RESUMO
Thirty-nine multiparous Holstein cows were used to measure the effect of propylene glycol treatment around parturition on milk yield, reproductive efficiency and some hormone and metabolite concentrations. Cows were assigned randomly to control (n = 19) or propylene glycol treated (n = 20) groups. Propylene glycol (300 g) was administered directly mixed with the diet from day 10 prior to the expected calving date until parturition (day 0) and orally after dilution in 1 l water on days 3, 6, 9 and 12. Blood samples were collected on days -20, -5, 0, 3, 10, 25 and 50 while milk samples were taken weekly until 13 weeks post partum. Body condition scores, recorded on days -20, 15 and 50, were not affected by propylene glycol administration. Propylene glycol did not significantly affect milk yield or composition but linear somatic cell score measured from the first 13 weeks post partum was reduced by propylene glycol administration (P < 0.01). Moreover, propylene glycol reduced milk urea (-25 mg/l, P < 0.05), especially during the first 9 weeks post partum. Plasma insulin concentrations were similar in both groups during the experiment while insulin-like growth factor I (P < 0.05) and insulin-like growth factor-binding protein 3 (P < 0.001) levels were higher on days 10, 25 and 50 post partum in the propylene glycol group. Propylene glycol administration decreased plasma non-esterified fatty acid concentrations (P < 0.05 to P < 0.01) but increased total cholesterol levels (P < 0.01) after parturition while 3-hydroxybutyrate levels were unaffected by the treatment. Changes in the hormone and metabolic concentrations after propylene glycol administration in the last few days of gestation and the first week of lactation seem to indicate that energy balance in the treated group was probably more positive than in the control group. There was also evidence that propylene glycol administration prevented fatty liver syndrome and hastened the resumption of oestrous cycles (P < 0.001).
