Effect of Abomasal Ferrous Lactate Infusion of Dairy Cows on Milk Proteins

Abstract Text: Water makes up more than 80% of the total weight of milk. However, the influence of water chemistry on milk quality has not been extensively studied. Heavy metals in bovine drinking water may affect the synthesis of milk and subsequent milk quality.  The objective of this study was to determine the interaction of ferrous lactate infusion in dairy cows, representing the intake of iron through drinking water, on qualitative changes in protein composition of their milk. Four ruminally-cannulated cows each received aqueous infusions of ferrous lactate at 0, 200, 500 or 1,250 mg of Fe/d in a Latin Square design. A wash-out period (7 days) existed between each infusion period (7 days). Raw milk was collected at day 6 of each infusion period and was homogenized and pasteurized before analysis.  Two-dimensional electrophoresis (2-DE) coupled with Matrix-Assisted Laser Desorption/Ionization Time-of-Flight/ Time-of-Flight (MALDI-TOF/TOF) high-resolution tandem mass spectrometry analysis was applied to characterize the milk proteins. About 56 protein spots were identified and represented the major and minor casein and whey proteins.  Although the protein compositions were similar across cows, the intensity of specific protein spots such as α-S1-casein and k-casein showed differences among different cows. Within-cow comparison demonstrated diminished spot intensity and less focusing along the pI gradient for some spots with increasing ferrous infusion. Such variation may indicate that high iron in bovine drinking water affects some cows more than others.  Cow D presented the most stable and consistent protein spots both in position and intensity throughout the infusion period.  The content of copper and iron in milk from this cow was consistent and was very near the four cow average.  In contrast, milk from cow C presented more α-S1-casein spots when consuming high iron-contaminated water then when consuming regular drinking water; the iron and copper concentration in her milk decreased with increasing infusion concentration. However, cow A lost several α-S1-casein spots when drinking high ferrous sulfate concentration water.  The iron-binding protein, lactoferrin was observed at both control and high ferrous infusion periods for cows.  There is qualitative evidence that iron in drinking water may affect milk proteins differently in different cows. 

Keywords: Proteins, lactoferrin, iron