Peer review

Twenty-four Yorkshire × Landrace gilts were used in an experiment to determine the lysine requirement for reproduction. L-lysine·HCl was added to a fortified corn diet to attain four lysine levels of .2, .3, .41 and .55% lysine (equal logarithmic spacing). The diets were fed at the rate of 1.82 kg daily before mating and during two reproductive cycles. During each 3-week lactation, all animals were fed the same 13% crude protein corn-soybean meal diet. Littersize and feed intake were standardized during both lactations. Nitrogen balance trials were conducted before mating and during each trimester of pregnancy. As dietary lysine increased, urinary nitrogen decreased and nitrogen retention increased linearly (P<.005). Beyond .41% dietary lysine, the urinary excretion decrease and the nitrogen retention increase were minimal. Similarly, plasma urea nitrogen decreased and plasma lysine increased (linear component was significant at P<.005) as dietary lysine levels increased with inflections in the response curves beyond the .3% lysine level. Lactation milk production, milk composition and nursing pig weights were affected by dietary lysine levels fed during pregnancy. Milk yield, milk solids and nitrogen composition were near maximum in those sows fed .41 % lysine. Pig weights were near maximum at .3% lysine. There were no differences in nitrogen retention among the treatments during day-15 to day-20 of lactation, but nitrogen retention less milk nitrogen was mínimal for the sows fed .41 % lysine. Considering all the parameters, it was concluded that .41 % lysine satisfied the requirements for reproduction. When lysine is supplied by corn and soybean meal in a swine diet, a level of .43% lysine (7.8 g/day) would allow for some undigested lysine and still meet the lysine requirement.

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