8 Jan 2016
Ceva Animal Health
Job Title
The incidence of milk leakage is an indirect indicator of the three axes at dry-off: management, udder health and welfare.
Presented below is an excerpt from the publication The incidence and importance of milk leakage in the dry cow by Ana I de Prado, corporate technical manager, Ceva Santé Animale (France).
The cessation of milking at drying-off results in dramatic changes in the composition of the mammary gland secretion which could pose a risk of new IMI. In addition, the flushing of bacteria from the streak canal ceases and teat dipping stops. The slow transition to the involuted state delays the protective effects of lactoferrin and immunoglobulins, whilst fat and casein levels remain high inhibiting leukocyte function.
The keratin plug formation, an important defence against IMI, may vary between cows and it has been reported that 50% of the teat canal still remained open 10 days after drying off.
Milk is no longer being removed from the gland but cows continue to produce milk for some days. As a result, there is marked engorgement of the cisternal spaces, ducts and alveoli of the gland. The udder volume and pressure are increased due to milk accumulation. Cows may suffer pain and milk leakage (ML) can occur. This facilitates bacterial penetration of the streak canal during the first few days until involution is complete.
Each of the biochemical changes, the increased intramammary pressure (IMP) related to the level of milk production at the moment of dry-off and the subsequent leaking of milk are believed to contribute to susceptibility to new IMI in the early dry period.
The National Mastitis Council recommends abrupt cessation of milking when the target of 15 litres per day has been achieved. The reason why it is recommended to reduce the milk production to that level at dry-off is due to the fact that the higher the milk production at the moment of dry-off, the higher the risk of new IMI.
A study was conducted in Ontario (Canada) to evaluate the association between milk production at dry-off and IMI. Dairy Herd Improvement (DHI) records were examined during 1998 and 1999. A new IMI was defined as a change in linear score from less than 4.0 at the last test prior to drying off to linear score greater than 4.0 at the first test in the next lactation. Only 16% of cows producing less than 13kg of milk at dry-off developed new IMI compared to 26% of cows producing greater than 21kg.
Another study concluded that for every 5kg increase in milk production at dry-off above 12.5kg, the odds of a cow having an IMI at calving increases by 77%. Other data showed that for each litre increase in yield at drying off, the odds of a quarter being infected with an Enterobacterial organism post calving increased by 1.06. This equates to doubling the risk of new IMI in the dry period for every 12 litre increase in yield at drying off.
It has been hypothesised that there is also an association of milk production and teat-canal closure. The keratin plug is the udder’s natural defence mechanism as it prevents bacteria from entering the teat canal during the dry period.
In a study conducted in North America the authors found an association between milk production and closure of the teat canal. At the end of the first six weeks of the dry period, 47% of quarters from cows producing 21kg or more were still classified as open compared with only 19% of quarters from cows producing less than 21kg. Observations of the dynamics of the teat canal closure for a group of 756 dairy cows after dry-off were also reported in a New Zealand study. The investigators demonstrated that 50% of teats were still open at day seven after drying off.
It is clear that the decline in milk production has a positive effect on decreasing the rate of new IMI during the dry period. It could ameliorate new IMI incidence not only by the increased risk of mastitis associated with milk leaking from quarters but also by the association of production and teat-canal closure. Although there are more factors that may influence the presence of ML, milk production and ML seem to have a strong relationship.
Download the full publication to continue reading about the incidence of milk leakage in dry cows, the causes and importance of milk leakage, and recent milk leakage data.
