Effects of Trichostrongylus colubriformis on phosphorus and protein metabolism in sheep

Abstract

Three trials were conducted to investigate the effects of gastrointestinal parasite T.colubriformis on phosphorus and protein metabolism in sheep.

In the first trial, taurine urinary excretion was investigated to determine whether it could measure change in S amino acid metabolism due to parasitic infection. Two diets were used : one in which the amino acid supply would came predominantly from microbial protein (MP) and the other with a substantial contribution of UDP from fishmeal (FP). Twenty four lambs were divided into two groups and placed in metabolism cages. The "high" protein and "low" quality protein diets contained 209 gCP/kgDM and 182 gCP/kg DM and were estimated to supply 71 and 73 g MP(Metabolisable protein)/day, respectively. Each dietary group was divided into two groups and one infected with 2,000 larvae/day T.circumcincta and 2,000 larvae/day T. colubriformis, another group acting as a pair-fed control group. Plasma concentration and 24 hr urinary excretion of taurine was measured weekly during a 12 week trial. Nitrogen balance studies were performed during weeks 3, 6, and 9 after infection started. Faecal egg counts were monitored twice weekly throughout the infection. Lambs were slaughtered at the end of the trial for determination of worm burdens. Infection had no significant effect on dry matter intake, weight gain or nitrogen balances. FEC was 47 % higher in the FP than in the MP group but significantly so only during weeks 6 and 7. Worm burdens in the abomasum were 1,660 and 6,260 in FP and MP group respectively. In the intestine, on the other hand, worm burdens were higher in the FP group viz 11,275 and 2,970, respectively. Urinary taurine concentrations were 486 % higher in the FP than in the MP and were not affected by the infection.

In Trial 2 the combined effects of infection with T. colubriformis and low dietary P concentration on ability to withstand infection was studied. Microbial protein production was estimated from urinary purine excretion. Four groups of 7 four month old lambs were offered 4 diets NPrNP (179 gCP/kg, 4.27 gP/kgDM), NPrNPI (179 g CP/kg DM). NPrLPI (171 gCP/kg DM and 2.25 gP/kgDM) and HPrLPI (249 gCP/kgDM and 2.25 gP/kgDM). Lambs were infected with 2,500 larvae/day of T. colubriformis and FEC were monitored twice weekly. N balance studies were performed during weeks 4, 8 and 12 after infection. Blood samples were taken weekly to determine plasma protein, plasma P and plasma urea concentrations. Lambs were slaughtered after 12 weeks to determine worm burdens. Rumen samples were taken at slaughtered for P concentration in the liquid phase of the rumen. Treatment did not affect DMI but LWG was reduced to 89% in the infected compared to the uninfected group. Highest FEC was observed in the low phosphorus group during week 5 but subsequently decreased to the same levels as in the high phosphorus group after that. Worm burdens were very low (190, 97 and 88 worm in NPrNPI, NPrLPI and HPrLPI respectively). Infection and low P in the diet did not decrease rumen P concentration in the liquid phase significantly to have effect on microbial protein production.

The third trial was effective a repeat of trial 2, but with lower dietary P concentration. In addition to the measurement made in trial 2 the effect of infection on rumen fermentation was monitored. Fourteen 7 month old lamb were cannulated with T shape cannula to allow sequential sampling of rumen contents. One group (YLPI, n=6) was offered a low P (1.8 gP/kgDM) and the second group (YNPI, n=4) a normal P (3.6 gP/kgDM) and infected with 3,000 larvae of T. colubriformis /d from week 4. The remainder (YPF, n=4) was uninfected pair-fed to YLPI and offered the low P diet. A further group of 19 month old sheep OLPI (n=4) was offered the low P diet and infected with 3,000 larvae of T. colubriformis /d. To enable the establishment of infection the immune system was suppressed by weekly injection of 2 ml Depo Medrol (methylprednisolone acetate 40 mg/ml, Upjohn). It was anticipated that in these animals would still reduce P absorption and lead to hypophosphataemia but that with reduced skeletal demand for P that normal rumen P concentration may be maintained. Samples were taken weekly for plasma protein, albumin and P analysis, rumen P and volatile fatty acid (VFA) concentration and urine for purine analysis. OLPI sheep maintained very high faecal egg counts (3,000-6,214 epg) and had extremely large worm burdens at slaughtered - mean 238,000 worms. Despite this DMI was maintained and positive LWG (145 g/d) was achieved. Plasma P concentration decreased from 55to 37 mgll. Rumen P concentration (80 mg/100 ml) was lower than in young sheep that the rate of microbial protein production (21 g/kgOM dig in rumen) was similar to that in control sheep (27 g/kgOM dig in rumen). Peak epg in young sheep was greatest in YLPI sheep at 4,350 epg during week 5 declining to only 2,566 epg at the of the trial, compared to only 2,316 and 200 epg, respectively in YNPI sheep at the same time. Plasma P concentration fell down from 82 to 61 and from 72 to 86 mg/l in YLPI and YNPI respectively compared to 72 mg/l in pair-fed. LWG were 50, 123 and 27 g/d in YLPI, YNPI and YPF groups, respectively. Rumen P concentration were 93, 117, 102 and 80 Mg/l at the end of the period in YLPI, YNPI, YPF and OLPI, respectively. VFA concentration were 393, 405, 402 and 352 mg/100ml in YLPI, YNPI, YPF and OLPI respectively. Microbial protein production was not, however, affected being 27.4, 22.8 and 25.1 g/kgOM dig in rumen in YLPI, YNPI and YPF groups respectively.