Effects of period of stay in feedlot on growth performance and carcass characteristics of Tanzanian long fat-tailed sheep

E J M Shirima, L A Mtenga*, A E Kimambo*, G H Laswai*, D M Mgheni*, A T Mkwanda** and T S Lemoringata***

Ministry of Livestock and Fisheries Development, P.O. Box 9152, Dar-es-Salaam, Tanzania
shirimamussa@yahoo.co.uk
* Department of Animal Science and Production, Sokoine University of Agriculture,
P.O. Box 3004, Morogoro, Tanzania
** Ministry of Home Affairs, P.O. Box 534, Mtwara, Tanzania
*** Community Research and Development Services, P.O. Box 50 Kibaya-Kiteto, Tanzania

Abstract

Seventy castrated sheep (wethers) of Tanzanian long fat-tailed strain (21.1 ± 0.6 kg initial   body weight, aged 12 months) were used to evaluate growth performance and carcass characteristics under different fattening period  in feedlot. The experiment lasted for 84 days and the animals were randomly allocated to seven treatments as 0 (D0), 14 (D14), 28 (D28), 42 (D42), 56 (D56), 70 (D70) and 84 (D84) days to stay in feedlot each with 10 animals per treatment in a completely randomized block design. Animals in D0 (control) were slaughtered immediately after being purchased from livestock keepers. The experimental units (D14, D28, D42, D56, D70 and D84) were provided with ad libitum iso-caloric and iso-nitrogenous diets containing molasses based diet (MBD) and forage hay of Cenchrus ciliaris spp.  Data were collected on feed intake, growth rates, slaughter and carcass weights and carcass composition.  

The total dry matter intake (DMI) increased by almost 31% more for 84 days (D84)  treatment as compared to intake observed in the 14 (D14)   days treatment. The highest average daily gains and lowest feed conversion ratio were observed at 42 (D42) days treatment. Hot carcass weight (HCW) increased  from 6.5 kg to 13.5 kg in control (D0) to 84 days treatment (D84), respectively which was almost 108% weight increment  which was also corresponding with an increase in energy intake from 4.6 MJ ME/day to 6.2MJ ME/day. Also, dressing percentage (DP) was highest at 56 (D56) days treatment (47.7%) followed by 42 (D42) days treatment (45.2%). The proportion of carcass joints (as % HCW) of neck, ribs, breast, loin, and chump increased while that of  hind leg and shoulder decreased proportionally with increasing days to stay in the feedlot. Similarly,  the pooled proportion of  lean tissue in the joints showed that hind leg and shoulder were much leaner  (64.4% and 60.6% respectively) and  less fat deposits (12.9% and 12.5% respectively). The present study revealed that   the most appropriate fattening treatment  for 12 months old Tanzanian long fat-tailed with  MBD  was  42 days (D42)   for highest  daily gain and dressing percentage.  Also, it can be concluded that yield of  non-carcass components and wholesale cuts  respond differently  to  fattening  periods however,   42 days period was almost optimal to most of the parameters used. 

Key words: Carcass yield, fattening, indigenous sheep, molasses, wethers

Introduction

In Tanzania, indigenous sheep are source of meat and income as other animals such as cattle, goats, pigs and poultry.  Ideally, the improvement of indigenous sheep for production of quantity and quality carcass has become a challenge nowadays, the main reason being the shortage of quantity and quality feeds associated with seasonal fluctuation throughout the year. The indigenous sheep are raised extensively from natural pasture and experience a long period of feed scarcity. Under this system, the animals spend a longer period of about 3 to 4 years to attain market weight of 25kg live weight (FAO 1999). The resultant small market weight leads into low productivity of both carcass (10-12 kg) and non-carcass components at slaughter.  

At the moment, there is no strategic feeding such as supplementation or feedloting for improving the animals’ performance. Various studies have shown that, growth and carcass quantity yield from indigenous sheep could increase if strategic feeding is practiced (Sundstǿl and Owen 1984).  On the other hand, the yield of carcass and non-carcass components (head, skin, tail, legs, gut fill,  gut fill, GIT empty, kidney, heart,  lung and omental fats is greatly affected by breed, sex, age to enter into feedlot, period of stay in feedlot as well as the type and amount of feed offered during fattening (Sheridan et al 2003).  

While feedlot is referring to as the intensive mechanism of finishing sheep prior to slaughter at a confined yard containing concentrated energy, protein and mineral diet, period of stay in the feedlot involves the number of days required to fatten the animal to the desired market weight and meat quality (Schoonmaker  et al 2002).  Despite the importance  of  feedlot  in meat  production,  feedlotting sheep is not practiced in Tanzania and where applicable in other countries, the information on the exact period of the animal to stay in the feedlot is scarce.  The period of stay or days to stay in the feedlot depend on the type and amount of feed and age of the animals used (Sheridan et al 2003). The type of feed to be used and the age to enter in feedlotting determines the length of stay in the feedlot (Vestergaard et al 2007). For instance, if the period of stay in feedlot is prolonged, production cost is high and the animal may put more fats with less lean to make it unacceptable.  On the other hand if the animal is kept in feedlot for too short time, the cost of production is low, but the carcass weight desired in the market might not be reached.  With these two scenarios, research data are needed on the most appropriate period of the sheep to stay in the feedlot. Little information has been published on other quantity determinants of sheep meat production and number of days for fattening using high energy based diets such as molasses. Also, research intervention on high energy source diets to ruminants such as molasses for rapid fermentable carbohydrates has received little attention especially in less developing countries (Preston and Leng 1987). Similarly, there is a lack of appropriate information on proper period of stay in feedlot for ruminants in particular to indigenous sheep for acceptable carcass yield and quality.  There is also a limited research data on  use of relatively cheap energy source diets, such as molasses for fattening sheep.  This warrants for a study to look on to the number of days required to finish emaciated indigenous sheep to the desired market weight for an acceptable carcass weight and quality. 

The objective of this study was therefore, to  determine the  effect of period of stay in the feedlot on growth and carcass characteristics in Tanzanian log fat-tailed wethers when fed molasses-based concentrate as fattening  diet.

Materials and methods

Study area description

The feedlot study was conducted at Pasture Research Centre (PRC)-Kongwa and Dodoma Modern Abattoir (DMA), both located in Dodoma region in central Tanzania (36^o30’E,  6^o20’S).   The DMA is located 7 km South West of Dodoma town municipality and 60km from PRC Kongwa.  The mean annual temperature ranged between 14 and 32^oC.  The study area is semi-arid with mean annual rainfall of 550 mm where 90% of the rain  falls between December and April usually with a dry spell in February.  

Experimental animals and feed management

Seventy (70) castrated indigenous sheep (wethers) of Tanzanian long fat-tailed sheep (indigenous) breed (21.1 ± 0.6 kg initial body weight, aged 12 months) were used in the experiment carried out over an 84 day after 14 days preliminary period between December 2010 and February 2011. Immediately after being purchased, the first batch of 10 wethers was randomly identified from the whole herd then considered as treatment 1 (control group of 0 days  (D₀). The control group was transported by truck to the DMA for slaughter.  The remaining 60 wethers were weighed, identified by metal ear tagging, dewormed and sprayed for internal and external  parasites. These  60 animals  were randomly allocated to six   treatment periods  as   D₁₄,  D₂₈, D₄₂, D₅₆, D₇₀ and  D₈₄  representing 14, 28, 42, 56, 70 and 84 days (period) to stay in feedlot respectively. Each treatment period composed of 10 animals allocated in a completely randomized block design.  The wethers were housed in a group of  2 animals per pen in raised wooden  floor pens  (1.5 m x 2.0m).

The basal diet was made from Cenchrus ciliaris  grass hay mixture as roughage. This was manually chopped to a maximum of  10 cm long using a knife. Molasses-based concentrate diet  (MBD) was formulated using molasses (66.3%), maize bran (15.5%), cotton seed cake (11.5%),  rice polishing (4.6%), urea (1.6%), mineral premix (0.4%) and lime (0.1%).  Both roughage and concentrate were formulated to provide 10.6 ME MJ/kg DM and 110 CP g/kg DM required for maximum growth and maintenance and production in growing sheep according to NRC (1985).

Feeding trial

The concentrate and hay were offered ad libitum allowing 10% refusal rate while clean water was given ad libitum throughout the experimental period. The daily feed offered and refused was recorded once every morning (08.00 hrs) before offering fresh feed and water. The individual sheep was considered as the experimental unit. Therefore, the amount of feed intake from each pen was divided by two to obtain an individual intake. The total dry matter feed intake (DMI) was estimated from the difference between feed offered and refused. The average daily intake (ADI) was obtained by dividing the total feed intake with the total days the animal stayed in the feedlot. The ADI was divided by two to obtain an individual animal ADI.

The energy and protein intakes for each individual animal were calculated on the basis of amount of feed (forage + concentrate) intake. The values of 8.79 ME MJ/kg DM and 106 g/kg DM were used to calculate the concentration of energy and protein respectively in the concentrate diet. Also, the  energy (2.86 ME MJ/kg DM) and protein (32.1 g/kg DM ) values were used to calculate the amount consumed in hay forage.

The samples of feed offered and refused were dried and ground through a 1mm sieve, thoroughly mixed and stored in a bottle for subsequent analysis.  About 10g sample of each feed sample was put in a special glass for complete analysis by Near Infrared Reflectance Spectroscopy (NIRS) machine at the Central Veterinary Laboratory, Temeke Dar-es-Salaam and represented in Table 1.  

Growth rate was measured by weighing animals weekly during the adaptation and experimental periods.  Initial body weight (IWT) was determined by the average live weight for the first three days consecutively of the experimental period.  At the end of each period of stay (14 days interval), 10 animals were randomly selected (from 5 pens each with 2 animals) and weighed for three days   consecutively to obtain average final slaughter weight (FSW). The average daily gain (ADG) for each respective group was obtained from the difference between the FSW and  IWT divided by the number of days in the feedlot. Similarly, the feed conversion ratio (FCR) was computed from the ratio of total DMI and total weight gain (kg DMI/kg weight gain).

Measurements at slaughter

At the end of each stay period, a batch of 10 animals for slaughter  was randomly selected, then transported by truck to Dodoma Modern Abattoir.  At the abattoir, the animals were kept at the lairage, then fasted for 16 h with free access to water and weighed again in the morning prior slaughter to obtain shrunk body weight (SBW). Slaughtering of the first batch of 10 animals was commenced at day zero (D0) followed by the second batch (D14) after 14 days from the starting the experimental period. This continued for the subsequent batches of 10 animals per slaughtered period at an interval of 2 weeks until the seventh batch (D84) at 84 days treatment. Animals were manually slaughtered at the abattoir by severing both the carotid arteries and jugular veins on both sides as well as trachea using a sharp knife without stunning. After slaughter and complete bleeding, the head was removed at the atlanto-occipital joints while fore and hind feet removed at the carpus-metacarpal and tarsus-metatarsal joints, respectively (Garcia-Valverde et al 2008). This was followed by manual skinning, evisceration and splitting.   

Measurements on carcasses

The dressed carcasses were weighed when hot within 1 h post-mortem to obtain hot carcass weight (HCW). The carcasses were then splitted along the vertebral column into right and left sides. The left side was weighed hot to obtain hot carcass weight (HCW) and after chill at 4oC (Cold carcass weight- CCW) for 24 and 48hr then stored in chilling room (at 4 oC) for subsequent measurements.  The non-carcass components (NCC) namely skin, head, feet, heart, lungs, trachea, liver, kidney and gastro-intestinal tract (GIT) were separated from the carcass then weighed. The GIT  was weighed while full (GIT full), then emptied and washed with running tap water and allowed to drip and re-weighed to obtain GIT empty. The difference between GIT full and GIT empty was considered as  stomach content (GIT fill).  Empty body weight (EBW) was calculated by deducting the weight of GIT fill from the FSW. Also, the dressing percentages (DP = CCW/EBW x 100) was calculated on cold carcass weight basis and expressed as a proportion of  EBW.   All kidney, pelvic and thoracic fats were removed and  weighed as part of NCC.

The left side of the carcass was then jointed into seven wholesale cuts according to AUS-MEAT (1998) namely neck, ribs, breast, loin, chump, hind leg and shoulder. The wholesale cuts  were weighed and expressed as a percentage of the weight of the left half of carcass. The values obtained were multiplied by two to reflect the whole carcass weight. Each wholesale cuts were further dissected into components of lean meat, fat and bone and trimmed of all external fat (sub-cutaneous fat), boned out and followed by removal of intermuscular fat (IMF).  The IMF included all fat lying between muscles and between muscles and bones. The total of fat trim and IMF in each wholesale cut was used as the estimate of dissectible fat. Similarly, lean from each cut was used to estimate of dissectible lean and bone from each cut boned out as the estimate of bone. All the dissectible losses or trimmings (non lean and fat) were also measured. The four components were weighed separately to determine their relative proportions within cuts.

Similarly, lean: fat ratio was obtained from proportions of the weight of  lean to fat while lean: bone ratio from the weights of lean to bone. The sum of lean meat and fat was considered as carcass edible component while non-carcass edibles were the sum of head, feet, heart, lungs, trachea, liver and kidney and GIT empty.

Statistical analysis

The data were analyzed using General Linear Model (GLM) procedure of SAS (2001), where initial body weight was used as covariate in the analysis of the FSW and ADG.  Least square means were reported with pooled standard error. The difference between treatment means was compared using probability of difference (PDIFF) of the General Linear Model (GLM) procedure of SAS (2001).

Result and discussion

Diet intake and growth performance

The effects of days in feedlot on dry matter intake (DMI) and growth performance are presented in Table 2.  The daily DMI increased by almost 31% at 84 days treatment (D₈₄) as compared to intake observed in 14 days treatment (D₁₄).   The higher DMI in sheep at the 70 days treatment (D₇₀) and 84 days treatment (D₈₄) which was significantly higher than that of D14 and D₂₈ could be explained by their greater live weight than that of the D₁₄ and D₂₈. This is because the food requirements of animals on similar diets are normally considered to be a function of live weight or metabolic body weight, as reported by AFRC (1990) and Mustafa et al (2008). As expected, the period of stay was coupled by increase of live body weight which also affected total  ME intakes  with an enhanced rumen degradable nitrogen supply from the diet for microbial protein synthesis (Safari et al 2010). The increase in MBD intake which means increased dietary protein intake might also have coupled with an increase rate and extent of fibre digestion in the rumen. Safari et al (2010) reported an increase of DMI and higher ADG in Red Maasai sheep fed urea treated straw (higher energy and protein levels) as compared to untreated straw (lower energy and protein level). Also, the intake (% BW) increased gradually from D₁₄ to D₄₂   treatments by 0.7 unit then decreased again up to D₈₄ treatment by 0.67 units.  It is observed from the current study that as the number of days to stay in the feedlot increased, the average daily gain (ADG) increased which was in line with the increase of the dietary energy and protein intake. The ADG increased gradually from D₁₄ treatment (85.7 g/day) to D₄₂ days treatment (129 g/day) which was the maximum  gain almost by 44 units more, followed by significant gradual decrease in weight gain after D₅₆  treatment (111 g/day) to  D₈₄ days treatment  (116 g/day) by  4.5 units. Similarly, the higher rate of gain at the beginning (D₁₄ to D₄₂ treatments)  could possibly be due to compensatory growth mechanism attained  at that feeding period followed by attainment of mature weight from D₅₆ treatment onwards. Atti and Ben-Salem (2007)  noted  the compensatory growth mechanism to be more pronounced in growing animals than in mature ones.  The  FCR was not affected by treatment.

Carcass  characteristics

The present  study provide detailed  evidence that prolonged days on feed increases the apparent mature size of the animals  and  hence increase weights of  FSW, HCW, EBW, DP  and NCC  (Table 3).  Moreover, the animals stayed in feedlot for 42 days treatment and onwards attained  more than 25kg  FSW  and 10kg HCW,   the weights demanded in the niche markets (MLDF, 2008).  The FSW  increased  by almost 68.7%   from  D₀ to  D₈₄  treatments with 18.1 to 30.4 kg respectively.  Similarly, the observed FWS from D₄₂, D₅₆, D₇₀ and D₈₄ (25.4 – 30.5 kg) are within the FSW of Tanzanian long fat-tailed sheep of 25-45 kg reported by Devendra and McLeroy (1982). This might be attributed to their greater body mass and age compared to the other treatment periods. The MBD used in this study was considered to be high energy and protein sources diet, which provided substantial fermentable carbohydrates and  allowed deposition of fat, or marbling in the animal muscles. This implies that, as the animal stays more in the feedlot, the amount of MBD intake increased, which can be attributed to increase of carcass fatness and muscle mass as a result of excessive glycogen reserve  in the muscles (Lee et al 2008).  The result in the present study support findings by   Adam et al  (2010), Johnnson and McGowan (1988) and Sen et al  (2004) who observed  higher energy feed to have positive effect on growth rate and excess fattening in sheep.  HCW increased  from 6.5 kg to 13.5 kg in D₀ to D₈₄ treatments respectively implied an almost 108% increase in weight as the days to stay in the feedlot increased. The significant changes in EBW mass could be explained by the corresponding significant changes in FSW, DMI and  gut fill. Gut fill is known to increase with feeding high roughage diets and here low level of dietary fibre  intake as per body weight could be implicated (Suliman and Babiker, 2007;  Yagoub and Babiker, 2008). DP  increased from  D₁₄  to  D₈₄ treatments and vary between 41% to  48% respectively, which is generally inline  with the values  (40-50%) reported for various tropical sheep breeds (Devendra and McLeroy 1982). The highest DP observed from 56 days treatment onwards was associated with higher dietary energy consumption,  slaughter weights, amount of fatness and differences in gut fills. Similar observations were reported by Yakan and Unal  (2010)  where DP improved when high dietary energy was provided to Bafra sheep breed in Turkey.

 Non-carcass components yield

The current study showed that the weight of head, hocks,  pluck, testicles,  tail and internal fats were positively increased with increase  of period of fattening (Table 4). The weights of skin and GIT, though increased with increasing days in feedlot did not differ between the periods of fattening. In general,  proportion of most of the NCC (as %  EBW and FSW )  declined with increasing period of fattening until 42^th and 56^th day treatment which was almost 2 months after commencement of  the fattening period.  At this period, the animals were considered as still growing (younger) when there was an early maturing of the NCC organs such as head and legs (Kamalzadeh et al  1998,  Lambe et al  2007).  This is because animals at younger ages tend to grow faster than the older animals given the same conditions (Mushi et al 2009b). From these observations, it can be hypothesized that the head matured earlier which is highly related to the development of brain and bones  whereas that of hocks is associated to development of bones (Kamalzadeh et al 1998,  Lambe et al 2007). Similar observations were made by Mushi et al (2009b) in 9.5 months old Small East African x Norwegian crossbred goats. Similarly,  the proportion of NCC to the FSW shows that the NCC contributed 39-42% of the FSW, the figures above to 31-35% in Red Maasai sheep as reported by Safari et al (2010) and above  34% from  Small East African goats  reported by Safari (2010) in Tanzania.  The observed difference might be due to species, breed and diet used. Also, the decrease of proportion of GIT empty to the  EBW with increasing period of stay in the present study indicated less fibrous feed and higher concentrate intakes by animals on longer  period of stay relative to higher body weight.  In this respect, wethers at 14, 28 and 42 days treatment consumed more dry matter  from roughages which was very much associated  with increased energy expenditure by the GIT and stimulated its pronounced  development.  These findings are in agreement with those reported by Diaz et al (2002) and  Caneque et al (2003) working with pasture and stall-fed lambs.

 Yield of wholesale cuts                      

Yield of wholesale cuts or prime carcass cuts  and  proportion of individual joint  in  HCW of wethers  are given  in Table 5.  The current observation revealed that, while  there was an increase in weight of  neck,  ribs, breast, loin and chump there was a decrease weight of hind leg and shoulder joints as the duration  to stay in the feedlot increased.   The overall percentage increase of weight of joints/cuts  as proportion of HCW  (from day 0 to 84^th day) was in the order of loin  (70.83%) > ribs (40.36%) > chump (29.55%) > breast (26.82%) > neck (10.25%) > hind leg (-9.77%) > shoulder (-11.32%). These results indicate that the proportion of different cuts increases or decreases relative to HCW depending among other things on the amount of fat deposited during time in the feedlot.

Carcass composition

Carcass composition showed  an increase of  pooled carcass tissues i.e. lean, fat and bone yields as the number of days in feedlot increased (Table 6).  Fat tissue yield was the highest by 3.8,  followed by lean  2.8 and bone by 1.1 units as the animals were kept from the feedlot  from D₀ to D₈₄ treatment. Generally,  animals in D₀ treatment were most leaner, followed by  D₁₄, D₂₈ and D₄₂ and had  less fat deposits in the joints than the rest of the groups in D₅₆, D₇₀ and D₈₄. This means, the proportion of  lean and  bone tissues decreased  while that of fat tissues increased with advanced period of stay in the feedlot. This is because at 56 days period onward, the growth rates  decreased but  allows more deposition of   fats in the joints (Abouheif et al 1991). Also, the proportion of  lean tissue in joints was the highest in  hind leg (64.4%)  and shoulder (60.6%) and least in breast (39%). Similar observations were reported by Abouheif et al (1991) in Merino wethers’ carcasses, Zali and Ganjkhanlou (2007) in Iranian fat-tailed lambs, Marinova et al (2001) in male kids of local Bulgarian White goat breed and Simela et al (2011) in South African indigenous goats.  

Conclusions and recommendations

• The present research work showed that growth, yields of  carcass and non-carcass components in  Tanzanian long fat-tailed sheep (wethers) respond differently to periods to stay in feedlot.

• With the increase in the fattening period, slaughter weight, carcass weight and non-carcass components weight  increased. However, the length of the fattening period had no influence on DMI per kg of live weight gain (FCR).

• Ad libitum feeding of molasses based  concentrate diet  to one year old wethers for  42 -56 days period in feedlot for better growth performances and carcass characteristics is desirable.

• Since there are various breeds of sheep and different diet sources in different localities,  specific  studies are needed to establish the exact period  and cost of fattening the animals to suit the demand available in their  niche markets..

Acknowledgements

The authors are grateful to the Permanent Secretary, Ministry of Livestock and Fisheries Development for financing this research through ASDP project.

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Received 24 November 2011; Accepted 23 January 2012; Published 7 February 2012

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