Last update: November 30, 2010 01:50:28 PM E-mail Print

 

EVALUATION OF LARGE STOCK UNIT EQUIVALENTS FOR SHEEP

MJ Herselman

Grootfontein ADI, Private Bag X529, Middelburg, 5900

 


Introduction

The applicability of Large Stock Unit equivalents (LSU=s), as assigned  to different sheep breeds by the Conservation of Agricultural Resources Act (Act 43 of 1983) (Department of Agricultural Economics and Marketing, 1985), has for many years been  questioned in practice. This can possibly be attributed to the categorizing of sheep into Woolen, Mutton, Dual Purpose and Karakul sheep which does not reflect real differences in body weight. According to the aforementioned act, one set of body weights and thus one set of LSUs are associated with each category, but differences in body weight among breeds of the same category are not taken into account. For example, both Merino and Afrino sheep are classified into the woolen sheep category  (Meissner et al., 1983), hence the same LSU is used for both breeds. This does not recognize body weight differences of up to 20% in practice between these two breeds. According to Meissner et al. (1983), the classification of livestock for the realistic prediction of a biologically defined Large Stock Unit is based on the energy requirements of the animal. Accordingly, all aspects which influence energy requirements, such as body weight, production level and reproductive status, should be  reflected in LSUs. Energy requirements, on which current LSU=s for sheep are based, were calculated by a combination of the methods of the ARC (1965) and Hofmeyr (1972).The objective of this paper is to evaluate the applicability of prescribed LSU equivalents for different sheep breeds.

 

Material & Methods

The production and reproduction data of Merino, Afrino and Dorper sheep, which were kept for a four-and-a-half year period at two different localities, namely, Vlekpoort near Hofmeyr in the Eastern Cape and Carnarvon Experimental station in the Northern Cape, were used for this evaluation. At both localities, all three breeds were run as one flock (Snyman et al., 1991; Snyman et al., 2000). The energy requirements of the different breeds during different production stadia were calculated from the production and reproduction data (ARC, 1980). LSU=s were calculated by dividing energy requirements (MJ ME/day) by a factor of 75 MJ ME/day. The latter represents the daily ME requirement of a biologically defined Large Stock Unit (Meissner et al.,1983). For calculation of daily energy requirements, it was assumed that dry ewes gain 50 g/day in body weight; lactating ewes lose 100 g/day in body weight; metabolisability (q) of energy of the feed which sheep select in the veld is 0.41.

 

Results & Discussion

Body weight  of ewes at mating was 50, 65 an 66 kg respectively for Merino, Afrino and Dorper sheep, while 120 day weaning weight of lambs was 23.7, 32.2 and 33.4 kg for the respective breeds (Snyman et al., 2000). Pre-weaning growth rate was 196, 278 and 290 g/day for Merino, Afrino and Dorper lambs and post-weaning growth rate was 72, 89 and 88 g/day respectively. Body weight at one year of age was 41.3, 54.0 and 55.0 kg respectively. The production system which was followed in the trial, whereby all ewes were mated twice per year limited the use of fecundity values for the purpose of this evaluation and therefore fecundity values of 1.2, 1.4 and 1.4 were used for Merino, Afrino and Dorper sheep in the calculation of milk production, ME requirements and LSU=s of lactating ewes (ARC, 1980). Daily milk production, as calculated from fecundity and growth of lambs (ARC, 1980) was 1.368, 2.336 and 2.452 liter/day for Merino, Afrino and Dorper ewes respectively. The energy requirements and corresponding LSUs, calculated from the foregoing production figures are shown in Table 1.

 

Table 1  Daily energy requirements and LSUs of three sheep breeds calculated in this study

 

 Animal type 

MERINO

AFRINO

DORPER

MJ ME

LSU

MJ ME

LSU

MJ ME

LSU

Dry ewe

10.8

0.14

13.5

0.18

13.6

0.18

Pregnant ewe

11.8

0.16

14.2

0.19

14.3

0.19

Lactating ewe

14.8

0.20

25

0.33

26.1

0.35

Unweaned lamb

  3.4

0.05

  8.2

0.11

  8.9

0.12

Lamb 5 – 14 months

  9.1

0.12

12.7

0.17

12.9

0.17

 

According to Act 43 of 1983, no distinction is made for the different production stadia of the ewe and therefore, the LSUs shown in Table 1 is not directly comparable with those found in the act. In this regard, it is presumed that the increased energy requirement during lactation was assigned to the lambs. A value for ewes comparable to the prescribed LSUs was also calculated and is presented  in Table 2. This was obtained by combining the energy requirements for a dry ewe for 46 weeks and energy requirements during the last 6 weeks of pregnancy. The energy requirements for unweaned lambs in Table 1 is not in addition to that of the lactating ewe but reflects the increase in energy required by the ewe, expressed per lamb. In other words, the LSUs in Table 1 for lambs should not be used in conjunction with the LSUs for lactating ewes but rather together with the LSUs of a dry ewe. In Table 2, the prescribed  LSUs are compared with the calculated LSU of this study.

 

Table 2  LSUs of three sheep breeds as prescribed by Act 43 of 1983 and as calculated in this study

 

 Animal type 

 

MERINO

 

AFRINO

 

DORPER

 

Study

 

Act

 

Study

 

Act

 

Study

 

Act

 Unweaned lamb

0.05

0.05

0.11

0.05

0.12

0.08

 Weaned lamb

0.12

0.10

0.17

0.10

0.17

0.11

 Ewe

0.15

0.14

0.18

0.14

0.18

0.15

 Ram

0.19

0.19

0.23

0.19

0.23

0.23

 Number of ewes*

795

863

673

988

710

954

* Calculated for a  3200 ha farm with a carrying capacity of 16 ha/LSU

 

Calculated LSUs for unweaned Dorper and Afrino lambs were considerably higher than the prescribed values (Table 2). The relative low  LSUs prescribed by the act for unweaned Dorper and Afrino lambs are also not in accordance with energy requirements of lactating ewes (with milk production in access of two litre per day) which is approximately twice as high as that of dry ewes (ARC, 1980). The calculated LSUs for weaned lambs were also generally higher than the prescribed values  especially in the breeds with relative high weaning weights. The difference between calculated and prescribed LSUs for ewes can be explained by differences in body weight between the sheep of this study and those on which the LSUs of the act were based. The number of ewes in Table 2 was calculated with the simulation models of  Herselman et al. (1989). Using prescribed  LSUs,  the number of ewes which a farm of 200 LSU=s can carry, is generally overestimated, especially for Afrino and Dorper sheep. The relative difference in ewe numbers is of special importance when producers are considering changing from one breed to another. Farmers usually change from wool sheep farming to mutton production and according to current legislation, more mutton ewes can be carried on the same size of land than wooled sheep ewes. As this study contradicts the latter,  this  indicates that breed changes by farmers may in many cases be detrimental to the natural resource. Notwithstanding the higher calculated LSUs for Dorper sheep, more Dorper ewes can be kept than Afrino ewes (Table 2) because of the fact that Afrino lambs have to stay for a longer period on the farm than Dorper lambs to become marketable. The reason for this is that Dorper lambs grow faster than Afrino lambs and are normally slaughtered at a lower body weight due to fat accumulation.

 

Conclusion

The results of  this evaluation indicate towards certain shortcomings in current legislation regarding LSUs for sheep, which may impact  detrimentally on the utilization and conservation of the natural resource. The dangers associated with this justify a comprehensive survey of real differences in body weight and production among sheep breeds, whereby legislation can be revised. It is also concluded that the weight and production of sheep on a farm is of greater  importance for the determination of the LSUs than the breed.

 

References

Agricultural Research Council, 1965. The nutrient requirements of Farm Livestock. No. 2, Ruminants. London; HMSO.         

Agricultural Research Council, 1980. The nutrient requirements of Ruminant Livestock. Commonwealth Agricultural Bureaux, London.

Department of Agricultural Economics and Marketing, 1985. Conservation of Agricultural Resources Act, 1983 (Act 43 of 1983). Government Gazette No R 2687, 6 December, 1985.

Herselman, M.J. et al., 1989. Proceedings of the 28 th Congress of the SASAP, Ermelo, 11 - 13 April 1989.

Hofmeyr, H.S., 1972. Kwantifisering van faktore wat die brutodoeltreffendheid van energie-omsetting van voer by skape beïnvloed. D.Sc (Agric) verhandeling, Universiteit van Pretoria.

Meissner, H.H. et al., 1983. Classification of livestock for realistic prediction of substitution values in terms of a biologically defined Large Stock Unit. Technical Communication, Department of Agriculture, No. 175.

Snyman, M.A. et al., 2000. Grootfontein Agric. (Submitted)

Snyman, M.A. et al., 1991. Proceedings of the 30 th Congress of the SASAP, Port Elizabeth, 26 - 28 March 1991