IMPACT OF SUPPLEMENTAL PHOSPHORUS SOURCE AND FORM ON UTILIZATION IN LACTATING DAIRY CATTLE

Supplemental phosphorus (P) in varying forms and sources: pellet (PELLET), meal (MEAL), liquid (LIQUID) and corn dried distiller's grains with solubles (DDGS) were compared in twelve multiparous Holstein cows producing approximately 43 kg of milk (115 ± 55 DIM) in a 4x4 Latin square with 21d periods.PELLET and MEAL diets contained monocalcium phosphate with a wheat middlings carrier, and the LIQUID contained ammonium polyphosphate in a cane molasses base.The DDGS supplied an organic P source.Cows were blocked by parity, DIM and milk production and randomly assigned to treatments.Data were analyzed using the MIXED model procedure of SAS.Phosphorus intakes of 116, 116, 119 and 118 g/d were similar for PELLET, MEAL, LIQUID and DDGS diets, respectively.Cows consuming the LIQUID diet experienced greater sugar intakes (P<0.001).Fat intake was lower (P<0.001)for the PELLET, MEAL and LIQUID diets compared to the DDGS diet (1.14, 1.12, 1.07 and 1.36 kg/d, respectively).NE L intake was similar for all treatments (P=0.55).Milk yield differences (P=0.05)occurred with the DDGS diet yielding the most milk (34.6, 35.4,34.1 and 36.5 kg/d).No differences resulted for either milk fat (P=0.26) or milk protein (P=0.33)percentages or for daily lactose production (P=0.22).Excretion of P in feces tended (P=0.07) to differ between treatments (67.4,66.3, 57.5 and 60.0 g/d) resulting in a trend (P=0.10) for greater P retention in diets excreting less P. Secretion of P in milk did not differ (P=0.51) between treatments.Differences (P=0.04)occurred in P concentration between diets (0.47, 0.47, 0.49 and 0.47%), but the amount of P fed was not different (P=0.83).With similarities for DMI and P concentration in refusals (P=0.21) it may be deduced that sorting of the P supplement did not occur.