Nutrient digestibility as determined by the Lignin Ratio Technique and its relation to body parameters of lactating beef cows

An indicator digestion trial was conducted using twenty-one mature Angus cows in late lactation in order to establish possible relationships between cow and calf body parameters and nutrient digestibility. The cow-calf pairs were selected to represent a wide range of body types and structures. They were individually fed timothy (Phleum pratense) orchardgrass (Dactylis glomerata) silage and alfalfa (Medicago sativa) pellets once each day. Chromium sesquioxide (Cr₂O₃) was administered daily in 10 gram doses to each of the cows during a nine-day preliminary period and a seven-day collection period. Fecal samples were collected once a day over the collection period at a time established in a study by Thomas (1975) to find the optimal time for fecal collection to avoid error due to diurnal excretion of Cr₂O₃. Feed and feces samples were analyzed for dry matter, crude protein, acid-detergent fiber, acid-detergent lignin, and gross energy. Fecal samples were also analyzed for Cr₂O₃. Digestion coefficients were calculated using both Cr₂O₃ and lignin as the indicator. Under the conditions of this experiment, the lignin method was preferable. Therefore, the digestion coefficients derived using lignin as the indicator were used to evaluate the relationships between cow-related variables and digestibility. Differences in digestion coefficients between cows were quite marked (coefficients of variation were: dry matter; 5.40; gross energy, 4.77; acid-detergent fiber, 6.87; and crude protein, 8.52). This variation was due to differences in relative ability of cows to digest the nutrients and by error due to lack of refinement in indicator technique. The average dry matter, gross energy, ADF and crude protein digestibilities were 49.7 percent, 48.3 percent, 41.6 percent, and 41.8 percent, respectively. Dry matter, ADF and energy digestibilities were not correlated with cow weight or fat thickness, but there was a tendency for these variables to show a positive relationship with cow height and average daily gain. Crude protein digestibility was highly correlated (p<.01) with cow weight (r=-.71). It was shown that as mature cow weight increased, crude protein digestibility decreased at an increasing rate. The relationships between various cow-related variables and voluntary consumption were explored. Dry matter consumption was not related to cow weight, cow height or cow fat thickness, but the amount of dry matter consumption per unit of weight was found to be significantly affected by body weight, fat thickness and weight divided by height. An indicator ratio method for estimating intake by cows was presented which might be of value in future nutrition research.