Partitioning nitrogen and amino acids for pregnancy and lactation in swine: a review.

Nitrogen and amino acid requirements for maintenance, maternal growth, mammary growth and products of conception were partitioned on the basis of data from numerous sources. These data were compared with N retention values obtained from balance trials conducted during pregnancy. Carefully conducted N balance trials will yield N retention data that are reasonably comparable with N deposition data determined from tissue analyses. Based on indispensable amino acid (IAA) requirements for maintenance and pregnancy, the IAA were partitioned among maintenance, maternal growth, and products of conception including mammary growth. The nonspecific N requirement also was estimated in these calculations. Results indicate that the pregnancy requirements for total N and nonspecific N could be reduced considerably from present recommendations (NRC, 1988). Nitrogen and IAA requirements for lactation were partitioned between maintenance and milk production. Estimates of total N and nonspecific N that were derived factorially also were substantially less than present recommendations (NRC, 1988).