Saccharomyces cerevisiae
and nitrogenous
supplementation in growing steers
grazing tropical pastures
E.J.I. Cabrera, M.G.D. Mendoza
*, I.E. Aranda,
C. Garcia-Bojalil, G.R. BaÂrcena, J.J.A. Ramos
Colegio de Postgraduados, Programa de GanaderõÂa, Montecillo, km 35.5 Carr. MeÂxico-Texcoco, Estado de Mexico 56230, Mexico
Received 4 November 1998; received in revised form 30 June 1999; accepted 16 September 1999
Abstract
A grazing trial utilizing 42 individually supplemented growing steers (190
80 kg initial BW)
was conducted to study the effect of
Saccharomyces cerevisiae
(SC; 0 or 10 g per day) and two
protein supplements on the performance of steers grazing in a mixed pasture 1 of tropical grasses
during the dry season. 2 kg of supplement (DM basis) was offered daily (2.7±2.8% N) during the 90
days of the experiment. Nitrogen in supplements was administered from 100% urea, or 50 : 50%
urea and meat meal. Treatments consisted in a grazing control group (CG), a group receiving 10 g
per day SC (SC); and the supplements 100 and 50 U, with and without the yeast culture. Stargrass
(
Cynodon plectostachyus
) was the main grass of the diet (72.3%) followed by
Paspalum
conjugatum
(14.4%),
Brachiaria mutica
(8.9%) and others (4.4%). Non supplemented steers had
lower (
P
< 0.01) ADG (0.700 kg per day) than those supplemented (0.840 kg per day). Animal gain
(ADG) was similar to supplements containing meat meal (0.865 kg per day) or urea (0.815) without
effects of
Saccharomyces cerevisiae
. Supplement intake with urea (0.688 kg per day) was lower
(
P
< 0.01) than with meat meal-urea (1.333 kg per day) but forage intake was not affected. Total
tract digestibility of NDF and ADF were not affected by treatments. In conclusion
Saccharomyces
cerevisiae
did not improve either animal performance or fiber digestibility. Growing ruminants
grazing tropical grasses in dry season showed a positive response to nitrogenous supplementation.
#
2000 Elsevier Science B.V. All rights reserved.
Keywords:Steer; Protein;Saccharomyces cerevisiae; Nitrogen; Yeast culture; Urea 83 (2000) 49±55
*Corresponding author. Tel.:52-58-04-59-00/1716; fax:52-59-52-02-79.
E-mail address: gmendoza@colpos.colpos.mx (M.G.D. Mendoza).
1. Introduction
Low productivity rates of animal production are observed in cattle grazing in tropical
areas of Latin America (Vera and SereÂ, 1985). One of the main constrains under those
conditions, is the limited intake associated with a low N concentration and digestibility of
the tropical grasses (Stonacker, 1975). Therefore protein supplementation may be one
alternative to increase beef production in the tropics. Ruminally degraded protein and
escape protein are the two limiting nutrients for growing ruminants grazing these type of
forages (Ramos et al., 1998).
Direct-fed microbial products with
Saccharomyces cerevisiae
have been used to
improve fiber digestibility and animal production (Walli, 1994). The beneficial effects of
these microbial compounds are associated with an increase in cellulolytic bacteria
(Newbold et al., 1993; Wallace, 1994). They have been considered as a potential fed
additive to improve NDF digestion in low quality forages (Ayala et al., 1992; Sommart
et al., 1993). Therefore, the objective of our experiment was to determine whether
growing steers grazing tropical pastures during the dry season would respond to
supplemental protein formulated with urea and meat meal, and to determine if additions
of a yeast culture could improve fiber digestibility, intake and animal performance.
2. Materials and methods
Forty two crossbred (
Bos taurus
Bos indicus
) non implanted steers (initial BW
190
80 kg) were used in a completely randomized design. Treatments consisted in an
unsupplemented grazing control group, a group receiving 10
8g yeast culture per head per
day containing 10 colony forming units of
S. cerevisiae
(Levucell, Agrimerica,
Northbrook, IL), two supplemented groups where N was administered from 100% urea,
or 50 : 50% urea and meat meal (Table 1), and two groups with the same supplements and
Table 1
Supplement formulation and chemical composition of concentrates and main consumed forages (DM basis)
Supplements Forages
Urea Meat-meal Cynodon
plectostachyus
Paspalum conjugatum
Urea 4.0 2.0
Meat meal 10.3
Corn 84.0 75.7
Molasses 12.0 12.0
Analyses(%)
DM 83.2 85.1 30.0 33.8
OM 96.4 96.7 87.7 89.9
N 2.84 2.72 0.81 0.76
Insoluble N 1.27 1.96 0.66 0.64
NDF 4.25 5.98 75.4 67.7
ADF 2.29 4.42 47.3 40.6
yeast culture. All steers were offered 2 kg of supplement DM per day. Each morning
(06:30±07:00 hours) steers were fed individually in pens. Dose of yeast was administered
in a small paper soaked in molasses in the top of the supplement. The steers were returned
to pastures for grazing after 30 min of allowing to consume the daily supplement. All
steers grazed in one group and were rotated among two pastures on a monthly basis with
a mean forage availability of 6.2 t DM/ha. The stocking density varied between 4.6 and 7
steers/ha. Initial and final BW were averages of weights taken on three consecutive days.
Steers had free access to a mineral supplement throughout the study (15.8% Ca, 6.83% P,
4.38% K, 0.02% Mg, 1.75% S, Mn 0.07%, Cu 0.03%, Zn 0.15%, Fe 0.01%, Na 11.45%,
Co 2.63 ppm, Se 4.38 and I 36.75 ppm). The experiment was conducted at the
experimental station in Campus Tabasco (Gobierno del Estado de Tabasco, 1988) at
18
8
00
0N, 93
8
30
0W, altitude 9 m above sea level, during the dry season from 1 April to 5
July 1997.
Botanical composition of the diet was determined by the microhistological procedure
(Sparks and Malechek, 1968) using forage and fecal samples. Grass samples, clipped at
approximately 10 cm above ground level, were collected at the beginning and at the end
of each grazing period in five 0.5 m
2plots for each grass, and each third day when an
external marker was dosed. From day 62 onward, steers were dosed daily with chromic
oxide (5 g) during 15 days. A fecal grab sample was collected the last 5 days and then
was composited by animal. Chromium was determined by atomic absorption
spectro-scopy as described by Williams et al. (1962). Acid insoluble ash was analyzed in
supplements, forage, and fecal samples (Keulen and Young, 1977), and forage intake was
estimated as described by Geerken et al. (1987).
Nitrogen content was determined by the macro-Kjeldahl technique (AOAC, 1980),
NDF, and ADF was determined using procedures outlined by Van Soest et al. (1991).
Nitrogen solubility in bicarbonate-phosphate buffer (Poss-Floyd et al., 1985) was selected
to estimate ruminal protein degradation and in vitro digestibility was measured with the
Tilley and Terry (1963) technique.
Data were analyzed as a completely random design (Steel and Torrie, 1980) with steer
as experimental unit with the following model:
Y
ij
i
T
i
e
ij, where
Y
ijrepresented
the response variable measured in the
i
th treatment (
T
,
i
1,
. . .
, 7),
i
the population
mean and
e
ijis the residual error term (SAS, 1985). Initial body weight was used as a
covariable for ADG. The following contrasts were tested: (I) grazing versus supplement;
(II) with or without
S. cerevisiae
; (III) urea versus meat meal-urea in the supplement.
3. Results and discussion
The use of 10 g per day of
S. cerevisiae
did not improve animal performance (Table 3)
in grazing conditions. Most experiments evaluating yeast culture have been conducted
with penned animals fed concentrate diets and information of grazing steers is lacking.
Mir and Mir (1994) did not find response to
S. cerevisiae
with an alfalfa silage diet
evaluating two consecutive years. Lack of response to yeast culture with low quality diets
also has been reported in crossbred dairy cows (Kamalamma et al., 1996), goats
(Hadjipanayiotou et al., 1997), growing lambs (AvendanÄo et al., 1995) and steers (Plata
et al., 1994), indicating that no benefit is obtained in diets based in low quality forages.
Unsupplemented steers had lower (
P
< 0.01) daily gain and final weight (0.700 kg per
day, 255 kg) than those with supplement containing meat meal (0.865 kg per day, 266 kg)
or urea (0.815 kg per day, 266.5 kg) respectively, as observed by other authors in tropics
(Moss and Murray, 1992; Ramos et al., 1998). Animal gain observed in this study was
greater than the reported for other studies grazing stargrass (TrevinÄo et al., 1975; AlarcoÂn,
1995) which usually is below 0.5 kg per day. Differences to other experiments can be
associated to different factors like stocking density (Monroy et al., 1978). Chemical
composition and in vitro digestibility of stargrass is similar than reported by other authors
in Mexican tropics (PeÂrez and MeleÂndez, 1980; AlarcoÂn, 1995; Ramos et al., 1998).
Stargrass (
Cynodon plectostachyus
) was the main forage consumed in the diet (72.3%),
followed by
Paspalum conjugatum
(14.4%),
Brachiaria mutica
(8.9%) and others (Table
2). Studies relating botanical composition and supplementation effects are scarce
(O'Reagain and Grau, 1995).
Response to protein supplementation confirm that steers growth in stargrass is limited
by the supply of metabolizable protein to the animal (Ramos et al., 1998). In other
studies, supplements with meat meal improved ADG compared to urea-based
supplements (Sindt et al., 1994; Gibb et al., 1992; Klemesrud et al., 1998). Protein
digestibility could be affected by conditions of the process. Meat meal is a good source of
metabolizable lysine, but contains large amounts of collagen which has a low content of
essential amino acids, and is limited in sulfur amino acids (Gibb et al., 1992). Amino acid
balance in the escape protein mixture is important to obtain maximum growth (Knaus
et al., 1998).
Intake of the urea based supplement (0.688 kg per day) was lower (
P
< 0.01) than for
meat meal-urea supplement (1.33 kg per day) (Table 3). The steers did not consume the
2 kg of supplement administered probably because of the short time available to do it
(30 min). In several studies (Reyes-Balcazar et al., 1996; Ramos et al., 1998) supplement
intake has been reduced when urea is the main source of nitrogen compared to sources of
natural protein, associated to a low palatability (GonzaÂlez et al., 1991).
Forage intake tended (
P
< 0.08) to be reduced in supplemented steers showing a
substitutive effect and no differences were detected in total DMI (Table 3). The effects of
nitrogenous supplementation on intake of tropical pastures are variable, in some studies
slight increases have been reported (Geerken et al., 1980), in others the magnitude of the
response has been significant, particularly when forages have a low protein concentration
Table 2Botanical composition (%) and in vitro dry matter digestibility of the grassesa
Forage Diet (%) IVDMD (%)
Cynodon plectostachyus(Schum) Pilger 72.8 a 43.2 b
Paspalum conjugatumBergius 14.4 b 43.8 b
Brachiaria muticaForsk Stapf 8.9 c 51.5 a
Paspalum virgatumL. 2.0 d 23.8 d
Panicum tuckermaniFernald 1.7 d 36.6 c
Paspalum fasciculatumWilld 0.05 d 46.4 b
SEM 0.70 2.54
aMeans with different letters on the same column differ significantly (P< 0.05).
(Chico et al., 1971), and in others, a substitutive effect of the supplement by forage has
been observed (Ramos et al., 1998). Protein concentration, physical and chemical
characteristics of the fiber, level of supplementation, forage availability and other factors
could modify the effect of the supplement on forage and total DM intake.
Fiber digestibility was not affected by yeast culture (Table 3) as observed in other
studies with forage diets (AvendanÄo et al., 1995; Hadjipanayiotou et al., 1997).
Conversely, in other experiments, in vivo or in situ NDF digestibility of low quality
forages has been increased by yeast culture (Ayala et al., 1992; Sommart et al., 1993;
Plata et al., 1994; Mendoza et al., 1995). It is not clear which are the dietary factors that
promotes a positive response to yeast. Results from Roa et al. (1997) showed that quality
of the forages affects NDF digestion response to yeast culture, with more benefits with
good quality forages.
According to the results of this experiment, the addition of
S. cerevisiae
did not
improve fiber digestibility and steer performance in tropical pastures. However, gain can
be improved by nitrogenous supplementation with urea or urea-meat meal.
Acknowledgements
The technical assistance in the laboratory from Andres Lee is greatly appreciated.
Thanks are also extended to Edsel Bixtler, General Manager of ANGLO-CORP, MeÂxico,
who provided yeast culture for this study. This experiment was part of a project sponsored
by the CONACYT, MeÂxico.
Table 3
Performance, intake and digestibility in steers grazing tropical grasses with yeast culture (10 g per day Saccharomyces cerevisiae) and nitrogenous supplementation
Treatment Finala ADGa Intake (kg per day) Digestibility (%) weight (kg) (kg)
Supplement Forage Total NDF ADF
Unsupplemented
Control 254 0.71 ± 8.54 8.54 70.7 66.6
Yeast 256 0.69 ± 10.08 10.08 72.2 66.2
Supplemented
Urea 262 0.80 0.68 9.63 10.31 70.4 65.5
Yeast 271 0.83 0.70 7.66 8.36 68.1 63.2
Meat meal 266 0.83 1.42 7.33 8.74 64.4 59.5
Yeast 266 0.90 1.25 8.46 9.71 67.9 61.8
SEM 2.9 0.05 0.08 0.66 0.68 1.05 1.04
Contrastsb
I 0.05 0.05 0.08 NS NS NS
II NS NS NS NS NS NS NS
III NS NS 0.0001 NS NS NS NS
aAdjusted by initial weight as a covariate.
bProbability of error type I in the following contrasts Ð I: grazing versus supplement; II: with or without
Saccharomyces cerevisiae; III: urea versus meat meal-urea.
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