Effect of weaning on antibody responses and nematode parasitism in Merino lambs

The effect of weaning age on animal performance in lambs exposed to naturally acquired nematode infections

The effects of mixed gastrointestinal nematode (GIN) infections on animal growth and post-weaning activity patterns were investigated in grazing intact ram lambs when naturally exposed to two different infection levels and weaned at different ages. Ewes and their twin-born lambs were turned-out to graze in two permanent pasture enclosures naturally contaminated with GIN the previous year. Ewes and lambs in the low parasite exposure group (LP) were drenched before turn-out and at weaning, respectively, with 0.2 mg ivermectin per kg body weight, whereas those in the high parasite exposure group (HP) were left untreated. Two weaning ages were applied, early weaning (EW) (10 weeks) and late weaning (LW) (14 weeks), respectively. The lambs were then allocated to one out of four groups based on parasite exposure level and weaning age (EW-HP, n = 12; LW-HP, n = 11; EW-LP, n = 13; LW-LP, n = 13). Body weight gain (BWG) and faecal egg counts (FEC) were monitored, in all groups, from the day of early weaning and every four weeks, for 10 weeks. In addition, nematode composition was determined using droplet digital PCR. Activity patterns measured as Motion Index (MI; the absolute value of the 3D acceleration) and lying time were monitored continuously from the day of weaning until four weeks post-weaning using IceQube® sensors. Statistical analyses were performed in RStudio, using mixed models with repeated measures. BWG was 11% lower in EW-HP compared with EW-LP (P = 0.0079) and 12% lower compared with LW-HP (P = 0.018), respectively. In contrast, no difference in BWG was observed between LW-HP and LW-LP (P = 0.97). The average EPG was higher in EW-HP compared with EW-LP (P < 0.001), as well as in EW-HP compared with LW-HP (P = 0.021), and LW-HP compared with LW-LP (P = 0.0022). The molecular investigation showed that animals in LW-HP had a higher proportion of Haemonchus contortus compared with EW-HP. MI was 19% lower in EW-HP compared with EW-LP (P = 0.0004). Daily lying time was 15% shorter in EW-HP compared with EW-LP (P = 0.0070). In contrast, no difference in MI (P = 0.13) and lying time (P = 0.99) between LW-HP and LW-LP was observed. The results suggest that a delayed weaning age may reduce the adverse effects of GIN infection on BWG. Contrarily, an earlier weaning age may reduce the risk of H. contortus infection in lambs. Moreover, the results demonstrates a potential use of automated behaviour recordings as a diagnostic tool for the detection of nematode infections in sheep.

Lambs are more stressed at early weaning when housed with their twin

The objective of this study was to compare the behavioural and immunological responses of twin lambs housed together with their siblings or not after weaning. The study was performed with seven multiparous Milchschaf ewes and their twin lambs (n = 14), which were weaned abruptly at 63 days of age and assigned to two experimental groups: (1) lambs that were housed together with their sibling after weaning (group GT, n = 6) and (2) lambs that were separated from their siblings and remained with other lambs from the same flock (group GS, n = 8). Before and after weaning, the distance between twins, the number of times in which the sibling was the closest lamb, the lambs' behaviours, and the average daily gain were recorded. The lambs' immune response was assessed with the phytohemagglutinin skin test after weaning. The closest lamb before weaning was the sibling in all cases (P < 0.0001 for all). The frequency in which GT lambs were observed closest from its twin increased on the day of weaning (P = 0.002). During the day of weaning, GT lambs vocalised and paced more than GS lambs (P = 0.001 and P = 0.01, respectively). Twenty-four h after the phytohemagglutinin injection, the skinfold thickness was greater in GS than GT lambs (P = 0.03). In conclusion, twin lambs housed together with their siblings were more stressed at weaning, displaying more intensive behavioural changes and a poorer immunological status than twin lambs housed separated from their siblings.

What Do We Know and Need to Know About Weaning in Sheep? An Overview of Weaning Practises, Stress and Welfare

Artificial weaning is the separation of the mother and her lamb, involving the forced ending of suckling and milk supply by the ewes to their lambs. Artificial weaning time varies depending on the purpose of each sheep farm and the characteristics of the lambs, including age and weight of the lambs, and their ability to eat solid food. Artificial weaning is performed from 24 h postpartum until around the age of natural weaning (up to 12 mo of age). Artificial weaning results in the breaking of the ewe-lamb bond, the end of suckling and the complete replacement of milk by solid food, frequently added to changes in both the physical and social environment. It triggers behavioural, physiological and immunological changes that generate negative consequences on the health of both ewes and lambs, as well as on the growth of the lambs, rising animal welfare concerns. As artificial weaning is considered one of the most stressful situations in the life of farm mammals, it is important to consider the factors involved in those responses to develop adequate strategies and improve sheep welfare at weaning. The most frequently used method is the abrupt separation of the ewes and their lambs. However, the adaptation of the animals after weaning can be improved by alternative weaning methods (e.g., progressive, two-steps weaning and mixed regimes), hormonal treatments (e.g., administration of progesterone), and pre- and postweaning management (e.g., the use of creeping feeding, and the presence of conspecifics or humans after weaning). This review presents and summarises information on the stress response and animal welfare issues at artificial weaning in sheep and some management practises that can be used to reduce these problems. The major points included are the ewe-lamb bond at birth and during the lactation period; the stress response at weaning; the factors involved in the stress response at weaning; the different types and weaning methods and their repercussions on animal welfare; and some strategies that can be used to improve sheep welfare at weaning. Lastly, we propose directions for research needed to develop practical alternatives to minimise sheep's stress response at weaning.

Protective efficacy of Barbervax® in Merino weaner sheep trickle infected with five doses of Haemonchus contortus infective larvae

Barbervax® protects sheep against H. contortus infection; however, the level of protection afforded by the vaccine at different levels of larval challenge under field conditions has not been reported. Therefore, this study was designed to investigate the protective efficacy of Barbervax® at increasing doses of trickle infection with H. contortus third stage larvae (L3). Merino lambs (220) were randomly allocated to challenge treatment groups and received Barbervax® vaccinations at approximately 8, 11, 15 and 22 weeks of age or not vaccinated (control group). Animals within each treatment group were subjected to one of five levels of H. contortus L3 trickle infection (0, 300, 600, 1200 and 2400 L3/week in two split doses). Trickle infections started two weeks after the third vaccination (week 0). Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured at week 2 (start of trickle infection), week 5 and then every two weeks for 11 weeks. Vaccinated weaners had a significantly (P < 0.0001) lower faecal WEC than unvaccinated control animals. Vaccination induced significant specific antibody responses that were not influenced by level of trickle infection. Vaccination significantly reduced the number of weaners requiring salvage anthelmintic treatment (9.4% vaccinated weaners versus 33.6% unvaccinated). Vaccine protective index based on WEC was similar at all challenge levels (overall mean> 60%) and at the higher challenge levels did not reduce H. contortus infection to levels that would not require anthelmintic treatment. Therefore, it is suggested that under conditions of high larval challenge the use of Barbervax® should be integrated with other control methods.

Immune competence traits assessed during the stress of weaning are heritable and favorably genetically correlated with temperament traits in Angus cattle1

Selection for production traits with little or no emphasis on health-related traits has the potential to increase susceptibility to disease in food-producing animals. A possible genetic strategy to mitigate such effects is to include both production and health traits in the breeding objective when selecting animals. For this to occur, reliable methodologies are required to assess beneficial health traits, such as the immune capacity of animals. We describe here a methodology to assess the immune competence of beef cattle which is both practical to apply on farm and does not restrict the future sale of tested animals. The methodology also accommodates variation in prior vaccination history of cohorts of animals being tested. In the present study, the immune competence phenotype of 1,100 Angus calves was assessed during yard weaning. Genetic parameters associated with immune competence traits were estimated and associations between immune competence, temperament, and stress-coping ability traits were investigated. Results suggested that immune competence traits, related to an animal's ability to mount both antibody and cell-mediated immune responses, are moderately heritable (h2 = 0.32 ± 0.09 and 0.27 ± 0.08, respectively) and favorably genetically correlated with the temperament trait, flight time (r = 0.63 ± 0.31 and 0.60 ± 0.29 with antibody and cell-mediated immune responses, respectively). Development of methodologies to assess the immune competence phenotype of beef cattle is a critical first step in the establishment of genetic selection strategies aimed at improving the general disease resistance of beef herds. Strategies aimed at reducing the incidence of disease in beef cattle are expected to significantly improve animal health and welfare, reduce reliance on the use of antibiotics to treat disease, and reduce disease-associated costs incurred by producers.

Morada Nova sheep breed: Resistant or resilient to Haemonchus contortus infection?

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Resistance against Haemonchus contortus was assessed in a Morada Nova flock.

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More than 88% of the lambs had PCV ≥ 24% even with high fecal egg counts (FEC).

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Only susceptible lambs had decreased live weight due to parasitism.

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More than 98% of the ewes had FEC below 4000 EPG.

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PCV of the ewes was not affected by H. contortus infection.

Morada Nova is a Brazilian hair sheep breed that is well adapted to the country’s mainly tropical climate and has good potential for meat and leather production. This breed is reported to be resistant to Haemonchus contortus infection, a highly desired characteristic due to the large impact of this parasite on sheep farming. Therefore, the present study aimed to characterize 287 recently weaned Morada Nova lambs and 123 ewes in relation to their resistance against H. contortus. The animals were dewormed and 15 days later artificially infected with 4000 H. contortus L₃ (D0). They were individually monitored by periodic assessment of fecal egg count (FEC), packed cell volume (PCV), and live weight (LW). On D42, the sheep were again dewormed and submitted to a new parasitic challenge, following the same scheme. The animals of each category (lambs and ewes) were ranked according to individual mean FEC values, and classified as resistant (R, 20%), intermediate (I, 60%), or susceptible (S, 20%) to H. contortus infection. At weaning, high FEC were observed in all three phenotypes (P > 0.05). After the artificial infections, there was a significant difference (P < 0.05) among the three lamb phenotypes for the mean FEC (R < I < S), PCV (R > I > S), and LW (R = I > S). The infection levels (FEC) were negatively correlated with PCV (r = -0.66; P < 0.001), and LW (r = -0.30; P < 0.001). Despite this, the lambs were resilient, since more than 88% of these animals maintained the PCV above 24%, even when heavily infected. The importance of selective parasite control before weaning to reduce the negative impact on slaughter weight was evidenced, taking into account the high positive correlation between LW at weaning and final LW (r = 0.73; P < 0.001). The ewes, in turn, were strongly resistant to the parasite. Despite highly significant differences (P < 0.001) for mean FEC between phenotypes (R < I < S), 98% of the ewes maintained FEC below 4000 EPG. Their health was not affected, since PCV and LW did not differ between phenotypes, and these parameters were not significantly correlated with FEC (P > 0.05). With the phenotypic characterization performed here, it is possible to introduce procedures for parasite control in Morada Nova flocks, facilitating the target-selective treatment approach. The results of this study can also support improvement of meat production by the Morada Nova breed.

Growth is impeded by gastrointestinal nematodes in weaned rather than suckling meat-breed lambs in a high summer rainfall region, on the Northern Tablelands, New South Wales

The hypothesis tested in this experiment was that the effects of gastrointestinal nematodes (GIN) on growth of meat-breed lambs would be absent during the suckling period and greatest after weaning. The experiment was a single factor design conducted on five farms over 2012–2014, using meat-breed lambs (Poll Dorset × Border Leicester/Merino), which were either GIN-suppressed (SUP) or not (NSUP). The experiment commenced at lamb marking and continued for 5 months. SUP lambs were serially treated with short- and long-acting anthelmintics. NSUP lambs were not treated before weaning and at weaning received a short-acting multi-active drench with subsequent treatments varying between farms. Worm egg count (WEC) of NSUP lambs were significantly higher (P < 0.0001) than SUP lambs at weaning (1170 and 10 epg) and thereafter (P < 0.0001) reaching 920 epg 2 months after weaning. Haemonchus contortus was the predominant species present in NSUP lambs with smaller contributions from Trichostrongylus spp. There was no effect of GIN control on lamb growth during the pre-weaning period (SUP 17.2 kg vs NSUP 17.0 kg, P = 0.093), whereas GIN reduced growth of lambs by 0.5 kg (SUP 7.1 kg vs NSUP 6.6 kg, P = 0.002) in the last month of observation. There was no effect of GIN control on lamb mortality. GIN did not affect growth of suckling meat-breed lambs despite high WEC at weaning indicating resilience to GIN infection in lambs growing at 200 g/day. In contrast, post-weaning growth was reduced by GIN infection, despite effective treatment at weaning and movement to GIN ‘safe’ pastures. The susceptibility of weaned lambs to the effects of GIN infection highlights the importance of effective control measures at this time.

Physiological and behavioural responses to weaning conflict in free-ranging primate infants

Weaning, characterized by maternal reduction of resources, is both psychologically and energetically stressful to mammalian offspring. Despite the importance of physiology in this process, previous studies have reported only indirect measures of weaning stress from infants, because of the difficulties of collecting physiological measures from free-ranging mammalian infants. Here we present some of the first data on the relationship between weaning and energetic and psychological stress in infant mammals. We collected data on 47 free-ranging rhesus macaque infants on Cayo Santiago, Puerto Rico, showing that faecal glucocorticoid metabolite (fGCM) concentrations were directly related to the frequency of maternal rejection, with fGCM concentrations increasing as rates of rejection increased. Infants with higher fGCM concentrations also engaged in higher rates of mother following, and mother following was associated with increased time on the nipple, suggesting that infants that experienced greater weaning-related stress increased their efforts to maintain proximity and contact with their mothers. Infants experiencing more frequent rejection uttered more distress vocalizations when being rejected; however, there was no relationship between rates of distress vocalizations and fGCM concentrations, suggesting a disassociation between behavioural and physiological stress responses to weaning. Elevated glucocorticoid concentrations during weaning may function to mobilize energy reserves and prepare the infant for continued maternal rejection and shortage of energetic resources.

Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent

We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21, or 28 d after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentrations (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 d. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We concluded that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life.

Selection of Merino sheep for resistance to Haemonchus contortus: genetic variation

An animal model was used to estimate heritabilities of faecal egg count (FEC) and packed cell volume decline (PCVD) in lines of Merinos selected for divergent levels of resistance to Haemonchus contortus. The estimated heritability of FEC was 0·23 (s.e. 0·03) and of PCVD was 0·21 (s.e. 0·03). A cube root transformation was found to be effective in normalizing FEC data and reducing the range of within selection line-birth year variances from 118-fold to 10-fold. Transforming FEC data increased the heritability estimate to 0·29 (s.e. 0·03) and reduced selection bias due to heterogeneity of variance, but the further step of pre-adjusting the transformed data to a common variance had only a trivial effect. Heritability estimates for FEC in years with high means and variances were similar, as were estimates for transformed FEC. The estimated genetic correlations between measurements in years with high and low means and variabilities were 0·77 to 0·91.

PCVD and pre-adjusted transformed FEC had a phenotypic correlation of 0·48. Estimates for the genetic correlation ranged from 0·76 in the decreased resistance line to 1·00 in the increased resistance line and 0·87 with pooled data. Other effects on resistance included birth type and dam age, with twins and progeny of maiden dams being more resistant than their cohorts. Sex effects were unimportant for FEC but males had higher PCVD than females in most, but not all, years. Younger animals had higher FEC and PCVD than older animals. Maternal genetic effects were found to be unimportant, as were the effects of low levels of inbreeding.

Six costs of immunity to gastrointestinal nematode infections

The strength of the immune response and the outcome of the interaction of a host with a parasite are influenced by genetic and phenotypic characteristics of both parties, and by environmental variables. Allocation of host resources to immune defence reduces resources available for other life-history traits. This review identifies six potential costs to the host from immune activation. The costs are likely to be broadly applicable to other immune responses in vertebrate species. Five phenotypic costs arise from: (i) increased metabolic activity; (ii) reduced nutrient availability due to anorexia; (iii) altered priorities for nutrient utilization; (iv) change in size and turnover of pools of immune cells and proteins; and (v) immunopathology from inappropriate or excessive immune activation. Subsumed by these costs is the cost of altered efficiency of nutrient use. A sixth cost is the genetic cost which arises from a change in the capacity of offspring to express production and life-history traits following selection for parasite resistance. The sensitivity of immune responses to the phenotypic status of the host, and the role the immune system shares with the neuroendocrine system in controlling use of resources underpin the importance of immunocompetence to the life-history of the host.

Vaccines against blood-feeding nematodes of humans and livestock

This paper summarises the progress towards vaccine development against the major blood-feeding nematodes of man and livestock, the hookworms and Haemonchus contortus, respectively. The impact of the diseases and the drivers for vaccine development are summarized as well as the anticipated impact of the host immune response on vaccine design. The performance requirements are discussed and progress towards these objectives using defined larval and adult antigens, many of these being shared between species. Specific examples include the Ancylostoma secreted proteins and homologues in Haemonchus as well as proteases used for digestion of the blood meal. This discussion shows that many of the major vaccine candidates are shared between these blood-feeding species, not only those from the blood-feeding stages but also those expressed by infective L3s in the early stages of infection. Challenges for the future include: exploiting the expanding genome information for antigen discovery, use of different recombinant protein expression systems, formulation with new adjuvants, and novel methods of field testing vaccine efficacy.

Chronic stress in sheep: assessment tools and their use in different management conditions

Chronic stress occurs when animals are unable to deal with a persistent stressor with species-typical responses, or when several stressors are present concurrently. Chronic stress is most frequently considered in intensive systems, but it may also be a welfare concern for extensively managed species, such as the sheep. Here we review behavioural and physiological responses of sheep to experimentally induced chronic stressors to determine relevant indicators of chronic stress. Neuroendocrine responses to chronic stress are difficult to interpret because initial responses are followed by an apparent normalisation. Thus, cortisol or catecholamines may be at or below pre-stress levels during chronic stress, but this varies with different stressors. Chronic stress can also affect reproductive function, impair body and wool growth and meat quality, reduce immune function, and is associated with greater parasite burdens in sheep. Chronic stress induces alterations in behaviour patterns, particularly activity and feeding, and circadian rhythms of behaviour. Stereotypic behaviours, however, are infrequent in sheep and may occur only in experimental conditions of social isolation. Behavioural and physiological data suggest that rough handling and sheepdogs may be sources of chronic stress for sheep. Social subordination and weaning also act as chronic stressors, leading to higher parasitism in these animals and a greater response to additional stressors. Lameness and parasitism are associated with physiological and behavioural responses indicating that these are severe forms of chronic stress in sheep. It is unclear whether environmental stressors, such as weather and food availability, induce chronic stress in sheep. Under-nutrition may, however, be a welfare concern through its impact on lamb survival. The existence of many sources of chronic stress in the management of sheep suggests that the welfare of this species requires more attention than it has currently received.

Induction of protective immunity to Trichostrongylus colubriformis in neonatal merino lambs

The premise that any bias of immune reactivity in neonatal lambs towards T-helper (TH)2 responses could benefit the induction of protection against gastrointestinal nematodes was investigated. In two trials, lambs were either trickle-immunised with 2000 infective larvae of Trichostrongylus colubriformis (TcL3), 3 times weekly from the day of birth for 6 weeks or inoculated with a recombinant T. colubriformis 17 kDa antigen in incomplete Freund's adjuvant (IFA). In trial 1, trickle immunised and control neonates challenged at 7 weeks of age had similar worm counts 10 days after challenge, but from 25 days, significant reductions (P<0.01) in mean faecal egg count and worm count in excess of 75% were displayed by the immunised lambs. The results of a second, similar trial, gave 85-91% reductions in parasitism in trickle immunised neonates (P<0.001) and around 50% protection in neonates vaccinated with recombinant 17 kDa antigen. Parasitism in immunised neonates in Trial 2 was significantly reduced (P<0.001) compared to that in 4-month-old animals. Antibody responses in trickle-immunised (protected) and challenge control (infected) neonates were almost exclusively of the IgG1 isotype compared to vaccinated animals which exhibited increased levels of anti-17kD IgG2. Trichostrongylus colubriformis infection, but not specific vaccination, induced interleukin-5 production by mesenteric lymph node cells. The results offer the tantalising prospect of generating protective immunity to gastrointestinal parasites prior to weaning in sheep; this was most effectively generated by viable parasites in this investigation.

Field trials evaluating ivermectin controlled-release capsules for weaner sheep and for breeding ewes

OBJECTIVE

To confirm the efficacy of ivermectin released from a controlled-release capsule administered to young sheep and to breeding ewes under field conditions.

DESIGN

Randomised field trials.

PROCEDURE

In each of ten field trials 25 weaned lambs were treated with ivermectin controlled-release capsules and 25 remained untreated. Eight similar field trials were conducted using adult ewes. Efficacy against infections of gastrointestinal nematodes was assessed by faecal egg counts and faecal larval culture. Body weights were recorded and faecal soiling of the breech wool (dags) was assessed.

RESULTS

Nematode faecal egg counts in the two groups were not different (P = 0.13) before treatment in the weaner trials or before treatment in the ewe trials (P = 0.49), but thereafter eggs in the untreated sheep persisted, whereas counts in sheep given capsules were negligible (P < or = 0.01). In the weaner trials, dag scores for the two groups were not different at the start of the trials (P = 0.18) but at the end, untreated sheep had significantly more dags (P = 0.04) than treated sheep. In the ewe trials, dag scores remained low in both groups. Weaners treated with the capsule gained 1.4 kg (95% CL: 0.7, 3.1) more weight over the 16 week trial period compared to untreated weaners (P = 0.01). Both groups of ewes lost weight as a result of parturition but the mean loss by week 16 was greater for untreated (3.7 kg) (95% CL: -5.1, -2.2) than for treated ewes (1.8 kg) (95% CL: -3.3, -0.4). The mean change in ewe body weight for the two groups was however not significant (P = 0.07). Differentiation of nematode larvae recovered from cultures of faeces from untreated animals indicated that the capsules were effective against the common parasites of sheep.

CONCLUSION

The capsule was efficacious against gastrointestinal nematodes judging from faecal egg counts. It has the potential to significantly reduce contamination of pasture with nematode eggs. Treated weaners had less dags for 16 weeks and gained more weight than untreated weaners.

Some relationships between age, immune responsiveness and resistance to parasites in ruminants

In the Australian livestock industries, susceptibility to infectious diseases is generally greater in young than in mature ruminants. The increased susceptibility is manifest as respiratory and intestinal infections (viral and bacterial) of calves, as well as fleece rot, flystrike and, especially, gastrointestinal parasitic infestations of young sheep. Lower resistance to infectious disease in young ruminants appears to be due largely to immunological hyporesponsiveness, and is not simply a consequence of their not having been exposed sufficiently to pathogens to develop active immunity. Young sheep have significantly lower proportions of CD4+ and CD8+ lymphocytes, but similar proportions of T19+ and B lymphocytes in blood, lymph and skin compared with mature sheep. Blood lymphocytes from young sheep produce less interferon-gamma in culture and young sheep invariably mount smaller antibody responses than do mature animals. Taken together, these findings begin to explain why young ruminants are more susceptible to infectious diseases in general, and to gastrointestinal parasites in particular, when compared to mature animals. Haematological markers of disease resistance, the prevalence of non-selected diseases and immune responses to vaccination were examined in the internal parasite-resistance flocks in Armidale NSW and the fleece rot/flystrike selection flocks at Trangie NSW. Any programme that seeks to improve resistance to parasitic or any other disease should have the capacity to make contemporary measurements of resistance to other diseases which are important in, or threaten, the production system.

Effects of weaning, supplementation and gender on acquired immunity to Haemonchus contortus in lambs

This study was designed to investigate whether delaying the age of weaning, or feeding a protein-rich supplement alters the rate at which lambs develop immunity to Haemonchus contortus and whether there is any interaction between nutrition, stress of weaning, and gender and the development of this immunity. Ninety-six Merino lambs were allocated to one of four treatment groups: supplemented-unweaned; supplemented-weaned; unsupplemented-unweaned; unsupplemented-weaned. There were approximately similar numbers of male and female lambs in each group. Supplemented lambs received 80 g/head/day of a protein-rich pellet from 16 to 23 weeks of age. Over the same period the lambs were drenched with 300 H. contortus larvae twice per week. Faecal worm egg counts were determined every week, and PCV and liveweight every 2 weeks for each lamb. Neither weaning nor sex had any effect on PCV (P > 0.05) but from day 50 after the start of infection, the decline in PCV was more pronounced in unsupplemented than in supplemented lambs. Faecal worm egg counts were higher (P < 0.001) in unsupplemented-weaned than in supplemented-weaned lambs and in females when compared with castrates (P < 0.03). There was a weaning x supplementation x age interaction (P < 0.03) with unsupplemented-weaned lambs developing a higher faecal egg count than supplemented-weaned lambs. There was also a significant (P < 0.02) sex x weaning x age interaction with weaned-female lambs having a higher faecal egg count than weaned-castrate lambs; egg counts increased more rapidly in unweaned-female lambs than in weaned-female lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-dependent immune response in Merino sheep

The numerical and functional attributes of populations of lymphocytes were compared in the blood, lymph and skin of young and mature sheep. Young sheep, four to eight months old, had a lower proportion of CD4+ cells in blood, lymph and skin than mature sheep three to six years old. In contrast, B cells and T19+ cells were as prevalent or more prevalent in young sheep as in mature sheep. Blood lymphocytes from young sheep, cultured in vitro produced less interferon-gamma, both spontaneously and in the presence of concanavalin A than did lymphocytes from older sheep. The serum antibody responses of adult sheep to the T cell-independent antigen Brucella abortus lipopolysaccharide (LPS) were greater over a range of antigen doses, suggesting that an apparent excess of antigen could not overcome the relative immune deficiency of young sheep. The adjuvant Quil A corrected the depressed antibody response of young sheep to B abortus LPS, but dextran sulphate did not. The skin contact hypersensitivity of mature sheep to dinitrochlorobenzene was greater. However, the T cell phenotypes present in infiltrates of lymphocytes elicited by the intradermal injection of tetanus and diphtheria, but not tuberculin antigens, were comparable for the two age groups. The capacity of Quil A to raise the antibody responses of both young and mature sheep to a similar titre suggests that it may be possible to overcome the immunological hyporesponsiveness that may contribute to the disease susceptibility of young sheep.

Changes in liveweight and behaviour of alpaca dams and offspring following weaning

The effects of offspring sex, weight, age, and level of interaction with the dam on responses to weaning were examined to assist in the development of a weaning protocol for alpacas. In the first study, preand post-weaning activities, and weight change over Days -12-0,0-7 and 7-16 with respect to weaning, were recorded for 20 dam-offspring (hembra-cria) pairs aged 81-200 days. Pre-weaning changes in dam and offspring weights were positively related (P<0.05). Although heavier crias tended to be found closer to their dams than lighter crias (P<0.05) no additional effect of age on the dam-offspring relationship was found. Following weaning, cria growth rates were low over Days 0-7 but improved over Days 7-16, and hembra weight change followed the same pattern. Over Days 0-2, grazing and sitting activities of hembras and crias were replaced by standing and walking along paddock fencelines, although by Day 2 fenceline activities had decreased (P<0.05). Crias which were more frequently observed at fencelines had lower post-weaning growth rates (P<0.05). In the second study, pre-weaning sucking behaviour, and weight change over Days -30-0, 0-8 and 8-16 with respect to weaning, were recorded for 19 hembra-cria pairs aged 124-160 days. During 10 hours of observation on Days -5 and -4, the total duration of sucking by individual crias varied from 0-18 minutes, and the mean +/- SEM duration of sucking was 1.94 +/- 0.113 minutes. Cria sucking behaviour was positively related to growth rate prior to and weight at weaning (P<0.05). As in the first study, pre-weaning changes in dam and offspring weights were positively related (P<0.05). Following weaning, growth rates of the crias were depressed and the hembras lost weight over Days 0-8 and 8-16. The changes in growth rate and behaviour in Studies 1 and 2 indicated that weaning can be stressful for hembras and crias. However, there was no evidence from either study that pre-weaning behavioural or physical characteristics were related to the changes.

Epidemiology of Ostertagia ostertagi in cow-calf herds in the southeastern USA

Ostertagia ostertagi is commonly found in the brood cow and nursing calf in the southeastern USA, this information being derived from fecal egg counts, coproculture and necropsy results; however, clinical disease and large burdens of this parasite are rarely reported. Fecal egg counts in brood cows are routinely low and are generally reported to be 10 eggs per gram of feces (EPG) or less. Nematode egg counts in spring-born calves are also generally low prior to weaning; they increase steadily during the spring and summer and peak from late summer to fall weaning. That egg counts in spring-born calves are low for several months after birth is probably a reflection of minimal grazing activity. It appears that Ostertagia ostertagi may be of equal or less importance than other nematode genera for spring-born calves in the southeastern USA. The role that Ostertagia ostertagi plays in fall-born calves or in year-round calving herds has not been adequately investigated. Also, the role that the adult cow plays, with low egg counts and small Ostertagia ostertagi burdens, in contamination of pasture is not understood during either lactation or dry periods. Treatment of beef calves prior to, or at weaning can reduce contamination and transmission of gastrointestinal parasites on pastures which may be subsequently grazed by these or other weaned calves. Data on parasite population dynamics from tracer calf studies in cow-calf herds in the southeastern USA have identified peak periods of transmission and incidence of specific genera or stages. This information, in conjunction with routinely used cattle production and management practices such as time of calving, should provide means to more accurately define optimal timing for strategic parasite treatment programs and their overall effect on beef production in the southeastern USA.

Post natal ontogeny of immunological responsiveness in Merino sheep

Sheep in five age groups (two weeks, 10 weeks, 18 weeks, six months and four years old) were immunised systemically, twice, with ovalbumin or Brucella abortus (live or killed) and antibody responses in blood were measured. The animals were also infected with the nematode parasites Trichostrongylus colubriformis and Haemonchus contortus and faecal egg counts and serum antibody responses to larval antigens were measured. The experiments were designed so that, as far as possible, the effect of age per se could be dissociated from the combined effects of age and prior exposure to antigen. The effects of the age of sheep were more marked for antibody responses to Brucella abortus lipopolysaccharide than to ovalbumin. Older animals had much greater resistance to infection with internal parasites, as shown by the magnitude of the faecal egg count. In contrast to older lambs, neonatal lambs (infected with H contortus at two weeks old) had consistently declining concentrations of anti-H contortus antibody in their serum, mounted no detectable autogenous anti-H contortus antibody response in blood and appeared to develop no resistance to the parasite. Post natal ontogeny of immune responses was different for the various antigens/pathogens.