A cooperative research study involving 635 gilts was conducted at eight research stations to further estimate the
lysine requirement of finishing gilts. Dietary crude
protein levels of the five dietary treatments ranged from 16.0 to 24.4% with calculated
lysine levels of .80, .95, 1.10, 1.25, or 1.40%. Each station contributed a minimum of two replicate pens of pigs per treatment. Average initial and final weights were 53.6 and 116.4 kg, respectively. At the end of the experimental period, pigs were killed and hot carcass weight, 10th-rib fat depth, and longissimus muscle area were measured. Carcass fat-free lean percentage and fat-free lean gain were estimated from these data. Daily
lysine intakes averaged 21.8, 25.9, 30.5, 34.3, and 37.8 g/d for the five treatment groups, respectively. Increasing the dietary
lysine from .80 to .95% numerically increased
weight gain and gain:feed, but these increases were not maintained at higher levels of dietary
lysine. Overall, rate and efficiency of gain decreased (cubic, P < .01) with increasing dietary
lysine. Carcasses were leaner at the two higher levels of dietary
lysine as evidenced by reduced 10th rib backfat (linear, P < .01), increased longissimus area (quadratic, P < .04), and increased percentage of estimated fat-free lean (linear, P < .01). Carcass fat-free lean gain was not influenced by dietary
lysine except for a small numerical improvement (
P < .11) at the .95% level of dietary
lysine that paralleled the improvement in
body weight gain. The results indicate that the dietary
lysine requirement of finishing gilts with a mean carcass fat-free lean growth rate of 306 g/d from 54 to 116 kg
body weight is probably no higher than .80% of the diet to achieve maximum rate and efficiency of
body weight gain and carcass lean growth rate. The results also indicate that higher dietary
lysine levels may increase carcass
leanness in finishing gilts, possibly due to reduced intake of NE. Whether this response is due to the effects of
lysine alone,
protein (i.e., other
amino acids), or soybean meal is unknown.