Bone Characteristics of Dairy Cows Fed Diets Containing Different Amounts of Phosphorus

Bone Characteristics of Dairy Cows Fed Diets Containing Different Amounts of Phosphorus

Summary

This project is about developing research evidence tat will persuade dairy producers and their advisors that less phosphorus (P) can be fed to dairy cows without reducing animal performance. Dairy producers routinely feed 20-25% more P than the National Research Council (NRC) Dairy Feeding Recommendations call for. While the research that supports the NRC recommendations is old and very limited, recent research shows that the NRC recommendations are more than adequate. Phosphorus fed in excess of the cow’s needs is excreted in manure, increasing the potential of P release into surface waters and the consequential algal blooms in freshwater lakes.

There is a deeply ingrained mindset amongst producers, nutritionists, and veterinarians that high dietary P is necessary for acceptable reproductive performance of the herd. This is a myth that has its origin in research done in South Africa and Scotland in the first half of the 1900’s. These studies utilized diets of very poor quality. In all probability, the beneficial effect of P under such conditions was that of stimulating microbial growth in the rumen, thus improving digestibility of the diet and enhancing the supply of microbial protein for the cow. Modern dairy cows do not receive diets of the sort that 50 years ago led people to conclude that supplemental P could improve reproductive performance. This study will do much to convince the dairy industry that they can safely lower P content of dairy diets.

Objectives:
1) Measure strength and ash content of rib bone surgically removed from 30 dairy cows that are just finishing a 2-3 year study on three varying dietary P levels. Bone sheaer strength will be measured along with ash and Ca/P content. Bone structure will reflect the long-term P status of the cow.
2) To conduct on-farm research with 4-8 elite dairy producers having rolling herd averages of greater than 25,000 lbs milk. Ideally we would split the herd, with half receiving a diet containing less than NRC recommended P and the other half receiving about 20-25% in excess of recommended levels.

If it can be demonstrated that bone structure is normal for cows fed at or below NRC recommended P levels fro a 2-3 year period, then it is powerful evidence that NRC recommendations are adequate and that producers can trust them.

We plan to compare reproductive performance one year prior to, and one year after, the reduction in dietary P. Our goal is to demonstrate that dietary P in excess of NRC recommendations is not necessary to achieve acceptable reproductive performance.

Results of this study will be published in the Journal of Dairy Science. It is expected that results will also be presented at several regional extension conferences and nutrition/feed industry conferences. Articles will also be prepared for far/trade magazines, such as Hoard’s Dairyman and Dairy Herd Management.