Contribution to assessment of energy requirements in ruminant lambs of the Ouled Djellal breed

S Triki and A Larwence* 

INA, Département de Zootechnie, 16200 El-Harrach Alger,
* SUPAGRO, BP 5098 CS 24501  34093 Montpellier

trikiinnadz@yahoo.fr   ;   aristide.larwence@supagro.inra.fr 

Abstract 

Energy requirements of ruminant male lambs of the Ouled Djellal breed were assessed in three feeding trials over 4-month periods at different periods of the year. A total of 60 lambs, aged 6-8 months, individually penned, were given a mixed diet composed of vetch-oat hay fed ad libitum and 250 g/d of a barley based concentrate feed.

Diet organic matter digestibility (OMD), digestible organic matter intake (DOMI), metabolisable energy intake (MEI), net energy intake (UFLI), and daily weight gain (DWG) averaged 0.600, 351g, 1263 kcal, and 0.46 UFL/kg BW ^0.75 /d, and 97 g/d, respectively. Regression equations were computed between DOMI, ME, UFLI, and DWG expressed per kg BW ^0.75. Energy requirements of lambs could be assessed for DWG ranging from 50 to 150 g/d. Maintenance energy requirement averaged 23.0 g DOM, 80 kcal ME, or 0.029 UFL/kg BW ^0.75 /d. Energy requirements were computed for 50, 100 and 150 g BWG d^-1 in 20, 25, 30 and 35 kg body weight Ouled Djellal lambs. Partial requirement for slow growh averaged 460 kcal ME per 100 g DWG. These values were similar to those of slowly growing or small sized sheep breeds in southern areas, but lower than those of European or American breeds. The difference may result from differences in genetic type and nutritional history of lambs reared in harsh conditions.

Key-words: energy requirement, frugality, growth, maintenance

Contribution à l’évaluation des besoins nutritionnels en énergie de jeunes ovins de race Ouled Djellal

Résumé 

Les besoins énergétiques d'agneaux de la race Ouled Djellal ont été étudiés au cours d'essais alimentaires d'une durée de quatre mois, durant trois années consécutives à l’aide d’un modèle linéaire corrélant les gains moyens quotidiens (GMQ) aux quantités d’énergie ingérées exprimées en matière organique digestible ingérée (MODI), énergie métabolisable

ingérée (EMI) et en unité fourragère lait ingérée (UFLI).

Soixante agneaux mâles entiers âgés de 6 à 8 mois et pesant 17.6 ± 4.8 kg en début d’expérience, 29.9 ± 5.0 kg en fin d’expérience et 25.3 ± 3.4 Kg en moyenne, ont reçu une alimentation composée de foin de vesce-avoine distribué à volonté et de 250 g d'aliment concentré. La digestibilité de la matière organique était de 60 % et le GMQ de 97g.j^-1. Les quantités moyennes ingérées étaient de 351g de MODI, 1263 kcal d’EM et de 0.46 UFL par jour. Le besoin d’entretien était en moyenne de 23g de MOD, 80 kcal d'EM et 0,029 UFL. par kg.P^0.75 j^-1. La quantité d’EM supplémentaire nécessaire pour produire 100 g de croît était en moyenne de 460 kcal. Ces valeurs sont comparables à celles données pour d’autres races rustiques des pays du sud mais plus faibles que celles trouvées pour les races améliorées des pays du Nord. Le type génétique et l’histoire nutritionnelle des animaux dans ces zones, pourraient expliquer ces résultats. Enfin les besoins énergétiques d'agneaux de race Ouled-Djellal ont été calculés pour des poids de 20, 25, 30 et 35 kg et des gains de poids moyens de 50, 100, et 150 g par jour.

Mots-clés: besoins en énergie, croissance, entretien, frugalité

Introduction 

Frugality of ovine breeds in southern countries is well known (Chellig 1992, Silanikove 1996). Nevertheless, except few studies (Al Jassim et al 1996), nutrient requirements of ovine breeds in southern developing countries have not been investigated. Depending on the history of each country, the feeding tables used are those from ARC (Agricultural Research Council, UK), NRC (National Research Council, USA) or INRA (Institut National de la Recherche Agronomique, France)

.

In Algeria steppe pasture and move to cereal producing areas have always supplied the major feeding sources for small ruminants. Dismantling (breaking up) of self-managed estates in 1987 made the high plateau stubbles and fallow fields less available. In addition, steppe has been over-pastured. This resulted in settling of ovine breeding, which is presently increasing, in northern areas of Algeria. Consequently, better knowledge of nutrient requirements of ruminant is necessary to adjust nutrient allowances to needs.

The available methods to assess energy requirements, especially maintenance energy requirements of ruminants, have been previously reviewed (Van Es 1980). Feeeding trials including several feeding levels have often been used. They have the advantage of not being expensive, and keeping animals in usual breeding conditions. It is the reason why the feeding trial method has been chosen in the present study to assess maintenance and moderate growth energy requirements of ruminant lambs of the Ouled Djellal breed.

Material and methods 

Animals

The Ouled Djellal breed is the most important ovine breed in Algeria: it includes 14 of the 20 millions heads of the ovine flock. It is a meat breed with fine and white wool. The mature live weight averages 63 kg in rams and 47 kg in ewes. The prolificacy is  1.1 and growth potential is  250 g/d (Chellig 1996). The study was performed with 60 Ouled Djellal ruminant lambs from the Institute flock, aged 6-8 months. Mean liveweight was 17.9 ± 4.8 kg at the beginning of the experimental period. The lightest lambs were twins or triplets

Experimental design, feeds and diets

The study was carried out over three years (1994-1997) with groups of 20 lambs each year, at various periods: from October to January the first year, from February to May the second year, and from December to March the third year. The ambient temperature in the barn ranged from 16 to 25 °C. Lambs were kept (housed) individually in 4 m² stroh bedded pens. Each pen was equipped with a drinking trough and a feeder.

Lambs were given a mixed diet composed of medium quality vetch-oat hay (VO) harvested in June each year, and concentrate feed (C). Vetch-oat hay is the most common forage grown in Algeria. It was balled (17 kg balls) and stored under a shelter. The concentrate feed was composed of ground barley (78 %), poultry slaughter by-products (20 %), and commercial mineral-vitamin mixture (2 %). The daily ration was divided in two equal meals, distributed at 09.00 and 17.00. VO was offered ad libitum  (at least 15 % more than ingested), whereas C was distributed in limited amount (250 g/d, ie 125 g/meal) whatever the lamb live weight.

Measurements and calculations

After a 15 day adaptation period to the experimental diet, the quantities of VO and C offered and left were determined individually every day during the 4 month experimental period, using an accurate balance (2200 ± 0.1 g, Item, France). The dry matter (DM) contents of VO , C and hay leftovers were determined daily. DM intake per day (DMI) was calculated individually from the quantities of  hay and concentrate DM offered and left. The lambs were weighed every two weeks before the morning meal, using a 140 kg  ± 10 g scale. The mean daily weight gain (DWG) was calculated individually.

Diet organic matter digestibility (OMD) was determined individually by total collection of faeces during 10 days in all lambs with groups of 5 to 7 animals put in metabolic cages every three weeks. The DM, ash, crude protein (CP) and crude fibre (CF) contents of feeds and faeces were determined in triplicate using the AOAC methods (AOAC 1975). The metabolisable energy (ME) and lactation net energy (NEL) of the diet were assessed according to INRA (INRA). NEL was used, as for female lambs (INRA 1978), because of the low DWG of the experimental lambs. NEL intake was then expressed as lactation feed unit (UFL):

UFL = NEL (kcal) /1700 (kcal).

The average values over the whole experimental period were calculed individually for digestible organic matter intake (DOMI); metabolisable energy intake (MEI) and lactation net energy intake (UFLI).

Assessment of maintenance and growth energy requirements

DOMI, MEI, and UFLI were expressed per kg BW ^0.75 .d^-1 to take into account the differences in BW between lambs. The relationships between DOMI, MEI, UFLI, and mean DWG were computed using the following models:

DOMI = a₁ x DWG + b₁ ± ε₁

MEI    = a₂ x DWG + b₂ ± ε₂

UFLI  = a3 x DWG + b₃ ± ε₃

By definition the maintenance energy requirement corresponds to energy requirement for zero BWG, the organism of animals being supposed to be close to steady-state.

Statistical analysis

The effect of experimental year on each variable (BW, organic matter digestibility, dOM, MODI, MEI, UFLI, and DWG) was tested using the following model:  

Y_ij = μ+ σ_i + e_ij

where Y_ij  is the dependent variable,  μ the mean value, σ_i  the year effect, and e_ij  the residual error.

Models 1-4 were computed using S Plus Statistics (1978).

Results 

Chemical composition of diet

The mean crude protein and crude fibre contents of feeds were 89 ± 12 and 399 ± 3 g.kg DM^-1 for hay and 198 ± 1 and 52 ± 1 g.kg DM^-1 for the concentrate feed, respectively. The low CP content and the high CF content of the hay, agreed with the values usually obtained for vetch-oat hay harvested in Algeria. They can be explained both by late harvesting and a low percentage (15 to 30 %) of vetch in the forage.

Feeding value of rations

The proportion of concentrate in the diet ranged  from 18 to 39% and averaged 29.0 ± 4.6%. The CP content of feed DM averaged 13.5 % of DM. In addition, 45 % of CP intake was supplied by the concentrate feed. Diet CP and OM apparent digestibility did not vary significantly with year and averaged 0.543 ± 0.056 and 0.597 ± 0.043, respectively. However the inter-individual variability was high: OMD ranged from 0.501 to 0.681. The highest values were obtained with 20-22 % concentrate in the diet, suggesting that hay digestibility may have been reduced with the highest concentrate levels.

Feed DM intake ranged from 477 to 996g.d^-1  and averaged 623 ± 81 g.d^-1 , hay intake from 259 to 777 g.d^-1, an averaged 451 ± 59 g.d^-1  and concentrate intake from 219 g.d^-1 . Hay DM intake was slightly lower in year three probably because the weight of lambs was lower. Finally, DOMI, MEI, and UFLI ranged from 281 to 556 g.d^-1, from 1012 to 2002 kcal.d^-1, and from 0.36 to 0.71 UFL.d^-1. The average values are presented in Table 1.

Daily weight gain of lambs

Seven of the 60 lambs were discarded during the trial because of illness or very low feed intake (2, 3, and 2 in years 1, 2, and 3, respectively). At the end of the four months  experimental period, liveweight ranged from  19.1 to 33.1 Kg. The average liveweight was 25.3 ± 3.4 Kg (table 1). Mean DWG ranged from 64 to 144g (Figure 1) and averaged 97 ± 19g.  

It was significantly higher during the first than during the two following years (P<0.01; Table 1).

Growth and maintenance energy requirements of lambs

The regression analyses showed that DOMI (g. kg BW^{- 0.75}.d^-1), MEI (kcal.kg BW^-0.75.d^-1) and UFLI (BW^-0.75 .d^-1) were closely correlated to DWG (g.d^-1) (P<0.01).The estimated mean maintenance (DWG = 0) requirements were: 23 g DOM; 80 kcal ME and 0.029 UFL per kg BW ^0.75 (Table 2).

>From these data the energy requirements of 8-10 month old male lambs (20-35 kg) of the Ouled Djellal breed given similar diets could be estimated for DWG ranging from 50 to 150g.d^-1  (Table 3) using the following equations:

DOMI (g.d^-1) = 1.363 DWG (g) + 255.29 ± 23.39 ; p< 0.001  

s                        0.308                    22. 74

MEI(Kcal.d^-1 ) = 4.571  DWG ((g) + 904.81 ± 96.16 ; p< 0.001    

s                         1.11                          91.16

UFLI(.d^-1)= 0.0026 DWG (g) + 0.327 ± 0.030 ; p< 0.001  

 s                 0.00040                  0.0310

The partial energy cost of 100 g DWG (after deduction of maintenance energy requirement) in 20-35 kg male lambs of the Ouled Djellal breed averaged 460 kcal ME.

Discussion 

The present study was carried out over three years, and at different periods of the year.In addition, the type and chemical composition of the vetch-oat hay used, as well as the composition and the organic matter digestibility of the diet were similar to those usually observed in mediterranean areas (Haj-Ayed et al 2000, Larwence et al 1986).The CP content of the diet was high enough to sustain growth of the bacterial mass in the rumen (INRA 1989).

The maintenance energy requirement of the Ouled Djellal ruminant male lambs obtained in the present study (80 kcal.kg BW ^-0.75) was 16 % higher than the values (67 kcal ME or 0.024 UFL kgBW^{- 0.75}.d^-1 ) obtained in previous studies with 9-month-old Awassi lambs reared in Middle East countries (Al-Jassim 2002). However, they were about 19 % lower than the values obtained in European and American breeds: from 95 to 103 kcal ME or from 0.033 to 0.036 UFL.kg^-1 BW ^0.75.d^-1 (ARC 1988, INRA 1978, NRC 1985, NRC 2000).

The difference in maintenance ME requirement cannot be explained by differences in diet composition since the efficiency of ME utilization for maintenance and growth decreases when the diet CF content increases and diet digestibility decreases (INRA 1978).The diets offered to lambs of European or American breeds are much richer in concentrate and the hay more digestible than in Middle East countries. The lower maintenance ME requirement may partly result  from the likely lower physical activity of our experimental lambs penned individually, compared with group reared lambs.

As a matter of fact, maintenance energy expenditure of sheep vary with the genetic type and the nutritional history of animals (Freetly et al 2002), especially feed restriction. In the present study lambs were born and reared in a barn. However, their DWG from birth onwards was low (80-120g.d^-1  compared with a growth potential of 250 g.d^-1) probably due to poor nutritional conditions of ewes and lambs. Physiological and metabolic adaptations reducing energy expenditure take place in the organism as a result of chronic or experimental feed restriction: increase in body lipid reserves mobilisation, reduction in mass and metabolic rate of splanchnic organs, reductions in cell size and thyroid hormones secretion (Gomez et al 1999, Nozière et al 1999, Ortigues and Durand 1995), alteration of enzymatic systems regulation (Bocquier et al 2002). These phenomena, as well as differences in maturity may partly explain why the maintenance energy requirement of lambs of the Ouled Djellal and Awassi breeds reared in harsh rearing conditions are lower than those of European or American heavy meat or dairy breeds.

In other respects, the difference in maintenance energy requirement between lambs of the Ouled Djellal and Awassi breeds may partly result from differences in body composition (Webster 1978) because the metabolic rate of adipose tissues is much lower than that of muscular tissue (Graham et al 1974). Thus, in fat tail Awassi lambs (half of the animals had the tail cut at birth) who received the same amount of energy (500 kcal ME. d^-1), the undocked lambs had a higher body fat content (2189 vs 608 g) and a lower maintenance energy requirement (67 vs 85 kcal ME.kg BW ^0.75) than the docked lambs at nine months of age (Al Jassim 2002).

The total daily energy requirements of ruminant lambs of the Ouled Djellal breed have been assessed for DWG ranging from 50 to 150 g/d between 20 and 35 kg body weight. They cannot be predicted satisfactorily for higher DWG. The partial energy requirement for slow growth, as estimated after deduction of maintenance energy requirement from total energy requirement, was close to the values reported for slowly growing or small sized breeds: 460 vs 449 and 485 kcal ME per 100 g DWG, respectively (Antongiovanni 1994), INRA 1978). However, it was lower than the value (572 kcal ME) obtained in 9-month old Awassi undocked males lambs (El-Jassim 1996), probably because of the higher fat content of body weight gain in Awassi lambs.

Conclusions           

• The energy requirements of slowly growing Ouled Djellal ruminant male lambs have been assessed using the feeding trial method.

• The results have been obtained in 3 feeding trials during different periods of 3 following years.

• The energy requirements of the Ouled Djellal lambs for maintenance and slow growth were lower than those of lambs from European and American breeds.

• However, these results have to be improved and completed through further studies with diets enabling higher DWG.

Acknowledgments 

The authors are grateful to Dr M Vermorel (INRA, France) for his valuable advice, for revising and translating the text.

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Received 14 July 2008; Accepted 29 September 2008; Published 6 November 2008

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