Effects of feeding propylene glycol to mid-lactating dairy cows

Propylene glycol (PG) is a gluconeogenic precursor widely used to prevent and treat ketosis postpartum. The study has investigated the effects of PG administration to dairy cows at mid stage of lactation. According to a 3 × 3 latin square design, three Italian Brown lactating cows (125 ± 7 days in milk) fitted with rumen cannula were fed a corn silage based diet (CP 14.7%, NDF 41.1% DM) with 0, 200 or 400 g day⁻¹ PG added. Dry matter intake was increased by feeding PG with a significant quadratic component per dose (16.2, 17.2 and 16.5 kg day⁻¹ for 0, 200 and 400 g PG day⁻¹, respectively). Milk yield was not affected by PG, averaging 17.1 kg day⁻¹. Average daily gain increased from 64 to 206 and 302 g day⁻¹ when cows received 200 and 400 g day⁻¹ of PG (linear component per dose P < 0.05). Digestibility of the diet did not differ among treatments, whereas repeated rumen fluid samples, taken 0, 2, 4, 6 and 8 h after the meal, showed a consistently lower acetate to propionate ratio when feeding PG. Blood insulin was not affected by PG administration. Except for therapeutic treatments, PG administration to dairy cows at mid stage of lactation should be advised against. Despite the positive effect on intake, administration of the additive, increasing the molar percentage of rumen propionate, contributes to shift the energy partition from milk production to liveweight gain.