broilers distributed in 6 floor pens. They were given either a complete diet or an 8‐h whole wheat sequential feeding regimen from 25 to 46 d of age. The food intakes and the growth rates of the broilers were reduced (P<0–05) in die sequential feeding treatment by 9% and 5% respectively. There was no difference (P> 005) in litter moisture between the 2 treatments.     

A microbiological assay to estimate the antimicrobial activity of parenteral tildipirosin against foodborne pathogens and commensals in the colon of beef cattle and pigs

Tildipirosin (TIP) is a novel 16‐membered‐ring macrolide authorized for the treatment of bovine and swine respiratory disease. The pH dependency of macrolide antimicrobial activity is well known. Considering that the pH in the colon contents of growing beef cattle and pigs is usually below pH 7.0, the minimum inhibitory concentrations (MIC) of TIP against foodborne bacterial pathogens such as Campylobacter (C.) coli, C. jejuni and Salmonella enterica and commensal species including Enterococcus (E.) faecalis, E. faecium and Escherichia coli were determined under standard (pH 7.3 ± 1) or neutral as well as slightly acidic conditions. A decrease in pH from 7.3 to 6.7 resulted in an increase in MICs of TIP. Except for the MICs > 256 μg/mL observed in the resistant subpopulation of the C. coli and the Enterococcus species, the MIC ranges increased from 2–8 μg/mL to 64–> 256 μg/mL for Salmonella enterica and E. coli, from 8–16 μg/mL to 32–128 μg/mL for the two Campylobacter species, and from 4–32 μg/mL to 128–> 256 μg/mL for both Enterococcus species. To estimate the antimicrobial activity of TIP in the colon contents of livestock during recommended usage of the parenterally administered TIP (Zuprevo^®), and to compare this with the increased MICs at the slightly acidic colonic pH, we developed and validated a microbiological assay for TIP and used this to test incurred faecal samples collected from cattle and pigs. Microbiological activity of luminal TIP was determined in aqueous supernatants from diluted faeces, using standard curves produced from TIP‐spiked faecal supernatants. The limit of quantification (LOQ) for TIP was 1 μg/mL (ppm). In a cattle study (n = 14), 3 of 28 faecal samples collected 24 and 48 h post‐treatment were found to contain TIP above the LOQ (concentrations of 1.3–1.8 ppm). In another cattle study (n = 12) with faecal samples collected at 8, 24 and 48 h post‐treatment, TIP concentrations were above the LOQ in 4 of the 8 h samples (1.2–2.6 ppm) and one of the 24‐h samples (1.3 ppm). In a pig study (n = 12) with faecal samples collected 24, 48 and 72 h post‐treatment, only one sample contained TIP above the LOQ (concentration 1.5 ppm). In another pig study (n = 12), with samples collected at 8, 24 48 and 96 h post‐treatment, TIP concentrations were above the LOQ in one 8‐h sample (1.1 ppm) and two 24‐h samples (2.3 and 2.5 ppm). None of the 48‐h and 96‐h samples from these 4 studies contained measurable TIP concentrations. Thus, in cattle and pigs, only a small fraction of faecal samples collected up to 24 h postdosing contained measurable microbiologically active TIP, with its maximum limited to 2.6 μg/mL. This is several log₂ dilution steps below the MICs of TIP against foodborne pathogens and commensals collected under acidic conditions comparable with those in the colonic contents and may explain a lack of intestinal dysbacteriosis with parenteral tildipirosin in livestock.     

Fatness of laying hens and induced moulting regimens

1. A flock of laying hens was divided into two groups according to their fatness, which was estimated using abdominal fatness callipers.

2. A moult was induced in both groups by reducing day‐length and restricting food intake. The food restriction period lasted for 2, 3 or 4 weeks and the birds were given either 15 or 25 g of whole wheat/bird.

3. No differences were observed between the moulting treatments on post‐moult egg weights, shell strength or Haugh units, but maximum egg output (g/bird d) was obtained by the 4‐week food restriction period for the fat‐grouped birds but by the 3‐week food restriction for the lean‐grouped birds.

4. The birds restricted to 15 g wheat/bird d showed a more rapid regression of the ovary and oviduct, which may account for their increased egg numbers towards the end of the 22‐week laying period compared to the birds allocated 25 g/bird d.     

Magnetic resonance imaging of bone marrow in the pelvis and femur of young dogs

The purpose of this study was to determine the magnetic resonance (MR) imaging characteristics of bone marrow in the pelvis and femur of normal, young dogs. Six greyhounds were imaged at 4, 8, 12, and 16 months of age. Sagittal images of the femur and dorsal images of the pelvis were obtained with T1-weighted, fast spin echo (FSE) T2-weighted, and short tau (T1) inversion recovery (STIR) sequences. On T1-weighted images areas with high signal intensity, similar to fat, included the femoral heads, mid-diaphysis of the femur, femoral condyles, and the body of the ilium. T2-weighted images were characterized by uniform intermediate signal intensity (less than fat, but greater than muscle) in the femoral head, high signal intensity, similar to fat, in the mid-diaphysis of the femur and ilial body, and intermediate to high signal intensity in the femoral condyle. By 16 months high signal intensity was seen in the diaphysis and distal metaphysis on both T1- and T2-weighted images. On STIR images the femoral head had intermediate to low signal intensity, compared with muscle. The mid-diaphysis of the femur was of low signal intensity, similar to fat, and the body of the ilium had mixed signal intensity at all ages. The femoral condyle had inhomogenous, intermediate to low signal intensity at 4 months, but was of uniform low signal intensity at 8-16 months.     

Quantifying fish avoidance of small acoustic survey vessels in boreal lakes and reservoirs

Mobile hydroacoustic surveys are increasingly used to assess the distribution and abundance of freshwater fish; yet, fish may avoid moving vessels, potentially introducing bias in these assessments. In this study, avoidance in boreal lakes and reservoirs was quantified by developing a simple method based on paired drift:drift (D:D) and drift:motor (D:M) transects. Two systems in eastern Manitoba, Canada were studied: Lac du Bonnet reservoir and Nopiming. Acoustic data were collected using a digital DTX echosounder (BioSonics, Seattle, WA, USA), with a downward facing 200‐kHz split‐beam transducer, deployed from 5.5‐m vessels (Boston Whalers) modified for acoustic research. An avoidance coefficient (Ac) was developed based on comparisons of acoustic fish densities while the vessel moved over the same transects by drifting, and by motoring at survey speeds. Ac did not differ significantly from 1 (no avoidance) at Nopiming (median of 0.81, n = 13), but did at Lac du Bonnet (median of 0.51, n = 31, P < 0.05). Variability in Ac was as high in transect pairs and was unrelated to fish depth (mean 6.9 m at Lac du Bonnet; 13.1 m at Nopiming) or survey speed (up to 3.70 m·s^?1, 7 knots). Results indicated that fishes did not dive in the presence of the motoring vessel, nor was avoidance size‐based. We did not detect any evidence of fish attraction to our drifting vessel. Our results suggest that boat avoidance during acoustic surveys of shallow boreal lakes may vary in relatively similar water bodies but can be quantified experimentally.