Increased milk production by Holstein cows consuming endophyte-infected fescue seed during the dry period.

Ergot alkaloids in endophyte-infected grasses inhibit prolactin (PRL) secretion and may reduce milk production of cows consuming endophyte-infected grasses. We hypothesized that consumption of endophyte-infected fescue during the dry period inhibits mammary differentiation and subsequent milk production. Twenty-five multiparous Holstein cows were randomly assigned to 3 treatment groups. Starting at 90-d prepartum, cows were fed endophyte-free fescue seed (control, CON; n = 9), endophyte-free fescue seed and 3x/wk subcutaneous injections of bromocryptine (0.11 mg/kg BW; positive control, BROMO; n = 8), or endophyte-infected fescue seed as 10% of the as-fed diet (INF; n = 8). Although milk yield of groups did not differ at −90 d prepartum, at dry-off (−60 d) INF and BROMO cows produced less milk (P < 0.05) than CON (averaging 20, 11 and 14 kg/d for CON, INF and BROMO cows). Throughout the treatment period, concentrations of PRL in the circulation were lower in INF and BROMO cows than CON cows (P < 0.05). Basal concentrations of PRL in venous plasma averaged 25.3, 2.8 and 3.7 ng/ml for CON, INF and BROMO cows, respectively. Prepartum release of PRL was also reduced by ergot alkaloids, averaging 19.5, 9.2 and 1.1 μg PRL/ml*h (area under curve) for CON, INF and BROMO cows, respectively. At 10 d of lactation, when treatments were terminated, basal concentrations of PRL in plasma averaged 22.5, 1.6 and 1.4 ng/ml for CON, INF and BROMO cows, respectively. Three wk after the end of treatment, circulating concentrations of PRL were equivalent across groups (P > 0.05). Gestation length did not differ between groups. Although treatment 4 wk before dry-off reduced milk yield in INF and BROMO cows, milk production in the ensuing lactation was increased 8% and 9% in INF and BROMO cows relative to CON (P < 0.05). We reject our initial hypothesis, as data show that consumption of ergot alkaloids during the dry period increases milk production in the ensuing lactation. We propose that this effect is due to a reduction in PRL during the dry period, analogous to the production effect realized by exposing cows to reduced photoperiod (low PRL) during the dry period