Livestock Research for Rural Development 30 (11) 2018 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Growth, carcass and non-carcass characteristics of Central Highland and Boer x Central Highland goats under different levels of supplementation

Zeleke Tesema, Mekonnen Tilahun1, Liuel Yizengaw, Asres Zegeye, Asfaw Bisrat2 and Ayele Abebe2

Sirinka Agricultural Research Center, P O Box 74, Sirinka, Ethiopia
zeleke.t2007@gmail.com
1 Andasa Livestock Research Center, P O Box 27, Bahir Dar, Ethiopia
2 Debre Birhan Agricultural Research Center, P O Box 112, Debre Birhan, Ethiopia

Abstract

This study evaluated growth, carcass and non-carcass characteristics of Central Highland goats and their crosses with Boer goats fed different levels of concentrates on native pasture. Nine-month old intact male Central Highland (n=24) and Central Highland x Boer goats (n=24) with 18.20.35 kg and 23.70.97 kg initial weight respectively were used. The experiment was a 2 4 factorial arrangement (two breeds and four supplementation levels).The supplementation levels were: grazing/browsing only on native pasture as control, and grazing/browsing + 200, 400 or 600 g/day of concentrate.

Average daily gain for both genotypes increased with supplementation levels and the increment was greater for crossbred Boer goats, than for pure Central Highland goats. There was evidence of a genotype-nutrition interaction with local CH goats performing best on poor nutrition (grazing only) and Boer crosses being superior with highest level of supplementation. Carcass traits, except for total edible proportion as a percentage of slaughter weight and fat thickness, were higher for crossbred Boer goats than for Central Highland goats. Supplementation increased most of the carcass traits for both genotypes and increased more for crossbred Boer goats than for Central Highland goats.

Key words: feed conversion ratio, genotype-nutrition interaction


Introduction

Ethiopia has the largest livestock population in Africa with goats estimated to be about 29.7million (CSA 2016). Goats play tremendous roles by enhancing the livelihood of resource challenged farmers by enhancing their income from sale of live animals, skins, and manure and also creating alternative job opportunities. They also act as an income buffer to the risks associated with erratic climatic change apart from contributing to human nutrition in form of meat and milk.

Despite the huge number and their vital contribution, the productivity per unit of animal and the contribution of this sector to the national economy is relatively low. According to Ameha et al (2007), the annual meat production is estimated at 8–10 kg per sheep and goat slaughtered which is low. This might be due to different factors such as inadequate quantity, poor quality of the available feedstuffs and genetic potential of breeds (Mohammed et al 2012). In addition to the genetic potential, goat production is highly challenged by extreme fluctuations in feed quantity and quality. In many parts of Ethiopia, natural pasture is the major feed sources for livestock. However, availability and productivity of pasture are progressively declining because of increased cultivation area and overgrazing. Therefore, increasing the current level of productivity is essential to provide meat to the ever-increasing human population, to increase export earnings and household income thereby improving the living standard of smallholders.

Supplementation of grazing goats significantly increases feed intake and digestibility of feeds with a subsequent increase in growth rates and meat yield (Ben-Salem and Smith 2008; Kawas et al 2010). However, the exact levels of additional concentrates needs for grazing Central Highland and crossbred Boer goat have not been fully explored in goat production systems and need to be evaluated. Therefore, the objective of this study was to evaluate the growth and carcass characteristics of pure Central Highland and Boer-Central Highland crossbred goats fed different levels of concentrate.


Materials and methods

Description of the study area

The study was conducted from December 2016 to March 2017 at Sirinka Agricultural Research Center which is located 508 km away from Addis Abeba. The site is located at an altitude of 1850 m.a.s.l. The rainfall pattern is bimodal, with the two-rainfall seasons, belg (Feb./Mar.- April) and meher (July– Oct./Nov.); the mean annual rainfall is 950 mm. The area is a moderately warm temperature zone with mean daily temperature ranges 16 – 21oC.

Experimental animals and their management

Twenty four Central Highland goats with age of nine months, as estimated by dentition and information obtained from the owners, were purchased from the local market and twenty-four crossbred Boer goats with 50% blood level were selected from Sirinka and Ataye station. Totally 48 intact male goats, nine months old with a mean body weight of 18.2 kg for local and 23.7 kg for crossbreeds were used for this study. Experimental animals were quarantined for 21 days in isolated holding yard at Station and were treated for internal and external parasites and vaccinated against pasteurellosis, sheep and goat pox, and anthrax before the experiment. Following quarantine, the experimental animals were placed in an experimental house partitioned into individual pens (1.250.9 m) equipped with feeding trough and watering bucket. Animals were ear tagged and adapted to the experimental procedures and feed for 15 days before the commencement of the trial. The trial lasted for 105 days including adaptation period.

Experimental design and treatments

A 2 x 4 factorial treatment design was used to randomly allocate the 48 goats (24 pure Central Highland and 24 Central HighlandxBoer crossbreds, to the four supplementation levels. Animals in the control group stayed in the field during the day time while during the night they were sheltered in their individual pens. Animals in the supplemented groups were allowed 6 hour browsing/grazing and the rest of the times were in their individual feeding pens.

Measurements

The amount of feed offered and refused by each animal was recorded each morning using a sensitive balance with 1g precision. Representative samples of feeds were taken from feed offered and leftover from each animal, pooled per treatment and sub sampled for chemical analysis. The body weight was measured at the beginning of the experiment and at 15 day intervals during the experimental period. Body weight was measured after overnight feed withdrawal to account for differences in gut fill.

Slaughtering procedure and carcass trait measurements

After 90 day performance evaluation, 24goats (six goats from each treatment and 12 from each genotype) were randomly selected. Animals were fasted for 16 hours before slaughter but had access to water. Body weight was determined immediately before slaughter, followed by severing jugular veins and carotid arteries, skin removal, and decapitation at the atlanto-occipital joint. The esophagus was tied with nylon string to prevent contamination of carcass by the gut contents prior to skinning and the removal of the visceral organs from the carcass. The fore and hind legs were removed at the carpal and tarsal joints, respectively. Fasting loss was computed as the difference between final live weight at the farm and slaughter live weight. Hot carcass weights were measured right away after slaughter and removal of non-carcass components. The weights of non-carcass components were recorded. Carcasses were separated into five primal cuts: leg, loin, ribs, thin cut and foreleg+ shoulder+ neck. Gut fill was calculated as the difference between full and empty stomach and intestines. Empty body weight (EBW) excluded the gastro-intestinal tract contents. Dressing percentage (DP) was defined as the hot carcass weight expressed as a percentage of slaughter body weight (SBW). The total edible proportion (TEP) was the SBW minus the contents of gastro-intestinal tract, head, skin, feet and lungs, and trachea. All carcass measurements except fat thickness and rib-eye muscle area were measured on the hot carcass. Fat thickness and total tissue depths were measured at the 12th rib, 11 cm from the spinal cord on the left side of the carcass (Ponnampalam et al 2003). The rib- eye muscle area of each animal was determined by tracing the cross sectional area of the 12th and 13th ribs after cutting perpendicular to the back bone. The left and right eye muscle area was traced on a transparent water proof paper and the area was measured by using planimeter. The mean of the right and left cross section area was taken as the rib-eye muscle area.

Chemical analysis of feed

Feed samples were analyzed for DM by drying at 105 C for 24 hour, ash by ignition in a muffle furnace at 600 C for 6 hour, and CP by the Kjeldahl procedure (AOAC 2006). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined according to procedures of Decruyenaere et al (2009).

Table 1. Ingredients and chemical compositions of concentrate mix

Items

% as DM

Ingredients

Wheat bran

55.7

Noug cake

40

Limestone

3

Salt

1.3

Chemical composition, % of DM

Ash

8.98

OM

91.0

CP

30

Ether extract

5.6

NDF

12.3

ADF

8.86

ADL

2.34

DM dry matter, CP crude protein, OM organic matter, NDF neutral detergent fiber, ADF acid detergent fiber, ADL acid detergent lignin

Statistical analyses

The data were analyzed using the General Linear Model procedures of SAS (SAS 2002) according to a 2 x 4 factorial arrangement with breed and supplementation levels as main effects in a completely randomized design. Factors included in the model were genotype, supplementation levels, and genotype and supplementation levels and interactions in a factorial structure. Although initial weight was used as a covariate, it had no significant effect on parameters.

The model used was: Yijk = μ + Ti + Gj + T i Gj + eijk,

where Yijk is the dependent measured in the experimental unit “k”; μ is the population mean; Ti is the effect of supplementation levels “i”; Gj is the effect of genotype “j”; T i Gj is the interaction between effects of supplementation levels “i” and genotype “j”; and eijk is random error. Means were separated using the PDIFF option and declared significant if p<0.05.


Results and discussion

Feed intake and conversion ratio

Concentrate DM intake and its constituents were higher for Boer crossbred than for Central Highland goats (Table 2) and increased with supplementation levels for both genotypes. The higher concentrate DM intake of Boer crossbreds was in agreement with Asizua et al (2014) and Cameron et al (2001). Preston and Leng (1987) noted that in the absence of environmental and nutritional constraints, DM intake is determined by the genetic potential of the animal. This might have been the case for the supplemented goats in this experiment. However, relative to their body weight the intake of Central Highland goat was higher than that of crossbred goats. The efficiency of concentrate utilization among genotypes was similar. This result agrees with the report of Asizua et al (2014) for Mubende and Boer x Mubende goats.

Body weight and ADG

The study exhibited that the growth rate of grazing Central Highland goats and its crossbred with the Boer can be considerably improved through supplementation, with greater responses for the latter breed (Table 2).The results demonstrate a genotype*nutrition interaction with local CH goats performing best on poor nutrition (grazing only) and Boer crosses being superior with highest level of supplementation (Figure 1).

Figure 1. Live weight gain of CH and their crossbreds with Boer
goat under different levels of supplementation

This study demonstrated that performance benefits from Boer crossbreeding may only be realized with moderate to high nutritional plane. This result is consistent with other studies (Joemat et al 2004; Negesse et al 2007; Ngwa et al 2009) where reported performance has been greater for crossbreed Boer goats compared with other genotypes when diet quality was high, but was similar on diets with low to moderate quality. This result suggests that selection for improved goat performance should be done in conditions harsher than expected in the commercial production environment. Animals selected for increased growth rates in a good, nutrient-rich environment could lose fitness and experience performance problems when placed in a challenging, nutrient-restricted environment (James 2009; Wilson 2009).

Table 2. Effects of genotype and supplementation level on feed intake, growth rate and efficiency of concentrate utilization

Traits

CH

CH x Boer

SEM

p

0

200

400

600

0

200

400

600

G

F

G x F

Concentrate intake

DMI, kg/day

0

0.200e

0.385d

0.573b

0

0.198f

0.399c

0.599a

0.02

<.0001

<.0001

<.0001

%BW

0

0.78d

1.47c

2.14a

0

0.65d

1.29c

1.76b

0.09

0.0005

<.0001

0.214

%BW 0.75

0

1.76d

3.32c

4.87a

0

1.52d

3.04c

4.25b

0.20

0.0008

<.0001

0.2678

CP, g/day

0

55.0e

106d

157.8b

0

54.6f

110c

165a

7.35

<.0001

<.0001

<.0001

OM, g/day

0

182e

350d

522b

0

180f

364c

545a

24.3

<.0001

<.0001

<.0001

EE, g/day

0

11.2e

21.5d

32.1b

0

11.1f

22.4c

33.5a

1.49

<.0001

<.0001

<.0001

NDF, g/day

0

24.7e

47.8d

70.8b

0

24.5f

49.3c

73.9a

3.30

<.0001

<.0001

<.0001

ADF, g/day

0

17.7e

34.1d

50.8b

0

17.6f

35.4c

53.1a

2.37

<.0001

<.0001

<.0001

Weight gain  

Init. weight, kg

17.3b

18.7b

18.4b

18.5b

23.7a

23.9a

23.5a

23.7a

0.64

<.0001

0.956

0.969

Fin. weight, kg

19.8d

25.5c

26.5c

26.9bc

23.7c

31.1ab

31.9a

34.3a

0.81

<.0001

<.0001

0.795

TWG, kg

2.12c

6.80b

8.10b

8.40ab

0.06c

7.20b

8.46ab

10.5a

0.37

0.696

<.0001

0.089

ADG, g/day

23.5c

75.5b

90.0b

93.3ab

0.74c

80.0b

94.0ab

117a

4.18

0.696

<.0001

0.089

FCR, kg DM/kg gain

0

2.83c

4.86b

6.34a

0

2.57c

4.40b

5.20ab

0.27

0.100

<.0001

0.596

CHG central highland goat, SEM standared error of mean, G genotype, F supplementation levels. DMI concentrate dry matter intake, BW body weight, BW 0.75 metabolic weight, CP crude protein, OM organic matter, NDF neutral detergent fiber, ADF acid detergent fiber. TWG total weight gain, ADG average daily gain, FCR feed conversion ratio.
a b c d e f Means followed by different letters differ between treatments p < 0.05)

Carcass characteristics

Carcass traits except for total edible proportion as the percentage of slaughter weight and fat thickness were higher for crossbred Boer goats than for pure Central Highland goats (Table 3).The observed higher slaughter live weight, empty body weight and carcass weight of the Boer crossbreds were in agreement with results from other studies (Cameron et al 2001; Herold et al 2007; Asizua et al 2014; Mekonnen et al 2014). Carcass traits usually followed live weight differences between genotypes and were, therefore, higher in the crossbreds. Dressing percentage (DP) is both a yield and value determining factor and is, therefore, an important yardstick in assessing the performance of meat-producing animals (Yusuf et al 2014). Dressing percentage for Boer crossbreds was greater than for pure Central Highland goat. The value of DP (SBW) in this study was higher than the value 41.1% for Arsi Bale and their cross with Boer goat (Mohammed et al 2012) and the value for Central Highland (42.8%), 25% Boer crossbred (45.6%) and 50% Boer crossbred (44.4%) as reported by Mekonnen et al (2014). The overall mean carcass weight for crossbred Boer and pure CH goat (14 kg vs 10.8 kg) was higher than the result 9.23 kg for Boer x Arsi Bale goat and 6.23 kg for Arsi Bale goat as reported by Mohammed et al (2012). Carcass weight of crossbred Boer goat in this study was also higher than the report of Mekonnen et al (2014) which was 10.9 kg and 12.8 kg for 25% and 50% crossbred Boer goat respectively.

Carcass traits for crossbred Boer goat increased linearly as the supplementation level increased except fat thickness. Similarly, increased carcass weights resulting from different levels of concentrate supplementation have been reported by Hango et al (2007) in Small East African goats and Safari et al (2009) in the Small East African goats and their crossbreds with Norwegian goats. According to the report of Wolf et al (1980), larger rib-eye muscle area is associated with higher production of lean in the carcass and higher lean to bone ratio. The rib eye muscle area for crossbred Boer goats was higher than for pure Central highland goats and the values for both genotypes in this study were greater than the result 6.4 to 8.3 cm2 for Central Highland, Long-eared Somali and Afar goats with similar age (Ameha et al 2007).

Table 3. Effect of supplementation levels on carcass characteristics of CH and BoerxCH goats

CH

CH x Boer

SEM

p

0

200

400

600

0

200

400

600

G

F

GxF

PSBW, kg

19.3e

24.6cd

27.0cb

27.3cb

21.8ed

30.4b

31.9b

37.4a

1.22

<.0001

<.0001

0.1490

SBW, kg

18.1f

23.7cde

22.8de

25.5cd

20.9ef

27.7cb

30.1ab

34.2a

1.08

<.0001

<.0001

0.1592

Fasting loss, %

1.13

0.86

4.26

1.73

0.93

2.73

1.80

3.26

0.34

0.756

0.124

0.066

EBW, kg

16.7e

21.8cd

21.7cd

23.5c

18.8ed

25.4cb

27.6b

32.2a

1.03

<.0001

<.0001

0.096

HC, kg

8.33d

11.2c

11.6c

11.8c

9.63cd

13.9b

14.8b

17.6a

0.61

<.0001

<.0001

0.026

DP, SBW%

45.8d

47.5cd

50.8ab

46.2d

45.9d

50.1ab

49.1bc

51.7a

0.49

0.0019

<.0001

.0001

DP, EBW%

49.8b

51.6ab

53.4ab

50.2b

51.3ab

54.6a

53.5ab

54.9a

0.51

0.011

0.085

0.246

TEP, SBW%

59.0bc

60.5abc

61.6abc

61.7abc

58.6c

62.1abc

63.4ab

64.7a

0.57

0.145

0.027

0.671

REA, cm2

7.56c

9.26c

9.96c

11.6abc

10.7bc

11.5abc

14.2ab

15.1a

0.61

0.002

0.017

0.880

FT, mm

2.16

3.51

2.33

3.33

2.83

3.83

3.50

3.0

0.22

0.350

0.399

0.730

FQ, kg

5.03d

6.90c

7.10c

6.76c

5.83cd

8.56b

9.10b

11.0a

0.40

<.0001

<.0001

0.014

HQ, kg

3.55e

4.43de

4.56d

4.66cd

3.90de

5.46cb

5.73b

6.76a

0.22

<.0001

<.0001

0.053

CHG central highland goat, SEM standard error of mean, G genotype, F supplementation levels, PSBW pre slaughter body weight, SBW slaughter body weight, EBW empty body weight, HC hot carcass weight, DP dressing percentage, TEP total edible proportion, REA rib eye muscle area, FT fat thickness, FQ fore quarter, HQ hind quarter.
a b c d e f Means followed by different letters differ at p<0.05)

Carcass primal cuts

The increase in carcass weight as supplementation levels increased reflected an increase in the weight of primal cuts (thin cut, fore leg+ shoulder+ neck, ribs, loin and, leg) for crossbred Boer goats. The weight of primal cuts for crossbred Boer goat was higher than for pure Central Highland goat. Weight of primal cuts for crossbred Boer goat was increased with supplementation levels. However, the proportional yield as a percentage of EBW of the primal cuts was similar for both genotypes and all supplementation levels, except for the thin cut, which increased as supplementation increased and was higher for crossbred Boer goats (Table 4).

Table 4. Effect of feeding on carcass primal cuts of CH and CH x Boer goat

Carcass cuts

CH

CH x Boer

SEM

p

0

200

400

600

0

200

400

600

G

F

G xF

Cuts, kg

Thin cuts

0.33e

0.57d

0.48de

0.62cd

0.48de

0.75bc

0.82b

1.09a

0.04

<..0001

<..0001

0.065

FSN

3.08d

4.13cd

4.36cb

4.26cb

3.51cd

5.33ab

5.53a

6.23a

0.23

0.0002

0.0002

0.228

Rib

1.70e

2.20cd

2.48cb

2.31cd

1.90de

2.63bc

2.93b

3.63a

0.12

<..0001

<..0001

0.007

Loin

0.59e

0.77cde

0.78cde

0.90bcd

0.68de

0.96bc

1.08b

1.30a

0.04

0.0002

<..0001

0.214

Leg

2.86e

3.63cde

3.76bcd

3.73bcd

3.03de

4.33bc

4.50b

5.36a

0.17

0.0003

<..0001

0.056

PY(EBW), %

Thin cuts

1.99d

2.61bc

2.22cd

2.65bc

2.57bc

2.95ab

2.99ab

3.27a

0.09

<..0001

0.003

0.584

FSN

18.4

18.8

20.1

18.2

18.7

20.9

20.0

19.2

0.30

0.138

0.162

0.527

Rib

10.1

10.1

11.4

9.86

10.1

10.3

10.6

11.3

0.16

0.409

0.134

0.066

Loin

3.55

3.53

3.63

3.84

3.60

3.80

3.90

4.03

0.08

0.155

0.276

0.932

Leg

17.1

16.6

17.3

15.8

16.0

17.0

16.3

16.6

0.16

0.461

0.660

0.174

CH Central highland goat, G genotype, F supplementation levels, FSN fore leg + shoulder + neck, PY proportional yield.
a b c d e f Means followed by different letters differ between treatments at p<0.05)

Non-carcass characteristics

Meat dishes made from non-carcass components such as liver, kidney, intestines, tongue and others are commonly available in most parts of Ethiopia (Ewunetu et al 1998). Non-carcass components such as; testicle, spleen, heart, mesenteric fat, empty intestine and empty stomach did not vary among genotypes (Table 5). Kidney fat for Central Highland goat was higher for crossbred Boer goats. Kidney, liver, lung and trachea, skin, head, and leg with feet were greater for crossbred Boer goat than for Central Highland goat. Supplementation improved skin, liver, spleen, empty intestine and tail weight for both genotypes. For crossbred Boer goat head, carcass components such as head, skin, liver, spleen, lung and trachea and empty intestine weight increased linearly with supplementation levels (Table 5). However, there was no improvement among supplementation levels for non carcass components of pure Central Highland goats. Fat is nearly water free and high in energy density, this is enormous energy storage, with low slaughter value but very important as energy storage for the goat (Asizua et al 2014). Increase in internal and carcass fat in goats due to increased intake of energy in diets has been reported by various authors (Goetsch et al 2011; Zervas and Tsiplakou 2011). Similarly, in this study mesenteric fat for crossbred Boer goat was higher for supplemented than control (grazing only).

Table 5. Effect of supplementation levels on non-carcass traits of CH and CH x Boer goats

Traits

CH

CH x Boer

SEM

p

0

200

400

600

0

200

400

600

G

F

GxF

Head, kg

1.38e

1.46de

1.58de

1.50de

1.65cd

1.86bc

1.91b

2.23a

0.06

<.0001

0.003

0.042

Feet and leg, kg

0.75

0.87

0.87

0.85

0.83

0.98

0.91

1.13

0.03

0.023

0.073

0.378

Skin, kg

1.88d

2.50c

2.35cd

2.73bc

1.93d

2.78bc

3.10ab

3.53a

0.12

0.002

<.0001

0.144

Tail, kg

0.03c

0.05b

0.05b

0.04b

0.04bc

0.05ab

0.05b

0.07a

.002

0.014

0.004

0.192

Testicles, kg

0.18

0.18

0.22

0.23

0.18

0.26

0.22

0.26

.008

0.086

0.045

0.199

Digestive tract, kg

Empty stomach

0.81b

1.01ab

1.33a

1.10ab

0.83b

0.96ab

0.93b

1.16ab

0.04

0.273

0.047

0.206

Empty intestines

0.80c

1.15ab

1.12ab

1.11ab

0.88bc

1.10ab

1.13ab

1.30a

0.04

0.411

0.007

0.650

Pluck, kg

Liver

0.45d

0.57bcd

0.58bcd

0.66bc

0.53cd

0.68bc

0.73ab

0.87a

0.02

0.001

0.006

0.620

Lungs &trachea

0.34c

0.41c

0.36c

0.41c

0.36c

0.50b

0.54b

0.69a

0.02

<.0001

<.0001

0.001

Spleen

0.05d

0.08abc

0.06bcd

0.09ab

0.05cd

0.07bcd

0.08abc

0.11a

.004

0.220

0.001

0.377

Heart

0.12

0.15

0.16

0.16

0.14

0.16

0.18

0.19

.006

0.080

0.067

0.903

Kidney

0.07d

0.09bcd

0.09bc

0.09bcd

0.08cd

0.10ab

0.11a

0.12a

.003

<.0001

0.0008

0.278

Internal fat, kg

Kidney fat

0.02b

0.07a

0.03b

0.05ab

0.02b

0.04b

0.03b

0.03b

.004

0.043

0.015

0.441

Mesenteric fat

0.01d

0.17a

0.14ab

0.15ab

0.03cd

0.08bcd

0.10abc

0.14ab

0.01

0.096

0.0004

0.212

a b c d e f Means followed by different letters differ at p<0.05)


Conclusions


Acknowledgements

We would like to thank all the livestock research directorate staff of Sirinka Agricultural Research Center and Tesfaye Zewdie from Debre Birhan Agricultural Research Center. This work was financially supported by Ethiopian Institute of Agricultural Research and Amhara Regional Agricultural Research Institute so we thank these institutions.


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Received 12 August 2018; Accepted 16 October 2018; Published 1 November 2018

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