Realimentation of phosphorus deficient cattle

Summary

Steers that were previously fed diets with different phosphorus (P) content for six months were fed a diet of approximately 11% crude protein, 63% dry matter digestibility and 0.1% P, with supplementary P supplied to provide a total dietary P content of approximately 0.25% P/kg DM intake for three months. Total dry matter intake of steers that previously had a low P intake was increased to the intake of steers that previously had a high P intake within one week of starting the re-alimentation period (and after a two week adaptation period).

Steers that were previously fed a low P (0.09% P) diet increased their liveweight gain (1.33 kg/d) and rate of hip height change (57 mm/100 days) to a higher level than steers that were previously fed a high P diet (0.24% P) (0.70 kg/d and 34 mm/100 days, respectively) during re-alimentation. The concentration of P in the faeces and plasma responded to the high P diet within the first week of feeding, with little difference in concentration between steers, regardless of previous P intake. After three months of re-alimentation on a high P diet, steers that previously had a low P intake had lighter and leaner carcasses with lower dressing percentages than steers that previously had a high P intake, with no differences in ossification score, fat colour or meat pH. This just reflected that, although compensatory growth was occurring, the period of re-alimentation was not long enough for previously P deficient animals to catch up to the control animals. There were no differences in carcass characteristics when data was adjusted to a common carcass weight. In conclusion, steers that are fed on a low P diet will respond immediately to a high P diet, in terms of feed intake and liveweight gain, and the increased P intake will be reflected in increased concentration of P in the plasma and faeces, regardless of the P content of the diet previously consumed by the steers.