Effects of Prepartum Consumption of Endophyte-Infested Tall Fescue on Serum Prolactin and Subsequent Milk Production of Holstein Cows

¹ Department of Animal Science, The University of Tennessee, Agriculture Experiment Station, Martin 38238-5008

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

Key Words: fescue • endophyte • production • prolactin

Submitted on November 23, 1992
Accepted on February 12, 1993

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