The phosphorus requirement of a dairy heifer is 0.20 to 0.35 percent of dry matter intake, depending upon bodyweight. This is similar to the concentrations of phosphorus in the feeds fed to heifers. These factors suggest that heifers don’t need much phosphorus supplementation. Yet, there are no long-term studies on phosphorus feeding of dairy heifers — until now.
Researchers at the University of Wisconsin examined the effects of long-term phosphorus supplementation on heifer growth and reproductive performance, as well as health and lactation performance. Their results were published in the December 2011 Journal of Dairy Science.
During the study, the researchers fed 365 Holstein and crossbred heifers diets with or without supplemental phosphorus from four to 22 months of age. Supplemented diets contained 0.40 percent phosphorus. Diets without phosphorus contained 0.30 percent phosphorus, which was the amount naturally present in feeds. They evaluated the heifers for bodyweight, external bone/frame growth, dystocia, calf bodyweight, reproductive efficiency and first-lactation performance.
Here are some of the study’s findings:
- Heifers fed no supplemental phosphorus had average daily gains similar to supplemented heifers at 170 to 410 and 410 to 650 days of age.
- At 22 months of age, there were no differences in bodyweight, hip height, hip width, body length, heart girth, cannon bone circumference or pelvic area between heifers fed no supplemental phosphorus and supplemented heifers.
- Blood concentrations of phosphorus did not differ at eight or 18 months of age between supplemented and non-supplemented heifers.
- Heifers fed supplemental phosphorus excreted more phosphorus than non-supplemented heifers (29.2 vs. 24.2 grams/day).
- Services per conception and age at pregnancy were not different between both treatment groups.
- Dystocia scores and calf bodyweight were similar at calving between the two treatment groups.
- First-lactation data (305-day) show milk, fat and protein yields of cows fed no supplemental phosphorus as heifers were similar to cows fed supplemental phosphorus as heifers.
- Days open, days in milk at first breeding and services per conception also were similar.