This is a very interesting and pertinent question.

There is no physiological reason for milk to be rejected due to hormonal changes associated with oestrus. Concentrations of oestradiol are physiological and would be no different from those of human females during the peri-ovulatory period. So I really don't understand the basis for this question. Incidentally dairy cows can resume ovulation and cyclicity from as early as day 12 post partum. Usually the first ovulation is silent in terms of heat expression. See some of the review papers on this topic on my profile.

Hi Demissie and Others colleagues. It is true that during estrus, the milk production decrease due to effects of increasing estrogen and reduction pf progesterone that limit prolactin and other peptides effects on galactopoiesis. As a result, you could detect some modifications in Fat (increase) and protein (decrease) contents and, if animals are in a subclinical status of mastitis, you could also seen a rise in Somatic cell concentration that could lead to penalties in countries where this criteria is taken in account.. Additionally, it is well described that estrogen concentration in milk increase also during this period and can reach physiological active level for human/babies. That was unfortunately used by some peoples to ask for discarding milk or rejecting it by dairy plants. It is absolutely not useful because, as written by mark before, all theses modifications are physiological, natural and in range of effects easy to manage. Additionally ,excepted in totally synchronized flock, generally animals in estrus never express heats simultaneously and the dilution of such light modification of their milk in the tank make impossible any significant detection of modification of milk. Keep in mind that some river water after flowing near big town in developed countries are all contaminated by residue of contraceptive pills (xeno--oestrogen) that reach very active concentration and act really on human and animal physiology and metabolism (endrocine perturbator) and are much more a problem than natural estrus of our ruminants species even in region with intensive production....

Concerning milk very soon after calving, it is different, because the first milk produced is contaminated by colostrum rich in non clotting proteins (Immunoglobulin and albumins). Such a pasage of theses proteins is due to leakiness of epithelium due to lack of cortisol before calving and is rapidly corrected after 2 to 4 milking/suckling and tight junction synthesis/epithelium polarisation. Such a " first milk" have no good and stable composition and it is necessary to discard milk for the 2 first days at least (7 first days in France by example). It is also a security to avoid residue of large range and long acting antibiotics used generally at drying to clean mammary gland from germs and that could be always released during some days after calving and impact drastically milk technological characteristics.

best regards

From the dairy industry point of view, this is marginal issue because the milk of those cows is diluted in the farm dairy tank and dairy plant silo with milk coming from many more cows that are not in heat. Furthermore, if milk was collected just from in cows in heat, it would most likely not violate current criteria used by dairy plants in western countries to collect milk.

However, from physiological point of view, your question is very interesting: Also not much research was done, it is known that during this period milk production is reduced and as noted by my colleague Pierre Guy Marnet, these changes are associated with some modifications in fat and protein contents in milk. These changes are consistent with the "milk-born negative feedback system", based on activation of plasmin system in milk. According to this system, active peptide released from casein would reduce more acutely lactose secretion (hence milk liquid volume), resulting in relative concentration of milk particularly fat but may also  include protein. Similar response occur under acute inflammation of mammary gland, acute response to milk stasis, acute response to heat stress, acute response to dehydration. Downloadable publications, which support the above claims, are available through my publication in Researchgate. Thus, the changes in milk secretion rate and composition during 'cows heat' may be part of these responses. The physiological basis might be an effort to save on energy devoted to milk secretion to support increase energy and metabolic resources demands for reproduction. Thus, I hope that you are going to research this interesting topic.

Dear Scholars, thank you very much for your interesting responses.

@ Mark A Crowe, The question is very clear and is based on what I read from manual. Actually, you come up with your thought as this hormone doesn’t have influence on milk quality which may result rejection and I don’t imagine that you don’t understand the question. I raised the question because it is something new from my experience that I didn’t see any farm which rejects milk during hormonal change and I don’t read as this hormones have influence on milk quality before. Therefore, if you are confident enough to say, I will be very happy with your answer which says here is no physiological reason for milk to be rejected due to hormonal changes associated with estrus and progesterone than asking basis of the question.

@ Pierre Guy Marnet,  Nissim Silanikove,  Thank you very much for your interesting responses. I know as there is sharp decline in milk production during estrus which may be resulted from the decline in feed intake associated with those hormones.  I accept the rest of your responses as it is.

@Nissim Silanikove, This days, I am looking to get PhD abroad where practical applicability of this interesting discipline is true. So, if my dream comes true, I am very interested to do research in this and other interesting laboratory works and I hope it will be true. I hope you will help me in making my dream true!

Thank you very much!!!

@ John P Kent, Thank you very Much!

For more information about the initial point of the question, it is possible to see http://www.dairyafrica.com/africandairyportal/sites/default/files/Dairy%20Farmers%20Training%20Manual%20Final3%5B1%5D.pdf  on page 63.

With Best Regards,,,

Two publications are ATTACHED. One deals with influence of estrogen and progesterone on oxidized flavor in milk. One deals with influence of estrogen and progesterone on milk lipids. These were part of my MS thesis.

@Jack Haiden Britt, Thank you very much for sharing your interesting work!!! 

Hi I could not get the link to load on the dairy Africa website.  There is a decrease in milk yield associated with oestrus and this is when oestradiol is high, progesterone is low.  I suspect this is mostly due to the activity associated with oestrus and also decreased feed intake. I also like the work of Jack Britt on the steroid effects on milk lipids.  Within the physiological concentrations of oestradiol and progesterone changes once dairy cows become cyclic, I do not believe there is a reason for milk to be with held from the food chain.  I also agree with the earlier responder who says on a herd level the specific high levels of oestradiol for the animals in oestrus are diluted by the other cows in the herd (unless whole herd synchronisation is being practiced).  Even with whole herd synchronisation, it would be highly unlikely for all cows to undergo simultaneous synchronisation; Plus in normal dairy production the milk from one herd gets pooled with milk from many other herds as well.

Hi to all,

The answer of mark make me thinking about another point often underestimated about the effect of cyclicity on milk quantity and quality. During estrus, we always focus on estrogen and less on progesterone decrease but at the basis you have to keep in mind that this period relates to luteolysis and concomitant follicles rises. But during luteolysis, there is also another hormone that disappear. It is Oxytocin that is also well known to affect milk ejection (and fat matter extraction - biggest fat globules were for a part unable to transfer from alveoli to cisterns and need alveoli contraction to be expelled) but more recently milk secretion (Lollivier et al, 2006 J. Physiol- see on my contribution pages for references). We have clearly shown in dairy ewes (labussière et l, 1993, Reprod, nutr dev.) and later with US colleagues (MsKusick et al, J Dairy Sci. 2002) that this luteal OXT is very efficient in the milk transfer from alveoli to cisterns between milking and in the galactopoiesis phenomenon (In cows, Lollivier et al, 2002 reprod.nutr. dev.) and this impact is independent to steroid action. The fat percentage of milk is thus increased with OT action during all the corpus luteum life span.

best regards

@ Pierre Guy Marnet,   Mark A Crowe, Thank you very much for sharing your knowledge once again. This is the ways that we especially young professionals can enrich our knowledge. I really learn a lot from this question. E.g I don’t know as ‘first milk’ is subjected to be rejected for 2 or 7 days due to colostrum before.   As I mentioned in the question, rejection of milk due to hormonal change is not common. I also agree with Pierre Guy Marnet that specific high levels of oestradiol for the animals in oestrus are diluted by the other cows in the herd (unless whole herd synchronization is being practiced). Keeping dilution matters in mind, let we see what will happen on milk quality when there is high level of estrogen and progesterone on individual level. If we do this together, it will give us a base to say that this hormone has effect on quality and vice versa based on the finding and we can see its effect on dilution matters on different level if we find quality problem.  I think this is the way that we scholars can have findings in every matters concerning our discipline.

@ Mark A Crowe, they put  additional website, www.livestock.go.ke, but it says it is temporary unavailable.  Try it and if it stays unavailable I can send it via email or you can search it with its manual name, Dairy  Farmers Training Manual, Ministry of Livestock Development, Nairobi, Kenya 2012. Please let we see Pierre Guy Marnet current response , he is showing us diifrent works on the effect of those hormones in quality and quantity.

Thank you very much once again!!!

Hi Denissie, yes you are true. To see and conclude really of such an effect of steroids (physiological concentrations) could need a trial with synchronized animals but, I do not remember if such a work was already done...

About the delay needed between  calving - lambing and first collection of processable milk, the true is well known. 4 milking is sufficient to reduce drastically all soluble somatic proteins coming from blood because of the tight junction increasing number and efficiency - integrity after cortisol and prolactine rises. You can find residual IgG concentration until 8 milking in some animals but the concentrations make milk totally usable (may be with a reduced cheese yield) and you understand that waiting more than 4 days is not necessary....BUT! one other reason explaining why milk is forbidden to collect before 7 days (at least in France) is due to the time needed to eliminate "inhibitors" of flora (the risk of residue of antibiotics used for drying period is real because, they are very large spectra antibiotic s and very long acting formula that could be deleterious for milk clotting). Penalties for antibiotic residues in milk are very important and enough dissuasive to convince milker to not ply with fire!!

Hi Demissie,

The concept of 'Naturally Occurring' may be important here.

For example in eggs of different species, it is known for some years that hormone in the egg have effects on the development of the offspring post hatching. And hormone levels within the egg change within a clutch or sequence of laid eggs.  For example, in geese as the laying season progresses the levels of Testosterone increase within the egg and the eggs also get smaller as the season progresses (Kent et al 2013).  However in the said study it is in the outer layer of the yolk that these changes are detected and secondly the findings suggest that it is in the area of the outer layer closest to the germinal disc that the changes are most profound. However, are the changes profound from the consumers or from the germinal discs perspective. It is noted that few people consume Goose eggs in Europe. From the germinal discs perspective with is few, if very few cells who's development is influenced the very small quantities of the 'naturally occurring' hormone may be significant but in terms of the entire egg the levels of hormone are most likely to be difficult to detect.  

In cows, is suspect the reproductive hormonal action and functions are most prominent at the level of the ovary and reproductive system as has been found in sheep and horses by scientists trying to examine factors that determine birth sex ratios (following Kent 1995) among other things. These hormones as you are aware are detected  in milk and milk sampling is often used as a means to measure same, with the real action and effects elsewhere in the anatomy / physiology.  

However what might interest you is the levels of Urea that are detected  in milk. when looking at different studies with dairy cows one notices studies using Urea as an indicator of nutritional status in different countries with different systems of production. In some countries with grass based systems and others with meal based systems the levels of Urea may differ and it is known that urea has effects on reproductive system of cows. In some circumstance the leves of urea in milk could be regarded as 'naturally occurring' .

The question is, what happens if the levels are above 'naturally occurring' and are a reflection of feeding and breeding regimes,  or indeed milk storage and processing regimes  and if so do they compromise the food safety quality of milk for human consumption. It is essential that 'naturally occurring ' levels are established especially if Urea should have effects that compromise  milk quality and safety.

John