EFFECTS OF PREPARTUM CONSUMPTION OF ENDOPHYTE-INFESTED TALL FESCUE ONSERUM PROLACTIN AND SUBSEQUENT MILK-PRODUCTION OF HOLSTEIN COWS

A pharmacologically induced reduction in prolactin secretion during th e days preceding parturition diminishes the quantity and composition o f milk produced during the succeeding lactation. To determine whether the impairment in prolactin secretion that accompanies the ingestion o f fungus-infested fescue has a similar effect, primiparous (n = 15) an d multiparous (n = 19) Holstein cows were divided by parity, previous production, age, and calving date and assigned to one of two treatment s 28 d prior to expected parturition. Treatments in the replicated tri al were 'Kentucky 31' tall fescue hays of similar quality infested wit h Acremonium coenophialum or not infested. Cows were individually fed hay for ad libitum consumption supplemented with 1.8 kg/d of concentra te until 10 d prior to parturition at which time concentrate was incre ased to 3.6 kg/d. After parturition, all cows received a ration based on corn silage without fescue hay. No difference was detected in intak e of hay (mean of 5.3 kg/d) during the prepartum period. Prolactin sec retion in the cows consuming infested fescue was reduced by approximat ely 30% in the 5 d preceding parturition and by 23% during the prolact in surge that began the day before and ended the day after parturition . The quantity of milk produced was not affected, but the concentratio n of milk constituents, especially fat, was numerically lower in milk from cows that consumed the fungus-infested fescue hay.