Effects of level of larval intake on the productivity and physiological and metabolic responses of lambs infected with Trichostrongylus colubriformis

Abstract

The interrelationships between level of exposure to Trichostrongylus colubriforn~i.s infection, production loss, and the physiological and metabolic changes associated with the development of the disease were studied over 24 weeks in groups of weaner lambs on larval dosing regimes (LDR) of either 0, 300, 950, 3000, 9500 or 30,000 infective larvae per week. During the first 12 weeks faecal egg counts generally accorded with the level of larval dosing, but thereafter declined, and at 24 weeks worm counts showed that most animals were resistant to parasite establishment. Liveweight gain over the 24-week infection period was significantly depressed only on LDR 3000, 9500 and 30,000 being, respectively, 67, 61 and 49% of the gain on LDR 0. These differences reflected reduced rates of gain, or, on LDR 30,000, loss of weight, during the first 12 weeks; rates of liveweight gain were similar on all LDR between 12 and 24 weeks. Wool growth rate was significantly depressed on LDR 3000, 9500 and 30,000, the maximal effect being recorded during weeks 8-12, when the growth rate was reduced to 79, 47 and 44% respectively of the rate on LDR 0. Thereafter, wool growth rate on these three LDR increased and by weeks 20-24 had returned almost to the level in uninfected sheep. Food consumption was significantly depressed on LDR 3000, 9500 and 30,000, the maximal effect occurring between weeks 8 and 12 when food consumption was 71, 61 and 44% respectively of that on LDR 0. By weeks 20-24 food consumption on these LDR had returned to the level in uninfected sheep.On LDR 30,000 there was a significantly increased excretion of nitrogen (g/100 g nitrogen intake) in faeces during the 8th, 12th and 24th weeks of infection and in urine durlng the 4th, 8th and 12th weeks. Nitrogen retention (g/100 g nitrogen apparently digested) was significantly reduced on LDR 30,000 during the 4th, 8th and 12th weeks.Enteric loss of plasma was significantly increased on LDR 950 and above, this effect occurring earlier and being more pronounced with increasing level of larval dosing; maximal losses were recorded during the 12th week when on LDR 30,000 sheep were losing approximately four times as much plasma into the gut as on LDR 0. The development and degree of hypoalbuminaemia in infected sheep paralleled the development of enteric plasma leakage, significantly reduced albumin levels being recorded on LDR 950 and above during the 12th week. By the 24th week both enteric plasma loss and plasma albumin concentration in sheep on these four LDR had returned to values similar to those in uninfected sheep. Measurements of albumin kinetics indicated that rates of albumin turnover and irreversible loss were increased in infected sheep only during the early stages of infection.Depletion of the albumin pool was accompanied by a significantly reduced rate of irreversible albumin loss during the 12th week on LDR 3000 and above.Measurements of the RNA/DNA ratio in liver and muscle at 4, 10 and 17 weeks indicated that protein synthesis in these tissues was significantl...

Adult Trichostrongylus colubriformis infection did not affect protein synthesis rate in whole-body, intestinal, hepatic and skeletal muscle tissues of lambs fed fresh Lucerne (Medicago sativa)

“…Parasitic infection has increased the rates of synthesis of hepatic constitutive proteins Bermingham et al 2006). The 4% decrease (P < 0.15) in skin FSR I observed in the current study is consistent with previous studies in parasitized sheep (Symons and Jones 1975;Steel et al 1980Steel et al , 1982. Whilst these studies have shown decreased skeletal muscle protein synthesis during parasitic infection, similar infection protocols to the current study showed that an adult T. colubriformis infection did not affect the FSR of the biceps femoris (Bermingham et al 2006).…”

“…This point was covered in detail in Bermingham et al (2006). Briefly, the majority of the studies in sheep reported in the literature have involved long-term constant (at least weekly) infection procedures (e.g., Steel et al 1980;Jones and Symons 1982;Yu et al 2000) and/or larger infection dose (Steel et al 1980;Jones and Symons 1982). It is also possible that alterations in whole-body and tissue protein synthesis would have been observed at an earlier stage of parasite establishment, such as when the lamb was first infected with T. colubriformis and when faecal egg production was at its highest point during the infection (around 26 d post-infection).…”

“…Trichostrongylus colubriformis, the major sheep parasite in New Zealand, imposes a severe financial cost on farmers, due in part to its negative effects on liveweight gain (van Houtert et al 1995) and wool production (Steel et al 1980(Steel et al , 1982. Protein is the major constituent of muscle and wool.…”

Protein supply influences the nutritional penalty associated with the development of immunity in lambs infected with Trichostrongylus colubriformis

“…Without pairfed controls it is difficult to separate and quantify the precise importance of the two components of reduced feed intake and increased nutrient costs for overall efficiency. The calculation of the effect of infection on both VFI and nutrient utilization is heavily dependent on the duration and extent of the pathophysiology of infection, which several studies have shown is greatest during the period immediately preceding the host's ability to limit FEC (Steel et al, 1980;Kimambo et al, 1988). The benefit of the higher protein diet in the present work appears to have been in either permitting or accelerating the development of an effective immune response as H-IF sheep were able to regulate FEC by day 70 while there was no evidence for such ability in L-IF sheep.…”

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

“…mucus, plasma leakage or sloughed cells; Kimambo et al, 1988) and/or as N excretion in urine and faeces (Sykes and Coop, 1976). These effects may, in part, explain the decreased growth performance (Sykes and Coop, 1976;van Houtert et al, 1995) and production (Steel et al, 1980 and that is observed during parasite infections in lambs.…”