A trial was conducted to determine the total rumen degradable protein intake (RDPI) required to
maximise the digestible organic matter intake (DOMI) of beef cows consuming low quality grass
hay from the Northern variation of Cymbopogon-Themeda pasture type (pure grassveld).
Thirty five pregnant Afrikaner x Simmentaler crossbred cows (±517.08kg, SD 53.06) were
randomly allocated to 5 treatments. Treatments provided the following RDP levels/cow/day 0g,
180g, 360g, 540g and 720g. A RDP source, calcium caseinate (90% crude protein (CP) on dry
matter basis and 100% rumen degradable) was used and mixed with molasses based concentrate.
The cows had ad lib access to low quality grass hay (2.26% CP, 73.94% neutral detergent fibre).
The trial period consisted of 14 days adaptation, 21 days intake study and 7 days digestibility
study. No statistical significant (P > 0.05) influence of RDP level on the apparent digestibility of
dry matter (DM), organic matter (OM) and neutral detergent fibre (NDF) was detected. The grass
DM intake (DMI), DOMI and metabolisable energy intake (MEI) increased in a linear and
quadratic manner (P < 0.05) with increasing levels of supplemental RDP. The single broken-line
model predicted DOMI/kg BW0.75 with higher accuracy (R2 = 0.45) than the quadratic regression
procedure (R2 = 0.07). According to this model 4.03g daily RDPI/kg BW0.75 or 8.07% RDP of
DOM was required to maximise DOMI of pregnant beef cows consuming winter grassveld hay.
In a second trial the potential to substitute true protein with urea was investigated. Urea replaced
0%, 25%, 50%, 75% and 100% of the natural supplemental RDP. The same procedure as described
in the first trial was followed. The increasing proportion of urea did not significantly (P > 0.05)
influence the apparent digestibility of DM, OM and NDF. There was a linear increase in grass
DMI (P = 0.0355) at increasing levels of urea, with the highest intake observed when urea was
used as a sole source of nitrogen (N). DOMI and MEI increased in both linear and a quadratic
manner (P < 0.05) with increasing levels of urea. The molar proportions of acetic, propionic and
butyric acid were not affected (P < 0.05) by the substitution of urea, while the molar percentages of
iso-butyric and iso-valeric acid were significantly decreased (P < 0.0001) with increasing urea
levels. Ammonia N increased linearly (P = 0.0426) while the ruminal pH was not affected
(P > 0.05) by increasing the proportion of urea. It seems that urea can be the sole RDP source in
supplements for pregnant beef cows consuming the low quality grass hay. In the third trial, the influence of replacing natural protein with urea on the performance of beef
cows grazing natural winter grassveld was investigated. Pregnant Afrikaner x Simmentaler
crossbred cows were randomly allocated to the two treatments. The number of cows per treatment
varied between 18 and 28 each year. The trial was executed over four consecutive winter periods
from 2003 to 2006. The treatment licks comprised of: 1) 100% supplemental RDP from urea and
2) 50% supplemental RDP from urea and 50% from cottonseed oilcake. Lick provision was
controlled to ensure the total RDPI as recommended in the first trial. Increasing the proportion of
supplemental RDP from urea did not have a significant (P = 0.9938) effect on the end live mass of
the cows. The urea levels did not significantly influence (P > 0.05) weaning mass, corrected
weaning mass and average daily gain of the calves. The lack of significant lick treatment effect on
live mass, body condition score and performance of the calves suggests that urea can be used as a
sole source of RDP.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07142011-122358 |
| Date | 14 July 2011 |
| Creators | Bareki, Mathuto Abigail |
| Contributors | Dr AV Ferreira, Dr CHM de Brouwer, Prof HJ van der Merwe |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07142011-122358/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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