EFFECTS OF FEEDING PROPYLENE-GLYCOL TO MID-LACTATING DAIRY-COWS

Propylene glycol (PG) is a gluconeogenic precursor widely used to prev ent and treat ketosis postpartum. The study has investigated the effec ts of PG administration to dairy cows at mid stage of lactation. Accor ding to a 3 x 3 latin square design, three Italian Brown lactating cow s (125 +/- 7 days in milk) fitted with rumen cannula were fed a corn s ilage 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 signif icant 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 affect ed 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 aff ected by PG administration. Except for therapeutic treatments, PG admi nistration to dairy cows at mid stage of lactation should be advised a gainst. Despite the positive effect on intake, administration of the a dditive, increasing the molar percentage of rumen propionate, contribu tes to shift the energy partition from milk production to liveweight g ain.