Forty-eight finishing gilts (initial BW = 70.6 +/- .95 kg) were randomly assigned to one of eight experimental treatments in a 2 x 2 x 2 factorial arrangement with main effects including dietary
lysine (.60 vs 1.00%), source of
amino acid fortification (intact
protein vs synthetic
amino acids formulated on an ideal
protein basis), and environmental temperature (thermoneutral [TN]: 20 degrees C vs hot, diurnal [HD]: 27.7 to 35 degrees C). The ideal
protein diets were formulated by using corn and soybean meal to meet the fifth-limiting
amino acid; synthetic
lysine,
threonine,
tryptophan,
methionine, or
isoleucine were added to meet the gilts' estimated requirements. The ratios of other total
amino acids relative to
lysine were as follows:
threonine, 66%;
tryptophan, 17%;
methionine and
cystine, 56%; and
isoleucine, 63%. Average daily gain, ADFI, and feed efficiency (G/F) were similar for gilts fed the intact and those fed the ideal
proteins diets (P > .10). Increasing dietary
lysine improved d 0 to 14 ADG (P < .01), but no differences were observed for the overall experiment. Gilts in the HD environment ate less feed and had lower ADG than gilts in the TN environment (P < .01). A temperature x
lysine interaction was observed (P < .02) for G/F. Increasing dietary
lysine had no effect on G/F of gilts in the TN environment but improved G/F of gilts in the HD environment. Gilts fed the intact
protein diets had higher (P < .01) N intake and plasma
urea concentrations. Gilts fed the ideal
protein diets had lower (P < .05) plasma
essential amino acids, with the exception of
lysine. Carcass
protein and
lipid contents were improved (P < .01) for gilts in the HD environment and for those fed 1.00%
lysine. Backfat thickness and longissimus muscle area (P < .01) were improved and
lipid accretion rate tended to decrease (P < .08) in gilts fed 1.00%
lysine. The source of
amino acid fortification did not influence carcass characteristics (P > .10). Rectal, skin, and ear temperatures were higher for gilts in the HD environment (P < .05). Metabolic heat production was elevated by feeding gilts the ideal
protein diets (P < .03). In conclusion, increased dietary
lysine improved G/F and carcass
leanness in gilts to a greater extent in HD than in TN environments. However, no improvements in growth performance or carcass traits resulted from feeding ideal
protein diets.