Reducing phosphorus inputs for grazing Holstein steers

¹ University of Wisconsin-Madison Department of Animal Sciences, WI 53706
² University of Wisconsin-Madison Department of Agronomy, WI 53706

^* To whom correspondence should be addressed. E-mail: jwl{at}ansci.wisc.edu.

	Abstract

A 2-yr study was conducted to confirm that managed pastures can provide Holstein steers adequate phosphorus to meet their daily requirement. Treatments offered were trace mineralized salt with or without additional phosphorus. In the first year, 80 Holstein steers (248 kg) were assigned to 4 grazing groups. Treatments were trace mineralized salt only (TM) or a 67:33 mixture of trace mineralized salt and dicalcium phosphate (TMD). Steers rotationally grazed a cool-season grass/legume mixture for 137 d. Fecal bags were placed on 3 steers from each grazing group (n = 12) over a 4-d period for estimation of forage DMI and forage contribution to daily P intake twice during the grazing season. Analyzed pasture samples contained 3.28 mg P/g DM. During the second year, 72 Holstein steers (297 kg) were blocked by weight into 2 weight groups and subsequently assigned to 1 of 4 pasture groups. Steers rotationally grazed the same forage base as the first year for 126 d. Pasture samples contained 3.27 mg P/g DM. No significant differences (P < 0.10) were detected for BW, ADG, or free-choice supplemental mineral intake. Forage provided 126% of the recommended NRC phosphorous requirement. Thus, supplemental phosphorous was not required for Holstein steers grazing mixed cool-season grass/legume pastures.

Key Words: Cattle, Grazing, Holstein, Mineral, Phosphorus