Whole-body valine and cysteine kinetics and tissue fractional protein synthesis rates in lambs fed Sulla (<I>Hedysarum coronarium</I>) and infected or not infected with adult <I>Trichostrongylus colubriformis</I>

Abstract

Poor growth during parasitic infection may be due to a redistribution of amino acids away from skeletal muscle protein synthesis to the intestinal site of infection. The effect of a Trichostrongylus colubriformis infection on whole-body amino acid kinetics and tissue fractional protein synthesis rates were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d). Lambs were dosed with 6000 L3 Trichostrongylus colubriformis larvae daily for 6 d (n 6) or kept as parasite-free controls (n 6). On day 45 post-infection, the lambs received an intravenous injection of 2H2O and infusions (8 h) of [35S]sulphate to measure the size of the whole-body water and sulphate pools, respectively. On day 48, the lambs were continuously infused for 8 h with [3,4-3H]valine into the jugular vein as well as with [1-13C]valine and [35S]cysteine into the abomasum. After the 8 h infusions, the lambs were killed and tissue samples collected from the duodenum, ileum, mesenteric lymph nodes, liver, spleen, thymus, muscle and skin. Feed intake (769 v. 689 (sd 47) g DM/d) was not affected by infection, whereas liveweight gains (50 v. -50 (sd 70) g/d) were lower and intestinal worm burdens (240 v. 18,000 (sd 7000) worms) higher in the infected lambs. Parasitic infection increased the fractional protein synthesis rates in the small intestine, mesenteric lymph nodes and liver but did not affect skin and skeletal muscle fractional protein synthesis rates during the established parasitic infection.

Intestinal amino acid absorption in lambs fed fresh Lucerne (Medicago sativa) during an established Trichostrongylus colubriformis infection

“…The DM content of the Lucerne was determined daily to adjust the amount of wet forage given to maintain the DM offered at approximately 800 g/day. The level of 800 g DM/day was chosen to minimise the effects of parasite infection on intake (Bermingham et al, 2006). The lambs were fed hourly from overhead feeders and water was available ad libitum.…”

“…One week after surgery (day 1 of the experimental period), six sheep were given 6000 T. colubriformis L3 larvae per day orally for 6 days (parasite treatment) while the remaining six sheep were drenched with ivermectin once (Ivomec; Merial New Zealand Limited) to serve as controls. The infection protocol used was essentially short-term dose, with the larval challenge spread across 6 days to minimise rumen by-pass and maximise larvae establishment in the small intestine as described in full in Bermingham et al (2006). Due to the time consuming nature of the surgical procedure, a maximum of four lambs were surgically prepared with catheters in any one week (one lamb per day), with two lambs allocated to the parasite group, and two to the controls.…”

“…Sample processing and chemical analysis DM, alkanes, N and AA were determined in feed and refusals, faeces and digesta samples as described elsewhere (Mayes et al, 1986;Shenk and Westerhaus, 1991;Bermingham et al, 2001 and2006).…”

“…To determine the concentration of AA in plasma, 0.5 ml was treated with 80 mmol/l dithiothreitol and 3 mmol/l norleucine (as an internal standard, in 0.1% phenol) and stored at 2858C, as described in Bermingham et al (2006). PAH was measured by the method of Katz and Bergman (1969), with an additional deacylation step as described by Lobley et al (1995).…”

“…This is likely to be the cause of the increased fractional protein synthesis in the small intestine (Symons and Jones, 1975;Bermingham et al, 2006) and leucine oxidation and protein turnover in the gastrointestinal tract (Yu et al, 2000) that have been observed during parasitic infection.…”