Response of the muscles of growing pigs to dietary lysine levels

Abstract Two independent experiments were conducted to investigate the response of the muscles of two classes of pigs (10 kg and 23 kg liveweight) to varying levels of total lysine in diet. The two classes were given diets of 20 and 18 % crude protein based on yellow maize and ground‐nut cake supplemented with graded levels of L ‐lysine monohydrochloride. Total lysine level in the diets ranged between 0.52 and 1.42% for 10 kg pigs and 0.50 to 1.20 for the 23 kg pigs. Only bicep femoris, psoas major, longissimus dorsi and quadricep femoris were significantly (p < 0.05) influenced by total dietary lysine level. Both adductor and tricep brachii showed greater sensitivity to extreme deficiency of lysine in diet. At the end of the experimental periods, the muscles were over 100% above their initial weights at any dietary level except adductor and tricep brachii of pigs fed 0.50% total lysine in diet. While 1.02% total lysine in diet will promote optimum development of the muscles of 10–23 kg pigs, a lower amount of lysine in diet ranging between 0.7 and 0.9 % will be adequate for positive encouragement of the growth of the muscles of 23–62 kg pigs. The exponents of Huxley's allometry equation gave an estimation of the order of maturity of the ten muscles investigated in the two classes of pigs. In the 10–23 kg pigs, adductor grew fastest and gastrocnemius grew slowest relative to the total weight of the muscles. In the 23–62 kg pigs, bicep femoris grew fastest and psoas major slowest. The percentage of individual muscle gain which could be attributed to a different ‘sensitivity’ of most of the muscles to dietary lysine concentration in 10–23 kg and 23–62 kg ranged from 30 to 40% and 27 to 69% respectively. The data tend to suggest that gastrocnemius in 23–62 kg pigs was least influenced by the size of the muscles per se (R 2 =0.27) and was possibly the most ‘sensitive’ to dietary lysine concentration.