The effect of nutrition on the periparturient parasite status of sheep

Abstract

Four trials were conducted to investigate the role of nutrition in the periparturient breakdown of resistance to gastrointestinal parasitism in mature sheep. In the first trial pregnant ewes were housed seven weeks prior to parturition and fed either to gain (HE) or lose (LE) maternal body weight. From five weeks prior to parturition ewes were trickle infected with 4,000 T. circumcincta larvae day⁻¹. Faecal egg counts were monitored throughout the infection period. Ewes were slaughtered either at partum (S0) or six (S6) or nine (S9) weeks post partum for determination of worm burden. S6 and S9 groups received an additional challenge infection of 25,000 T. circumcincta larvae, 21 days prior to slaughter. Live weight gain was significantly greater in HE than LE ewes viz. 15.5 kg and 6.0 kg, respectively. Despite this difference mean faecal egg counts were significantly higher in LE sheep only in the week preceding parturition viz. 23 and 252 eggs g⁻¹ faeces, for HE and LE groups, respectively. Nutrient supply had no effect on worm burdens at any of the three slaughter times.

Trial 2 examined the combined effects of current nutrient intake and level of larval challenge on the magnitude of the periparturient breakdown. Ewes were housed nine weeks prior to parturition. One group was fed above the recommended energy requirements (H10, n=12) and trickle infected with 10,000 T. circumcincta larvae day⁻¹ from 8 weeks before lambing. Groups LS, L10 and L20 (n=12) were fed below their recommended energy requirement and trickle infected with 5,000, 10,000 and 20,000 T. circumcincta larvae day⁻¹, respectively. Faecal egg counts were recorded throughout. Ewes were slaughtered at parturition. Again, despite significant differences in live weight gain and body condition score between Hand L groups, there was no effect of nutritional treatment on parasite status. Similarly, larval challenge did not affect parasite status.

Results from Trials 1 and 2 thus questioned the role of dietary energy intake in maintaining resistance to gastrointestinal parasitism. The latter study also demonstrated the unimportance of larval intake on the periparturient breakdown.

Trial 3 was undertaken to assess the relative importance of metabolisable energy and metabolisable protein supply. Utilising a 2x2 factorial design for energy (E) and protein (P) single and twin bearing ewes were fed either a basal ration (adequate E and P) or at a supplemented level (E and P in excess of requirements). Energy levels were altered by varying the hay:grain ratio of the diet. Protein supplementation was achieved by inclusion of 75 g fishmeal kg⁻¹ dry matter in rations. Ewes were trickle infected with 10,000 T. circumcincta and 7,000 T. colubriformis larvae day⁻¹ from seven weeks before lambing. Larval dosing ceased at parturition and the ewes were slaughtered three weeks later. There was no effect of energy supplementation on worm burdens and only a short term effect on faecal egg counts in the week before lambing. Protein supplementation significantly reduced faecal egg counts from 21 days before lambing and throughout the remainder of the trial. Worm burdens in protein supplemented sheep were significantly lower than those on the basal protein ration viz. 1,540 worms compared with 12,020. Single bearing sheep had significantly lower worm burdens than twin bearing sheep (2,300 compared with 8,100). Worm burdens comprised mainly Teladorsagia spp. Less than 4% of total worm burdens consisted of Trichostrongylus spp. There was no effect of nutritional treatment on lymphocyte stimulation in response to various parasite antigens and mitogens. Similarly, inhibition of larval migration in response to small intestinal mucus was unaffected by nutritional treatment. Results from Trial 3 indicated the relative importance of protein supply over energy intake in periparturient resistance to gastrointestinal parasitism.

A fourth and final trial was undertaken to determine the appropriate threshold level of protein supplementation required to achieve reductions in the extent of the periparturient breakdown. Three treatment groups of twin bearing ewes (n=10) were established ten weeks prior to parturition. Diets were designed to provide approximately the same level of metabolisable energy but to differ in their metabolisable protein provision. This was achieved by the inclusion of 0, 100 and 200 g of fishmeal kg⁻¹ dry matter in the diet of groups F0, F10 and F20, respectively. The ewes were housed eight weeks prior to parturition and trickle infected daily with 10,000 T. circumcincta and 7,000 T. colubriformis larvae, during the 42 days before parturition. Infective dosing ceased at parturition. Eleven days later five animals from each group were given a further single challenge infection of a 25,000 T. circumcincta and 17,500 T. colubriformis infective larvae. All ewes were slaughtered ten days later. Faecal egg counts of the F20 group remained below 100 eggs g⁻¹ of faeces throughout the course of the experiment. Faecal egg counts immediately prior to slaughter were significantly lower in sheep which had received the post partum challenge infection. Worm burdens of both species decreased with increasing protein supply. Sheep which had received the post partum challenge infection had significantly higher numbers of L4 larvae than those trickle infected only. Establishment of Trichostrongylus spp. from the post partum challenge infection was significantly higher in F0 than F20 sheep. Establishment rates were calculated to be 15.2, 9.4 and 5.9% in Teladorsagia spp. and 9.3, 3.4 and 0.9% in Trichostrongylus spp., for groups F0, F10 and F20, respectively. These results confirmed that protein supplementation can moderate the periparturient breakdown. Results from the post partum challenge infection provided evidence that the effects of protein on worm burdens may have occurred at the establishment stage against incoming larvae.

Results from this study indicate that protein supplementation may be an important component in strategies aimed at moderating the deleterious effects of the periparturient breakdown. Energy supplementation, ewe body condition and larval challenge appear to be less important but may impact under more intense conditions. The means by which protein supply affects resistance to parasitism in the mature ewe deserves further investigation.