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Residual Milk


Residual Milk

Cows walking to the barn.

About 15-25% of the total amount of milk in the udder at the start of milking is not removed during milking. This milk is referred to as residual milk. Residual milk is also called complementary milk. The only way to get residual milk out is by injection of oxytocin. Usually this is done by intravenous injection of 10 IU of oxytocin or injection of 20 IU oxytocin either subcutaniously or intramuscularly. However, 0.5 IU (intravenous) can be as effective as 16 IU. The response dependsup on the cow and other circumstances. In some cases as little as 0.02 IU may work. Oxytocin injection (given 3 min. after start of udder preparation, but prior to attachment of milking machine) for an entire 305-day lactation resulted in over 800 Kg more milk during the lactation (see J. Dairy Sci. 1991 74:2119)

Twice daily injection of oxytocin immediately after normal milking followed by remilking resulted in substantially greater milk yields, but, the percentage of milk collected at the normal milking declines over time, while the percentage of residual milk increases. Repeated injections of large doses of oxytocin interferes with normal secretory activity of mammary epithelia and inhibits the normal milk ejection reflex.

Continuous oxytocin infusion (at 100 or 200 IU/day) decreases milk yield (see J. Dairy Sci. 1973 56:181).

After injection of oxytocin and removal of residual milk, concentrations of Na, Cl and whey proteins (probably serum-derived) are increased and lactose concentrations decreased in the next milking . This change in milk composition persisted for several milkings (see Wheelock et al., 1965, J. Dairy Res. 32:255).

Lactating heifers have less residual milk than older cows. The percentage of residual milk is greater for lower producing cows than for higher producing cows. Cows with a higher percentage of residual milk usually have a lower persistency of lactation

Residual milk decreases in proportion to milk yield as lactation progresses; that is, the percentage of residual milk remains the same throughout a lactation. The genetic heritability of residual milk is ~.34, and the repeatability between lactations for a cow is ~.77

Percentage of milk present in the udder at the beginning of milking that remains as residual milk after milking.

Residual
Milk

Milking intervals ranging from 4 -24 hr.

9.6 - 17.8 %

Comparison of lactation number:

First

10.0 %

Second and third

15.2 %

Fourth and later

17.9 %

Comparison of effect of machine stripping:

Machine-stripped cows

12.8 %

Nonmachine-stripped cows

14.0 %

Cows receiving oxytocin subcutaneously

16.8 %

Cows measured for one year

12.2 %

See Schmidt GH 1971, Biology of Lactation, p. 151.


 
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