Optimum dietary crude protein level for ®nishing Awassi lambs
S.G. Haddad
*, R.E. Nasr, M.M. Muwalla
Faculty of Agriculture, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan
Accepted 30 May 2000
Abstract
Awassi is a multi-purpose sheep breed. Awassi lambs being ®nished are usually offered an 18% crude protein (CP) diet. The growth rate of Awassi lambs is lower than other meat breeds. Therefore, this high content of dietary CP is questionable. The objective of this study was to estimate the optimum CP level for ®nishing Awassi lambs. Fifty male Awassi lambs (23:01:2 kg) were fed ®ve high concentrate isocaloric diets (10 lambs per diet) that contained 10, 12, 14, 16, and 18% CP in
a totally mixed diets for 9 weeks using a completely randomized design. Lambs were fed twice daily, and feed offered and feed refusals recorded for each feeding. Individual lamb intakes were calculated using daily feed offered and feed refused averaged over the interval of the experiment. Digestibility estimates were measured by total fecal collection. Lambs fed diets that contained 10, 12, and 14% CP gained less weight than those fed the 16 and 18% CP diets (P<0:05). Dry matter and CP
intakes increased (P<0:05) with increasing levels of dietary CP. No difference (P>0:10) was observed in feed-to-gain ratio
between diets except for the diet that contained 10% CP (P<0:05) which had a lower ratio. Organic matter and CP
digestibility were lowest in lambs fed the 10% CP diet. Results suggest that the optimum CP concentration is 16% and that any increase above this level will not result in any improvement in production.#2001 Elsevier Science B.V. All rights reserved.
Keywords:Awassi sheep; Crude protein; Finishing diets
1. Introduction
Production ef®ciency of meat animals can be de®ned as the return of salable product per unit of feed input (Beermann et al., 1986). In the Middle East, 80% of the production cost of red meat from fattening Awassi lambs is attributed to feed cost (Harb and Habbab, 1989). Protein supplements are the most expensive. For example, soybean meal is 320% more costly than barley grains. Therefore, any improvement in feed ef®ciency would have a tremendous effect on production ef®ciency.
Very studies having for objective the determination of the optimum dietary crude protein (CP) level for fattening Awassi lambs have been published. Although, it is the common practice to offer lambs diets with 18% CP, Harb (1994) fed Awassi lambs six high concentrate diets that contained a range of 14.7± 19.9% dietary CP and obtained no signi®cant differ-ence in average daily gain and feed conversion ratio. For lambs fed on a high plane of nutrition from 15 to 40 kg body weight, maximum weight gain and nitro-gen retention occurred at about 17% dietary CP (Andrews and Orskov, 1970). However, the NRC (1985a) recommends 14.5% dietary CP for ®nishing early-weaned lambs fed for maximum growth. There-fore, the use of 18% dietary crude protein diets for ®nishing Awassi lambs is questionable.
*Corresponding author. Tel.:962-2-7095111 ext. 22220;
fax:962-2-7095123.
E-mail address: [email protected] (S.G. Haddad).
The Awassi breed is a multipurpose breed that is used for meat, milk, and wool production. The growth rate for Awassi lambs is consistently lower than that obtained with western breeds. Muwalla et al. (1994) fed Awassi lambs a 100% concentrate, ®nishing diet that contained 14.4% CP and obtained an average daily gain of 275 g per day. On the other hand, Beauchemin et al. (1995) fed Romanov lambs a 95% concentrate, ®nishing diet with a 14.6% CP and obtained an average daily gain of 368 g per day. This large difference in growth rates between breeds should be re¯ected on the nutrient requirements. The objective of this experiment was to determine the optimum dietary CP percentage for maximum growth and ef®-ciency of growing Awassi lambs.
2. Materials and methods
This experiment was conducted in March, 1998 at the Agriculture Center for Research and Production at Jordan University of Science and Technology located in the northern part of Jordan at 328300
N and an altitude of 850 m. Fifty male Awassi lambs were weaned at the age of 70 days and were then adapted to high concentrate diets for another 40 days. The adaptation period consisted of a 65:35 forage to con-centrate ratio for a 10-day period. This ratio was then gradually decreased until it reached the ratio of 12:88. During the adaptation period, lambs were fed at maintenance level. Lambs were then assigned ran-domly to ®ve diets that contained ®ve dietary CP levels (Table 1) in a completely randomized design. Crude protein percentages were optimally 10, 12, 14, 16, and 18% (DM basis) (Table 2). All diets were formulated to contain a 12:88 forage to concentrate ratio.
Barley grain is the major feed used for fattening lambs in Jordan. Therefore, it was used as the major feed in diets 2, 3, 4, and 5. In diets 1, corn grain substituted barley grain due to its lower CP (8.5%), because it was impossible to formulate a 10 CP diets with high amounts of barley grains. All diets were isocaloric. The metabolizable energy content of the diets was calculated using the NRC (1985a).
Lambs were housed in individual metabolism crates with constant illumination and unlimited access to water. Feed was offered as a total mixed diets and was
fed twice daily in amounts to insure 10% orts. A feed selection problem was noticed during the adaptation period prior to the beginning of the experiment. For-cing the lambs to eat the sorted feed solved this problem and was accomplished by not offering any other fresh feed until the feed buckets were empty.
Feed ingredients were sampled to insure proper mixing of the diets. On week 5 of the experiment, total fecal collection was carried out for 6 days, and a 10% representative sample was air dried for further analysis. Samples of individual ingredients, rations, orts, and feces were analyzed for CP by Kjeldahl (AOAC, 1990), dry matter by oven drying for 40 h at 968C, ash by combustion at 5508C for 5 h, acid detergent ®ber (ADF) by the procedure of Goering and Van Soest (1970), and neutral detergent ®ber (NDF) by the procedure of Van Soest et al. (1991). Animals were weighed weekly prior to the morning feeding. The experiment lasted 9 weeks.
Table 1
Formulation (% DM basis) of the experimental diets fed to Awassi lambs
Limestone 1.5 1.5 1.5 1.5 1.5
Vitamins and mineral mix
Table 2
Chemical composition of the experimental diets offered to Awassi lambs
Item (% of DM) CP level (%)
10 12 14 16 18
Dry matter 89.0 89.2 89.1 88.7 88.8 Organic matter 90.4 90.7 91.5 92.8 93.1
Ash 9.6 9.3 8.5 7.2 6.9
NDF 33.5 31.2 35.1 35.4 36.3
ADF 11.3 13.9 13.8 14.7 15.2
CP 10.1 12.0 14.1 16.0 18.0
MEa(Mcal kgÿ1) 2.56 2.54 2.54 2.55 2.56
aME; metabolizable energy. Calculated according to NRC
Data were subjected to ANOVA for a completely randomized design using the GLM procedures of SAS (1985). Differences among treatment means for sig-ni®cant dietary CP level effects were detected using the LSD procedure of SAS. Furthermore, the effect of dietary CP level on average daily gain (ADG) was tested by polynomial regression using orthogonal contrasts for equally spaced treatments (Steel et al., 1997) estimated by the GLM procedures of SAS (1985). Unless otherwise stated, signi®cance was declared atP<0:05.
3. Results
The experimental diets had a similar chemical composition with the exception of CP (Table 2). The lowest dietary CP diet (diet 1) was used as the negative control whereas the highest dietary CP diet (diet 5) was used as the positive control. All diets had similar DM (avg. 88.9%), OM (avg. 91.7%), NDF (avg. 34.3%), ADF (avg. 13.8%), and metabolizable energy (avg. 2.55 Mcal kgÿ1).
Treatment means of initial weights of lambs were similar (Table 3). However, the average ®nal weight was greatest (P<0:05) for the 16, and 18% CP diets
(avg. 40.3 kg) compared with the negative control (30.2 kg). The 12 and 14% CP diets had intermediate ®nal weights (avg. 35.4 kg). The average body weight of the lambs throughout the experiment is shown in Fig. 1. Lambs fed the 16% CP diet had higher average body weights throughout the entire experiment. The difference in ®nal weight is re¯ected in weight gain of the lambs during the experiment. The negative control (10% CP) had the lowest (P<0:05) overall weight
Table 3
Effect of dietary CP level on production responses, nutrient intakes, and digestibility in Awassi lambsa
Item CP level (%)
10 12 14 16 18 S.E.
No. of lambs 10 10 10 10 10
Initial weight (kg) 23.1 23.2 23.1 23.0 23.1 1.2
Final weight (kg) 30.2c 35.7b 35.0b 41.2a 39.5a 2.7
Weight gain (kg) 7.1c 13.2b 13.0b 16.6a 15.1a 2.3
ADG (gram per day) 148c 227b 223b 287a 259a,b 39
Feed: Gain 5.6a 4.5b 4.6b 4.4b 4.6b 0.8
DMI (gram per day) 833c 1029b 1040b 1230a 1178a 130
CPId(gram per day) 87c 128b 153b 188a 186a 29
MEIe(Mcal per day) 2.2c 2.7b 2.7b 3.1a 3.0a 0.1
Digestibility (%)
DM 69.5 70.1 70.3 72.4 72.1 1.2
OM 71.6b 72.3a,b 74.0a 74.5a 73.9a 0.9
CP 74.2b 77.1a 77.3a 76.2a 76.6a 1.1
NDF 48.5 47.0 45.5 45.8 46.8 3.1
ADF 45.1 44.3 46.1 45.2 44.6 2.8
a,b,cMeans within a row with different superscripts differ (P<0:05).
dCPI; crude protein intakes. Calculated after adjusting for orts crude protein. eMEI; metabolizable energy intake.
gain compared with the highest CP diets of 16 and 18% dietary CP. Lambs fed the 12 and 14% CP diets had a higher (P<0:05) weight gain compared with the negative control and lower than those fed the 16 and 18% dietary CP.
ADG was highest (P<0:05) in lambs fed the 16% dietary CP diet (Table 3). The 10% CP diet had the lowest (P<0:05) ADG. Lambs fed the 12 and 14% CP diets had intermediate ADG. A linear and quad-ratic response (P<0:10) of dietary CP on ADG was observed. Increasing the dietary CP levels results in an increase in ADG up to the 16% dietary CP level as observed in Fig. 2. The 18% dietary CP diet was not different than the ADG of 12, 14, or 16% CP (P>0:1; Table 3).
Dry matter intake (DMI) was greatest (P<0:05) for the 16 and 18% CP diets (avg. 1204 g per day), whereas the 12 and 14% dietary CP diets had a lower (P<0:05) DMI (avg. 1035 g per day). The 10% CP diet had the lowest (P<0:05) DMI (833 g per day). Similarly, lambs fed the 16 and 18% CP diets consumed more (P<0:05) protein and energy (avg. 187 g per day and 3.1 Mcal per day, respectively) compared with the 12 and 14% CP diets (avg. 140 g per day and 2.7 Mcal per day, respec-tively). The 10% CP diet had the lowest (P<0:05) CPI and MEI (87 g per day and 2.2 Mcal per day, respectively).
All diets had similar DM, NDF, and ADF digest-ibilities. However, OM and CP digestibility were higher lowest (P<0:05) for lambs fed the higher CP percentages compared with the negative control. Feed to gain ratio was highest (P<0:05) for the 10% dietary CP, whereas the rest of the diets had a similar ratio (Table 3).
4. Discussion
Barley grain is widely used as the predominant grain source for fattening Awassi lambs in the Middle East area. Therefore, it was used in diets 2, 3, 4, and 5. In diets 1 corn was substituted for barley to attain the desired CP percentages (10%). Harb and Habbab (1989) studied the effect of grain type (corn versus barley) on growth of Awassi lambs and concluded that no signi®cant effect of grain type was observed on growth rate or feed ef®ciency when feeding either source in proportions similar to their energy values found in the NRC (1985a). Hussein et al. (1991) compared the effect of feeding corn versus barley in high concentrate diets on total tract nutrient digest-ibility and observed that there was no difference in nutrient digestibility when soybean meal was used as the protein source of the experimental diets. There-fore, we feel that the use of high quantities of corn instead of barley in diet 1 had no effect on our production measures.
Several researchers have observed no effect of dietary CP content on OM and DMI (Beauchemin et al., 1995; Merchen et al., 1987). In contrast, Drouil-lard et al. (1991) observed a 7% increase in DMI when lambs were fed a 14.5% CP diet compared with an 8.9% CP diet. Fluharty and McClure (1997) also observed an increase in DMI when lambs were fed a high protein diet (18.9% CP) compared with a lower CP diet (14.5% CP). In our experiment, a continuous increase in DMI was observed as dietary CP content increased being highest (P<0:05) for the 16 and 18% CP diets (Table 3). The differences in the metaboliz-able energy content of the experimental diets were minimal (avg. 2.51 Mcal/kg). Therefore, lambs in diets 1, 2, and 3 were de®cient in protein. An increase in DMI and growth rate after protein supplementation is a good indicationthat protein was de®cient(NRC, 1985b). Organic matter and apparent CP digestibility were higher (P<0:05) for lambs fed diets that contained 12, 14, 16, and 18% CP compared with the 10% CP diet. The CP digestibility showed a similar response. These data are similar to the ®ndings of Manso et al. (1998) who observed an increase in OM and CP digestibility when lambs were fed two diets differing in their CP content (168 g per day versus 86 g per day). Bunting et al. (1987) and Sultan and Loerch (1992) obtained similar results.
The highest ADG was obtained with the 16 and 18% CP diets (Fig. 2; Table 3). Fluharty and McClure (1997) observed a 19% improvement in ADG for fattening lambs when fed an 18.0% CP diet compared with a 14.5% CP diet. The ADG of 287 g for Awassi lambs used in this experiment was higher than that obtained by Harb (1994), Faqih (1987), and Muwalla et al. (1994). We suggest that part of this difference may be due to the genetic potential of the lambs used in this experiment as well as some other management practices. The Awassi herd at Jordan University of Science and Technology had undergone a genetic improvement program based on lamb growth rate for the past 6 years. Other management practices include improved disease control, better growing facilities, and the general management of the lambs before weaning.
When calculating the CP percentage as a function of the grams protein required and DMI for lambs with moderate growth potential according to the NRC (1985a), the requirement drops from 16.7% in lambs weighing 20±30 kg to 14.7% in lambs weighing 30± 40 kg. However, in this experiment, weight gain of lambs fed the 16 and 18% remained higher throughout the experiment (Fig. 1). These results suggest that for Awassi lambs, a 16% CP diet is still needed even if lambs have reached approximately 30 kg body weight.
Awassi is a multipurpose sheep breed. Awassi lambs usually are considered to have a much slower growth rate compared with other breeds of sheep. However, data obtained in this experiment suggest that Awassi lambs are capable of rapid growth and may even attain growth rates that are comparable to other rapid growing western breeds.
5. Conclusion
The optimum dietary CP requirement for fattening Awassi lambs appeared to be 16% of the ration DM. This CP level must be maintained even if lamb weight reaches 30 kg. The growth rates and feed conversion ratios obtained in this experiment emphasized that although, the Awassi breed is a multipurpose breed, Awassi lambs have the potential for acceptable growth rates when they are managed properly and fed appro-priate amounts of dietary CP.
Acknowledgements
The authors would like to acknowledge the assis-tance of B. Obeidat, M. Abu-Ishmais, and H. Talafaha for their contribution in data collection and laboratory analyses. The assistance of the farm staff led by I. Tahat at the Center of Agriculture and Production at Jordan University of Science and Technology is greatly appreciated.
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