Recent report (Spore, 2007) showed that pork is the world most widely consumed meat making up about 40 per cent of the total meat consumed worldwide. The high pork consumption has been attributed to the high cost of beef and the fear of avian influenza for poultry (Spore, 2007). In Africa, however, it barely accounts for 10% of meat consumed. From 1990 to 2005, its production has risen from 500,000 to 800,600 tonnes, probably as a result of rapid urbanization which interestingly has boosted production (Spore, 2007). In Nigeria, FAO (2005) reported a 4 per cent increase in the annual growth rate for pig production from 1990 to 2000 and this was adjudged to be the highest among other livestock species.
These reports are an indication that swine production has the potential for bridging the protein deficiency gap in this country. This is because pigs are endowed with natural genetic potentials that support rapid growth and high reproductive performance. For instance, pigs have a rapid growth rate and demonstrate excellent capacity for reproduction being litter-bearing in nature (Holness, 2005). They are characterized also by the best efficiency of nutrient transformation into high quality animal protein (Spore, 2007). These attributes have not been completely harnessed in this country thus leading to the slow increase in the supply of pork.
The performance of the breeding herd is fundamental to the financial success of any pig enterprise. According to White (1996) and Whittemore (1998), pig production is often assessed based on the number of litters produced per sow per year, the number of piglets produced per litter, and the viability of those piglets. Also, the lifetime productivity of the female within the herd is taken into account. Thus, the young gilt represents the future of any pig enterprise and if not fed properly, is unlikely to achieve her reproductive potential of rearing 60 to 70 pigs over 6 to 7 parities (Scharlach, 1998). It is therefore necessary to provide gilts with adequate nutrition in order to maximize litter growth rate, and minimize empty sow-days thus increasing the size of subsequent litters. Good nutritional preparation of the gilt from selection to first farrowing is essential in achieving this goal. Soede et al. (2007) reported that good nutritional management of gilts makes them to be mature, well grown and in good body condition at service, resulting in better conception rate and litter numbers. They emphasized that far too many gilts are weaned in poor condition and do not conceive or have poor second litters leading to an inexcusable waste of breeding potential.
The types of feedstuff, environment, feeding system for pigs differ around the world, and the nature of these differences is reflected in the growth and reproductive efficiency of pigs around the world. Thus, there is variation within and between temperate and tropical breeds of pigs in age of puberty, maturity, gestation length, age and weight of pigs at weaning which are major determinants of performance (Dritz, 2004; Pluske, 2006). As a result, most pigs in the tropics hardly reach the live weight of those exposed to temperate feeding system. Therefore, it is necessary to categorize pigs in the tropics according to weight ranges obtainable in the zone.