When it comes to drying off cows today, it’s a case of “too much of a good thing.” Cows still milking heavily at the end of lactation have a hard time switching gears when they enter the dry period.
Attendees of a recent Iowa State University dairy extension webinar learned the modern realities of milk production make it almost impossible to achieve the dry-off goal issued by the National Mastitis Council, which is 33 pounds of milk per cow per day or less.
University of Minnesota dairy researcher Luciano Caixeta said the 33-pound threshold is a standard in need of an update. The assistant professor in the Department of Production Medicine in the university’s College of Veterinary Medicine said it now excludes approximately 93% of dairy cows at dry-off. The median production at dry-off in Minnesota herds currently sits at about 62 pounds per cow per day.
“Cows milking heavily at dry-off are more susceptible to environmental mastitis infections,” shared Caixeta. “They are at greater risk of milk leakage and have delayed formation of the keratin plug in the teat orifice.”
He said mammary swelling at dry-off also is a welfare issue, noting that cows with engorged udders are more uncomfortable and reluctant to lie down and rest.
Researchers have explored various methods of supporting end-of-lactation milk production decline. Caixeta said it can be accomplished by reducing milking frequency; feeding a lower quantity or concentration of TMR; or injecting cows with a prolactin-release inhibitor.
“All of these methods can work, but changing milking or feeding routines may not be practical for some dairies in terms of labor availability, facilities, or both,” noted Caixeta. “And currently, there are no FDA-approved injectable prolactin-release inhibitors available in the U.S.”
Another potential approach is administering acidogenic boluses enhanced with ammonium chloride to create an acetic environment in cows’ digestive tracts. This incites a temporary, mild decrease in blood pH, resulting in decreased lactose synthesis and a moderate decline in dry-matter intake.
After preliminary research in Spain showed the bolus treatment to be effective, Caixeta and his team were commissioned to conduct a larger study involving more than 800 cows from commercial Minnesota herds.
Approximately half the cows were treated at dry-off with 2 boluses, each containing 102 grams calcium chloride, 40.8 grams calcium sulfate, and 20.4 grams ammonium chloride (Bovikalc® Dry). Caixeta said the ammonium chloride is key to creating the acidogenic effect that induces a mild, temporary metabolic acidosis. All cows received blanket intramammary dry-cow therapy, including teat sealant, as well.
The study followed the health and performance of both groups through their next lactation. Compared to the untreated controls, cows receiving the boluses were found to have:
- Longer periods of rest – about 17 minutes per cow per day – in the first week after dry-off, with no difference in rumination behavior.
- Approximately 10% less subclinical mastitis, measured via somatic cell count (SCC) at 70 days in milk.
- Approximately 20% lower incidence of clinical mastitis cases in their next lactation.
- No significant difference in milk production or reproductive performance.
- A greater total economic advantage – assessed via a partial-budget analysis – of $34,074, or about $78.69 per cow.
Caixeta said it appeared that herds with higher incidence of mastitis would benefit the most from the practice, as they would retain the most revenue by averting the cost of mastitis therapy, sick-cow labor, discarded milk, and involuntary culling.
