Diet and nutrition of range goats on a sarcocaulescent shrubland from Baja California Sur, Mexico

Available online at www.sciencedirect.com

Small Ruminant Research 76 (2008) 166–176

Diet and nutrition of range goats on a sarcocaulescent shrubland from Baja California Sur, Mexico R. Ram´ırez-Ordu˜na a , R.G. Ram´ırez b,∗ , E. Romero-Vadillo c , H. Gonz´alez-Rodr´ıguez d , J.A. Armenta-Quintana a , R. Avalos-Castro a a

Departamento de Zootecnia, Universidad Aut´onoma de Baja California Sur, Apartado Postal 676, La Paz Baja California Sur 23080, Mexico b Facultad de Ciencias Biol´ ogicas, Universidad Aut´onoma de Nuevo Le´on, Apartado Postal 142, Sucursal F, San Nicol´as de los Garza, NL 66450, Mexico c Departamento de Biolog´ıa Marina, Universidad Aut´ onoma de Baja California Sur, Apartado Postal 676, La Paz Baja California Sur 23080, Mexico d Facultad de Ciencias Forestales, Universidad Aut´ onoma de Nuevo Le´on, Km. 12.5 carr. Linares-Cd. Victoria, Linares, NL, Mexico Received 30 June 2005; received in revised form 15 December 2007; accepted 19 December 2007 Available online 4 February 2008

Abstract Botanical composition of diets of range goats was studied to determine seasonal preference indices of forage species and nutritional quality of selected diets on a sarcocaulescent shrubland from the Sonoran desert in Baja California Sur, Mexico. Extrusas from five esophageal cannulated adult female goats (40 kg of BW) were collected at the beginning and at the end of each season from April of 2001 to March of 2002. At the end of spring, goats selected higher amounts of browse legumes and cacti species, but during late summer, autumn and winter goats mainly preferred browse non-legumes followed by forb species. Goats selected a constant diet in truly digestible crude protein (annual mean = 11 ± 0.4% DM) and metabolizable energy (2.4 ± 0.1 Mcal kg−1 ) throughout the year. However, during late spring and early summer, goats selected diets higher in non-structural carbohydrates (NSC), truly IVDOM and truly digestible NSC. Dietary Ca, Mg, K, Mn, Fe were in substantial amounts to meet requirements of a range goat weighing 40.0 kg BW consuming 76.3 g DM kg0.75 d−1 in all seasons. It is concluded that range goats may require supplementary protein and energy to overcome pregnancy and lactation requirements throughout the year. Copper content appeared marginally deficient almost the entire year and Zn during late summer and autumn. © 2007 Elsevier B.V. All rights reserved. Keywords: Range goats; Botanical composition; Preference indices; Nutrient content

1. Introduction ∗

Corresponding author. Tel.: +52 81 83294048; fax: +52 81 83294049. E-mail addresses: [email protected] (R. Ram´ırez-Ordu˜na), [email protected] (R.G. Ram´ırez), [email protected] (E. Romero-Vadillo), [email protected] (H. Gonz´alez-Rodr´ıguez). 0921-4488/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2007.12.020

Range goats are known to utilize a variety of native browse and herbaceous species, they are capable to select diets with high nutritional quality (Ram´ırez et al., 1990, 1991, 1993; Provenza, 1995). Voluntary feed intake depends on intrinsic factors of forages and animals

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(Provenza et al., 2003), however, low nutrient intake is the most common limiting factor that affects productivity of range animals (Forbes, 1995). Baja California Sur, Mexico is part of the Sonoran Desert, considered as an extremely arid zone (FAO, 1987), about 92% of its flora is composed of shrubs and 23% of these are endemic species (INEGI, 1981). Within the subdivision of the Sonoran Desert into areas which correspond to the natural botanical features of its several parts (Shreve, 1951; Shreve and Wiggins, 1964; Turner and Brown, 1982; INEGI, 1981; INEGI, 1980–1988; Zippin and Vanderwier, 1994), the sarcocaulescent desert includes Baja California along the Gulf coast in a coastal strip, about 40 km wide from 29.5◦ N to the almost the tip of the peninsula (Zippin and Vanderwier, 1994) and is characterized by trees with trunks of exaggerated diameter, including Bursera and Jatropa genera, although these striking trees are, in their abundance, distinctive of the area, they are actually outnumbered by Olneya, Cercidium, Fouquieria and Prosopis genera and by small-leaved shrubs, the identity of which is often determinable only in a favorable season (Shreve and Wiggins, 1964). Livestock and animal feeds production in these regions is limited for low rainfall (annual mean = 172 mm) and alkaline soils (INEGI, 1996) in these areas. Livestock production is based mainly on free ranging goats and beef cattle without a defined strategy of range management (Arriaga and Cansino, 1992). Most of the farmers are traditional smallholder, this low-input system is characterized by a very low animal density (0.13–0.36 individuals/ha), severe and prolonged drought periods, continuing low per-animal performance and uneconomical production, farmers are unlikely to build fences for handling livestock or to buy supplementary feed to increase animal production; farmers have traditionally used shrub and tree fodders to feed their animals on the basis experience and convenience as a practical means of rearing animals. Traditionally goats are allowed to browse freely throughout the day and confined in corral overnight, thus goats browse around the corral within an area limited by the forage available, therefore this area is overgrazed, however the information on the nutritive value of animals diet is sparse, therefore no supplementation or grassing programs are carried out. Ram´ırez-Ordu˜na et al. (2003a,b) evaluated the nutritional quality of prominent browse species, growing in these regions, they reported a period of low nutritional quality during spring and summer. Non-legume species had low crude protein, low non-structural carbohydrates and low effective degradability of DM and CP.

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High cell wall and lignin contributed to the reduction in quality of these plant species. Conversely, legumes showed higher nutritional quality throughout the year. However, there are no scientific studies on nutritional quality of the annual diets selected by range goats. Thus, the objectives of this study were to evaluate and compare, seasonally, the preference indices for forage species, and the nutritional quality of goat diets on a sarcocaulescent shrubland of Baja California Sur. 2. Materials and methods The study was conducted in the ranch “Palmar de Abajo” (800 ha) located in La Paz, Baja California Sur, Mexico situated at 23◦ 38 40 north latitude and 110◦ 18 07 west longitude (DGETENAL, 1980). It is 200 m over sea level. Vegetation is composed mainly of shrubs from 1 to 3 m, and trees from 4 to 10 m of height (COTECOCA, 1975). The climate of the region is arid with annual mean temperature of 21.2 ◦ C. The annual precipitation is about 182 mm, generally (80%) recorded from July through September. Rainfall and temperature patterns from 1977 to 2002 are shown in Fig. 1. The main soils are of the types alkaline, regosol, eutric and calcareous which are very permeable (Flores, 1998). The state of Baja California Sur is located in a subtropical zone which is characterized by a very dry and warm weather BWhw, with rains during summer and early autumn; however, rainfall may occur in winter (Hern´andez, 1989). From April 2001 to March 2002 five esophageal cannulated adult female range goats (40 kg of BW) were used to collect extrusa samples. Collections were carried out in periods: spring 14–20 of April (spring early) and from 26 of May to 1st of June (spring late), summer 18–24 of August (summer early) and 10–16 of October (summer late), autumn 17–23 of November (autumn early) and 17–23 of December (autumn late) and winter from 30 of January to 5 of February (winter

Fig. 1. Means and standard errors of seasonal precipitation (mm), maximum and minimum air temperature (◦ C) from 1977 to 2002 at Todos Santos meteorological station, Baja California Sur, Mexico.

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early) and 19–25 of March (winter late). In each collection period, animals were sampled during 6 consecutive days; first 3 d at 08:00 and the rest at 17:00 h. Goats were fitted with canvas collection bags with screen wire bottoms and allowed to graze freely during 45 min. After collection, animals were allowed to browse freely with the herd and at the end of the day were confined in corral overnight for fasting. Goats remained with the herd the rest of the year and were treated the same way. Fistula extrusa samples were mixed thoroughly by hand, placed in plastic bags and frozen (−4 ◦ C). Subsequently, samples were thawed and pooled across the 6-d collection period for each animal. Later, samples were partially dried in a forcedair oven at 55 ◦ C for 72 h, ground to pass a 1 mm screen in a Wiley mill to reduce all plant fragments to a uniform size. Two subsamples were taken and stored in plastic containers for microhistological and chemical analyses. Because the entire botanical composition of the browsing area was of interest, and some species are randomly distributed, while some are clumped and others are regularly dispersed, with a wide range of abundance, then a large rectangular quadrant was considered as the sampling area, transect, an extension of a rectangular quadrant was used in the form of a simple line (Whalley and Hardy, 2000; Franco-L´opez et al., 2001). With a line transect individuals and species touching the tape or string are recorded and the lengths of the intercept occupied by individuals touching the line are recorded (Whalley and Hardy, 2000; Franco-L´opez et al., 2001). To determine the botanical composition of the study area, in each collection period, 21 transects (30 m long) permanently established and randomly distributed around the corral, where goats normally browse, within a 3000 m2 area were sampled by the line-intercept method. Identified species were classified as non-legume trees and shrubs (NLTS), legume trees and shrubs (LTS), cacti, forbs, agaves or grasses. Individuals of each species were counted and measured to determine relative frequency of occurrence, relative density and relative canopy cover (Whalley and Hardy, 2000; Franco-L´opez et al., 2001). The mean of these three values were considered as the importance value (IV) for each plant type (Shannon, 1971; Hart, 1985; Franco-L´opez et al., 2001). As a separate data collection, leaves, flowers and fruits of all plants encountered within a 20 m perpendicular to transects but not on the transects were collected and slides prepared as a reference for plant identification in esophageal samples. Botanical composition (BC) of selected diets was determined by the microhistological technique (Sparks and Malechek, 1968). Calculated relative frequency for each species was converted to relative density using the formula F = 1 − e−x where F is frequency and x is the density, solving for x the percent for each species in the diet was the calculated (Johnson, 1982), then plants were classified as one of the six types considered for the determination of the IV in the study area. Preference indices (PI) of goats for plant species were determined as the quotient of the percent of each plant type in diet and the percentage of each plant type in the study area (Kruger, 1972); however, the proportion of each plant type in the study area was substituted by the proportional IV (percent of each specie from the summation of all IV) for each specie as a more

comprehensive measure of vegetal structure. An Index of 1.0 indicates that the percentage of species in diets was the same as that in available herbage. Indices greater that 1.0 indicate preference by goats, whereas indices near zero indicate avoidance of that species. Extrusas were analyzed for NDF, cellulose, hemicellulose, acid detergent lignin (ADL), non-fiber carbohydrates (NFC; Van Soest et al., 1991), CP, EE (AOAC, 1990), insoluble protein in neutral (NDIP) and acid detergent (ADIP; Van Soest et al., 1991). Available cell wall protein was calculated as NDIP–ADIP (Goering and Van Soest, 1970; Krishnamoorthy et al., 1982). The true in vitro organic matter digestibility (TIVDOM) was determined by procedures of Goering and Van Soest (1970). Rumen fluid was obtained from three non-fistulated goats that browsed with esophageal fistulated goats. True digestibilities of non-fiber carbohydrates (TDNFC), CP [TDCP], fatty acids [TDFA] and NDF (TDNDF) were calculated according with procedures by Weiss et al. (1992) and NRC (2001) and were used according to NRC (2001) to calculate digestible energy (DE). Metabolizable energy (ME) content of dietary samples was estimated using the following equation: ME (Mcal kg−1 ) = [1.01 × (DE) − 0.45] + 0.0046 × (EE − 3.0). Extrusas were dry ashed at 550 ◦ C for 6 h and then were prepared for mineral analysis using the wet ashing (HCl–HNO3 ) procedure (AOAC, 1990). Using an atomic absorption spectrophotometer brand Varian Model 3000 with air/acetylene flame, concentrations of Ca, K, Mg, Cu, Fe, Mn and Zn were calculated. 2.1. Statistical analysis Because the proportion of botanical composition and the Index of preferences are not independent within each collection date, these variables were compared using the nonparametric test of Friedman and Page’s trend test (Lehmann, 1975; Siegel, 1986). To determine the effect of collection date on botanical composition of diet, preference Index and nutritive composition of diet, an analysis of variance of each these variable was performed between dates. In the same way, an analysis of variance was performed to determine the effect of the collection dates in each nutrient of the botanical composition. All test were performed with alfa = 0.05.

3. Results and discussion Non-legume trees and shrubs such as Ruellia peninsulares, Jatropha cinerea, Lysium torreyi, Adelia virgata and Bursera microphylla were the most abundant plants encountered in the study area throughout the year, followed by the legume trees and shrubs (Prosopis articulata, Pithecellobium confine, Cercidiun floridum, Acacia peninsulares, Caesalpinia pannosa), and cacti (Opuntia cholla, Machaerocereus gummosus, Pachycereus pringlei, Mamilaria sp., Lemairocereus thurberi).

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Table 1 Seasonal importance values for plant types on a sarcocaulescent shrubland from Baja California Sur, Mexico Plant type

Sampling periods Spring

Importance value Agaves LTS NLTS Cactuses Forbs Grasses

Summer

Autumn

Winter

Early

Late

Early

Late

Early

Late

na 40 70 40 32 2

2 36 69 35 24 na

na 38 72 34 11 na

2 38 67 29 38 na

2 35 52 27 51 30

2 38 53 29 62 12

Early 2 40 64 31 45 4

Late 2 41 62 31 41 2

LTS: legume trees and shrubs, NLTS: non-legume trees and shrubs, na: no appeared on transects.

In general, all species belonging to these three plant types had a constant IV throughout the year. On the other hand, forbs (most abundant = Aristida adscensionis, Antigonon leptopus, Solanum hindsianum, Ambrosia psilostachya and Amaranthus palmeri) were higher in autumn than in other seasons. Grasses such as Eragrostis pilosa, Sporobolus airoide, Bouteloa curtipendula, Cenchrus palmeri and Cloris gayana and agaves such as Aloe vera followed similar pattern as forbs (Table 1). During spring early goat diets were composed mainly of NLTS followed by cacti, LTS and forbs; however during spring late diets were composed mainly of LTS and cacti, followed by NLTS and forbs. During summer, autumn and winter diets were composed mainly of NLTS followed by forbs, LTS and cacti (Table 1). NLTS such as A. virgata, Manguifera indica, J. cinerea, L. torreyi and Fouquieria diguetii were in higher proportions along the year. All plant type significantly varied between collection periods being LTS and cacti higher in spring late and summer early, whereas NLTS were

lower in spring late and forbs were higher in autumn early (Fig. 2). Preference indices of goats for LTS and cacti were higher in spring late and decreased thereafter; conversely, NLTS was significantly lower in spring late and higher from summer late to autumn late (Fig. 3). Forbs did not significantly vary between collection periods. This pattern may indicate a substitution effect of NLTS for cacti and LTS during spring late and summer early (Fig. 3). Ram´ırez et al. (1993) also reported that range goats, from northeastern Mexico, preferred more leaves of browse than forbs, grasses or agaves throughout the year. In this study, the most proffered species in each collection period are shown in Table 2 . It seems that forb preference indices were inconsistent throughout the year. Similar findings were found by Ram´ırez et al. (1993) who reported that forbs were consumed in proportion to their occurrence in herbage or at lower ratios. These data also coincide with Laribi et al. (1988) who indicated that Spanish and Angora goats selected many forbs, but forb preference indices

Fig. 2. Means and standard errors (n = 10) of the contribution of legume trees and shrubs (LTS), non-legume trees and shrubs (NLTS), cacti, forbs and grasses to botanical composition (BC) of goat diets on a sarcocaulescent shrubland from Baja California Sur, Mexico.

Fig. 3. Means and standard errors (n = 10) of preference indices (PI) of legume trees and shrubs (LTS), non-legume trees and shrubs (NLTS), cacti, forbs and grasses by range goats on a sarcocaulescent shrubland of Baja California Sur, Mexico.

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Table 2 Preference indices of goats by plant species on a sarcocaulescent shrubland from Baja California Sur, Mexico Item

Sampling periods Spring

Summer

Autumn

Winter

Early

Late

Early

Late

Early

Late

Early

Late

Agaves Aloe vera

na

0

na

0

0

0

0

0

Legume trees and shrubs Acacia farnesiana Acacia peninsularis Caesalpinia pannosa Calliandra californica Cassia covesii Cercidiun floridum Cercidiun praecox Haematoxylon brasiletto Lysiloma candida Mimosa xantii Pithecellobium confine Prosopis articulata

nd 2 0.4 1 0 0.3 0 1 nd 0 0.4 0.4

nd 4 0 1 0 2 1 nd 0 nd 1 0.3

nd 11 0 0 0 2 0 0.4 na 0 0.1 0.5

0 0 0 0.3 0 0 0 5 na 2 0.1 0.1

0 0 0 0.2 0 4 Na 1 na 3 0.1 2

2 1 0 0 0 0.2 0 4 na 0.2 4 0.3

6 1 0.1 0.5 0 9 0 1 na 1 2 1

0.1 0.2 0.3 3 0 2 0 3 na 0.2 2 1

6 0 0 0 0 0.1 na na na na 0 1 0.4 1 0 0 1 na 0 0.4 0 13 0.3 na na 0 0 0 8 0 0 0

1 0 0 0 0 0.5 na na na na 0 1 0 0.5 0 0 0 0 0 0 0 5 0 na na 0 na 0 0.5 0 0 0

1 0 nd 0 0 0 na na na na 0 0.3 1 1 0 na 0 na 0 0.2 0 17 0 na na 0 0 0 1 0 2 1

3 12 0.2 0 0 0.6 0 na na na 0 5 0 0 0 nd 0 na 0 2 0 12 0 na 0 0 na 0.1 0.1 0 0 7

4 12 0 0 na 1 0 0 0 0 0 0.6 0.5 0.6 0 na 1 0 2 0.5 0 16 nd na 0 0 na 0.4 0 0 0 0

1 13 0 0 0 3 0 0 0 0 0 0.3 0 0.2 0 na 0 0 nd 2 0 1 14 0 0 0 na 1 0 2 0 0

0 13 0 0 0 0.1 0 0 0 0 0 0.2 0 2 0 0 na 0 na 2 0 15 1 0 0 0 na 0.1 0 0 0 0

0.3 4 0 0 0 0.2 0 0 0 0 0 0.3 0.4 2 0 0 0 0 na 0.4 0 14 0 na 0 0 na 0.3 0 2 0 1

na na 0

na na na

0 0 na

0 0 0

0 0 0

0 0 0

0 0 na

0 0 0

Non-legume trees and shrubs Adelia virgata Ambrosia magdalena Bourreria sonorae Bursera microphylla Caesalpinia californica Cirtocarpa edulis Citrus limon Colubrina glabra Encelia farinosa Erythea brandegeei Euphorbia misera Fouquieria diguetii Hymenoclea monogyra Jatropha cinerea Jatropha cuneata Karwinskia humboldtiana Koeberlinia spinosa Krameria parviflora Lippia palmeri Lysium torreyi Malva parviflora Manguifera indica Melochia tomentosa Nicotiana glauca Pauteria campechiana Pedilanthus macrocarpus Porophyllum gracile Ruellia peninsularis Sapium biloculare Turnera diffusa Vallesia glabra Viguiera deltoidea Cacti Echinocereus brandegeei Ferocactus sp. Lemairocereus thurberi

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Table 2 (Continued ) Item

Sampling periods Spring

Summer

Autumn

Winter

Early

Late

Early

Late

Early

Late

Early

Late

0.1 0 1 0 6 na

4 .00 1 na 2 na

3 0 1 na 1 na

0.3 0 0.4 na 0 0

0 0 0.2 na 0 0

0 0 1 na 0 0

0 0 1 na 0 0

0 0 1 na 0.3 0

Forbs Alternanthera repens Amaranthus palmeri Ambrosia psilostachya Antigonon leptopus Aristida adscensionis Cnidoscolus angustidens Cucumis dipsaceus Cyperus ferax Datura discolor Euphorbia polycarpa Ibervillea sonorae Matelea cordifolia Merremia aurea Solanum hindsianum Viguiera laciniata

na nd 0.00 1 0 na na na na nd na na na 2 na

na na 0.00 0.3 0 na na na 0 nd na 0 na 1 na

na na 0 nd na na na na na nd 0 0 na 0.3 na

na 8 0 0.2 0.1 0 0 0 na 0.1 na na 0 5 na

0 11 0.3 0.2 1 na na 0 0 1 0 na 0 0.4 0

na 6 0 0.3 0.2 na na na 0 0 0 na 0 3 0

na 5 0.2 2 1 na na na 0 na 0 na 0 0.5 0

na 4.95 0 4 0.3 na na na na nd 0 na 0 2 0

Grasses Bouteloa curtipendula Cenchrus palmeri Cloris gayana Eragrostis pilosa Mentzelia aspera Sporobolus airoide

na 0 na na na na

na na na na na na

na na na na na na

na na na na na na

0 0 0 0 na 0

na 0 0 0 na 0

na na na 0 0 na

na na na 0 0 na

Machaerocereus gummosus Mamilaria sp. Opuntia cholla Opuntia clavellina Pachycereus pringlei Wilcoxia striata

na: Not intercepted in transects nor in diets, nd: appeared in diets but not in transects, 0: appeared in transects but not in diets.

were inconsistent. Only a small group of species was highly preferred (PI > 1.0) by goats throughout the year, also it appears that this preference is more dependent on the specific species than the plant type. Legume and/or non-legume trees and shrubs explained at least 50% of the botanical composition of goats diet and were preferred (PI > 1.0) all around the year. Similar to this results, Silanikove (2000) reviewed results on grazing strategy of browse by goats indicating that browse constitute at least 50% of the forage selected by goats and that although goats take advantage from the abundance of highly digestible forage, they maintain the intake of browse sufficiently high to preserve their acclimatization to tannin-rich food maintaining their specific advantage in digesting the food that is available to them in large amounts all around the year. Dietary NDF (annual mean = 46.2 ± 0.5%) varied through collections being lowest in spring late and summer (Table 3). Conversely, NSC content (annual

mean = 21.1 ± 1.0%) was highest in spring late and summer (Fig. 4). Similar responses were reported by Ram´ırez-Ordu˜na et al. (2003a) in five legumes browsed by range goats. They also reported that five non-legumes

Fig. 4. Means and standard errors (n = 10) of neutral detergent fiber (NDF), non-structural carbohydrates (NSC), cellulose, hemicellulose and lignin content to goat diets throughout the year.

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Table 3 Means and standard errors (n = 10) of mineral content of goat diets on a sarcocaulescent shrubland from Baja California Sur, Mexico Itema

Sampling periods Spring

Summer

Early Ca (g kg−1 ) Mg (g kg−1 ) K (g kg−1 ) Cu (mg kg−1 ) Fe (mg kg−1 ) Zn (mg kg−1 ) Mn, (mg kg−1 ) a

11 4 11 7 293 22 144

± ± ± ± ± ± ±

Late 0.68 0.16 0.46 0.20 26.58 0.53 9.97

6 3 9 7 149 23 54

± ± ± ± ± ± ±

Early 0.64 0.13 0.49 0.12 15.78 0.58 8.63

8 3 17 6 413 24 131

± ± ± ± ± ± ±

Autumn Late

1.16 0.31 0.92 0.26 70.28 1.16 14.32

12 5 22 10 136 43 64

± ± ± ± ± ± ±

Early 0.86 0.42 0.68 0.22 10.91 2.07 4.20

17 5 25 9 212 37 92

± ± ± ± ± ± ±

Winter Late

0.91 0.28 1.82 0.17 19.10 2.44 4.27

19 5 22 9 191 33 106

± ± ± ± ± ± ±

Early 0.58 0.12 2.64 0.20 5.92 1.36 3.91

19 6 24 8 452 28 107

± ± ± ± ± ± ±

Late 0.97 0.28 2.00 0.24 16.04 1.32 3.69

16 4 13 8 356 23 105

± ± ± ± ± ± ±

0.38 0.22 0.86 0.22 15.77 0.55 5.33

Dry matter basis.

had higher NDF and lower NSC in spring and summer. In this study, low NDF and high NSC in spring and summer might have related to higher consumption of fruits of cacti and fruits and flowers of LTS species. In general, NDF values registered in this study are lower than those found by Ram´ırez et al. (1991, 1993) who reported values above 60% in the annual diet of range Spanish goats in a shrubland of northeastern Mexico. Moreover, they mentioned that cell wall and lignin content were highest when goats selected diets with high browse species. Conversely, in this study higher cell wall levels corresponded to higher forb content in goat diets (autumn and winter) composed mainly by Amarantus palmeri and Antigonon leptopus. However, it has been reported that forb intake of range goats is negatively correlated to dietary NDF (Ram´ırez et al., 1991) and positively to grass content (Van Soest, 1994; Holechek et al., 1989). Whereas, in this study, grasses were consumed in lower amounts (annual mean < 1%). Cellulose content significantly varied across collection periods being lower in spring late, summer and winter late and higher in spring early, autumn late and winter early (Fig. 4). Lignin also varied, being lower in summer late and higher in winter late (Fig. 4). Lower cellulose levels corresponded to those seasons when animals selected diets with higher content of fruits and flowers from LTS and cacti species. Dietary CP with an annual mean value of 14.2 ± 0.3% varied across collection periods being lowest during spring and summer early (Fig. 5). Ram´ırez-Ordu˜na et al. (2003b) evaluated seasonally the CP content in 10 browse species (five legumes and five non-legumes) that grow in these regions and are consumed by range goats. They found that during spring and summer all plants had lower CP than in other seasons. However, legumes were higher (annual mean = 13.8%) than non-legumes (6.6%). In this study LTS and cacti appeared in higher proportions in goat diets and were more preferred in spring

late and summer early than in other seasons (Table 2). This fact might have influenced the CP content of goat diets in these seasons. Additionally had been reported that legume trees and shrubs selected by goats maintain an average 5.8–7.0% (of the dry matter) of tanniniferous compounds around the year and were higher than non-legume trees and shrubs (Ram´ırez-Ordu˜na et al., 2003a), this may negatively affect the protein availability during spring late and summer early. Ram´ırez et al. (1990) reported that when range goats selected more forbs, dietary CP was higher. Moreover, Holechek et al. (1989) found that forbs had more CP than shrubs or grasses that grow in arid regions of New Mexico, USA. In this study, the highest CP content occurred in autumn and winter when NLTS and forbs represented the most important plant type of goat diets (Fig. 2), whereas legume contribution in goat diets was the lowest (16%). According to this result and if intake is not a limiting factor, crude protein was in sufficient amounts to satisfy goat’s maintenance requirements developing low

Fig. 5. Means and standard errors (n = 10) of crude protein (CP), neutral detergent insoluble protein (NDIP), acid detergent insoluble protein (ADIP) and available cell wall protein (NDIP–ADIP) content in goat diets browsing on a sarcocaulescent shrubland from Baja California Sur, Mexico.

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to medium activity and a daily gain of 50 g d−1 , therefore it a strategic regimen of supplementation may be necessary, throughout the year, with protein resources according to the available digestible OM. Recently the use of polyethylene glycol (PEG) mixed with a small amount of concentrate has been reported and provided to animals to reduce the antinutritional effect of tannins in Mambers and Anglo-Nubian goats (Gilboa et al., 2000). Mambers goats increased their body weight during pregnancy, had higher kid birth weight and body weight gain until weaning, whereas Anglo-Nubian goats increased milk yield but no response in kid weight at birth. In Baja California Sur the production system is a dual purpose, mixed breeds with a high proportion of Anglo Nubian goats are raised for slaughter, kids and milk, goats are hand milked twice daily and had an average production of 850 g d−1 (Monroy et al., 2003), under this situation the use of PEG as a supplement may be an economical alternative to increase milk production, however this deserve an evaluation. Dietary NDIP was significantly lower in spring late to reach their maximum level in autumn late. Similarly ADIP (22.8%) was lower during spring late and summer and highest during autumn late, but available cell wall protein (NDIP–ADIP; annual mean = 24.6%) was low during spring late and autumn late (Fig. 5), however the TDCP content (annual mean = 11% DM) was highest in summer late (Fig. 6), when the CP content was highest. Higher ADIP values (>40% of CP) were reported by Ram´ırez et al. (1993) in goat diets browsing in a shrubland of northeastern Mexico. They also found that annual mean dietary protein was 16%. Thus, considering that ADIP can not be degraded by rumen microbes (Van Soest, 1994) because it is associated to lignin, tannins

Fig. 6. Means and standard errors (n = 10) of truly digestible non-fiber carbohydrates (TDNFC), truly digestible crude protein (TDCP), truly digestible fatty acids (TDFA) and truly digestible neutral detergent fiber (TDNDF) in goat diets on a sarcocaulescent shrubland from Baja California Sur, Mexico.

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and Maillard compounds (Krishnamoorthy et al., 1982), only 9.4% of dietary protein was considered available for ruminal digestion, which is insufficient for a 40 kg adult range goat. In this study, 11% of dietary CP was available for digestion. In this study, dietary EE resulted with higher values (annual mean = 11.9%) than those reported for conventional forages such as Medicago sativa (5.3%; Palmquist and Jenkins, 1980). Almost 50% of EE of forages is constituted of saponificable compounds such as waxes, cutin, and chlorophyll, while the other 50% are fatty acids (Palmquist and Jenkins, 1980; Van Soest, 1994). Moreover, plant fat extraction with ether diethyl may increase the presence in the EE of water soluble compounds such as urea and hexoses given values artificially higher (Palmquist and Jenkins, 2003). EE and therefore TDFA were highest in autumn early and winter (Fig. 6). The IVTDOM (annual mean = 63%; Table 3) significantly varied between collection periods being higher in spring and summer and decreased thereafter until winter late (Fig. 7). Higher values in spring may be related to high proportions of NSC when many selected legumes are producing flowers and fruits. Additionally, during this season, goats selected diets with the highest TDNDF (Fig. 6). Ram´ırez et al. (1991), Ram´ırez et al. (1993) who reported lower levels of IVDOM (34–43%) also found seasonal variations in goat diets from northeastern Mexico. In this study, lower IVTDOM during autumn may be related to lower content of TDNFC and higher lignin (Fig. 4). This later assumption may be the reason behind decreased the TDNDF (Fig. 6). Goats selected diets with ME values (annual mean = 2.4 Mcal kg−1 DM; Fig. 7) in substantial amounts to meet maintenance requirements of an adult range goat developing medium to high activity with a daily gain of 50 g d−1 (Kearl, 1982). Similar pattern was followed by Ram´ırez et al. (1990, 1993) who reported

Fig. 7. Means and standard errors (n = 10) of ether extract (EE), in vitro true digestibility of organic matter (IVTDOM) and metabolizable energy (ME) in goat diets on a sarcocaulescent shrubland from Baja California Sur, Mexico.

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goat diets had insufficient ME for maintenance plus minimum activity throughout the year and dietary CP was high, but only 50% was available. Conversely, Mellado et al. (1991) reported that browsing goats selected diets deficient in ME, even for maintenance. In this study, dietary TDCP was sufficient to meet only the maintenance requirements of an adult range goat. Ca content in goat diets significantly varied between collection periods (Table 3) being lower during spring late when rainfall was sparse and air temperature is ascending, and was higher during summer late through winter, after the main rainy season and air temperature is descending. Ram´ırez-Ordu˜na et al. (2005) found lower Ca content in spring in browse legumes and non-legumes, collected in the same regions. Whereas, Ram´ırez et al. (2001, 2006) found higher Ca content during summer in browse species collected in northeastern Mexico. In addition, Greene et al. (1987) argued a highly variable Ca content and extremely difficult to interpret relative to seasonal dynamics. Seasonal inter-species variation in Ca content has been reported (Ram´ırez et al., 2001; Ram´ırez-Ordu˜na et al., 2005). They found that cacti species had high Ca content than legume species. In this study, goats selected Ca, during all seasons, in sufficient amounts to meet requirements of an adult range goat (1.3–3.3 g Ca kg−1 DM; NRC, 1981; Kessler, 1991). In this study, Ca content in esophageal samples and offered forage was highly correlated and therefore may be used to predict Ca content in diets (Ram´ırezOrdu˜na et al., 1995). Dietary Mg (annual mean = 4.3 ± 1.4 g Mg kg−1 ) was lower during spring late and summer early. Similar values (annual mean = 4.1 g kg−1 ) were found by Ram´ırez-Ordu˜na et al. (2005) in browse species growing in these regions. In this study, dietary Mg was in sufficient amounts (Table 3) to meet requirements (0.8–2.5 g Mg kg−1 DM; NRC, 1981) of a range goat weighing 40 kg and consuming 76.3 g DM kg0.75 d−1 . Similar finding were reported by Ram´ırez et al. (1993) and Cerrillo-Soto et al. (2004). Magnesium content in esophageal samples and forage offered was highly correlated and therefore may be used to predict Mg content in diets (Ram´ırez-Ordu˜na et al., 1995). Dietary K was lowest in spring late and highest during autumn (Table 3). However, it has been established that K concentration appeared to vary as a function of absolute age of leaf, environmental conditions and water availability (Charley, 1977; Greene et al., 1987; Grings et al., 1996). Under water stress K uptake may be limited and K deficiency may develop (Salisbury and Ross, 1994a,b; Miller and Doescher, 1995). In this study, range goat could eat substantial amounts to meet requirements

(1.8–2.5 g K kg−1 ; NRC, 1981) in all seasons. Similar findings were reported by Ram´ırez et al. (1990, 1991, 1993) and Cerrillo-Soto et al. (2004) who evaluated K content in extrusas samples from goats browsing in arid regions of northeastern and north Mexico, respectively. A wide variation in Mn content between and within plant species has been reported. Ram´ırez-Ordu˜na et al. (2005) found that Mn varied within species and might be the reason of lack of seasonality (Table 3). However, Ram´ırez et al. (2001) and Moya-Rodr´ıguez et al. (2002) found higher Mn concentration in winter and spring than in other seasons. In this study, goats selected diets with inconsistent Mn content (Table 3) but in sufficient amounts to meet requirements (30–40 mg Mn kg−1 DM; Kessler, 1991) in all seasons. However, there is evidence that suggest that high dietary Ca may increase Mn requirements (Hidiroglou, 1979), and the availability of Mn may be compromised when a high proportion (22–94%) is located in the cell wall (Spears, 1994). Therefore particular attention to Mn requirements in this particular situation must be required. Dietary Cu significantly varied between collection periods (Table 3). During spring and early summer, Cu concentrations were below the critical concentrations for promoting deficiency (<8 mg Cu kg−1 DM; Warly et al., 2003) and were marginal for the rest of the year (Table 3). It has been established that decreasing forage Cu concentration may occur when advancing maturity (Spears, 1994). Ram´ırez et al. (2001) found Cu concentration, in shrubs northeastern Mexico, was higher during spring indicating that, in these regions, spring is the period of active vegetative growth; however, in Baja California Sur, Mexico, spring is the period of drought and dormancy. High pH of soil may cause low Cu levels in plants (Spears, 1994). Low Cu concentrations are also reported in shrubs from semiarid regions (Barnes et al., 1990; Ram´ırez et al., 2001; Cerrillo-Soto et al., 2004). In this study, dietary Fe varied inconsistently between collection periods (Table 3). Moreover, goats selected diets with sufficient Fe to meet requirements (35 mg Fe kg−1 DM; NRC, 1981). Furthermore, Ram´ırez et al. (2001) and Moya-Rodr´ıguez et al. (2002) sustained that Mexican shrubs growing in semiarid regions had Fe levels in substantial amounts to meet requirements of range goats. Dietary Zn was significantly lower during spring, increasing toward summer late when Zn level was maximum and decreasing thereafter until winter late (Table 3). Peaks of Zn levels appeared to be related to summer rainfall (Ram´ırez-Ordu˜na et al., 2005). Some shrubs consumed by small ruminants that occur in Texas, USA

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(Barnes et al., 1990), and northeastern Mexico (Ram´ırez et al., 2001; Moya-Rodr´ıguez et al., 2002) had Zn levels that varied seasonally, but only a few of them had levels of Zn to meet requirements (30 mg Zn kg DM in the diet; Kessler, 1991). In this study, only during summer late and autumn dietary Zn was in adequate concentration to satisfy range goats requirements (Table 3). 4. Conclusions Goats preferred diets with a high proportion of nonlegume followed by legume trees and shrubs species and forbs, and less cacti and grasses, however during spring late when rainfall is spare and air temperature is reaching the maximum level, legumes and cacti appear to be an important resource for goat feed. It appears that this preference is more dependent on the specific species than the plant type. In general, nutrient content in goat diets remained about the same across collection periods. However, if intake is not a limiting factor, crude protein and metabolizable energy were consumed in amounts to satisfy goat’s maintenance requirements developing low to medium activity and a daily gain of 50 g d−1 . Zinc (during all year) and Cu (in spring and summer) resulted also insufficient. Thus, to obtain a better performance of range goats in this regions, a regimen of supplementation, throughout the year, with energy and protein resources and trace elements such as Zn and Cu is necessary. References AOAC, 1990. Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Arlington, VA. Arriaga, L., Cansino, J., 1992. Pr´acticas pecuarias y caracterizaci´on de especies forrajeras en la selva Baja caducifolia. In: Alfredo Ortega (Ed.), Uso y Manejo de los Recursos Naturales en la Sierra de la Laguna Baja California Sur. La Paz, M´exico, pp. 155–184. Barnes, T.G., Varner, L.W., Blankenship, L.H., Fillinger, T.J., Heineman, S.C., 1990. Macro and trace mineral content of selected south Texas deer forages. J. Range Manage. 43, 220–223. Cerrillo-Soto, M.A., Nev´arez-Carrasco, G., Ram´ırez-Lozano, R.G., N´un˜ ez-Gonz´alez, A., Garc´ıa-D´ıaz, G., Ju´arez-Reyes, A.S., 2004. Mineral profile of diets consumed by range Spanish goats in a shrubland of North Mexico. S. Afr. J. Anim. Sci. Suppl. 1, 117– 119. Charley, J.L., 1977. Mineral cycling in rangeland ecosystems. In: Soseebe, R.E. (Ed.), Rangeland Plant Physiology. Society for Range Manage, Denver, Colorado, pp. 215–256. COTECOCA, 1975. Coeficientes de agostadero de la Rep´ublica Mexicana: Estado de Baja California, Sur. Secretar´ıa de Agricultura y Ganader´ıa, M´exico, p. 67. DGETENAL, 1980. Direci´on General del Territorio Nacional. Carta geogr´afica El Rosario. 119 F121333. FAO, 1987. Committee on Agriculture (Ninth Session). Improving Productivity of Dryland Areas. FAO, Rome, pp. 353–375.

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