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Keywords

phosphorus, heifers, conception, reproduction

Abstract

In Northwest Arkansas, soil phosphorus concentrations have increased where livestock manures have been repeatedly applied, leading many to question if supplementing phosphorus in this area is necessary. The effects of phosphorus intake on beef heifer growth performance and conception rates were investigated. In this study, crossbred Angus heifers (n = 72), approximately 30 days after weaning, were stratified by body weight (average initial weight 251 ± 3.9 kg) and allocated randomly into 8 groups. Groups were assigned randomly to 1 of 2 treatments. Treatments were delivered through either a free-choice-mineral mix that contained no supplemental phosphorus (CON), or a free-choice-mineral mix with 4% supplemental phosphorus and identical concentrations of other supplemental minerals (4PMIN). Heifers grazed 2.42 ha mixed grass pastures with a history of livestock manure application and were supplemented with soy hulls (0.5% of body weight) daily. Data were analyzed using the mixed procedures of SAS with group as the experimental unit. Total mineral intake through day 112 did not differ (P = 0.55) between treatments. On days 84 and 112, any heifers greater than 273 kg body weight (n = 58) had an ultrasound evaluation of their reproductive tract. Reproductive tract score (1, infantile to 5, corpus luteum present) did not differ (P = 0.65) due to treatment. Body weights were not different (P ≥ 0.59) through day 264, 409 ± 6.0 kg and 412 ± 6.0 kg for CON and 4PMIN, respectively. When grazing pastures with a history of livestock manure application, heifers did not need supplemental phosphorus throughout the breeding season.

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