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Research Update: “Dry Propylene Glycol: An Alternative Readily Available Energy Source for Fresh Cows.”

Posted: September 5, 2005

Ketosis is one of the most common metabolic disorders occur during the first month of lactation in high producing dairy herds. Ketosis is caused by negative energy balance due to insufficient energy intake to support energy output in milk after parturition.

Although clinical signs of ketosis are not specific, they may include poor appetite, muscle weakness, abnormal rumen contraction, high urine ketone test, decreased milk yield and lost of body weight. Subclinical ketosis differs from clinical ketosis in that there are excess circulating ketone bodies in blood but there is an absence of clinical signs of ketosis. Clinical ketosis has been reported to be associated with increased risk of metritis, displaced abomasum and mastitis while subclinical ketosis is associated with reduction in milk, increased risk of clinical ketosis, metritis and impaired reproductive function. Cost of treating clinical ketosis, including the cost of lost production is estimated to be at $ 150 per case and $ 78 per case for subclinical ketosis. The incidence rate of clinical ketosis has been reported to be between 5 to 16 % and subclinical ketosis to be between 9 to 34 %.

Oral drenching of liquid propylene glycol (PG) is a typical practice in the prevention and treatment of ketosis in fresh cows. Liquid drenching, however, requires skilled personnel and can be labor intensive and sometimes can be detrimental to the animal who receives the oral drench. In a recently completed study, we investigated the use of a commercial dry PG product as an alternative readily available energy source to alleviate negative energy balance and reduce the prevalence of subclinical ketosis in fresh cow group. We demonstrated that mixing dry PG into the fresh cow TMR significantly reduced circulating concentrations of blood β-hydroxybutyratic acid (βHBA; a ketone body) during the first 3 weeks of lactation.

Thirty-nine Holstein cows in that trial received no dry PG (control group; 5 cows and 8 first-calving heifers) or 250 g of dry PG per cow per day either by mixing dry PG into the TMR (7 cows and 7 first-calving heifers) or dry PG top-dressed onto the TMR (7 cows and 5 first-calving heifers). Dry propylene glycol contained 65 % pure propylene glycol and was fed once daily starting at calving to 3 weeks after parturition. The weekly average serum βHBA concentrations were 1628, 1135, and 976 μmol/L for cows receiving no dry PG, dry PG top-dressed and dry PG mixed into the TMR, respectively. The reported serum βHBA threshold concentration used to define subclinical ketosis ranges from 1000 to 1400μmol/L. Based on this range, cows in our study receiving dry PG top-dressed were at lower risk of clinical ketosis compared to control cows. Cows receiving dry PG mixed into the TMR had normal serum βHBA level indicting that cows were in more positive energy balance compared to cows fed no dry PG and cows top-dressed dry PG. Dry matter intake was not different between groups. However, cows receiving the dry PG increased their intake more rapidly over the 3 weeks of lactation compared to the control cows. In a more recent study, we demonstrated that 250 g of dry PG per cow per day elicited a surge (92 % increase) in the concentration of circulating insulin 1 hour after the administration of the dry PG top-dress. We used 6 multiparous Holstein dairy cows from 6 to 16 weeks of lactation. This surge in blood insulin indicated a similar biological response to drenching of liquid PG. Dry matter intake did not differ between groups in this study.

We conclude from our studies that dry PG can be fed either by mixing into or top-dressing onto the TMR. Mixing dry PG into the TMR distributes readily available energy at a slower rate for a longer period of time while top-dressing dry PG onto the TMR stimulates a surge of insulin similar to drench of liquid PG. Mixing dry PG into the TMR for a few days to a week after freshening can help to reduce incidence of ketosis and is economically equal to drenching liquid PG during this same time frame. The use of dry PG can provide additional energy to cows that are not eating well after freshening and/or are ketotic and can be used in place of liquid PG drenching.

Ruby Chung, Graduate Student and Dr. Gabriella Varga, Distinguished Professor of Animal Science, Dairy & Animal Science