Effect of propylene glycol supplementation on microbial protein production in transition dairy cows

Abstract

Limited research suggests that propylene glycol (PG) supplementation can have inhibitory effects on ruminal microbes. Our hypothesis was that PG supplementation would reduce microbial protein production. The objective of this study was to determine the effect of PG supplementation on microbial protein production in transition dairy cows. Sixteen pregnant cows (seven primiparous and nine multiparous) were paired based on expected calving dates and then randomly assigned within each pair to either a basal diet (control) or basal diet plus 624 g d-1 of PG. Diets were fed twice daily for ad libitum intake, and PG was fed in equal amounts as a top dress from day -7 to day 45 (transition period). Sample collection was carried out at three time intervals starting at day -14 ± 5, day 15 and day 38 relative to calving, with the first collection period (day -14 ± 5) being the pretreatment period. Propylene glycol supplementation had no effect on total urine purine derivatives (PD; allantoin + uric acid) excretion; consequently, microbial N supply, estimated using total urinary PD excretion, was not affected by PG supplementation. There was an increase in urine total PD excretion and, thus, estimated microbial N supply, with time relative to calving. Microbial efficiency did not change with time relative to calving and, therefore, the increase in dry matter intake during the post-partum period led to the increase in estimated microbial N supply. Results from this study indicate that supplementing PG over the transition period had no effect on microbial protein production in the rumen.Key words: Transition dairy cow, propylene glycol, microbial protein production