Calcium profile in dairy cows: Implications for animal health and milk quality according to lactation stage, breed, and parity

Introduction
The transition period in dairy cows is characterized by significant metabolic changes, particularly in calcium metabolism. Hypocalcemia is a common disorder that can affect animal health, milk production, and reproductive performance. This study aimed to evaluate the evolution of blood calcium levels in dairy cows throughout lactation and to analyze the influence of intrinsic factors such as breed, age, and parity.

Methods
The study was conducted on 20 dairy cows belonging to different breeds (Holstein Black Pied, Fleckvieh, and Montbéliarde) distributed across two farms located in northern Algeria. The animals were monitored at different stages of lactation (early, mid, and late). Blood samples were collected and analyzed to determine calcium concentration using a spectrophotometric method.

Results
The results showed significant variations in calcium levels according to the stage of lactation. Mean concentrations were 77.67 mg/L in early lactation, 102.61 mg/L in mid-lactation, and 87.86 mg/L in late lactation. A marked decrease was observed in early lactation, related to the high calcium demand for colostrum production.

Parity also influenced calcium levels, with multiparous cows showing higher concentrations (93.27 mg/L) than primiparous cows (83.95 mg/L). Differences between breeds were observed, with higher values in Holstein Black Pied cows (98.56 mg/L) compared to Montbéliarde (78.97 mg/L) and Fleckvieh (53.77 mg/L).

Conclusion
Calcium levels vary significantly depending on lactation stage, breed, and parity. Early lactation represents a critical phase with a higher risk of hypocalcemia. These findings highlight the importance of metabolic monitoring and appropriate nutritional management to prevent metabolic disorders and improve the zootechnical performance of dairy farms.