The tree of oak is an important component of silvopastoral systems in Mediterranean areas, constituting the plant roof of the system and carrying out various functions; (1) to produce wood, (2) to provide food for livestock (browse, fruit, etc.). Extensive production of meat goats in the hill areas of northern Tunisia is mainly based on tree and shrubs. The small holders recognize the fodder potential of leaves and fruits. Recently, Gasmi-Boubaker et al. (2005) evaluated the nutritive value of various tree and shrub leaves browsed by goats. However, few studies have been performed on acorns (Kayouli and Buldgen, 2001). Proximate analyses have revealed the chemical composition of acorns to be similar to that of cereals. Starch is the main component of acorns, amounting to over 55% of the kernel (Saffarzadeh et al., 1999). No study involving the impact of oak acorn supplementation on diet utilisation by kids is available in the published literature. Such research would be useful in the Tunisian mountainous areas because of the use of acorn in the smallholder farming system goats and their availability in bulk (October-January) when the nutritive value of shrub vegetation is reduced. The aim of this study was to evaluate the performance and the apparent digestibility of goat diets which contain cork oak acorn in replacement of barley grain.
Materials and Methods
Animals and Diets
Ten male Boer kids with an average weight of 26.5 kg (SD = 2) and approximately
of 8 months of age, previously treated against parasites, were randomly divided
into a control (n = 5) and an experimental (n = 5) group. They were alloted
to individual cages. Kids in both groups were fed 500 g/day per head of chopped
oat hay and 600 g of concentrate containing barley grain (Control group) or
oak acorn (Experimental group). Hay was offered twice daily (08.00 and 16.00
h), concentrate was offered three times per day at 08.30, 13.00 and 17.00 h
and water was available at all times.
Two concentrates were formulated to contain either barley (conventional
concentrate) or oak acorn (tested concentrate) and included mainly, soybean
meal, salt, mineral and vitamin supplement (Table 1). Acorn
from Quercus suber was chosen to carry out the experiment as it is the
main Quercus species in the West-North of Tunisia. Acorn samples consisted
in whole fruit (hull and kernel) collected in January 2005. To ensure safer
and longer storage of experimental concentrate, the acorn samples were incorporated
in the concentrate after being air-dried in the shade for 2 weeks. Ideally the
acorn should have been offered not ground to resemble the situation in field
conditions, but it was difficult to allow homogenous mixing with the others
ingredients of the concentrate, so, it was decided to ground the whole acorn.
The formulation of concentrate mixtures and their chemical compositions are
shown in Table 1.
The digestibility trial was carried out and lasted 21 days, using the technique
of total collection of feces and urine. The 14 first ones were destined to the
adaptation of the animals to the diets. After this adaptation, Faeces samples
were collected daily, weighed and a sub-sample was taken each day for individual
animals. They were frozen to await determination of Dry Matter (DM), Organic
Matter (OM), Crude Protein (CP) and Crude Fibre (CF). Amount of urine collected
was measured daily for individual animals and acidified (pH = 3.0) with 100
mL L-1 of H2SO4 (approximately 5-10 mL) to
prevent ammonia volatilisation. Urine samples were stored at -20°C until
analysed. After this first experimental phase, the growth trial was carried
out and lasted 73 days. Animals were weighed weekly in the morning before feeding.
Chemical Analyses and Measurements
The samples, composed of the ingredients, rations and feces, were carried
to the laboratory to run the chemicals analysis. All analysis were carried out
on duplicate samples. Procedures described by AOAC (1999) were used to determine
DM, ash and Kjeldahl nitrogen (N). Neutral Detergent Fibre (NDF), Acid Detergent
Fibre (ADF) and lignin (ADL) were analysed according to Van Soest et al.
(1991). Condensed tannins (CT) were measured by the vanilline/HCl method (Porter
et al., 1986). Catechin was used as a source for CT standard. The CT
were measured separately in acorn, hay and barley samples extracted with 1%
HCl in methanol. After the extraction, the samples were centrifuged in 1000xg
for 20 min and CT were determined in the supernatant. Coefficient of apparent
digestibility of nutrients were determined by the following equation: Digestibility
= [(nutrient in feed-nutrient in feces)/nutrient in feed ] * 100. Nitrogen retention
was calculated as the difference between the average N intake and N excretion
(in feces and urine) during the 7 days collection period.
A complete randomized design was used, with 2 treatments and five replicates
to the growth, digestibility and nitrogen balance trial. All data were analysed
with the software SAS (1989) and submitted to an analyses of variance.
One animal fed the control diet was replaced at 3-week after the start for
failing to eat, while the kids fed the experimental diet remained in apparent
good health throughout the trials.
Chemical Composition of Feeds
The acorn-based concentrate had 7.9, 14.4, 9.7 and 3.8% units higher CF,
ADF, ADL and CT content, respectively, than the barley based concentrate (Table
1). The acorn-based concentrate was kept well throughout the feeding trial
with no change of odour or fungal contamination.
Apparent Digestibility of Diets and Nitrogen Balance in Kids
Inclusion of acorn in the concentrate did not result in any change in intake
of the diet, but there were significant decrease in apparent digestibility coefficients
for DM, OM and CP. There were, however, no significant differences in the digestibility
of CF between animals fed barley diet or acorn diet. Nitrogen balance was positive
in two groups, but the highest N excretion in feces was recorded in the group
fed acorn concentrate, that resulted in low retention of N by the experimental
group (Table 2).
||Intake, diet digestibility and N balance in barley and acom
|*: p<0.05; NS: p>0.05
||Live weight changes in barley and acorn diets
|*: p<0.05, NS: p>0.05
Kids initial live-weights were similar (p>0.05) among groups (Table
3). Animals fed the barley diet gained 80 g/day, whereas kids fed the acorn
diet gained 43 g/day. Nevertheless, data indicated that kids fed the acorn diet
lost 42 g/day during the first 3 weeks of the experimental period. After that,
control and experimental groups presented a continuous increase in weight gain.
Some variation in the chemical composition of acorn can be expected because of variation in production site, Quercus species and stage of maturity. Compared to other oak species, the CP content of acorn used in this experiment was comparable to the value (80.5 g kg-1 DM) reported by Ventanas et al. (2006), higher than 62.5 reported by Nieto et al. (2002) for Quercus suber but lower than 11-12% suggested by NRC (1985) as adequate to meet requirements of growing kids. CF content was similar to 111 g kg-1 DM (Nowar et al., 1994), but lower than 253 g kg-1 DM Al Jassim et al. (1998) reported for Quercus coccifera. Condensed tannin content (45 g kg-1 DM) was higher than (39.1 g kg-1 DM) reported by Nieto et al. (2002).
All kids have been offered 600 g of concentrate, they consumed all of it within a very short period of time and had similar DM and N intakes. The organic matter digestibility of the control diet was high due to the high proportion of concentrate mixture in the total diet, improving the activity of the cellulolytic bacteria in the rumen and promoting an increase in the nutrients digestibility.
The lower digestibility of DM, OM and CP with the experimental diet compared to the control diet supports the results reported by Al Jassim et al. (1998) where decreased digestibility of organic constituents was found with inclusion of acorns in the diet of growing lambs. These results could be due to the substrate being protected by tannins from hydrolysis and by the direct inhibition of digestive enzymes by tannins. Lignin incrustation of cell wall is also an important factor which can potentially limited feed digestibility. The chemical composition confirmed that the acorn concentrate contained higher condensed tannin and lignin contents compared to the barley concentrate. Nevertheless, the replacement of barley grain for oak acorn resulted in a similar utilization of crude fibre. This result apparently contradicts what is to be expected, knowing that tannins are cellulolytic inhibitors which have been reported in many Mediterranean shrubs (Gasmi-Boubaker et al., 2005). The reason for the similar digestibility of CF may be related to the fact that feeding grains high in starch to the control group can be associated with adverse effects on the digestibility of crude fibre. The total digestible CP intake observed with the two diets were much higher than the values recommended for maintenance of growing kids (NRC, 1985). Consequently, the N retention was positive in the control and experimental groups.
The maximum growth rate in this study of 80 g/day in the barley diet is slightly lower than that recorded for Omani goats fed conventional diets (Mahgoub, 1997). This could be due to effects of feeding regimes, but may also result from different breeds.
Feeding acorn to kids did not visibly affect their health, as there was no clinical signs of constipation, diarrhoea or loss of appetite. This is in agreement with Silanikove et al. (1996) who reported no ill effects of CT when present at concentration close to 60 g/day. Nevertheless, the pattern of body weight gain of kids fed acorn diet indicates that kids may need time to adapt to acorn feeding before gaining body weight.
The lower growth performance of kids fed acorn diet has been shown previously with growing lambs (Al Jassim et al., 1998). This may be explained by the lower provision of available nutrients to these animals, as reflected by the amounts of digestible OM and CP intakes.
These results suggest that the inclusion of acorns in the concentrate mixture of goats can be economically advantageous particularly in automn and winter when scarcity of feedstuffs occurs. Nevertheless, we need further investigations in order to improve utilisation of acorn.
This study was supported financially by the Ministry of Scientific Research in Tunisia. L. Tayachi is thanked for the analysis.