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Metabolisable energy requirements for maintenance and growth of castrate Zimbabwean (Matabele) goats offered diets differing in roughage content either ad libitum or restricted

P.R. Hatendi1, L.R. Ndlovu2, T. Smith3 and A.N. Said4

1 Grasslands Research Station, P. Bag 3701, Marondera, Zimbabwe

2Department of Animal Science, University of Zimbabwe
P.O. Box MP 167, Mount Pleasant, Zimbabwe

3Matopos Research Station, P. Bag K5137, Bulawayo, Zimbabwe

4International Livestock Centre for Africa
P.O. Box 5689, Addis Ababa, Ethiopia


Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
Acknowledgements
References


Abstract

Feed intake and liveweight changes of 53 stall-fed Matabele goats were monitored for 94 days. They were offered diets containing 9.9, 11.3, 12.1 or 12.5 MJ metabolisable energy (ME) per kilogram dry matter, either ad libitum or restricted.

ME intake (MEi) was regressed against liveweight change and liveweight change was regressed against MEi. Calculated estimates of ME requirements for maintenance (MEm) and liveweight change (MEg) from the regression of MEi and liveweight change were 519 kJ/kg0.75 per day and 25.2 kJ/g, respectively. For the reversed regression, the estimates for MEm) and Meg) were 482 kJ/kg0.75 per day and 34.2 kJ/g, respectively.

Besoins en énergie métabolisable pour l'entretien et la croissance de caprins castrés du Zimbabwe (Matabele) recevant des rations à base de fourrage

Résumé

La consommation alimentaire et l'évolution pondérais de 53 caprins Matabele alimentés en chèvrerie ont été observées sur une période de 94 jours. Les rations, offertes à volonté ou rationnées, présentaient des teneurs de 9,9, 11,3, 12,1 et 12,5 MJ d'énergie métabolisable par kilo de matière sèche.

L'énergie métabolisable ingérée a été ramenée par régression à l'évolution pondérale, et vice versa. La valeur calculée de l'énergie métabolisable requise pour l'entretien et la croissance que l'on a obtenue à partir de la première régression était de 519 kJ/kg0.75 par jour pour l'entretien et de 25,2 kJ/g pour la croissance. En ce qui concerne la régression inverse, les valeurs calculées étaient respectivement de 482 kJ/kg0.75 par jour et de 34,2 kJ/g.

Introduction

Prediction of an animal's response to nutrients is central to the science and practical application of nutrition. Prediction implies extrapolation (AFRC, 1991), the inherent assumption being that the animals used in determining response are representative of the general population to which the results will be applied (Morton and Ridgeman, 1977).

There are few published reports on the energy requirements of goats. Recommendations used have often been extrapolated from sheep without validation (NRC, 1981; Prieto et al, 1990). It is notable that in those experiments where direct comparisons have been made between goats and sheep, maintenance energy (MEm) values differ. Mohammed and Owen (1980) reported MEm values for mature and castrate sheep and goats of 434 v 301 kJ ME/kg0.75 (P>0.01), respectively. Conversely, Alam et al (1991) reported MEm values of 440 v 370 kJ ME/kg0.75 (P>0.05) for growing, castrated kids and lambs, respectively. Such results underscore species differences and the need for efficient and effective diet formulation to generate information specific to goats.

This paper reports estimates of the metabolisable energy (ME) requirements for maintenance and growth of castrate, indigenous Zimbabwean (Matabele) goats fed cereal-based diets in confinement.

Materials and methods

64 castrate Matabele kids, initially about eight months old and weighing approximately 10 kg, were used in an experiment of 94 days duration. Animals were housed in wire mesh pens in an open-sided, asbestos-roofed, concrete-floored barn. No bedding was provided and accumulated manure was removed once a week. Each pen had separate feed and water troughs.

Table 1. Treatment die/formulation (g/kg) and dry-matter composition (g/kg DM).

 

Diet

1

2

3

4

Formulation

Veld hay*

500

330

220

100

Cottonseed meal

142

1.18

102

84

Maize meal

238

432

558

696

Molasses

80

80

80

80

Urea

20

20

20

20

Salt

7

7

7

7

Limestone flour

5

5

5

5

Gypsum

5

5

5

5

Vitamins and minerals**

3

3

3


Composition

Dry matter (g/kg)

902

903

902

905

Ash

106

71

63

54

Crude protein

200

187

194

182

Crude fibre

183

126

93

66

Ether extract

37

39

43

40

Metabolisable energy*** MJ/kg DM

37

39

43

40

* For general description of mixed veld hay see Topps and Oliver (1978).
** 1 kg = 3x106 i.u. retinol, 35 g manganese, 35 g zinc, 0.6 g cobalt, 0.1 g selection and 0.12 g iodine.
*** MAFF (1984).

At the beginning of the experimental period animals were allocated to one of four experimental diets (Table 1) offered either ad libitum (A) or restricted (R). Initial numbers and live weights of goats in the eight treatment groups are shown in Table 2.

Animals fed ad libitum were offered feed daily at a level of 20% above the preceding day's intake. For animals on the restricted feeding regimes, those in group R1 were offered air-dry feed daily at the rate of 6% of metabolic body weight. Goats in groups R2, R3 and R4 were offered their respective diets at a level iso-energetic to that offered to animals of the same weight in treatment R1. Feeding levels of animals on restricted diets were adjusted once a week. Daily ME intake was calculated by the difference between the ME content of feed offered and that of feed refused. Water was freely available to animals at all times. Animals were weighed at seven-day intervals and liveweight changes subsequently determined using polynomial regression analysis (Allen et al, 1983). Initial liveweight and linear regression coefficients of each animal were used to estimate live weight (LW) at the mid-point of discrete time periods. Metabolic weight (LW0.75) was derived from these estimates of LW.

Table 2. Initial numbers and live weights of goats in the eight treatment groups.

Feeding level

(Live weight (kg)

Diet

n

Mean

SE

Ad libitum (A)

1

10

10.2

0.54


2

6

10.3

0.64


3

6

10.1

0.83


4

10

10.1

0.45

Restricted (R)

1

10

10.1

0.59


2

6

10.5

0.73


3

6

9.9

0.80


4

10

10.2

0.54

Metabolisable energy requirements for maintenance and growth of the goats were estimated by regression analysis of the ME intake, growth and mean metabolic weight data.

Two equations were fitted; equation 1, as suggested by Abate (1989), and its converse, equation 2, as suggested by Zemmelink et al (1991):

Equation 1

ME intake (MEi) (MJ/kg0.75 per day) = a + (b*ADG)

where;

a = ME requirement for maintenance (MEm) (MJ/kg 75 per day),
b = ME requirement for growth (MEg) (MJ/kg)
ADG = average daily gain (g/kg0.75 per day)

Equation 2

ADG = a + (b*MEi)

where:

a = MEm = -ab-1
b = Meg = b-1

Animal performance data were analysed using the General Linear Model procedure of the SAS (1990) statistical package. Model variance was apportioned to:

Diet: 3 df, Contrast 1
Feeding Level: 1 df, Contrast 2
Diet* Level: 3 df
Error: (n-1)-7) df
Total: n-1 df

Least squares means are presented for relevant treatment comparisons. Standard errors were calculated using the error mean square as an estimate of residual variance. Where appropriate, means were contrasted as described in SAS (1990). Regression analysis was carried out using the SAS (1990) programme.

Results

Two animals on ad libitum feeding and nine animals on restricted feeding were removed from the experiment because of refusal to eat the diets or because they died. Final numbers in each treatment sub-group are shown in Table 3. Initial live weight of animals which completed the feeding trial in each treatment sub-group was different from that of the total number of animals initially allocated to their sub-groups (Tables 2 and 3). However, differences between treatment sub-groups were not significant (P>0.05).

Performance of the goats tended to improve with time (Table 3). Liveweight gains in this experiment had a high coefficient of variation (70%). Overall mean liveweight gains of feeding levels R and A were 5 and 47 g/day (P<0.001), respectively. Though energy intakes of animals on restricted feeding were similar (P>0.05), diets influenced liveweight gains (P>0.05), indicating differences in nutrient utilisation. Gross conversion of energy to liveweight gain (LWG) for feeding level A ranked A2>A3>A1>A4 (82, 92, 122 and 130 MJ ME/kg LWG, respectively) from days 68 to 94. The diet x level interactions were not significant (P>0.05) for all variables.

Coefficients of energy intake regressed on liveweight change (equation 1) and its converse (equation 2) for the period 33-68 days are shown in Tables 4 and 5, respectively. Derived estimates of MEm and MEg for this period are shown in Table 6. Estimates of MEm and MEg from the two estimation methods followed a similar trend between diets.

Table 3. Performance of goats offered diets differing in roughage content either restricted or ad libitum.

Table 4. Linear regression coefficients daily energy intake (MJ ME/kg0.75 per day) on liveweight change (g/kg0.75 per day) (Equation 1), for the period 33-68 days, of Matabele goats offered diets differing in roughage concentration.

Diet

df

a

sea

b

seb

Syx

r2

Significance

1

16

0.508

0.0169

0.225

0.00284

0.061

0.808

P<0.001

2

9

0.551

0.0299

0.0231

0.00494

0.090

0.732

P<0.0016

3

9

0.471

0.0388

0.0251

0.00464

0.074

0.785

P<0.0001

4

15

0.518

0.0328

0.0311

0.00433

0.097

0.7 87

P<0.0001

All

53

0.518

0.0144

0.0252

0.00207

0.085

0.744

P<0.0001

Syx = regression error mean square.

Table 5. Linear regression coefficients of liveweight change (g/kg0.75 per day) on daily energy intake (MJ ME/kg0.75 per day) (Equation 2), for the period 33-68 days, of Matabele goats offered diets differing in roughage concentration.

Diet

df

a

sea

b

seb

Syx

r2

Significance

1

16

-17.628

2.665

35.869

4.520

2.403

0.808

P<0.0001

2

9

-16.969

4.162

31.680

6.783

3.336

0.732

P<0.0016

3

9

-13.308

3.798

31.303

5.801

2.596

0.785

P<0.0001

4

15

-12.004

2.480

25.271

3.519

2.755

0.787

P<0.0001

All

53

-14.257

1.562

29.560

2.429

2.909

0.744

P<0.0001

Table 6. Estimates of metabolisable energy requirements for maintenance (MEm) (KJ ME/kg0.75 per day) and liveweight gain (MEg) (KJ/g) for the period 33-68 days, of castrate Matabele goats offered diets differing in roughage content.

Diet

MEm

Meg

Equation 1

Equation 2

Equation 1

Equation 2

1

508

481

22.5

27.9

2

551

536

23.1

31.9

3

471

425

25.1

31.9

4

518

475

31.1

39.6

All

519

482

25.2

34.2

Discussion

The differences in dry matter intake (DMI) and the similarity in energy intake among animals on restricted feeding are artifacts of the planned treatments. Differences in the rate of liveweight gain among these animals may indicate differences in absorption, partitioning and efficiency of utilisation of nutrients. Animal performance on the ad libitum feeding regime followed trends similar to those reported previously for mature castrates fed similar diets (Hatendi et al, 1992).

Treatments in this experiment resulted in a wide range of growth rates. The data set was thus amenable to estimation of energy requirements for maintenance (MEm) and liveweight gain (MEg) by regression analysis. MEm is defined here as the level of metabolisable energy required to maintain liveweight stasis. This definition is not synonymous with zero energy retention as found from calorimetric or comparative slaughter studies (Armstrong and Blaxter, 1984). Use of the MEm estimates based on liveweight stasis is arguably more relevant in the practical feeding of livestock for meat production, where liveweight changes can be measured with relative ease and accuracy.

This study compared two forms of regression, used interchangeably in literature (Zemmelink et al, 1991). The first regressed energy intake (y) on liveweight change (x) (equation 1). In the second, liveweight change (y) was regressed on energy intake (x) (equation 2). The question of which variable should be used as the dependent variable has been comprehensively discussed by Zemmelink et al (1991), who argue that liveweight gain is the observed response to energy intake and therefore should be considered the dependent variable. This approach is similar to that used in the ARC (1980) feeding standards and is central to the theories of animal response to nutrients as developed by AFRC (1991). Our acceptance of these arguments, and therefore equation 2, represents a change from our earlier publication on this subject (Hatendi et al, 1990), in which equation 1 was used to apportion energy utilisation.

The overall estimates of MEm in the period 33 to 68 days were 519 and 482 KJ ME/kg0.75 per day for equations 1 and 2 respectively. These results are consistent with estimates presented in the literature (Abate, 1989; Hatendi et al, 1990; Zemmelink et al, 1991; Sauvant et al, 1991). Similarly, the MEg estimates of 25.2 and 34.2 kJ/g liveweight gain for equations 1 and 2, respectively, are consistent with the findings of other workers (Abate, 1989; Hatendi et al, 1990; Zemmelink et al, 1991).

If the inverse of MEg is considered as an estimate of efficiency of energy use for liveweight gain (Abate, 1989), then the efficiency of gain decreased with increasing dietary energy content and duration of feeding. Efficiencies in this experiment are similar to those reported for kids by Alam et al (1991). Estimated feeding levels in this experiment, based on equation 2 estimates of MEm, were 1.03 and 1.49 times maintenance for the restricted and ad libitum feeding regimes, respectively.

Conclusion

The estimates of MEm and MEg presented in this paper are of direct application to confined castrate Matabele goats offered similar diets. However, they may be judiciously applied to related breeds of eastern and southern African goats under similar husbandry systems. Similarly, the increments for medium and high activity proposed by NRC (1981) serve as guidelines and may, as appropriate, be added when considering the energy requirements of goats in other systems such as free-range grazing.

Acknowledgements

We thank the officers and staff of Matopos Research Station, where this work was undertaken, for their assistance and encouragement. Thanks are also due to Mr J. Sherington and Ato Solomon Zewdie of the International Livestock Centre for Africa (ILCA) for biometrical assistance.

The senior author is grateful to the Rio Tinto Foundation (Zimbabwe) and ILCA for grants of postgraduate and research fellowships, respectively, to facilitate, in part, the conduct and write-up of this work.

References

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