A rate equation model of stomatal responses to vapour pressure deficit and drought     

D Eamus  ST Shanahan 《BMC ecology》2002,2(1):8-14

Background  

Stomata respond to vapour pressure deficit (D) – when D increases, stomata begin to close. Closure is the result of a decline in guard cell turgor, but the link between D and turgor is poorly understood. We describe a model for stomatal responses to increasing D based upon cellular water relations. The model also incorporates impacts of increasing levels of water stress upon stomatal responses to increasing D.  相似文献   

片形吸虫病病原的研究概况   总被引：1，自引：0，他引：1  

顾有方  沈永林 《中国兽医寄生虫病》2000,8(2):55-59

片形吸虫病是反刍动物的一种重要的寄生虫病之一，可引起严重的经济损失。近年来有关片形吸虫病病原的研究较为迅速，尤其是病原的种类以及病原代谢的研究更为热烈。本文将从病原的种类及分布、病原的糖类代谢、脂类代谢和蛋白质代谢作一简单概述。  相似文献   

The effects of recreation on freshwater plants and animals: A review     

M.J. Liddle  H.R.A. Scorgie 《Biological conservation》1980,17(3):183-206

This paper reviews the impacts of recreation on freshwater plants and animals. A distinction is made between water- and shore-based activities, and between physical and chemical effects. The impacts of water-based recreation, which result mainly from boating, are discussed in terms of wash, turbulence and turbidity, propeller action, direct contact, disturbance to animals, pollution from outboard motors and sewage. Those resulting from shore-based activities, such as angling and swimming, include trampling and associated effects, as well as sewage and other chemical impacts. The effects of management for recreation are also considered. There is relatively more information on the effects of recreational activities on plants than on animals, but the authors consider that further research is required in both fields. Some possible approaches are presented.  相似文献   

Gas chromatographic determination of polychlorinated biphenyls (as Aroclor 1254) in serum: collaborative study   总被引：3，自引：0，他引：3  

V W Burse  M P Korver  L L Needham  C R Lapeza  E L Boozer  S L Head  J A Liddle  D D Bayse 《Journal of the Association of Official Analytical Chemists》1989,72(4):649-659

A gas chromatographic-electron capture detection method for determining the concentration of polychlorinated biphenyls (PCBs) as Aroclor 1254 (AR 1254) in serum was evaluated through a 2-phase collaborative study. In Phase I, each collaborator's lot of Woelm silica gel (70-150 mesh) was evaluated for elution and recovery of AR 1254, which had been added in vitro at 25 ng/mL to a serum extract. In Phase II, each collaborator analyzed a series of bovine serum samples that contained the following: (1) in vitro-spiked AR 1254; (2) in vivo AR 1254 and 8 in vitro-spiked chlorinated hydrocarbons; (3) in vivo AR 1254 only; (4) 8 in vitro-spiked chlorinated hydrocarbons only; and (5) neither AR 1254 nor chlorinated hydrocarbons above the detection limit of the method. In Phase I, the average recovery of AR 1254 from silica gel for the 6 collaborators was 87.9 +/- 15.44% (mean +/- 1 SD; N = 18; range = 52.3-105.8%). In Phase II, the analysis of in vitro spikes of AR 1254 in serum at 8.58, 16.8, 41.8, and 84.3 ppb gave mean (means) interlaboratory recoveries of 89.0, 83.3, 79.4, and 76.9%, respectively, with within-laboratory (repeatability) relative standard deviations (RSDr) of 18.8, 20.5, 10.2, and 14.1%, respectively, and among-laboratory (reproducibility) relative standard deviations (RSDR) of 21.5, 21.1, 14.6, and 20.8%, respectively. The determination of in vivo AR 1254 in samples containing approximately 10, 25, 50, and 100 ng/mL of AR 1254 resulted in interlaboratory means of 10, 22, 39, and 79 ng/mL, respectively, with RSDr = 6.7, 9.7, 6.4, and 5.8%, respectively, and RSDR = 20.6, 16.0, 10.9, and 10.3%, respectively. The precision of the method for incurred AR 1254 showed a maximum RSDr of less than 10% and a maximum RSDR of less than 21% for a concentration range of 10-100 ng/mL. The accuracy of the method as demonstrated by the mean recovery of in vitro-spiked AR 1254 over a concentration range of 8.58-843 ng/mL was 82.2%. The method has been approved interim official first action.  相似文献   

PHYSICAL BREAKDOWN IN RELATION TO SOIL DEVELOPMENT     

R. J. ST. ARNAUD  E. P. WHITESIDE 《European Journal of Soil Science》1963,14(2):267-281

  相似文献   

Hyperkeratosis induced by sunlight degradation products of the major polybrominated biphenyl in Firemaster     

D G Patterson  R H Hill  L L Needham  D L Orti  R D Kimbrough  J A Liddle 《Science (New York, N.Y.)》1981,213(4510):901-902

Sunlight photodegradation of 2,2', 4,4', 5,5' -hexabromobiphenyl, the major component of Firemaster, gave a mixture that produces severe hyperkeratosis of the rabbit ear. This component in its pure state does not cause hyperkeratosis. One or more of the four major photolysis products must be responsible for this activity. A similar photodegradation pattern was observed for 2,2', 3,4,4', 5,5' -heptabromobiphenyl, the second largest component of Firemaster.  相似文献   

Identification of Polymorphisms in the Osteopontin Gene and Their Associations with Certain Semen Production Traits of Water Buffaloes in the Brazilian Amazon     

ST Rolim Filho  HFL Ribeiro  GMF de Camargo  DF Cardoso  RR Aspilcueta‐Borquis  H Tonhati  KB Nunes  WG Vale  EM Barbosa  KC de Sousa 《Reproduction in domestic animals》2013,48(5):705-709

The osteopontin gene may influence the fertility of water buffaloes because it is a protein present in sperm. The aim of this work was to identify polymorphisms in this gene and associate them with fertility parameters of animals kept under extensive grazing. A total of 306 male buffaloes older than 18 months, from two farms, one in the state of Amapá and the other in the state of Pará, Brazil were used in the study. Seven SNPs were identified in the regions studied. The polymorphisms were in gene positions 1478, 1513 and 1611 in the region 5′upstrem and positions 6690, 6737, 6925 and 6952 in the region amplified in intron 5. The SNPs were associated with the traits, namely scrotal circumference, scrotal volume, sperm motility, sperm concentration and sperm pathology. There were significant SNPs (p < 0.05) for all the traits. The SNP 6690 was significant for scrotal circumference, sperm concentration, sperm motility and sperm pathology and the SNP 6737 for scrotal volume. The genotype AA of SNP 6690 presented the highest averages for scrotal circumference, sperm concentration and motility and the lowest total number of sperm pathologies. For the scrotal volume trait, the animals with the largest volume were correlated with the presence of the genotype GG of SNP 6737. These results indicate a significance of the osteopontin gene as it seems to exert a substantial influence on the semen production traits of male buffaloes.  相似文献   

The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs     

PR Kenyon  ST Morris  DM West 《New Zealand veterinary journal》2013,61(5):321-325

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs.

METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial.

RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning.

CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.  相似文献   

Does sward height grazed by ewes in mid- to late-pregnancy affect indices of colostrum intake by twin and triplet lambs?     

PR Kenyon  KJ Stafford  PCH Morel  ST Morris 《New Zealand veterinary journal》2013,61(5):336-339

AIMS: To determine if sward height grazed by ewes in mid- to late-pregnancy affects subsequent indices of colostrum intake by twin and triplet lambs, and the extent of the variation in colostrum intake between twin and triplet litter-mates.

METHODS: Blood samples were collected from 75 twin and 46 triplet litters, respectively, 24–36 h after birth. Samples were not collected from lambs that died before this age. Lambs were born to ewes which had grazed one of four sward heights (2, 4, 6 and 8 cm) during mid- to late-pregnancy. Serum samples were analysed for gamma-glutamyl transferase (GGT) activities and glucose concentrations. The number of lambs present at weaning was used to determine lamb survival rate.

RESULTS: GGT activities of lambs born to ewes that grazed swards 2 cm high were lower than those born to ewes that grazed swards 4 and 6 cm high (p=0.053 and p=0.037, respectively). Glucose concentrations were higher in twin than triplet lambs (p=0.003) and in lambs born to ewes grazed on swards 6 cm high than those born to ewes grazed on swards 2 cm high (p=0.033). These differences were not evident after correction for differences in birthweight. There was significant (p<0.001) variation within litter-mates for GGT activities and glucose concentrations in both twins and triplets. The blood constituent status of lambs that died before the 24–36 h collection period is not known. However, lambs which died after this period had significantly lower GGT activities (p=0.009) and glucose (p=0.010) concentrations at the time of sampling than those which survived.

CONCLUSIONS: Farmers should ensure twin- and tripletbearing ewes in mid- to late-pregnancy are grazing at least 4 cm of herbage to ensure colostrum intake of lambs in the postpartum period is not adversely affected.  相似文献   

The effect of individual liveweight and condition scores of ewes at mating on reproductive and scanning performance     

PR Kenyon  PCH Morel  ST Morris 《New Zealand veterinary journal》2013,61(5):230-235

Abstract

AIMS: To determine the effects of liveweight (LW) and condition score (CS) of ewes at mating on both mating performance and scanning percentage, and to determine if effects of CS were independent of LW.

METHODS: Two groups of ewes, comprising 1,780 mixedaged Romney (Rom MA) and 692 composite two-tooth (? East Friesian 1/16 Finn 13/16 Romney, Comp TT) ewes were grazed separately with harnessed rams for two reproductive cycles. Romney rams were used for the first 17 days of mating and then replaced on the morning of Day 18 by Suffolk rams. Ewes were weighed and CS assessed on a scale of 0–5 before the introduction of the rams. Ewes were identified as having been mated during the first cycle only, during both cycles, during the second cycle only, or not mated. All mated ewes were scanned using ultrasound, 50 days after the end of mating, and identified as being either non pregnant, single-, twin- or triplet-bearing.

RESULTS: Linear relationships (R²=0.99) between mean LW and CS at mating were evident for both Rom MA and Comp TT ewes and the mean increase in LW per unit increase in CS was greater in the Rom MA ewes (7.88 kg) than the Comp TT (4.78 kg) ewes (p<0.05). Ewes mated in the second cycle only were significantly (p<0.05) lighter than those mated in the first cycle only. In Rom MA ewes, a greater proportion were mated in the first cycle only if CS was .2.0 than if CS was <2.0, and the proportions of ewes mated in the first cycle only or in both cycles did not differ if CS was ≥2.5. In Comp TT ewes, there was no difference in the proportions mated in the first cycle or both cycles, if CS was ≥2.0. Triplet-bearing ewes were heavier than twin-bearing ewes, which were in turn heavier than both singleton-bearing and non pregnant ewes. Twin-bearing ewes had higher CS than both single-bearing and non pregnant ewes (p<0.05) but differences were not significant if LW was included as a covariate. In both Rom MA and Comp TT ewes, greater proportions were non pregnant and lower proportions had twins if CS was <2.0 than if CS was ≥2.0. In Rom MA ewes only, a greater proportion again had twins and a lower proportion had singletons if CS was ≥3.0 than if CS was <3.0. In Comp TT ewes, the proportion that were non pregnant or twin-bearing did not vary with CS if CS was ≥2.0. Reproductive performance was maximal for Rom MA and Comp TT ewes that had CS at mating ≥3.0 and ≥2.0, respectively, equating to LW of 62.6 and 48.5 kg, respectively.

CONCLUSIONS: In both groups of ewes, CS and LW at mating positively affected reproductive performance measured at the time of mating and at scanning, however, no reproductive advantage was evident above a minimum CS of 3.0 and 2.0, equating to LW of 62.6 and 48.5 kg, for Rom MA and Comp TT ewes, respectively. Sheep farmers should direct management to ensure that no ewes are below these minimum targets rather than ensuring high average LW and/or CS of a mob.  相似文献