I'm not an expert in the area but it must be a carotenoid just like how pasture grass contributes to the yellow colour of cream and milk. Alfalfa is a rich source of carotenoids.

Thank you Naim but I am asking about red colour not yellow colour 

I know what you are saying but carotenoids can contribute red (eg astaxanthin, lycopene) color too. It might be mastitis induced blood as well.

Never I think the red color due to the mastitis and by the end of milking season and the color from red blood cell this is clearly in case of buffalos milk

Dear Collegue,

Carotenoids are a big family of compounds that are synthesized by too many plants and they can modify the color of milk and dairy products. For example lycopene could be responsible for red coloring. Please have a look to this interesting paper:

 https://www.researchgate.net/publication/228629261_Carotenoids_for_ruminants_From_forages_to_dairy_products

In any case, I agree with Mohamed, red color in raw milk could be related to the presence of  blood due to the mastitis problems.

Article Carotenoids for ruminants: From forages to dairy products

thank you Naim very much

Mr. Mohamed 

no blood cell in milk  by lab examination , no mastites 

Dear Antonio, Thank you

its a problem in comercial dairy farm   and i am searching for explanation

the ration is rich with alfalfa hay (7 kg/d) no forage or green plants  

Dear Ehab,

To my knowledge, alfalfa hay  usually does not give problems of milk red coloration if hay is well preserved.

It is maybe possible a microbial problem. How often does this coloration occur?

Thank you very much Antonio 

CMT were used to tested sub clinical mastitis and no problem founded , the other problem is high acidity of milk 

DIM is night or late location stage 

Thanks for replaying me 

Your article is very useful 

Dear Ehab,

The high acidity of milk you have found, could be related to a high total bacterial count. This can have different causes, among these poor hygienic conditions and no milk refrigeration.

You have to check this parameter.

In my opinion the red milk coloration could be due, as I already suggested, to the microbial problem (Serratia marcescens, Micrococcus roseus, ecc.).

 Here some document which could be useful:

http://livestocktrail.illinois.edu/uploads/dairynet/papers/Bacteria%20Counts%20in%20Raw%20Milk%20DD%202008.pdf

 http://articles.extension.org/pages/11811/sources-and-causes-of-high-bacteria-counts-in-raw-milk:-an-abbreviated-review

 https://www.slideshare.net/AnilShrestha15/contamination-preservation-and-spoilage-of-milk

Dear Colleague,

Using Alfalfa hay is pretty common in dairy cows nutrition, usually it never results in any type of coloration in the produced milk. However, in some unusual circumstances, the used alfalfa could contain some toxins as a results of fungal contamination. And as far as I know, bloody milk could be a sign of severe toxicity. I recommend consulting a vet. for that issue. Good luck

Thank you Dr. Mohamed  

Dear Ehab the red milk coloration could be due,blood from mastitis or the microbial problem (Serratia marcescens, Micrococcus roseus, ecc.). you can centrifuge a sample of milk to differentiate from the two causes