We had a heifer we had to pull a calf from. We started to milk her to give the calf colostrum, and her bag was hot and hard, and the milk was a brown color. We thought we had an orphan and a cull cow on our hands. We figured the cow had mastitis. We gave the calf a colostrum replacer, and the next day, it was up nursing, and the milk and the bag were almost normal. What do you think was going on here?
I have seen this several times during my 38 years of practicing, and I bet it happens a lot more than we realize since we rarely see the milk of beef cows after calving unless you have a problem. I think this happens more with heavier milkers or those whose bags fill early.
My theory is either inflammation or mild trauma leads to a hemorrhage in the udder in the weeks leading up to calving. As the blood breaks down, the heme pigment in hemoglobin turns to a rusty brown color. It is, after all, an iron-containing molecule. If trauma occurs close to or at calving, the milk may have a pink to red color. It may even have clots in it. It takes very little blood in milk to change color.
I doubt this is an infectious mastitis, and it probably does not need to be treated. I also think if this cow completes a normal lactation and raises a good calf, this problem is not likely to recur.
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