Relation of Protein Utilization in Dairy Cattle to Soil Fertility

Abstract

The effect of soil fertility on protein utilization of orchardgrass hay for lactation was studied. Four plots of orchardgrass were topdressed with 112kg of nitrogen, 98.5kg of phosphorus, and 186kg of potassium per hectare in the combinations PK, P, NP, and NPK. A fifth plot was top-dressed with 225kg of nitrogen plus phosphorus and potassium (2NPK). Four hays (PK, P, NP, and NPK) were assayed with four lactating Holstein cows in a 4×4 Latin square nitrogen balance design. Hay 2NPK was assayed with the same cows but not as a part of the Latin square.All cows were in positive nitrogen balance. Total efficiency of nitrogen utilization, which included both milk nitrogen and body nitrogen retained, was increased (P<.05) by nitrogen fertilized hays. Fertilizer treatment did not significantly affect voluntary hay dry matter intake or 4% fat-corrected milk production. Feeding nitrogen fertilized hay increased (P<.05) milk crude protein. Significantly greater ruminal butyric acid concentrations were observed with increasing protein content of the hays.Apparent digestibility of crude protein was higher (P<.05) for nitrogen fertilized hay and reflected an increased protein intake. The percentage nitrogen from fertilized hays utilized for milk synthesis is just as great as for hays receiving no nitrogen fertilizer. The total grams protein utilized for milk synthesis and body maintenance was greater for fertilized than for nonfertilized hay.