Congratulations Dr. Vincent Habimana for a successful defending your PhD – Department of Animal, Aquaculture and Range Sciences

Dr. Vincent Habimana pursued his PhD research in the Department of Animal, Aquaculture, and Range Sciences at the College of Agriculture, Sokoine University of Agriculture. His study, “Evaluation of Heat Stress Effects on Milk Yield Traits and Metabolites in Dairy Cattle Reared in the Tanga Region, Tanzania,” demonstrates the potential of integrating physiological, metabolic, and genetic markers to enhance the resilience of dairy cattle under heat stress. By identifying biomarkers and assessing genetic diversity in Tanzanian herds, the research provides practical tools and models for sustainable breeding, improved productivity, and can lead to climate-smart livestock systems in tropical regions.

Heat stress is one of the most pressing challenges to dairy production worldwide, particularly in tropical regions where high temperatures and humidity prevail. In Tanzania, the Tanga region represents a critical case because of its rapidly growing dairy sector, dominated by crossbred cattle that are especially vulnerable to heat stress. Dr. Habimana’s research examined the effects of heat stress on milk yield, composition, physiological responses, and genetic resilience, with the goal of identifying biomarkers of tolerance and developing strategies for genetic improvement to help farmers adapt to climate change.

Heat stress negatively affects feed intake, reproductive efficiency, milk production, and animal welfare. It alters milk components such as fat, protein, and solids-not-fat, while elevating physiological indicators like rectal temperature, respiratory rate, and panting scores. The research objectives, therefore, sought to:

Examine the effects of temperature-humidity index (THI) on milk yield, composition, and physiological traits.
Identify milk metabolites that signal resilience to heat stress.
Assess genetic variation in heat tolerance genes.
Develop quantitative models for evaluating heat stress-tolerant animals.

Four interconnected studies were conducted using Holstein Friesian × Zebu crossbred dairy cows at the Tanzania Livestock Research Institute (TALIRI) in Tanga, together with Ayrshire, Jersey, and indigenous Zebu cattle.

Study 1 measured the effects of THI on milk production and composition across hot and cool seasons.

Study 2 applied high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to quantify milk metabolites—creatinine, citrate, and β-hydroxybutyrate (BHB)—under different THI levels.

Study 3 analyzed genetic variation in heat stress response genes (HSF1 and HSPA6).

Study 4 estimated genetic parameters such as heritability, repeatability, and correlations for milk yield, composition, and physiological traits.

The research study generated strong evidence of heat stress impacts on dairy cattle performance in Tanga:

Physiological responses: As THI increased (76–78 to 82–84), cows exhibited higher core body and rectal temperatures, elevated respiratory rates, and increased panting scores.

Milk yield and composition: Milk yield declined significantly with higher THI, accompanied by increased milk fat percentage and slight reductions in protein, solids-not-fat, and lactose.

Milk metabolites: Creatinine, citrate, and BHB levels decreased as THI rose, confirming their role as reliable biomarkers of heat stress resilience. The HPLC-MS/MS method developed proved accurate and reliable for these measurements.

Genetic diversity: Zebu cattle displayed greater haplotype and nucleotide diversity in heat stress-related genes than crossbreds, confirming their importance as reservoirs of adaptive traits. Gene flow among populations was evident.

Genetic parameters: Heritability of milk yield and composition traits ranged between 0.34–0.41, while repeatability estimates were between 0.60–0.62. Heritability of physiological traits ranged from 0.10–0.61, indicating potential for selective breeding.

The findings have significant implications for dairy development in Tanzania and other tropical regions. Incorporating heat tolerance into breeding programs is essential to sustain productivity under climate stress. Identifying milk metabolites as biomarkers provides practical tools for screening resilient animals, while the observed genetic diversity in Zebu and crossbreds offers opportunities to harness indigenous adaptive traits through structured breeding.

The research study contributes to a deeper understanding of how tropical heat impacts dairy cattle performance at physiological, metabolic, and genetic levels. By integrating field data, metabolomic profiling, and genetic analysis, it provides a holistic framework for climate-smart dairy management. The research also lays a foundation for balanced breeding programs that optimize both productivity and resilience.

Dr. Habimana’s PhD research highlights that heat stress is not only an environmental challenge but also a genetic and metabolic one, requiring integrated solutions. His findings provide actionable insights for policymakers, scientists, and farmers to develop climate-resilient dairy systems in East Africa and all Sub-Saharan countries. By identifying biomarkers, exploring genetic diversity, and developing selection models, the research bridges scientific discovery with practical livestock improvement, setting a benchmark for sustainable dairy production in the face of climate change.

Dr. Habimana’s research work was supervised by Prof. Sebastian W. Chenyambuga (Animal Genetics and Aquaculture expert) and Dr. Athumani S. Nguluma (Animal Breeding and Genetics specialist), both from Sokoine University of Agriculture. This research work produced seven scientific publications, including papers in Frontiers in Genetics, Frontiers in Veterinary Science, MDPI Animals, and the South African Journal of Animal Science, with additional manuscripts submitted and in preparation. These outputs underline the quality, relevance, and international recognition of the work.

List of Scientific Publications from Dr. Vincent Habimana’s PhD research work:

Habimana, V., Ekine-Dzivenu, C.C., Nguluma, A.S., Nziku, Z.C., Morota, G., Chenyambuga, S.W., & Mrode, R. (2023). Genes and models for estimating genetic parameters for heat tolerance in dairy cattle. Frontiers in Genetics, Livestock Genomics Section (https://doi.org/10.3389/fgene.2023.1127175).

Habimana, V., Nguluma, A.S., Nziku, Z.C., Ekine-Dzivenu, C.C., Morota, G., Mrode, R., & Chenyambuga, S.W. (2023). Heat stress effects on milk yield traits and metabolites and mitigation strategies for dairy cattle breeds reared in tropical and sub-tropical countries. Frontiers in Veterinary Science, Animal Nutrition and Metabolism Section. (https://doi.org/10.3389/fvets.2023.1121499).

Habimana, V., Mrode, R., Chenyambuga, S.W., Ekine-Dzivenu, C.C., & Houaga, I. (2025). The role of genetics in understanding and improving heat tolerance in tropical African livestock. Accepted for publication at CABI Animal Science Cases – Case Study ID ASC-2024-0033.

Habimana, V., Nguluma, A.S., Nziku, Z.C., Ekine-Dzivenu, C.C., Morota, G., Mrode, R., & Chenyambuga, S.W. (2024). Heat stress effects on physiological and milk yield traits of lactating Holstein Friesian crossbreds reared in Tanga region, Tanzania. MDPI Animals (https://doi.org/10.3390/ani14131914).

Habimana, V., Nguluma, A.S., Nziku, Z.C., Ekine-Dzivenu, C.C., Morota, G., Mrode, R., & Chenyambuga, S.W. (2025). An HPLC-MS/MS method for the quantification of heat stress-related milk metabolites in milk from Holstein-Friesian cross-bred cows in Tanzania. South African Journal of Animal Science. (https://dx.doi.org/10.4314/sajas.v55i3.07).

Habimana, V., Nguluma, A.S., Nziku, Z.C., Ekine-Dzivenu, C.C., Morota, G., Mrode, R., & Chenyambuga, S.W. Assessing genetic variation and phylogenetic relationship of dairy cattle breeds reared in Tanga region, Tanzania using HSF1 and HSPA6 genes responsible for heat tolerance. Submitted to the East African Journal of Science, Technology and Innovation (https://eajsti.org/index.php/EAJSTI/authorDashboard/submission/1348)

Habimana, V., Ekine-Dzivenu, C.C., Nguluma, A.S., Nziku, Z.C., Morota, G., Chenyambuga, S.W., & Mrode, R. Estimation of genetic parameters for physiological and milk production traits of Holstein Friesian crossbreds reared in Tanga region, Tanzania. Manuscript in preparation.

Dr. Vincent Habimana, with some of the Viva Voce panelists, was congratulated by the Chairman of the Panel, Prof. Sharadhuli I. Kimera

Dr. Vincent Habimana was congratulated by the Head of the Department of Animal, Aquaculture and Range Sciences, Prof. Anthony Z. Sangeda, who was also a Viva Voce panelist member