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Title: Use of cuticular wax alkanes to estimate digestibility and intake of cows as pasture with a view to estimating efficiency.

Author
item Coleman, Samuel
item Chase, Chadwick - Chad
item Riley, David

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 8/17/2007
Publication Date: 2/6/2006
Citation: Coleman, S.W., Chase, C.C., Riley, D.G. 2006. Use of cuticular wax alkanes to estimate digestibility and intake of cows as pasture with a view to estimating efficiency [abstract]. Journal of Animal Science Supplement. 84(1): Page No. 447.

Interpretive Summary:

Technical Abstract: Determination of feed efficiency requires estimates of intake and digestibility of the diet, but they are difficult to measure on pasture. The objective of this research was to determine if plants cuticular alkanes were suitable as markers to estimate intake and diet digestibility of grazing cows with sufficient precision to determine differences among breeds. Purebred Angus (A), Brahman (B) and Romosinuano (R) cows grazing Bahiagrass pastures, all nursing 2 to 3 mo old calves were used. External markers were administered to four cows of each breed using an intraruminal device that continuously delivered 320 mg of C32 and C36 daily. After 7 d for equilibration, forage and feces (10 samples/cow) were collected over the next 2 wk. All samples were lyophilized and ground to pass a 1mm screen. Alkanes were extracted and analyzed by gas chromatography. Digestibility was calculated from the ratio of C31, C33, or C35 in the forage and feces. Ratios of C31/C32, C32/C33, and C35/C36 in feces were to quantify fecal output and intake as a proportion of body weight (BW). Digestibility and intake values were analyzed using a repeated measures model where animals were repeated measures over days using a compound symmetry covariance structure. Coefficients of variation (CV) in digestibility among animals were 2.44, 3.49, and 5.98% for C31, C33, and C35, respectivgely, quite low and similar to pen fed measurements, Digestibility was different (P<0.05) among breeds when estimated with C31 (73, 75, and 73%) or C35 (64, 63, and 59%, for A,B, and R cows, respectivly. Estimates made with C33 approached significance(P=0.055) with estimates of 71, 71, and 68% for A, B, and R cows. Intake CVs were 27, 20, and 28% for ratios of C31/C32, C32/C33, and C35/C36, respectively. mean intakes were 53, 39, and 46g/kg BW daily for the three alkanes, and were not different among breeds. Mean intake values appeared to be biased upward, possibly due to rather large adjustments for the amount of C32 (13.5ppm) and C36(24.6 ppm) in forage samples. Use of other forage species with lower amounts of C32 and C36 should improve estimates of intake. Estimates of intake and digestibility differed with different alkane pairs.