Nastis, 1993). The nutritive value of grasses decreased rapidly after seed matura- tion, while that of legumes remained at higher levels (Yiakoulaki, 1987; Yiakoulaki and Nastis, 1993). During the first growing stage, CP of almost all species could satisfy goats’ nutritional requirements for lactation. However, after seed matura- tion CP content of grasses could not satisfy even their maintenance requirements.
Chemical composition of woody species
There are several studies on the chemical composition of woody species in different Mediterranean environments such as Sardinia (Congiu et al., 1978;
Cabidduet al., 2000), Tuscany (Sottini and Geri, 1971), Corsica (Leclerc, 1984), Israel (Kababyaet al., 1998; Perevolotskyet al., 1998), Greece (Yiakoulaki, 1987;
Yiakoulaki and Nastis, 1993; Papachristou and Papanastasis, 1994), Tunisia (Boubakeret al., 2004; Ammaret al., 2005) and Croatia (Rogosicet al., 2006b).
As expected, such studies confirmed that woody species generally have low CP content and high lignin and tannin content. However, such values vary greatly among species and plant phenological stages. For example, CP level is usually higher in young leaves and stems than in other plant parts (Leclerc, 1984), even if
Forage species Season CP NDF IVOMD P Ca
Grasses
Dactylis glomerata L. Spring 148 581 67.7 1.7 6.6
Summer 82 709 56.8 1.3 3.8
Autumn 92 758 38.9 1.2 3.4
Festuca valesiaca Schleich. Spring 129 688 57.9 1.9 3.2
Summer 66 761 41.7 0.9 2.4
Autumn 39 839 36.6 0.6 2.2
Chrysopogon gryllus (L.) Trin. Spring 91 710 61.2 1.3 4.6
Summer 74 749 57.9 1.5 3.9
Autumn 26 820 40.8 0.6 2.3
Legumes
Trifolium hirtum All. Spring 220 550 67.1 1.3 20.0
Summer 170 576 57.9 1.5 14.6
Autumn 170 685 39.4 1.4 12.2
Trifolium campestre Shreber. Spring 173 486 52.9 1.9 14.0
Summer 163 669 44.3 2.0 10.6
Autumn 106 722 29.2 1.7 10.0
Trifolium purpureum Loisel. Spring 177 495 65.1 1.9 12.9
Summer 158 547 61.6 1.4 12.5
Autumn 147 705 35.6 1.3 14.2
CP, crude protein; NDF, neutral-detergent fibre.
Table 8.1. Chemical composition (g/kg dry matter) andin vitro organic matter digestibility (IVOMD; %) of some herbaceous species commonly found in Mediterranean shrublands.
(Adapted from Yiakoulaki, 1987; Yiakoulaki and Nastis, 1993.)
it is sometimes associated with higher tannin content (Decandiaet al., 2004a). As the growing season progresses and plants mature, the quality of woody species worsens, since CP content decreases and tannin level increases. The chemical composition of some important woody species browsed by Sarda goats during spring and summer is presented in Table 8.2. CP content was usually low with the exception ofPyrus amygdaliformisL.,R. alaternusL. andRubus ulmifoliusSchott.
Sunlight strongly influences the nutritive value of shrub species. Leaves of shadedQ. cocciferaL. shrubs had higher CP, neutral-detergent fibre (NDF) and lignin content than those of sun-exposed shrubs, but tannin level was not signifi- cantly different between them (Koukoura, 1988) (Table 8.3). The combined effects of the above changes resulted in lowerin vitroorganic matter digestibility for the leaves of shaded shrubs (Koukoura, 1998). In contrast, Decandiaet al.
(2004a) found that the shaded leaves ofP. lentiscusL. had higher CP content and a lower tannin level than sun-exposed ones, even if differences were not significant (Table 8.3).
Woody species Season DM OM CP NDF ADF ADL TPa
Cistus spp. Spring 329 933 113 346 235 114 120
Summer 412 938 106 331 219 90 155
Pistacia lentiscus L. Spring 441 942 102 421 287 162 185
Summer 400 939 95 377 297 163 206
Lonicera implexa Aiton. Spring 278 923 103 363 230 88 16
Summer 365 910 99 357 216 94 23
Myrtus communis L. Spring 401 942 97 347 218 105 118
Summer 394 951 102 388 255 91 141
Chamaerops humilis L. Spring 489 928 108 472 284 70 29
Summer 488 928 87 520 339 76 37
Pyrus amygdaliformis L. Spring 347 939 143 387 241 100 47
Summer 447 927 120 429 245 104 28
Quercus ilex L. Spring 479 957 103 548 351 145 49
Summer 540 954 93 526 351 136 69
Quercus suber L. Spring 431 932 98 494 327 142 110
Summer 459 949 111 505 319 130 106
Rhamnus alaternus L. Spring 344 917 133 308 189 72 57
Summer 413 912 110 267 182 88 63
Rubus ulmifolius Schott. Spring 359 925 132 371 211 77 126
Summer 405 938 114 374 219 73 121
OM, organic matter; CP, crude protein; NDF, neutral-detergent fibre; ADF, acid-detergent fibre;
ADL, acid-detergent lignin; TP, tannic polyphenols.
aDetermined by the Folin–Ciocalteu method.
Table 8.2. Dry matter (DM) content (g/kg) and chemical composition (g/kg DM) of woody species commonly found in the Mediterranean shrublands during 1996–2000. (Adapted from Cabidduet al., 2000.)
Digestibility of woody species
Digestibility assessment is the most important step for determining forage nutri- tive value. Measuring digestibility in woody species is often negatively affected by the high presence of ligneous fractions, tannins and other secondary compounds (alkaloids, cumarins). In particular, tannins greatly interfere within vitrodigestibil- ity (Makkaret al., 1997). More accurate estimation of the nutritive value of these plants, which are considered as non-conventional forages, has been obtained within vivodigestibility studies. These experiments require, as much as possible, the simulation of real pasture conditions including the daily administration of fresh material, in order to put the animals in a free-choice situation (Meuret, 1989).
Due to the low intake of some woody species, the experiments are sometimes carried out using a basic diet of known digestibility. Shrub digestibility is usually underestimated by thein vitrocompared with thein vivomethod (Table 8.4), mainly due to the presence of tannins (Sidahmed et al., 1981; Robbins et al., 1987; Nastis and Malechek, 1988; Nastis, 1993). Nevertheless,in vitrodigestibility values allow one to obtain a high number of estimates of plant nutritive values.
Factors that mainly affect the nutritive value of woody plants are different from those of herbaceous species. The relationships between CP content and fibre fractions with the organic matter digestibility (OMD) are stronger in woody spe- cies than in herbaceous forages, based on data in sheep and dromedaries (Ben Salemet al., 1994). Species with highest OMD values do not always have higher CP content and lower fibre fractions. A chemical parameter that has an impor- tant effect on OMD is the N linked to acid-detergent fibre (ADIN), which is usually very high in shrubs. When OMD ofQ. ilex, browsed by dry and lactating goats, was predicted on the basis of its chemical composition (CP, acid-detergent fibre, ADIN, acid-detergent lignin and neutral-detergent solubles), the ADIN free N fraction explained about 75% of the OMD variance (Meuret, 1989).
Tannins
Tannins are widely distributed in the plant kingdom. They are complex polyphenolic compounds with relatively high molecular weight (1000–20,000)
Species CP NDF ADL IVOMD Tannins
Quercus coccifera L. Sun 85b 434b 115b 40.3a 2.69a Shade 101a 539a 158a 35.7b 2.73a
Pistacia lentiscus L. Sun 89 386 160 – 162
Shade 103 402 160 – 144
CP, crude protein; NDF, neutral-detergent fibre; ADL, acid-detergent lignin.
a,bIn each species, mean values in a column with different superscript letters were significantly different (P≤0.05).
Table 8.3. Chemical composition (g/kg dry matter) andin vitro organic matter digestibility (IVOMD; %) ofQuercus coccifera L. (Koukoura, 1988) and Pistacia lentiscus L. (Decandia et al., 2004a) leaves grown in the shade and in the sun.
containing sufficient hydroxyl and carboxyl groups to precipitate proteins and to form strong complexes with carbohydrates. According to their structure and reactiv- ity, tannins are classified as hydrolysable and condensed tannins. Hydrolysable tan- nins are esters of glucose and phenolic acid, with low molecular weight, whereas condensed tannins are polymers of flavonoid units with varying composition and molecular weight. Since the hydrolytic cleavage of condensed tannins yields anthocyanidins, they are now commonly described as proanthocyanidins.
Tannins can protect plants from herbivores (Provenza, 1995) and patho- genic microorganisms by complex and multifactorial mechanisms. Some authors suggest that their toxicity is the basis for plant defence, while others state that deterrence (i.e. rejection based on taste only) is often independent from their toxicity (Silanikoveet al., 1996b). The effects of tannins on protein utilization in
Breed Diet composition Season
Intake (g/kg BW0.75)
In vitro DMD
In vivo DMD Yearling
Greeka
100%Quercus coccifera Spring 74 37.0 69.0
100%Q. coccifera Summer 55 32.0 51.0
Spanishb 35%Quercus dumosa – 48 49.0 55.7
100%Q. dumosa – 19 29.0 46.9
Greekc (local breed)
100%Q. coccifera Spring 79 50.0 70.0
100%Q. coccifera Summer 51 45.0 53.0
100%Q. coccifera Autumn 59 46.0 55.0
100%Q. coccifera Winter 58 48.0 56.0
Alpined 100%Quercus ilex – 90 – 47.8
Q. ilex + soybean meal – 104 – 51.6
Mambere 100%Quercus calliprinos – 63 35.8 45.4
Sardaf 100%Q. ilex Summer 58 – 57.9
Q. ilex + 200 g supplementi Summer 63 – 61.8
Q. ilex + 400 g supplementi Summer 57 – 64.6
Sardag Pistacia lentiscus + 200 g supplementi
Summer 34 – 67.8
P. lentiscus + 400 g supplementi
Summer 38 – 59.8
Mamberh 100%Q. calliprinos – 46 – 25.8
100%Ceratonia siliqua – 55 – 46.9
100%P. lentiscus – 32 – 24.5
DM, dry matter; BW, body weight; DMD, DM digestibility.
Data source:aNastis and Malechek (1988);bSidahmedet al. (1981);cNastis and Liacos (1982);
dMeuret (1989);ePerevolotskyet al. (1993);fM. Decandia (unpublished data);gDecandiaet al. (1999);
hSilanikoveet al. (1996a).iSupplement composition: 66.5% beet pulp and 33.5% soybean meal, on DM basis.
Table 8.4. Comparison of intake (g DM/kg BW0.75),in vitro and in vivo DMD values for goats fed woody species.
forage plants is particularly important, since they form strong complexes with proteins and some structural carbohydrates, reducing their availability to the animals and inactivating some enzymes in the digestive tract (Kumar and Vaithiyanathan, 1990). The presence of high tannin concentration in the diet reduces digestibility and feed intake even in goats, known to be more tolerant to tanniferous species than other domestic species (Provenza, 1995; Silanikoveet al., 1996a, 1997; Decandiaet al., 1999). By contrast, tannins in low concentrations (2–4%) induce beneficial effects, which are associated with suppression of bloat in ruminants (Mueller-Harvey, 2006) and protection of dietary proteins in the rumen.
Tannin effects have been measured by using different compounds which form complexes with hydrolysable and condensed tannins, thus reducing their anti-nutritional activity. Among these compounds, polyethylene glycol (PEG) gave the best results. PEG is a polymer, with molecular weight of 4000–6000, that can bind tannins irreversibly over a wide range of pH (2–8.5), reducing the formation of protein–tannin complexes (Jones and Mangan, 1977). As a result, the availability of certain macronutrients, particularly proteins, increases.
In Sarda goats fed fresh branches of lentisk and supplemented with increasing levels of PEG (0, 25 and 50 g/day),in vivoCP digestibility increased significantly (Table 8.5). PEG-supplemented goats spent more time foraging on tanniferous species than on herbaceous (Decandia et al., 2000a,b; Titus et al., 2001) (Fig. 8.6) and had higher intake compared with the goats unsupplemented with PEG (Silanikoveet al., 1996a; Decandiaet al., 2000a; Tituset al., 2001; Ben Salemet al., 2003). In Mamber goats, supplementation with increasing amounts of PEG (from 0 to 40 g/day; Silanikoveet al., 1996a) increased the DM intake
200 g concentrate/day 400 g concentrate/day
PEG0 PEG25 PEG50 PEG0 PEG25 PEG50
DMI
Lentisk (g) 449 491 479 520 604 538
(g/kg BW0.75) 34 37 36 38 44 37
Total diet (g) 620 662 634 870 954 887
(g/kg BW0.75) 47a 50ab 48a 64bc 71c 63bc
In vivo digestibility
OM (%) 67.8 70.1 70.2 59.8 65.9 73.1
CP (%) 37.4a 63.3ab 71.5b 30.9ac 61.4ab 73.7b
NDF (%) 45.4 51.5 55.0 31.9 53.1 68.9
ADF (%) 34.5 45.6 47.7 23.4 21.1 59.5
BW, body weight; OM, organic matter; CP, crude protein; NDF, neutral-detergent fibre;
ADF, acid-detergent fibre.
a,b,cMean values in a row with different superscript letters were significantly different (P≤0.05).
Table 8.5. Effects of different levels of concentrate (concentrate composition: 66.5% beet pulp and 33.5% soybean meal, on dry matter basis) and daily amount (g/day) of polyethylene glycol (PEG) on dry matter intake (DMI) andin vivo digestibility of Sarda goats fed lentisk.
(Adapted from Decandiaet al., 1999.)
(DMI) of leaves of Quercus calliprinos (from 660 to 900 g/head per day), of P. lentiscus(from 470 to 800 g/head per day) and ofCeratonia siliqua(from 800 to 1250 g/head per day). PEG supplementation generally increased DMI and protein and energy digestibility of browsing goats, and the production responses differed among breeds. For example, higher live weight gain of pregnant goats and higher birth weight of their kids occurred in the Mamber breed (Gilboa, 1996), while marked increases of milk yield were observed in Anglo-Nubian (Gilboaet al., 2000) and, to a lower extent, in Sarda goats (Decandiaet al., 2000a,b).