Pre- and Postvaccination Effects on Milk Yield and Quality Among Dairy Farms and Lactating Cows in Mekelle, Ethiopia: An Ambispective Study.

Abstract

Background: Vaccination plays a critical role in improving animal health and productivity; however, its impact on milk yield and quality under field conditions remains insufficiently quantified in Ethiopia.

Aims: This study aimed to evaluate the pre- and postvaccination effects on milk yield and quality among medium-dairy farms and lactating cows in Mekelle, Ethiopia.

Methods: An ambispective study design was employed, integrating retrospective data (June 2023-May 2024) and prospective observations (October 2024-May 2025). A total of 156 dairy farms were selected using stratified random sampling for the assessment of vaccination status and milk yield. Additionally, 56 lactating cows were selected for milk quality evaluation, with pre- and postvaccination comparisons. Milk composition analysis was conducted on a subset of 40 cows meeting strict inclusion criteria. Data were analyzed using R software (version 4.3.3).

Major findings: Vaccination coverage reached 78.85% in 2023/24 and 73.08% in 2024/25, mainly against anthrax, blackleg, and lumpy skin disease. Most farmers (80.71%) observed a short-term decline in milk yield postvaccination, while 68.29% reported no long-term yield change. Prior vaccination was a significant predictor of higher yield postvaccination (β = 2.93, p < 0.001). Laboratory results showed significant reductions in bacterial load (p = 0.0019) and significant increases in milk fat (p = 0.0218), protein (p = 0.0123), SNF (p = 0.0056), lactose (p = 0.0023), and ash (p = 0.0088).

Conclusions: Cattle vaccination improved milk quality while causing only temporary yield declines. Strengthening regular vaccination programs and farmer awareness could enhance milk safety, nutritional value, and farm profitability, supporting Ethiopia's broader food security and One Health goals.