In Brazil, the northeast region comprises 18.27% of the national territory with 1 561 177.8 km², of which 969 589.4 km² correspond to the Brazilian semi-arid region, which would represent the sum of the territory of Germany, Italy, Cuba and Costa Rica together (^{Araújo, 2011}). In this semi-arid region of the country, the vegetation that exists is very diverse and is adapted to environmental conditions, such as the case of forage nopal, which belongs to the group of crassulaceae for presenting a differentiated metabolism, opening the stomata essentially at night, when the ambient temperature is low, and thereby reducing losses due to evapotranspiration.

Its water use efficiency is 11 times higher than that of C3 plants (^{Ferreira et al., 2008}), while for C4 plants, such as corn or sugar cane, the efficiency of Opuntia sp. it is triple under similar environmental conditions (^{Nobel, 2002}), characteristics that make it especially attractive for use in the semi-arid region, mainly as a source of animal feed. It is estimated that in the Brazilian Northeast there are approximately 500 thousand hectares of fodder nopal, where the states where it has been planted on a larger scale are Pernambuco and Alagoas (^{Santos et al., 2006}).

In Pernambuco there is a predominance of three cultivars, Gigante, Redonda and Miuda, the latter has been characterized by its rusticity (^{Galvão et al., 2014}); however, the Gigante and Redonda cultivars are susceptible to the cochineal pest, which has caused great damage to producers in the semi-arid region (^{Cavalcanti et al., 2008}). Selection work for clones resistant to mealybug showed that cultivars Miuda (Nopalea cochenillifera Salm-Dick), Oreja de Elefante Africana (Opuntia sp.) and Oreja de Elefante Mexicana (Opuntia stricta Haw) show resistance to the pest (^{Vasconcelos et al., 2009}).

The cultivar Oreja de Elefante Mexicana was introduced in the Brazilian northeast recently, approximately thirteen years, this cultivar is not very demanding regarding soil fertility; however, its palatability and handling may be compromised due to the presence of thorns.

^{Vasconcelos (2011)} mentions that it is important to define an improvement program that contemplates the selection of clones that have agronomic, zootechnical and resistance resistance to mealybug. Therefore, the objective of the research was to evaluate among clones of the cultivar of the Oreja de Elefante Mexicana nopal (Opuntia stricta Haw), which presented both agronomic and zootechnical characteristics and proposed it as the clone with forage potential.

The experiment was carried out at the experimental station of the Agronomic Institute of Pernambuco (IPA) in the municipality of Arcoverde, which has a climate classified as semi-arid tropical (^{Ministerio de Integración Nacional, 2005}) and is located in the rural region of the state of Pernambuco, an area known as the transition between the humid and semi-arid tropical forest zone.

Located between the coordinates 08° 25’ 15’’ south latitude and 37° 03’ 41’’ west longitude, at an altitude of 663 masl, the average annual precipitation (average of 60 years) is 692 mm. The establishment of the experimental phase was carried out in January 2014 and the evaluations were made in July 2015, the experiment was established in an area 5.5 m wide by 15.4 m length.

The clones used were Lisa 1, Lisa 2, Seg CV, mãe plant, Seg 1, Seg 2, Seg 3, Seg 4, Seg 5 and Seg 6. The sowing was done with vegetative material (10 cladodes per treatment) in lines with separation between rows of 1.4 m and between cladodes of 0.5 m, this material was obtained from 10 mother plants of the Oreja de Elefante Mexicana nopal (Opuntia stricta Haw), which were the treatments to be evaluated. For the fertilization, 20 tons of bovine manure per hectare were applied only at the beginning of the experiment. Soil samples were collected in the experimental area at a depth of 0-20 cm for evaluation of chemical characteristics. The results are shown in Table 1.

The evaluated variables were production (t of DM ha^-1), number of cladodes in plant (NC), height of the plant (PH), width of the plant (PWI), amount of thorn (AT), size of thorn (ST) and amount of glochidium (AG), within each plant was measured in cladodes, perimeter (P), length (LC), width (WID), thickness (TH), number of lines (NLI) and number of buds (NBU). For the determination of the number of cladodes in the plant, these were counted directly, while the height was determined by the direct measurement of each plant considering the apex of the highest cladode and the base of the plant, this in relation to the ground level.

The width of the plant was determined by measuring the plant horizontally, considering the most distant cladodes of the extremities in all plants. The number of thorns and glochids and the size of thorns were estimated following the classification references of ^{Gallegos-Vázquez et al. (2005)}. Line and bud measurements were performed by counting directly only in primary order cladodes, due to the lack of more orders in some clones.

Cladode measurements were made after cutting the secondary orders in each plant, the length was measured from the apex to the base of the cladode, the width measuring the cladode horizontally taking the largest edges, the thickness was measured in the central region of the cladode with the help of a vernier and the perimeter was obtained by measuring the edge of the cladodes with tape measure.

To estimate the production (t DM ha^-1), the cladodes were cut just maintaining the mother plant, they were immediately weighed, after which a homogeneous subsample of the cladodes of each plant was taken, which was dried in a forced circulation stove of air at 55 °C, until there was no variation in weight at room temperature, with it the production of dry matter was estimated. The statistical analysis of the data was carried out using a completely randomized design, using the SAS V.9.4 statistical package, for the test of comparison of means when there were differences between the evaluated variables, the Tukey test was used (p( 0.05).

Differences between treatments were presented in the evaluated variables (Table 2; p≤ 0.05), the number of cladodes ranged from 6 to 74, the width of the plant ranged from 66 to 161 cm, the height between 50 and 99 cm. These results were lower than that reported by ^{Ferreira et al. (2003)} who, when evaluating morphological characteristics in clones of fodder cactus Opuntia fícus-indica Mill, observed maximum and minimum heights of 70 and 122 cm, in plants cut 24 months after establishment, which explains the lower height of the plants in this work since they were cut at 20 months.

The Seg CV clone was the one that presented the highest NC, PH, PWI and dry matter production (67.41 t ha^-1), characteristics that would make it the most attractive nopal clone for its reproduction and diffusion as a forage plant; however, authors such as ^{Silva et al. (2010)} indicate that in forage nopal improvement programs, when the objective is to increase the production of dry matter (t ha^-1) in cuts every 24 months, the selection of clones that present greater height and width of plant.

However, variables such as the presence, quantity and size of thorns and glochids must also be analyzed, in order that it could be used in animal feed, ^{Santos et al. (2019)} indicates that in the cultivar Oreja de Elefante Mexicana it has thorns and glochidia that limit its forage quality.

The Seg CV clone that presented the best characteristics with respect to production also presented the highest EC, ST and TG (Table 2). The clone with the lowest AT was Lisa 2, while for ST, the Lisa 1 clone was the one with the lowest ST and the lowest AG, coinciding with the lowest dry matter production. The clones mãe plant and Seg 3 showed intermediate production values with 38.61 and 30.84 t ha^-1 respectively; in relation to variables such as AT, ST and AG, they obtained lower values with respect to Seg CV.

Differences were presented in the variables evaluated in cladodes (Table 3), the perimeter varied from 58 to 96 cm, the length from 21 to 33 cm, the width from 16 to 30 cm, the thickness from 14 to 22 mm, the number of lines and buds in primary cladodes ranged from 3.6 to 5.4 and from 3.8 to 5.2 respectively.

The mãe plant clone was the one with the largest perimeter, related to its greater cladode length and width. ^{Silva et al. (2010)} mention that the most productive nopal clones in addition to presenting a greater height and width in the plant, the cladodes are also wider and longer. However, the results in this work show that this can be variable, since the clone that presented the greatest height and width in the plant did not present the largest cladodes.

This can be attributed to the characteristics of the clone, although different opinions emerge as ^{Sales et al. (2003)} who indicate that in addition to the genetics of the plant, climatic oscillations influence the width and length of cladodes, thus affecting production, which could have happened in the present study given the edaphoclimatic conditions of the area study.

The thickness of the cladode was greater in the Seg CV clone, indicating according to ^{Mondragon-Jacobo et al. (2002)} which is indicative of a water reservoir, this characteristic is useful because it indicates a greater adaptation to low water availability, as is the case in the Brazilian Semi-arid region. The clones mãe plant and Seg 3 showed values higher than Seg CV in the variables PC, LC and WID, showing adequate agronomic and zootechnical characteristics.

The number of lines in primary cladodes was greater in the clone Seg 4. ^{Hills (2001)} mentions that the number of buds is important because when cladodes are subjected to adequate environmental conditions, they can give rise to new cladodes, this work showed that only the clones Seg CV and Seg 5 showed a lower number of buds in primary cladodes, compared to the clones Lisa 1, Lisa 2, mãe plant, Seg 1, Seg 2, Seg 3, Seg 4, Seg 5 and Seg 6 maintained values similar between five buds.