There is a possibility of death due to injury and eventual infection if a dairy cow is not milked. Many wild or "less-domesticated" (if you'll allow) breeds of cattle, bison and other bovines don't suffer from the same danger.
Immediately, the real problem is that the udders will swell and cause the cow severe pain and stress if not released. Generally the milk will stop producing and not cause a literal rupture at some point, but the udders may be so tight they become very vulnerable and inflamed. This can lead to infections and other health problems, which can then lead to death.
Pro Tip: Be kind and milk dairy cows at least every day or two while lactating.
Oh, in case the summary version isn't clear:
- Yes, it will probably become infected.
- It can dry from the pressure. Any hormonal transition can have effects on health. You dont want to attempt this with a cow that just started a lactation cycle. The best way is to let the current cycle run on then dry using low-calorie high fiber diets.
Effect of genetic merit, milk yield, body condition and lactation number on in vitro oocyte development in dairy cows
S.E.M. Snijders 1, 2, P. Dillon 2, D. O'Callaghan 3, M.P. Boland 1
Support info, severity of mastis, links to inflammation, variability in milk production:
Georgette Vandeputte-Van Messom, Christian Burvenich, Eddy Roets, Anne-Marie Massart-Leën, Roger Heyneman, Wim D. J. Kremer and Arie Brand (1993). Classification of newly calved cows into moderate and severe responders to experimentally induced Escherichia coli mastitis. Journal of Dairy Research, 60, pp 19-29. doi:10.1017/S002202990002731X.
Compiled research including udder strain during transition to non-milking, many references in article
Inflamed udders create good environment for mastis-friendly bacteria
ISOLATION OF PROTOTHECA ZOPFII
FROM INFLAMED SECRETION OF UDDERS
EDWARD MALINOWSKI, HENRYKA LASSA
AND ANNA KŁOSSOWSKA
Department of Pathophysiology of Reproduction and Mammary Gland,
National Veterinary Research Institute,
85-090 Bydgoszcz, Poland
Effects of Diet on Short-Term Regulation of Feed Intake by Lactating Dairy Cattle
Michael S. Allen
Department of Animal Science, Michigan State University, East Lansing 48824-1225
A Dairy Cow Body Condition Scoring System and Its Relationship to Selected Production Characteristics
E.E. Wildman 1, G.M. Jones, P.E. Wagner 2, R.L. Boman 3
H.F. Troutt Jr., T.N. Lesch
20 years raising cattle and various livestock
- Oregon State