Relationships between in vitro ruminal fermentation parameters and dairy performance

Abstract Text:

The in vitro gas production technique (IVGPT) is a valuable tool to evaluate feeds for ruminants by estimating the extent of digestion, rates of digestion of the different carbohydrates fractions, and end products of fermentation. One hundred sixty samples of dairy TMR of known animal performance (FCM, and DMI) were analyzed using an IVGPT (IFM, Alltech, Inc.). Feed samples were fed to cows at various stages of lactation, averaging  159±43 DIM,  milk yield 36.2±5.9 kg, FCM 34.3±5.4 kg, and feed efficiency (FE; FCM/DMI) 1.49±0.19. Nutrient concentrations DM, CP, NDF, ADF, starch, NFC, TDN were 48±6.2, 17.5±1.56, 31.7±4.28, 19.45±3.17, 25.9±4.48, 38.5±5.3, 69.0±3.65% (DM basis).

Fermentation profile reflected the variation in chemical composition of the feeds. Fast pool gas production (FP) and its corresponding rate were 63.3±9.6 mL/g DM and 20.0 ±4.02%/h, respectively; whereas values for the slow pool (SP) were 112.6±9.7 mL/g DM and 4.56±0.47%/h, respectively. Total gas production (TGP) was 176±12.6 mL/g DM. Estimated starch degradation rate averaged 10.69±1.30%/h. True dry matter digestibility averaged 79.1±3.17%. Microbial biomass (MBM) and net VFA production averaged 109 mg/g DM and 24.0 mM, respectively.

Samples were stratified into deciles based on milk yield and correlation and multiple regression analyses were conducted. The FCM was positively correlated (P < 0.05) with FP (r= 0.63), SP degradation rate (r= 0.73), TGP (r= 0.91), starch degradation rate (r= 0.79), TDMD (r= 0.86), VFA (r= 0.63). The MBM was negatively correlated with FCM (r= -0.66) but when it was calculated based on the level of DMI (r=0.73), the relationship was highly positive. Similar correlation strengths were observed for DMI and FE. Of the dietary nutrient concentrations, only carbohydrate fractions were correlated with FCM and DMI. Specifically, fiber (NDF, ADF, lignin) were negatively correlated with FCM, DMI, and FE (r= - 0.86 to - 0.75), whereas starch, NFC, and TDN were positively related to FCM, DMI, and FE (r= 0.68 to 0.92).

Regression of FCM against fermentation profile parameters resulted in a predictive equation that included TGP, SP rate of degradation, and VFA (FCM= -480.5+34.4× SPR+1.57 ×TGP+4.55×VFA; R²=0.95), demonstrating the importance of fermentability, and fiber digestion rate in defining milk production level. Feed intake was similarly predicted by TGP and SP degradation rate (DMI = -94.7+10.27×SPR+0.58×TGP; R²=0.87). Among the chemical composition parameters, TDN concentration explained 82.2% of the variation observed in milk yield. For DMI, NDF concentration explained 69% of the observed variation in DMI. The IFM can be a useful tool to evaluate the nutritive value of dairy TMR.

Keywords:

in vitro ruminal fermentation, digestion kinetics, dairy performance