Search

The benefits of white clover ( Trifolium repens L.) in pastures are widely recognized. However, white clover is perceived as being unreliable due to its typically low content and spatial and temporal variability in mixed (grass-legume) pastures. One solution to increase the clover proportion and quality of herbage available to grazing animals may be to spatially separate clover from grass within the same field. In a field experiment, perennial ryegrass ( Lolium perenne L.) and white clover were sown as a mixture and compared with alternating strips of ryegrass and clover (at 1·5 and 3 m widths), or in adjacent monocultures (strips of 18 m width within a 36-m-wide field). Pastures were stocked by ewes and lambs for three 10-month grazing periods. Over the 3 years of the experiment, spatial separation of grass and clover, compared with a grass-clover mixture, increased clover herbage production, although its proportion in the sward declined through time (0·49-0·54 vs 0·34 in the mixture in the first year, 0·28-0·33 vs 0·15 in the second year and 0·03-0·18 vs 0·01 in the third year). Total herbage production in the growing season in the spatially separated treatments decreased from 11384 kg DM ha−1 in the first year to 8150 kg DM ha−1 in the third year. Crude protein concentration of clover and grass components in the 18-m adjacent monoculture treatment was greater than the mixture treatment for both clover (310 vs 280 g kg−1 DM) and grass (200 vs 180 g kg−1 DM). There was no clear benefit in liveweight gain beyond the first year in response to spatially separating grass and clover into monocultures within the same field. [ABSTRACT FROM AUTHOR]

He, C, and Sr isotopes are used to infer spring sources in a water-stressed area. Spring-water origins and pathways in the Cuatrociénegas Basin are revealed by linking structure and geochemistry via regionally extensive fault networks. This study presents the fi rst dissolved noble gas and He isotopic data from northeastern Mexico. Basementinvolved faults with complex reactivation histories are important in northeastern Mexico tectonics and affect hydrogeologic systems. The importance of faults as conduits for northeastern Mexico volcanism is recognized, but connections between faulting and the hydrogeologic system have not been extensively investigated. This research tests the hypothesis that Cuatrociénegas Basin springs are divided into two general classes based upon discharge properties: (1) regional carbonate aquifer discharge (mesogenic) mixed with contributions from deeply sourced (endogenic) fluids containing 3He and CO2 from the mantle that ascend along basement-involved faults; and (2) carbonate aquifer discharge mixed with locally recharged (epigenic) mountain precipitation. Carbonate and/or evaporite dissolution is indicated by Ca-SO4 hydrochemical facies. He isotopes range from 0.89 to 1.85 RA (RA is the 3He/4He of air, 1.4 × 10-6) and have minimal 3H, from which it is inferred that basement- involved faults permit degassing of mantle-derived He (to 23% of the total He) and CO2 ( pCO2 10-1 atm). Mantle degassing is compatible with the thinned North American lithosphere, as shown in tomographic images. Sr isotopes in both Cuatrociénegas Basin springs and spring-deposited travertine (87Sr/86Sr = 0.707428-0.707468) indicate that carbonate rocks of the regional Cupido aquifer (87Sr/86Sr = 0.7072-0.7076) are the main source of Sr. Rock-water interactions with mafi c volcanic rocks (87Sr/86Sr = 0.70333-0.70359) are not inferred to be an important process. Groundwater-dissolved inorganic C origins are modeled using major elements and C isotopes. C isotope data show that ∼30% ± 22% of CO2 in spring water is derived from dissolution of aquifer carbonates (Ccarb = 30%), 24% ± 16% is from soil gas and other organic sources (Corg = 24%), and 46% ± 33% is from deep sources [Cendo (endogenic crust and mantle) = 46%]. This study demonstrates the presence of mantlederived 3He and deeply sourced CO2 that ascend along basement-penetrating faults and mix with Cupido aquifer groundwater before discharging in Cuatrociénegas Basin springs. [ABSTRACT FROM AUTHOR]

The principles of maedi-visna eradication programmes were applied to a field trial for the eradication of ovine pulmonary adenocarcinoma (OPA). In two maternal flocks the prevalence of gross and histological lesions in slaughtered animals was 18.3 per cent and 29.8 per cent, respectively. The lambing period was supervised for three consecutive years from 1999 to 2001, during which the lambs were taken away from their mothers at birth, deprived of maternal colostrum, and hand-reared away from other sheep. Over the three-year period, 322 hand-reared animals, mainly male lambs between 10 and 14 months old, were slaughtered; their lungs were examined grossly, 52.5 per cent of them were examined histologically, and 105 samples of caudal mediastinal lymph nodes were examined by PCR. NO OPA tumours were detected in the slaughter specimens from the derived flock, but one lamb had histological lesions in one lung location; intrauterine transmission was ruled out in this case. No clinical OPA has subsequently been observed in the hand-reared flock. Bronchoalveolar lavage samples from the breeding stock were examined by PCR in order to rule out further subclinical cases of OPA. NO Jaagsiekte retrovirus was detected in any of the 488 samples. [ABSTRACT FROM AUTHOR]