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Plasma acetoacetate concentration in the 1st mo of lactation and its relation to BW change, milk yield, DMI, and BW postpartum were studied in 361 first lactation cows during 6 yr. The cows were fed concentrate at 6 and 3 kg/d. Calvings took place from August to December. Single observations for all cows were fitted by a multitrait animal model that accounted for all genetic relationships. Heritability for acetoacetate was .11 with a genetic correlation of .87 for milk yield, –.65 for weight change, and –.13 for BW postpartum. Acetoacetate was higher at 3 kg/d of concentrate than at 6 kg/d, and calving after 3 to 4 mo of indoor feeding was related to higher acetoacetate than was calving shortly after the pasture season. Acetoacetate was related to weight loss postpartum, but at a different degree in different years. In some years, compounds of the silage caused strongly elevated plasma concentrations of acetoacetate after feeding. Experiments were performed to compare hay with silages of different qualities. Rumen concentration of different amines 3 h postfeeding was taken as an index of the amine load of the cow. The concentration of several amines in rumen fluid were high after feeding ketogenic silage.

Thyroid hormone levels before and after thyrotropin releasing hormone (TRH) injection were compared at four different stages in relation to parturition in nine heifers. Basal thyroxine (T4) levels were similar before conception and two weeks before calving, but the T4 responses to TRH were reduced near parturition. Hormone levels and responses were low 2 weeks as well as three months after parturition. Both basal levels of T3 and T3 responses to TRH were low near parturition. Three months after parturition both basal level and TRH responses were comparable to those observed before conception. Low basal levels of thyroid hormones near parturition were not associated with an increased disappearance rate. Reduced thyroid secretion activity during early lactation must be the main explanation for the low thyroid hormone levels seen at this stage.

A feeding experiment was performed on 16 cows in order to test the effect of naturally occurring substances in silage on forage intake, ketonemia, and milk yield. The cows were divided into a control group and three experimental groups. The cows in the three experimental groups were fed 100 g/d of putrescine, 200 g/d of valeric acid, or 200 g/d of butyric acid through a ruminal tube for 3 d. Butyric acid increased plasma acetoacetate; the effect was largest in high yielding cows. Putrescine influenced both milk yield and forage intake and may possibly be a contributory factor, alone or combined with other amines, for the development of ketonemia. Valeric acid did not influence feed intake or plasma acetoacetate concentration. A rapid method for acetoacetate analysis also is described.

Minimum plasma calcium level around parturition and its relation to BW at parturition, milk yield, and weight change in mo 1 of lactation were studied in 334 first lactation Norwegian cows. Minimum plasma calcium level was reached 18 to 30 h postpartum. Single observations for all animals were fitted with a multitrait animal model including all genetic relationships. Heritabilities of the traits were calcium postpartum, .11; milk yield, .35; BW, .65; and weight change, .17 with standard errors about .10. Genetic correlations between calcium postpartum and the other traits were milk yield, –.49; BW, –.66; and weight change, .42 with standard errors about .25. Environmental factors with detectable effect on hypocalcemia were age at parturition and calving season. Regression of calcium postpartum on age was –2.66 × 10–4 mmol/L per d. Calvings shortly after the pasture season were related to higher calcium postpartum than calvings after 3 to 4 mo with indoor feeding.

Sixteen bull calves were fasted during two periods, 3½ and 7 months old. Blood samples were taken every 6 h during an experimental period of 9 days: 2 control days, 5 fasting days and 2 refeeding days. During the control days with ad libitum feeding, T3, T4 and TSH increased during the day. During the fasting period, T4 decreased with a half-life of 3.5 days and T3 with a half-life of 3 days. TSH decreased in a less regularly way to a mean of 60% of control mean. Six h after refeeding, TSH had increased to 300% of control mean. T3 and T4 had a maximum 12 h after refeeding. As the T4 decreased with a rate nearly similar to the T4 disappearance rate in starving bulls, the secretion of T4 from the thyroid gland must have been almost stopped during the starvation period. The morning values were below normal for all three hormones after 2 days of refeeding.

(1977). Serum Levels of Thyroid Hormones in Lines of Pigs Selected for Rate of Gain and Thickness of Backfat. Acta Agriculturae Scandinavica: Vol. 27, No. 1, pp. 41-44.

A method for preparing highly purified glutaminase (EC 3.5.1.2, l-glutamine amidohydrolase) from pig renal cortex is described. The main steps consist of sodium sulfate fractionation followed by alternative solubilization by dialysis against Tris-HCl buffer and precipitation with phosphate-borate. The final enzyme preparation contains no impurities which could be detected by sucrose gradient centrifugations, sedimentation velocity experiments, immune diffusion, or disc electrophoresis. Glutaminase has been found to exist in different interconvertible molecular forms. A Tris-soluble enzyme form (Tris-HC1 enzyme), obtained by dialysis against Tris-HCl, has an average sedimentation coefficient of 7.3 and an apparent molecular weight of 140,000 to 160,000, as determined by sucrose gradient centrifugation and Sephadex gel filtration. Another enzyme form (phosphate enzyme), obtained by dialysis of the Tris-HCl enzyme against phosphate, has an average sedimentation coefficient of 10.8 and an apparent molecular weight of 250,000 to 290,000. A phosphate-borate-precipitated form (phosphate-borate enzyme), with an average sedimentation coefficient of 50 and an apparent molecular weight of about 2,000,000, is obtained by addition of borate to the phosphate enzyme. Sulfate has an effect on the sedimentation coefficient similar to that of phosphate, and glutamate, citrate, and malonate have an effect similar to that of Tris-HCl. The sedimentation coefficients of both the Tris-HCl enzyme and the phosphate enzyme are increased by borate and the dye bromthymol blue. The sedimentation coefficient of the phosphate enzyme is lowered by chloride and urea. The Tris-HCl enzyme has a pH optimum of about pH 9, whereas no distinct optimum in the pH range 8 to 9 has been shown for the phosphate-borate enzyme. These forms of glutaminase are activated not only by anions, but also by ammonium ions and bromthymol blue, which suggests allosteric properties.

(1964). The enzymatic determination of ammonia in blood and tissues. Scandinavian Journal of Clinical and Laboratory Investigation: Vol. 16, No. 4, pp. 433-439.

Phenotypic and genetic parameters for thyroid activity (T4 serum level, T4 apparent distribution volume, T4 fractional turnover rate and T4 degradation), and for certain production traits (roughage dry matter intake, daily weight gain and roughage dry matter/kg weight gain), were investigated in cattle. In the experiment, 480 growing heifers were studied, daughters of 20 AI sires previously tested for thyroid activity. Repeatabilities for thyroid traits 2-3 months apart varied, with an average 0.3-0.6 for the different traits. Heritability estimates based on sire components were 0.1-0.4 for the thyroid traits, 0.16 +/- .10 for roughage intake and 0.18 +/- .11 for daily gain. The sire component for feed efficiency (roughage dry matter/kg weight gain) was 0, and genetic correlations between thyroid traits and the production traits in growing heifers were low with large standard errors.

Highly purified pig renal glutaminase has been subjected to electron microscopy. It is shown that the polymers formed after addition of phosphate-borate to enzyme dissolved in Tris-HCl buffer consist of long, double-stranded helices. Addition of phosphate to the Tris-HCl form of the enzyme probably induces the formation of dimers of the Tris-HCl units. It is further demonstrated that the rate of formation of the phosphate form and phosphate-borate form from Tris-HCl units, closely follows the increase in the catalytic activity of the enzyme.

Kinetic properties of two enzyme forms of purified pig kidney glutaminase, the phosphateborate and Tris-Cl enzymes, have been investigated. Plots of velocity versus phosphate concentration are sigmoidal for both forms. However, with α-ketoglutarate present, double reciprocal plots of velocity versus phosphate are linear for the phosphate-borate enzyme, and parabolic for the Tris-Cl enzyme. Inhibition by glutamate is non-competitive for the phosphate-borate enzyme, and competitive for the Tris-Cl enzyme. Moreover, with α-ketoglutarate present, phosphate activates the phosphate-borate enzyme only slightly, but it counteracts the inhibitory effect of glutamate strongly. When glutamine is the variable substrate, phosphate decreases the apparent Michaelis constant and increases maximal velocity for both enzyme forms. Using glutamate as the fixed variable and glutamine as the variable substrate, double reciprocal plots are linear, showing non-competitive inhibition between glutamine and glutamate for both enzyme forms. Replots of slopes versus glutamate are non-linear and of intercepts versus glutamate, linear. The experimental data are explained by assuming an ordered mechanism in which glutamate is the first product to be released.

The correlation between measured enzyme activity and enzyme concentration has been tested for aspartate aminotransferase and creatine kinase. Some conditions where this is non-linear have been described. The correlation was independent of the source of the enzyme: serum enzymes or purified enzyme solutions. By isotope technique a back reaction has been demonstrated for aspartate aminotransferase. Difficulty of measuring true initial reaction rates in manual routine methods has been demonstrated. When methods with a non-linear correlation curve have to be used, the estimation of serum concentration of enzyme must be based on a correlation curve between enzyme concentration and enzyme activity.