Herbage intake by cattle on tarchonanthus veld in the Northern Cape as affected by stocking rate and grazing system 1

Abstract

In a trial with young Bonsmara cattle, four different stocking rates (10, 7, 6 and 4 ha/large stock unit) were applied in both a rotational and continuous grazing system. Feed intake was estimated during spring, summer, autumn and winter for four consecutive years starting in 1977.

Irrespective of the grazing system, feed intake declined with an increase in stocking rate. On average the highest intake was recorded in January and reached the lowest levels in October and July.

Livemass gain was found to be closely related to feed intake.     

Deactivation of the biological activity of paraquat in the soil environment: a review of long-term environmental fate

During the many years of paraquat usage, wide ranges of investigations of its environmental impact have been conducted. Much of this information has been published, but key, long-term field studies have not previously been presented and assessed. The purpose of this review is to bring together and appraise this information. Due to the nature of paraquat residues in soils, the major part (some 99.99%) of a paraquat application that reaches the soil within the typical Good Agricultural Practice (GAP) is strongly adsorbed to soils of a wide variety of textures. This is in equilibrium with an extremely low concentration in soil solution. However, the paraquat in soil solution is intrinsically biodegradable, being rapidly and completely mineralized by soil microorganisms. The deactivation of the biological activity of paraquat in soils, due to sorption, has been investigated thoroughly and systematically. It is recognized that the determination of total soil residues by severe extraction procedures provides no insight into the amount of paraquat biologically available in soil. Consequently, the key assay developed for this purpose, namely, the strong adsorption capacity-wheat bioassay (SAC-WB) method, has proved to be valuable for determination of the adsorption capacity relevant to paraquat for any particular soil. This method has been validated in the field with a series of long-term (>10 years) trials in different regions of the world. These trials have also shown that, following repeated applications of very high levels of paraquat in the field, residues not only reach a plateau but also subsequently decline. This demonstrates that the known biodegradation of paraquat in soil pore water plays an important role in field dissipation. The biological effects of paraquat in the field have been assessed under unrealistically high treatment regimes. These trials have demonstrated that the continued use of paraquat under GAP conditions will have no detrimental effects on either crops or soil-dwelling flora and fauna. Any such effects can occur only under extreme use conditions (above the SAC-WB), which do not arise in normal agricultural practice.     

Sudden acquired retinal degeneration ('silent retina syndrome') in two dogs.

Two unrelated adult dogs developed idiopathic, acute-onset, bilateral total blindness. The ophthalmoscopic changes were minimal and no electroretinographic response could be detected in either dog. The retinas were examined ultrastructurally 10 days (dog 1) and two-and-a-half months (dog 2) after they became blind. There was widespread loss of the outer segments of rod and cone photoreceptors. Where the outer segments persisted, there was marked tubulovesicular change with loss of normal orientation in their lamellae. Second order neurons (bipolar cells) and ganglion cells were unaffected. The cause of this selective and massive disruption of rod and cone endings was not established, but acute toxicity is proposed as a possible mechanism.     

Colonic adenocarcinoma with osseous metaplasia in a horse

Rectal palpation of a 30-year-old mixed-breed mare with chronic weight loss and intermittent, refractory abdominal pain revealed a mass in the right caudoventral portion of the abdomen. Hematologic and serum biochemical findings were normal except for slight mature neutrophilia and mildly high alkaline phosphatase activity and total bilirubin concentration. Cytologic examination of a specimen obtained by abdominocentesis revealed equal numbers of nondegenerative neutrophils and macrophages, but no evidence of neoplastic cells. The mare continued to have signs of abdominal discomfort and was euthanatized. Necropsy revealed a large mass at the junction of the right dorsal colon and transverse colon, and several smaller masses in the liver. Histologic characteristics of the small-colon mass were consistent with colonic adenocarcinoma with osseous metaplasia.