Haemonchosis Susceptibility Factors: Age, Sex, and Hematological Markers in Goats

Last Updated: January 17, 2026
Estimated reading time: ~6 minutes
Word count: 1330

Effective management of parasitic gastroenteritis requires more than just knowing which parasite is present; it requires a deep understanding of the host’s intrinsic risk profile. Haemonchosis susceptibility factors vary significantly across a herd, influenced by the animal’s age, sex, and physiological maturity. By identifying which demographic groups are most vulnerable, veterinarians and producers can stratify their flocks, applying intensive care to high-risk individuals while sparing resistant ones from unnecessary treatment.

This educational summary dissects the specific host factors that determine the severity of Haemonchus contortus infection in Jamunapari and Sirohi goats. Beyond the external influence of seasons, this study provides critical data on how age groups differ in their immune competence, why biological sex influences parasite burdens, and how hematological markers like Packed Cell Volume (PCV) serve as reliable indicators of disease progression.

• Kids aged 3–6 months represent the most vulnerable demographic due to immature immune systems and weaning stress.
• Females generally exhibit higher infection rates than males, independent of the lactation spike.
• Hemoglobin and PCV show a strong negative correlation with worm burden, validating their use as diagnostic markers.
• Eosinophil counts are a variable indicator of resistance and do not always correlate with lower egg counts in all breeds.
• Acquired immunity develops progressively, with adult animals showing significantly lower Faecal Egg Counts (FEC) than juveniles.

Host Factors Influencing Haemonchus Infection Dynamics

Age-Dependent Susceptibility Patterns

The development of immunity against gastrointestinal nematodes is a slow process in ruminants, often taking months or even years to fully mature. This study categorized goats into specific age groups (0–3, >3–6, >6–9, >9–12 months, and adults) to map the trajectory of susceptibility. The data revealed a clear “window of vulnerability” in young animals, particularly those recently weaned and transitioning to grazing.

“The incidence of H. contortus infection was found to be highest in 9-12 m for both Jamunapari (5.61±0.07 egg/gm) and Sirohi (5.89±0.21) goats. Lowest intensity of infection was observed in 0-3 m in Jamunapari” (Agrawal, 2009, p. 79).

While very young kids (0–3 months) often showed lower counts likely due to limited grazing (and thus limited larvae intake), the intensity surged in the post-weaning phase. The study noted that as animals aged into adulthood, their Faecal Egg Counts (FEC) generally stabilized or declined relative to the larval challenge, indicative of acquired immunity. However, the period between 3 and 12 months remains critical. During this phase, the animal is biologically capable of hosting worms but immunologically immature, leading to high contamination rates. For students, this distinction is vital: “low exposure” in neonates must not be confused with “resistance.”

Student Note / Exam Tip: Acquired immunity to Haemonchus is age-dependent; kids aged 3–12 months are at peak risk because they graze actively but lack a fully developed immune response.

Age Group	Jamunapari Incidence (%)	Sirohi Incidence (%)	Vulnerability Context
0–3 months	4.07	0.00	Low Exposure (Milk fed)
>3–6 months	18.75	3.08	Weaning Stress
>6–9 months	32.23	38.24	Rising Grazing Intake
>9–12 months	41.83	25.00	High Exposure/Developing Immunity
Adult	58.28	39.07	Established Population

Fig: Age-wise incidence of Haemonchus contortus infection (Reformatted from Agrawal, 2009, Table 3).

Professor’s Insight: In exam questions regarding “highest prevalence,” adults often show higher rates of infection (prevalence) due to chronic exposure, but young animals typically suffer higher intensity (clinical disease) and mortality.

Biological Sex and Infection Intensity

The interplay between sex hormones and immune function creates distinct patterns of parasitic susceptibility. This thesis analyzed infection rates in male and female goats across both breeds. The findings corroborated the general parasitological consensus that females are often more susceptible to nematode infections, a trait likely linked to the physiological demands of reproduction and hormonal modulation of the immune system.

“The analysis of sex wise grouped data revealed that in either breed the percentage infection was more in females as compared to males… 45.20 and 37.93 percent in Jamunapari and Sirohi breed, respectively” (Agrawal, 2009, p. 76).

While the “peri-parturient rise” explains susceptibility during lactation, the study found higher infection rates in females even when analyzing general flock data. Males (bucks) consistently demonstrated lower infection percentages and, in some comparisons, lower absolute egg counts. This sexual dimorphism in resistance is an important consideration for flock management. In many production systems, males are culled early for meat, leaving a flock dominated by the more susceptible female demographic. Understanding this bias helps in modeling pasture contamination rates, as the “average” flock immunity is largely determined by the female population.

Student Note / Exam Tip: Females are generally more susceptible to Haemonchus contortus than males, exhibiting higher infection prevalence (e.g., 45.20% vs 38.13% in Jamunapari).

Professor’s Insight: While females are more susceptible, never neglect bucks; a highly infected “super-shedder” breeding buck can contaminate the entire farm as he moves between different herds.

Correlation of Hematological Markers

Diagnosing haemonchosis without faecal analysis relies heavily on hematological markers. Since Haemonchus contortus is a blood-feeding parasite, it directly alters the host’s blood profile. This study performed a rigorous statistical correlation analysis between Faecal Egg Counts (FEC) and key blood parameters: Hemoglobin (Hb), Packed Cell Volume (PCV), and Eosinophil counts (Eos). The results mathematically validated the link between parasite burden and anemia.

“A negative correlation was established between EPG and Hb values. The correlation coefficients in Jamunapari and in Sirohi breed were -0.15 and -0.26, respectively… A similar correlation was observed in Hb and EPG” (Agrawal, 2009, p. 95).

The “negative correlation” means that as egg counts go up, Hb and PCV go down. This relationship was stronger in the Sirohi breed (-0.26 and -0.36) compared to Jamunapari (-0.15 and -0.16). This suggests that in the more resistant Sirohi breed, the blood parameters might be more sensitive indicators of infection status, or that the breed maintains a tighter homeostatic balance until a threshold is breached. For veterinary students, this data underscores why PCV is the “gold standard” for clinical assessment (e.g., in the FAMACHA system). It is a direct measure of the pathology caused by the worm.

Student Note / Exam Tip: There is a significant negative correlation between FEC and PCV/Hb, meaning high parasite loads reliably predict anemia.

Parameter Pair	Jamunapari Correlation (r)	Sirohi Correlation (r)	Interpretation
FEC vs PCV	-0.16	-0.36	Moderate Negative Correlation
FEC vs Hb	-0.15	-0.26	Moderate Negative Correlation
FEC vs Eosinophils	+0.21	-0.003	Variable/Weak Correlation

Fig: Correlation coefficients between Parasitological and Hematological parameters (Reformatted from Agrawal, 2009, Table 17).

Professor’s Insight: Note the difference in Eosinophil correlation between breeds. In Jamunapari, high worms meant high eosinophils (active response), but in Sirohi, there was almost no correlation, suggesting different immune strategies.

Eosinophils: A Complex Indicator

Eosinophilia (increased eosinophils in blood) is classically taught as a sign of parasitic infection. However, this study revealed that its reliability as a marker for resistance is complex and breed-dependent. While Jamunapari goats showed a positive correlation (r=0.21) between egg counts and eosinophils—suggesting the immune system was actively “chasing” the infection—Sirohi goats showed effectively zero correlation (-0.003).

“The eosinophil count in infected goats increased with increase in FEC only in Jamunapari goats… Contrary to it no significant change was observed in Sirohi breed” (Agrawal, 2009, p. 95).

This discrepancy challenges the simplified notion that “more eosinophils = better resistance.” In the Sirohi breed, which is generally more resistant, the lack of systemic eosinophilia despite infection might imply that their defense mechanisms are localized (e.g., within the gut mucosa) or rely on other pathways (like IgA) rather than systemic cellular recruitment. It highlights that peripheral blood eosinophilia is a marker of infection presence or allergic response, but not necessarily a direct measure of an animal’s success in killing the worm.

Student Note / Exam Tip: Peripheral Eosinophilia is an inconsistent marker for resistance; it varies significantly by breed and does not always correlate with lower worm burdens.

Reviewed and edited by the Professor of Zoology editorial team. Aside from direct thesis quotations, the content is educational and original.

Real-Life Applications

• Flock Segregation: Producers should separate weaners (3–6 months) from adults and graze them on the “cleanest” available pastures (those not grazed by adults for months) to minimize larval uptake during their most vulnerable window.
• Clinical Diagnosis: When assessing a herd, veterinarians should prioritize PCV testing (hematocrit) over eosinophil counts, as PCV correlates more reliably with the actual worm burden and clinical status across different breeds.
• Breed Management: In mixed herds, farmers must recognize that Jamunapari goats will likely show clinical anemia sooner than Sirohi goats for the same worm burden, requiring more frequent monitoring.
• Culling Strategies: Since females are the primary demographic and more susceptible, strict culling of does with chronically low PCV or high FEC is the most effective way to improve overall herd genetic resistance.

Key Takeaways

• Haemonchosis susceptibility factors include age (kids are most vulnerable) and sex (females are more susceptible).
• Infection prevalence increases with age due to exposure, but incidence/intensity is often more damaging in young animals (3–12 months).
• PCV and Hemoglobin are robust, negatively correlated markers of infection; as worms increase, these values decrease.
• Sirohi goats show a stronger correlation between FEC and anemia markers compared to Jamunapari, potentially making them easier to phenotype for resistance.
• Peripheral Eosinophilia is not a universal marker of resistance; its expression depends heavily on the breed’s specific immune architecture.

MCQs

1. Which age group in Jamunapari goats recorded the lowest intensity of H. contortus infection?
A) Adults
B) 0–3 months
C) 9–12 months
D) 3–6 months

• Correct: B
• Difficulty: Easy
• Explanation: The study found the lowest infection intensity in the 0–3 month age group, likely because these animals are primarily milk-fed and have minimal exposure to contaminated pasture (Agrawal, 2009, p. 79).

2. What is the statistical relationship between Faecal Egg Count (FEC) and Hemoglobin (Hb) observed in this study?
A) Strong positive correlation
B) Weak positive correlation
C) Negative correlation
D) No correlation

• Correct: C
• Difficulty: Moderate
• Explanation: As the parasite burden increases (higher FEC), the hemoglobin levels decrease due to blood loss, establishing a negative correlation (r = -0.15 to -0.26) (Agrawal, 2009, p. 95).

3. Regarding sex-based susceptibility, which statement is supported by the thesis data?
A) Males were significantly more susceptible than females in both breeds.
B) Females showed higher percentage infection rates than males in both breeds.
C) Sex had absolutely no effect on infection rates.
D) Males showed higher egg counts only during the rainy season.

• Correct: B
• Difficulty: Moderate
• Explanation: The data analysis revealed that females had higher infection percentages (45.20% Jamunapari / 37.93% Sirohi) compared to males (38.13% / 24.90%) (Agrawal, 2009, p. 76).

FAQs

Q: Why are kids aged 3-6 months so susceptible?
A: This period coincides with weaning stress (loss of maternal antibodies from milk) and the initiation of grazing, which drastically increases their intake of infective larvae while their own immune system is still immature.

Q: Can I use eosinophil counts to select resistant goats?
A: It is not recommended as a standalone marker based on this study. The correlation between eosinophils and resistance was inconsistent (positive in Jamunapari, absent in Sirohi), making it less reliable than FEC or PCV.

Q: Which blood parameter is the best indicator of Haemonchosis severity?
A: Packed Cell Volume (PCV). It showed a consistent and significant negative correlation with worm burden across breeds, directly reflecting the blood-sucking pathology of the parasite.

Q: Do males and females require different deworming schedules?
A: Potentially. Since females generally showed higher infection rates (compounded by lactation stress), they act as the primary contaminators of the pasture and often require more intensive monitoring and treatment than bucks.

Lab / Practical Note

Diagnostic Precision: When running correlations between FEC and blood parameters in a lab setting, ensure samples are paired (collected from the same animal at the same time). A delay of even a few days between faecal collection and blood draw can skew results due to the rapid regeneration of blood or sudden maturation of worms.

Sources & Citations

Thesis Citation:
Comparative Study on Immune Response and Resistance Status in Indian Goat Breeds Against Haemonchus contortus Infection, Ms. Nimisha Agrawal, Supervisor: Dr. D.K. Sharma, Central Institute for Research on Goats (CIRG), Makhdoom, Mathura, 2009, pp. 76–80, 94–96.

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Author Box

Author: Ms. Nimisha Agrawal (PhD Candidate/Scholar at time of publication)
Affiliation: Central Institute for Research on Goats (CIRG), Makhdoom, Mathura, India.

Disclaimer: This content is an educational summary of a specific scientific thesis and does not constitute veterinary medical advice.

Reviewer: Abubakar Siddiq

Note: This summary was assisted by AI and verified by a human editor.