The reproductive performance of phosphorus-deficient mature cows improved rapidly when given supplementary phosphorus in the Victoria River District of the Northern Territory

Context There is little published information on how long it takes for the performance of phosphorus (P)-deficient mature cows to improve once they start receiving P supplements, or whether their long-term performance is impaired by P deficiency early in life. Aims The performance of mature P-deficient and P-adequate Brahman cows was compared over 3 years to investigate the time it takes for the performance of P-deficient mature cows to improve once they are supplemented with P, and whether their long-term performance is compromised by P deficiency early in life. Methods Cows that had been a part of a P-supplementation trial at Victoria River Research Station from weaning until they were 5.5 years old were used for this study. One treatment group had received continuous P supplement (P+) since weaning and the other treatment had never received any P supplement (P−). At the conclusion of the original trial, 42 cows were randomly selected from each treatment and then grazed together in the same paddock for 3 years, during which time they were given P supplement continuously. Performance attributes were measured and compared. Key results This study found that P supplementation rapidly improved the liveweight, body condition, reproductive performance and survival rate of the P-deficient (P−) mature cows. Within a year of receiving P supplement, their performance improved to be similar to that of P+ cows. However, P deficiency early in life did have some residual stunting effects, resulting in lower mean hip height and liveweights of P− cows. Conclusions The performance of P-deficient mature cows improved rapidly once they were given P supplements and matched that of cows that had always been supplemented. However, P deficiency early in life caused stunting, resulting in mature cows being shorter and lighter. Implications Cattle producers in P-deficient country should see a rapid improvement in performance and return on investment once they start supplementing P-deficient cows. However, it is better to supplement cattle throughout their lives in P-deficient areas to avoid stunting.