Examples of nutritional stress in conifer seedlings caused by competing ericaceous species (e.g. Calluna and Kalmia), have been reported in several parts of the world. Nutritional stress (primarily N deficiency) has been reported in Sitka spruce (Picea sitchensis) plantations growing in association with an ericaceous species, salal (Gaultheria shallon), in coastal British Columbia. Nutritional interference by salal was investigated on a chronosequence of sites up to 10 yr after clearcutting and slashburning. No direct evidence for an allelopathic contribution to the N stress was obtained. However, the rapid accumulation of salal fine roots and rhizomes, and the nutrients contained therein, provides a partial explanation for the observed stress symptoms. Soil analyses and seedling bioassays demonstrated a reduction in fertility in the period 8 to 10 yr after clearcutting and slashburning in comparison to the period 2 to 4 yr, which is believed to impose further nutritional stress on Sitka spruce. It is concluded that the nutritional stress in these Sitka spruce plantations is caused by a combination of (1) salal competition for nutrients and their subsequent immobilization in salal biomass, and (2) declining site fertility caused by the termination of the flush of nutrients (the assert period) that occurs in the immediate post-clearcutting and slashburning period. Sustaining good growth of plantations under such circumstances will require site nutrient management as well as vegetation management. 相似文献
1. An experiment was done under commercial conditions to investigate the physiological effects of isolating broody turkey hens, for 72 h, in sand and wire floored pens on the third, 10th and 16th weeks of production.
2. Hens identified as broody and removed from the flock had higher plasma prolactin concentrations than the laying hens at each of the three experimental stages.
3. Confinement in sand and wire floored pens, induced a decline in plasma prolactin concentrations. This decline probably impeded immediate development of broody behaviour. Alternately, levels of prolactin higher than those of laying hens were again measured 7 and 14 days after treatment during third week but not after the 10 th and 16th week of production.
4. Confinement did not induce consistent changes in luteinising hormone (LH) and progesterone concentrations from one period to an other.
5. An increase in the plasma concentration of D‐(/?)‐hydroxybutyrate was observed in the hens which had an egg present in the oviduct on day 2, 3 and/or 4 of the treatment. Subsequently, a decrease in ovulation rate was observed in the hens with higher concentrations of D‐(β)‐hydroxybutyrate while under treatment, during the 10th week of production.
6. These data confirm that the effectiveness of the traditional methods for broodiness prevention under commercial conditions is related to the induction of a decrease of prolactin. 相似文献
With ileum cannulated sows were tested the apparent precaecal and faecal digestibility of crude nutrients from raw and thermically treated fodder sugar beets of size "Rosamona". Two samples from two different harvest years, differing extremely in the content of disaccharides were tested. The crude nutrient digestibility affected stronger by content of sucrose then by treatment. Fodder sugar beets with contents of disaccharide lower then 400 g/kg DM showed low precaecal and faecal digestibilities. A longer cooling phase decreased the feed value of steamed beets through the microbial attack in the formation of precaecal indigestible sugar alcohols (mannitol). 相似文献
Five field trials evaluated whether immunization of beef cattle prior to weaning, at weaning, or immediately upon arrival at the feedlot with a commercial bovine respiratory syncytial virus (BRSV) vaccine would reduce subsequent treatment for respiratory disease.
Bovine respiratory syncytial virus vaccination was associated with a significant (p<0.05) reduction in treatment rate in one of three groups of calves immunized prior to weaning (−12%) and in calves immunized upon arrival at the feedlot (−4%).
There was no significant (p>0.05) effect of the BRSV vaccine on treatment rate in calves immunized at weaning, in calves immunized upon arrival at the Saskatoon bull test station, or in yearlings immunized upon arrival at the feedlot.
Although the trend in these field trials was to a sparing effect of the BRSV vaccine, the small reduction in treatment rate may not justify the cost of the vaccination program.
Squash mosaic virus (SqMV, comovirus) is seed-transmitted in severalCucurbitaceae. Therefore, the use of virus-free seed is important to prevent establishment of this virus in the Netherlands and to avoid spread to other countries.This study was undertaken to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of SqMV in melon seeds. An antiserum was produced to a serotype 1 isolate from melon. Two ELISA variants were investigated viz. an ELISA variant with simultaneous incubation of sample and enzyme conjugate (ELISA 1) and an ELISA variant with successive incubation of sample and enzyme conjugate (ELISA 2). The sensitivity of ELISA was tested by mixing fluor of ground infected and non-infected seeds in different proportions. SqMV was detected by both ELISA variants at dilutions of 1 160 (1 part of infected flour mixed with 159 parts of non-infected flour) or higher after a substrate incubation period of 4 h. However, ELISA 1 gave relatively higher absorbance values than ELISA 2 for nearly all dilutions. Since ELISA 1 is also faster than ELISA 2, ELISA 1 is advised for routine testing. In these test, using subsamples of 100 melon seeds SqMV is detected reliably. ELISA 1 is now used in the Netherlands for routine-indexing of melon seed lots for SqMV.Samenvatting Het pompoenemozaïekvirus gaat over met het zaad van verscheideneCucurbitaceae. Het gebruik van virusvrij zaad is belangrijk om te voorkomen dat het virus zijn intrede doet in Nederland en zich naar andere landen verspreidt.Een antiserum werd geproduceerd tegen een serotype 1 isolaat van meloen. Met behulp van dit antiserum werd een ELISA ontwikkeld om pompoenemozaïekvirus in zaden van meloen aan te tonen. Twee varianten van ELISA werden vergeleken, namelijk een variant waarbij monster en enzymconjugaat gelijktijdig geïncubeerd werden (ELISA 1) en een variant waarbij monster en enzymconjugaat na elkaar geïncubeerd werden (ELISA 2). De gevoeligheid van de ELISA varianten werd uitgetoetst door meel van zieke zaden in verschillende verhoudingen te mengen met meel van gezonde zaden. Het pompoenemozaïekvirus werd met beide ELISA varianten aangetoond in verdunningen van 1 160 (1 deel meel van zieke zaden gemengd met 159 delen meel van gezonde zaden) of hoger na 4 uur incubatie met substraat. ELISA 1 gaf doorgaans hogere extinctiewaarden dan ELISA 2 voor bijna alle verdunningen. Omdat ELISA 1 ook nog sneller is dan ELISA 2, wordt ELISA 1 aanbevolen voor routinematig gebruik. Wanneer voor routinematig gebruik 100 meloenezaden per submonster getoetst worden, kan het pompoenemozaïek virus betrouwbaar worden aangetoond. In Nederland worden momenteel per zaadpartij 20 submonsters van 100 zaden getoetst. 相似文献
Colleges and universities have an obligation to teach the basis of animal husbandry and welfare and must prepare students so that they can respond effectively to challenges by proponents of the animal welfare and animal rights movements. Veterinary curricula must now contain formal instruction in professional ethics and humane stewardship of animals for accreditation by the American Veterinary Medical Association. It is helpful if students have an understanding of farm animal behavior, stress physiology and methods of assessing welfare prior to learning about the animal welfare/rights movement's philosophies and issues. A review of early judicial practices, "classical" Judeo-Christian philosophy, the philosophy of Rene Descartes, Jeremy Bentham, Albert Schweitzer, and current philosophers and the entertainment media places the movements in perspective. Students should be familiar with such concepts as the mind-body controversy, equality of suffering, self-awareness or intelligence, and speciesism. After acquiring an appreciation of the basics, a knowledge of the issues facing animal agriculture and the arguments for and against each issue are necessary. Graduates of colleges of agriculture need to realize the potential effects the movements can have and take the initiative to improve the image of animal agriculture. 相似文献