Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/1999
Publication Date: N/A
Citation: Interpretive Summary: Many dairy farmers have applied more phosphorus (P) in the form of manure and fertilizer to their fields than the crops can utilize, resulting in an excessive build-up of soil P levels. This has resulted in increased P loss to streams and lakes during water runoff events, resulting in excessive algae growth and lowered water quality of fresh water bodies. Increasingly stringent federal and state regulations regarding use of P in agriculture will be introduced over the next several years, and these regulations have the potential of being very costly for some dairy producers. This research was conducted to determine if less P could be fed to dairy cows than is now currently fed, and if reduced feeding levels of P would compromise dairy cow performance. A two year lactation study was conducted. In year 1, 42 Holstein cows were used. In year 2, 12 additional cows were used, giving 53 cows that went on to finish the experiment. Two levels of dietary P were tested, with the low level ranging between .31% and .38%, and the high level between .44% and .48% of diet dry matter. There was no effect of dietary P level on milk production or reproductive performance. Blood serum levels of P were lower for the low P diet, but still within normal range. This study demonstrated that lower levels of dietary P than are typically fed by dairy producers can be fed without adverse effect on the dairy cow. A 20% reduction in dietary P will result in a 25-30% reduction in manure P. This reduction in manure P would greatly assist dairy producers in being compliant with coming regulations on P management.
Technical Abstract: Performance of lactating Holstein cows in response to P supplementation was determined in a 2-yr study. Each year included confinement feeding for approximately the first two-thirds of lactation, and grazing for the remaining one-third of lactation. In yr 1, 42 cows were randomly assigned at calving to a low or high P diet. Fourteen cows from the low P group and 16 cows from the high P group continued with their treatments for a second year. Also in the second year, 12 new cows were included in the low P group and 11 in the high P group. Thus, a total of 53 cows were used in yr 2. Cows in the low P group did not receive supplemental P, while cows in the high P group were supplemented with monosodium phosphate and dicalcium phosphate. The dietary P levels were 0.38 and 0.48% during confinement feeding, and approximately 0.31 and 0.44% during grazing for the low and high P treatments, respectively. Milk yield for 308 d of lactation was 9131 1and 8860 kg in yr 1, and 9864 and 9898 kg in yr 2 for the low P and high P groups. Milk protein content averaged over the lactation was 3.05 and 3.16% for the low P and high P groups in yr 1, and was similar in yr 2. Milk content of other components was similar between treatments in both years. Blood serum P concentrations were lower for the low P than for the high P group, but were within normal ranges. Reproductive measures were similar between groups in both years. Reducing dietary P from 0.48 to O.38% for two yr did not impair milk production or reproductive performance. Formulating diets with little or no supplemental P is possible and would be more environmentally friendly and more economical.