4. RUMINANT LIVESTOCK PRODUCTION SYSTEMS

Main production systems
Cattle and sheep growth depends on diet, and therefore the following systems can be distinguished:

1. Rearing animals on natural pastures, with loss of weight in winter (15 to 25 kg), large weight gains in spring and moderate gains in summer and autumn. Often, in these conditions, when a steer is a year old it weighs less than when it was six months. The growth curve has a saw tooth shape characteristic of growing animals on natural pastures and is the result of the low feeding level. When a “campo steer” is three years old, it can weight 330 to 380 kg and needs more than 160 kg until slaughter weight. This implies one more year of fattening.
   
2. Rearing animals on improved pastures, for which varied technological options exist, is based on obtaining weight gains in winter which allow stock to take better advantage in spring and summer to accelerate growth. A steer often reaches 380 kg at the age of two and with less than a year of fattening could be slaughtered.
   
3. In intensive rearing systems weights greater than 350 kg per year are attained when steers are a year old and inclusive slaughter weights above 440 kg.

Steers raised on natural pasture, 50 percent of the present offtake, have, generally, low daily liveweight gains (0.3 kg/day) during the year, with losses in winter, which necessitate a late age to slaughter and heavy weight. This type of animal is associated with extensive production systems, based on natural pastures, with low input levels and investment, simple management practices, with low meat production (60 to 70 kg/ha/year).

Natural pasture of average quality allows weight gains of 0.25 kg/day and meat production of around 80 to 100 kg/year. Campos of good quality allows greater weight gains (of 0.35 kg/day) and production of up to 150 kg/year. The technologies of strategic feeding and supplementation on the campos (with concentrates, forage reserves or rationed grazing of cultivated pastures) allow the constraints of energy and protein of the forage to be overcome. Its use is more efficient when used to correct the low ranks of gain. The main source of energy concentrates used are grains and agro-industrial by-products produced in the country such as corn, sorghum, wheat, barley, oat, bran rice, wheat and rice bran, gluten feed, citrus pulp. The most used protein concentrates come from agro-industrial production: meat and bone flour, blood flour, fish flour, expeller sunflower, and soybean and bean flour.

Campo improved by over-seeding shows substantial increases in daily gain (0.6 to 1.0 kg/day) and production of meat/ha (greater than 250 kg/year). Cultivated pastures, annual and “perennial”, allow average gains of 0.6 to 1.3 kg/day and meat production from 240 to 400 kg/year. Correct management of the grazing system is the key to taking advantage of its high productivity and quality of the forage produced and to obtain high production of meat per hectare. The available technologies of strategic supplementation have been very important in correcting deficiencies of these pastures and to maintain high stocking rate throughout the year. Its effect is reflected in improvements in the daily gain but fundamentally in a greater production of meat (450-800 kg/ha).

According to the campo characteristics, associated with mixed grazing with set stocking, cattle production has several limitations mainly due to nutritional restrictions. Some of most important are: advanced age of mating of heifers (three years on average); low calving rate (65 percent); low liveweight gains of calves with consequent low weaning weight (130-140 kg); late slaughter (four years) and low rate of off take (18-20 percent). In such conditions the production of meat in extensive systems with outdoors grazing year round in natural pastures is around 65 kg/ha/year.

Livestock grazing natural pastures depend almost exclusively on the nutrient contents of the pasture, which varies with the different seasons of the year. The crude protein (CP) (N x 6.25) levels of native species are lowest during summer and highest during winter. In summer many of the species flower and seed, particularly the grasses. The level of CP that the majority of native species provide is enough to satisfy the needs of cattle but ewes that give birth at the beginning of the spring have some deficiencies at the end of the gestation. The P levels of the natural pastures are also lowest in summer and highest in winter. In spring and summer the amount of P is not enough to cover the requirements for maintenance (of sheep and cattle) and this unbalance rises during the lactation. In order to cover these deficiencies, animals are fed in the field, mixing phosphates (monocalcic, bicalcic or tricalcic) with salt (Na Cl). In spring and summer calving takes place and cows and ewes are in full lactation; mating of the cows takes place in summer. Although there is no clear evidence that Na and Cl are deficient, farmers use them as a supplement all year round. The Ca content of the grasses and forbs is enough to cover the needs of cattle and sheep (see: Berretta, 1998; Montossi et al., 2000). Sometimes, deficiencies in Cu and I [Iodine] are reported, but they are not so important. Cu toxicity has been reported in sheep grazing red clover.

Table 6 compares two management systems, with or without sheep, in basaltic campos. Both systems have been evaluated over four years in grazing conditions with continuous stocking and stocking rate of one cow equivalent per hectare.

Considering the high stocking rate and the simple management used, the results show higher animal productivity than those obtained in extensive production systems. The annual differences in the rates of calving and weaning are the main factors that determine animal productivity. Weaning rates are higher in the system with cattle alone, whereas in the mixed system weaning weight and total productivity are greater (Berretta et al., 2000).

The effects of different strategies of feeding, management and sanitary control have their effect on flock productivity. Research is oriented to improve the efficiency of wool and meat production, considering the quality of both products.

Table 7 shows different technological options adapted to different conditions of extensive production systems. The levels of feeding breeding ewes in the traditional systems are insufficient during the last third of the gestation, with consequent low weight and poor condition score (CS) at the time of lambing. This has negative effects on survival of the lambs (20 to 30 percent of mortality), being the main cause of low reproductive performance of the national flock. CS represents energy store (fatness), scored from 1 (skinny) to 5 (over fat) scale.

To improve the reproductive performance of ewes carrying only one lamb and reduce their mortality to 10 percent, it is necessary to stockpile forage, accumulating between 1,300 and 1,500 kgDM/ha of forage (5 to 8 cm of height) at the beginning of the last third of pregnancy. The CS of Corriedale sheep at birth must be between 3 and 3.5 degrees.

On improved campo, with a stocking rate twice (10 sheep/ha) that of non improved campo, and the same CS at birth, it is possible to reach a lamb mortality of 10 percent. The recommended amount of deferred forage must be between 1,900 and 1,100 kgDM/ha, equivalent to an approximate height of 7 and 4 cm, respectively. The quality and quantity of forage will depend on the proportion of legumes in the improved campo.

Considering the autumn average growth rate of campo and improved campo on the basaltic zone and the normal lambing season, it is necessary to begin the deferring period between 70 and 50 days in the campo, and between 40 and 30 days in the improved campo, before lambing. These values also depend on the meteorological conditions of each year and their effect on the pasture growth and also on the amount of existing forage at the beginning of the accumulation period.

Most hoggets are mated at thirty months (4 teeth) since a high proportion (40-60 percent) do not reach the minimum mating weight at eighteen months. This has adverse productive and economic consequences for the industry, when the number of lambs per ewe throughout their life is reduced, affecting the advancement of the genetic improvement of the flock and the level of efficiency of the resources used by the producer. In order to improve lamb supply, it is very important to increase the reproductive rate of hoggets.

Several management strategies have been defined to improve hogget liveweight gain in extensive production systems in campo on basaltic zone. The use of improved campo and annual forage crops allow the reaching of adapted gains of liveweight during winter (60 to 90 gr/animal/day). These rates of gain allow a higher number of hoggets (80-90 percent) to reach the first mating liveweight recommended when having two teeth, weights greater than 32 and 35 kg for hogget Merino and Corriedale, respectively. For a hogget to obtain these weight gains during winter a minimum sward mass of 1,500 kgDM/ha is necessary, with a sward height of five to six centimetres in the campo and 1,000 kgDM/ha, with a height of four to five centimetres in improved campo (Berretta, 1998).

The Animal Health Department of the Ministry of Agriculture and Fisheries, is carrying out a compulsory eradication programme for Foot and Mouth Disease, ticks (Boophilus microplus, responsible for transmission of Piroplasma and Anaplasma), Brucellosis and Tuberculosis. An epidemiological surveillance and monitoring programme is being implemented for Bovine Spongiform Encephalitis (BSE) [see Ministry of Livestock Agriculture and Fisheries and European Commission Report ]. For sheep there are compulsory eradication campaigns for ectoparasites (mange and lice).

5. THE PASTURE RESOURCE

The scarce data from the first colonists allow some inferences to be drawn about the original vegetation. The primitive population, through hunting for food or inter-tribal conflicts, caused changes in vegetation through the use of fire, as the existing herbivores were small compared to current cattle and horses, the most important being deer (Ozotocerus besoarticus) and ñandú (Rhea americana). Deer live together with cattle but are displaced by sheep, therefore the existing number of deer is very small and in protected areas. The ñandú, a running herbivorous bird of 1.5 metres in height, lives currently in campos together with cattle, sheep and horses, particularly where the agriculture is not developed.

The climax vegetation, hypothetically, before the introduction of cattle and horses, would have had a larger proportion of bushes and shrubs, particularly the genus Baccharis. In some wetter habitats, tall herbs and grasses, commonly named “straws” could prevail. Generally the campo would have had more humidity due to the accumulation of dead material from big forbs and bushes that would stop rain water running off, while mulch would protect soil from water stress, thus keeping humidity excesses for much longer periods. Annual native species and small forbs have probably a rupestral origin; at present the most frequent annual species are exotic.

Cattle and horses were the first large domestic herbivores introduced to the country by Hernandarias in 1611. Sheep increased by the mid nineteenth century. Human action, through the introduction of domestic animals to the natural grassland system, has caused changes in vegetation life forms so grazing is the main factor which keeps the campos in a herbaceous pseudo-climax phase.

The present state of natural pastures is far removed from their potential. In the climax there would be a prevalence of bushes and tall grasses of low palatability and nutritive value; though they can be biologically productive, they would be poorly suited to feeding cattle and horses. Therefore, the present situation of pastoral disclimax seems to be more suitable for feeding grazing animals.

In this situation of pastoral disclimax, soil that has never been cultivated can suffer from degradation, particularly under high stocking rates. It can recover, except in extreme situations of impoverished and eroded soil degradation, by excluding grazing for long periods and with careful subsequent management. The application of low doses of inorganic fertilizers and the introduction of legumes in some of these stages allow the pasture to be taken to a better condition.

When areas that have been grazed for centuries are excluded from grazing, changes occur in their floristic composition. In an area which has been protected since 1984, the beginning of caespitose grasses, and a reduction of small ones was observed; also sub-shrubs and bushes like Eupatorium buniifolium, Baccharis articulata, Baccharis spicata, and Baccharis trimera begin to grow, whereas Baccharis coridifolia decreased since it thrives when grasses are weakened due to grazing. After six years Baccharis dracunculifolia was recorded, a bush three metres high, with branches easily breakable by domestic animals. The Baccharis articulata population persisted for about five years, when plants died almost simultaneously; after a similar period the population had resettled and died again and actually new plants are developing. The original individuals of Eupatorium buniifolium persist and there are younger ones too. The size of grass tufts increased and the number of individuals like Stipa neesiana, Paspalum dilatatum, Rottboellia selloana, Schizachyrium microstachyum decreased. Grasses of very low frequency and scarce flowering under grazing conditions, like Paspalum indecorum, Schizachyrium imberbe, Digitaria saltensis, show a large development in this situation. The native legumes, though infrequent, have also a larger development. With continued exclusion of grazing a high storage of litter is also produced which brings about important alterations in soil water retention, which, together with the height of grasses and bushes, modifies the microclimate. Therefore, the described situation could be somewhat similar to that previous to the introduction of cattle.

Vegetation. Most important campos types
Natural Campo is defined as a vegetative cover formed by grasses along with herbs and associated shrubs, where trees are scarce. The campo is an environment with great species richness, plants as well as animals.

The most numerous botanical family is the Gramineae = Poaceae, with about 400 species, both summer (C4) and winter (C3) ones, this association a remarkable characteristic of these pastures. The most important tribes are: Paniceae, which includes the genera with the largest number of species, Paspalum, Panicum, Axonopus, Setaria, Digitaria, etc.; Andropogoneae, with the genus Andropogon, Bothriochloa, Schizachyrium, etc.; Eragrostea, with the genus Eragrostis, Distichlis, etc.; Chlorideae, with the genus Chloris, Eleusine, Bouteloua, etc., with few species. The tribes of winter grasses, a high number of cultivated species are adapted to these conditions, are: Poeae (= Festuceae), with the genera Bromus, Poa, Melica, Briza, Lolium, Dactylis and Festuca, etc.; Stipeae, with the genera Stipa and Piptochaetium, with majority of native species; Agrostideae, with the genus Calamagrostis, Agrostis, etc., with scarce species (Rosengurtt et al., 1970). In general the presence of winter species is associated with soil type, topography, altitude, fertility and livestock management. Along with the Gramineae there are different vegetative type species, belonging to other families such as: Compositeae (= Asteraceae), Leguminoseae (= Fabaceae), Cyperaceae, Umbelliferae, Rubiaceae, Plantaginaceae, Oxalidaceae, etc. Native herbaceous legumes are represented by many genera: Trifolium, (T. polymorphum, T. grandiflorum, T. argentinense, T. riograndense) Adesmia, Desmodium, Desmanthus, Galactia, Zornia, Mimosa, Tephrosia and Stylosanthes; nevertheless, the sum of their frequencies is very low, always less than three percent in all types of campos, except in very particular habitats.

Campo types dedicated to extensive livestock systems, with a low degree of modification correspond with the main types of soils and agro-ecological zones previously defined (Figures 4 and 6). The floristic characteristics of each type of campo are given firstly by the type of soil, its physical and chemical conditions and to a lesser extent by the topography and the exposure to solar radiation.

Some species are present in different types of campos with variable frequencies; others are present in some, while others are characteristic and indicators of certain habitats. Within each type of campo gradients of vegetation associated with the location according to the topographic position exist (hill, slope, valley) that, due to the differences in soil depth and to the conditions of humidity, develop particular habitats which stand out in the landscape physiognomy. In these habitats characteristic species which are not present in the campo, can be found. In marshland, paludal species like: Cyperus spp., Heleocharis spp., Canna glauca, Leersia hexandra, Luziola peruviana, Paspalum hydrophillum, Pontederia cordata, Sagittaria montevidensis and Thalia spp. are found.

In all campos perennials of different botanical families predominate, annuals generally have a low frequency but become conspicuous at some seasons of the year or by the effect of management such as grazing methods, fertilization, legume introduction, etc.

In campos plant communities it is possible to establish a relationship between the percentage of the species that compose them and their contribution to the soil cover. Research on different vegetation types, throughout the seasons of the year, shows variable relations between 30/70 and 20/80, resulting in 30 percent of species producing 70 percent of the forage. In most of the native plant communities, about 12 species contribute 70 to 80 percent of the total forage. This relationship is kept around the year, but there are some changes in the type of species. Species identification in the different communities is very important to follow the changes occurring in the communities mentioned, which are related to climatic factors and grazing management (Berretta, 2001a; 2001b).

In Table 8. Daily Growth Rates (DGR), their standard deviation and the production Seasonal Distribution (SD) of different campo types are detailed. On some soils growth according to depth or topographic position is shown which leads to vegetation types composed of different species or different frequencies.

On campos on Basaltic soils (group I, 1) three main types of vegetation can be distinguished, directly related to soil depth. On shallow brown red soils (SBR) vegetation covers 70 percent approximately, stones or rocks being 10 percent, and the rest bare soil and litter; these values have some oscillations with the seasons and change noticeably during drought. The DGR, expressed in kgDM/ha/day, varies according to the season and between years. The greater proportion of annual forage production is in spring and summer, this season is the one that presents greater variability due to the high risk of drought on this type of soil. The most frequent species are: Schizachyrium spicatum, Chloris grandiflora, Eragrostis neesii, Eustachys bahiensis, Microchloa indica, Bouteloua megapotamica, Aristida venustula, Adesmia punctata, Dichondra microcalyx, Eryngium nudicaule, Micropsis spathulata, Soliva pterosperma, Oxalis spp. and Selaginella spp.

In the same type of soil, but with an A horizon about 15-20 cm deep, other species are found, such as the summer grasses, Paspalum notatum, Bothriochloa laguroides, and the winter grasses, Stipa neesiana, Piptochaetium stipoides and Piptochaetium montevidense. The presence of these more productive grasses causes changes in the seasonal distribution, with spring and autumn the seasons of greater production, although total annual production is similar.

On shallow black soils plant cover is 80 percent, the dead material and bare soil vary between and within the seasons. The most frequent species are: Schizachyrium spicatum, Chloris grandiflora, Eustachys bahiensis, Bouteloua megapotamica, Aristida murina, Aristida uruguayensis, Carex spp., Dichondra microcalyx, Eryngium nudicaule, Chaptalia piloselloides, Oxalis spp., Nostoc spp. and Selaginella spp. Less frequent are Stipa neesiana, Piptochaetium stipoides, Bothriochloa laguroides, Paspalum notatum, Paspalum plicatulum, Rottboellia selloana, Trifolium polymorphum, and Adesmia bicolor.

When the top horizon is deeper most of the species previously mentioned as having low frequency when the soil is shallow, become frequent. Annual total forage production in these deeper parts is rather higher, but the seasonal distribution is different, spring and autumn being the seasons of greater growth, with a little over 70 percent of the total.

Deep soils of greater fertility have a plant cover about 90 percent, dead material being the other component of importance. The main species of these soils are: Paspalum notatum, Paspalum plicatulum, Paspalum dilatatum, Paspalum indecorum, Rottboellia selloana, Panicum milioides, Andropogon ternatus, Bothriochloa laguroides, Axonopus affinis, Aristida uruguayensis, Leptocoryphium lanatum, Schizachyrium microstachyum, Schizachyrium spicatum, Carex spp., Stipa neesiana, Piptochaetium stipoides, Piptochaetium bicolor, Piptochaetium medium, Poa lanigera, Bromus auleticus, Calamagrostis spp., Trifolium polymorphum and Adesmia bicolor. The main weed in basaltic campos is Baccharis coridifolia, a toxic shrub.

On basaltic soils the spatial variability is emphasized, related to the intricate mosaic formed by these different types of soils. This edaphic variability is reflected in different vegetation types which, by the type of species that compose them, require different management. To this spatial variability it is necessary to add that related to the climate, particularly rainfall.

Campos on granitic soils (group III, 4A and 4B) also have different productivity associated with changes in soil depth. Campos production over deep soils reaches 4,125 kgDM/ha/year, concentrated in spring and summer (Table 8). The vegetation of these soils has a high proportion of summer species but is scarce in winter species. The most frequent species are: Andropogon ternatus, Rottboellia selloana, Paspalum notatum, Paspalum plicatulum, Paspalum dilatatum, Bothriochloa laguroides, Axonopus affinis, Aristida murina, are summer growers; the winter species are: Stipa charruana, Briza subaristata, Piptochaetium stipoides, Piptochaetium lasianthum, Agrostis montevidensis, Vulpia australis, Gaudinia fragilis, Carex spp. or forbs such as Chevreulia sarmentosa, Eryngium nudicaule and Micropsis spathulata.

Annual production of the campos of Eastern hillocks (Lomadas) is 3,626 kgDM/ha/year and about 2,100 kgDM/ha/year in the East Sierras. Most campos species, 80 to 85 percent, are summer perennials. In spite of the biodiversity, the number of species that contribute to forage production is low. The association Paspalum notatum - Axonopus affinis, is the main contributor. The forage normally has low digestibility (48-62 percent).

On sandy soils (group IV, 5A) changes in the proportions of species of the campos are mainly associated with topographic position. In Table 8 the rate of daily growth and the seasonal distribution of forage production of a high slope and on a low slope, in the same topographic sequence, are shown. The annual production of the high slope is 5,144 kgDM/ha and of the low slope is 5,503 kgDM/ha. In this type of campo production is concentrated in spring and summer, with 80 percent of the total. This is related to soil physical characteristics (water depth, texture, water storage, etc.) and mainly, to a vegetation dominated by summer species such as: Paspalum notatum, Axonopus argentinus, Axonopus affinis, Sporobolus indicus, Rottboellia selloana, Panicum milioides, Panicum sabulorum, Andropogon lateralis, Paspalum nicorae and Eragrostis purpurascens - a characteristic plant of these soils. The most frequent winter grass is Piptochaetium montevidense. Forbs such as: Soliva pterosperma, Eryngium nudicaule, Chevreulia sarmentosa, Chevreulia acuminata, Oxalis spp., Dichondra microcalyx, Spilanthes decumbens, Richard humistrata, Hypochoeris spp. and Hypoxis decumbens, are relatively frequent. Native legumes are less frequent, Desmodium incanum being the most representative. The main weeds are: Baccharis coridifolia and Vernonia nudiflora.

It is common practice, on these soils to burn at the end of winter, to refine the campo and obtain a tender regrowth, free of dead material and therefore of better quality, in spring. The summer hard grasses, with high annual yield but low quality, stand out from the sward and have little or no palatability for domestic animals, except in very particular circumstances, so dry leaves and floral culms accumulate in winter, when they become even less palatable. The main species with these characteristics are: Erianthus angustifolius, Paspalum quadrifarium, Andropogon lateralis, and Schizachyrium microstachyum, in conjunction with some shrubs and bushes which grow in these conditions and lead to “dirty” campos.

The natural plant communities of the campos of the Northeast (groups III and V, 5B) are rich from the point of view of the number of species present; it is possible to find between 50 and 60 species in an area of 12 m². Thirty percent of the species represent 70 percent of the plant cover. The most abundant species are grasses of which 70 percent are summer growing. Through different practices of management in some cases the pastures are covered by small shrubs or include native trees. Under grazing the proportion of legumes is small. The most frequent plants are: Paspalum notatum, Paspalum dilatatum, Bothriochloa laguroides, Rottboellia selloana, Axonopus affinis, Panicum milioides, Setaria geniculata, Sporobolus indicus and Eragrostis neesii of summer growth and cool season species, less frequent, represented by Piptochaetium stipoides, Piptochaetium montevidense, Stipa neesiana, Stipa charruana, Chascolytrum sp., Trifolium polymorphum, Carex spp., Cyperus spp., and also forbs such as Chevreulia sarmentosa, Chaptalia piloselloides, Eryngium nudicaule and Richardia stellaris, also with low frequency. The main weed is Eryngium horridum. The forage quality of natural pastures varies between 48 and 62 percent of OMD (organic matter digestibility), with crude protein content between 6 and 12 percent and P concentration below 0.10 percent (Olmos and Godron, 1990).

In some parts of this zone Eupatorium buniifolium, a summer-growing deciduous shrub that can reach up to about two metres in height, occupies large areas, damaging the vegetation underneath, by competing for light, water and nutrients; besides it makes livestock handling difficult, especially sheep and also reduces forage accessibility. Another plant which creates problems for grazing management is Erianthus angustifolius, a hard grass very little eaten by animals, that accumulates old and dry leaves quickly. In order to reduce its incidence one solution is burning; the tender regrowth is sometimes grazed.

The calculated stocking rate for this campo varies from 0.40 AU/ha in East Sierras to 0.9 AU/ha on sandy and deep basaltic soils. The animal unit (AU) is equal to a cow of 380 kg which weans a calf each year. The reduction in sheep numbers during the past decade reduced the stocking rate which may save the natural pasture from degradation. In some agro-ecozones degradation is difficult to prevent, particularly on basaltic soils where the sheep density was very high (Rosengurtt, 1946; Millot et al., 1987; Formoso, 1996; Risso and Berretta, 2001).

The most intensive beef and sheep production systems are in the western zone, on highly fertile soils (group V). Due to its high production potential this area has a long cropping tradition. Continued and intensive cultivation resulted in the substitution of the best native pasture species with a weed grass invasion (mainly Cynodon dactylon) and adversely affected the chemical and physical properties of the prevailing soils. Following research in the early 1970s, the adoption of a rotation of crops and cultivated pastures (ley-farming systems) became important. Because cultivated pastures have such a high production potential, they made it possible to overcome the difficulties of the low annual and winter production and forage quality of the degraded native vegetation, so resulting in improvements in the efficiency of the breeding and fattening processes of both cattle and sheep. Since the introduction of cultivated pastures there has been an intensification of breeding and fattening processes in a context which ensures the bioeconomic sustainability of predominant production systems (Carambula, 1991).

Traditionally cultivated pastures may be annual, short rotation or perennial, lasting approximately four years. The main forages used are shown in Table 9. For each forage, INIA (Instituto Nacional Investigacion Agropecuaria) has developed at least one cultivar adapted to local ecological conditions and predominant production systems. The breeding strategy is a continuing process with periodic releases.

In addition to efforts in plant improvement, emphasis is placed on developing technologies of pasture management and use which ensure the expression of potential productivity of all species and cultivars consistent with good persistence and nutritive value (Berretta et al., 2000).

To avoid forage scarcity in winter and autumn farmers of intensive beef and dairy production systems sow and use annual forages. Number of farms, sown area and the percentage of area with direct drilling in 1999/2000, is given in Table 10. A large area of annual forages is sown by direct drilling, indicating that farmers have adopted this technique quite easily and are decreasing conventional land preparation using the plough.

Table 11 shows the commonest sown forages. Improved or cultivated pasture could include one or more species and the same for overseeding. The area under cultivated pastures is much greater than for improved pasture (oversowing). Most of the cultivated pasture is in intensive production systems as is almost all the area of pasture improvement.

Farmers in intensive production systems, particularly those engaged in dairying and fattening, conserve forage to transfer the feed surplus to seasons when food is scarce; that is winter or drought periods. The commonest ways of conserving forage are:
a) hay from cultivated pastures, improved campo and annual forages;
b) silage from cultivated pastures, to preserve spring forage surplus is made during the vegetative stage of the pasture, until flowering according to species;
c) silage from cultivated pastures, campo and annual forages;
d) hay from these three pastures, and
e) wet grain silage from annual forages, particularly maize and sorghum.

Intensive production systems store forage as cylindrical bales of hay ranging between 250 to 600 kg according to the raw material. Prismatic bales are used but less frequently. Silage is an alternative which is widespread in this type of production system mainly because of:
a) the difficulties of harvesting and managing large volumes of hay;
b) the increasing availability of silage making machinery ;
c) the use of old tyres to fix the nylon in order to obtain an adequate silage coverage;
d) easier to use facilities to feed the animals, and
e) to improve the application efficiency according to the production potential of summer forages, especially maize and sorghum.

Figure 6. Photographs from the various agro-ecological zones (click to view full image)

Campos on Basaltic shallow soils, Agroeco zone 1.		Campos on Granitic soils, Agroeco zone 4A.
Campos on Eastern hillock, Agroeco zone 4B.	Landscape of Sierras, Agroeco zone 2.	Campos on Sandy soils, Agroeco zone 5A.
Mixed grazing	Landscape with sheep and cattle, Agroeco zone 1.	Grazing management, deferring forage for winter grazing
Improved rice fallows by aerial seeding of forage (cultivated pastures) Agroecozone 6A	Cultivated pastures, white clover, birdsfoot trefoil and cocksfoot.	Hay for winter feeding.
Corn for silage, intensive systems, Agroeco zone 7.		Oxalis species on native campo
Photographs by author

Limitations of the forage resource
Natural campo is known to have limitations that prevent adequate animal production throughout the year. The main limitation is seasonality, with a very reduced growth in winter due to the predominance of summer growing species. Scarce winter growth means that animals lose weight. To reduce this problem it is convenient to defer forage from autumn to be grazed in winter.

The quality of the natural pasture is another important limitation since most native species have low nutritive value, with values of crude protein between 5 and 15 percent, depending on the season; the higher values are registered in winter and spring, independent of the growth cycle of the plants and lower in summer when the amount of forage available is suitable, outside droughts. Phosphorus is deficient in practically all soils, with values between 0.12 and 0.21 percent depending on the soils and the seasons. Grasses have greater concentrations of this nutrient in the same seasons as protein.

The main problem of natural pastures is the risk of degradation and loss of species, related to continuous stocking, high stocking rate and high sheep/cattle ratios. Degradation signs are the increase of forbs and stoloniferous grasses adapted to such grazing conditions and reduced frequency of bunch grasses, as well as a reduction in species number. Such changes in botanical composition result in a 12 percent reduction in annual forage production, which is seldom noticeable over short periods of time. When stocking rates are adjusted to the grassland potential, and grazing management includes rest periods, it is possible to keep a campo in good condition, with variations caused by seasonal changes. The campos ecosystem is highly stable, and is capable of recovering after violent events such as drought.

The number of paddocks is based on the type of operation of the farm, cattle and sheep raising and fattening is the one that requires a greater number of them to facilitate management. The main restriction is the supply of good quality water in a sufficient amount to satisfy the needs of the animals. Due to the differences among plant communities the paddocks must be divided or subdivided covering homogenous areas. Their area is a function of the soil fertility and vegetation type, paddock size being of considerable importance in the management of natural pastures. Uniformity of vegetation and a greater number of paddocks make the design of grazing systems easier which allows alternate periods of null or low stocking with others of high stocking depending on the season, vegetation type and animal category.

Usually, the number of paddocks in extensive production systems is low, less than 10 per farm, which complicates herd and flock management. Fences that separate properties or divide them from public places (roads, parks, towns, etc.) have a uniform legal height of 1.4 metres, with seven wires, one of which may be barbed. Internal farm fences may be the same or may have one wire less. They might also be formed by only one to three wires, but electrified. Fence structure includes different diameter posts, according to their function. In early times hard wood (Prosopis spp. and Acacia spp.) was used, imported from neighbouring countries, but now they are almost exclusively Eucalyptus. Barbed wire is no longer used.

In the last two decades farmers have increased the number of paddocks by using electrical fences, improving the livestock management and the utilization of improved and cultivated pastures. In intensive systems, managed with rotational stocking and strip grazing, a high number of paddocks and electrical fences are very common.

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