The major objective of feeding amino acids to gilts during the prepubertal period is to support and balance the growth of gilts with reproductive maturity. Gilts in the prepubertal stage gain lean tissue rapidly. However, as gilts approach puberty, lean tissue gain starts decelerating whereas fat tissue gain starts accelerating. Due to the extensive genetic selection of pigs for a high leanness over the last decades, breeding pigs are also leaner than those in 1979 (MLC, 1979, 1999). As consequences of the selection for leanness, growth rate, feed efficiency and mature size have been improved, whereas voluntary feed intake has been reduced (Kanis, 1990; Smith et al., 1991). Genetically increased leanness appears to be unfavourable to reproductive performance through an association with delayed physiological maturity (Kirkwood and Aherne, 1985).
Gilts from five different genetic lines were used in efforts to affect the overall reproductive performance by changing the body composition of gilts through manipulation of dietary protein levels (Stalder et al., 2000). Feeding diets with different protein levels produced females with different lean and fat gains. The effects were inconsistent. For gilts from two genetic lines, dietary
© CAB International 2003. Amino Acids in Animal Nutrition, 2nd edition (ed. J.P.F. D'Mello)
modification influenced reproductive performance quantified as the number of pigs born and litter birth weight. However, these effects were not evident in gilts from three generic lines. This supports the conclusion that nutrition interacts with genotype as it affects reproductive performance of lean-type pigs.
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