Whole genome sequencing reveals signals of adaptive admixture in Creole cattle

The Creole cattle from Guadeloupe (GUA) are well adapted to the tropical environment. Its admixed genome likely played an important role in such adaptation. Here, we sought to detect genomic signatures of selection in the GUA genome. For this purpose, we sequenced 23 GUA individuals and combined our data with sequenced genomes of 99 animals representative of European, African and indicine groups. We detect 17,228,983 single nucleotide polymorphisms (SNPs) in the GUA genome, providing the most detailed exploration, to date, of patterns of genetic variation in this breed. We confirm the higher level of African and indicine ancestries, compared to the European ancestry and we highlight the African origin of indicine ancestry in the GUA genome. We identify five strong candidate regions showing an excess of indicine ancestry and consistently supported across the different detection methods. These regions encompass genes with adaptive roles in relation to immunity, thermotolerance and physical activity. We confirmed a previously identified horn-related gene, RXFP2, as a gene under strong selective pressure in the GUA population likely owing to human-driven (socio-cultural) pressure. Findings from this study provide insight into the genetic mechanisms associated with resilience traits in livestock.

Mixed Grazing and Dietary Supplementation Improve the Response to Gastrointestinal Nematode Parasitism and Production Performances of Goats

Small ruminants are very affected by gastrointestinal nematode (GIN) parasitism worldwide. The improvement of the host protective response and the reduction of the probability of contact between hosts and parasites appear as very promising strategies. The objective of this study was to evaluate the effect of a combination of two components of these two strategies on natural GIN infection and production performances of Creole goat kids: dietary supplementation and a rotational mixed grazing system. One hundred and twenty weaned Creole kids and six Creole heifers were divided into four experimental batches: Splus (supplemented) vs. Szero (non-supplemented) × Mixed grazing (kids associated with heifers) vs. Control (kids alone), and grazing plots of forage grasses were balanced for live weight (LW) in both species. The feed intake, blood, and parasitological parameters and production performances between 3 and 11 months of age were monitored. The fecal egg count (FEC) was significantly lower and the packed cell volume (PCV) significantly higher in the Mixed grazing groups. No effect of supplementation was observed for FEC. In contrast, PCV, body condition score, and live weight were significantly higher in supplemented animals whatever the groups. Mixed grazing system and supplementation had significant effects on the slaughter parameters (P < 0.05), but there was no significant interaction. Our results suggested that the advantage driven either by mixed grazing or dietary supplementation on kids' performances would be equivalent, and the combination of both would improve the animal performances.

Mixed grazing of adult goats and cattle: Lessons from long-term monitoring

Mixed grazing of breeding goats and cattle (goats to cattle ratio: about 50 %, based on metabolic weight) was monitored for 2 years on a rotational pasture with the two species grazing together, then for 5 years with cattle grazing immediately after goats. For both modalities, the level of goat parasite infection was not significantly different from that of the control groups. Nevertheless, the association allowed a slight improvement in kid growth and goat productivity, probably in relation to a better food quality. The response of adult goats to mixed grazing is therefore very different from that previously obtained with kids post-weaning. The question of the relationship between heterogeneity of pastures, knowledge of their environment, grazing behaviour of adult goats and risk of infection with gastrointestinal nematodes requires further investigation.

Dynamic transcriptomic changes of goat abomasal mucosa in response to Haemonchus contortus infection

Gastrointestinal nematode (GIN) infections are one of the major constraints for grazing sheep and goat production worldwide. Genetic selection for resistant animals is a promising control strategy. Whole-transcriptome analysis via RNA-sequencing (RNA-seq) provides knowledge of the mechanisms responsible for complex traits such as resistance to GIN infections. In this study, we used RNA-seq to monitor the dynamics of the response of the abomasal mucosa of Creole goat kids infected with Haemonchus contortus by comparing resistant and susceptible genotypes. A total of 8 cannulated kids, 4 susceptible and 4 resistant to GIN, were infected twice with 10 000 L3 H. contortus. During the second infection, abomasal mucosal biopsies were collected at 0, 8, 15 and 35 days post-infection (dpi) from all kids for RNA-seq analysis. The resistant animals showed early activation of biological processes related to the immune response. The top 20 canonical pathways of differentially expressed genes for different comparison showed activation of the immune response through many relevant pathways including the Th1 response. Interestingly, our results showed a simultaneous time series activation of Th2 related genes in resistant compared to susceptible kids.

Transcriptome variation in response to gastrointestinal nematode infection in goats

Gastrointestinal nematodes (GIN) are a major constraint for small ruminant production. Due to the rise of anthelmintic resistance throughout the world, alternative control strategies are needed. The development of GIN resistance breeding programs is a promising strategy. However, a better understanding of the mechanisms underlying genetic resistance might lead to more effective breeding programmes. In this study, we compare transcriptome profiling of abomasal mucosa and lymph node tissues from non-infected, resistant and susceptible infected Creole goats using RNA-sequencing. A total of 24 kids, 12 susceptible and 12 GIN resistant based on the estimated breeding value, were infected twice with 10,000 L3 Haemonchus contortus. Physiological and parasitological parameters were monitored during infection. Seven weeks after the second infection, extreme kids (n = 6 resistant and 6 susceptible), chosen on the basis of the fecal egg counts (FEC), and 3 uninfected control animals were slaughtered. Susceptible kids had significantly higher FEC compared with resistant kids during the second infection with no differences in worm burden, male and female worm count or establishment rate. A higher number of differentially expressed genes (DEG) were identified in infected compared with non-infected animals in both abomasal mucosa (792 DEG) and lymph nodes (1726 DEG). There were fewer DEG in resistant versus susceptible groups (342 and 450 DEG, in abomasal mucosa and lymph nodes respectively). ‘Cell cycle’ and ‘cell death and survival’ were the main identified networks in mucosal tissue when comparing infected versus non-infected kids. Antigen processing and presentation of peptide antigen via major histocompatibility complex class I were in the top biological functions for the DEG identified in lymph nodes. The TGFβ1 gene was one of the top 5 upstream DEG in mucosal tissue. Our results are one of the fist investigating differences in the expression profile induced by GIN infection in goats.

Goats worm burden variability also results from non-homogeneous larval intake

For small ruminants, Gastrointestinal Nematodes (GINs) are responsible for severe economic losses and they are also an animal welfare problem. GIN use their host to reproduce and disperse eggs on the pasture, from where they can re-infect another animal. The high density of hosts on the pasture and the extreme tolerance of GIN to environmental constraints make GIN eradication almost impossible. In addition, significant resistance to anthelmintic treatment requires sustainable and integrated management to maintain the health and financial well-being of livestock farming. In this context, models of the complex interactions between host, GIN and environment can help us to design long term optimal management strategies. To build such models, quantitative information is needed but are generally very challenging to collect. In this article, we focus on the number of ingested larvae per animal, which we propose to characterise by using a simulation framework based on the estimation of the spatial distribution of the host over time. Our framework allows us to show that worm burden individual variation is not only explained by the host’s genetics, as is often the case, but is also a result of the grazing spatial process.

A user-friendly and scalable process to prepare a ready-to-use inactivated vaccine: the example of heartwater in ruminants under tropical conditions

The use of cheap and thermoresistant vaccines in poor tropical countries for the control of animal diseases is a key issue. Our work aimed at designing and validating a process for the large-scale production of a ready-to-use inactivated vaccine for ruminants. Our model was heartwater caused by the obligate intracellular bacterium Ehrlichia ruminantium (ER). The conventional inactivated vaccine against heartwater (based on whole bacteria inactivated with sodium azide) is prepared immediately before injection, using a syringe-extrusion method with Montanide ISA50. This is a fastidious time-consuming process and it limits the number of vaccine doses available. To overcome these issues, we tested three different techniques (syringe, vortex and homogenizer) and three Montanide ISA adjuvants (50, 70 and 70M). High-speed homogenizer was the optimal method to emulsify ER antigens with both ISA70 and 70M adjuvants. The emulsions displayed a good homogeneity (particle size below 1 μm and low phase separation), conductivity below 10 μS/cm and low antigen degradation at 4 °C for up to 1 year. The efficacy of the different formulations was then evaluated during vaccination trials on goats. The inactivated ER antigens emulsified with ISA70 and ISA70M in a homogenizer resulted in 80% and 100% survival rates, respectively. A cold-chain rupture assay using ISA70M+ER was performed to mimic possible field conditions exposing the vaccine at 37 °C for 4 days before delivery. Surprisingly, the animal survival rate was still high (80%). We also observed that the MAP-1B antibody response was very similar between animals vaccinated with ISA70+ER and ISA70M+ER emulsions, suggesting a more homogenous antigen distribution and presentation in these emulsions. Our work demonstrated that the combination of ISA70 or ISA70M and homogenizer is optimal for the production of an effective ready-to-use inactivated vaccine against heartwater, which could easily be produced on an industrial scale.

Fifteen years later, anthelmintic resistances have dramatically spread over goat farms in Guadeloupe

Faecal egg count reduction tests (FECRTs) were performed on 21 goat farms in Guadeloupe (FWI). Anthelmintic resistance (AR) to netobimin (benzimidazole) was found in all 15 herds in which it was tested. AR to ivermectin (avermectin) and levamisole (imidazothiazole) were also very largely spread (14 out of 17 farms and 7 out of 9 farms, respectively). AR to the final moxidectin (milbemycin) released was already present in 2 out of 9 farms in which it was tested. Haemonchus was the dominant genus of gastrointestinal nematodes and was more frequently found to be resistant to netobimin, ivermectin and moxidectin than Trichostrongylus, the latter appeared to be more often resistant to levamisole. A first survey 15 years ago revealed only AR to benzimidazoles and one suspected case of AR to ivermectin.

Simulated selection responses for breeding programs including resistance and resilience to parasites in Creole goats

The Creole goat is a local breed used for meat production in Guadeloupe (French West Indies). As in other tropical countries, improvement of parasite resistance is needed. In this study, we compared predicted selection responses for alternative breeding programs with or without parasite resistance and resilience traits. The overall breeding goal included traits for production, reproduction, and parasite resilience and resistance to ensure a balanced selection outcome. The production traits were BW and dressing percentage (DP). The reproduction trait was fertility (FER), which was the number of doe kiddings per mating. The resistance trait was worm fecal egg count (FEC), which is a measurement of the number of gastro-intestinal parasite eggs found in the feces. The resilience trait was the packed cell volume (PCV), which is a measurement of the volume of red blood cells in the blood. Dressing percentage, BW, and FEC were measured at 11 mo of age, which is the mating or selling age. Fertility and PCV were measured on females at each kidding period. The breeding program accounting for the overall breeding goal and a selection index including all traits gave annual selection responses of 800 g for BW, 3.75% for FER, 0.08% for DP, -0.005 ln(eggs/g) for FEC, and 0.28% for PCV. The expected selection responses for BW and DP in this breeding program were reduced by 2% and 6%, respectively, compared with a breeding program not accounting for FEC and PCV. The overall breeding program, proposed for the Creole breed, offers the best breeding strategy in terms of expected selection responses, making it possible to improve all traits together. It offers a good balance between production and adaptation traits and may present some interest for the selection of other goat breeds in the tropics.

Effects of single or trickle Haemonchus contortus experimental infection on digestibility and host responses of naïve Creole kids reared indoor

The objective of this study was to compare the effects of the type of Haemonchus contortus experimental infection (trickle infection, TI versus single infection, SI) on feed intake, nutrients digestibility, parasitological and haematological measures, and plasma leptin in Creole kids. The animals were infected over 2 periods (challenge 1 and challenge 2) of 6 weeks each, corresponding respectively to the primary and the secondary infection. Periods prior infection (1 week each) were considered as controls. The primary infection was realized with 35 Creole kids (18.40±3.76 kg BW) housed in individual boxes and fed a hay-based diet. The secondary infection continued with 29 kids (21.90±3.40 kg BW) from the initial 35. A total of 6 kids and 8 kids were slaughtered for measuring nematode burden at the end of the primary and the secondary infection, respectively. Measurements of nutrients digestibility were made at 0, 3 and 5 weeks post-infection for both challenges. Faecal egg count (FEC), blood eosinophilia and packed cell volume (PCV) were monitored weekly. Feed intake (dry matter intake, DMI) and nutrients digestibility were negatively affected by H. contortus infection only during the primary infection. Plasma leptin changed significantly over time (P=0.0002) but was not affected by the infection type. Effect of infection type was observed only on crude protein digestibility during the primary infection, which was lower in the TI group (P<0.01). The overall level of blood eosinophilia was significantly higher in the TI group (P<0.0001) during both challenges. The overall FEC mean was significantly higher in the SI compared with the TI groups, during both challenges (P<0.02). These results were related to the mean female length significantly higher in the SI group compared with the TI group during challenge 1 (P=0.004), and the number of adult nematode significantly lower in the TI group compared with the SI group during the challenge 2 (P=0.05). The results showed that the response of Creole kids to H. contortus experimental infection was in part dependent on the type of experimental infection. Our data suggest that plasma leptin would not be involved in the response of Creole kids against H. contortus infection, as no relationship between its plasma level and the transient reduction in voluntary feed intake observed in both groups during the primary infection was observed.

Effect of dietary supplementation on resistance to experimental infection with Haemonchus contortus in Creole kids

The aim of the present study was to test the effect of dietary supplementation on resistance to experimental infection with Haemonchus contortus in Creole kids. One trial with three replicates involved a total of 154 female kids that were chosen from three successive cohorts of the Creole flock of INRA-Gardel in 2007. The kids were placed into four treatments according to the amount of concentrate they received: G0 (no concentrate and a quality Dichantium spp. hay ad libitum, HAY), G1 (HAY+100g commercial concentrate d(-1)), G2 (HAY+200 g commercial concentrate d(-1)), G3 (HAY+300 g commercial concentrate d(-1)). The G0-G3 groups were infected with a single dose of 10,000 H. contortus third stage larvae (L(3)) at Day 0 (D0). Each infected group was comprised of one half resistant and one half susceptible genetically indexed kids. The average breeding values on egg excretion at 11 months of age were distant of 0.70, 0.65, 0.61 and 0.61 genetic standard deviations in G0, G1, G2 and G3, respectively. The faecal egg count (FEC), packed cell volume (PCV), eosinophilia (EOSI) and dry matter intake (DMI) indices were monitored weekly until 42 days post-infection. Enzyme-linked immunosorbent assay was carried out on serum samples to determine the level of IgA anti-H. contortus L(3) crude extracts and adult excretion/secretion products (ESP). The 10,000 L(3) dose received by the kids induced a severe infection: 8000 eggs per gram at the FEC peak, a PCV less than 15% and mortality. Interestingly, the supplemented animals in G3 showed a higher level of EOSI but a lower level of IgA anti-L3 and IgA anti-ESP than non-supplemented animals (G0). Resistant and susceptible kids had significantly different FEC variations within the groups. Susceptible kids had a 1.6 times higher egg output than resistant kids in G0. This difference was not found in the supplemented groups. The results of this study showed that supplementary feeding improved resistance of Creole kids to H. contortus experimental infection.

Growth performance, carcass quality, and noncarcass components of indigenous Caribbean goats under varying nutritional densities

Studies were conducted to determine the effects of feeding regimens on growth and carcass quality of the Creole goat, a genotype indigenous to the Caribbean. Forty kids weighing 9.0 +/- 1.2 kg of BW were reared indoors after weaning. Four supplement amounts were compared (10 kids per treatment): the G0 group received the basal diet (tropical forage, 8.8 MJ of ME and 108 g of CP/kg of DM) without concentrate, whereas the G100, G200, and G300 groups were offered 130, 230, and 310 g/d of concentrate (13.6 MJ of ME and 209 g of CP/kg of DM), respectively, in addition to the basal diet. The kids were slaughtered according to the standard procedure at 22 to 24 kg of BW for assessment of carcass traits and meat quality. Total DMI increased significantly, from 51 to 78 g/kg of BW(0.75), for G0 to G300 kids, whereas their ADG doubled from 42 to 84 g/d (P < 0.01; P < 0.01, respectively). The G:F values reached 125 to 130 for the G200 and G300 diets and were satisfactory compared with literature values. The carcass weight and dressing percentage (P < 0.01) increased from group G0 to G300, from 9 to 13 kg and from 42 to 51%, respectively. The proportions of the different cuts (related to the carcass weight) did not vary by diet. The conformation score increased significantly (P < 0.05) among the 4 groups from an average score of 3.2 to 4.0 (score/5). There was a significant effect (P < 0.01) of supplement amount on the accumulation of internal fat tissues: the kidney fat weight increased from 113 to 253 g from the G0 to the G300 group. Regardless of the feeding level and amount of internal fat, the carcasses had an acceptable fat cover score, which remained less than 2.6 (score/5). A significant effect was not observed for the ultimate pH and the main color variables of the meat. The cooking loss and the shoulder DM content varied (P < 0.05) with the supplement amount. By increasing the nutritional density of the diet, it was possible to obtain well-conformed and heavy carcasses, with no excessive fattening. Indigenous Creole goats have potential as meat animals when fed to gain more than 80 g/d. The optimal supplement supply with good-quality grass would be approximately 3.69 MJ of ME/d in our conditions. Further studies are required on meat sensory parameters and fatty acid profiles.

Evaluation of targeted drenching using Famacha© method in Creole goat: Reduction of anthelmintic use, and effects on kid production and pasture contamination

Haemonchus infection was monitored for 2 years (six kidding periods) in a Creole goat flock grazing under oceanic-tropical climate. Two hundred and thirty individual does were involved from late pregnancy to weaning. Anaemia diagnoses using Famacha method and packed cell volume (PCV) were compared. The best agreement (Kappa=0.33) was found if anaemia was declared when PCV values fell to 16 or below and Famacha score was 4 or 5. Drenching policy according to Famacha method was compared to systematic drenching policy. Using the Famacha method allowed a dramatic decrease in anthelmintic use during the periparturient period (0.57 individual dose instead of three doses for the control). The proportion of the nematode population on the pasture not derived from previously-treated goats (in refugia) was estimated to about 79% (65-90%) of the pasture contamination derived from the Famacha group. On the average, goats which needed to be drenched produced less than the control or undrenched goats (kid average daily gain was decreased by about 15%). The repeatability of the need for drenching individual does was estimated to 0.41. The older goats or the goats in poorer body condition at kidding needed more drenching than the younger animals and the animals in good body condition. Consequently the Famacha method may be used as an additional tool for the culling management.

Genetic variability in resistance to gastro-intestinal strongyles during early lactation in Creole goats

The study was undertaken in a Creole goat flock at INRA-Gardel in Guadeloupe, to evaluate the opportunity to use artificial selection as a means of controlling gastro-intestinal infection during early lactation. The flock grazed all year on Digitaria decumbens pastures. Faecal and blood samples were taken from kids at 11 months of age and from does at kidding before drenching (week 0) and at weeks 4 and 6 after kidding. Faecal egg counts (FEC) were estimated using a modified McMaster method. Blood samples were used to determine packed cell volume (PCV) and eosinophil concentrations (EOS) values. Haemonchus contortus, Trichostrongylus colubriformis and Oesophagostomum columbianum were the main strongyle species identified in faecal cultures. The data came from 1092 litters obtained from 688 does sired by 142 bucks and 413 dams. Variance and covariance components for genetic and residual effects were estimated with multivariate animal models using the restricted maximum likelihood VCE package. Repeatability and overall heritability for FEC during the post-partum period were 0·17 and 0·10±0·02. The genetic correlations between FEC and PCV were −0·56±0·11 at 4 weeks after kidding and −0·79±0·13 at 6 weeks after kidding. The genetic correlations between FEC and EOS were 0·37±0·15 at 4 weeks after kidding and 0·68±0·17 at 6 weeks after kidding. Hence, does that contributed least to pasture contamination during the postpartum period also had low EOS and high PCV breeding values. The genetic correlations between FEC measured at 11 months of age and FEC during periparturient period ranged from 0·57±0·12 to 0·76±0·16. Therefore, breeding goats for increased resistance during the post-weaning period will lead to a less marked and less persistent rise in doe FEC during early lactation. The epidemiological implications of this selection have to be quantified in terms of lower pasture contamination, lower kid parasitism, and higher milk production of does.

Impact on productivity of peri-parturient rise in fecal egg counts in Creole goats in the humid tropics

The control of gastrointestinal nematodes requires an understanding of their epidemiology so that particular parasite stages can be targeted. Dam infection during early lactation is one example of this in ruminant nematode infections. The existence of the peri-parturient relaxation in immunity and its impact on productivity were examined in a Creole goat flock from Guadeloupe, exposed to mixed natural infection (predominantly Haemonchus contortus and Trichostrongylus colubriformis). A total of 1,511 l were obtained from 909 does resulting from 463 dams and 150 sires. Fecal and blood samples were collected at kidding before anthelmintic drenching, 4 and 6 weeks after kidding. The traits analyzed were logarithm transformed fecal egg counts (FEC), packed cell volume (PCV), and logarithm transformed blood eosinophilia counts (EOS) for does at each sampling point and changes in these during the postpartum period. With the exception of the PCV values measured at kidding, lactating does had significantly higher FEC and lower PCV than control dry does at every sampling point. Geometric means of FEC in lactating does were 819 +/- 174, 677 +/- 146 and, 699 +/- 160 eggs per gram (EPG) at kidding, 4 and 6 weeks after kidding respectively. Geometric means of FEC in dry does were 187 +/- 57, 89 +/- 28, 133 +/- 43 at these time points, respectively. EOS differences were not consistent between groups and probably not specific enough for variations in Creole goats' peri-parturient rise to be discussed. As does aged, their egg output decreased and primiparous does always had greater egg output than multiparous ones. Overall, does' FEC at 4 weeks after kidding decreased by 1.3% each year. The higher the litter size, the higher the FEC at kidding and inverse applied for PCV measurements. Does that stopped lactating had significantly lower FEC and higher PCV values than lactating does with low milk yields. Higher infection rates during early lactation in Creole goats were recorded in does with lower maternal ability assessed by the average daily weight gain of kids between 10 and 30 days of age. Kids from dams with higher FEC (i.e. >600 EPG higher than corresponding does) had 17% lower average daily weight gain between 30 and 70 days postpartum and were approximately 1 kg lighter at weaning than kids from dams with lower FEC. Thus, it is clear that a peri-parturient rise in FEC exists in Creole goats. By controlling the intensity of this peri-parturient rise in FEC, herd health and productivity could be substantially improved.

A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential.

Mortality of Creole kids during infection with gastrointestinal strongyles: a survival analysis

Mortality due to strongyles infection in small ruminants is a critical component of flock productivity in a tropical climate. In goat production, few experiments have been conducted to estimate the variability of this trait. A survival analysis study was carried out in the Creole experimental flock of INRA-Gardel (Moule, Guadeloupe) to identify management and genetic factors influencing mortality of kids reared at pasture and infected with gastrointestinal strongyles, predominantly Haemonchus contortus and Trichostrongylus colubriformis. Survival curves from 3 and 11 mo of age were analyzed for 837 kids sired by 48 bucks and 250 does. The causes of death were recorded. Mortality due to gastrointestinal strongyles was the variable considered. The flock management included drenchings with levamisole every 8 wk. Fecal egg counts and packed cell volume were regularly measured after 7 wk of natural infection. All but 6.7% of the records were uncensored, with an average failure time of 165 d. The probability of death following gastrointestinal infection was more than three times greater in males than in females. Kids raised by their mother before weaning had a lower (P < 0.05) relative risk of dying than those reared in nursery (0.40 vs. 1). Parity of the dam and litter size effects were not significant. The risk of death was reduced by approximately 80% during the 3 wk that followed a drenching (P < 0.01). Risk decreased by about 25% for each additional kilogram of body weight at weaning. Live weight, fecal egg counts, and packed cell volume all had significant effects on risk of death when introduced as time-dependent covariates in the model (P < 0.0001 for live weight and packed cell volume, and P < 0.01 for fecal egg counts). The estimated genetic variability was small and inaccurate. These results demonstrated that risk of death from gastrointestinal infection could be reduced with appropriate flock management. High infection levels increased the risk of death, but they were not the direct cause. The important mediation of reduced body weight and anemia in likelihood of death is highlighted. More data are needed to better assess the possibility for genetic improvement of viability in Creole kids during gastrointestinal strongyle infection.

Assessment of genetic variability of resistance to gastrointestinal nematode parasites in Creole goats in the humid tropics

Goat production is widespread in the tropics. Goats are very susceptible to gastrointestinal nematode infection, but there is less evidence of their genetic resistance. Genetic resistance of Creole goats to gastrointestinal nematodes has been studied at Guadeloupe in the French West Indies since 1995. The objective of this research was to investigate genetic variation for resistance to gastrointestinal nematode infection, in order to introduce this trait into breeding schemes. Genetic variability was assessed within a Creole experimental flock. Forty-nine sire groups were characterized at weaning and 55 during fattening after weaning. Kids were naturally infected, mainly by Haemonchus contortus and Trichostrongylus colubriformis. Fecal egg counts were determined once at weaning and every 6 and 7 wk after drenching during fattening. Blood samples were collected every 7 wk during fattening for determination of packed cell volume. Live weights were recorded at weaning and at the beginning and middle of every infection period during fattening. Genetic parameters were estimated using the REML for multivariate animal models. The heritability estimate for transformed fecal egg count was 0.37+/-0.06 at weaning. During fattening, it increased from 0.14+/-0.05 at 4 mo to 0.33+/-0.06 at 10 mo. Heritabilities of packed cell volume ranged from 0.10 to 0.33. At weaning, maternal heritability of fecal egg count reached 0.26 and direct heritability 0.20. After 6 mo of age, maternal effects were found to be unimportant for fecal egg count and packed cell volume. Live weights presented significant genetic variability. Genetic relationships between fecal egg counts and live weight in infected pastures were never significant. Genetic correlations between packed cell volume and live weight decreased from 0.47 to 0.10 from weaning to 10 mo of age. These results demonstrated the feasibility of breeding for improved resistance to nematodes in Creole kids.

Genetic variability in resistance of Creole goats to natural infection with trichostrongylids in Guadeloupe

The objective of this study was to show the existence of genetic variability in resistance of Creole goats to natural infection with intestinal nematodes. Four successive cohorts of male and female kids were reared from weaning during 9 months in intensive pangola pastures (stocking rate 1.4 t/ha, regrowth of 21 days, 300 kg N/ ha/year of fertilization). All cohorts considered, 203 offsprings from 13 bucks and 149 goats were used in the experiment. Animals were treated with an oral dose of ivermectin every seven weeks, from 3 to 11 months of age. They were sampled for fecal egg counts (FEC) and packed cell volume (PCV), 6 weeks after drenching, when 6 and 10 months old. Haemonchus contortus and Trichostrongylus colubriformis were the predominant species. Data of one cohort when 6 months of age and another one when 10 months old were not included in calculations because a self-cure occurred during a rainy season. Estimated means of FEC after square-root transformation were 1054 and 711 respectively for 6-month-old and 10-month-old kids. Phenotypic correlations between FEC and PCV were -0.46 (p < 0.001) and -0.29 (p < 0.01) when 6 and 10 months old, respectively. FEC repeatabilities estimated as variance ratio were 0.47 and 0.06 for within-age measures (data recorded at one week interval) and between age measures (6 vs. 10 months) respectively. No sire effect was significant for PCV. Sire effect on FEC was more significant when 6 months old (p < 0.03) than when 10 months old (p < 0.15). Further studies are now being carried out to confirm this genetic determinism of resistance to natural infection with strongyles in Creole goats.

Comparison of methods for counting third stage larvae of gastrointestinal nematodes of small ruminants in tropical pastures

The accuracy and the precision of a simple and reliable technique for the extraction and the counting of third stage larvae densities of gastro-intestinal strongyles of ruminants from pasture samples are assessed in tropical conditions, i.e. for pangola pastures and for the genera of Haemonchus and Trichostrongylus. To separate the larvae from herbage samples, water washings obtained by a centrifuge spin-dryer were put to sediment in disposable plastic bags. The extraction and counting of larvae from sediments were achieved by exhaustion of sediments with repeated sucrose/water interface procedures. The recovery rate of third stage infective larvae (L3) added to the sediment was 79.1% (+/- 9.49%). The accuracy, estimated as recovery rate of L3 added to herbage samples, was 76.5 (+/- 11.31%). The recovery by the sedimentation method was 3.5 times higher than that of a filtering method through a 20 microns sieve. The detection limit was estimated to be 130 L3 kg-1 dry matter. Precision, estimated as the residual standard deviation of duplicate assays, was 1857 L3 kg-1 dry matter (mean 9164 L3 kg-1 dry matter). Results obtained in routine epidemiological surveys of gastro-intestinal strongylosis of small ruminants in West Africa and in the West Indies demonstrated the usefulness of the technique.

Worm population characteristics and pathological changes in lambs after a single or trickle infection with Teladorsagia circumcincta

The regulation of the worm population and of its pathological effects was studied after a single or trickle infection with T. circumcincta. One hundred and twenty lambs, 60 Romanov and 60 Mérinos d'Arles, 3 months old, were distributed in four balanced groups: non-infected (G0), infected with 7000 L3 per animal once and slaughtered after 4 weeks (G14) or 8 weeks (G18), and infected 8 times and slaughtered after 8 weeks (G88). Parasitological, histological, haematological parameters and weight gains were recorded on each animal. Female and artificially nursed lambs had lower worm burdens and egg counts (epg) than males and naturally suckled lambs. No difference in parasitological parameters was seen between the two breeds, but Mérinos lambs infected once, had a higher increase in pepsinogen concentrations than Romanov lambs. In the infected animals, a significant proliferation of mast and eosinophil cells was observed in the abomasum wall. Serum pepsinogen concentrations were significantly higher 3 weeks p.i. and the weight gain was depressed during the first month p.i. The worm population was more numerous and younger in group G14 compared with G18 in which 24% of the worms had been expelled during the second month p.i. The female worms in G18 were longer and had more eggs in utero and higher egg output. After the trickle infection (G88) the take was reduced, female worms were longer with more eggs in vagina (pars ejectrix) and there was a higher variability in the number of eggs (compared with G18 data). The pepsinogen rise was smaller but no specific effect was seen on histological and haematological parameters.(ABSTRACT TRUNCATED AT 250 WORDS)