Abstract
Background: Pre-weaning dairy calf and replacement heifer mortality represents significant economic loss, limits genetic improvement and growth of the herd and indicates poor management and animal welfare status on the farm.

Aim: Currently, the rates and causes of dairy calf and replacement heifer mortality in Jordan are not known. Therefore, the objective of this study was to determine the incidence rates and causes of mortality of pre-weaning calves and replacement heifers in Jordan. In addition, the age and seasonal distribution of mortality are determined in the study.

Methods: Data extracted from the farm management record software over 3 years (January 2016 to December 2018) were used in this study. Calf-specific data included the day and month of birth, and sex. Health-related data included age at death, necropsy findings, laboratory findings if available, and the presumptive diagnosis. Descriptive analysis was performed to determine the 3-year overall mortality rate as well as the yearly mortality rate in pre-weaning calves and replacement heifers using excel spreadsheets of Microsoft Word 10.

Results: Only female calves (n= 724) born alive during the study period were used in the analysis. The overall calf mortality rate was 8.9% with a yearly rate ranging between 5.9% to 12%. The majority of deaths occurred in calves less than 50 days of age with an average age of 17 days. There was a seasonal pattern for calf mortality with the majority of deaths occurred during the colder months of the year (December, January, February, March). The highest number of pre-weaning calves died because of enterotoxemia (39%) and pneumonia (30%). Other causes of calf mortality were abomasal ulcer (8%), enteritis (6%), septicemic salmonellosis (5%), meningitis (4%), rumen drinkers (3%), aspiration pneumonia (3%), septic arthritis (1%), and omphalitis (1%). The overall 3-year heifer mortality rate was 4%. The average age of dead heifers was 8 months (range 3 months to 23 months). The highest number of heifers died because of neurologic disease (37%) and enterotoxemia (33%). Other causes of heifer mortality were abomasal ulcer (11%), enteric salmonellosis (7%), chronic rumen tympany (7%), and chronic pneumonia (4%).

Conclusion: Data presented in this study are essential to construct and implement effective preventative health programs and improve farm management practices to reduce calf and heifer losses.

Key words: Dairy herds, calf health and welfare, replacement heifers, genetic improvement