**1. Introduction**

Sustainable livestock production is imperative on the African continent, to reduce poverty and ensure household food security. It is estimated that edible products from animal origin

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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account for more than 40% of the total value of South Africa's agricultural output [1]. Only 15% of South Africa is suitable for arable farming, and more than 40% of the remaining 85% receive less than 375 mm rain per annum [2], which explains the relatively low agricultural production potential of the Southern African region. The South African National Strategic Plan for Agriculture endorses the fact that there is very little room for horizontal expansion of agriculture, due to environmental constraints [1], so increased agricultural production can only be achieved by improving the efficiency of production [3] and exploiting vertical integration in regions with a moderate or higher agricultural potential [4, 5].

reason why traits such as mature weight, height and length, are included in selection criteria [13]. In the late seventies and eighties there was an international trend to select for larger cattle [17], resulting in a net increase in growth rate, but it had a negative impact on female fertility

Effect of Bioregion on the Size and Production Efficiency of Bonsmara Cattle in Semi-Arid Parts…

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The maintenance overhead is one of the most important factors that determine the biological efficiency of beef cattle, for example an adult cow require more than 50% of her total energy intake for maintenance [11]. Kleiber's theory, however, states that metabolic weight = (live weight)0.75 [19]. Larger cows therefore consume more nutrients than smaller cows but the percentage additional nutrient requirement of larger cows are less than its additional weight as a percentage. For example, a cow with mature size of 545 kg weighs 20% more than a 454 kg

The results of [21] suggest that when nutrient availability is limited, breeds with a moderate genetic potential for growth and milk production are generally more efficient because of higher conception rates. Similar results were reported in [10] in extensively managed Santa Gertrudis cattle in a semi-arid environment. At high levels of nutrient availability breeds with the highest genetic potentials for growth and milk production are most efficient because feed availability is sufficient for the genetic potentials to be expressed. Cow efficiency is thus maximized at a level of feed intake that do not limit reproduction and also provides sufficient energy for milk production to meet the growth potential of the breed as

The Bonsmara cattle breed and the concept of "breeding for functional efficiency" was coined by [8], and this concept is effectively employed by the Bonsmara Cattle Breeders Society of South Africa. The Bonsmara is now one of the predominant beef cattle breeds in Southern Africa (>100,000 registered animals; see [27]), and it was created based on a 5/8 Afrikaner and 3/8 Exotic (Shorthorn/Hereford) breeding admixture [8]. Considerable emphasis was placed on the adaptability of the breed. The functional efficiency concept is based on the presumption that selection for phenotypic traits that influence an animal's ability to adapt to the environment, will improve the animal's ability to express its reproductive and productive potential. It was also commonly presumed that specific types or sizes of cattle are better adapted to specific production regions than animals of a different size or type, but this concept was only

The natural variation in size of the same species of wild animals occurring in different locations is an indication that nature defines the "right" genetic material for efficiency in different ways in different environments [20]. The influence of production region on cattle production has been investigated by [23], and the notion of an optimal size for a specific environment was

The study by [22] which includes records of ca. 12,500 fully registered Bonsmara cows representative of a 20 year period, confirmed that bioregions (Central bushveld, Eastern Kalahari

cow, but its maintenance requirements are only 13% higher [20].

**3. Functional efficiency and cow size in semi-arid regions**

verified for beef cattle in Southern Africa in a recent study [22].

previously proposed by several other researchers [8, 11, 17, 20, 24].

traits [18].

expressed in the calf [21].

Long term improvement of the efficiency of animal production can only be achieved through the identification and selection of genetically superior animals for breeding purposes [3, 6]. Selection can be done based on a combination of pedigree information, appearance, and performance recorded information and breeding values [7]. Beef cow efficiency will be highest when cow size is tailored to the environment and the animals are well adapted [8–10]. Cow size has an important influence on the way the cow responds to its production environment [11] and the adaptability of the animal [8]. Adapted animals are tolerant to adverse environmental conditions and are able to maintain reproduction efficiency [6]. In order to improve beef cow efficiency in Southern Africa it is therefore important to optimize cow size, adaptability and employ effective management practices.

The adaptability of beef cattle in extensive production systems is critical and genetic gains in this regard can be best achieved by implementing some beef industry recommendations as listed in [12] namely:

