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The 2001 Dairy NRC Ration Evaluation Software effectively predicts dietary strong ion and DCAD concentrations in lactating dairy cow diets
Recent research suggests that increasing DCAD concentration using buffers in lactating dairy cow diets results in increased milk yield and milk fat percentage. Dietary buffers, such as NaHCO3 and K2CO3, alter DCAD concentration and have been used in lactating dairy cow diets for decades. However, most of the published work on buffer supplementation was conducted prior to the development of the DCAD concept. Thus, these data have not been included in previous meta-analyses of DCAD effects on dairy cow performance. One problem with the use of these data is the lack of measured concentrations for each of the minerals required for calculation of DCAD (Na + K – Cl, meq/kg DM). To overcome this obstacle, a study was conducted to determine if the 2001 Dairy NRC Ration Evaluation Software could be used to estimate missing dietary ion concentrations. Data from 44 journal articles on the effects of buffers and DCAD that were published from 1965 to 2011 were used in the study. Experimental diets where Na, K, and Cl concentrations were analyzed were used as “test” observations. Ingredient information for each diet was extracted from each article and entered into the 2001 NRC software to estimate dietary mineral concentrations. The NRC predicted Na, K, Cl and DCAD were regressed on the respective measured concentrations and the regression statistics are reported. The root mean prediction square error (RMPSE) expressed as a fraction of the mean concentration was small. Chloride data were clustered in two distinct populations (0.25 to 0.5 and > 1.0%) which may have resulted in slope confidence intervals different from 1. However, the regression slopes for Na, K, and DCAD were not different from 1 (P > 0.05). Intercept values when significant (Na and Cl) were small compared to the mean concentration for each mineral. Residual plots indicated no mean or linear bias. In conclusion, the NRC software accurately estimated mineral and DCAD concentrations and could be used to estimate missing ion concentrations in future meta-analyses of DCAD experiments.
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Item |
Obs |
Mean |
SD |
Slope |
95% CI |
Int |
P < |
R2 |
RMPSE |
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Na, % |
129 |
0.39 |
0.18 |
0.98 |
± 0.065 |
0.04 |
0.003 |
0.88 |
0.06 |
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K, % |
137 |
1.45 |
0.52 |
0.96 |
± 0.072 |
0.04 |
0.511 |
0.84 |
0.21 |
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Cl, % |
84 |
0.71 |
0.40 |
0.86 |
± 0.091 |
0.12 |
0.002 |
0.81 |
0.17 |
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DCAD, meq/kg |
60 |
343.9 |
143.9 |
0.96 |
± 0.102 |
-23.4 |
0.266 |
0.86 |
54.7 |
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Keywords: DCAD, NRC Software, dairy cows