The effect of feeding dairy heifers diets with and without supplemental XXXX on growth, reproductive efficiency, health, and lactation performance.

@entity3151 @entity1266 @entity291
The @entity3151 requirements for dairy heifers (0.20-0.35%) and endogenous concentrations (0.20-35%) of P in feeds fed 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   Jersey heifers were offered diets with (SP=0.40% of dry matter) and without (NP=0.30% of dry matter) supplemental P from 4 to 22 mo of age in a replicated pen design. Forty-eight pens of 8 heifers each were split evenly by breed and treatment group. Heifers were evaluated for body weight (BW), external bone/frame growth, @entity1266 , @entity291 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 from 410 to 650 d of age compared with 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 with heifers fed SP. Blood P concentrations between heifers fed SP or NP did not differ at 8 or 18 mo of age, and heifers fed SP excreted more P (29.2 vs. 24.2g/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 @entity1266 scores and @entity291 were similar in BW. Complete first-lactation data (305 d) were available for 333 primiparous @entity291 , and @entity291 fed NP as heifers produced similar milk, fat, and protein compared with @entity291 fed SP as heifers. Days open, days in milk at first breeding, and services per conception also were similar for primiparous @entity291 fed NP or SP as heifers. No growth, reproductive, or lactation benefit was found by feeding dairy heifers diets containing 0.40% P compared with 0.30% P. Furthermore, P supplemented to SP heifers was simply excreted in the feces and not retained.
