The relationship between sward structure, ingestive behavior and dietary quality in cattle grazing a Chloris gayana pasture.

The relationship between sward structure, ingestive behaviour (bite size, biting rate and intake rate) and dietary crude protein (CP) content was studied on a Chloris gayana pasture at different growth stages using oesophageally-fistulated steers. As the pasture matured, leaf table height, plan height, disc height, stemminess and standing herbage increased while leaf density and leaf percentage (%) declined. In conjunction with these changes, biting rate and dietary CP declined sharply, while bite size increased. Intake rate remained relatively constant for all sward structures. Animals adjusted biting rates to compensate for changes in bite size and thus maintained rates of intake. Bite size and dietary CP were negatively correlated. It was argued that, in the present study, leaf table height, stemminess, leaf density and leaf % were the main determinants of dietary CP and ingestive behaviour.Keywords: bite size; biting rate; cattle; cattle grazing; chloris gayana; crude protein; dietary crude protein; dundee research station; grazing; growth stage; herbage; intake rate; leaf table height; natal sour sandveld; oesophageal fistula; pasture; south africa; sward structur

An evaluation of the empirical basis for grazing management recommendations for rangeland in southern Africa.

Analysis of over 50 grazing experiments conducted in southern Africa does not support certain management recommendations. Furthermore, the conclusions of some experiments are questionable owing to poor experimental design or confirmation bias. Simple grazing systems using adaptive and opportunistic management are recommendedLanguage: EnglishKeywords: Continuous grazing; Resting; Rotational grazing; Stocking rates; Veld types; animal production; cattle; grazing systems; management; multi-camp systems; range condition; seeding; sheep; stocking rate; grazing management; goats; southern afric

Leaf silicification in grasses - a review.

Silica is absorbed from the soil by many grasses in an active or passive manner depending upon depending upon the species involved. It is carried upwards in the transpiration stream and deposited throughout the plant where it polymerizes to form amorphous silica gel. Deposition appears to be a passive process but some active mechanism may be involved. Deposition follows a set sequence and may be initiated before leaf expansion. Silica benefits most plants but may have adverse effects upon herbivores ingesting this plant silica. A number of possible roles have been suggested for silica deposition in plants such as the "light window" hypothesis or as a defence against large herbivores and these are discussed in the light of the available evidence. It is concluded that leaf silicification evolved in response to invertebrate herbivory and is primarily aimed at reducing tissue loss to these herbivores.Keywords: adaptive significance; benefits; deposition; distribution; functions; grass; grasses; herbivory; hypothesis; large herbivores; leaf; leaves; process; role; silica; silicification; transpiration; uptak

The effect of veld condition on the quality of diet selected by cattle grazing the Natal Sour Sandveld.

The quality of diet selected by steers fistulated at the oesophagous was related to veld condition in a simulated rotational grazing system on the Natal Sour Sandveld. Six camps, ranging in veld condition score from 8, 5 to 53%, were grazed simultaneously for a two-week period in spring, summer, autumn and winter. Fistula samples were collected on the first, middle and last day of a period of occupation in a camp. Samples were analysed in terms of crude protein (CP), in vitro digestibility (IVD) and plant-part (% leaf, % stem and % dead material) composition. Dietary quality in terms of CP, IVP and plant-part composition was not related to veld condition but was dependent largely (P < 0, 01) upon season and to be a lesser extend upon period of occupation in a camp. It was concluded that in sourveld areas, where dietary quality may be limiting, the veld condition score may be a poor index of potential animal production.Keywords: animal production; cattle; cattle grazing; composition; crude protein; digestibility; dundee research station; grazing; in vitro digestibility; leaves; natal sour sandveld; oesophageal fistulas; period of occupation; plant part composition; production; rotational grazing; south africa; veld condition; veld condition scor

Sequence and process of species selection by cattle in relation to optimal foraging theory on an old land in the Natal Sour Sandveld.

The sequence in which cattle grazed four grass species during a grazing period was monitored at four stages through the grazing season. Data collected revealed that: (i) species could be classed as being of preferred, avoided or intermediate acceptability, (ii) grazing of classes always proceeded in a set sequence; cattle first grazed preferred, then intermediate classes but largely resisted grazing avoided species, (iii) classes were grazed at different rates through the grazing period, (iv) utilization of intermediate and avoided classes was largely dependent on the extent of grazing of preferred species and exhibited a threshold relationship and (v) observed trends were in general agreement with those predicted on the basis of optimal foraging theory. The data suggests that non-selective grazing systems may be based upon faulty grazing philosophy.Language: EnglishKeywords: acceptability; acceptability class; Acceptability classes; Cattle; dundee research station; grasses; Grazing rates; grazing systems; Livestock; non-selective grazing; Old land; optimal foraging theory; rate of grazing; south africa; Species selectio

Nutrition of sheep under rangeland conditions

The following chapter addresses specific problems associated with the nutrition of sheep on rangelands, including variable feed quality and water availability, as well as the use of supplementary feeding to correct nutrient deficiencies for sheep grazing in these environments. Variability in feed quality and intake are discussed in terms of spatial (plant, patch and landscape levels) and temporal (short- to medium-term, longer intra-annual, and interseasonal variability) variations in forage quality and supply. The chapter elaborates on sustainable resource management of rangeland systems and feed supplementation under rangeland conditions

Nutrient loss and water quality under extensive grazing in the upper Burdekin river catchment, North Queensland

Increased sediment and nutrient losses resulting from unsustainable grazing management in the Burdekin River catchment are major threats to water quality in the Great Barrier Reef Lagoon. To test the effects of grazing management on soil and nutrient loss, five 1 ha mini-catchments were established in 1999 under different grazing strategies on a sedimentary landscape near Charters Towers. Reference samples were also collected from watercourses in the Burdekin catchment during major flow events. Soil and nutrient loss were relatively low across all grazing strategies due to a combination of good cover, low slope and low rainfall intensities. Total soil loss varied from 3 to 20 kg ha−1 per event while losses of N and P ranged from 10 to 1900 g ha−1 and from 1 to 71 g ha−1 per event respectively. Water quality of runoff was considered moderate across all strategies with relatively low levels of total suspended sediment (range: 8–1409 mg l−1), total N (range: 101–4000 μg l−1) and total P (range: 14–609 μg l−1). However, treatment differences are likely to emerge with time as the impacts of the different grazing strategies on land condition become more apparent. \ud Samples collected opportunistically from rivers and creeks during flow events displayed significantly higher levels of total suspended sediment (range: 10–6010 mg l−1), total N (range: 650–6350 μg l−1) and total P (range: 50–1500 μg l−1) than those collected at the grazing trial. These differences can largely be attributed to variation in slope, geology and cover between the grazing trial and different catchments. In particular, watercourses draining hillier, grano-diorite landscapes with low cover had markedly higher sediment and nutrient loads compared to those draining flatter, sedimentary landscapes. These preliminary data suggest that on relatively flat, sedimentary landscapes, extensive cattle grazing is compatible with achieving water quality targets, provided high levels of ground cover are maintained. In contrast, sediment and nutrient loss under grazing on more erodable land types is cause for serious concern. Long-term empirical research and monitoring will be essential to quantify the impacts of changed land management on water quality in the spatially and temporally variable Burdekin River catchment