In the first experiment, forage samples (n = 39) were collected during 4 years (2006
? 2009) from pastures grazed by Santa Gertrudis cattle at the King Ranch, TX. The in vitro
gas production technique (IVGP) was performed to understand the pattern of fermentation
parameters of the forage and obtain fractional digestion rate (kd) values to predict total
digestible nutrients (TDN). The best nonlinear model to describe the IVGP values of the
forages was the two-pool logistic equation. The passage rate (kp) of 4%/h was used.. The kp
predicted by the Large Nutrient Ruminant System (LNRS) model was 3.66%/h. The average
TDN was 55.9% compared to 53.8% using a theoretical equation. In the second experiment,
Brahman bulls (n = 16) grazed Coastal bermudagrass pastures [Cynodon dactylon (L.) Pers.]
and stocked at a moderate to low grazing pressure. Three periods of fecal collections were
made within each period. Bulls were individually fed at 0700 and 1900 h of 400 g of corn
gluten pellets containing C32 n-alkanes. Each period was divided in 2 sub periods in which fecal samples were collected 4 times a day (0700, 1100, 1500 and 1900 h). N-alkanes in the
forage and feces were determined using gas chromatography. In the third experiment, four
methods were used to estimate dry matter intake (DMI): C31 or C33 with or without
adjustment for forage C32 (C31_0 and C33_0, respectively). There was a difference between
morning (0700 and 1100 h) and afternoon fecal collections (1500 and 1900 h) on the
predicted DMI using C31 (P = 0.0010), C33 (P = 0.0001), C31_0 (P = 0.0010), or C33_0 (P <
0.0001). There was no difference in average daily gain (ADG) between low and high
residual feed intake (RFI) (P = 0.5709). The nonparametric analysis indicated that preranking
animals for efficiency under confinement conditions does not guarantee (P <
0.0001) similar ranking under grazing conditions when using the alkane technique to
determine forage DMI. In order to estimate DMI at least 5 d of fecal collection and 2 times a
day of collection (0700 and 1500h) are needed to decrease the variability.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7773 |
| Date | 2010 May 1900 |
| Creators | Aguiar, Andre D. |
| Contributors | Tedeschi, Luis O., Rouquette, F. Monte |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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