INTRODUCTION The northeastern states of Coahuila, Nuevo León and Tamaulipas have dedicated 77, 70 and 59 percent of their land area, respectively, to livestock activities. The establishment of pastures and forage crops is a common alternative in animal feeding within the extensive production systems of the region.

The state of Coahuila has 90,000 hectares (ha) of pastures, mainly buffelgrass (Cenchrus ciliaris) and annual ryegrass (Lolium multiflorum). Nuevo León has 500,000 ha of buffelgrass and Tamaulipas has 1,063,000 ha of buffelgrass, guineagrass (Panicum maximum) and stargrass (Cynodon pleystotachus). Besides these planted areas there is a potential for 5 million more hectares of pastures in northeastern Mexico (COTECOCA 1996) . The northeastern part of Mexico can be divided into two regions based on environmental conditions; the gulf coast plains and the high-plains. The gulf coast plains are located near the coast of Tamaulipas, in the north of Nuevo León and northeast of Coahuila. The altitude is less then 700 m above sea level and the annual precipitation is more than 400 mm. The climate of the Gulf Coast Plains is warm, sub-humid and there is low frost frequency.

The high-plains are located in the northwest of Coahuila as part of the chihuahuan desert, in the south of Coahuila and Nuevo león, and in the southwestern part of Tamaulipas. The altitude is more than 1,000 m and precipitation is between 200 and 500 mm. The climate is dry temperate, with extremely hot summers, cold winters and high frost frequency. A transition area between the two regions also exists.

The objective of this paper is to analyse the scientific and technological information that exists in the region for different types of pastures in order to define the needs for research, training and technology transfer to exploit the cattle potential in the area. As a reference point, it is estimated that for each ton of dry matter (DM) produced, 2.5 animal unit months (AUM) can be maintained.

DESCRIPTION OF PASTURE TYPES

Rain-grown pastures. These non-irrigated pastures grow during the rainy season in the gulf coastal plains and in the area of transition were the precipitation is more than 400 mm and altitude is less than 700 m above sea level. Under these conditions the most common species are buffelgrass, bermudagrass, guineagrass, stargrass, kleingrass, pretoria and forage sorghum.

In order to establish pastures, the natural vegetation is removed mechanically for seed-bed preparation. It is important to consider only partial removal of the natural vegetation in the areas of high potential for wildlife in order to provide browse during the dry years and winter (Hinojosa 1996).

The most important pasture grass in the northeast of Mexico is buffelgrass. Buffelgrass was introduced into central Texas in 1917 and became available for use in 1949 in South Texas (Holt 1985). In Mexico buffelgrass was introduced by cattleman during the fifties and it adapted favorably. From 1960 to 1980, 3 million ha were bulldozed and planted to buffelgrass in Coahuila, Nuevo León and Tamaulipas. At the present time there are only 1 million ha left.

The economic impact of buffelgrass pastures can be observed in the state of Tamaulipas where carrying capacity increased from 35,000 animal unit years (AUY) in natural vegetation to 120,000 (AUY) with an area of 350,000 ha of buffelgrass pastures (Saldivar 1991). Buffelgrass pastures in precipitation areas of 800 mm have a carrying capacity of 3.7 (AUY) (COTECOCA 1978).

Recent research on buffelgrass has been carried out by UANL, UAT and UAAAN. At UANL germplasm has been introduced and the results demonstrate that various Australian and Argentine genotypes have better adaptation and yields than common buffelgrass (López 1996). The UAT research focuses on establishment and persistancy of buffelgrass (Saldivar 1998). Researchers at UAT have also been interested in looking for material that would adapt buffelgrass to the high-plains of Tamaulipas, such as "Nueces" and "Llano" (Astello 1993). After buffelgrass, other pasture species in order of importance are stargrass, guineagrass and bermudagrass with 216,000, 139,000 and 13,000 ha, respectively, just in the state of Tamaulipas (SAGDR 1995). The yield of bermudagrass depends on precipitation and temperature and can vary from 6 to 15 tons/ha/year (t/ha) of DM (Zárate 1995). Guineagrass pastures in precipitation areas of 1,200 to 1,300 mm have a carrying capacity of 1.7 to 3.0 AUY (COTECOCA 1978).

Rain-grown pastures are also planted in areas of low precipitation (less than 400 mm) and at high altitudes where there is higher risk and less production. Buffelgrass, kleingrass, and native species of the Bouteloua genus are usually planted under these conditions. In the state of Coahuila, it is estimated that there are 62,000 ha of such pastures (INEGI 1991). Efforts have beeen made to establish rain-grown pastures in semi-arid environments in the northeast of Coahuila. These experiments were conducted by CNIZA (Centro Nacional de Investigaciones para el desarrollo de las Zonas Aridas) between 1972 and 1978. The focus was on the use of micro-watersheds to establish mixtures of buffelgrass, Leptochloa dubia, Atriplex canescens, Chloris gayana and Bouteloua curtipendula. The results show that a ratio between the area planted and the drainage area of 1:3 to 1:4 was the most adequate (Garza and Rodríguez 1982).

Irrigated pastures. Irrigated pastures are used were natural precipitation limits forage production. This ocurrs in the high-plains were summer precipitation is very low and where there is a high demand for forage for animal feeding during winter. Irrigated pastures are also planted at a lesser scale in the transition zone and in certain areas of the coastal-plains.

Summer annuals. In the Laguna area (Coahuila-Durango) corn silage is used for feeding dairy cows. Experimental yields for corn silage have been approximately 20 tons per hectare (t/ha) of DM, with a crude protein content of 8 to 9 percent and net energy for lactation of 1.4 to 1.5 megacalories per kilogram (Mcal/kg) of dry matter (DM) (Herrera 1996). Forage sorghum has also been planted on 20,000 ha in Coahuila (INEGI 1991). The yield has been between 12 and 18 t/ha of DM. The Laguna area has two cycles for corn and one for oats (Avena sativa) and it may produce 35 to 40 t/ha of forage DM per year. Recent research at UAAAN has focused on plant breeding for better corn silage production and they have reported experimental yields of up to 30 t/ha of DM with the varieties AN-446 and AN-773 (Urquiza 1998).

Winter annuals. Winter annual pastures are important all over the northeastern region, but are more significant in the high-plains due to low temperatures and lack of humidity that reduce the availability of rangeland forages and rain-grown pastures. The main species planted are oats and annual ryegrass. For the autumn-winter period during 1996-1997 in Coahuila, 10,100 ha of oats, 1,710 ha of annual ryegrass and 1,100 ha of barley were planted (SAGADR 1997). For Nuevo León, 1,850 ha of oats and 664 ha of annual ryegrass were planted for the same period (INEGI 1996). Annual ryegrass pastures can produce up to 12 t/ha DM and oat pastures from 8 to 10 t/ha. However, in places with a high frequency of frosts, oats are not recomended due to lack of resistance to low temperatures and annual ryegrass has low yields during the coldest months before yields increase again through spring. An example of this occurred during the last autumn-winter period (1997-1998) when most of the oats in the state of Coahuila were frozen and the annual ryegrass produced only one to two grazing periods.

In a series of experiments with annual ryegrasses and oats planted in Chihuahua, Coahuila, Nuevo León and Tamaulipas, yields were between 7.4 and 13.5 t/ha of DM for annual ryegrass and 5.2 to 8.1 t/ha DM for oats. There were lower yields for both species in the coastal areas compared to the high-plains due to lack of cool temperatures. The annual ryegrass pastures are planted from August to October depending on the temperature. The first grazing period on ryegrass is in December or January with three more grazing periods in February, March and April. The optimum stocking rate is 2,000 to 2,500 kg animal liveweight per hectare, or 10 to 12 steers of 200 kg each.

In the high-plains region where there is a high frost frequency, the use of grazing, green chop and silage of small-grain cereals has been increased due to the hardiness of these species. The most common species are triticale (X Triticosecale Wittmack) and barley. Research on small grains has been directed primarily to grain yield and quality without much emphasis on forage materials. This led Antonio Narro University to develop a long-term research program that would generate triticale forage varieties for grazing, green chop and silage. Also, a barley forage program has been established in the last five years. Experimental yields of 22 t/ha DM have been reported for triticale AN-31 variety and some barley varieties report yields of 13 t/ha DM (Lozano et al. 1997; Colín et al. 1997). A great genetic diversity exists in cereals from spring genotypes with rapid growth to winter genotypes with slow growth but with a high regrowth capacity. The planting periods, yields and stocking rates are similar to annual ryegrass, however, the cereals are ready for grazing earlier. In the search for a pasture that would decrease the time between planting and grazing with a grazing frequency of three to five periods, various mixtures of triticale and annual ryegrass have been evaluated. Total DM yield for mixtures was similar (17 t/ha) compared to annual ryegrass yield (16 t/ha), but mixtures show more homogenous yields through all the grazing periods than the single species pastures. A mixture of berseem clover (Trifolium alexandrinum) with triticale produced experimental yields of 18 t/ha DM, more constant yields and a higher nutritive value as compared to single pasture species (Espinosa 1993).

Warm season perennials. The most commonly used irrigated pastures in the northeast of Mexico are buffelgrass, stargrass, bermudagrass, pretoria and kleingrass. It is reported that there are 24,000 ha of these types of pastures in Tamaulipas (SAGADR 1995). This same information was not available for Coahuila and Nuevo León, neverthless, these types of pastures are very important in areas were buffelgrass, bermudagrass, kleingrass and pretoria are used. Pastures of these species are planted in spring and can be grazed the first time 4 months later. In areas with mild winters, there is high production in spring and autumn and lower production in winter. In areas with colder winters, there is plant dormancy during winter and regrowth in spring as temperatures increase. Irrigated bermudagrass pastures can yield from 15 to 29 t/ha DM depending on temperature (Zárate 1995).

Legume-grass mixtures reduce the need for nitrogen fertilizers and improve the quality of animal diets. In the north part of Coahuila, a kleingrass (Panicum coloratum) and sabine (Desamnthus illinoensis) mixture has been evaluated. The results indicate that a sowing rate of 3 kilograms per hectare (kg/ha) of pure live seed (PLS) of kleingrass plus 4.5 kg/ha of sabine produce a plant density of 14 plants of kleingrass and 19 plants of sabine/m2 .

Cool season perennials. Cool season perennial pastures are seeded mainly in the high-plains area. In warmer areas these grass species often suffer mortality from hot temperatures and weed competition, such as common bermudagrass. The preferred sowing date for cool season perennials is from August to October. They can also be seeded in spring, but there are greater problems with weeds. The first grazing period is obtained 5 to 6 months after the planting date. Seven to 12 grazing periods may be obtained, depending primarily on temeperature. The highest DM yields from these species are in March and April with 3 to 4 t/ha/month, while lower yields are observed in January (1 t/ha DM). The major species are orchardgrass (Dactylis glomerata), perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea) and bromegrass (Bromus inermis), with some alfalfa (Medicago sativa) or clovers (Trifolium sp.). It is estimated that there are about 3,000 ha in Coahuila of this type of pasture. In experimental trials, yields of 20 to 25 t/ha have been reported (Gutiérrez 1991; Sosa et al. 1994). Díaz (1995) reports yields of nearly 20 t/ha DM, crude protein content from 16 to 21% and acid-detergent fiber from 29 to 34%. Mixtures of cool season grasses with rhodesgrass (Chloris gayana) were compared with a commercial mixture and with each individual species (Sosa et al., 1994). As expected, the rhodesgrass mixture yielded more than other treatments.

With good management practices cool season perennial pastures can persists over several years without the need of planting and seedbed preparation twice a year as in a conventional system. On private farms dedicated to dairy heifer development, yields of 14 to 16 t/ha/year DM have been reported and the costs reduced by 1/3 as compared to a conventional system (Díaz 1992). Cool season pastures are a good alternative for special purposes like flushing bulls, heifer development and calving.

CONCLUSIONS AND RECOMMENDATIONS

1. The northeastern regions of Mexico have various types of vegetation and grasslands that require special attention to solve their problems.

2. Inefficiencies in the transformation of natural vegetation in the grasslands shows that the available technology has not yet solved establishment and persistence problems. This is why it is necessary to develop regional research and extension programs for technology transfer in areas with potential for improved forages.

3. The need for regional programs supercedes the national production of seeds for forage species and the low diversity of germplasm available for such an extensive area. It is necessary to develop germplasm and promote the production of seed for distinct areas.

4. There is currently no regional research , training and technology transfer program that undertakes to solve the problems of production of forage for livestock. LITERATURE CITED Astello, N. 1993. Efecto del suelo en la producción de 20 variedades de zacate buffel. Tesis de Maestría. UAM Agronomía y Ciencias. Universidad Autónoma de Tamaulipas. Cd. Victoria, Tamps. México.

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