Nutritional strategies to optimize reproduction in pigs.

The relationships between nutrition and reproduction have been reviewed on many occasions (e.g. Cole, 1982; Hardy & Frape, 1982; Aherne & Kirkwood, 1985). The approach adopted in this paper is somewhat different in that while it examines, in broad terms, the influences which may be involved within the reproductive cycle and their role in long term strategies, it also seeks to move towards a particular strategy. The development of a nutritional strategy necessitates the clear identification of objectives followed by the use of sound scientific principles as a basis for realistic application. This may result in some aspect of the science or practice completely outweighing the other or it may result in a compromise between the two. For example, meat is virtually the total saleable product from pigs and considerable emphasis is placed on the production of the pig to slaughter weight. Consequently, no attention is given at this stage to treating the small pig as a potential breeding animal. It is fortuitous that the nutrition of meat pigs gives an adequate basis for future breeding and it is likely that reproduction will be optimized in the early stages (e.g. the gilt litter) by more attention being paid to the tactics to be adopted around puberty and first mating. However, strategies for sow nutrition imply attention to long term reproductive performance. Consequently, when examining the influences of nutrition at different stages of the reproductive cycle it is important to consider their effect on the whole breeding life-time. In this context, body condition and how it is influenced by the level and pattern of supply of energy and nutrients is generally considered of key importance. Relationships exist between the different phases of the reproductive cycle and their influence needs to be accommodated in developing an appropriate strategy.