In those experimental conditions, CP and PT/CP in the diet were related to the percentage of grass in the pasture, determined by the method of Daget and Poissonet (1969), and milk urea (MU), as follows:
CP = 5.10 + 0.20 Grass + 0.119 MU; n= 31;
R2= 0.82;P< 0.001 (8.3)
PT/CP = 1.21 + 0.019 MU−0.012 Grass; n= 29;
R2= 0.49;P< 0.001 (8.4)
where CP is crude protein in the diet (%), PT/CP is the percentage ratio between polyphenolic tannins and crude protein, Grass is the percentage of herbaceous species in the pasture and MU is milk urea level (mg/100 ml).
The regression equations (8.1) and (8.3) have higherR2than equations (8.2) and (8.4) and seem more suitable for application at farm scale. Using these rela- tionships, a prediction model of DMI of browsing goats on shrublands rich in high- tannin species is proposed (Fig. 8.7). By estimating the percentage of herbaceous species in the pasture, and measuring the urea level in the milk, CP (%) in the diet can be predicted using Eqn (8.3) (Fig. 8.7a). If the dietary CP level is known, the measurement of FCM yield allows the prediction of DMI on pasture (Eqn (8.1);
Fig. 8.7b). For instance, if the grass component in the pasture is 20% and milk urea is 25 mg/100 ml, the predicted CP (%) should be 12 (Fig. 8.7a). If the FCM is on average 1200 (g), the DMI should be 80 (g/kg BW0.75per day; Fig. 8.7b). Even if this model is not general, it can be applied in conditions similar to those in which the experiments used to fit the equations were conducted, that is: (i) goat breed of low–medium production level; (ii) limited access time to the pasture (5–7 h/day);
(iii) shrubland with high-tannin species (e.g. based onP. lentiscusL.); (iv) low con- tribution of grass in the botanical composition of shrubland (10–30%); and (v) low–moderate supplementation level (200–400 g DM/head per day).
In general, a high level of energy supplement (cereal-based concentrates) allows the recovery of body condition but usually reduces the grazing activity of goats. In fact, in behaviour studies, goats fed low concentrate amounts spent more time grazing than those fed high concentrate amounts (75 and 59% of total observation time, respectively) (Landauet al., 1993).
Estimated CP in the diet (%)
0 2 4 6 8 10 12 14 16 18
MU (mg/100 ml)
10.00 20.00 30.00 40.00
Grass10 Grass20 Grass30 (a)
0 20 40 60 80 100 120
400 800 1200 1600
FCM (g) Estimated DMI on shrubland (g/kg BW0.75)
CP10 CP12 CP14 (b)
Fig. 8.7. Prediction model of goat intake browsing on shrublands with high-tannin species. (a) Estimated crude protein (CP) in the diet as a function of percentage of herbaceous species in the pasture (Grass) and milk urea (MU) level:
CP = 5.10 + 0.20 Grass + 0.119 MU;n = 31; R2= 0.82;P < 0.001. (b) Estimated dry matter intake (DMI) as a function of CP in the diet and 4% fat-corrected milk (FCM): DMI =−18.63 + 6.75 CP + 0.02 FCM;n = 38; R2= 0.77;P < 0.001 (see text). BW, body weight.
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Autumn Winter Spring Summer
ME (Mcal/day)
ME intake ME requirements
0 20 40 60 80 100 120
Autumn Winter Spring Summer
DP (g/day)
DP intake DP requirements Maintenance level
End gestation Parturition Early lactation Mid lactation End lactation Maintenance level
Fig. 8.8. Estimated metabolizable energy (ME) and digestible protein (DP) requirements and supply (calculated according to NRC, 1981) of Sarda goats grazing on Mediterranean shrubland throughout the year. (Adapted from Decandia et al., 2004b.)
0 0.5 1.0 1.5 2.0 2.5 3.0
30 38 51 71 85 113
Milk (l/head per day)
Days of lactation
0 1 2 3 4 5 6 7 8
Fat (%)
HC fat LC fat HC milk LC milk
Fig. 8.9. Milk yield (l/head per day) and milk fat content (%) of Damascus goats supplemented with high (HC, 1500 g/head per day) and low (LC, 750 g/head per day) levels of commercial concentrate (metabolizable energy = 2.6 Mcal, crude protein = 175 g/kg). (Adapted from Landauet al., 1993.)
Protein level of goats’ diet is affected by pasture botanical composition and, particularly, by the herbage/shrubs ratio. In Greece, local goats browsing on three shrublands (A, B and C) with varying shrubby and herbaceous vegetation cover (A: 53 versus 32%; B: 62 versus 20%; C: 66 versus 12%, respectively) selected a diet with higher CP content from the pasture with the highest proportion of herbaceous species (Yiakoulaki and Nastis, 1995). In general, the reduction of shrub cover from 66 to 53% improved the nutritive value and increased intake of goats’ diet.
Although MU level of goats browsing high-tannin species is an index of CP intake, this index is not as good as in sheep (Cannaset al., 1998; Molleet al., 2000). In fact, MU level in Sarda goats browsing a lentisk-based shrubland was positively correlated with CP intake only in animals that received PEG as supple- ment (Fig. 8.10).
In the Mediterranean region spring is very short and in 3 months the nutri- tive value of grass decreases rapidly. As a consequence, goats spend more time searching for plants and plant parts with higher nutritive value, thus reducing their total energy intake. In this situation, provision of moderate amounts of concen- trates with highly degradable fibre and ruminally degradable protein, i.e. formu- lated on the basis of the specific digestive kinetics of browsing animals, increased milk yield by 10% (Meuret, 1989). Sarda goats increased their intake of lentisk (from 449 to 520 g/head per day) when the supplementation level (mixture of sugarbeet pulp, 66.5% of DM, and soybean meal, 33.5% of DM) doubled (from 200 to 400 g/day) (Decandiaet al., 1999). In general, supplemental energy and protein enable animals to consume more foods with plant toxins such as terpenes, tannins and saponins (Provenzaet al., 2003).
PEG y = 0.21x– 4.03
R2 = 0.77 P < 0.05
0 5 10 15 20 25 30
0 50 100 150 200
CP intake (g)
Milk urea (mg/100 ml)
Control PEG
Control y = 0.12x+ 4.38
R2 = 0.39 P < 0.18
Fig. 8.10. Relationships between crude protein (CP) intake (g) and milk urea (mg/100 ml) in Sarda goats either supplemented (PEG, continuous line) or not (control, dashed line) with polyethylene glycol 50 g/day. (Adapted from Decandia et al., 2000a.)