Milk production, milk fatty acid composition and conjugated linoleic acid (CLA) content in dairy ewes raised on feedlot or grazing pasture

Livestock Science 104 (2006) 121 – 127 www.elsevier.com/locate/livsci

Milk production, milk fatty acid composition and conjugated linoleic acid (CLA) content in dairy ewes raised on feedlot or grazing pasture N. Atti a,*, H. Rouissi b, M.H. Othmane a a

INRA-Tunisie, Laboratoire de Productions Animales et Fourrage`res, rue He´di Karray, 2080 Ariana, Tunisia b Ecole Supe´rieure d’Agriculture de Mateur, Mateur, Tunisia Received 3 October 2005; received in revised form 1 March 2006; accepted 22 March 2006

Abstract To evaluate milk production and milk fatty acid (FA) composition and conjugated linoleic acid (CLA) content, 75 SiciloSarde ewes were used on three dietary treatments during 89 days. Two groups were conducted on rotational grazing in separate pastures of green barley grass (GB group) or perennial ryegrass (RG group) and receiving daily 300 g of concentrate/ewe. A third group was conducted in feedlot (FL group) on oat hay and silage and receiving 500 g of the same concentrate per ewe per day. Milk production did not differ among GB and RG pasture treatments (617 ml/day) but it was higher ( p b 0.01) than FL one (363 ml/day). Milk fat and protein content were higher for ewes in FL than for ewes raised on both pasture treatments (88.8 and 56.7 vs. 74.5 and 54 g/kg for fat and protein, respectively). However, fat and protein yields were higher for pasture groups than FL one. The palmitic, oleic, miristic, stearic, and caprinic acids were dominant for all regimens. Short-chain FA (C4:0–C10:0) did not differ among all treatments. The medium chain FA content was significantly higher in milk fat from FL group. Conversely, the long chain ones increased for grazing groups. Milk from pasture groups had a higher C18:3 proportion than that from FL sheep (4.5 vs. 2.7 g/1000 g). The CLA content was significantly ( p b 0.001) higher for grazing groups than for FL one (7.3 and 10.3 for GB and RG, respectively, vs. 2.4 g/1000 g for FL). Pasture-based diets increased the concentrations of longchain unsaturated FA and desirable FA in milk fat. D 2006 Elsevier B.V. All rights reserved. Keywords: Dairy ewes; Grazing; Feedlot; Milk production; Conjugated linoleic acid

1. Introduction

* Corresponding author. Tel.: +216 1 230024; fax: +216 1 752897. E-mail address: [email protected] (N. Atti). 1871-1413/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2006.03.014

Due to the evolution of consumers’ demand, more attention has been given to traits related to food safety, health and nutritional value. In this framework, animal products play an important role in relationship to its

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composition in fatty acid (FA) impact on human health. In fact, fat nutritional aspects have been assuming an increasing importance as positive or negative predisposing factors for human health. Recently, research focused on conjugated linoleic acid (CLA), the increasing interest on CLA is attributed to its potential health benefits such as anticancerigenic, antiatherogenic, antidiabetic and antiadipogenic (Banni and Martin, 1998; Pariza and Cook, 1998). Food products from ruminants are the richest source of CLA for humans, with milk having higher concentration than meat. Among factors affecting this concentration, animal diets appear the most important (Khanal and Olson, 2004). Previous research showed that dietary factors such as the nature of forages, including pasture, and the supplementation of dairy rations with protected or unprotected vegetable or fish oil can substantially increase CLA content in milk of ruminants (Chilliard et al., 2001). Compared with total mixed ration (TMR) diets, pasture-based diets have resulted in higher concentrations of unsaturated long-chain FA and CLA in milk (Kelly et al., 1998). A substantial increase of milk fat CLA contents in dairy cattle after turning out to pasture were showed later in a series of experiments (Dhiman et al., 1999; Stockdale et al., 2003; Ward et al., 2003; Kay et al., 2004). Particularly, Dhiman et al. (1999) observed a highly positive effect of fresh lush green pasture on CLA content. Given these information, increasing the CLA content in milk has become an important objective in dairy cattle feeding strategies because of its potential benefits for human health. However, information on this topic is very scarce in ewes. Only few studies (Cabiddu et al., 2001, 2005; Piredda et al., 2001) have compared dairy sheep performance between feedlot and pasture-based diets and their effect on milk FA composition and specifically on CLA content of grazing ewes. On the other hand and under South Mediterranean conditions, information on dietary factors affecting CLA content in milk is also very scarce. Feeding systems and management in this region are moreover different from those in other regions. The objective of this study was to compare the effects of feeding hay and silage diet or pasture-based diets on milk yield and composition and FA composition in the Sicilo-Sarde sheep, which is the unique dairy breed ewe in the North Africa.

2. Material and methods 2.1. Experimental design and treatments The experiment was carried out with 75 lactating Sicilo-Sarde ewes from the dairy experimental farm of the National Institute of Agricultural Research of Tunisia (INRAT). The parturition occurred late October 2003, and then lambs were weaned at 60 days post partum. At this time, animals were gathered into three homogeneous groups according to age (4.4 F 1.9 years), body weight (36.7 F 4.7 kg) and milk production (488 F 142 ml/day). Two groups of 25 ewes each were conducted on rotational grazing with a stocking rate of 25 ewes/ha in separate pastures of green barley grass (GB group) or perennial ryegrass (RG group). The pasture assigned to each group was divided into 6 paddocks of equal areas. At the experiment beginning, the grazing height was 17 cm; when the grazing height becomes 7 cm ewes have been changed for the following paddock and so forth. Both grazing groups received a daily supplementation of 270 g/ewe of concentrate on basis of dry matter (DM), it is a mixture of barley, soya bean and mineral/ vitamin supply (160 g of crude protein (CP) and 1 forage unity (FU) per kg DM). The green barley grazing period extended to 89 days from December 22 to March 16. The ryegrass grazing one started in the same time (December 22) and went on until April 4 but we consider only the same grazing period as GB (89 days). The third group was reared during the same period indoors in feedlot (FL group) and fed with oat silage (264 g DM/kg, 82 g CP and 0.72 FU/kg DM) ad libitum and received 450 g DM of oat hay (81 g CP and 0.6 FU/kg DM) and 450 g DM of the same concentrate per head daily. 2.2. Feed collection and analyses Herbage mass was determined before entering each paddock by cutting 14 quadrates (0.25 m2/quadrat) of pasture at 6 cm above the ground, the whole grass production was calculated according of this sample weight and the paddock area. The samplings were pooled, two subsamples were taken for chemical composition. Indoors, uneaten feed, particularly silage were removed daily at 09:00 before supplying fresh feed. A subsample of feed was collected once a week

N. Atti et al. / Livestock Science 104 (2006) 121–127

for analysis. Chemical composition of all foods was determined (Tables 1 and 2). Grass, concentrate, hay and silage samples were dried at 60 8C in a forced-air oven, ground through a 1-mm screen, and analyzed for DM (105 8C in a forced-air oven for 24 h) mineral content (450 8C for 8 h), crude fiber (Weende) and CP (Kjeldahl). 2.3. Milk control and analysis Ewes were daily milked at 07:30 and 16:30 during all experimental period. Individual milk yield was recorded weekly during the whole observation period and individual milk samples (20 ml) were kept (4 8C) and analyzed for milk fat (F) and protein (P) using a MilkoScan 4000 (FOSS ELECTRIC, Integrated Milk Testingk). Milk samples for FA analysis were taken once at two milking control. However, and given the high cost of the FA analyses, each group of 25 ewes was divided into 5 sub-groups of 5 animals. The milk samplings of the 5 ewes were pooled and mixed and one subsample was kept for analysis by gas chromatography.

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Table 2 Total herbage production, chemical composition and nutritive value of green barley and ryegrass during the two grazing passages

Fresh matter (kg) DM (g/kg) DM production (kg) OM (g/kg DM) CF (g/kg DM) CP (g/kg DM) Ash (g/kg DM) FU/kg DMa Total FU a

Green barley

Ryegrass

1st grazing

2nd grazing

1st grazing

2nd grazing

13400 187 2501 890 242 146 110 0.87 2109

3456 220 760 883 263 134 118 0.84 661

3620 228 827 859 265 130 141 0.79 656

5454 230 1254 868 270 132 132 0.81 1016

FU: forage unity (INRA, 1978).

of saturated fatty acids (SFA), mono-unsaturated FA (MUFA), poly-unsaturated FA (PUFA), unsaturated FA (UFA) and desirable fatty acids (DFA) as well as the PUFA/SFA ratios were calculated. The DFA correspond to the sum of all unsaturated fatty acids and C18:0 (Rhee, 1992). 2.5. Statistical analysis

2.4. Fatty acid analyses Lyophilised samples of frozen ewes’ milk were extracted by Soxhlet with petroleum ether/ethyl ether (1:1, v/v) to characterise the fatty acid composition. The fatty acid methyl esters (FAMEs) prepared by direct transesterification (Christie, 1993) were separated by HRGC using a HP-5890 gas chromatograph equipped with a flame ionization detector and split (1:24) injector. Separations were performed using a HP-FFAP capillary column (25 cm  0.2 mm i.d.  0.3 Am). Fatty acid content was expressed in percentage of the total amount of the fatty acids identified. After individual FA determination, the sum

a

Oat hay

Oat silage

Concentrate

842 914 75 285 86 0.6

264 888 82 348 112 0.6

935 960 158 74 40 1.0

FU: forage unity (INRA, 1978).

(FL) vs. (GB + RG): global effect of grazing GB vs. RG: effect of grazed forage species.

3. Results and discussion 3.1. Forage production

Table 1 Chemical composition of experimental foods

Dry matter (g/kg) Organic matter (g/kg DM) Crude protein (g/kg DM) Crude fiber (g/kg DM) Ash (g/kg DM) Energy (FU/kg DM)a

The mean daily milk production as well as the total milk production and the milk composition were analyzed using a one-way ANOVA design. Data analysis was carried out using the General Linear Model Procedures (SAS, 1987). The following contrasts were used to compare the effects of the different diets:

Herbage production, chemical composition and nutritive value of green barley and ryegrass were reported in Table 2. The grass amount produced by the whole green barley plot during the first grazing was 13.27 t fresh matter or 2.35 t DM/ha, while the ryegrass production for the same time was lower, 3.62 t fresh matter or 0.789 t DM/ha. For both species, an increase in herbage production was noted since the

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second paddock traducing plant growth. The CP content of herb was high for both species (Table 2); they contained more CP and less CF than oat hay and silage. The herb growth allowed a second grazing for green barley pasture but only on four paddocks, for the two other paddocks, the herb became hard and no palatable and they were not grazed. However, the whole pasture of ryegrass was grazed twice. During the second grazing, the green barley grass production was 3.456 t of fresh mater or 1.081 t DM/ha, while ryegrass produced 5.45 t of fresh mater or 1.24 t DM/ha. Since then, barley production was less important, with higher content of CF and lower content of CP in the second than in the first grazing. The ryegrass herb production was higher in second than in the first grazing passage with the same chemical composition (Table 2). 3.2. Milk yield and composition The average milk yield and fat and protein contents observed during the experimental period were reported in Table 3. Milk yields of these ewes were low with average daily production of 518 ml/day. This value is similar to that recorded for the same breed in other studies (Jemali et al., 1995; Atti and Rouissi, 2003; Othmane, 2004). The low milk production is the problem of the Sicilo-Sarde, unique dairy sheep breed in the North Africa, for which a crossbreeding program with the Sarde breed sheep was planned since 2 years. The diet nature influenced milk yield, which was higher for grazing groups (GB and RG) than for FL one, the first contrast [Feedlot vs. Grazing] being highly significant ( p b 0.01). In this way, Atti and Haj-Taeib (1989) and Atti and Abdouli

Second grazing 800 700

MP (ml/day)

124

600 500

FL

GB

RG

400 300 200 0

1

3

5

7

9

11

13

15

Weeks Fig. 1. Daily milk yield of dairy ewes raised on feedlot (FL) diet or grazing green barley (GB) or ryegrass (RG) pastures.

(2001) reported for native sheep and under the same feeding conditions that growth rate was higher for grazing lambs than for feedlot ones. The milk yield was declined during the 4 first weeks of experiment for the FL and GB groups and then was stabilized for the FL group. For the GB group, the milk yield increased and remained higher than RG one until the end of the first grazing and then decreased and became lower than the RG milk production (Fig. 1). This tendency for milk production was the consequent of the herb production, since GB herb production was higher during the first grazing and the RG production was higher during the second one. Milk fat and protein proportions were higher for FL group than for both grazing ones (Table 3). The higher quantity of concentrate for FL group could explain these results, since the distribution of increas-

Table 3 Average milk yield and composition of dairy ewes rose on feedlot (FL) diet or grazing green barley (GB) or ryegrass (RG) pastures Group

FL

GB

RG

S.E.

p

C1

C2

Milk yield (ml/day) 1st grazing 2nd grazing Total Fat (g/kg) Fat (g/day/ewe) Protein (g/kg) Protein (g/day/ewe)

367 358 363a 88.8a 32a 57.6a 21a

667 565 616b 77.2b 48b 54.6b 34b

608 628 618b 76.8b 47b 53.b 33b

37.2 36.3 37.5 1.15 3.2 0.51 2.1

*** *** *** *** *** *** ***

*** *** ** ** *** ** ***

ns ns ns ns ns ns ns

Mean values with different letters in the same row are significantly different. C1: contrast 1: feed lot vs. grazing. C2: contrast 2: green barley vs. ryegrass. **pb0.01; ***pb0.001.

N. Atti et al. / Livestock Science 104 (2006) 121–127

Fat yield (g/d)

65

3.3. Milk fatty acids

45

25 FL

GB

RG

5 1

3

5

7

9

11

13

15

Weeks Fig. 2. Evolution of milk fat yield in dairy ewes raised on feedlot (FL) diet or grazing green barley (GB) or ryegrass (RG) pastures.

ing yields of concentrate lead to a considerable increasing in fat and protein milk content (Bocquier and Caja, 2001). Another explanation could be the effect of dilution (Othmane et al., 2002) associated to a greater milk production in GB and RG grazing groups compared to that of FL one. Similar depression of fat and protein has been previously reported in dairy cows fed pasture-based diets (Schroeder et al., 2003) compared to that fed TMR diet. The lower quantity of concentrate offered to grazing groups resulted in a higher forage: concentrate ratio in grazing treatments, which could increase the losses of highly degradable N of the pasture and explain the lower milk protein concentration (Table 3). However, milk fat and protein yields (in gram per day) were higher in both grazing groups than in FL one (Table 3). This result was related to a higher milk production in the two first groups. The progress of milk fat and protein yield for the three treatments during the experiment were shown in Figs. 2 and 3, respectively. 45

Protein yield (g/d)

125

30

15 FL

GB

RG

0 1

3

5

7

9

11

13

15

Weeks

Fig. 3. Evolution of milk protein yield in dairy ewes raised on feedlot (FL) diet or grazing green barley (GB) or ryegrass (RG) pastures.

Results presented in Table 4 show the prevalence of palmitic (C16:0), oleic (C18:1), miristic (C14:0), stearic (C18:0), and caprinic (C10:0) acids for all regimens. These acids accounted for about 760 g/kg of the total fatty acids; this result was in agreement with values commonly reported for dairy sheep (Sevi et al., 1998; Carta et al., 2003; Chiofalo et al., 2004). The short chain FA (C4:0–C10:0) content was similar for all treatments (Table 3). This result confirmed those of Carta et al. (2003) in dairy ewes and Schroeder et al. (2003) in dairy cows. The medium chain FA content was significantly higher in milk fat of FL group. However, the long chain FA Table 4 Average fatty acid (FA) profilea in milk fat (g/kg) of dairy ewes rose on feedlot (FL) diet or grazing green barley (GB) or ryegrass (RG) pastures

C4 C6 C8 C10 C12 C14 C16 C16:1 C17 C18:0 C18:1 C18:2 CLA C18:3 C4–C10 C12:0–C16 SFA MUFA PUFA UFA PUFA/SFA UFA/SFA DFA

FL

GB

RG

SE

p

C1

C2

18.1 17.4 19.4 70.0 39.5 120.3 318.8 17.5 19.4 70.3 191.2 15.6 2.4 2.7 125 518 715 215 20.6 236 0.29 0.33 306

17.8 18.7 22.0 72.5 38.2 107.6 261.8 13.3 20.5 85.7 214.1 17.2 7.3 4.7 130 445 668 233 29.2 263 0.44 0.39 348

17.9 16.9 18.7 62.0 33.9 112.3 276.5 13.4 19.3 90.9 211.5 16.2 10.3 4.4 115 452 687 230 30.9 261 0.45 0.38 352

10.8 0.90 1.02 1.11 1.23 1.87 7.08 0.65 0.60 2.50 6.69 0.34 0.83 0.23 5.5 9.3 8.1 6.8 1.15 7.4 0.020 0.015 9.1

ns ns ns ns ns ** ** ** ns ** ns ns *** *** ns ns ns ns *** ns *** ns *

ns ns ns ns ns ** ** ** ns ** ns ns *** *** ns *** * ns *** ns *** ns *

ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns

SFA: saturated fatty acids, MUFA: mono-unsaturated FA, PUFA: poly-unsaturated FA, UFA: total unsaturated FA, DFA: desirable fatty acids (the sum of all unsaturated fatty acids and C18:0). C1: contrast 1: feed lot vs. grazing; C2: contrast 2: green barley vs. ryegrass. a The used column is a 25 m GC one, so it cannot separate out 18:1 fatty acid isomers, in particular oleic acid (cis-9 18:1) from (trans 18:1) isomers. * pb0.05; **pb0.01; ***pb0.001.

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increased for grazing groups. On the whole, average values of all chain FA classes (short, medium and long) were very closed to those obtained in dairy cattle (Schroeder et al., 2003). The palmitic acid was significantly ( p b 0.001) higher for FL group, the stearic acid was significantly lower ( p b 0.001) for this group than for grazing ones (Table 4) while the oleic and linoleic acids were similar for all groups. The linolenic content was significantly ( p b 0.001) higher for grazing groups than for FL one. High milk content of C18:3 was previously observed in cows consuming high-quality pastures because this is the most abundant FA in forages (Dewhurst et al., 2001; Mackle et al., 2003; Schroeder et al., 2003). The CLA content was significantly ( p b 0.001) higher for grazing groups than FL one. This result was in agreement with those of Cabiddu et al. (2001) and Piredda et al. (2001), who found that ryegrass pasture-based diets increased CLA content in ewe’s milk. Average values obtained in the actual study were consistent with previous results in dairy sheep (Piredda et al., 2001; Secchiari et al., 2001; Carta et al., 2003), but they were lower than that obtained by Delogu et al. (2000) for Sarde sheep grazing during the spring (32.85 mg/g fat). The CLA content was higher for RG group (10.3) than for GB one (4.3) but the contrast [GB vs. RG] was not significant; forage species could affect milk fat CLA content (Addis et al., 2005). The CLA content was averagely 3 and 4.3 fold higher ( P b 0.01) on the GB and RG treatments, respectively, compared with the FL treatment (Table 4). Similar results were observed for dairy cows fed pasture compared with cows fed TMR (Kelly et al., 1998; White et al., 2001; Schroeder et al., 2003). Alimentation based on grazing pasture, a rich food in PUFA, resulted in a significant increase of this fatty acid class to the detriment of the saturated class. The same tendency was observed for the DFA class, so the PUFA/SFA ratio was higher ( p b 0.001) in the milk of both grazing groups than in that of the FL one (Table 4). This result is very interesting since it has been shown the increasing healthfulness of milk by reducing the saturated FA content and increasing the long-chain unsaturated FA (Pariza, 1999). Otherwise, these results were in accordance with those observed on lactating cows (Schroeder et al., 2003; Khanal and Olson, 2004) and ewes (Cabiddu et al., 2001; Piredda

et al., 2001) reared on grazing comparative to that fed indoors on concentrate and conserved forage.

4. Conclusion These first results on FA contents in milk of the Sicilo-Sarde dairy ewes agree with previous studies on other dairy sheep breeds. Compared with ewes on the FL group, ewes on the two pasture-based diets had more milk production and less milk fat content, but they had higher fat and protein yields. Grazing ewes had a reduction in the content of medium FA and an increased content of C18:3 and CLA, it could be concluded that the pasture-based diets increased healthfulness of sheep milk. Further researches are needed to identify strategic supplements in pasturebased diet in the aim to maximize CLA and unsaturated FA content in milk enhancing its nutritional and health values.

Acknowledgements The support of the OEP for milk analysis is acknowledged. The authors are indebted to H. Aloui, A. Bouselmi, J. Khlil and H. Marjouaa for their technical help during this work. The authors also thank Dr. M. Chakroun and A. Mezni for the ryegrass prairie plant.

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