Nutritional evaluation of south-west Queensland pastures. 2. The intake and digestion of organic matter and nitrogen by sheep grazing on Mitchell grass and mulga grassland associations

Abstract

The intake and digestion of organic matter and nitrogen by sheep grazing two Mitchell and one mulga/ grassland association was studied under a variety of seasonal conditions. The in vitro digestibility of the diets selected by sheep grazing both pasture types was in the range 60-70% when seasonal conditions were good, but fell to 52.3% and 48.2% for the Mitchell and mulga/ grasslands respectively when the pasture were dry. Digestible organic matter intakes of intact sheep grazing the Mitchell grass pastures were 14.0-16.3 g (kg W)-1 day-1 when seasonal conditions were average to good and 13.5 g (kg W)-1 day-1 after the pastures had dried out. Comparable figures on the mulga/grassland pastures were 17.8-18- 1 g (kg W)- day- with good seasonal conditions and 11.8 g (kg W)-1 day-1 with dry pasture. The nitrogen concentrations in the diets varied from 7 to 26 g/kg OM on the Mitchell grass associations and from 17 to 34 g/kg OM on the mulga/grassland. Apparent digestion of dietary N within the rumen ranged from 70% to 90% on both sites when there was green forage in the diets, but fell to 58.5% and 37.6% on the Mitchell and mulga/grassland respectively when the pastures were drought affected. Under the latter conditions the quantity of amino acid N absorbed from the small intestines was depressed at both sites, as was the efficiency of microbial N production in sheep grazing the Mitchell grass pastures. These findings are discussed in relation to the protein and energy requirements of sheep grazing the two pasture associations.

Forage intake by and site and extent of digestion in beef cattle grazing midgrass prairie rangeland or plains bluestem pasture throughout the summer.

“…Microbial efficiency ( MCOEFF; Table 7 ) was relatively high in respect to other research (Funk et al, 1987a;Stokes et al, 1988). Estimates of MCOEFF for both forage types were within previously reported ranges (NRC, 1985;McMeniman et al, 1986;Minson, 1990). In June and August, intake of ruminally degradable N (RDN)/RDOM was as low as 9 g/kg (Gunter et al, 1995b), which is well below the suggested requirement of 20 g RDN/kg RDOM (McMeniman and Armstrong, 1977;Nolan et al, 1986).…”

Objective `Safe' Grazing Capacities for South-West Queensland Australia: Development of a Model for Individual Properties.

“…The amount of forage eaten (intake) was assumed to be 400 kg/DSE/year (McMeniman et al 1986). The intake of leaf from the mulga tree (Acacia aneura) is also considered in this study and an intake of 600 kg/DSE/year is assumed to be required for maintenance of sheep consuming solely mulga.…”

Near-real time financial assessment of the Queensland wool industry on a regional basis

“…Corbett et al (1987) reported pastures of grasses with C4 photosynthetic pathways may have as little as 50%) of ingested cmde protein degraded in the mmen. McMeniman et al (1986b) found intake of tropical pastures with digestible organic matter levels of 53 and 48% had 58 and 37%) of nitrogen apparenfiy digested in the mmen.…”

“…A much smaller data set existed for mulga grasslands in terms of diet selection, 16 observations of dietary nitrogen were available from the Halton experiment (Beale 1975) and the Arabella (McMeniman et al 1986b) grazing trial. Additionally, the data collected at Halton (13 observafions) required modification for reasons already discussed (table 4.3).…”

“…The potential degradation of protein decreases with decreasing feed quality, as indicated by lower crude protein and digestibihty (Wilson and Strachan 1981, Webster et al 1982, McMeniman et al 1986b. Corbett et al (1987) reported pastures of grasses with C4 photosynthetic pathways may have as little as 50%) of ingested cmde protein degraded in the mmen.…”