Effect of dietary lysine level on thyroid activity and body temperature in the chick
Creators: name: Pastro, Kenneth Ralph
Publisher: name: University of British Columbia
Year: 2011

description: Experiments were conducted to study the effect of dietary lysine level on thyroid activity and body temperature in White Leghorn cockerel chicks. Thyroid activity was measured in birds 4-to-5 weeks of age and body temperature was measured in birds 4-to-8 weeks of age. Three diets based on corn and sesame meal and containing 20% protein and 0.64% (basal diet), 1% (control diet) or 2% of L-lysine respectively were used. These diets contained deficient, optimal and excessive amounts of L-lysine respectively. Thyroidal experiments were conducted at different times of the year. Thyroid activity was assessed by measuring the level of I¹³¹ in the plasma and thyroid or thyroid only at various times after an intravenous injection of 0.55 μc of I¹³¹ 100 gm of body weight. In August-September, thyroidal response to diet was investigated in birds fed the test diets for either 1 or 17 days prior to administration of I¹³¹. When the test diets were fed for 1 day prior to the injection of I¹³¹, data for per cent I¹³¹ per unit of thyroid weight and for the ratio of thyroidal to plasma I¹³¹ (T/P ratio) indicated that either a deficiency or an excess of dietary lysine enhanced thyroid activity. Feeding the test diets for 17 days appeared to attenuate the responses observed in the 1-day trial. In January, thyroidal response to diet was assessed in birds fed test diets either 1 day before or 3 days after the injection of I¹³¹ . Only the diets containing 0.64% and 1% of L-lysine were fed. When appropriate, 0.2% thiouracil was added to block thyroidal uptake of recycled I¹³¹. When all four diets were fed, I¹³¹ level per unit of thyroid weight and T/P ratio calculated from data obtained 5 minutes, 1 and 3 hours after I¹³¹ administration indicated that dietary lysine deficiency under the circumstances of the experiments reduced thyroidal uptake of the isotope. When I¹³¹ was injected 3 days prior to imposition of the test diets, the values for I¹³¹ per unit of thyroid weight after the feeding trials started indicated that the lysine deficiency reduced the rate of release of thyroidal I¹³¹. In a further experiment, levels of thyroidal I¹³¹ measured 5, 10, 24, 48, and 72 hours after I¹³¹ injection verified that the lysine deficiency reduced thyroid activity. In March, the effect of ambient temperature on thyroidal response to dietary lysine level was investigated. Thyroidal I¹³¹ was measured 6 hours after I¹³¹ administration to birds which had been fed the deficient diet for 1 day. Dietary lysine level and environmental temperature had an interacting effect on total thyroidal I¹³¹ and per cent I¹³¹ per 100 gm of body weight. Under the conditions of the experiment, lysine deficiency enhanced I¹³¹ uptake in a warm environment but has no effect or depressed activity in a cold environment. Temperatures were measured with thermistor probes inserted into the cloaca, the brain and the pectoral is muscle. When fed for either 18-to-30 hours or for 2 weeks, the lysine deficient diet increased muscle temperature. The diet had no apparent effect on brain or cloacal temperature but detection of a response may have been obviated by the technique used to measure temperatures in these two locations. Feeding sub-optimal or excessive levels of dietary lysine for only 1 day caused a change in thyroid activity. In a warm environment, both sub-optimal and excessive levels of lysine enhanced thyroid activity. Environmental temperature appeared to modify the thyroidal response to dietary lysine level. In a warm environment, a deficiency of lysine increased muscle temperature.