Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2011
Publication Date: 12/12/2011
Citation: Bjelland, D.W., Weigel, K.A., Hoffman, P.C., Esser, N.M., Coblentz, W.K. 2011. The effect of feeding dairy heifers diets with and without supplemental Phosphorus on growth, reproductive efficiency, health, and lactation performance. Journal of Dairy Science. 94:6233-6242. Interpretive Summary: The dietary requirements of phosphorus for replacement dairy heifers (0.20-0.35%) and typical levels of phosphorus in feeds (0.20-0.35%) are similar, suggesting that the need for supplemental phosphorus in dairy-heifer diets may be minimal. On this basis, dairy producers may be able to capture some savings in mineral costs while limiting the potential environmental burdens created by excreted excess phosphorus. Dairy heifers (365) were offered diets with or without supplemental phosphorus from 4 to 22 months of age. Heifers were evaluated for body weight, external frame size, dystocia (calving difficulty), reproductive efficiency, and first lactation milk production performance. Performance of heifers, or subsequently as first-lactation cows, did not differ for any trait evaluated on the basis phosphorus supplementation strategy. The amount of phosphorus excreted also was examined, and all excess phosphorus consumed by heifers was excreted in the feces and not retained. These results suggest there is no benefit to feeding phosphorus above recommended levels to dairy heifers, provided phosphorus concentrations in feedstuffs are adequate to meet established feeding guidelines.
Technical Abstract: The P requirements for dairy heifers (0.20-0.35%) and endogenous levels (0.20-0.35%) of P in feeds offered to dairy heifers are similar, suggesting that the need for supplemental P in dairy-heifer diets may be minimal. Because long-term P feeding studies on dairy heifers are unavailable, 183 Holstein heifers and 182 backcross Holstein x Jersey heifers were offered diets with (SP = 0.40 % of DM) and without (NP = 0.30 % of DM) supplemental P from 4 to 22 mo of age in a replicated pen design. Heifers were evaluated for BW, external bone/frame growth, dystocia, calf BW, reproductive efficiency, and first lactation performance. Growth phase data were analyzed using pen-based statistical models, and lactation data were analyzed using mixed linear models with effects of season of birth, age of dam, heifer pen, sire, sire birth year, and days in milk. Heifers fed NP had similar average daily gain from 170 to 410 and 410 to 650 d of age when compared to heifers fed SP. At 22 mo of age, heifers fed NP did not differ in BW, hip height, hip width, body length, heart girth, cannon bone circumference or pelvic area compared to heifers fed SP. Blood P concentrations were numerically greater at 8 (8.26 vs. 8.21 mg/dl) and 18 (7.60 vs. 7.31 mg/dL) mo of age for heifers fed SP, but heifers fed SP excreted more P (29.2 vs. 24.2 g/d) than heifers fed NP. As heifers, services per conception and age at pregnancy were not different between heifers fed NP or SP. At parturition, heifers fed NP or SP had similar dystocia scores and calves were similar in BW. Complete first lactation data (305 d) were available for 333 primiparous cows, and cows fed NP as heifers produced similar milk, fat, and protein compared to cows offered SP as heifers. Days open, days in milk at first breeding, and services per conception also were similar for primiparous cows fed NP or SP as heifers. Data suggest that there was no growth, reproductive or lactation benefit to feeding dairy heifers diets containing 0.40% P compared to 0.30% P. Furthermore, P supplemented to SP heifers was simply excreted in the feces and not retained.