Update on Current Research at the Penn State Dairy Center

Effect of dry propylene glycol vs. drenching: a preliminary report

Propylene glycol (PG) is a compound that has been shown to be effective in treating and preventing ketosis in dairy cows.

Cows in early lactation are very susceptible to ketosis. Routine drenching of liquid PG is used on many dairy farms to prevent clinical and subclinical ketosis in early postpartum cows. The convenience of feeding a dry form of PG compared to routine liquid drenching has drawn much attention recently. A study conducted at Penn State Dairy Research and Education Center this past summer provided a direct comparison on the efficacy of dry PG feeding vs. PG liquid drenching. A dose that is recommended to prevent subclinical ketosis was used. Multiparous Holstein cows were orally drenched with 200 ml (~8 oz.) of liquid PG once per day using a drench gun for 4 days (treatment 1).

Cows were also provided the same amount of dry PG via a rumen cannula to ensure that all the dry PG was consumed everyday for 4 days (treatment 2). Effectiveness of feeding dry PG by mixing it into a TMR was also evaluated (treatment 3). Rumen fluid and jugular blood were sampled for 4 h after PG administration. Rumen fluid was analyzed for volatile fatty acids and blood was analyzed for glucose and insulin as they are metabolic indicators for PG metabolism in the rumen and the host animal, respectively. Preliminary analysis showed that the production of propionate in the rumen increased significantly 4 h after delivery of PG either by oral drenched or via rumen cannula. For cows receiving PG as a part of their TMR, the production of propionate also increased but to a smaller magnitude. Propionate is one of the volatile fatty acids produced in the rumen and is the major precursor for glucose biosynthesis needed for milk lactose production.

Milk lactose percentage was significantly increased for cows receiving PG administration regardless of method of delivery indicating that the biosynthesis of milk lactose by the mammary gland is responsive to extra glucose provided from PG. Feed intake and milk yield were not affected by PG administration. In summary, our preliminary results show that PG was substantially metabolized in the rumen, and providing dry PG via the rumen cannula is as effective as oral liquid drenching in stimulating propionate production.

Based on the results from this study while drenching liquid PG may still be the best therapeutic treatment for ketosis, if prevention of subclinical ketosis or correcting negative energy balance is the management goal, top dressing dry PG can replace routine oral liquid drenching.

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Ruby Chung, graduate student and Gabriella Varga, University Distinguished Professor of Animal Science

Dairy and Animal Science Extension