Estrous Behavior and Endocrine Status of Dairy Heifers with Varied Intakes of Phosphorus

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Abstract
The effect of dietary P on estrous intensity of heifers was investigated. A total of 48 heifers (Holstein and Jersey) were allotted to diets containing approximately 73% (low), 138% (medium) or 246% (high) of the P recommended by the National Research Council [USA]. 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 (SD) after prostaglandin, with onset randomly throughout the day. Standing estrus lasted 15.4 .+-. 4.1 h (SD), and heifers stood to be mounted 3.68 .+-. 2.38 (SD) times/h. Dietary P concentration altered inorganic P 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. A dietary P inadequacy does not alter reproductive endocrine function or estrous intensity in heifers.