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Biomedical subjects

L J Koong

Publications and source records attributed to L J Koong.

10 recordsLinked to original sources
PubMed1992

Nitrogen and lipid metabolism in heifers fed at increasing levels of intake.

The relationship between N and lipid metabolism was investigated in heifers fed five different levels of feed intake (five heifers per treatment group). Targeted ME intakes were 84, 123, 157, 191, and 225 kcal per kt.75 per day, which were .76x, 1.12x, 1.43x, 1.74x, and 2.05x (times) the estimated ME requirement for maintenance. After 120 d on trial, the heifers were moved to a confinement building for 7 d, and feces and urine were collected over a 3-d period. On the 1st d of confinement, blood samples were collected every 15 min for a total of 15 samples. Because the group fed at 1.43x maintenance was fed improperly during the period in confinement, this group was omitted from the study. Adipose tissue samples were obtained at slaughter to obtain in vitro measures of lipid metabolism. As feed intake increased, N retention increased (P less than .05) from 1.7 to 24.3 g/d. Daily urinary N tau-methylhistidine excretion was significantly different between the .76x and 1.74x treatments (769 vs 1,575 mumol/d, respectively). The fractional breakdown rate of myofibrillar proteins also was significantly different between these two groups of heifers (1.49 vs 2.44%/d, respectively). Plasma glucose and insulin were lowest (P less than .05) at the lowest level of feed intake. Conversely, plasma nonesterified fatty acids were lowest (P less than .05) in those animals receiving the highest level of feed intake. Subcutaneous adipocytes were smallest (93 microns) in the heifers fed at 33% ad libitum intake and largest in heifers fed at 76 or 90% ad libitum intake (115 and 110 microns, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1990

Effects of short term nutritional manipulation on organ size and fasting heat production.

Two studies were conducted to study the effects of short term nutritional manipulation on the organ size and the fasting heat production of pigs and sheep. The results of these studies indicate that fasting heat production can differ up to 40 per cent for animals of same age and weight, but with different nutritional backgrounds. Those animals on a higher plane of nutrition preceding measurements had higher fasting heat production, in spite of being the same age and body weight. At the same time, the weights of metabolically active organs such as the stomach, the small and large intestine, the liver and the kidneys are also very sensitive to the nutritional manipulation, in a parallel direction to that observed with fasting heat production. These findings provide strong evidence that the energy expenditures of the metabolically active tissues account for a significant amount of basal metabolic activity far in excess of the proportional weights of these tissues.

Animals↗
PubMed1976

Utilization of energy for maintenance and for fat and lean gains by mice selected for rapid postweaning growth rate.

The metabolizable energy intake (MEI) required for maintenance and the efficiency of utilization of metabolizable energy available for gain (MEA) were determined for a line of mice (rapid growth) selected for 41 generations for rapid postweaning weight gain and for a contemporarily mated line (control) that had been randomly selected. Feed intake of individually housed rapid growth and control males was restricted above maintenance or was ad libitum from 21 to 42 days of age. Regressions of change in body energy per unity metabolic body size on MEI per unit metablic body size showed that the maintenance requirement for each line of mice was 176 kcal per unit metabolic body size per day and that the rapid growth line was more efficient than the control line in utilizing MEA (50% vs. 23%) to promote an increase in body energy. Although the proportions of MEA used for fat (PF) and lean (PL) gains and the net efficiencies with which those proportions were utilized for fat (NF) and lean (NL) gains were unknown, the products of proportion and efficiency for fat gain (PF X NF or fat energy deposition coefficient) and for lean gain (PL X NL or lean energy deposition coefficient) were determined. The results demonstrate that 41 generations of selection for rapid postweaning weight gain did not change the lean energy deposition coefficient, but did alter the fat energy deposition coefficient. These data suggest that the two lines of mice use different proportions of MEA for fat gain and/or utilize MEA for fat gain at different efficiencies.

Adipose Tissue↗
PubMed1976

Lactational efficiency complex of rats: provisional model for interpretation of energy balance data.

In experiments to determine maintenance requirements and partial efficiencies of conversion of diet and body tissue to milk, correlations between independent variables interfered with multiple regression procedures usually used in analyzing nutritional energetic data. Therefore, an alternative of a largely deterministic model of energy transformations in lactating rats was developed. Food intake, initial and final body weights, and diet composition were inputs to the model. These inputs were partitioned among the several metabolic functions of lactating rats within the model, and estimates of milk energy, heat increment of production, energy used for maintenance, and heat increment of maintenance were computed. The model was validated with rats and diets not used in model development. Inferences were: (a) average efficiency of body energy conversion to milk is 83%; (b) average gross and net efficiencies of milk production on balanced rations are 57 and 80%; and, (c) maintenance requirements vary as a function of food intake. A logistic function relating maintenance to food intake was developed based on the postulate that changes in intake of food cause changes in weights of several vital organs changing the maintenance requirement. This postulate explains, in part, changes in maintenance requirements during long food restriction and during gestation and lactation.

Animals↗
PubMed1975

Iterative computation of metabolic flux and stoichiometric parameters for alternate pathways in rumen fermentation.

A model is presented which has been derived to compute the end-products of rumen fermentation from knowledge of the input of feedstuff. The model comprises a set of algebraic equations for the fermentation of each of the following feedstuff components: soluble sugars, starch, cellulose, hemicellulose and protein. The equations were derived from known biochemical stoichiometric relationships. A iterative, non-linear least sqares method (steepest descent) was used to estimate parameter values. In a sample run the inputs used were from an experiment where eight sheep were fed white clover. The model predicted values were in good agreement with the experimental values.

Animals↗
PubMed1975

A model of heat flow in the sheep exposed to high levels of solar radiation.

The fleece is an important component in thermoregulation of sheep exposed to high levels of solar radiation. A model written in CSMP has been developed which represents the flow of energy between the sheep and its environment. This model is based on a set of differential equations which describe the flux of heat between the components of the system--fleece, tip, skin, body and environment. It requires as input parameters location, date, time of day, temperature, relative humidity, cloud cover, wind movement, animal weight and linear measurements and fleece length. At each integration interval incoming solar radiation and its components, the heat arising from the animal's metabolism and the heat exchange by long-wave radiation, convection, conduction and evaporative cooling are computed. Temperatures at the fleece tip, skin and body core are monitored.

Animals↗