Livestock Research for Rural Development 19 (9) 2007 Guide for preparation of papers LRRD News

Citation of this paper

A study on growth performance and carcass characteristics of Small East African goats under different feeding regimes

A Hango, L A Mtenga, G C Kifaro, J Safari, D E Mushi and V R M Muhikambele

SokoineUniversityof Agriculture, Department of Animal Science and Production
 PO Box 3004. Morogoro, Tanzania
mtenga@suanet.ac.tz   ,   danielmushi@yahoo.com

Abstract

Thirty-two (10-16 months, 17.25 0.70 kg live weight) castrated male Small East African goats were used to determine growth performance and carcass characteristics under different levels of concentrate feeding. Eight goats were slaughtered at the beginning of the experiment (control, C0). The remaining 24 goats were randomly allocated to three (8 goats each) concentrate supplementation treatments namely 12 g, 18 g and 24 g DM per kg body weight per day (C34, C54 and C71, respectively). The concentrate consisted of hominy meal (77 %), cotton seed cake (21 %) and minerals (2 %) with average crude protein of 16 % and energy of 12.41MJ ME/kg DM. In addition to the supplement, all animals were fed a basal diet consisting of Chloris gayana hay ad libitum and water was available all the time. The experiment was carried out for 115 days after which, the animals were slaughtered for determining carcass characteristics. To facilitate the interpretation of the results, the treatments were assigned the descriptions of C34, C54 and C71, based on the actual proportions (%) of the diet consumed as concentrates.

Daily average dry matter intake was comparable (P>0.05) between treatments and was 630 g/ goat /day. Daily intake of CP and ME increased as the level of concentrate feeding increased. The differences in growth rates between C34 and C54 and C34 and C71 goats were significant (P<0.05) and were 15 and 21 g/day respectively. Dressing percentage, proportions of carcass muscle, fat and bone were not affected (P>0.05) by concentrate supplementation. Relative to the control goats, there was a significant (P<0.05) increase in the amount of carcass lean and fat. The relative increase in these tissues was significantly (P<0.05) affected by dietary treatments. Goats under C34, C54 and C71 had relative gains in carcass lean of 24.3, 37.3 and 45.6 %, respectively and fat of 200, 238 and 285 %, respectively.

It is concluded that the quantity and quality of the carcasses from goats currently sold in the local markets can be improved significantly through feed supplementation. However, there is a need to establish the appropriate age-at-entry to feedlot fattening to obtain good response and avoid the costly excessive fat deposition in the carcass. Further, the demand for such carcasses in different income groups and the economic viability of such feeding practices need to be worked out.

Key words: Carcass characteristics; feedlot; growth; Small East African goats


Introduction

In the tropics, meat is the most important product in raising goats. Goat meat accounts for about 30 % of meat consumed in Africa (Reed et al 1988) and most people prefer goat meat to other kinds of meat (Devendra and McLeroy 1982). This preference is due to attributes such as high tenderness and juiciness (Babiker et al 1985). In addition, there are no religious or traditional taboos against goat meat. Thus, this product is an important source of animal protein in rural areas. However, the productivity of indigenous goats in terms of meat yield is usually low. Apart from their low genetic potential, poor nutrition has been identified as a major factor that contributes to low production. In Tanzania, goats are usually raised and finished on natural pastures, and hence take a long time (over 2 years) to reach slaughter weight (25 kg) with daily growth rates of less than 21g/day and often produce low quality carcasses (Mtenga and Shoo 1990).

Modifying the traditional production systems may improve the eating quality of goat meat (Arsenos et al 2002). It is generally known that raising young animals on high concentrate diets result in higher daily gains, dressing percentage and carcass quality than on a forage system (Johnson and McGowan 1998; Johnson et al 2005; Kosum et al 2003; Warmington and Kirton 1990). Concentrate supplementation reduces age to slaughter, increases carcass quality and increases meat output thereby improving access to animal protein and income to households in the traditional sector (Mtenga and Kitalyi 1990). This suggests that finishing goats in Tanzania by supplementing them with available feed resources may contribute to improved household food security. The target should therefore be to produce an animal of particular weight and carcass quality for a shorter time. This study was therefore carried out to determine the growth performance and carcass characteristics of Small East African goats under different levels of concentrate feeding.
 

Materials and methods

Experimental site

The experiment was carried out at Research Farm (Magadu) of Sokoine University of Agriculture.

Experimental animals and management

Thirty-two castrated male Small East African goats of comparable size (10-16 months, 17.25 0.70 kg live weight) were purchased from a local market in Morogoro, Tanzania in March 2004. These animals were transported to the Research Farm for a feedlot experiment. Eight goats were slaughtered at the beginning of the experiment to represent animals normally slaughtered in the market where the experimental goats were obtained(control, C0). The remaining 24 goats were blocked by weight and assigned to one of three (C34, C54 and C71) treatments, 8 goats in each, in a randomized complete block design. Goatswere weighed weekly for determination of body weight changes.

Feeds and feeding

The concentrate feed was made up of a mixture of hominy meal (77 %), cotton seed cake (21 %) and mineral mix (2 %) and had a crude protein and energy contents of 16 % and 12.41 MJ ME/kg DM, respectively. Further, the contents of the Malick minerals as percentage of the total mineral mix were Ca (17.00), Mg (2.49), Na (12.76), Fe (0.35), Cl (19.74), I (0.031), Zn (0.23), Mn (0.15), Cu (0.20), Co (0.015), S (0.25) and P (8.5), based on specifications by the manufacturer (Welcome, Dar-es-Salaam, Tanzania).The C34, C54 and C71 goats received concentrate supplementation at 12 g, 18 g and 24 g DM per kg body weight per day, respectively. In addition to the supplement, the goats were fed a basal diet consisting of Chloris gayana hay (5 - 10 cm long) ad libitum and water was available all the time.

Goats were subjected to a 14 days adaptation period where they were kept in individual pens and fed ad libitum amount of Chlorisgayana hay (5 - 10 cm long) and 200 g of the concentrate per goat per day. The supplementation was carried out for a period of 115 days after which, the animals were slaughtered for determining carcass characteristics. Feed offered and refusals were weighed daily to enable calculation of daily feed intake.

Slaughter procedure and carcass evaluation

Goats were slaughtered as described by Ruvuna et al (1992). Carcasses were split into two halves longitudinally along the median plane of the vertebrae using a hand meat saw. These carcasses were then chilled at 4C for 24 hours. The left carcasses were jointed into seven joints (hind leg, chump, loin, rib, breast, neck and foreleg) as described by Mushi et al (2002). The joints were weighed and separated into dissectible muscle, bone and fat.

Feed evaluation

Feed samples (hay and concentrates) and refusals were oven dried to constant weight for determination of dry matter content. Chemical analyses of feeds were carried out in accordance with procedures of AOAC (1990) where as in vitro digestibility and fibre contents were determined using Tilley and Terry (1963) and Van Soest et al (1991) methods respectively. Metabolizable energy contents of feeds were estimated from the formula established by MAFF (1975), i.e. ME (MJ/kg DM) = 0.012 CP + 0.031 EE + 0.005 CF + 0.014 NFE, where CP, EE, CF and NFE are in g / kg DM.

Derived information

The difference in slaughter characteristics between C0 animals and those under different supplementation regimes (C34, C54 and C71) was used as a basis for evaluating relative changes in slaughter characteristics and carcass quality brought about by different amounts of concentrate offered to the goats. Hence the relative changes (%) were derived as: [(Wt kg of component in C34 or C54 or C71 - Wt kg of component in C0)/ Wt kg of component in C0] x100.

Data analysis

Data from feeding trials and slaughter characteristics were analyzed as a randomized complete block design using the GLM procedures of SAS (2000). Model statement included terms for treatments and block.
 

Results and discussion

Nutritive value of feeds used

Results on chemical composition of feeds used in the present experiment (Table 1) indicate that feeding Chloris gayana hay alone would not be adequate to support optimum goat production due to its low energy content.


Table 1.   Mean chemical composition (g/ kg DM), in vitro digestibility (%) and ME (MJ/kg DM) values of feeds used in the study

Component

Feeds

Hay

HM

CSC

Concentrate

DM

970

940

941

972

Ash

97.0

37.2

60.7

57.9

CP

90.3

102

371

160

EE

9.40

102

71.8

79.5

CF

420

75.6

347

201

NFE

384

683

149

501

NDF

480

496

643

575

ADF

422

89.3

308

118

IVDMD

52.0

59.2

48.2

71.9

IVOMD

53.2

60.2

50.0

72.1

ME

6.92

14.3

10.5

12.4

HM = hominy meal, CSC = cotton seed cake

Energy content in the concentrate feed used in this study was above the minimum recommended level of 5.7-7.3 MJ ME/day for diets of ruminants (Abate 1980). The nutritive value of the different dietary treatments used in this experiment compares favourably with the recommendation by Barkley (2004) and Flint (2005) that rations for intensive feeding of goats should contain 90 % dry matter, 30-35 % Neutral Detergent Fibre with a crude protein between 15 and 17 % and a metabolizable energy (ME) of 9-12 MJ ME/ kg DM.

Feed and nutrients intake

The substitution intake between hay and concentrate was observed in the present study (Table 2). Dry matter intake of hay decreased (P< 0.05) as the amount of concentrate dry matter on offer increased from 12 g (C34) to 24 g /kg body weight (C71).


Table 2.  Least square means and standard errors for feed intake (g/d), protein intake (g/d) and energy intake (MJ / d) by the goats

Parameter

Treatments

SEM( + )

SL

C34

C54

C71

DMI       Hay

414a

292b

188c

26.3

***

                Concentrate

217

347

451

 

 

                TDMI

631

639

639

29.9

NS

DMI, % BW

3.33

3.23

3.19

0.14

NS

CPI         Hay

37.4a

26.4b

17.0c

2.37

***

                Concentrate

34.6c

55.5b

72.1a

1.26

***

                Total CPI

72.0c

81.8b

89.1a

3.04

**

ME         Hay

2.87a

2.02b

1.30c

0.18

***

                Concentrate

2.69

4.31

5.60

 

 

                Total ME

5.56b

6.33a

6.90a

0.23

**

P:E ratio

13.0a

12.9b

12.9c

0.003

*

In this and subsequent tables; C34, C54 and C71 = concentrate supplementation at 12 g, 18 g and 24 g DM  per kg body weight per day respectively; DMI=dry matter intake; TDMI= total dry matter intake; W0.75 =metabolic body weight; CPI=Crude protein intake; ME=Metabolizable energy; BW= Body weight; P:E=Protein energy ratio. abcMeans with different superscripts within rows differ significantly;*, **, *** = Significantly different at 5 %, 1 % and 0.1 %, respectively. SEM=Standard error of the mean; SL=Significance level; NS=Not significant.

These findings compare favourably to those reported by Van Soest et al (1991) who observed that provided bulkiness is not a limiting factor, animals eat food mainly to satisfy their desire for energy. Thus in this study, total dry matter intake remained constant while the energy intake increased with increasing amount of concentrate. It is established that as concentrate: roughage ratio increases, the digestibility of roughage declines and hence its intake. The total daily dry matter intake of goats in this study was about 3 % of the body weight and this value is in agreement with the findings reported by Devendra and Burns (1983) and those reported by Mtenga and Kitalyi (1990) for Small East African goats. The observed daily energy intake of 5.56 to 6.90 MJ ME in this study is above the maintenance requirements of 3.25 - 6.47 MJ for goats (Devendra and McLeroy 1982). The crude protein intake of 7.9 - 9.4 g/kg W0.75 was also above the minimum requirements for maintenance of 4.15 g CP / W0.75 (NRC 1981). Although the availability of these nutrients to the animals depends on several factors, including their digestibility, the dietary treatments in the present study provided adequate nutrients to support maintenance and limited growth of 29.25 - 50.50 g/ d.

Growth performance

Growth rate increased (P<0.05) with increasing concentrate intake (Table 3).


Table 3. Least square means and standard errors for growth performance, body condition score and feed conversion ratio in goats

Parameter

Treatments

 SEM( + )

 SL

C34

C54

C71

Initial weight, kg

17.2

17.3

17.2

0.71

NS

Final weight, kg

20.6b

22.4a

23.1a

0.55

*

Weight change, kg

3.36 b

5.12a

5.81a

0.55

*

Daily gain, g/day

29.2b

44.5ab

50.5a

4.80

*

BCS

3.30b

3.50b

3.90a

0.12

**

FCR, g feed/g gain

42.9a

14.7 b

13.4b

9.49

*

FCR=Feed conversion ratio, BCS = body condition score

The differences in growth rates between C34 and C54 and C34 and C71 goats were 15 and 21 g/day, respectively. The growth rate of goats (29.2 g/d) at the lowest level of supplementation (C34) observed in this experiment is higher than the 19.6 - 25.1 g/d reported by Ayo (2002) but within the range of 19 - 32 g/d reported by Ntakwendela et al (2002) for similar Small East African goats supplemented with leguminous proteins. The disparity in growth rate between studies could be attributed to differences in the age of animals and in energy concentrations of the diets and the amount offered between the present and above cited studies. Goats in the present study were ready for marketing and as stated by Devendra and McLeroy (1982) even higher growth rates could have been obtained if younger goats under self-accelerating phase of growth were used in this study. Nonetheless, growth rates of goats in the present study, increased with increasing level of supplementation, a trend similar to other findings (Mtenga and Kitalyi 1990; Mtenga and Shoo 1990; Ayo 2002; Ntakwendela et al 2002; Morand-Fehr 2005). The superior growth performance observed in goats in treatments C54 and C71 can be attributed to both higher intake of energy and protein and hence feed utilization efficiency than those in C34 (Table 3).

Killing out characteristics

The empty (minus gut fill) gastrointestinal tract (GIT) weight for C54 and C71 goats were heavier (P<0.05) than for C34 goats (Table 4).


Table 4.  Least square means and standard errors on slaughter characteristics of goats   

Parameter

Treatments

 SEM( + )

 SL

C34

C54

C71

SW, kg

19.7b

21.3a

22.3a

0.51

**

Full GIT, kg

4.65

4.70

4.74

0.22

NS

Full GIT, %SW

23.6

22.1

21.2

0.75

NS

Gut fill, kg

2.89

2.66

2.65

0.20

NS

Gut fill, %SW

14.7

12.6

11.8

0.81

NS

Empty GIT, kg

1.77b

2.04a

2.09a

0.08

*

EBW, kg

16.8b

18.6a

19.6a

0.44

***

HCW, kg

9.09b

10.1a

10.8a

0.28

**

CCW, kg

8.84b

9.85a

10.5a

0.28

**

Chilling loss, %

2.75

2.66

2.66

0.30

NS

Dressing percent, %

 

 

 

 

 

HCW/SW

46.1

47.3

48.4

0.72

NS

HCW/EBW

54.1

54.1

54.9

0.72

NS

In this and subsequent tables, BCS=Body condition score; SW=Slaughter weight; GIT=Gastro intestinal tract; EBW=Empty body weight; HCW=Hot carcass weight; CCW=Chilled carcass weight

Fat free GIT is an early maturing tissue in goats and the possibility of changing its proportion relative to live weight through dietary manipulation is small (Mtenga 1979). Thus the observation in the present study could possibly be explained by higher fat content on the surface of GIT of goats under C54 and C71 than those on C34. Mtenga and Kitalyi (1983) reported that goats fed high concentrate diets tend to put on more fat on GIT and hence the tendency for this component to be heavier with increase in the amount of concentrate on offer. On the other hand, results in the present study are in disagreement with a report by Priolo et al (2005) that goats on high concentrate allowance have less developed digestive tract due to the less roughage intake compared to those on low concentrate intake. Higher roughage intake stimulates GIT development that support peristaltic movements involved in their digestion.

Similarly, carcass weight and dressing percentage increased (P<0.05) with increasing amount of concentrate on offer. This observation can be attributed to increased carcass fatness and muscle mass as a result of increased energy and protein intake. Results in the present study corroborate reports by Johnson and McGowan (1998) and Sen et al (2004) that higher energy feeds have positive effects on growth rate and rate and extent of fattening in goats.

The treatment effect was not significant when the weights of carcass lean, fat and bone were expressed as percentage of carcass weight (Table 5).


Table 5.  Least square means and standard errors for total weight of tissues in half carcass, their percentages and ratios

Variable

Treatments

SEM( + )

SL

C34

C54

C71

Total tissues in  1/ carcasses, kg

 

 

 

Lean

2.90b

3.20a

3.39a

0.10

**

Fat

0.69

0.78

0.89

0.06

NS

Bone

0.87

0.89

0.89

0.03

NS

Tissue as % 1/2 carcasses1

 

 

 

Lean

64.7

63.7

64.3

1.12

NS

Fat

15.5

15.6

16.6

1.03

NS

Bone

19.5

19.1

16.9

0.85

NS

Tissue ratios

 

 

 

 

 

Lean : Fat

4.28

4.30

4.06

0.37

NS

Lean : Bone

3.33

3.60

3.83

0.09

NS

Lean+Fat:Bone

4.13c

4.46b

4.83a

0.12

**

1 left sides of chilled carcasses

However, the absolute weight of carcass lean in C34 was lower (P< 0.05) than in C54 and this may reflect the differences in live weight and hence carcass weight at slaughter. The values of lean, fat and bone tissue shown in Table 5 are in agreement with values reported in earlier studies (Mtenga and Kitalyi 1990). In the present study, the carcass fat proportions were not significantly different between treatments and were 15.5 % for carcases in C34 and 16.6 % for carcasses in C71. It has been shown that Small East African goats have low fat content (6.7 %) in the carcass and with supplementation; this value can be increased to 14 % (Mtenga and Kitalyi 1990). This is an indication that although goats have been shown to deposit less carcass fat and more internal fat (Sen et al 2004), with concentrate supplementation, carcass fatness can be improved substantially. Overall, in the present study, edible meat yield (lean + fat) increased with increased concentrate allowance. These results suggest that both the quantity and quality of the carcasses from goats currently sold in the local markets can be improved significantly through feed supplementation.

Significant differences were observed in relative changes (relative to C0) in SW, EBW, HCW, CCW and total non-carcass components between treatments (Table 6). These components increased (P < 0.05) with levels of concentrate allowances.


Table 6.  Least square means and standard errors for relative changes (%) in slaughter characteristics and carcass components

Parameter, %

Relative changes

SEM ( + )

SL

C34

C54

C71

SW

20.3b

30.4a

36.3a

3.11

**

EBW

24.3b

38.2a

45.5a

3.27

***

HCW

30.2b

44.9a

54.4a

4.0

**

CCW

29.8b

44.6a

54.0a

4.1

**

Total non-carcass

18.7b

33.8a

40.4a

3.57

***

Total Tissues in carcass1

 

 

 

Lean

24.3b

37.3a

45.6a

4.08

**

Fat

200

237

285

27.6

***

Bone

2.16

4.25

4.77

3.48

NS

RTx = Relative changes in C34, C54 or C71;  1left sides of chilled carcasses.

The increase can be attributed to increased deposition of fat and muscle mass as energy and protein intake increased. The higher rate of growth of fat tissue compared to lean and bone observed in the present study support the phenomenon that fat is the most labile tissue (Berg and Butterfield 1976) that is highly affected by plane of nutrition (Bowman and Robinson 1983).


Conclusions

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Received 28 September 2006; Accepted 31 July 2007; Published 5 September 2007

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