Effect of complex catalytic supplementation with non-protein
nitrogen on the ruminal ecosystem of growing goats
pasturing on shrub land in Mexico
M.A. Galina
a,b,c,*, M. Guerrero
a,b, G. Serrano
b, R. Morales
b,c, G.F.W. Haenlein
d aFacultad de Estudios Superiores Cuautitlan, UNAM, 54000 Cuautitlan, MexicobPosgrado Interinstitucional en Ciencias Pecuarias, Universidad de Colima, 28000 Colima, Mexico cGranja Puma, Municipio del Marques, QuereÂtaro, Mexico
dDepartment of Animal and Food Sciences, University of Delaware, Newark, DE 19717-1303, USA
Accepted 20 August 1999
Abstract
Thirty-eight young Alpine goats, 16.1 (0.370) kg body weight (BW), were reared at QuereÂtaro, Mexico, grazing on a
semi-arid woody brush (Caducifolio espinoso) range land. The experimental goats (n20) were pastured daily and supplemented with 200 g/day of a complex catalytic feed (CCF). It consisted of molasses (14±18%), urea (8±10%), salt (3± 4%), limestone (3±4%), cottonseed meal (13±18%), rice polishing (10±13%), corn (11±12%), poultry litter (9±10%), commercial mineral salt (1.3%), ammonium sulfate (0.3±0.5%), cement kiln dust (1.5%), and animal lard (10±15%). The control goats (n18) were supplemented daily with 300 g of a balanced concentrate (BC), containing 1.5% commercial mineral salt, 60% corn, 32.5% wheat bran, and 4% soybean oil meal. Stocking rates varied from 1.45 to 1.85 AU/ha and daily stocking rate from 36.4 to 58.6 AU/ha. At all times, ®brous forages were available exceeding the voluntary dry matter intake. One ®stulated goat was kept in each group. Growth of the experimental goats averaged 95 g/day (3) compared to 76 g/day (5) of the controls (P< 0.005) in 150 days from June to November. Supplementation per kg BW was from 17.5 to 10.4 g BC/ day for the control goats; the experimental goats received 12.2±6.5 g CCF/day. Weight gain in response to fermentable carbohydrates (FC) averaged 8.95 g BW gain/g FC/day for the control BC goats, compared to 28.2 g BW gain/g FC/day for the experimental CCF goats. Daily supplies of FC to goats on CCF supplementation were always below the limits for celullolysis at 6 g/day, while FC supplies of BC rations to the control goats always exceeded them. After 2 h of shrub land pasture, the ruminal pH rose when CCF was offered and stayed above 6.6 during 12 h, while the ruminal acidity in BC goats went down to pH 5.57 at 6 h and rose to 6.5 by 12 h. Ammonia (NH3 mg/l) in ruminal liquid of CCF goats was higher (P< 0.01) in average and all but one sample. Total cost per animal per day including shrub land pasture, management, medicine and salaries was US $0.06 for experimental goats and US $0.09 for controls (market price for goat meat was US $1.15/kg; US $1.0010 Mexican Pesos, November 1998). Daily gain varied during the study period from 77 to 85 g/day in BC control goats compared to 92±97 g/day in experimental CCF goats. CCF supplementation to shrub land pasturing resulted in signi®cantly greater weight gains apparently due to elevated ruminal pH, higher availability of fermentable carbohydrates and ruminal ammonia, augmenting ruminal ecosystem, digestibility and voluntary feed intake. The use of local shrub land
*Corresponding author. Tel.: 0052-331-411-33; fax: 0052-331-275-81.
E-mail address: galina@cgic.ucol.mx (M.A. Galina).
resources and complex catalytic supplementation with non-protein nitrogen provided greater pro®tability from this feeding system for growing goats than the traditional balanced concentrate feed supplementation.# 2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Nutrition; Goats; Growth; Ruminal ecosystem; Supplementation; Shrub land; Urea
1. Introduction
Goats raised on shrub range land, which is rich on ®brous forages, have low performance in body weight (BW) gain of no more than 50 g/day (Galina et al., 1993). Forages and crop residues, rich in ®ber and low in protein are the most abundant feeds for ruminants in third world nations (Preston, 1995). Recent studies in Mexico with large ruminants aimed at achieving better performance from local forages by using complex catalytic feed (CCF) supplementation (Galina et al., 1997). Strategies to improve utilization with CCF feeds in dairy goats have been reported (Morales et al., 2000).
Utilization of high ®ber diets with CCF needs to develop new feeding standards, because ruminal pro-tein and energy will add to the nutritional offer in the feed to the animal (Jackson, 1980; Galina, 1994; Graham, 1983; Preston, 1995). Goat requirements have been reviewed (AFRC, 1998), after the work of Morand-Fehr and Sauvant (1988) and NRC (1981). Energy requirements for goats are 104.7 kcal/kg
BW0.75 for maintenance plus 25±50% increase to
cover cost of walking, grazing and other activities, and 13.8 Mcal/kg BW gain (AFRC, 1998). Present information on energy and protein contents of a feed has little bearing on how animals utilize their feed, when digestibility is improved due to bacterial aug-mentation from favorable energy contents in ration, resulting in more intestinal true protein. It have even been suggested that traditional nutritional approaches should be abandoned for forage-based diets under ®brous forage management (Leng, 1990).
Nutritional utilization of ®brous forages requires that the imbalance of nutrients for both rumen micro-organisms and the host animal must be corrected for better nutrition of rumen bacteria by providing energy and nitrogen, which then results in improved bypass nutrients to reach the intestines for higher production by the host animal with lowered cost (érskov, 1994;
Wells and Russell, 1996; Russell and Wilson, 1996; Weimer, 1996).
Better understanding of rumen function and the role of CCF supplementation has been tested in Mexico (Galina et al., 1997). Recent studies lead to the con-cept of ``balancing nutrients'' by providing high pro-tein to energy ratios in absorbed nutrients, and improving productive ef®ciency (Leng, 1990). Goats can be considered as animals with a two-compartment system (Morales et al., 2000). Ef®cient microbial fermentation relies on the products of the rumen and those digestible feed components that escape fermentation (Preston, 1995). Under laboratory con-ditions, many factors can be isolated and studied in detail, but few studies have attempted to elucidate simultaneously the interaction of many factors that result in the ef®ciency of end-product utilization by the animal in production trials (Leng, 1990). The importance of the type of supplement used when evaluating forages has been emphasized by many studies (Sanson, 1993). The addition of soluble car-bohydrates to diets can have a negative effect on forage intake and ®ber digestibility (Purroy et al., 1993). The hypotheses for this decrease in intake include decreased ruminal pH, a substitution effect, competition for essential nutrients among cellulolytic and non-cellulolytic bacteria, and the possible use of alternative energy sources by cellulolytic bacteria (Mould, 1989). Many workers found that supplement-ing basic forage diets of low digestibility with small quantities of feed that are rich in digestible cellulose or hemicellulose will increase forage digestibility (Juul-Nielsen, 1981).
in QuereÂtaro, Mexico, with 38 goats pasturing brush land and supplemented with complex catalytic feeds. The study should allow balancing the nutrients needed by the rumen bacteria and measure the effects of modifying the ecosystem with suf®cient bypass nutri-ents on goat growth and economic feasibility. Tradi-tionally balanced supplementation (Morand-Fehr and Sauvant, 1988) was to be employed for control goats.
2. Material and methods
The study was conducted on the ``Puma'' farm in
the Cerro Prieto region, QuereÂtaro, Mexico, at 208350
latitude North and 1008180 longitude West. The
alti-tude was 1950 m above sea level. Climate is classi®ed as Bs 1 kw (w) (e), described as dry semiarid with isolated rains in the winter and a total of 460 mm of average precipitation per year (GarcõÂa, 1973). The research was performed on 40 ha of shrub range land
with grasses:Bouteloua curtipendula,Chloris virgata,
Bothriochloa saccharoides,Leptochloa saccharoides, Leptochloa dubia, Rhyncheltythurum roseum, Pani-cum obtusum,Bouteloua repens,Aristida adscensio-nis, Setaria parvi¯ora, Urochloa fasciulata;
leguminous trees:Prosopis laevigata,Acacia
farnesi-ana, Acacia schaffneri, Mimosa biuncifera; and
shrubs: Celtis pallida, Jatropha dioica, Zalazania
augusta,Verbasina serrata,Opuntiaspp.
A production of 800 kg DM/ha/year was calculated (Galina et al., 1998). Grazing management and tech-niques for shrub land evaluation was published by Puga (1998). Stocking rates varied from 1.45 to 1.85 AU/ha and daily stocking rate from 36.4 to 58.6 AU/ha. At all times, ®brous forages were avail-able exceeding the voluntary dry matter intake.
Thirty-eight young Alpine goats, 16.1 (0.37) kg
BW, were allocated into two treatment groups in a production function design. Animals were weighed every 15 days. On experimental group of 20 goats were pastured daily and supplemented with 200 g/day of a complex catalytic feed mixture (CCF) consisting of molasses (14±18%), urea (8±10%), salt (3±4%), limestone (3±4%), cottonseed meal (13±18%), rice polishing (10±13%), corn (11±12%), poultry litter (9± 10%), commercial mineral salt (1.3%), ammonium sulfate (0.3±0.5%), cement kiln dust (1.5%), and animal lard (10±15%). The control group of 17 goats
was kept on similar management but fed 300 g/day of a traditional balanced concentrate (BC) composed of 1.5% commercial mineral salts, 60% corn, 32.5% cottonseed meal, and 4% soybean oil meal. Chemical feed analyses were performed according to AOAC (1995); determination of ®ber contents according to Van Soest and Wine (1967) and Goering and Van Soest (1975) methods; total energy with a calorimetric bomb after Hill et al. (1958) and Robinson (1984); shrub land forages were combined for chemical analyses with the method of Puga (1998).
Cellulolysis and rumen eco-environment was deter-mined by using one ®stulated goat in each treatment
group to measure pH and ruminal ammonia (N±NH3)
levels. Each goat was sampled every 2 h after supple-mentation every 15 days, as described by Beatman (1970), with a portable recorder (Orion 250-A) equipped with an ion selective electrode for ammonia (Orion 95-12). From the chemical analyses of the two supplements the contents and supplies of fermentable carbohydrates were calculated in g/day. Supplementa-tion in g/day was also recorded monthly in g/kg BW. Daily voluntary intake was determined for both sup-plements and for the forages in pasture according to INRA (1988).
Statistical analyses for pH and ammonia were performed comparing means with SAS (1996)
procedures (P< 0.05). The statistical model was:
YijmtiEij, whereYijis pH or NH3jth
observa-tion of the ith treatment; m the overall mean; t the
treatment effect; ithe ith treatment (i1, 2
supple-ment type); j is the jth observation (j1, 2, . . ., 4
(pH); 1, 2, . . ., 4 (NH3) observation); andEij is the
error.
Statistical analyses of the 44 Latin square design
were performed with ANOVA (SAS, 1996), and differences between means were analyzed according
to Tukey (P< 0.05). The model was:YijklmAi
BjTtEijkl; whereYijklare variables such as goat
growth, supplementation g/kg BW, fermentable car-bohydrates in g/kg BW, and supplementation g/day/g
BW gain;mis the overall mean;Aithe effect from the
ith line (goat);Bjthe effect from thejth column (time);
Ttthe effect of treatment shown in thejth line/column;
andEijklis the error associated with the experimental
unit line/column (ij).
Monthly consumption and nutrient requirements as suggested by Morand-Fehr and Sauvant (1988) were dependent variables. By regression equation, the nutri-ent density of the feeding treatmnutri-ents and the total requirements of the grazing goats were the determi-nants of probable consumption.
3. Results
Table 1 shows monthly BW of the control and experimental groups. The amounts of voluntary intake of BC supplementation went from 17.5 g/day/kg BW at the beginning of the trial in control goats to 10.4 g/ day/kg BW at the end, when the 300 g/day were offered. The intake of CCF supplementation went from 12.2 to 6.5 g/day/kg BW, when 200 g/day were offered. At the end of the trial, BC supplementation was 59% lower from initial consumption, CCF sup-plementation 53% lower. While the amounts offered remained constant throughout the trial, the BW increased almost two-fold. Total dry matter intake (DMI) by the CCF group increased from 3.1% to 3.8% of BW, while the DMI of the BC group decreased from 3.3% to 2.9% of BW. Forage intake increased from 265 to 536 g/day in BC, while in CCF
goats it changed from 311 to 973 g/day. Goats in the CCF group consumed signi®cantly more forage than the BC controls.
Experimental CCF goats showed an average growth
of 95 g/day (3) compared to 76 g/day (5) (Table 1)
for BC controls during 150 days from June to
Novem-ber (P< 0.005). The rotationally grazed shrub land
pasture consistently had more total forage available during midsummer and late summer. However, once the period of plant regrowth ®nished in early autumn, the rotational pasture had similar or less total forage standing, while grass was available at all times exceeding the voluntary dry matter intake. Experi-mental CCF feeds were consumed for 6±8 h after offering, in comparison with BC rations, which were eaten in 15±30 min after supply.
Fig. 1 shows the amounts of fermentable carbohy-drates consumed daily/kg BW calculated from the chemical analyses of the feeds. Response to fermen-table carbohydrates in terms of grams BW gain/day/g FC averaged 8.95 for BC, compared to 28.27 for CCF
goats (P< 0.05) (Table 1). Daily supplies of FC to
goats on CCF supplementation were always below the limits of 6 g/day for cellulolysis (Mould, 1989), while FC supplies of BC rations to the control goats always exceeded them.
Table 1
Monthly BW, supplement fed/kg BW/day, fermentable carbohydrates supplied/kg BW/day and gain/day in each period for CCF and BC supplement treatments (BW: body weight; FI: forage intake; BC: balanced concentrate; CCF: complex catalytic feed; DMI: dry matter intake; d: day; FC: fermentable carbohydrates; ab: statistical difference (P< 0.05) among pairs with same shading)
Days 0 30 60 90 120 150 Mean
BW (kg), BC goats 17.14 19.45 21.55 21.40 26.60 28.84 22.444.4 BW (kg), CCF goats 16.41 19.29 22.19 25.06 27.93 30.68 25.595.35 BC total (g/day) 300 300 300 300 300 300 300 CCF total (g/day) 200 200 200 200 200 200 200 FI±BC group (g) 265 387a 400a 346a 478a 536a 40295.7a
FI±CCF group (g) 311 536ab 617ab 752ab 832ab 973ab 670234b
Total DMI BC (g) 565 687 700a 646a 778a 836a 70295.7a Total DMI CCF (g) 511 736 817b 952b 1032b 1173b 870234b DMI (%) BW±BC 3.3 3.5 3.2 3.0a 2.9a 2.9a 3.10.24a DMI (%) BW±CCF 3.1 3.8 3.7 3.8b 3.8b 3.8b 3.70.28b BC (g/kg) BW 17.50 15.42 13.92 12.44a 11.27ab 10.40ab 13.392.66 CCF (g/kg) BW 12.18 10.36 9.01 7.98b 7.16ab 6.51ab 8.972.31 FC (g/day) BC 11.02a 9.71a 8.76a 7.83a 7.10a 6.55a 8.491.67a FC (g/day) CCF 4.62b 3.93b 3.42b 3.03b 2.72b 2.47a 3.360.80b
FC (g/g) BW BC gain 7.92a 7.99a 10.85a 11.69a 11.45a 8.95a
FC (g/g) BW CCF gain 24.42b 28.36b 31.68b 35.29b 37.24b 28.27b
BC gain (g/day) 77a 70a 85a 83a 75a 76a
Table 2 shows the chemical composition of forages, CCF and BC supplements. Crude protein contents for both forages were 7.68% and 8.10%, respectively; metabolizable energy was 2.12 and 2.49 Mcal for BC and CCF forages, respectively. Supplements con-tained 19.8% crude protein for BC and 26.13% for CCF, due in part to the amount of urea. The table also
shows crude ®ber, NDF, ADF, cellulose, hemicellu-lose and lignin contents, the later above 8% in both forages.
Table 3 summarizes the ruminal kinetics of pH over time in goats fed CCF or BC while pasturing shrub land. After 2 h on CCF the pH rose and stayed above 6.6 for 12 h, while the ruminal acidity in
Fig. 1. Total supplementation g per day, total fermentable carbohydrates g/day and limit of carbohydrate supplementation g/day for Cellulolysis according to Elias (1983).
Table 2
Chemical composition of forages, BC and CCF supplements (CCF: complex catalytic feed; BC: balanced concentrate; CCF forage: mixture of forages consumed by CCF goats; BC forage: mixture of forages consumed by BC goats)
BC forage CCF forage BC CCF
Dry matter (%) 93.69 99.65 90.53 93.12
Ash (%) 5.08 9.21 5.60 18.89
Ether extract (%) 2.70 1.08 4.07 9.88
Crude protein (N6.25) (%) 7.68 8.10 19.83 26.13
Crude fiber (%) 36.04 35.81 12.56 5.00
Neutral detergent fiber (%) 75.17 68.82 68.40 37.84 Acid detergent fiber (%) 39.73 45.75 13.16 16.66 Cellular content (%) 34.83 31.17 31.59 62.15
Cellulose (%) 32.90 31.67 7.84 8.01.
Hemicellulose (%) 67.27 65.37 55.23 21.18
Lignin (%) 8.54 9.48 4.86 4.90
Nitrogen free extract (%) 61.50 60.80 57.94 40.10 Total digestible nutrients (%) 95.49 92.91 99.89 99.99 Metabolizable energy (Mcal)a 2.12 2.49 2.83 3.05
Digestible energy (Mcal)a 3.59 3.35 3.61 3.71
Total energy (Mcal)a 4.37 4.08 4.39 4.53
BC goats went down to pH 5.57 at 6 h and rose to 6.5 by 12 h.
Table 4 shows the ruminal kinetics of ammonia
(NH3mg/l) over time in goats fed CCF or BC while on
shrub land pasture. Ammonia was higher (P< 0.01) in
the CCF group on an average and in all but one sample.
Total cost per animal per day including grass, management, medicine and salaries was US $0.06 for the experimental CCF goats but US $0.09 for control BC goats. Market price per kg meat was US $1.15 calculated in Mexican Pesos per dollar
exchange rate of November 1998 (1 US $10 Pesos).
Daily gain varied during the trial from 70 to 85 g/day in control BC goats to 92 to 97 g/day in experimental CCF goats (Table 1).
4. Discussion
Results showed differences in growth rate
(P< 0.05) for experimental over control goats,
sug-gesting that daily gains of 100 g (AFRC, 1998) can be obtained with good nutritional management. The pro-tein needs of the experimental goats for growth were met by correcting the nutrient imbalance of the grasses and providing a continuous non-protein nitrogen source of urea (Hennessay and Williamson, 1990) or ammonium sulfate to the rumen bacteria (Leng, 1990; Silva et al., 1989). Ruminal bypass protein, e.g. ®shmeal, and bypass carbohydrates in corn and rice polishings have proven important in cattle perfor-mance when fed ®brous forages (Elliot et al., 1978; Leng et al., 1977; Naidoo et al., 1977; Galyean, 1996; Poppi and McLennan, 1995). Bypass protein in our experiment was supplied by the legume tree leaves (Puga, 1998). Growth in the control goats was sup-ported mainly by the high protein content in the BC ration, which hand a substitution effect for the poor forages (Tables 1 and 2). Low rumen pH and less ammonia contents in the control goats explained the effects of concentrate intake in pastured goats. The high amounts of fermentable carbohydrates also affected cellulolysis (Elias, 1983; Madrid et al., 1998). When microbial protein is the main source of nitrogen for growth, there must be considerable concern covering the requirements by rumen microbes for ef®cient growth. Meang et al. (1989) suggested that microbial growth ef®ciency was improved in washed rumen microbes by including amino acids as well as urea in the incubation medium. Amino acids such as leucine, lysine, threonine and tryptophan were supplemented in the CCF experimental diet by the addition of poultry litter as also demonstrated by Zinn et al. (1996).
Previously, Elias (1983) has shown that small amounts of easily available energy from fermentable carbohydrates like in molasses, sugar cane or starch could increase cellulose digestibility because ruminal microorganisms are not capable to obtain energy from cellulose for their cellular functions until the molecule is digested. Therefore, goats, sheep and cattle supple-mented with low levels of sugars between 2 and 6 g/kg BW/day could improve cellulose digestibility because rumen microorganisms now have energy for their cellular functions. Similar ®ndings have been reported
Table 3
Ruminal kinetics of pH over time in goats fed CCF or BC on shrub land pasture (CCF: complex catalytic feed; BC: balanced concentrate;*A,B: means with different letters indicate statistical
signi®cance (P< 0.01); a,b: means with different letters indicate statistical signi®cance (P< 0.01))
Hours CCF BC
Rumen kinetics of ammonia over time (NH3mg/l); ruminal liquid
from goats pastured on shrub land supplemented with CCF or BC (CCF: complex catalytic feed; BC: balanced concentrate; a,b: means with different letters have statistical signi®cance (P< 0.01)
when low amounts of citrus by-products were supple-mented at 100 g/day and improved digestibility and intake of DM of urea±NaOH treated straw based diets (Madrid et al., 1998). The explanation was that at low levels the supplementation with degradable carbohy-drates such as from citrus by-products supplied energy for ruminal microorganism and improved the ruminal ecosystem for cellulolysis and straw digestion (Madrid et al., 1998). However, at more than 6 g of fermentable carbohydrates (FC) per kg of BW, cellu-lose digestibility diminished because concentrate sup-plementation substituted for forage. It has been shown that moderate amounts of cellobiose added to pure cultures of cellulolytic bacteria inhibit cellulose hydrolysis, which suggests an enzyme depressing system based on less speci®c activity for cellulose from microorganisms growing in a cellobiose-rich environment (Elias, 1983). Similar results have been published by Madrid et al. (1998), when higher levels of digestible carbohydrates in supplements depressed the digestion of straw. This is also explained by the negative effects on cellulolytic activities of the rumen micro¯ora, when high levels of energy supplements decrease ruminal pH (Rihani et al., 1993). In our study, CCF fermentable carbohydrates were always below the above limits (4.62±2.47 g FC/day) (Table 1) favor-ing the ruminal ecosystem to stimulate feed intake and BW gain, while FC from the BC ration was always above the limits (11.02±6.55 g/day) apparently affect-ing cellulolysis.
Daily weight gain in the present work apparently did not equal the levels of metabolizable energy in the forages (Table 2). Increased voluntary dry matter intake supplied more energy, because of improved digestibility from the improved action of cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus albus, R. Flavefaciens) favored by the continuous presence of non-protein nitrogen (Leng, 1990; Fon-devila and Dehority, 1995; Preston, 1995; Brown et al., 1988). This is indicated by the higher levels of
ruminal ammonia (17.37 mg/l;P< 0.01) (Table 4) in
CCF supplemented goats compared to the BC goats (10.30 mg/l), creating a favorable protein/energy ratio for bacterial protein formation (Leng, 1991). The experimental CCF supplement was consumed over a period of 6±8 h, while the commercial BC supple-ment was ingested in less than 30 min after offering (15±30). This mixture could have insured suf®cient
ammonia for microbial growth (50±80 mg NH3±N/l
rumen ¯uid) (Leng, 1991), but the level of ammonia needed is dependent on the pH of the rumen (Smith, 1984).
Forage offer was kept high all time through the rational technological mobile grazing (RTMG) system developed by Puga (1998), boosting digestibility of the basal diet (Juul-Nielsen, 1981; N'dlovu and Buchannan-Smith, 1985). Grass was allowed to re-grow before returning to be pastured (Puga, 1998). Sudana and Leng (1986). Showed that supplements must provide continuous adequate levels of ammonia for persistent growth of both ®brolytic and sacchar-olytic microorganisms, by providing in the supple-ment high concentrations of salt±urea and molasses± urea to aviod fast intake. Supplementation with branched-chain VFA has been reported to increase the apparent ¯ow of microbial-N to the duodenum (Silva and érskov, 1988). Ruminal pH supported by calcitic limestone and cement kiln dust could have played a key role of maintaining cellulolytic bacteria in our experimental animals (Wheeler, 1979; Wheeler et al., 1981a, b; Noller et al., 1980).
Rumen acidity is produced by high intake of starches. Amylose and amylopectin are broken down early under the in¯uence of amylases. Ruminal pH environment for microbial activity was lower in the BC supplemented goats (Table 3). CCF supplementa-tion kept pH above 6.6 all the time, while BC decreased pH to 5.57 inhibiting celullolysis (Leng, 1991). This may explain the lesser growth of the BC control goats, depending on energy and protein from their supplementation, because of less bacterial pro-tein formation. As rumen pH is depressed below 6.2 (Istasse et al., 1986), cellulolysis progressively decreased and ceased altogether at rumen pH of around 5.9 (érskov, 1994; Russell and Wilson, 1996; Russell et al., 1979; Weimer, 1996).
(érskov, 1991). Long-chain fatty acids in animal lard, as provided in the CCF supplement, potentially gen-erate reduced nicotinamide adenine dinucleotide
(NADPH) and electron acceptors (NAD
) for increased use of acetate. This and the high energy density of the animal lard may explain the better growth performance of the CFF goats on less supple-ment (200 vs 300 g/day) than the BC controls (Houtert, 1993).
Molasses as a cheap source of FC, and the buffer effects of limestone and cement kiln may explain the complex relationships established by this feed in manipulating ®ber digestion in the rumen (érskov, 1991). High levels of molasses±urea have been suc-cessfully used for fattening of cattle on pasture in Australia (Anon, 1984), Colombia (Huerta and Gon-zaÂlez, 1987) and Cuba (ValdeÂs and Delgado, 1990).
It could be suggested from the present results that goat kids adequately supplemented with small quan-tities of essential nutrients performed equally well on a lower digestibility feed, as animals on higher digest-ibility forage. Pasture management was the other key to obtain gains from grass offered throughout the study (Puga, 1998). Heat increment of added acetogenic substrates will depend on the pattern of fermentation in the rumen, VFA and the balance of protein available from the intestine. Goats need to oxidize acetate, the major thermogenic substrate. Ruminants con®ned to calorimeters are usually maintained at what is sup-posed to be thermoneutrality, however, in our study, animals were exposed to heat and cold (rain) stress and they responded metabolically according to the insu-lative properties of their skin. Variances in weekly gains were related to environmental effects. Aceto-genic substrate is the major source of ATP for muscle metabolism (Pethick, 1984), therefore acetate forma-tion in this study could explain the growth of the supplemented goats (Leng, 1990).
5. Conclusion
Utilization of ®brous diets by ruminants can be manipulated in various ways. Digestibility and intake was improved as evidenced by superior weight gain of 95 g/day for CCF goat kids compared to 76 g/day by BC goats. This was apparently due to elevated rumen pH and ammonia levels augmenting the bacterial
ecosystem by offering essential amino acids, long-chain fatty acids, non-protein nitrogen, calcium, sulfur and phosphorus, which in turn improved cellulose digestion. Direct bypass protein and glycogenic car-bohydrates from the rumen are other key ingredients to the present results. Use of the local resources of shrub land pasture provided the economical feasibility and pro®tability of the diet.
Acknowledgements
This research was supported by projects SIMOR-ELOS CONACYT 9501075, 970301029 and PAPIIT 217798 UNAM.
References
AFRC, 1998. The nutrition of goats. AFRC Technical Committee on Responses to Nutrients, Report 10. CAB International, UK and New York, 118 pp.
Anon, 1984. Molasses8% urea. The supplement that saved North Queensland cattle in the big drought of 1982 and 1983. Beef cattlemen's Union. Mackay region. Australia 35 pp. AOAC, 1995. Of®cial Methods of Analysis. Association of Of®cial
Agricultural Chemist, 16th ed. Washington, DC, USA, 600 pp. Beatman, J.V., 1970. In: Herrero-Hernandez (Ed.), NutricioÂn Animal. Manual de MeÂtodos AnalõÂticos (Animal Nutrition. Manual for Analytic Methods). Mexico, 60 pp.
Brown, W.F., Pitman, W.D., Mislevy, P., 1988. Intake and digestibility and performance by cattle grazing Cynodon
varieties. Nutr. Rep. Int. 38(6), 1201 ±1209.
Elias, A., 1983. DigestioÂn de pastos y forrajes tropicales (Digestion of tropical pastures and forages). In: Los Pastos en Cuba. Instituto de Ciencia Animal, Cuba, pp. 187±247.
Elliot, R., Ferreriro, H.M., Priego, A., Preston, T.R., 1978. Rice polishing as a supplement in sugar cane diets: the quantities of starch (glucose polymers) entering the proximal duodenum. Trop. Anim. Prod. 3, 30±35.
Fondevila, M., Dehority, B.A., 1995. Interaction between Fibro-bacter succinogenes,Prevotella ruminicola, andRuminococcus ¯avefaciensin the digestion of cellulose from forages. J. Anim. Sci. 74, 678±684.
Galina, M.A., 1994. Sistemas Pecuarios biosostenibles y biodi-versos. Una alternativa de produccioÂn animal ante el deterioro ambiental y la contaminacioÂn. (Biodiverse and biosustainable livestock production systems. An alternative to animal produc-tion and deterioraproduc-tion of the environment and polluproduc-tion). Av. en InvestigacioÂn Agropecuaria, Mexico 3, 48±75.
Galina, M.A., Pineda, J., Rosado, J., Aguilar, A., Puga, D.C., Rubio, C., Murillo, J.C., 1997. Fattening of steers ZebuF1 cross fed high fermentable carbohydrate diet of a continuous non-protein nitrogen and bypass protein supplement. Adv. Agric. Res. MeÂxico. 6, 22±32.
Galina, M.A., Puga, D.C., HernaÂndez, A., Haenlein, G., 1998. Biodiverse and biosustainable system with goats in Mexico: importance of the forage bank. Small Rumin. Res. 27, 19±23.
Galyean, M.L., 1996. Protein level in beef cattle ®nishing diets: industry application, University research and systems results. J. Anim. Sci. 74, 2860±2870.
GarcõÂa, E., 1973. Modi®caciones al sistema de clasi®cacioÂn climaÂtica de KoÈppen (Modi®cations of KoÈppen climatic classi®cation system). Instituto de Geogra®a, Universidad Nacional AutoÂnoma de MeÂxico, MeÂxico, DF, 33 pp. Goering, H.K., Van Soest, P.J., 1975. Forage Fiber Analyses
(Apparatus, Reagents, Procedures, and Some Applications). Agriculture Handbook No. 379. United States Department of Agriculture, Agricultural Research Service, Washington, DC. Graham, N.Mc., 1983. Feeding standards: an outmoded concept in
ruminant nutrition. In: Farrel, Pran Vohora (Eds.), Recent Advances in Animal Nutrition in Australia. University of New England, Armidale, Australia, pp. 184±191.
Hennessay, D.W., Williamson, P.J., 1990. Feed intake and liveweight of cattle on subtropical native pasture hays. I. The effect of urea. Aust. Journal Agric. Res. 41, 1169±1177. Hill, W.H., Seals, J., Montiegel, E., 1958. Destruction of animal
and vegetable tissue by combustion in the Parr oxygen bomb. Am. Ind. Hyg. Assoc. J. 19, 378.
Houtert, M.F.J., 1993. The production and metabolism of volatile fatty acids by ruminants fed roughages. A review. Anim. Feed Sci. Technol. 43, 189±225.
Huerta, H., GonzaÂlez, H., 1987. Ceba de bovinos en pastoreo suplementados con urea (Fattening of cattle on pasture supplemented with urea). Bol. Sugerencias de investigacioÂn y transferencia. SeccioÂn ganado de carne. CRI. La Libertad. Instituto Colombiano Agropecuario ICA, Colombia.
INRA, 1988. Alimentation de bovines, ovins and caprins (Nutrition of cattle, sheep and goats), INRA Paris France, 880 pp. Istasse, L., Reid, G.W., Tait, C.A.G., érskov, E.R., 1986.
Concentrates for dairy cows: effects of feeding method proportion in diet and type. Anim. Feed. Sci. Technol. 15, 167±182.
Jackson, M.G., Who needs feeding standards? Anim. Feed Sci. Technol. 6, 101±104.
Juul-Nielsen, J., 1981. Nutritional principles and productive capacity of the Danish straw-mix system for ruminants. In: Maximum Livestock Production From Minimum Land in Bangladesh. Bangladesh Agricultural University, pp. 287±299. Kunju, P.J.G., 1986. Urea molasses block lick: a feed supplement for ruminants. In: Ibrahim, Schiere (Eds.), Rice and Related Feeds in Ruminant Rations. Wageningen, Pudoc, Netherlands, pp. 261±274.
Leng, R.A., 1990. Factors affecting the utilization of ``poor quality'' forages by ruminant animals particularly under tropical conditions. Nutr. Res. Rev. 3, 277±303.
Leng, R.A., 1991. Application of Biotechnology to Nutrition of Animals in Developing Countries. FAO, UN, Rome, No. 90, 146 pp.
Leng, R.A., Kempton, T.J., Nolan, J.V., 1977. Non-protein nitrogen and bypass proteins in ruminant diets. AMRC Rev. 33, 1±21.
Madrid, J., HernaÂndez, F., Pulgar, M.A., Cid, J.M., 1998. Effect of citrus by-product supplementation on the intake and digest-ibility of urea sodium hydroxide-treated barley straw in goats. Small Rumin. Res. 28, 241±248.
McDowell, L., Conrad, J.H., Ellis, G.L., 1984. Mineral de®ciencies and imbalances and their diagnosis. In: Gilchrist, Mackie (Eds.), Herbivore Nutrition in the Subtropics and Tropics. The Science Press, Craighall, South Africa, pp. 67±88.
Meang, W.J., Chang, M.B., Yun, H.S., Choi, I., 1989. Dilution rates on the ef®ciency of rumen microbial growth in continuous culture. Asian±Australian J. Anim. Sci. 2, 477±480.
Morales, A.R., Galina, M.A., JimeÂnez, S., Haenlein, G., 2000. Improvement of biosustainability of a goat feeding system with key supplementation. Small Rumin. Res., in press.
Morand-Fehr, P., Sauvant, D., 1988. Alimentation des caprins (Goat feeding). In: R. Jerrige (Ed.), Alimentation des bovins, ovins et caprins. Institut National de la Recherche Agronomi-que, Paris, France, pp. 282±304.
Mould, F.L., 1989. Associative effects of feeds. In: E.R. érskov (Ed.), Feed Science. Elsevier, The Netherlands, pp. 192±229. Naidoo, G., Delatiere, C., Preston, T.R., 1977. Effect of maize and
®sh meal supplements on the performance of steers fed steam-cooked bagasse and urea. Tropical Animal Production 2, 117± 124.
N'dlovu, L.R., Buchannan-Smith, J.G., 1985. Utilisation of poor quality roughages by sheep: effect of alfalfa supplementation on ruminal parameters, ®ber digestion, and rate of passage from the rumen. Can. J. Anim. Sci. 65, 693±703.
Noller, C.H., White, J.L., Wheeler, W.E., 1980. Characterization of cement kiln dusts and animal response. J. Dairy Sci. 63, 1947± 1952.
NRC, 1981. Nutrient Requirements of Goats. National Research Council. National Academy Press, Washington, DC, USA, 76 pp.
érskov, E.R., 1991. Manipulation of ®ber digestion in the rumen. Proc. Nutr. Soc. 50, 187±196.
érskov, E.R., 1994. Recent advances in understanding of microbial transformation in ruminants. Livestock Prod. Sci. 39, 53±60. Pethick, D.W., 1984. Energy metabolism in skeletal muscles. In:
Baker, Gawthorne, Purser (Eds.), Ruminant Physiology: Concepts and Consequences, Perth, Australia, pp. 277±287. Poppi, D., McLennan, S., 1995. Protein and energy utilization by
ruminants at pasture. J. Anim. Sci. 73, 278±290.
Preston, T.R., 1995. Tropical Animal Feeding. A Manual for Research Workers. FAO Animal Production and Health, Paper No. 126. Rome, Italy, 305 pp.
Purroy, A., Jaime, C., MunÄoz, F., Treacher, T.T., 1993. A note on change in body condition in Raza Aragonesa ewes given ammonia-treated barley straw after weaning. Anim. Prod. 56, 409±412.
Rihani, N., Garret, N.N., Zinn, R.A., 1993. In¯uence of level of urea and method of supplementation on characteristics of digestion of high-®ber diets by sheep. J. Anim. Sci. 71, 1657±1665. Robinson, C.H., 1984. Metabolismo EnergeÂtico. Fundamentos de
NutricioÂn Normal (Energy Metabolism. Nutritional Normal Bases). CECSA, MeÂxico, pp. 100±102.
Russell, J., Wilson, D., 1996. Why are ruminal cellulolytic bacteria unable to digest cellulose at low pH? J. Dairy Sci. 79, 1503± 1509.
Russell, J.R., Young, A.W., Jorgensen, N.A., 1979. Effect of sodium bicarbonate and limestone addition to high grain diets on feedlot performance and ruminal and fecal parameters in ®nishing steers. J. Anim. Sci. 51, 996±1002.
Sanson, D.W., 1993. Effect of increasing of corn or beet pulp on utilization of low-quality crested wheatgrass hay by lambs and in vitro dry matter disappearance of forages. J. Anim. Sci. 71, 1615±1622.
SAS, 1996. Statistical Analysis System. User's Guide: Statistics, Version 6th ed. SAS Institute Inc. Cary, NC, USA.
Silva, A.T., Greenhalgh, J.F.F., érskov, E.R., 1989. In¯uence of ammonia treatment and supplementation on the intake, digestibility and weight gain of sheep and cattle on barley straw diets. Anim. Prod. 48, 99±108.
Silva, A.T., érskov, E.R., 1988. The effect of ®ve different supplements on the degradation of straw in sheep given untreated barley straw. Anim. Sci. Technol. 19, 277±287. Smith, R.H., 1984. Mineral and rumen function references. In:
Nuclear Techniques in Tropical Animal Disease and Nutrition
Disorders. International Atomic Energy Agency, Vienna, Austria, pp. 79±96.
Sudana, I.B., Leng, R.A., 1986. Effects of supplementing a wheat straw diet with urea or urea±molasses block and/or cottonseed meal on intake and liveweight changes in lambs. Anim. Feed Sci. Technol. 16, 25±35.
ValdeÂs, G., Delgado, A., 1990. SuplementacioÂn proteõÂco energeÂtica para la ceba de ganado en pastos y forrajes (Protein and energy supplementation in cattle fattening with pasture and forages) ProduccioÂn de carne en el troÂpico. EDICA. Instituto de Ciencia Animal, La Habana, Cuba.
Van Soest, P.J., Wine, R.H., 1967. Use of detergents in the analysis of ®brous feeds. IV. Determination of plant cell-wall constitu-ents. J. Assoc. Of®cial Anal. Chem. 50, 50±55.
Weimer, P., 1996. Why don't ruminal bacteria digest cellulose faster? J. Dairy Sci., 79, 1496±1502.
Wells, J., Russell, J., 1996. Why do many ruminal bacteria die and lyse so quickly? J. Dairy Sci., 79, 1487±1495.
Wheeler, W.E., 1979. In¯uence of cement kiln dust on reticuloru-men parameters of beef steers fed complete diets. Journal of Animal Science 49(5), 1364±1370.
Wheeler, W.E., Noller, C.H., White, J.L., 1981a. In¯uence of rate reactivity of calcitic limestone and level of calcium addition on utilization of high concentrate diets by beef steers. J. Anim. Sci. 53, 1120±1134.
Wheeler, W.E., Noller, C.H., White, J.L., 1981b. Comparison between limestone and cement kiln dusts of similar rates of reactivity used in high concentrate diets for beef steers. J. Anim. Sci. 52, 873±881.
