1. Pure swards of perennial ryegrass (Lolium perenne L. cv. Melle) or white clover (Trifolium repens L. cv. Blanca) were harvested daily as either primary growth (May--June) or mid-(July) and late-(August-September) season 4-week regrowths and offered to Friesian steers at two levels of feed allowance (1 8 and 24 g dry matter (DM)/kg live weight), to examine the effect of forage species and stage of harvest on nutrient digestion and supply.2. The early-and mid-season grasses had low nitrogen (23 g/kg DM) and high water-soluble carbohydrate (169 g/kg) contents whilst the late-season grass had a higher N content (28 g/kg). All clover diets had high N (average 45 g/kg) and low water-soluble carbohydrate (89 g/kg) contents, and DM digestibility on all diets ranged from 0.77 to 0.83 (mean of two feeding levels).3. Mean total rumen volatile fatty acid concentrations were significantly (P < 0.001) higher on the clover diets, whilst on the grass diets molar proportions of propionate showed a slight but not significant decline with advancing season and tended to be higher than those on the clover diets. Mean rumen ammonia concentrations were significantly (P < 0.001) lower on the early-and mid-season grasses (59 mg NH,-N/I) than the late-season grass (242 mg/l) and early-season clover (283 mg/l) which were all significantly (P <: 0.01) lower than the midand late-season clovers (372 and 590 mg/l) respectively.4. Rates of organic matter (OM) and N digestion in the rumen were estimated using established nylon-bag techniques and found to be high on all diets, but significant effects due to forage species (clover > grass; P < 0,001) were detected, whilst overall potential degradability in the rumen exceeded 0.89 for both OM and N on all diets. 5. Significantly (P < 0.001) more OM entered the small intestine of calves fed on white clover (10.2 g/kg live weight) than those fed on ryegrass (8.33 g/kg) and similar effects due to level of feeding (g/kg; low 7.9, high 10.6; P < 0.05) and stage of harvest (g/kg; early 8.3 v. mid 10.0, late 9.50; P < 0.05) were also detected. Non-NH,-N (NAN) flow (g/kg) to the small intestine was increased by forage species (grass 0.56, clover 0.69; P < 0.05) and stage of harvest (early 0.59 v. mid 0.65, late 0.64; P > 0.05) whilst NAN flow/N intake ranged from 0.96 to 1.65 g/g (mean 1.25) on the grass diets and from 0.64 to 0.84 g/g (mean 0.75) on the clovers (P < 0401). 6. Microbial N flow to the small intestine averaged 0.72 of duodenal NAN (grass 0.76, clover 0.69). Efficiency of microbial N synthesis was high on all diets, (g/kg OM tivly digested in the rumen; grass 33.5, clover 36.3), as was the estimated extent of in vivo feed N degradation (g/g N intake; grass 0.75, clover 0.79). 7. A model is described to simulate the progress curves of the ratio, degraded N:degraded OM in the rumen for the six diets, using indices obtained in the present study. The results are ratified with the in vivo observations of N utilization in the rumen for the grass and clover diets.8. It is concluded that both for...

SUMMARY: This paper describes the scale and nature of agricultural production in urban, suburban and peri-urban zones of

1. A total of twenty Friesian steers were grazed on pure swards of either perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca) from May to late August to examine the effect of forage species and season on nutrient digestion and supply. Within each forage species, two daily allowances of forage (i.e. 30 and 60 g dry matter (DM)/kg live weight) were given, and nutrient flow into the small intestine was measured on thirteen separate occasions (viz. seven grasses and six clovers).2. Total nitrogen content of the grasses varied between 28 (early season), 19 (mid-) and 33 (late) g/kg DM, whilst the clovers showed a much narrower range and all values were higher (39-45 g/kg DM). In vitro organic matter (OM) digestibilities of plucked samples ranged from 742 to 809 g/kg OM (grass) and 712 to 790 g/kg OM (clover), the lowest values being noted in late June (grass) and midJuly (clover).3. OM intakes calculated from estimated faecal OM output (using unlabelled ruthenium) and predicted OM digestibility of the consumed forage indicated mean values of 20.9 (grass) and 26.0 (clover) g/kg live weight ( P <0.001), whilst the higher forage allowances increased OM intake by approximately 8% on both grass and clover (P < 0.01) compared with the low allowance. OM intake was significantly ( P < 0.01) lower on the two primary growths of grass examined in May (mean 16.8g/kg live weight) than the other five grass diets.4. Rumen molar propionate levels declined with season but were at all times higher on the grass than on the clover diets, whilst acetate levels were unaffected by forage species. Apart from the late-season grass, mean rumen ammonia concentration was less than 100 mg NH,-N/I on all grass diets, whilst values on the clover diets ranged from 200-350 mg/l. 5.Daily duodenal OM flows in relation to animal live weight were approximately 20% higher on the clover than on the grass diets (grass 9.2, clover 11.2 g/kg live weight, P < 0.001), but estimates of the proportion of digestible OM apparently digested in the rumen were not significantly influenced by forage species (grass 0.69, clover 6. Non-NH,-N (NAN) flow to the small intestine varied from 0.41 to 0.76 g/kg live weight on the grass diets in response to season and forage allowance compared with values of 0.6W.94 g/kg on the clover diets, with the overall forage species effect being statistically (P < 0.001) significant (grass 0.60, clover 0.76 gfkg live weight).In relation to estimated N intakes, however, these findings revealed a considerable loss of N between mouth and duodenum on the clover diets equivalent to approximately 35% of N intake. 7. A significant regression of NAN flow/unit N intake (NI) (g/g) on N content in the forage OM (g/kg) was obtained for all forages examined:indicating that efficiency of utilization of the N in fresh forages in the rumen was more closely related to forage N content than forage species per se. 0.71).NAN/NI = 1.507-0.0185 m/OM], residual SD 0.007, r 0.929, Forages contribute over 70% of the metabo...

1. Pure swards of perennial ryegrass (Lolium perenne cv. Melle) and white clover (Trifolium repens cv. Blanca)were harvested daily as primary growth (grass in May, clover in June) or regrowths (clover only in July) and offered, in the long form, to growing cattle at a feeding rate of 22 g dry matter/kg live weight. With each forage, two treatments were compared with the untreated forage (C): monensin (100 g active ingredient/kg, 250 mg/d) addition to the rumen (treatment M) or formaldehyde (30 g/kg crude protein (nitrogen x 6.25)) application to the diet (treatment F). The objective of the experiment was to examine means of manipulating N metabolism in the rumen and the duodenal non-ammonia-N (NAN) supply derived from fresh forages. 2.The apparent digestion of ingested organic matter (g/kg) in the rumen was unaffected by treatment M (C 509, M 497) but was significantly ( P < 0.01) reduced by tieatment F (443). The extent of cellulose digestion in the rumen was not affected by any of the treatments imposed and the changes in organic matter digestion were due mainly to effects on N digestion and rumen microbial synthesis. On the untreated diets, duodenal NAN supply averaged 0.74 g/g N intake and treatment M caused a small but non-significant increase (M 0.79 g/g N intake).In contrast, the effect of treatment F was much larger (F 0.91 g/g N intake; P < 0.01). These differences were accompanied by corresponding reductions in rumen NH, concentrations (mg/l; C 350, M 310, F 220; P < 0.001).3. Of the increased flow of NAN to the small intestine observed on the white clover only diets with treatment F, 0.70 was accounted for by an increased net synthesis of microbial N, while treatment M had no effect on microbial N synthesis and a marginal reduction in feed N degradability only with the regrowth white clover diet. Treatment F reduced feed N degradability to a limited extent on both clover diets (C 0.82, M 0.81, F 0.77). No corresponding measurements were made for the ryegrass diets.4. It is concluded that the extensive loss of N from the reticulo-rumen of cattle fed on fresh forages can be reduced by the use of agents to reduce protein solubility. However, the study demonstrated that treatment F may in some circumstances increase N supply to the small intestine more through enhancing microbial N synthesis within the rumen than through increasing the passage of undegraded feed N to the small intestine. The use of monensin, to manipulate proteolytic or deaminative activity in the rumen, or both, was not found to confer any beneficial effects on duodenal-NAN supply.There have been several studies to evaluate the digestion of fresh forages and the nutrient supply arising from such diets (Beever et al. 1971(Beever et al. , 1976(Beever et al. , 1978b Ulyatt & Egan, 1979; VtritC et al. 1984). Recent experiments with growing cattle (Ulyatt et al. Beever et al. 1985 Beever et al. , 1986a have demonstrated that as the amount of nitrogen in the crop increases, considerable losses of N between mouth and duodenum (up to 0.40 of N...

A study of prickly pear was carried out with 100 producers of the fruit using a semi-structured survey to ascertain the nature of cultivation and economic environment. The Prickly pear region includes an area of 12,000 ha, planted with prickly pear variety Opuntia amiclaea, Opuntia violacea and Opuntia matudae. The size of the orchard in the villages studied was of 1-20 ha, with a predominance of 1-3 ha. The productive life for the prickly pear orchard varied between 20 and 60 years. The cow manure is used as a source of organic matter and the dose applied depends on the amount of organic wastes produced by the cattle and age of the cactus (an estimated 500 t ha -1 ). The average volume of fruit production per ha is 10 to 15 t of prickly pear. In economic analysis of gross margin was U.S. $ 1,920.00 per ha, each farmer obtained an average annual gross income of $ 5.376 for an average production. 44.7% (U.S. $ 12.672 million) of these profits are distributed initially in the population, by way of inputs and labor. Sustainability factors equivalent to providing environmental services are discussed.