Estrous behavior and endocrine status of dairy heifers with varied intakes of phosphorus

We investigated whether dietary phosphorus affected estrous intensity of heifers. A total of 48 heifers (Holstein and Jersey) were allotted to diets containing approximately 73% (low), 138% (medium), or 246% (high) of the phosphorus recommended by the National Research Council. Heifers were observed continuously for 48 h beginning 36 h after an estrous-synchronizing treatment of prostaglandin F2 alpha. Heifers began standing estrus 55 +/- 12.6 h (standard deviation) after prostaglandin, with onset randomly throughout the day. Standing estrus lasted 15.4 +/- 4.1 h (standard deviation), and heifers stood to be mounted 3.68 +/- 2.38 (standard deviation) times per hour. Dietary phosphorus concentration altered inorganic phosphorus of blood serum but did not affect significantly overall estrous behavior or blood serum concentrations of progesterone, estradiol, or luteinizing hormone measured around the time of estrus. We conclude that a dietary phosphorus inadequacy as in this study does not alter reproductive endocrine function or estrous intensity in heifers.