COMPARISON BETWEEN 3-METHYLHISTIDINE PRODUCTION AND PROTEINASE ACTIVITY AS MEASURES OF SKELETAL-MUSCLE BREAKDOWN IN PROTEIN-DEFICIENT GROWING BARROWS

This experiment was conducted to determine the relationship between S- methylhistidine (3MH) production and proteinase activity in skeletal m uscles of growing barrows, Barrows at 13 wk of age were randomly assig ned to either control diet available on an ad libitum basis (21% of ME consisted of protein; control group), control diet fed restricted (pa ir-fed with barrows in protein-free group; intake-restricted group), o r protein-free diet available on an ad libitum basis (protein-free gro up) for 14 d. During the last 3 d, blood samples were collected for de termination of 3MH production rate, which is a measure of myofibrillar protein breakdown. At slaughter, two muscles were taken: masseter (M) and longissimus (L) muscles. The muscle samples were analyzed for cal pastatin, p-calpain, m-calpain, multicatalytic proteinase (MCP), cathe psin B, cathepsins B+L, and cystatins activities. Both muscles were al so analyzed for amounts of DNA, RNA, total protein, and myofibrillar a nd sarcoplasmic proteins. Growth rate (kilograms/day) was influenced b y dietary treatments (P < .05). Fractional breakdown rate (FBR, percen tage/day) of skeletal muscle, as calculated from 3MH production rate ( micromoles . kilogram(-1). day(-1)), was 27% higher for the protein-fr ee group than for the control group. However, no differences in protei nase activities were observed, except for lower MCP activity in the M muscle of the protein-free group than in that of the other groups (P < .05). In the present study, no direct relation was observed between m yofibrillar protein degradation rate and proteinase activities in skel etal muscle during a protein-free feeding strategy.