Try to measure the gene expression of both prolactin and oxytocin.

Wishes,

Bassem

thank  you very much Doctor.

Here is a good reference with the abstract for genetic parameters of milking speed:

J Dairy Sci. 1976 May;59(5):957-64.

Genetic parameters of several measures of milk flow rate and milking time.

Miller RH, Pearson RE, Weinland BT, Fulton LA.

Abstract

Heritabilities and genetic correlations of milking rate, time, and yield were estimated by intrasire regression of daughter on dam for 252 Holstein pairs. Heritabilities were: lactation yield, .51 +/- .11; peak rate, .47 +/- .11; bucket milk yield, .38 +/- .10; average rate, .37 +/- .12; milk yield to .45 kg/min, .19 +/- .12; total time, .17 +/- .12; duration of peak rate, .10 +/- .10; strip time, .08 +/- .15; yield during peak rate, .07 +/- .11; and strip yield, .01 +/- .17. The genetic correlation of peak rate with lactation milk yield was .69 +/- .08, indicating substantial genetic improvement in milking rate by selecting for milk production. The genetic correlation between total milking time and lactation milk yield was .50 +/- .20, indicating an increase in total milking time due to selection for milk. Direct selection for peak rate would provide an opportunity to reduce total milking time.

PMID: 1270653 [PubMed - indexed for MEDLINE]

tank you very much doctor. this paper is a complete reference for my subject.

I agree with Basseem Refaat that oxitocin and prolactin may be most important causative agents in the milking speed variable, but I would rather measure their concentration, in blood, rather than their gene expression (in tissue biopsies? from the hypotalamus and the hypophysis?). Besides, these hormones are stored in the pituitary gland, and their secretion may be delayed from expression and synthesis events.

I think that the reference given by Jack Haiden Britt is a very complete work on the subject, but I wonder if milk yield and milking speed do just co-variate, and thus increasing one variable is associated with an increase in the other one... or else one variable directly causes the other one. In this case I could think that higher milking speed causes higher milk yields, rather than the other way around.

I would suggest that you consider also the "old school" parameters like udder conformation, teat position and size and (why not) ultrasound cross-section imaging of teats and udders, in association with the milk flow curve measurement... there is some work done on the heritability of these morphological traits, I suppose, maybe a google.scholar search will be useful for your purposes.

Leonardo Bianchi has some very good ideas. Milk speed is a function of myoepithelium contraction forces, sizes of ductules, gland cistern and teat cistern and  relative size and dilation of the streak canal. Larger volume of milk exerts greater pressure through force of gravity. One could experimentally standardize size of streak canals by using fixed-size teat dilators and then measure response to standard doses of oxyttocin or udder massage and stimulation. If machine milking is used, the amount of vacuum at the teat end can be regulated to determine its effect. Of course, too much vacuum can cause congestion around the streak canal by preventing effective blood circulation. This all would be worthy of study in a population large enough to make reliable estimates of genetic parameters.

Dear Jack Haiden Britt  and Leonardo Bianchi your answer is very helpful for me. now I know what genetic parameters  affect on milking speed. we know except genetic parameters, udder conformation and..., other factor (such as management,worker behavior, animal welfare and...) and the correlation between them are effective.but in overall view I want to know which of them are importance from other and I must measure it.

Many companies manufacture and sell milk monitoring systems that are used on commercial dairy farms. These systems record milking rate (volume/min). Many dairies have sire and dam information for each cow. If you can find dairies that have both of these, then you can get a lot of information quickly by mining the data.

I agree with Jack Haiden Britt.

dear Jack Haiden Britt. tank  you. exactly I understand what data important for me.now with this information I hope can start my thesis.

I would agree with the researcher who suggests that you measure the blood concentration of hormones which influence milk let down. However, we may also assume that different environments will elicit different concentrations ( i.e. stressful environment). There are other counteracting hormones which may depress milk let down. The other question hormone concentration of indigenous and exotic breeds, is it the same or those of  dairy breeds and beef breeds. I don't know. These should also be taken into account.

Hi Davod, working in this field for 28 years now, You could find a lot of articles speaking about milk ejection kinetics, fist measured in my lab by my predecessor Jacques labussière in dairy ewes and cows. I do not agree totally with the answer of Never just before because it is now well known that oxytocin level are not correlated to milk flow quantitatively but can affect milk kinetics. If you search about a genetic basis of milk flow, you have to focus on the max milk flow at the morning milking that generally is the limit possible due to streak canal sphincter resistance. You can measure it with special apparatus as milk meter (Lactocorder is  a portable one that is the most known for cows and goats but you could find alos some other for milking parlor..afifree by example for dairy ewes and so on). You have a very big correlation between this milk flow and teat canal resistance that you can measure with an apparatus I have build some years ago (Vacuometer) and that measure vacuum before ejection of the fist spurt of milk under normal vacuum of milking but without pulsation. Finally, genetician alos measure indirectly this milking speed by the way of simple measurement as milk obtained in the fist minute of milking and total individual milking duration (without any over-milking thus generally when milk is ejected at more that 100 to 200 ml/min). You could find some more information in my publications. do not hesitate to contact me if needed

Thanks & good.

I would agree with the researcher who suggests that you measure the blood concentration of hormones which influence milk let down.

In your research if you are to use REML procedures you need to identify significant  fixed effects to model to derive accurate genetic parameters.(ie diet, stressful vs something, milking methods, management style -suckling with milking, breed -beef vs dairy, indigenous vs exotic etc)

pierre Guy & Jay Kathiriya and Never Assan Thanks. your information is useful for me.

Very interesting discussion..As physiologist and specialist of oxytocin and milk flow characteristics during milking, I can insist on the fact the hormone expression and/or level have no interest in this goal of genetic selection. As explained by another contributor, all the regulatory endocrine pathways are adaptive systems that make the environmental parameters more important and able to down or up regulate gene expression and Hormone sensitivity. It is not a good way. Selection about milk flow rate have also limit even if the best and simple way today. The limit is mastistis: when you select on high milk flow, you select larger or more compliant streak canal sphincter that increase the mastitis risk significantly. Do not forgot too that a selection one one factor could also be deleterious for another one. ...

best regards.

For all reader, do not hesitate to ask me for collaboration on this subject....

I have seen cows come into the milking parlor from the field with a teat end almost completely excised from some injury. Once their udder is stimulated for milking, milk will gush from this cut teat, illustrating clearly the role of the streak canal in limiting flow. So one could make various measurements on the streak canals within and among cows and then look at how genetics affects this. In fact, one might be able to go into large herds and make thousands of measurements and then use pedigrees to assess genetic effects.This might be a way of actually tying flow rate to traits (measurements) that have a genetic basis.

Dear Jack Haiden Britt Exactly You sign to my purpose. if I go to a farm with thousands of animal, I want to estimate of genetic parameters, with very large amount of data, I write a suitable genetic model for data (any important parameter affecting milking speed, and I can record it) and analyze with genetic software, but I Don't know what parameters are important( and related to genetic) and I can measure that.

I agree with Mr. Davod Rostami. Thanks.

I think I would focus on the teat and the streak canal and teats and not worry about hormones. One could measure teat length and teat diameter at the udder and the end. One might develop a "cone-shaped" device that could be inserted into the streak canal to estimate maximum diameter and if this were attached to a pressure gauge, one could measure "relative resistance" to insertion of the device. I'd probably start by collecting teats from cows being harvested for meat and study them closely before making measurements on live animals. You might use collected teats and to determine pressure required to force milk through the teat end using some makeshift device in the lab. These are just ideas.

I agree with Mr. Jack Haiden Britt