Full Length Research Paper
ABSTRACT
An experiment arranged in 2×2 factorial was carried out to evaluate the effect of concentrate levels, targeted live weights, and their interaction on live and carcass performance of Afar lambs. Forty yearling lambs were divided into 5 groups; one group was slaughtered at the beginning of the experiment and the other groups were randomly assigned to four treatments. Significantly (P≤0.05) higher dry matter intake DMI (740.38 g) was noted for lambs assigned to a higher (500 g) concentrate supplemented groups than 688.03 g recorded for lower (300 g) concentrate supplemented categories. Lambs finished for 30 kg live weight took longer (P≤0.001) feeding days (180) than the group targeted 30 kg slaughter body weight, which lapsed 91 days. Animals allotted to 500 g concentrate feed supplementation showed higher (P≤ 0.001) DWG (112.6 g) and FCE (0.15) than 300 g supplemented groups. The effect of concentrate levels and targeted body weights were significant on the majority parameters measured. It could be concluded that 500 g concentrate feed supplement and 30 kg target slaughter weight (T3) is the best strategy to finish yearling Afar lambs in 70 days of feeding for improved performance and economic of feeding.
Key words: Afar sheep, carcass, concentrate, slaughter weight, Tef straw.
INTRODUCTION
Sheep is an important farm animal in Ethiopia mainly as a source of income and food, varying with the socio-economic class of the people. There are 29.33 million sheep population in the country (CSA, 2014). However, sheep production in Ethiopia is mainly characterized by low input, and getting the production under the animal’s genetic potential in terms of quantity and quality. Inadequate and poor quality feeds are among other constraints blamed to lower birth weight, weight gain, and slaughter weight of sheep and profitability of sheep farming in Ethiopia (Belete, 2009; Alemu, 2008).
The major available feed resources for sheep are crop residue, natural pasture grazing and hay, and industrial-by products which are either deficient in required nutrient or have lowest fibre that could not be enough for ruminant animals.
Tef is adapted to a large variety of environmental conditions and widely grown crop (Bereket et al., 2011). Tef straw is among crop residues available as feed resources for sheep production.
However, dietary energy and protein content of Tef straw is not enough even for maintenance requirement of the animal. Most of the time Tef straw contains CP lower than 7%, which is the minimum requirement to support optimal microbial activity in the rumen (McDonald et al., 2002). There is a need to improve nutrient availability from Tef straw to maximize production from the animals. Afar sheep is one of the potential breeds for meat production for which improving utilization of easily accessible feed resources is imperative.
Concentrate feed supplementation is the one of the ways used to improve nutrient availability of Tef straw. Supplementation can be used to improve low quality and quantity feed resources by providing ideal environment for rumen microbes in order to improve fermentation, digestion and absorption (Olfaz et al., 2005). Small scale sheep fattening activities are being undertaken by concentrate supplementation on low quality feeds in different parts of Ethiopia targeting mainly seasonal domestic meat consumption or for export market.
Sheep fattening practices can be used to improve carcass yield and producers’ income, and reduce the length of time needed to reach slaughter weight (Alemu, 2008). Moreover, according to McDonald et al. (2002), Olfaz et al. (2005) and Majdoub et al. (2013), nutritional levels are related to carcass yield, carcass quality and fat tissue development and composition. However, there is limited information on whether the growth and carcass characteristics of Afar sheep are differently influenced by concentrate feed level and body weight.
Therefore, it was worthwhile to evaluate growth performance and carcass characteristics of yearling Afar sheep finished at different target body weights and fed different concentrate levels supplementation on Tef straw basal diet.
The objectives of the study include evaluation of the growth performance, carcass characteristics and feed cost per unit gain of yearling afar sheep finished at 25 and 30 kg live weights and the determination of finishing duration and concentrate level supplementation for yearling afar sheep for the targeted market live weights.
MATERIALS AND METHODS
Description of the study area
The experiment was conducted at sheep research station of Debre Zeit Agricultural Research Centre, located at 45 km South East of Addis Ababa (08°44'N 38°,58'E; average altitude of 1900 m a.s.l), Ethiopia. The area is known for bimodal rainfall pattern with average annual rainfall of 845 mm and annual minimum and maximum temperature of 10 and 22°C, respectively. The area is characterized by mixed-crop livestock production system; with major crops grown include Tef (Eragrostis Tef), wheat, chick pea and lentil.
Experimental animals and diets
Forty yearling male Afar sheep were purchased from local market, ear tagged and de-wormed for parasite and vaccinated against sheep pox, Anthrax and Ovine pasteurellosis. Then, the animals were randomly assigned to 8 groups (block) of five animals based on their initial body weight, which was determined by two weighing average after overnight fasting at the end of the adaptation period of 15 days. The average initial body weight of experimental animals was 16.5 ± 0.26 kg (mean ± SD). One of the groups was slaughtered for initial carcass analysis and the others groups were kept and allotted to treatments in individual pens.
The concentrate feed was formulated from 39% wheat middling, 40% noug seed cake, 20% ground maize grain, and 1% common salt, on DM basis. The proportions of these concentrate feed ingredients were fixed based on practical preliminary observation to contain 22.7% CP, which resulted in better performance of sheep. Intact Tef straw was fed ad libitum to each animal, and also tap water was freely accessed.
Experimental treatments and design
Randomized complete block design (RCBD) with factorial arrangement of treatments was used to undertake feeding experiment. Four dietary treatments (two concentrate levels X slaughter weights) were arranged as: T1 = 300 g concentrate feed supplement and 25 kg target slaughter weight; T2 = 300 g concentrate feed supplement and 30 kg target slaughter weight; T3 = 500 g concentrate feed supplement and 25 kg target slaughter weight; T4 =500 g concentrate feed supplement and 30 kg target slaughter weight.
All animals were fed Tef straw ad libitum with 20% refusal and concentrate was given in equal quantity twice daily at 8 a.m. and 2 p.m according to plan.
Feed intake, live weight and feed conversion efficiency measurement
Once the feeding trial was commenced, data on feed offer and refusal were taken daily, the feed intake was calculated as the difference between feed offered and refused while live weight measurements were done at ten-day interval after overnight fasting, using a 100 kg movable weighing scale with a sensitivity of 0.5 kg. The average daily body weight gain was calculated as the difference between the initial and final live weight of the lambs divided by the number of experimental days. Feed conversion efficiency (FCE) of the lambs was determined as average daily body weight gain divided by average daily DM intake.
Carcass evaluation
When the animals reached about the target weight, feeding was stopped; animals were kept in fasting overnight then slaughtered for carcass evaluation. After slaughtering and flaying the skin the hot carcass weight and non-offal components were measured immediately. Hot carcass weight and non-offal components were measured immediately after slaughter. The carcass was chilled at 4°C for 24 h and weighed. It was then dissected, at median line into left and right half. The full reticulo-rumen was weighed using plastic buckets. The left carcass part of each animal was deboned using group of people and quantified as lean, fat and bone and multiplied by two to make whole carcass component.
Feed cost analysis
The feed cost per unit live weight gain was determined using the feed ingredients cost of each respective feed treatment divided by live body weight for each respective treatment.
Data analysis
Data were analysed using SAS software program SAS (2002). Mean comparison was done using Duncan's multiple range test and significant differences between the treatment groups were declared at P≤ 0.05.
The model fitted to calculate the different parameters were:
Where, Yij = Response variables, μ = Over all mean, ai = ith effect of concentrate level, bj = jth effect of targeted body weight, (ai * bj) k = kth effect of concentrate level and target slaughter weight interaction if it was significant in the model and eijk = Effect of the ijkth random error.
RESULTS AND DISCUSSION
Feed and nutrient intake
The main and interaction effects of concentrate feed levels (CFL) and targeted market live body weights (LBW) on the average daily feed dry matter intake (DMI) are presented in Table 1. Concentrate feed levels affected the straw, concentrate (P≤0.001) and DMI intake (P≤0.01).
The effect of CFL was significant (P≤0.001) on feeding days which were the days waited for to attain the targeted body weight. The straw DMI of lambs was higher for lower (300 g) CFL supplemented groups than the higher (500 g) ones. The higher straw intake of animals was to fulfill the nutrient requirement from more straw eating. Higher total DMI was recorded for lambs were assigned for higher CFL supplemented groups.
Similar study has been reported that higher concentrate supplementation increased total DM intake in yearling sheep (Dessie et al., 2010). Formerly Getahun (2014) reported total DMI 710.6 g for Afar yearling sheep fed Tef straw, and 300 g concentrate feed supplement was partially similar to the present 731.6 g DMI. Contrary to the present result, DMI was reduced as the proportion of concentrate increased in the ration (Papi et al., 2011). In the present study the higher DMI of sheep at higher concentrate supplemented group was due to the fact that the palatability of concentrate was higher than the straw.
The lambs supplemented with lower concentrate level took longer days (173) to attain the required weight. This may be due to the limited nutrient intake. Target slaughter weight had no effect (P> 0.05) on straw and total DMI. The live body weight effect was significant on concentrate feed level DMI (P≤0.01) and days (P≤0.001) to reach the target body weight. The lambs reached market weight of 30 kg live body weight in 180 days of feeding than the 25 kg target slaughter body weight groups, which was attained in 91 days.
The Interaction effect of CFL and body weights was not significant (P≥ 0.05) on straw and total DMI. Concentrate intake and number of feeding days were influenced (P≤0.001) by concentrate levels and body weights interaction.
Feed intake trend of experimental animals is shown in Figure 1. Lambs registered high feed intake during the first 40 days, thereby decreased for 10 days and then, increased up to the end of the feeding days; while this trend remained in the case of T2, and then increased inconsistently. Lambs fed on T3 showed higher feed intake during 50 days and thereafter increased inconsistently. However, the feed intake trend was similar in the case of T4 in first 50 days, but at lower rate thereafter.
The lowered feed intake rate for T1 in between could be due to environmental change, since the experiment started during dry season but terminated in wet season. The irregular feed intake trend of lambs in T2 also could be due to seasonal variability as the feeding experiment undertaken was in dry season and partly at the ending of rainy season. The lower feed intake trend at the end of experimental period in T3 and T4 could be because the animals got saturated energy density from high amount of concentrate feed.
Table 2 illustrates the main and interaction effects of concentrate level and target slaughter weights on energy, crude protein, calcium and phosphorous intake of yearling ram lambs. The CFL effect was significant (P≤0.001) on energy, crude protein (CP), calcium (Ca) and phosphorous (P) intake. Lambs that received 500 g concentrate level showed higher energy, CP and P intake. Calcium intake of experimental animals was lower for higher concentrate supplemented groups. Crude protein intake was higher (P≤0.05) in lambs slaughtered at 30 than at 25 kg live weight. Phosphorus intake was higher (P≤0.05) for higher slaughter weight categories as compared to the lower groups. There was no interaction effect (P≥ 0.05) on nutrient intake.
The higher energy, CP and P intake was due to higher amount of concentrate feed intake and higher concentration of these nutrients in the offered concentrate feeds. The higher Ca intake from lower concentrate feed supplemented groups was unjustifiable.
Live body weight change and feed conversion efficiency
The main and interaction effects of concentrate levels and target slaughter weights on body weight change and feed conversion efficiency (FCE) of yearling ram lambs is presented in Table 3. The initial, final and total body weight gains of the experimental animals were not statistically different (P≥ 0.05) between concentrate level groups. The main effect of concentrate level was significant (P≤ 0.001) on daily body weight gain and FCE. Animals allocated to 500 g supplemented group showed higher daily body weight gain and FCE than those in 300 g supplemented categories. This was because the experimental animals got higher amount of nutrients from more dry matter intake. In agreement with the present study, Eligy et al. (2014) reported higher body weight gain of sheep at higher level of concentrate supplement. The main target slaughter body weight effect was significant (P≤ 0.001) for final body weight, total body weight gain, daily body weight gain and FCE. The final body weight gain and total body weight gain of experimental animals were higher at 30 kg target slaughter body weight than the 25 kg ones. Daily body weight gain (DWG) and FCE was higher for 25 kg targeted groups than the 30 kg market body weight categories. The interaction effect was not significant (P≥ 0.05) on all body weight change parameters. Higher DWG and FCE recorded for lower body weight experimental animals could be because for the younger and smaller sized animals the body weight gain rate was higher.
The body weight trend of experimental animals is shown in Figure 2. Those lambs assigned to T1 group had no increasing body weight during the first forty days; then it increased at the end of feeding days with a little bite up and down trend. In T2 the feed intake trend did not increase during the first 20 days and then, from onwards it increased with higher rate until the end of the experimental days. Lambs supplemented 500 g concentrate feed and targeted for 25kg market live body weight (T3) showed increasing body weight with higher rate except a little bit slower rate at the end of experiment. The body weight change trend in T4 increased all the time with down rate between 70 and 90 days and highest rate after that up to the end. From this body weight change trend one could say that higher body weight gain rate can be achieved within short feeding time by supplementing with higher amount of concentrate feed for growing yearling lambs.
Carcass yield and non-carcass components
Carcass yield parameters as affected by concentrate levels and targeted body weights and their interaction are show in Table 4. The concentrate level main effect was not significant (P≥0.05) on all carcass yield parameters except for trimmings. In disagreement with the present study Melese et al. (2017) reported that sheep consuming high level of concentrate supplement had significantly heavier carcass weight than supplemented in the low level. There are no similar responses of sheep for concentrate levels in terms of carcass yield between the present and previous study. This could be due to breed and environmental variation, and the concentrate level difference was not big enough to show considerable carcass yield differences. The slaughter weight, hot and cold carcass weight, dressing percentage (DP), carcass lean, fat and bone varied (P≤ 0.001) between targeted body weights. The yearling Afar lambs finished for 30 kg target slaughter body weight showed higher slaughter body weight, DP, carcass weight, carcass lean, fat and bone weight. The proportion of carcass lean and bone was similar (P≥0.05) between the two targeted body weights whereas, the carcass fat proportion was higher (P≤ 0.05) for lambs targeted for 30 kg body weight than the 25 kg body weight targeted lambs and initially slaughtered animals. This could be related with experimental animals got higher dietary energy from higher concentrate feed and stayed for longer time in feedlot. In line with the present report Majdoub et al. (2013) stated that higher lamb slaughtered weight resulted in more carcass yields.
Interaction effect was not significant (P≥0.05) on all carcass yield parameters except for carcass bone weight and carcass lean proportion. The carcass bone weight was higher (P≤ 0.01) for the 300 g concentrate feed supplemented and 30 kg target slaughter body weight interaction groups (T2). The carcass lean proportion was smaller (P≤ 0.01) for the interaction of 500 g concentrate feed supplement and waited for 25 kg target body weight (T3). The heavier bone recorded for T2 could be related with stayed longer time in feedlot with lower concentrate feed developing heaver bone.
Non-carcass components of finished Afar sheep as affected by concentrate levels and targeted body weights and their interaction are shown in Table 5.
The concentrate level main effect was not significant (P≥0.05) on all non carcass components except on kidney fat and liver weights. Except spleen, heart and testicles weight non- carcass components were affected significantly (P≤ 0.001) by targeted body weights. Interaction effect was not significant (P≥0.05) almost on all non-carcass components. The higher carcass yield recorded from heaver lambs is expected and again it could be related with higher nutrient intake. Except proportion of carcass lean all carcass and non-carcass parameters were lower for lambs slaughtered initially than the experimental lambs slaughtered after feedlot.
Feed cost analysis
The analysis of cost in feedlot as affected by concentrate levels and targeted body weights and their interaction are shown in Table 6. The effect of concentrate levels and targeted body weights main (P≤0.001) and their interaction (P≤0.05) were significant on feed cost per kg body weight gain. The feed cost per kg body weight gain for 300 g concentrate supplement was higher than for 500 g concentrate supplemented groups. The 30 kg targeted market body weight was required high feed cost per body weight gain than the 25 kg ones. Total feed cost was higher for 300 g concentrate feed level and 30 kg body weight interaction groups (T2) than T1 and T4 followed by T3 interaction categories. Lambs in T3 showed less feed cost per unit body weight gain as compared with the other groups. This was due to highest weight gain of lambs at higher concentrate supplementation (T3) groups within short feeding time.
CONCLUSION
Concentrate level and target slaughter weight main effects were significant on BWG and FCE, but the interaction effect was not significant on body weight change. Animals allocated to 500 g supplemented group showed higher BWG and FCE than 300 g supplemented categories. It could be concluded that 500 g concentrate feed supplement and 25 kg slaughter body weight (T3) is the best strategy for finishing of Afar sheep yearling lambs in 70 feeding days for better average DWG, FCE, carcass yield and less feed cost per weight gain.
CONFLICT OF INTERESTS
The authors declare that they have no conflict of interest.
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