Diphtheria toxin subunit active in vitro

Exposure of diphtheria toxin to dithiothreitol (and similar thiols) resulted in a subunit which was active in catalyzing the adenosine diphosphateribosylation of mammalian aminoacyl-transferase II in the presence of nicotinamide adenine dinucleotide. At the same time there was a marked increase in total ADP-ribosylation activity. A molecule which was apparently identical to the derived subunit in size and activity was detected in partially purified preparations of toxin.     

Letters

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Effects of thermal stress and level of feed intake on portal plasma flow and net fluxes of metabolites in lactating Holstein cows

Six Holstein cows (averaging 475 kg body weight, 2.3 parities and 96 d in lactation) fitted with catheters in the hepatic portal vein, mesenteric vein and intercostalis posterior artery were exposed to treatments of thermal comfort environments with libitum or restricted (75% of ad libitum) DM intake and a thermal stress environment with ad libitum intake in two balanced 3 x 3 latin squares to evaluate effects of thermal stress on portal plasma flow and net fluxes of metabolites. Portal plasma flow was measured by administering a primed, continuous infusion of para-aminohippurate into a mesenteric vein and determining its concentration and dilution in portal vein plasma. Thermal stress treatment increased rectal temperatures and respiration rates. Dry matter intake decreased from thermal comfort ad libitum level (15.1 kg/d) to lower levels in thermal comfort restricted (11.5 kg/d) and thermal stress (11.1 kg/d) treatments. Portal plasma flow was related directly to level of DM intake, declining about 14% with thermal comfort restricted intake and thermal stress environment treatments compared with the thermal comfort restricted intake and thermal stress environment treatments compared with the thermal comfort ad libitum intake treatment. Net flux of alpha-amino N was reduced 20 and 35% by thermal comfort restricted intake and thermal stress treatments compared with the thermal comfort ad libitum intake treatment. Net fluxes of urea N, ammonia N and glucose were not affected by experimental treatments. A portion of the negative effects of thermal stress on milk production can be explained by decreased nutrient intake and decreased nutrient uptake by the portal-drained viscera of the cow.     

Increasing Yields of Channel Catfish Using a Combination of Cage and Open Pond Production Systems1

Channel catfish (lctalurus punctatus) fingerlings stocked at a rate of 450 fish/0.04 ha pond were simultaneously cultured with fingerlings stocked in 1.25 m³ cages (0, 250, 350, or 450 fishlcage; one cage/pond). The fish in the cages were cultured and harvested for a 90–330 g (whole fish) market. The fish in the open ponds were cultured and harvested for a 490–1,140 g market. Harvest weights of open pond fish in all treatments were similar indicating that the presence of the caged fish and the associated higher daily pond feeding rates did not affect open pond production. Ninety-five to 99% of the caged fish and 96 to 98% of the open pond fish were of marketable size at harvest. Survival and food conversion ratios were similar among treatments. Results of this study indicate that total pond production can be increased (in this case up to 19%) by using a combination of open pond and cage techniques and by simultaneously producing fish for two markets.     

Effect of number of conceptuses on maternal hormone concentrations in the pig

This study examined the effect of number of conceptuses on maternal concentrations and profiles of estrogen sulfate, estrone, estradiol-17 beta, progesterone and prolactin in gilts. Estradiol-valerate injections were used to induce pseudopregnancy (O conceptuses; n = 5) and oviduct ligation or no treatment were utilized to obtain pregnant gilts with 4 to 7 (n = 4), or 8 to 11 (n = 4) conceptuses, respectively. Blood samples were collected every 10 d from d 10 through 110 of pregnancy or pseudopregnancy. At 110 d after onset of estrus, all gilts were slaughtered and numbers and(or) weights of fetuses, corpora lutea, placentae and the empty uterus were determined. Concentrations of estrogen sulfate and estrone, but not progesterone or prolactin, were associated with fetal number, total fetal weight, total placental weight or empty uterine weight. In contrast, only progesterone was highly correlated with number of corpora lutea. Results suggest that most conjugated estrogen, estrone and estradiol were of fetal-placental origin, whereas little, if any, placental production of progesterone or prolactin occurred. Increases in estrogen sulfate and estrone concentrations were observed at gestation d 30 and from d 70 to 100. The latter increase coincides with previously established increases in the rate of maternal mammary development and fetal growth.     

Nucleic acid, metabolic and histological changes in gilt mammary tissue during pregnancy and lactogenesis

Changes in mammary gland histology, dry weights, nucleic acids and in vitro rates of substrate oxidation in incorporation into lipid were measured in mammary biopsies of three gilts each on d 30, 45, 60, 75, 90, 105 and 112 of pregnancy, and d 1 and 4 of lactation. Histological changes noted were progressive duct growth early in pregnancy followed by rapid lobulo-alveolar development between d 75 and 90 to complete mammogenesis. Colostrum and lipid were evident by d 105 with marked distension of alveolar lumina on d 112. Complete differentiation of the secretory process was apparent on the day of parturition. Concentrtion of dry, fat-free tissue (DFFT) and DNA changed little before d 60 but increased fourfold between d 75 and 90. No further increases in DFFT or DNA were noted. RNA concentrations paralleled DNA through d 90, after which they steadily increased. Rates of acetate and glucose oxidation increased transiently during midpregnancy then declined and remained low until initiation of lactogenesis. Substrate incorporation into lipid increased slightly at midpregnancy and again at d 105, after which it increased markedly. Collectively, results indicate that mammogenesis is complete by d 90, after which lactogenesis is initiated in a two-stage process. Metabolic rates expressed on a DNA basis indicated considerable rates of oxidation, but not of lipogenesis by proliferating mammary tissue. Preferential metabolism of acetate vs glucose near parturition suggests coordination of metabolism between the mammary gland and other maternal tissues.     

A self-propelled, constant-speed spray vaccinator for commercial layer chickens

Vaccination of commercial layer chickens is labor intensive and often results in poor rates of seroconversion, which, in turn, generally correlate with decreased flock uniformity and performance. Attempts to improve the vaccination process include numerous variations of individual shop-built vaccinators in use by the layer sector of the poultry industry. Each of these vaccinators has limitations that contribute to poor vaccinations. Major problems include the nonuniform speed of the applicator system and pressure fluctuations at the spray nozzles, which contribute to sporadic dispersion of the vaccine as the vaccinator is pushed or carried past the cages. A battery-powered, self-propelled, constant-speed vaccinator was designed and constructed that operates with constant nozzle pressure. In field use, this vaccinator has resulted in both labor savings (reduction of manpower from five to one to vaccinate 75,000 chickens) and time savings (from 45 min to 7.5 min/poultry house) as well as improved vaccination results (higher positive seroconversion rates) against the poultry pathogen Mycoplasma gallisepticum (MG), a bacterium associated with losses of 15.7 eggs/hen over a 45-wk laying period in MG-infected layers as compared with layers maintained free from infection with MG.