Improving phosphorus utilization by dairy cows

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Senaratne, Vidura
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The primary objective of the thesis research was to identify strategies to improve the utilization of dietary phosphorus (P) on commercial dairy farms. In the first study, a survey was carried out on 19 commercial dairy farms in Manitoba to determine relationships between dietary, animal, and management factors and the P utilization. Multiple regression analysis of variables showed that high dietary P concentrations and free-stall instead of tie-stall housing were most associated with a high P concentration of feces. The second study determined the effects of SARA and Saccharomyces cerevisiae fermentation products (SCFP) on the rumen pH and apparent total tract digestibility coefficient (ADC) of dry matter (DM), neutral detergent fiber (NDF), starch and P in 32 lactating Holstein cows. Cows were assigned to four treatments; 1) control and three SCFP supplementations, including 2) 14 g/d Diamond V Original XPC™ (XPC, Diamond V, Cedar Rapids, IA), 3) 19 g/d NutriTek® (NTL, Diamond V), or 4) 38 g/d NutriTek® (NTH, Diamond V). Subacute ruminal acidosis (SARA) challenges were conducted during wk 5 and wk 8 by switching from a moderate-grain diet containing 18.6% of DM starch to a high-grain diet containing 27.9% DM starch. On average, the SARA challenges increased the duration of the rumen pH below pH 5.6 from 13.6 to only 179 min/d. In cows on the NTH treatment, this increase was shorter (P<0.05) at 79.3 min/d. Across SCFP treatments, the SARA challenges reduced the ADC of NDF and tended to increase that of starch. The combination of both SARA challenges reduced the ADC of DM and P in all treatments. Our results show that NTH can increase rumen pH during high grain feeding and increase NDF digestion, which is particularly important when cows are at risk of SARA, and that prolonged high grain feeding can reduce the P digestibility of dairy cows. The results of these studies show that the utilization of dietary P by dairy cows on Manitoba dairy farms can be improved by more closely matching the demands and requirements of P by dairy cows and reducing the risk of SARA.
Dairy cows, Phosphorus, SARA, Saccharomyces cerevisiae fermentation products