Even though it’s not groundbreaking news that reproductive efficiency in the dairy herd depends on multiple factors, it is good to reflect on how certain situations affect reproduction. In this line, a group of scientists from Cornell University, led by Jessica McArt, D.V.M., has recently published a study associating subclinical hypocalcemia with reproductive performance.
The research occurred in New York on four commercial dairy herds of 1,000 cows or more. As a first step, the investigators categorized 697 cows as having normal concentrations of calcium in the blood (8.8 mg/dL or more, normocalcemic cows) or hypocalcemic concentrations of calcium in the blood (less than 8.8 mg/dL, hypocalcemic cows) after determining the concentration of calcium on Day 4 after calving. After this classification, the investigators assessed the association between hypocalcemia status with pregnancy risk at first service and the proportion of cows pregnant by 150 days in milk.
The investigators classified 515 cows as normocalcemic and 182 cows as hypocalcemic. Normocalcemic cows had a pregnancy risk at the first service equal to 27.4%, whereas hypocalcemic cows had a pregnancy risk at the first service of 18.1%. Mean days at first service did not differ between these groups (71.6 versus 70.6 days, respectively).
Half of the normocalcemic cows got pregnant by 103 days in milk, whereas half of the hypocalcemic cows got pregnant by 119 days in milk. Altogether, 70.7% of the normocalcemic cows and 65.4% of the hypocalcemic cows were pregnant by 150 days in milk.
In their discussion, the investigators highlighted that subclinical hypocalcemia can be associated with reduced feed intake (which exacerbates the negative energy balance), lessened immune capacity, and a greater risk for uterine diseases. Even though many readers might have been aware of this association before, this study neatly brings new data reinforcing that, beyond reproductive management, herd health and transition cow management are paramount to ensure a sound and effective reproductive program.