1579
Total tract NDF digestion predicted using rumen in vitro measures is related to commercial dairy in vivo total tract nutrient digestion
Dairy diet in vivo total tract digestion estimates of OM and NDF have been correlated to animal performance and used in the field to assess opportunities for improvement. Measuring in vivo digestion on commercial farms however is time consuming and relatively costly. Our objective was to determine if total tract NDF digestion estimates predicted from rumen in vitro data (TTNDFD) were related to in vivo apparent total tract organic matter (OM) and carbohydrate digestion coefficients. Commercial dairy total mixed ration (TMR) samples (n=50) submitted for in vivo digestion analysis (% of nutrient, using 120h iNDF as an internal marker) were further digested in duplicate for 24, 30 and 48h using Combs-Goeser rumen in vitro techniques. Potentially digestible NDF (pdNDF, % of NDF) was estimated using 120h NDFD measures and NDF Kd was calculated using log-linear transformed 24, 30, and 48h uNDF residues. TTNDFD was predicted by Kd/(Kd+Kp) and a Kp based on NDF passage. In vivo organic matter and carbohydrate digestion coefficients (OMD, NDFD, pdNDFD and starchD) were also determined. TMR nutrient content and in vivo digestion coefficient descriptive statistics were calculated. TTNDFD estimates were regressed on in vivo OMD, NDFD, pdNDFD, and StarchD using SAS JMP Pro v11.0 and residuals assessed for normality. The TTNDFD was significantly (P<0.01) related to OMD, NDFD, and pdNDFD. The regression equation parameters are outlined in Table 1. These data suggest further evaluation is warranted but demonstrate a significant relationship between TTNDFD predictions and in vivo total tract digestion measures. On commercial dairies, in vitro TTNDFD measures may help identify dairy nutritive opportunities.
Table 1. TMR nutrient and digestion coefficient descriptive statistics and regression model parameters in relation to TTNDFD. Results followed by * or ** differ from zero (P<0.05 and P<0.01, respectively).
|
OM |
NDF |
pdNDF |
Starch |
TMR Nutrient Content (% of DM) |
||||
Mean |
92.01 |
31.93 |
19.30 |
25.15 |
StDev |
1.03 |
3.74 |
3.22 |
4.04 |
in vivo TMR Digestion Coefficient (% of Nutrient) |
||||
Mean |
58.82 |
37.80 |
61.88 |
94.73 |
StDev |
9.45 |
11.14 |
14.62 |
4.66 |
Regression Model Parameters in Relation to TTNDFD |
||||
Intercept |
38.50** |
1.09 |
24.98** |
92.36* |
Slope |
0.56** |
1.01** |
1.01** |
0.07 |
R2 |
0.14 |
0.30 |
0.18 |
0.01 |
RMSE |
8.86 |
9.39 |
13.38 |
4.68 |
Keywords: Total tract, NDF, Digestion