Productive indicators of lambs in native grasslands, supplemented with Acacia cochliacantha, in the dry tropic of Guerrero, Mexico

Indicadores productivos de corderos en praderas nativas, suplementados con Acacia cochliacantha, en el trópico seco de Guerrero, México

E.J. Mireles,^I D. Rodríguez,^II H. Jordán ,^II Aurora H. Ramírez,^III Águeda García,^III I. Gutiérrez,^I

^IUnidad Académica de Medicina Veterinaria y Zootecnia de la Universidad Autónoma de Guerrero, México. km 2.5. Carretera Cd. Altamirano-Iguala Cd Altamirano Gro. CP 40660.
^IIDepartamento de Rumiantes, Instituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, Cuba. ^{]]> III}Departamento de Nutrición Animal y Bioquímica, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México.

ABSTRACT

In order to quantify some productive indicators and the botanical composition of diets for lambs, supplemented with ground and whole pods of Acacia cochliacantha, related to the requirements of dry matter intake, 60 Pelibuey-Black Belly x Dorper-Katadhin lambs were used, with 20.4 ± 2.1 kg of LW, divided by a completely at random experimental design, with six treatments. During the dry period, the treatments were: grazing (Pas), grazing plus 15 % of supplementation with ground pods (Pas 15), and grazing plus 30 % of supplementation with ground pods (Pas 30) for 105 d. During the rainy period, the treatments were: grazing (Past), grazing plus 30 % of ground pods (Past 30M), and grazing plus 30 % of whole pods (Past 30E) for 84 d. The daily weight gain was determined every 21 d. At the end of this study, six animals of each group were slaughter to determine hot carcass yield, and register the weight of some viscera, and pericardial and perirenal fat.  The analysis of variance and the test of Duncan (P < 0.05) were applied to the data. During the dry period, the daily weight gain was 68, 59 and 63 g, and the hot carcass yield was 37.09, 37.85 and 39.10 % for grazing, grazing plus 15 % of supplementation with ground pods, and grazing plus 30 % of supplementation with ground pods, respectively. During the rainy period, the gain was 120, 105, and 113 g, and the yield was 40.51, 42.02 and 40.10 % for grazing, grazing plus 30 % of supplementation with ground pods, and grazing plus 30 % of supplementation with whole pods, respectively. It can be concluded that the botanical composition of the diets for lambs was similar during both seasons. Irrigated native grasslands produced less daily weight gain and hot carcass yield during the dry season than during the rainy period. The supplementation with ground or whole pods of Acacia cochliacantha had no influence on the studied indicators.

Key words: lambs, native grasslands, productive indicators.

RESUMEN

Para cuantificar algunos indicadores productivos y la composición botánica de la dieta de corderos que pastaron, suplementados con diferentes porcentajes de vaina molida y entera de Acacia cochliacantha, en relación con los requerimientos de ingestión de materia seca, se utilizaron 60 corderos, de 20.4 ± 2.1 kg de PV, de raza Pelibuey-Black Belly x Dorper-Katadhin, divididos en diseño completamente al azar. En el período seco se aplicaron los tratamientos: pastoreo (Pas); pastoreo y 15 % de suplementación con vaina molida (Pas 15) y pastoreo más 30 % de suplementación con vaina molida (pas 30) durante 105 d en el período seco, pastoreo(Past); pastoreo más 30 % de vaina molida (Past 30M) y pastoreo más 30 % de vaina entera (past 30E) durante 84 d en el período lluvioso. Se determinó, cada  21 d, la ganancia diaria de peso. Al final del trabajo, seis animales de cada grupo se sacrificaron para determinar el rendimiento en canal caliente y registrar los pesos de algunas vísceras y de la grasa  pericárdica y perirenal. Los datos se sometieron a  análisis de varianza y a la prueba de Duncan (P< 0.05). Para el período seco, la ganancia diaria de peso fue de 68, 59 y 63 g, y el rendimiento en canal caliente de 37.09, 37.85 y 39.10 % en pastoreo, pastoreo más 15 % de vaina molida y pastoreo con 30 % de vaina molida, respectivamente. Para el lluvioso, la ganancia fue de 120, 105, 113 g, y el rendimiento de 40.51, 42.02 y 40.10 % en pastoreo, pastoreo más 30 % de vaina molida y pastoreo más 30 % de vaina entera, respectivamente. Se concluye que la composición botánica de la dieta de los corderos fue similar en los períodos seco y lluvioso. Las praderas nativas irrigadas produjeron menor ganancia diaria de peso y rendimiento en canal caliente en el período seco con respecto al lluvioso. La suplementación con vainas molidas o enteras de  A. cochliacantha no influyó en los indicadores estudiados.

Palabras clave: corderos, praderas nativas, indicadores productivos.

INTRODUCTION

Ovine meat production in Mexico is not enough to cover the demand of this product. Therefore, more than 40 % of the national consumption is imported (Martínez et al. 2009). The intensive fattening is expensive due to the high prices of grains and pastes of oleaginous plants to obtain daily weight gains of 250 g or more (Macedo and Castellanos 2004 and Macías-Cruz et al. 2010). 

In order to reduce costs, non-conventional feeds are used, which represent a different option (Albuernez et al. 1996 and Marshall 2000). Another alternative is the use of forages as a more economical feed in the dry tropic during the long dry period, in which the obtaining of nutrients is difficult all the year. It is not the same in irrigation systems, available in all Mexico, although in the state of Guerrero, 60 % of the irrigation surface is not cultivated (CONAGUA 2009).  The objective of this study was to determine the botanical composition of diets, the daily weight gain and hot carcass yield of lambs in irrigated native grasslands and supplemented with ground or whole pods of A. cochliacantha.

MATERIALS AND METHODS

This study was carried out during the dry period,  from October, 2012 to January, 2013, and during the rainy period from June to September, 2013, at the Unidad Académica de Medicina Veterinaria y Zootecnia de la Universidad Autónoma de Guerrero. This institution is located at km 2.5 de la carretera Altamirano-Iguala, Pungarabato municipality, Tierra Caliente region, Guerrero, Mexico. This area is located at 18º 20` 30” NL and 100º 39` 18” WL. The climate, according to a classification of Köopen, is sub-humid warm AWo type.

Animals. An amount of 60 Pelibuey-Black Belly x Dorper-Katadhin lambs were used, with 20.4±2.1 kg of liveweight. They were orally wormed with albendazole (7.5 mg/kg of weight). An amount of 500,000 IU of vitamin A and 75,000 IU of vitamin D were applied intramuscularly, as well as 50 mg of vitamin E. Supplementation with ground pods and whole pods had different percentages, regarding the requirements of DM ingestion, depending on the metabolic weight (W^0.75) and the daily weight gain (DWG) according to DMI= -0.124 + 0.0711 W^0.75 + 0.0015 DWG g (Pulina et al. 1996). Lambs were distributed according to a completely random design, divided into six treatments. During the dry period, the treatments applied were 1) grazing plus 0 % of supplementation (Pas), 2) grazing plus 15 % of supplementation with ground pods (Pas15M), and 3) grazing plus 30 % of supplementation with ground pods (Pas30M). During the rainy period, the treatments were 4) grazing plus 0 % of supplementation (Past), 5) grazing plus 30 % of supplementation with ground pods (Past30M), and 6) grazing plus 30 % of whole pods (Past30E).

Grasslands and supplements. Six native grasslands were selected at random, with 20 x 40 m and rotational grazing of five days per 30 d of recovery. Every grassland was divided into three for the grazing of the six groups, three per each period. They were irrigated every seven days by flooding during the dry period and they were fertilized once a year with ovine manure, at a rate of 10 t/ha (González 1995). Weeds were extracted from the root. The grass was cut every three months for avoiding the growth of shrubs over 50 cm high. The grasslands were composed by grasses (Chloris virgata Sw., Cynodon dactylon L. Pers., Bouteloua media E. Fourn Gould et Kapadia, Paspalum notatum Flüggéy, and Setaria spp,), shrubs (Acacia cochliacantha, and Acasia farnesiana L. Willd), herbaceous plants (Ipomoea pedatisecta Mart. et Gal, Anoda acerifolia Cav., Cyperus esculentus L., and Desmanthus virgatus L. Willd), and weeds (Sida rhombifolia L., Senna obtusifolia L. H.S. Irwin et Barneby, previously called Cassia tora L., and Asclepias curassavica L.). The chemical composition of the pod was: DM (94.0), CP (11.9), EE (3.1), ashes (6.4), CF (32.3), NFE (46.4), ADF (46.2), NDF (59.9), cellular content (40.1), hemicellulose (13.7), cellulose (33.5), lignin (12.1) and in vitro digestibility of dry matter (31.7 %).  

Management and feeding. Lambs had a period of adaptation of 10 d. They grazed daily from ]]> 9:00 a.m. to 6:00 p.m. in the Pas15M, Pas30M, and Past30M treatments. The animals were provided with 102, 205, 205 g of ground pods, respectively, and 205 g of whole pods in the Past30E treatment. The bromatological composition of the consumed grassland was determined according to AOAC (1990), at the Laboratorio de Bromatología y Bioquímica de la Universidad Nacional Autónoma de México (UNAM), as well as the NDF and ADF, regarding van Soest et al. (1991). The in vitro digestibility of dry matter (IVDDM) was determined according to Tilley and Terry (1963).

A proximal chemical analysis was performed to the plants that formed the botanical composition of diets provided to lambs. The botanical composition of diets was determined from the samples obtained with two exclusion cages of 1 m² (FAO 1996) per each treatment, placed in three of the six grasslands selected at random. Inside the cages, the proportions of plants were manually cut, which were previously ingested by the lambs during the dry and rainy seasons.

The animals were weighted every 21 d, after feeding. Six lambs were sacrificed from each group, selected at random. The living animal and the hot carcass were weighed in a balance with a scale of 500 kg and of 0.2 kg. A balance of 2,610 g, with a 0.1 g scale, was used to register the weight of the pericardial and perirenal fat, heart, kidneys, liver and gallbladder. 

The variables botanical composition of diets, daily weight gain, hot carcass yield, weight of perirenal and pericardial fat, heart and liver were studied.

An analysis of variance was applied to the data and the means of each treatment were compared using the test of Duncan (P < 0.05), according to reports of Balzarini et al. (2012).

RESULTS AND DISCUSSION

In the botanical composition of diets, there was no significant difference among the six treatments or among grasses, shrubs, legumes and herbaceous plants. This could be caused by the extraction of weeds from their roots after each grazing, by the periodical cutting of shrubs and by the irrigation during the dry period. This irrigation probably stimulated the growth of some plants as Setaria spp and Pithecellobium dulce and during the rainy period, the presence of Rhynchosia spp. was confirmed (table 1). Abusuwar and Ahmed (2010) reported 87 % for grasses and 13.28 % for herbaceous plants in the Pas15M group, in semiarid lands of Sudan. These figures are similar to those of this study. 

The percentages of CP during the dry period were different from those in the rainy period (P<0.001). There was similarity only between Pas and Past30M, which means between the treatment of the lowest percentage during the rainy period and that of the highest percentage during the dry season (table 2). Percentages of CP from dry period are in the necessary minimum limit (Bondi 1989) to establish an acceptable fermentative activity of ruminal microorganisms. On the contrary, in the rainy period, it was around 13 % in the ration, figure that the cited author points as necessary for the best ruminal protein synthesis.

CP percentages during the rainy period were higher than 11 %. This value is close to that reported by Ma et al. (2014) in ovine grazing native grasslands during the autumn (11.4 %) and at the end of spring (13.1), but it is lower than the amount of CP reported for the summer (17.7 %).

Lignin content during the dry period was different (P < 0.001) from that during the rainy period (table 2). These percentages of lignin had an effect on the nutritional value of diets, because after the union of lignin with cellulose and hemicellulose, the degradation of feed decreases in the rumen, so there is a lower nutritional value of feed at a higher lignin percentage (McDonald 2006).

The percentages of NFE, ADF, NDF, cell content, hemicellulose and IVDDM in the six groups of lambs were statistically similar (table 2). The differences observed in CP and lignin can be possibly attributed to the highest percentage of legumes with 1.32, 5.35 and 2.27 % during the rainy period. During the dry period, the figures were lower than 0.10 % (table 1). The herbaceous plants followed this performance, with more than 7 % during the rainy period. In Pas and Pas30M, it was not higher than 0.5 %, except Pas25M (13.89 %), but with lower percentage of shrubs and grasses (table 1).

The mean DWG (P < 0.05) were 63 g during the dry period and 113 g during the rainy season (table 3). This was caused by the highest percentage of CP during the rainy period, and the lowest percentage of lignin, regarding the dry period (table 2), which possibly produced higher digestibility of ingested food and, consequently, a better use of energy during the rainy period. It may also be caused by the higher forage availability due to the effect of rains. Vázquez et al. (2012) reported 8 g of DWG in Pelibuey x Dorper lambs, in grasslands of Paspalum notatum and Axonopus compressus. There is a difference because the grasslands used in this study were constituted by grasses, shrubs and herbaceous plants. However, the cited authors, after supplementing with nutritional blocks of 20 % of Leucaena leucocephala, obtained 48 and 68 g of DWG, with the inclusion of 20 % of wheat bran in the block. Ekiz et al. (2013) reported 87.15 g of DWG in lambs fed in grasslands of temperate areas, with 52 % of grasses (Festuca spp. and Lolium spp.), legumes (Trifolium spp., Medicago spp., and Vicia spp.) and 26 % of other families, compared to the DWG obtained in this research during the dry season. This could be attributed to the 11.5 % of CP compared to less than 9 % obtained in the dry period (table 2), which is confirmed after comparing the DWG of lambs during the rainy period, with more than 11.5 % of CP in the diet. Dickhoefer et al. (2014) reported DWG of 98 g with light grazing and 62 g with intensive grazing in a study with lambs grazing in native grasslands in a semi-arid climate from the steppes of Mongolia, China.

Retama et al. (2012), after feeding lambs in a silvopastoral system with irrigation in the dry tropic, with 65 % of Cynodon nlemfuensis, 30% of Leucaena leucocephala and 5 % of shrubs and herbaceous plants, reported 33 g of DWG. However, the value was 80 g after supplementing with 1.5 % of LW with ground grains of maize. This figure was higher than the one of this study during the dry period, which can be attributed to the energy and protein provided by maize. However, it was inferior to the value reported during the rainy season. 

Fernández et al. (1997) reported 71 g of DWG in lambs grazing in native grasslands complemented with nutritional blocks. Ortiz et al. (2007) obtained 77 g in native grassland of Bothriochloa pertusa in lambs supplemented with molasses (6 g kg^-1 LW). Getu et al. (2012) referred 75.3 g in native grasslands of Andropogon, Pennisetum  and clover species, which are similar amounts to those obtained in this study in the dry period. However, the values of DWG from rainy period were similar to those obtained by the cited authors after they used native grassland hay, 160 g of cotton seed paste and 200 g of wheat grains, obtaining 114 g of DWG.

Díaz (2010) reported 61.3 g of DWG in a study with lambs of 22 kg, which were grazing in grasslands of Cynodon plectostachyus, with 13.9 % of CP, irrigation and fertilization with urea (33 kg de N ha^-1). These animals consumed 180.5 g of DM of a supplement with 26.8 % of CP and obtained 61.3 g of DWG. These gains are similar to those reported in this research during the dry period and inferior to those of the rainy season. After the animals also received 25 mL of a semi-liquid compound, known as Vitafert, the DWG was 73.7 g. This could be attributed to the reduced IMS (456.5 and 450.4 g) reported by Díaz (2010) for the group that received Vitafert and the other that did not receive it, respectively.

Frías (2010) reported DWG of 85 g, inferior to those from the rainy period, in Pelibuey x Katahdin and Dorper lambs, fgrazing 6 h in star grass and intake of  600 g animal d^-1 of Saccharina, plus Vitafert. This author referred that, after feeding stabulated Pelibuey lambs with intake of 4 kg of green king grass Pennisetum purpureum CT-115, 100 g/d of a commercial feed and 537.5 g of Saccharina animal d^-1, DWG of 109 g animal d^-1 were achieved, which was close to the 121, 105 and 114 g obtained in this study with Past, Past30M and Past30E, respectively.

Engadine Swiss lambs, in grasslands of Ryegrass and clovers, had an average DWG of 105 g, inferior to the amount obtained (122 g) in a study of Willems et al. (2013) with Valaisian Blacknose sheep. This last value was similar to the one obtained in this study with Past, Pas30M and Past50E (121, 105 and 114 g, respectively). However, these values were slightly superior to those reported by Ma et al. (2014), who stated 83 and 99 g of DWG in lambs grazing in native grasslands of semi-arid climate in China, at the end of the spring and the autumn, respectively, but inferior to those of autumn with 135 g.

The hot carcass yield (HCY) was statistically similar among the groups of the dry period. The same performance occurred during the rainy period (table 3). However, the value of Past30M (42.0 %) was superior (P < 0.05) to the Pas (37.1 %) and to the Pas15M (37.9 %). This could possibly be attributed to the effect of supplementation with 30 % of the pods, compared to the supplementation in Pas and with 15 % in Pas15M, because the HCY, in the treatment with Past30M (39.1 %) during the dry period, was statistically similar to that obtained in the rainy period. The values of this study were similar to those reported by Ekiz et al. (2013) in Kivircik lambs, which were grazing in wheat stubbles and in native grasslands, composed by 52% of grasses, 22% of legumes and 26 % of other plants, with 11.5 % of CP in the grassland and 10.5 % in the stubble. The cited authors referred 38.52 % of HCY.

Willems et al. (2013) obtained 38.4 % of HCY in a study with Swiss Valaisian Blacknose sheep, in grasslands with Ryegrass and clovers and poor, medium and high quality of nutrients, at different heights over the sea level (400 to 2,150 m). This value was similar to the one obtained in this study.

In this study, the HCY in Past30M was 42.02, similar to that informed by Ekiz et al. (2013) (42.31 %) in a study with lambs fed with alfalfa hay and concentrate, with 17.67 % of CP consumed ad libintum. It was also similar to the values obtained by Partida et al. (1989), who reported 41 % of HCY with the use of 2.6 Mcal ME/ kg of DM in the diet. The HCY was inferior to that reported by Ortiz et al. (2007), who reached 45.8 %, after feeding the lambs in native grasslands of Bothriochloa pertusa and supplemented with molasses (6 g kg^-1LW). This could be attributed, possibly, to the highest ingestion of energy represented by supplementation.

In Pelibuey x Katahdin Dorper lambs, grazing star grass during 6 h and intake of 600 g animal d^-1 of Saccharina plus Vitafer, Frías (2010) reported 43.09 % of HCY, which is slightly superior the value obtained in the rainy period. However, the cited author obtained 42.04 % of HCY after feeding Pelibuey lambs with 4 kg of  P. purpureum cv. CT-115, 537.5 g of Saccharina and 100 g of a commercial feed, which was similar to the 42.02 % referred for Past30M.

Willems et al. (2013) reported 43.9 % of HCY for Swiss Engadine Sheep lambs in grasslands of Ryegrass and clovers. This value is higher than the one reported in this study.

The weight of liver and heart were similar among the non supplemented lambs and those supplemented  with 30% and superior to (P < 0.05) 15% (table 3).  This was probably related to the highest LW reached by lambs at slaughtering, because these lambs showed the highest weight of liver and kidney, and the lowest (373.5 g liver and 86.3 g heart) corresponded to 26.4 kg of LW in the treatment Pas15M. The values of liver were inferior to those reported by Ortiz et al. (2007) with 537 g in lambs in grasslands of Bothriochloa pertusa, supplemented with molasses (6 g kg^-1LW). This could be attributed to the contribution of sugars represented by the molasses, because the content of sucrose is metabolically transformed into an energy reserve in the liver as glycogen and, consequently, increases its weight, because up to 10% of the weight of this organ may correspond to hepatic glycogen (McDonald et al. 2006).

The weights of the kidneys were statistically similar in every treatment (table 3) and similar to that reported by Ortiz et al. (2007), who informed 79 g. The weights of the pericardial fat were similar in the six groups. Heart weights were matched to those reported by Nuernberg et al. (2008) in grazing lambs slaughtered with 25 kg of LW and heart weight of 100 g.

The weight of the perirenal fat was 140.8 g (P<0.05) in Past, regarding the figures during the dry period and the 100.8 g of the Past30E (table 3). This low value can be probably attributed to the supplementation with whole pods provided to this group.

CONCLUSIONS

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Received: June 26, 2014
Accepted: April 15, 2015

E.J. Mireles, Unidad Académica de Medicina Veterinaria y Zootecnia de la Universidad Autónoma de Guerrero, México. km 2.5. Carretera Cd. Altamirano-Iguala Cd Altamirano Gro. CP 40660. Email: emirelesmartinez@gmail.com