Effect of dietary lysine level and environmental temperature during the finishing phase on the intramuscular fat content of pork

This study was designed to investigate the effects of dietary lysine level on the intramuscular fat content of the longissimus in finishing pigs reare d at two environmental temperatures. Seventy-two hybrid gilts were individu ally penned and given ad libitum access to either a diet formulated to meet their lysine requirement (6.4 g/kg lysine) or a lysine-deficient diet (4.8 g/kg). Rigs were held at one of two environmental temperatures (thermoneut ral [18 degrees C] or hot [32 degrees C]). The study was carried out betwee n approximately 90 and 126 kg live weight; pigs in the thermoneutral and ho t environments were on test for 5 and 7 wk, respectively. There were no int eractions between dietary lysine level and environmental temperature. Dieta ry lysine content did not influence feed intake or average daily gain; howe ver, pigs on the lysine-deficient diet had a poorer gain:feed ratio than th ose fed to requirement (P < .01). High environmental temperature decreased feed intake (P < .001) and average daily gain (P < .01) but improved gain:f eed ratio (P < .01). Backfat at the 10th rib was increased and loin eye are a and estimated percentage lean in the carcass were decreased for pigs on t he lysine-deficient diet. The higher environmental temperature resulted in an increase in carcass length but had no effect on other carcass measuremen ts or intramuscular fat. Feeding the lysine-deficient diet resulted in an i ncrease of .55 percentage unit in longissimus intramuscular fat content (P < .01); however, there was no difference in subjective marbling scores betw een the diets. Warner-Bratzler shear force values were not affected by diet ary lysine level or environmental temperature. Results from this study sugg est that feeding of lysine-deficient diets at the end of the finishing peri od can increase intramuscular fat deposition under thermoneutral and hot co nditions.