Effects of glyphosate contamination in dairy cow diet on feed digestibility, nitrogen balance, milk production, and blood profiles of lactating dairy cows

Abstract

Importance of the work: Glyphosate is one of the most widely used herbicides globally. However, glyphosate residues in feed may affect milk production and composition in dairy cows, raising concerns about its potential impacts on dairy performance and animal health.

Objectives: This study aimed to evaluate the effects of concentrate feed contaminated with low and high levels of glyphosate on milk production, nutrient digestibility, nitrogen balance, and blood profiles in lactating dairy cows.

Materials and Methods: Three crossbred Holstein Friesian cows, averaging 33.67±18.18 days in milk and 16.75±1.99 kg of daily milk yield, were allocated to 3×3 Latin square design. The experimental treatments included a control group, a Low-GL group (4 mg/kg DM), and a High-GL group (8 mg/kgDM).

Results: Feeding dairy cows with Low-GL and High-GL diets did not affect feed intake, milk yield, or milk composition. However, lactose production decreased when cows were exposed to 47.52 mg/day of glyphosate. Dry matter nitrogen-free extract content increased linearly with higher dietary glyphosate levels, as did fecal nitrogen excretion. Blood profiles showed no significant effects on complete blood counts; however glyphosate exposure exceeding 34.75 mg/day led to a decreased proportion og neutrophils and eosinophils and an increased proportion of lymphocytes.

Main finding: Concentrate feed contaminated with glyphosate at a daily exposure of 47.52 mg had no effects on milk production, nutrient digestibility, nitrogen balance, or blood cell counts. However, glyphosate exposure decreased lactose production and altered specific blood cell proportion, with reduced neutrophil and eosinophil conuts and increased lymphocyte proportion.