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

Ergot alkaloids in endophyte-infected grasses inhibit prolactin (PRL)\r\nsecretion and may reduce milk production of cows consuming\r\nendophyte-infected grasses. We hypothesized that consumption of\r\nendophyte-infected fescue during the dry period inhibits mammary differentiation\r\nand subsequent milk production. Twenty-five multiparous\r\nHolstein cows were randomly assigned to 3 treatment groups. Starting\r\nat 90-d prepartum, cows were fed endophyte-free fescue seed (control,\r\nCON; n = 9), endophyte-free fescue seed and 3x/wk subcutaneous injections\r\nof bromocryptine (0.11 mg/kg BW; positive control, BROMO; n\r\n= 8), or endophyte-infected fescue seed as 10% of the as-fed diet (INF;\r\nn = 8). Although milk yield of groups did not differ at −90 d prepartum,\r\nat dry-off (−60 d) INF and BROMO cows produced less milk (P < 0.05)\r\nthan CON (averaging 20, 11 and 14 kg/d for CON, INF and BROMO\r\ncows). Throughout the treatment period, concentrations of PRL in the\r\ncirculation were lower in INF and BROMO cows than CON cows (P\r\n< 0.05). Basal concentrations of PRL in venous plasma averaged 25.3,\r\n2.8 and 3.7 ng/ml for CON, INF and BROMO cows, respectively. Prepartum\r\nrelease of PRL was also reduced by ergot alkaloids, averaging\r\n19.5, 9.2 and 1.1 μg PRL/ml*h (area under curve) for CON, INF and\r\nBROMO cows, respectively. At 10 d of lactation, when treatments were\r\nterminated, basal concentrations of PRL in plasma averaged 22.5, 1.6\r\nand 1.4 ng/ml for CON, INF and BROMO cows, respectively. Three\r\nwk after the end of treatment, circulating concentrations of PRL were\r\nequivalent across groups (P > 0.05). Gestation length did not differ\r\nbetween groups. Although treatment 4 wk before dry-off reduced milk\r\nyield in INF and BROMO cows, milk production in the ensuing lactation\r\nwas increased 8% and 9% in INF and BROMO cows relative to CON (P\r\n< 0.05). We reject our initial hypothesis, as data show that consumption\r\nof ergot alkaloids during the dry period increases milk production in the\r\nensuing lactation. We propose that this effect is due to a reduction in\r\nPRL during the dry period, analogous to the production effect realized by\r\nexposing cows to reduced photoperiod (low PRL) during the dry period