Estimating yields of salt- and water-stressed forages with remote sensing in the visible and near infrared.

In arid irrigated regions, the proportion of crop production under deficit irrigation with poorer quality water is increasing as demand for fresh water soars and efforts to prevent saline water table development occur. Remote sensing technology to quantify salinity and water stress effects on forage yield can be an important tool to address yield loss potential when deficit irrigating with poor water quality. Two important forages, alfalfa (Medicago sativa L.) and tall wheatgrass (Agropyron elongatum L.), were grown in a volumetric lysimeter facility where rootzone salinity and water content were varied and monitored. Ground-based hyperspectral canopy reflectance in the visible and near infrared (NIR) were related to forage yields from a broad range of salinity and water stress conditions. Canopy reflectance spectra were obtained in the 350- to 1000-nm region from two viewing angles (nadir view, 45 degrees from nadir). Nadir view vegetation indices (VI) were not as strongly correlated with leaf area index changes attributed to water and salinity stress treatments for both alfalfa and wheatgrass. From a list of 71 VIs, two were selected for a multiple linear-regression model that estimated yield under varying salinity and water stress conditions. With data obtained during the second harvest of a three-harvest 100-d growing period, regression coefficients for each crop were developed and then used with the model to estimate fresh weights for preceding and succeeding harvests during the same 100-d interval. The model accounted for 72% of the variation in yields in wheatgrass and 94% in yields of alfalfa within the same salinity and water stress treatment period. The model successfully predicted yield in three out of four cases when applied to the first and third harvest yields. Correlations between indices and yield increased as canopy development progressed. Growth reductions attributed to simultaneous salinity and water stress were well characterized, but the corrections for effects of varying tissue nitrogen (N) and very low leaf area index (LAI) are necessary.

Enhanced low vision rehabilitation for people with age related macular degeneration: a randomised controlled trial.

AIM: To compare the effectiveness of three models of low vision rehabilitation for people with age related macular degeneration (AMD) referred for low vision rehabilitation (LVR): (a) an enhanced low vision rehabilitation model (ELVR) including supplementary home based low vision rehabilitation; (b) conventional low vision rehabilitation (CLVR) based in a hospital clinic; (c) CLVR with home visits that did not include rehabilitation (CELVR), intended to act as a control for the additional contact time with ELVR. METHOD: A single centre parallel group randomised controlled trial in participants' homes and the low vision clinic, Manchester Royal Eye Hospital. People referred for LVR with a primary diagnosis of AMD and visual acuity worse than 6/18 in both eyes and equal to or better than 1/60 in the better eye. The main outcome measures were vision specific quality of life (QoL) (primary outcome, VCM1) and generic health related QoL (SF-36); psychological adjustment to vision loss; measured task performance; restriction in everyday activities; use of low vision aids (LVAs). RESULTS: 226 participants were recruited (median age 82 years); 194 completed the trial (86%). Except for SF-36 physical and mental component summary scores, arms did not differ significantly for any of the outcomes. Differences for the VCM1 were ELVR v CLVR, 0.06 (95% CI to 0.17 to 0.30, p = 0.60); ELVR v CELVR, 0.12 (95% CI to 0.11 to 0.34, p = 0.31); CELVR v CLVR, -0.05 (95% CI -0.29 to 0.18, p = 0.64). Differences for the SF-36 favoured CLVR compared to ELVR (ELVR v CLVR: physical = -6.05, 95% CI -10.2 to -1.91, p = 0.004; mental = -4.04, 95% CI -7.44 to -0.65, p = 0.02). At 12 months, 94% of participants reported using at least one LVA. CONCLUSION: ELVR was no more effective than CLVR. Researchers should be wary of proposing new LVR interventions without preliminary evidence of effectiveness, given the manifest lack of effectiveness of the model of enhanced LVR evaluated in the trial.

An evaluation of the effects of intermittent sulfadoxine-pyrimethamine treatment in pregnancy on parasite clearance and risk of low birthweight in rural Malawi.

The prevalence of infection with malarial parasites and the incidence of anaemia and delivery of infants with low birthweight (LBW) were investigated in 575 Malawian mothers who received one, two or three doses of sulfadoxine-pyrimethamine (SP) during pregnancy. All the subjects were enrolled at their first antenatal visit and all delivered at hospital. The prevalence of Plasmodium falciparum infection at first antenatal visit was 35.3% in primigravidae and 13.6% in multigravidae (P < 0.001). Mean haemoglobin concentration was significantly lower in primigravidae than in multigravidae (8.8 v. 9.5 g/dl; P < 0.001). Of the 233 women tested for HIV infection, 18.8% of the primigravidae and 23.7% of the multigravidae were seropositive. At delivery, there was no significant difference in parasite prevalence in peripheral or placental blood between women who had received one or two antenatal doses of SP. The multigravidae who had received two doses of SP had higher mean haemoglobin concentrations than those who had received just one (P = 0.009) [this difference was not seen in the primigravidae (P = 0.92)]. However, linear regression analysis indicated that the haematinic supplements given to the subjects contributed more to this increase in haemoglobin concentration than the SP. The mean birthweights were higher, and incidence of LBW lower in babies born to primi-and multi-gravidae who had received two or three doses of SP treatment than those seen in babies born to women who had had just one dose (P < 0.03 for each). The odds ratio for LBW in primigravidae compared with multigravidae decreased from 3.2 to 1.0 as the number of SP doses increased from one to three. The benefit of three doses (compared with none) was equivalent to the population-attributable risk of LBW in primigravidae being reduced from 34.6% to 0%. Subjects who were seropositive for HIV were twice as likely to give birth to LBW babies as the other subjects. The use of SP was not associated with maternal side-effects or perinatal complications. The present results indicate that multiple doses of SP taken during pregnancy will lead to a highly significant reduction in the incidence of LBW in infants born to primigravidae, even if the women have HIV infections. This reduction is observable even when parasite prevalence at delivery is high because of re-infections in late pregnancy; reduction in parasite prevalence earlier in pregnancy, as the result of SP treatment, leads to improved foetal growth.

PIP: The effect of antimalarial treatment followed by chemoprophylaxis during pregnancy on low birth weight (LBW) and anemia was investigated in a study conducted in Chikwawa District Hospital, Malawi, in 1993-94. The 575 women from this malaria-endemic community who were enrolled at their first prenatal visit and delivered at the Chikwawa Hospital were included in the data analysis; 24.3% were primigravidae. At enrollment, the prevalence of Plasmodium falciparum infection was 35.3% in primigravidae and 13.6% in multigravidae. At delivery, there was no significant difference in parasite prevalence between women who had received 1 or 2 antenatal doses of sulfadoxine-pyrimethamine (SP). Multigravidae--but not primigravidae--who received 2 SP doses had higher mean hemoglobin levels than those who received just 1 dose; however, linear regression analysis indicated that hematinic supplements contributed more to this increase than SP. The mean birth weights of infants born to primi- and multigravidae who received 2 or more doses of SP were significantly higher than those of infants whose mothers received only 1 dose. The odds ratio for LBW in primigravidae compared with multigravidae decreased from 3.2 to 1.0 as the number of SP doses increased from 1 to 3. The benefit of 3 doses compared with no treatment was equivalent to the population-attributable risk of LBW in primigravidae being reduced from 34.6% to 0. HIV-positive women (18.8% of primigravidae and 23.7% of multigravidae) were twice as likely to have LBW infants than HIV-negative women. The reduction in LBW deliveries was significant even when parasite prevalence at delivery was high as a result of reinfection in late pregnancy.

Epidemiology training for primary health care: the use of computer-assisted distance learning.

The Liverpool Epidemiology Programme, based in the Liverpool School of Tropical Medicine, has designed a series of computer-based modules for use in distance learning. The purpose of this paper is to highlight the role of computers in training health workers in epidemiology in developing countries. The aim of the modules is to provide health workers with solutions to problems which they face in their everyday work. The modules are written in hypertext software for IBM compatible machines and interact with the epidemiological software Epi Info. Four modules are described: LEP-Nut which deals with nutritional surveillance, LEP-Ref which looks at the role of epidemiology within a refugee health care programme, LEP-Surv dealing with health surveillance and LEP-Rap which introduces the concept of rapid appraisal. They are also easily distributed, particularly with the development of the Internet. The modules are carefully evaluated before and after distribution. Issues related to their evaluation and subsequent revision are discussed, in particular is the content important, adequate, communicated and useful? A major advantage of computer-based learning materials is that they can be easily updated with new advancements of knowledge and experience from the field.

Epidemiology of lameness in dairy cattle: the influence of cubicles and indoor and outdoor walking surfaces.

A survey of cubicles and indoor and outdoor walking surfaces on 37 farms served by four veterinary practices in Somerset, Cheshire, Wirral and west. Wales was carried out in 1989 to 1991. A study of the space requirements of Friesian/Holstein cows at pasture showed that they required approximately 240 cm x 120 cm lying space and a further 60 cm lunging space for rising. By these standards, 87 per cent of the cubicles were too short and 50 per cent were too wide or too narrow. Over 1500 observations on cows lying down, rising and standing indicated that only 12 per cent of the cubicles permitted real freedom of movement; 91 per cent of top partition rails were judged to be too low and 70 per cent of bottom rails too low or too high. In addition, the kerb was very high in 76 per cent of the cubicles. As a result, 10 per cent of cows appeared moderately or severely restricted when lying down, 33 per cent when rising and 55 per cent when standing. Over 2000 cubicle beds were also studied; 75 per cent had a concrete base and of those, 63 per cent were judged to have too little bedding and 11 per cent next to none. Higher incidences and prevalences of lameness were associated with limited borrowing space (P < 0.01) low bottom rails (P < 0.05), high kerbs (P < 0.05) and inadequate bedding (P < 0.01). Of 3190 walking surfaces, only 25 per cent were classified as satisfactory in the first winter and 34 per cent in the second. In general, surfaces in silage bays were too rough and those in other sites were too smooth. The farms with the smoothest indoor walking surfaces had a significantly higher incidence of lameness (P < 0.01). Of 3335 outdoor walking surfaces only 25 per cent were classified as satisfactory, and 70 per cent were too rough. The incidence of lameness was not significantly related to these findings.

Incidence and prevalence of lameness in dairy cattle.

A survey was made of 37 dairy farms in Wirral, mid-Cheshire, mid-Somerset and Dyfed, Wales, to assess the incidence and prevalence of lameness in the cows between May 1989 and September 1991. The incidence was obtained from records made whenever a cow was examined for lameness or received preventive foot-trimming. The mean annual incidence was 54.6 new cases per 100 cows with a range from 10.7 to 170.1 and the mean values during summer and winter were 22.9 and 31.7, respectively. The prevalence of lameness was measured by regular visits at which locomotion was scored on a scale of 1 to 5, and the prevalence of lameness was calculated for each visit as the proportion of cows with scores of 3 or more. The mean annual prevalence over the whole period was 20.6 per cent with a range from 2.0 to 53.9 per cent for the 37 farms. The mean prevalences during summer and winter were 18.6 and 25.0 per cent, respectively. The prevalence measured at a single visit in midsummer or midwinter was significantly correlated with the mean prevalence over the whole corresponding period and may be useful as an assessment of the extent of lameness in a herd and the efficacy of control measures. There was evidence that training farmers to recognise early cases of lameness and request veterinary treatment resulted in a marked reduction in the duration of cases of lameness.

Epidemiology of lameness in dairy cattle: description and analysis of foot lesions.

Information from 37 dairy farms, in four regions of England and Wales provided data on 8991 lesions and the preventive trimming of 4837 cows' feet. Of the total of 13,828 forms returned, veterinary surgeons treated 32 per cent and farmers or stockmen 46 per cent. Of the 8645 lesions associated with episodes of lameness, lesions in the hindlimbs accounted for 92 per cent, of which 65 per cent were in the outer claw, 20 per cent in the skin and 14 per cent in the inner claw. Sole ulcers (40 per cent) and white line lesions (29 per cent) were the predominant diseases of horn, and digital dermatitis (40 per cent) was the most common disease of the skin. Subjective assessments showed that sandcrack, penetration of the sole by foreign bodies and interdigital necrobacillosis were associated with the most severe cases of lameness. There was a significant seasonal effect in the reporting of lesions.

Observer variation in field data describing foot shape in dairy cattle.

A qualitative scoring method was devised to describe foot shape in dairy cattle, which relied solely on visual observations. Four independent trained observers used the method to assess the foot shape of 248 cows located on three farms on two different occasions, and the percentages of agreement and near-agreement for intraobserver and interobserver variation on scores for foot shape were calculated. Score assessment methods were suitable for describing features with a broad variation within one score value; reducing the number of observers did not improve best agreement between separate observations by more than 80 per cent.