Targeted supplementation of sheep to control gastrointestinal nematode populations : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

One potential approach to control GIN parasite and to improve ewe’s immunity during the periparturient period is nutritional supplementation. However, there is limited data regarding the long-term effects of nutritional supplementation on grazing periparturient ewes that have a naturally acquired GIN infection where two or more parasite species are infecting ewes and lambs. This thesis describes a series of experiments designed to analyse the effects of targeted supplementation to twin-bearing ewes on pasture and determine whether the supplementation can provide long-term benefits to their lambs after weaning. Three experiments were carried out at LincolnSheep, Canterbury, New Zealand, over three sequential years (August 2015-April 2018). Before lambing, twin-bearing crossbred ewes (n=140 in 2015, n=128 in 2016, and n=160 in 2017) were randomly allocated to one of two treatments, viz. supplemented and unsupplemented. Ewes on the supplemented paddocks were introduced to an advantage feeder with approximately 50 g/head/d of sheep pellets starting three weeks before lambing and then increased to 0.5 kg/head/d during the first four weeks of lactation. All sheep were allowed to graze on perennial ryegrass/white clover pasture. After weaning, all lambs were drenched and then exposed to a targeted selective treatment (TST) regime while grazing the areas in which ewes had been or not supplemented to determine if any epidemiological benefit of supplementation existed. Weaned lambs (n=240 in 2015, n=210 in 2016, and n=180 in 2017) originating from each treatment were stratified across the treatment area. For each lamb replicate, growth potential was assessed using sentinel lambs that were treated with a long-acting anthelmintic. The remaining lambs in each replicate were subjected to a TST regime where the need for anthelmintic was based on animals achieving acceptable growth rates. Within each farmlet, lambs were rotationally grazed for the remainder of the grazing season, with lambs grazing freshly grown forages, followed by the ewes. In the first study (year 2015 and 2016, Chapter 4), the ewes were undrenched, consequently allowing the development of pre-existing parasite infections. The results in both years showed that supplementation of ewes did not affect ewe LW and BCS or the weight of lamb weaned per ewe (P>0.05 for all). However, supplementation was successful in reducing ewe's FEC to 50% reduction during lactation periods. However, in 2015, the effect was transient, as FEC of supplemented ewes increased and was not different at week 12 of lactation. In 2015, climatic conditions were not favourable for pasture growth, resulting in low pasture availability, with mean pasture mass declining to less than 700 kg DM/ha in all paddocks, and may have resulted in unintentional nutritional stress and increased the concentration of eggs in the faeces. In the 2016 trial, the reduction in ewe FEC was more consistent throughout lactation, indicating a longer-term benefit to the ewe as this extended beyond the pre-patent period of any larvae that would have been ingested after supplementation. The declining number of eggs observed in 2016 at late pregnancy until the 8th week of lactation agrees with the increase of IgA at the same time, which may be due to an improvement in immunity. However, unexpectedly, the T. colubriformis-specific L3 IgA absorbances in supplemented ewes were significantly lower than unsupplemented ewes throughout the experiment in 2016. The reasons for this are unclear but may reflect differences in the larval challenge. Moreover, supplementation also did not have any significant effects on serum proteins, serum urea, and serum phosphorus of the ewes. Before weaning, there was no difference between the mean LW of lambs reared by supplemented or unsupplemented ewes in 2015 (P=0.27), while in 2016, lambs reared by unsupplemented ewes were significantly heavier than those raised by supplemented ewes (P=0.02). After weaning, there were no differences in the performance of lambs between the two treatments in all years (P>0.05 for all), except for a higher number of drenches administered per lamb (P=0.04) of TST lambs in areas where ewes had not been supplemented in 2015. These findings allowed the conclusion that supplementation of ewes during the first four weeks of lactation had no effect on ewe performance but was successful in temporarily reducing faecal eggs by 50%, presumably reflecting better maintenance of immune function through higher nutrient supply, even though this was not detected in parasite specific-immunoglobulin. However, the reduction in parasite contamination was insufficient to provide a measurable and consistent epidemiological benefit to the grazing lambs after weaning. The second trial (year 2017, Chapter 5) aimed to evaluate the effect of supplementation to reduce the establishment of larvae following short-acting drench pre-lambing. The results showed the benefits of ewe supplementation when the existing population is removed, such as the difference in FEC, the greater serum albumin concentrations, and the consistently higher milk protein contents. Similar to the previous studies, supplementation of ewes in 2017 also did not affect ewe LW and BCS or the weight of lamb weaned per ewe (P>0.05 for all). The reduction in FEC following supplementation was not accompanied by the increase in T. colubriformis-specific L3 IgA absorbance; the values decreased over time (P<0.001), possibly indicating that the immune response to ingested larvae was unaffected. The level of serum IgG of supplemented ewes was similar to unsupplemented ewes (P=0.83). However, there was treatment and time interaction (P=0.001) on serum IgG concentrations, reflecting high IgG responses at week 4 of lactation, which then decreased with time in all groups; however, the decline was higher in unsupplemented ewes than their supplemented counterparts at week 8 of lactation. Similarly, supplementation on ewes did not affect milk production and composition (P>0.05 for all). There were extremely weak associations between milk production and lamb growth rate during the lactation period, except for the unsupplemented group in week 4 (P<0.001). Moreover, pastures grazed by supplemented ewes tended to have threefold lower pasture larval than unsupplemented pastures, which can be seen from the tendency of fewer L4 in the tracer lambs grazed areas where ewes had been supplemented. This lower pasture contamination, therefore, resulted in a slight difference in the FEC profile of lambs, effectively delaying the increase in FEC in the lambs throughout the summer. FEC of lambs after weaning increased significantly throughout the grazing season for both groups, although tended to be delayed in TST lambs grazing the areas where ewes had been supplemented, which reached a peak of 65 days after weaning compared with 51 days after weaning in TST lambs grazed unsupplemented areas. The difference in the growth rate of the sentinel lambs and TST lambs clearly shows that there was a substantial larval challenge, with the benefits of supplementation possibly masked due to the TST regime, even though there was no difference in the number of anthelmintic treatments administered. The reduction in the FEC of lactating ewes drenched pre-lambing was not sufficient to result in an epidemiological advantage to their lamb, as shown by results on FEC, worm burden, and growth performance from birth to reach slaughter weight while grazing pastures that were infected naturally by GIN parasites. The third trial (year 2017, in conjunction with the second trial) indicated that supplementation and treatment with moxidectin at the end of supplementation (week four of lactation) appeared to assist the ability of the ewes to limit egg excretion. FEC of supplemented-undrenched and unsupplemented-undrenched groups was significantly increased throughout the lactation period, except at week eight of lactation, where FEC of all groups decreased. Surprisingly, the FEC of supplemented-undrenched ewes rapidly elevated to 1,400 epg at week 12 of lactation, compared to 650 epg in unsupplemented-undrenched ewes. The reason for the speedy elevation of FEC in the first group was probably associated with a decrease in ewes’ immunity, as indicated by lower T. colubriformis-specific L3 IgA and T. colubriformis-specific L3 IgG levels, even though the effect on these values was not significant. Additionally, both drenced and undrenched groups had significantly lower serum albumin concentrations, indicating there was damage to the mucosa of the GI tract of ewes by GIN parasites, which resulted in body protein loss. As expected, long-acting injections of moxidectin at the end of the supplementation period resulted in a consistent trend of higher LW than undrenched groups due to lower parasitic load. Similar to the results from previous trials, supplementation of ewes and administration of long-acting anthelmintic at the end of the supplementation period did not provide clear benefits to their lambs before weaning. However, lambs raised by supplemented and drenched ewes tended to have higher LW, LWG, and weight of lamb weaned per ewe (WLWE) than those raised by unsupplemented groups. It was concluded from the series of experiments from this study that supplementation of ewes during the first four weeks of lactation, whether undrenched, drenched pre-lambing or drenched at the end of the supplementation period, did not affect ewe performance. However, it was temporarily successful in reducing faecal egg counts, presumably reflecting better maintenance of immune function through higher nutrient supply, although this was not detected in parasite-specific immunoglobulins. However, the reduction in parasite contamination was insufficient to provide a measurable and consistent epidemiological benefit to the grazing lambs that may assist with parasite control. If the supplementation of ewes during this time is to be employed as a means of reducing the need for anthelmintics to control parasitism, then the refinement, including an understanding of the specific amino acid requirement and any interaction with BCS, needs to be investigated.