Measurements In Sheep Research Articles

Repeatability of computer tomography scan measurements in sheep

Computer tomography (CT) has the potential to measure body composition and form in live farm animals accurately and objectively in ways not possible with longer established assessment methods. Preliminary reports (Young, Logan, Nsoso and Beatson, 1996) verified that this is so but concluded that registration errors and subjective interpretation of tissue boundaries during image analysis affect accuracy. However, their study did not allow an assessment of the relative significance of these effects. The trial reported here was designed to quantify such effects by determining the repeatability of CT scan measurements.

A wave transmission model of the umbilicoplacental circulation based on hemodynamic measurements in sheep.

Electrical analog models of the umbilical circulation were developed based on hemodynamic measurements in fetal sheep. The umbilical artery was represented by a transmission line and the placenta by a resistive load. Model predictions of input impedance and pressure and flow waveforms agreed with in vivo measurements under baseline conditions, following placental embolization, and during angiotensin II infusion. A unique positive impedance phase observed at the heart rate frequency under baseline conditions was best explained by the unusual viscoelastic properties of the umbilical arterial wall and small load reflections. Furthermore, a short, less vasoactive segment of the umbilical artery in the retroperitoneal space had a large impact on the input impedance of the umbilical circulation, which was particularly apparent when the artery was constricted during angiotensin II infusion. The model indicated that reflections arising near the approximate location where the first arterial branches leave the main umbilical artery have a measurable impact on impedance spectra when load reflections are low.

Genetic variation in the feeding efficiency of maize genotypes evaluated from experiments with dairy cows

AbstractGenetic variation in the feeding efficiency of maize genotypes was evaluated from experiments with dairy cows. Maize genotypes were chosen to represent a range of digestibilities from previous experiments with standard sheep.The variation in milk yield observed with dairy cows fed genotypes with low or high digestibilities or energy values was about 1.0–2.0 kg per animal per day. Moreover, the range of variation in body weight was about 10–30 kg during the 3 months of the experiments. Hybrids with similar energy values had a similar effect on milk yield, but the intake of each hybrid could be very different when they were fed to dairy cows, even if no difference in intake had been observed in sheep. The higher silage maize intake of ‘DK265’ was mostly converted into a body weight gain rather than an increased milk yield, probably because the milk yield potential of the animals was soon reached. It appeared that those hybrids whose predicted energy value from sheep measurements was low led to relatively low performances in cows. Dairy cow performances also appeared to be related to the enzymatic solubility values of the whole plants.For maize breeders, the prediction of hybrid efficiency in dairy cow rearing must include digestibility and ingestibility factors. The most important challenge for maize breeders now will probably be the adjustment of a criterion for predicting intake because the stover digestibility and the starch content can be predicted reliably with the use of NIRS calibrations.

Relation of blood-free to blood-inclusive postmortem lung water measurements in sheep.

Our purpose was to see if the postmortem weight ratio of extravascular lung water to blood-free dry lung (blood-free ratio) was related to similar ratios in blood-inclusive lung and in blood. We developed linear regressions of blood-free ratio on ratios for blood-inclusive lung and blood together and for blood-inclusive lung alone for 73 sheep studied under 11 different protocols and for two subgroups of sheep, one with plasma space expansion and the other without expansion. The relation of ratios of blood-free to blood-inclusive lungs was different between the two subgroups. Although all regressions were highly correlated, the fits of the blood-free ratio on ratios for blood-inclusive lung and blood together were better than for blood-inclusive lung alone. The mean error of prediction of extravascular lung water for all sheep was significantly less for the regression of blood-free ratio on ratios for blood and blood-inclusive lung together (11 g) than for blood-inclusive lung alone (18 g). This study shows that weights of lung homogenate and blood samples before and after simple oven drying can be used to provide accurate inexpensive estimates of postmortem extravascular lung water.

Mimosine, administered orally, and two related compounds of chemical defleecing agents for sheep

Oral doses of mimosine (ranging from 400 to 800 mg/kg body weight) were given to 71 sheep, either as two successive daily doses (10 sheep) or as a single dose (61 sheep). The effectiveness of these treatments for defleecing was assessed and in some sheep measurements were made of the concentration of mimosine in plasma after dosing, and of the rate of wool growth before and after dosing. In addition, the effectiveness as defleecing agents of two related compounds (an analogue of mimosine, 'isomimosine', and a metabolite, 3,4-dihydroxypyridine (DHP)) was assessed. Two successive daily doses of mimosine (300 mg/kg/day) allowed all sheep to be defleeced. With sheep consuming a daily ration of 600 g, a single oral dose of mimosine (400 mg/kg) was sufficient to allow defleecing of most sheep; when the daily ration was 1200 g, a dose of 600 mg/kg was required to allow defleecing of most sheep. The effectiveness of oral doses for defleecing could be explained by the absorption of mimosine over a period in excess of 24 hr. Concentrations of mimosine in plasma were usually above 100 µmoles/l 24 hr after an effective dose. Failure to achieve complete cessation of fibre growth occurred occasionally, irrespective of dose level, and two sheep died after dosing. Fasting prior to dosing appeared to obviate the effects of previous high nutrition, but increased the risk of toxic effects. Fasting resulted in exceptionally high concentrations of mimosine in plasma (200–300 µmoles/l) 1 and 2 days after dosing. Both fibre diameter and mass of wool grown were increased in the early regrowth after dosing with mimosine. 'Isomimosine' had a similar potency to mimosine for stopping fibre growth in sheep, whether given as an intravenous infusion or as a single oral dose. DHP, given as an intravenous infusion, was ineffective as a defleecing agent.

The effects of various forms of gastrointestinal cannulation on digestive measurements in sheep

1. There was little difference in digestive (voluntary food intake, dry matter digestibility and nitrogen balance) and blood measurements (venous concentrations of corticosteroids, serum aspartate aminotransferase (EC 2.6.1.1), protein-bound iodine, urea and glucose) of intact sheep (eight animals) and of sheep prepared with rumen cannular (sixteen animals) and subsequently with either simple 'T-shaped' (eight animals) or re-entrant cannulas (eight animals) at the duodenum and ileum, when fed ad lib. a chopped medium-quality-hay ration. 2. Wool growth rates of the intact sheep were similar to those in sheep with rumen cannulas and with rumen cannulas plus simple 'T-shaped' cannulas, but higher (P less than 0-01) than those with rumen cannulas plus re-entrant cannulas. 3. When the sheep were subsequently given a restricted intake (800 g/d) of dried grass, retention times of solid- and liquid-phase digesta markers in the rumen and caecum were similar in all sheep. 4. The use of the different preparations in digestive physiology studies is discussed.

Plasma volume measurements in sheep using Evans’ blue and continuous blood sampling

After intravenous injection of 0.3-0.4 mg Evans' blue/kg liveweight in sheep, blood was collected continuously for 10 min into 10 tubes. Calculations using the dye concentrations in the plasma collected between 3 and 10 min gave values of plasma volume in close agreement with those obtained by intravascular dilution of labelled macromolecules. The dye has no adverse effects on carcase quality and can be used in standard holding pens.

Results and limitations of blood volume measurements in sheep

Summary Blood volume determinations were carried out in normal unanesthetized sheep using Cr51 and I131. Blood volume averaged 2.61 L./m.2 BSA (= 63.5 ml./kg.); the mean Fcells ratio was 1.16.

RELATIONSHIPS AMONG WEIGHTS AND LINEAR MEASUREMENTS IN SHEEP AND HERITABILITY ESTIMATES OF SOME OF THESE MEASUREMENTS.

Relationships among linear measurements and body weight were studied in approximately 1400 lambs. Measurements and weights studied were: metacarpus and metatarsus width and breadth, hook width, birth weight, adjusted 30-day weight and adjusted weaning weight. Simple correlations among these variables as well as multiple regressions of weaning weight and 30-day weight on the other variables are reported. Generally, birth weight was the most valuable for predicting weaning weight. Considering any linear measurements simultaneously with birth weight adds significant information, but the addition is too low to be practically useful. Sex, year, breeding-location and type of birth were significant sources of variation for all characters. Simple correlations between chilled carcass weight percent of live weight and the area of ribeye muscle were 0.00 and −.44 with metacarpus length, 0.80 and 0.51 with metacarpus lateral diameter, 0.46 and 0.51 with metacarpus anterior-posterior diameter, 0.31 and 0.37 with metatarsus lateral diameter, 0.32 and 0.57 with metatarsus anterior-posterior diameter and 0.44 and 0.71 with hook-bone width, respectively. Heritabilities as estimated from offspring-dam regressions and correlations at birth were 0.46 and 0.38 for cannon length and 0.38 and 0.37 for the hook-bone width, respectively.