Consumption of endophyte-infected fescue seed during the dry period does not decrease milk production in the following lactation

Ergot alkaloids in endophyte-infected grasses inhibit prolactin (PRL) secretion and may reduce milk production of cows consuming these grasses. We investigated the effects of consuming endophyte-infected fescue seed during late lactation and the dry period on mammary growth, differentiation, and milk production. Twenty-four multiparous Holstein cows were randomly assigned to 3 treatment groups. Starting at 90 ± 4 d prepartum, cows were fed endophyte-free fescue seed (control; CON), endophyte-free fescue seed plus 3×/wk subcutaneous injections of bromocriptine (0.1 mg/kg of body weight, positive control; BROMO), or endophyte-infected fescue seed (INF) as 10% of the diet on an as fed basis. Although milk yield of groups did not differ before treatment, at dry off (−60 d prepartum) INF and BROMO cows produced less milk than CON. Throughout the treatment period, basal concentrations of PRL and the prepartum increase in plasma PRL were reduced in INF and BROMO cows compared with CON cows. Three weeks after the end of treatment, circulating concentrations of PRL were equivalent across groups. In the subsequent lactation milk yield was not decreased; in fact, BROMO cows exhibited a 9% increase in milk yield relative to CON. Evaluation of mammary tissue during the dry period and the subsequent lactation, by quantitative histology and immunohistochemical analysis of proliferation markers and putative mammary stem or progenitor cell markers, indicated that feeding endophyte-infected fescue seed did not significantly affect mammary growth and development. Feeding endophyte-infected grasses during the dry period may permit effective utilization of feed resources without compromising milk production in the next lactation.