Milk production of goats grazing native pasture under different supplementation regimes in southern Italy

Small Ruminant Research Small Ruminant Research 17 (1995) 213-221

Milk production of goats grazing native pasture under different supplementation regimes in southern Italy R. Rubino”,“, B. Moiolib, V. Fedele”, M. Pizzillo”, P. Morand-Fehr” Wituto Sperimentale per la Zootecnia, Vi& Basento, 106, 85100 Potenza, Italy ‘Ystituto Sperimentale per la Zootecnia, Via 0. Panvinio, II, 00162 Roma, Italy ‘Station de Nutrition et Aliment&ion ([NRA), INA PG, 16 rue Claude Bernard, 75231 Paris Cedex. France Accepted 30 November

1994

Abstract In Experiment 1,48 goats from two breeds (Maltese and Rossa Mediterranea) received two levels of concentrate supplements ( 150 and 550 g per head day- ‘) in a 2 X 2 factorial design. In Experiment 2, the concentrate levels were the same, but with two levels of crude protein (CP) for each concentrate level (16.7% and 38.5% CP, and 11.6% and 16.7% CP, respectively). At low or high concentrate level, the net energy (NE) /CP ratio was the same. There was no significant difference between Maltese and Rossa Mediterranea breeds in milk yield and composition, although fat content tended to be higher in Rossa Mediterranea. Energy and N balance, body condition and blood parameters did not differ between breeds. Concentrate levels did not alter milk production significantly: 40 kg and 30 kg in Experiment 1 and 2, respectively, i.e. 1 kg and 0.7 kg milk were produced per kilogram of concentrate. Protein supplements did not improve milk production. The group at high protein level had a trend towards reduced milk production as a consequence of reduced ingestion from pasture. In grazing conditions of southern Italy, concentrates supplied at the level of 550 g might be economical depending on their price compared with that of milk and cheese. However, protein supplementation did not increase milk yield, and was therefore of no economic value. Keywords: Concentrate

supplement;

Energy and nitrogen balance; Goat; Grazing; Milk production

1. Introduction

As a result of their selective grazing behaviour, goats are weak users of intensively managed pasture, compared with sheep (Jagush et al., 1981; Morand-Fehr and Sauvant, 1987). Some researchers have tried to improve intake level and milk yield of goats, with limited success, by using the rationed grazing method (Masson et al., 1983,199l) or by complementinggrazing with concentrates (Masson et al., 1983; Garmo, 1986). During grazing, goats showed higher intakes * Corresponding

author. Telephone:

39-97 l-5445 1.

0921~4488/95/$09.50 Q 1995 Elsevier Science B.V. All rights reserved SSDIO921.4488(95)00696-6

and levels of milk production when fed a constant amount of concentrates even though the availability of nutrients in the pasture was highly variable during summer dry weather (Pilla et al., 1986). Little research has been done on the improvement of pasture utilisation by dairy goats, or to establish if any important differences exist between goat breeds, and which kind of supplements must be supplied. Native pasture is the main feeding system in southern Italy as well as in most Mediterranean areas. Dairy goats improved their milk productions when given energy (Morand-Fehr and Sauvant, 1980) or 1987), supplement (Hadjipanayiotou, protein

214

R. Rubino et al. /Small Ruminant Research 17 (1995) 213-221

although the response was limited by the milk potential of the breed (Zometa et al., 1985; Gihad et al., 1987). For this reason, we studied the response of the two main milk breeds raised in southern Italy (Maltese and Rossa Mediterranea) for effects of concentrate level supplied after grazing at pasture and of protein content of the concentrate. We have also measured blood parameters (nonesterified fatty acids, glycaemia and betahydroxybutyrate (P-HB) ) which provide information about the nutritional status and energy balance of the animal (Giger and Sauvant, 1982; Chaiyabutr et al., 1982; Sauvant et al., 1986), with the aim of understanding the effects of level and type of supplement on milk production.

2. Materials and methods 2.1. Methods common to Experiment

I and 2

The experiments were carried out at the Istituto Sperimentale per la Zootecnia, Bella (40”21’N, 15°30’25’E) on a native pasture consisting predominantly of Mediterranean herbaceous vegetation. An area of 4.0 ha was divided into eight equal paddocks with similar characteristics (soil type, slope, exposure, etc.). Forty-eight goats were divided into four groups used in each experiment. The four groups of 12 goats were homogeneous in time of parturition, number of kids reared and level of milk production. Each group grazed two paddocks alternately. The grazing periods were as follows: Experiment l-from 12 May to 28 July, and from 21 September to 29 October; Experiment 2-from 28 April to 18 July. In Experiment 1, the grazing period was suspended from 28 July to 21 September, when summer dryness caused a lack of herbage. In this period the groups received hay ad libidum in addition to the same quantities of concentrate they had previously been receiving. In Experiment 2, the grazing period was shorter because of drought conditions. The most representatives plants of the pasture were grasses (Dactylisglomerata (14%), L.&urn perenne (12%), Bromus spp. (8%)), legumes (Medicago polimorfa (7%), Vicia satiua (3%) ) and forbs (Cichorium spp. (9%)) Pichis echioides (6%)) Daucus carota (5%)) Ranunculus bulbosus (4%) ) (Fedele et al., 1993b). The meadows,

grazed by dairy goats for many years, have received 40 kg P ha- 1 annually. 2.2. Experiment

1

Forty-eight primiparous goats aged 1.5 year of two breeds (Maltese and Rossa Mediterranea) were given two levels of concentrate (low: 150 g per head day-‘; high: 550 g per head day- ‘) and used in a 2 X 2 factorial design. The four equal groups will be referred to as M 150, M 550, R 150 and R 550. 2.3. Experiment 2 In a similarly designed experiment, 48 pluriparous Maltese goats received one of two levels of concentrate and protein: at the lower concentrate level (150 g day-‘) protein content was either 16.7% or 38.5%; at the higher concentrate level (550 g day - ’ ) it was either 11.6% or 16.7%; therefore the NE/CP ratio was the same in both regimes. The goats, divided into four equal groups, received one of the four combinations of concentrate level and protein percentage (L 150, L 550, H 150 or H 550). 2.4. Animal measurements Machine-milking was done twice a day and milk production recorded every 21 days throughout the lactation. Milk yields were measured using a proportioning milk meter (Tru Test Co., Pa Kuzanga, N.Z.), fat percentage by the Gerber method and protein percentage by the Kjeldahl method. Body condition score (BCS) was assessed by the method proposed by Santucci et al. ( 1990), modified by Hervieu et al. ( 1990). BCS was recorded on the same days that energy and nitrogen balance were determined. 2.5. Sampling and chemical analysis On milk-sampling days blood was drawn, but only data referred to the first and last milk recording are reported. In the morning, between 0803 h and 08:30 h, jugular blood samples were collected in tubes containing sodium heparin ( 15 IU ml-‘) and centrifuged immediately at 2000 g for 15 min at 4°C. The plasma was separated and stored at - 30°C. Glucose concentration was determined using the Brown and Boston

R. Rubino et al. /Small Ruminant Research 17 (1995) 213-221

method (Polimak, Huston, TX); Wako Kits (Polidiagnostici, Milan) were used to measure nonesterified fatty acids (NEFA) and the Willianson and Mellanby method (Sigma Chemical Co., St. Louis, MO, USA) for P-HB. 2.6. Nitrogen und energy balance Within each group, three oesophageally fistulated goats were used to collect herbage samples. Intake was collected at 08:30 h on five consecutive days for 30 min. In Experiment 1, samples were taken in April (from 20 to 24), July (from 27 to 31) and October (from 12 to 16) ; in Experiment 2, in May (from 16 to 20) and July (from 20 to 24). Extrusa samples were dried at 60°C for 72 h; then they were subjected to an in vitro OM disappearance technique (Tilley and Terry, 1963) and were analysed for DM, CP and CF by standard procedures (AOAC, 1980). OM intake (OMI) was determined by the total faecal collection technique. At the same time as the bolus samples were collected, four mature goats, weighing about 37 kg and approximately 4 years of age, were fitted with faecal collection bags and grazed with the oesophageally fistulated goats. Faecal output was sampled by weighing faeces for 5 days. Faeces samples were analysed for total N determination by the Kjeldahl method. OMI was calculated as OMI (g day-‘)

=

OM faecal output (g day- ’ ) / 1 - IVOMD Goat milk NE was calculated: Milk NE (kcal) =710+ 11.13 (fat content (g kg-‘) -40) (Sauvant and Morand-Fehr, 199 1) . Net energy balance was calculated according to the equations of Vermorel et al. ( 1987). Urinary N was estimated from five goats in metabolism cages fed with the herbage cut in the same pasture. Collection of urine began on the second day of the experimental diet and the N content was calculated daily for 2 weeks. N balance was calculated as N balance = N intake - (faecal N + urinary N + milk N)

215

2.7. Statistical analysis In Experiment 1 an analysis of variance (ANOVA) was done on total milk yield, milk composition and duration of lactation using the standard model: Yti=brXcoj+e,,

(1)

where Yli is one of ( 1) duration of lactation in days, (2) total milk yield in kilograms, (3) percentage of protein in the milk or (4) percentage of fat; br X coi is the concentrate level: ii, low for Maltese; i2, low for Rossa Mediterranea; i,, high for Maltese; i4, high for Rossa Mediterranea; eii is the residual. Significance of differences was tested using Duncan’s multiple range test (SAS Institute. Inc. ( 1987), GLM procedure). A further ANOVA was done on glycaemia, P-HB and NEFA from samples at the beginning and end of lactation with Model ( 1) ; differences between groups were tested in the same way. BCS were also analysed with ANOVA (Model ( 1) ) , and mean values of the main effect period-breed-concentrate were tested again with Duncan’s multiple range test. Milk yield, milk composition and the duration of lactation in Experiment 2 were similarly investigated, using Yti= co Xpri + eij

(2)

where Yijis again ( 1) duration of lactation in days, (2) total milk yield in kilograms, (3) percentage of protein in the milk or (4 j percentage of fat in milk; co Xprlj is the protein X concentrate level: ii, low protein, low concentrate; i2, high protein, low concentrate; j,, high protein, low concentrate;j,, high protein, high concentrate; eij is the residual. The results were tested as above. Glycaemia, P-HB, NEFA and BCS were also analysed as in Experiment 1.

3. Results 3. I. Experiment 1 Table 1 shows no significant difference in total milk production between breeds or feeding regimes, although lactation tended to be longer at higher concentrate level and in Rossa Mediterranea. Only Groups M 150 and R 550 were different (P < 0.05). Milk con-

216

Table 1 Experiment

R. Rubino et al. /Small Ruminant Research 17 (1995) 213-221

I-

means and standard deviation of goat milk production Ml50

Lactation length (days) Total milk yield (kg) Protein (%) Fat (%) “.bDifferent superscripts

R 150

M 550

R 550

f

SD

f

SD

x‘

SD

x

SD

161.2b 188.9 3.0 3.8”

23.2 47.3 0.3 0.6

169.4ab 185.5 3.1 4.1b

16.8 41.3 0.2 0.4

170.2ab 227.0 3.1 4.1b

22.1 76.6 0.3 0.4

181.1” 228.2 3.0 4.6”

10.3 64.3 0.3 0.7

indicate differences

(P < 0.05).

Table 2 Experiment

1-

nitrogen

(g per head day-‘),

energy (kcal per head day-‘)

M 150

R 150

balance and body condition scores (BCS) M 550

iz

SD

z

April Nitrogen Energy BCS

0.8”b -732.7a 2.6b

3.8 202.8 0.6

- 1.2b - 598.9” 2.5b

1.5 64.3 0.6

2.7’ - 300.7b 2.8”

July Nitrogen Energy BCS

4.0b - 603.2” 2.3”

2.5 315.9 0.4

2.6b - 503.4” 2.5”

0.8 59.9 0.5

October Nitrogen Energy BCS

6.3b -536.1” 2.2”

2.7 43.9 0.4

6.4” - 450.6” 2.3b

0.9 102.7 0.7

abDifferent superscripts Table 3 Experiment

1 -body

indicate differences

SD

R 550

I

SD

x

SD

1.8 31.0 0.4

3.3” - 366.8b 2.6b

1.6 124.5 0.6

3.4b - 248.2” 2.3”

1.1 74.8 0.5

6.9” - 198.1b 2.5”

2.1 92.4 0.4

7.2b - 155.8b 2.6b

1.02 135.9 0.7

10.7” - 77.0b 2.7b

0.7 138.4 0.7

(P <0.05),

condition and blood parameters

at first and last record

M 150

R 150

M 550

R 550

f

SD

.i!

SD

f

SD

x

SD

402 154

903.0” 291.0bc

362 173

882.0” 2oo.obc

421 203

536.0b 128.0”

225 44

NEFA (PM)

First record Last record

974.0” 293.0bc

P-HB (mgdl-‘)

First record Last record

12.4a 4.6b

9.6 1.4

7.2b 5.4b

2.4 1.5

6.8b 5.4b

Glucose (mg dl-‘)

First record Last record

52.2’ 51.9a

13.1 7.2

55.88b 54.5ab

6.5 9.2

57.2”b 59.1ab

3.3 1.8 13.7 6.7

6.6b 6.3b

1.9 2.9

54.3”b 62.7”

11.9 4.9

B.b.CResultsin columns and rows are different (P < 0.05 )

tent (percentages of fat and protein) was unaffected by breed or level of concentrate. Energy and N balances increased throughout the period of lactation (Table 2). The energy balance of

the groups receiving high concentrate level was also higher (P <0.05) than that of the groups receiving lower levels, but differences were not significant between breeds. N balance of Groups M 550 and R 550

R. Rubino et al. /Small Ruminant Research I7 (1995) 213-221 Table 4 Experiment

2-

means and standard deviation of goat milk lactation length, production L 150

Lactation length (days ) Total milk yield (kg) Protein (% ) Fat (%) “,bDifferent superscripts Table 5 Experiment

2-

and composition

H 150

L 550

H 550

f

SD

I

SD

x

SD

x

SD

234.5 313.2 2.9 3.9”b

11.8 72.8 0.3 0.2

229.5 282.2 3.0 3.7h

13.5 54.6 0.1 0.3

230.0 333.2 2.9 4.0”

22.5 57.5 0.3 0.2

230.7 328.5 2.9 4.0a

15.0 60.0 0.2 0.4

indicate differences

nitrogen

217

(P < 0.05).

’ ) , energy (kcal per head day - I) balance and body condition scores ( BCS)

(g per head day-

L 150

H 150

x

L 550

H 550

SD

x

SD

I

SD

.r

SD

A4a.v Nitrogen Energy BCS

8.0” - 292.8b 2.8

3.3 98.6 0.7

5.0b - 645.0” 3.0

1.5 179.2 0.5

10.0” 109.9’ 2.7

1.7 74.7 0.5

5.2b - 155.9b 2.9

5.5 82.9 0.5

JUlY Nitrogen Energy BCS

3.3’ - 181.2’ 2.3b

2.5 51.8 0.5

8.6”b -528.1a 2.8”

1.8 180.9 0.4

6.7” 133.3’ 2.5”

1.6 71.0 0.4

9.7” - 123.6b 2.6”

1.1 65.9 0.5

“,h,cDifferent superscripts Table 6 Experiment

2-

indicate differences

(P < 0.05).

body condition and blood parameters

at first and last record

L 150

NEFA (PM)

First record Last record

P-HB (mgdl-‘)

First record Last record

Glucose (mg dl-‘)

First record Last record

L 550

H 150

H 550

z

SD

x

SD

x

SD

P

SD

306a 284a

84 53

358” 316”

104 82

355” 301”

88 82

339” 281a

79 78

8.1ab 5.9”” 52.0” 49.6”

1.8 4.0

8.4” 5.9h

1.9 2.8

7.0” 6.0””

2.5 3.3

7.4a 7.1a

2.5 3.1

3.1 4.7

53.0a 49.6”

4.5 7.8

53.7 52.6”’

4.1 3.7

54.6”” 54.9b

6.1 3.8

a,b,cResults in columns and rows are different (P < 0.05).

was higher than that of M 150 and R 150; but only the N balance of Group R 550 in July and in October was different (P < 0.05). BCS of goats in the four groups showed no significant differences, although at the end of lactation the groups at high concentrate level were in slightly better condition. At the beginning of the lactation the NEFA concentration in the blood of Group R 550 was lower

(P
218

R. Rubino et al. /Small Ruminant Research 17 (1995) 213-221

the others, whereas there was no difference content among the four groups.

in P-HB

estimation will show that the groups on 550 g of concentrate were at energy equilibrium, and groups on 150 g at a deficit.

3.2. Experiment 2 4.2. Breed effect Lactation length, total milk yield and milk protein of the four groups were not different, though milk yield of Group H 150 was lower than the rest. Only fat content of the groups receiving high concentrate level was higher than that on low concentrate level (Table 4). In May the energy balance of Group H 150 was lower (P < 0.05) and that of Group L 550 higher than those of Groups H 550 and L 150 (Table 5). The N balance of the groups at low protein level fell between May and July whereas that of groups at higher protein levels increased. In May the highest N balance was found in Groups L 150 and L 550; in July, this had been reversed: H 150 and H 550 were the highest. No significant difference was seen in BCS of the four groups in May, although in July Group H 150 was in better body condition than the rest. No significant difference was found in NEFA content between the first and last record, nor in NEFA content of the four groups for each record. j3-HB content seemed to decrease between the first and last record, although there was no difference among the four groups. Glycaemia tended to become lower from the first to the last record, but not significantly (Table 6).

4. Discussion 4.1, Energy balance A daily supplementary feed of 550 g of concentrate only produced an energy balance in Group L 550 in Experiment 2. The energy deficit of other Groups 550 was on one hand explained by the intake of pasture herbage ( - 30% average) and higher milk production ( + 17% average), and on the other probably due to the lack of precision in the methods used for the estimation of herbage intake. Within this work, the herbage intake estimation was done by total faecal collection and dry bolus in vitro digestibility. Work done by Fedele et al. (1993a) has shown that this method underestimates digestibility by about four percentage points and, consequently, underestimates herbage intake, too. Correction of the intake

The performances of the Maltese and the RossaMediterranea breeds were similar according to Pizzillo et al. ( 1994)) who observed between the two breeds significant differences in total milk production and duration of lactation or milk protein content. The only difference those workers detected was higher milk fat content by 0.6 percentage points in the Maltese vs. Rossa. Almost the same difference has been found in the current work (0.45 percentage points). 4.3. Effect of concentrate level In the two experiments, supplying 550 g concentrate instead of 150 g did not increase milk yield, which was 40 kg and 30 kg in Experiments 1 and 2, respectively, i.e. 1 kg and 0.7 kg milk were produced per kilogram of concentrate. This increase was similar to that recorded for the Alpine breed, which had, however, much higher potential yield (700-800 kg milk per lactation) when concentrates were added to a ration covering minimum energy requirements (Sauvant and Morand-Fehr, 1978; Garmo, 1986; Morand-Fehr et al., 1991;). The law of diminishing returns was noted for supplementary feeding in dairy cows (Morand-Fehr and Sauvant, 1987). Mowlem et al. (1985) have verified this for Saanen goats receiving between 0.4 and 1.4 kg of concentrates per day. This decrease is mainly due to the reduction in forage intake as consumption of concentrates increases. High levels of concentrates can lead to the coefficient of substitution of forage/concentrates being greater than one, and in this case the energy gained from concentrates is less than the decrease in energy ingested from grazing the pasture, where plants have generally high nutritive value. However, this reduction in milk yield appears at different levels of production, depending on breed milk potential. It starts at lower levels in breeds with low potential milk yields (Zometa et al., 1985; Gihad et al., 1987). As milk yield increased very little when the daily supplement of concentrate was increased from 150 g to 550 g, we suggest that under our experimental conditions both Maltese and Rossa Mediterranea goats

R. Rubino et al. /Small Ruminant Research I7 (1995) 213-221

covered their requirements with 150 g concentrate. The protein content of the milk was not modified, though it may be increased by energy supplements (MorandFehr and Sauvant, 1980; Gihad et al., 1987), which confirms that the increase in concentrates did not improve energy ingestion. However, the energy balance of the groups receiving 550 g of concentrate was higher compared with the groups receiving 150 g, although their NEFA content, which indicates fat reserve mobilisation (Giger and Sauvant, 1982; Dunshea et al., 1989), was not generally lower. Although BCS of the groups receiving 550 g concentrates did not show higher values at the beginning and mid-lactation, they did so by the end of lactation. The results support the hypothesis that over-supply of concentrates increases energy ingestion and fat deposition faster than milk synthesis. 4.4. E#ect of nitrogen supplement

level

Protein supplements did not improve milk production in these experiments; in Group H 150, it decreased. Morand-Fehr and Sauvant ( 1980) showed that protein supplements only increase milk yield when there is an insufficient supply of protein in the diet. Hadjipanayiotou (1987) found in Damascus goats that a N over-supply did not increase milk yield. Badamana and Sutton ( 1992) showed that the milk yield of Saanen goats was increased by an increase in the protein content of concentrates from 11% to 1X%, but unaffected by a further increase to 25%. Thomas et al. ( 1980) also reported that milk production of Saanen goats was increased by a protein supplement covering requirements, but reduced by over-supply of N. In this experiment the N balance of the four groups was always positive, confirming that all goats were over-supplied with N, even those in Groups L 150 and L 550, which received the concentrate lower in protein. This result has been confirmed by Martillotti et al. (1993) on fistulated dairy cows (Frisians grazing Festuca arundinacea swards). The NH, content of filtered rumen fluid after incubation in nylon bags for 20 h was significantly lower than initially observed ( 1.44 vs. 2.33 mmol), and it fell further to reach 7.00 mmol after 28 h. The initial degradability of CP was also 43% higher. If we assume that the average CP content of herbage ingested by goats was 20% in spring and 17% in summer, we can suppose that the grazing animals had high

219

levels of ammonia in the rumen. Giving concentrates with a high protein content caused a further increase in NH,, and consequently increased the risk of rumen alkalosis. This could explain the lower milk production in Group H 150, which received a 38.5% CP concentrate. It is therefore not too surprising that higher N levels did not increase milk yield. It is well known that in all ruminants, and goats in particular, a N overcharge can cause an increase in rumen ammonia which results in alkalosis, reduces forage ingestion and increases glucose requirements (Thomas et al., 1980; Brun Bellut et al., 1984). This could be the reason for the lower milk yield of Group H 150, which was given 1.50 g concentrate at 37% N. The significantly higher glycaemia in Group H 550, which received higher N supply from concentrates, suggests that gluconeogenesis in this group was more intense, thus supporting the above. Another reason could be the reduction in feed ingestion sometimes observed after the consumption of concentrates rich in fermentable digestible proteins (P. Morand-Fehr et al., unpublished data, 1993). This could have strongly reduced ingestion of forage from the pasture by goats. The increase of protein in concentrates had no influence on milk protein content, as already shown in dairy goats (Morand-Fehr and Sauvant, 1980; Morand-Fehr et al., 1991; BadamanaandSutton, 1992), incows (Remond, 1985) and sheep (Robinson et al., 1974). 5. Conclusions Under the grazing conditions of Southern Italy, supplements of 550 g concentrate day-’ did not seem to increase significantly milk yield of Maltese and Rossa Mediterranea goats compared with 150 g day-‘. Concentrates supplied at the level of 550 g might be economic depending on their price compared with that of milk and cheese. The protein supplement contained in concentrates did not increase milk yield and therefore had no economic interest. Energy and protein supplements might, however, give better results when fed to breeds of goats having a higher potential milk yield than the Maltese and Rossa Mediterranea. References AOAC, 1980. Methods of Analysis, DC.

13th edn. AOAC, Washington,

220

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Resume Rubino, R., Moioli, B., Fedele, V., Pizzillo, M. and Morand-Fehr, P., 1995. Milk production supplementation regimes in southern Italy. Small Rum. Res., 17: 213-221.

of goats grazing native pasture under different

Dans l’exp&ience I, 48 chbvres de race Maltese et Rossa Mediterranea recpivent 2 niveaux de concentms (150 et 550 g/t&e/jour) dans un dispositif factorielle 2 x 2. Dam l’experience 2, les niveaux de concent& sont les methes mais avec deux niveaux de mat&e azotee ( 150 g/ dte/jour de concentres : 16.7% et 38.5% de mat&e azotde totale (MAT); 550 g/tete/jour : I I .6% et 16.7% de MAT) Pour chaque niveau de concentre, le rapport Energie nette/MAT est identique. II n’y a aucune difference entre la race Maltese et la race Rossa Meditermnea sur la production et la composition du lait bien que le taux butyreux tend a Ctre plus Cleve chez les chevres Rossa Mediterranea. Les balances Cnergttiques et azot=&es,l’etat corporel et les parametres sanguins ne sont pas differents chez les 2 races. Le niveau d’aliments concentres n’apporte pas de variations significatives de la production laitiitre: 40 et 30 kg de lait respectivement dans les experiences I et 2, soit I ou 0.7 kg de lait par kg de concentn? ingere. Les apports supplementaires de matiere azotee n’ont pas ameliom la production laitiere; celle du groupe recevant le haut niveau de matiere azot&e tend a diminuer en raison d’une ingestion reduite au paturage. Dans les conditions de paturage de l’ltalie du Sud, un niveau de 550 g de concentres peut convenir si leur prix est compatible avec ceux du lait et du formage vendu. En revanche, les concentrations elevt?es de mat&e azotee dans l’aliment concentre n’apportent aucune amelioration sur la production laitiete, done elles n’ont pas d’intC&t Cconomique.