H. D. Johnson

Effect of programmed diurnal temperature cycles on plasma thyroxine level, body temperature, and feed intake of holstein dairy cows

Holstein cows exposed to simulated summer diurnal ambient temperature cycles of Phoenix, Arizona and Atlanta, Georgia and diurnal modifications of these climates displayed daily cycles fluctuations in plasma thyroxine (T4) and rectal temperatures (Tre). There were daily diurnal changes in T4 and Tre under all simulated climate conditions. Maximal values generally occurred in the evening hours and minimum values in the morning. Although the diurnal rhythm was influenced by the various simulated climates (diurnal modifications) a diurnal rhythm was very evident even under constant conditions at thermoneutral (Tnc) and at cyclic thermoneutral conditions (TN). The major significance of the study is that the initiation of night cooling of the animals at a time when their Tre was highest was most beneficial to maintenance of a TN plasma T4 level. There was a highly significant negative relationship of average T4 and average Tre. There was also a significant negative relationship of feed consumption and average temperature-humidity index (THI).These data suggest that night cooling may be a most effective method to alleviate thermoregulatory limitations of a hot climate on optimal animal performance. Decreasing the night time air temperature (Ta) or THI or increasing the diurnal range allows the cows to more easily dissipate excess body heat accumulated during the day and minimize the thermal inhibition on feed intake, and alterations in plasma T4 and Tre.

Effect of season on milk temperature, milk growth hormone, prolactin, and somatic cell counts of lactating cattle

Monthly fluctuations in milk temperature, somatic cell counts, milk growth hormone and prolactin of lactating cows were measured in milk samples over a 1 year period. The seasonal patterns in milk temperature, somatic cell count and milk prolactin concentration showed a positive trend with increasing environmental temperatures. Milk growth hormone concentration increased with lactation level and declined significantly during summer heat. Milk temperature and the measured hormonal levels may serve as indicators of the impact of the climatic environment on lactating cattle.

Environmental Heat Effects on Growth, Plasma T3, and Postheat Compensatory Effects on Holstein Calves

Abstract Five Holstein heifers, 5 months of age, were housed in the Missouri Climatic Laboratory and subjected to an experiment to measure the effects of heat stress on rates of growth, plasma triiodothyronine (T3) levels, and ability to compensate in rate of gain and thyroid function following the stress period. The experiment consisted of 3 weeks at thermoneutral (TN1), followed by S weeks of individually controlled heat stress conditions (32.S to 34°C) dependent on heat tolerance of individual animals. This was followed by a 4-week thermoneutral, postheat compensatory period (TN2). Average daily gains were significantly depressed during the heat stress period (HS). Following heat stress the average body weights attained the projected or expected levels within a 21- to 28-day period following return of animals to thermoneutral conditions. Ratios of feed intake/body weight (w0.75) were reduced during heat stress treatment indicating the thermal inhibition. Ratios or amount of feed intake per unit of gain were greater during HS treatment indicating less weight gain per unit of daily feed intake. Plasma T3 was reduced during heat treatment similarly to daily weight gain. Following the postheat treatment period (TN2) plasma T3 increased markedly as did daily weight gains to demonstrate strong compensatory responses in both measures. In summary, these results demonstrated parallel and positive changes of plasma T3 with daily weight gain during thermoneutral, heat, and postheat compensatory periods, and an inverse relationship of rectal temperature to weight gain and plasma T3.

High-performance liquid chromatographic analysis of biogenic amines in biological materials as o-phthalaldehyde derivatives☆

A remarkably sensitive, simple and selective reversed-phase high-performance liquid chromatographic (HPLC) method has been developed, allowing, for the first time, the direct measurement of histamine, norepinephrine, octopamine, normetanephrine, dopamine, serotonin and tyramine in a single sample of plasma (2 ml), tissue (0.2 g), or urine. The biogenic amines were modified by pre-column derivatization with o-phthalaldehyde which stabilizes the molecules, aids in extraction, and improves HPLC detection at the nanogram level. To minimize losses during the sampling procedure a careful collection procedure was designed. We developed a simple sample cleanup in which the samples were thawed, neutralized with KOH, immediately derivatized, extracted into ethyl acetate (EtOAc) and then chromatographed by HPLC. The derivatives were stable in EtOAc for more then 24 h. Interfering amino acids were removed from the EtOAc by partitioning twice with Na2HPO4 buffer (pH 10.0). Complete separation was achieved in ca. 60--90 min on a muBondapak phenyl column using a stepwise gradient of acetonitrile and/or methanol-phosphate buffer (pH 5.1). A variable wavelength fluorometer with a 5-microliter flow-cell was used (excitation 340 nm; emission 480 nm). Linearity ranged from 200 pg to 50 ng onto the column. Precision (R.S.D.) for retention times was 1% and for derivatization and injection 2.5%. Recoveries of the seven biogenic amines from plasma spiked with 25 ng/ml averaged 70%, with a relative standard deviation of 6%. Separation studies were also done using a muBondapak C18 column. The effects of various eluents are presented. Gas-liquid chromatography was also investigated but lacked the sensitivity achieved by HPLC. The HPLC method is used routinely for the determination of biogenic amines in plasma from pigs with malignant hyperthemia and thermally stressed bovine. Significant differences in levels of biogenic amines were noted between stressed and non-stressed animals. Data on rat brain tissue samples were compared with the trihydroxyindole method and canine heart tissue was analyzed for ventricular norepinephrine and dopamine. Application of the method to urine from normal persons and a patient with a brain tumor has been demonstrated.

Effects of recombinant bovine somatotropin (rbST) and season on plasma and milk insulin-like growth factors I (IGF-I) and II (IGF-II) in lactating dairy cows

During two studies, effects of recombinant bovine somatotropin (rbST) on plasma and milk IGFs in cows adapted to summer (S; 12 cows) or winter (W; 12 cows) conditions were evaluated. Each study consisted of on-farm periods (30 days) followed by climatology chamber periods (CC; 30 days). Cows were given daily injections of rbST, Sometribove, USAN (25mg/day; 6 cows each study) or saline (control; 6 cows each study). During on-farm periods, blood and milk (am and pm) samples were collected once weekly. During CC periods, blood samples were collected every 2 days and milk samples (am and pm) were collected daily. Plasma IGF-I and IGF-II were increased in cows treated with rbST. A pronounced seasonal pattern in basal and rbST-stimulated plasma IGF-I but not IGF-II was detected. Higher basal and rbST-stimulated plasma IGF-I concentrations in S occurred despite large decreases in feed intake and energy balance. Milk IGF-I and IGF-II was not affected by rbST treatment or season. Although milk IGF-I and IGF-II concentrations were unaffected by rbST treatment, total IGF-output increased due to increased milk yield. The observed seasonal patterns in plasma IGF-I may be indicative of seasonal differences in the coupling of the somatotropin-IGF axis. In particular, we failed to detect an uncoupling of the somatotropin-IGF-I axis in S despite an induced negative energy balance during thermal stress.

The effects of heat exposure (31 degrees C) on Zebu and Scottish Highland cattle.

Three Zebu and three Highland mature heifers were used to study the effect of a moderately high environmental temperature (31°C) on temperatureregulatory responses of cold- and heat-tolerant cattle to thermal stress. Following a 7-day period of adjustment to 31°C, the Highland heifers decreased their internal heat production by decreasing feed consumption by 31% and oxygen consumption by 19%. They also increased their evaporative heat losses by an increased respiration rate of 92% and total vaporization (33%). At 31°C, water consumption increased 190% and body fluid compartments showed a significant increase, with the exception of plasma volume. The Zebu decreased feed consumption by 19%, increased respiration rate 100%, total vaporization 80%, water consumption 58%, and plasma volume by 17%. The Highland cattle could not prevent hyperthermia upon exposure to the moderate high temperature, while the Zebus maintained normal rectal temperature. Breed differences in ability to maintain homeothermy are documented in this study.

Suppression of T‐Lymphocyte Blastogenesis by Ovine Trophoblast Protein‐1 and Human Interferon‐α May Be Independent of Interleukin‐2 Production

ABSTRACT: Cells derived from the trophoblast tissue of a day 15 sheep conceptus released substances that inhibit incorporation of [3H]thymidine into phytohemagglutinin (PHA)‐stimulated ovine lymphocytes. This effect was partially reversed by addition of antiserum to ovine trophoblast protein‐1 (oTP‐1), a major secretory product of day 13–21 sheep conceptuses and a protein structurally and functionally related to α‐interferons (IFN‐α). Human IFN‐a, unlike dexamethasone, inhibits phytohemagglutinin‐induced lymphocyte blastogenesis without reducing interleukin‐2 (IL‐2) production by the cultures, and conditioned medium containing IL‐2 does not promote [3H]thymidine incorporation into ovine lymphocytes when oTP‐1 is present. Thus, oTP‐1, by virtue of being an IFN, may have a local immunomodulatory role by selectively inhibiting the proliferative responses of certain maternal immune cells to IL‐2.

Effect of High Ambient Temperature (35°), and Feed Intake on Plasma T4 Levels in Sheep

Abstract An experiment was designed to determine the relative effects of environmental heat stress and accompanying decline in voluntary feed intake on plasma thyroxine. The sheep were divided into three groups of four animals each. The control animals and feedrestricted group were maintained at thermoneutrality (22°, 50% RH). The heat group was maintained at 35° and 67% RH. All groups were fed ad libitum except the feed-restricted group which was fed at the level of the heat-stressed group. Results indicated that environmental heat has both a direct temperature and an indirect temperature (feed) effect on plasma thyroxine (T4). The feed effect was determined by comparing the plasma T4 of the feed-restricted group at 22° to the high-temperature (35°) group. Both groups consumed similar levels of feed. The heat-stressed group with elevated temperature and feed intake similar to feed-restricted group at thermoneutral showed significantly greater reduction of plasma T4. Therefore the temperature effect was additional to the feed effect and the heat-stressed group displayed a significantly greater decline in plasma T4.

Rat adrenal cortical activity during exposure to a high (34°C) ambient temperature

A highly significant (P<.01) elevation of plasma corticosterone concentration was observed in rats exposed to heat (34°C) for periods ranging from 6 hours to 12 days. The highest level of plasma glucocorticoid (corticosterone) was attained at the end of the first day of exposure. At all exposure times with the exception of the animal groups at 30 hours and 13 days, the values were significantly higher than the 28°C average control values. These data suggested the occurrence of a transient rise in adrenocortical activity at 24 hours, followed by an under-compensation at 30 and 48 hours with some continued elevation of activity for most of the remainder of this exposure period. The increase in plasma corticosterone, a calorigenic hormone, may serve as a precursor for increased aldosterone production during acclimation to heat.

Relationship of thyroid and adrenal function to “fur-chewing” in the chinchilla☆

Abstract 1. 1. The fur-chewing chincillas showed increased thyroid activity (P , increased adrenalcortical function (P and decreased rectal temperature (P . 2. 2. This study suggested that increased endocrine activity could be due to the loss of insulation over the fur-chewed areas. 3. 3. It is possible, however, that endocrine activity could be a stimulus for fur-chewing. 4. 4. It is also possible that fur-chewing can be initiated or its incidence increased by “non-specific stressors’.