Masters Degrees (Animal, Wildlife and Grassland Sciences)

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Browsing Masters Degrees (Animal, Wildlife and Grassland Sciences) by Author "De Brouwer, C. H. M."

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    The degradable protein requirements of beef cattle consuming winter forage hay from the pure grassveld type
    (University of the Free State, 2010-05) Bareki, Mathuto Abigail; Van der Merwe, H. J.; De Brouwer, C. H. M.; Ferreira, A. V.
    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.
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    Supplemental degradable protein sources for beef cattle consuming low quality roughage
    (University of the Free State, 2005-05) Jacobs, Henry Lubbe; Van der Merwe, H. J.; De Brouwer, C. H. M.; Spangenberg, H. P.
    English: A study was conducted to determine the best natural source of rumen degradable protein (RDP) not provided by urea to maximize the digestible organic matter intake (DOMI) of a SA natural winter pasture hay (3.51% crude protein (CP) and 74, 23% neutral detergent fibre (NDF). The crude protein degradability of natural winter pasture hay (Cymbopogon- Themeda), cotton oilcake, soybean oilcake and sunflower oilcake was determined by means of the in- sacco- technique. These crude protein degradability values were used to formulate three RDP supplements according to current recommendations (4.01g RDP/kg W 0.75) using the three oilcakes respectively. Urea provided 50% of the supplemental RDP. The other feed ingredients were salt, begasse, molasses, feed grade sulphur and trace minerals. Seven steers (217 SD ± 9.91 kg) per treatment randomly divided were used. The experimental period consist of 14 -day's adaptation, 21- days' intake and 7 days collection period (conventional digestibility study). A significant (P< 0.0001) higher apparent digestibility of NDF occurred when the sunflower oilcake supplement was fed to the steers. The apparent digestibility of dry matter (DM), organic matter (OM), CP and gross energy (GE) was however not influenced significantly (P> 0.05) when different oilcakes supplements were fed. Likewise DOMI/kg W 0.75 , rumen volatile fatty acid concentration and rumen pH did not differ significantly (P> 0.05). The ammonia nitrogen (NH3N) concentration of the rumen fluid of steers that consumed the sunflower oilcake supplements were significantly (P< 0.04) lower than that of cotton oilcake. In a second study the optimum ratio of supplemented urea to the most available oilcake (cotton seed) was investigated. Urea replaced: 0%, 25%, 50%, 75% and 100% of the natural supplemental RDP. The same procedure as described in the first study was used. Steers with an average mass of 200 ± 19.96 kg were used. The replacement of natural supplemental RDP with urea did not significantly (P>0.05) influenced the apparent digestibility of DM, CP, NDF and GE. Accordingly DOMI/kg W 0.75did not differ significantly (P>0.05). The highest (P< 0.05) acetate and propionate concentration in rumen fluid of steers was recorded when urea replaced 75% of the natural RDP in the supplement. The highest (P= 0.008) value for isovalerate concentration in rumen fluid was found when 25% of the supplemental degradable protein was from urea. Increasing levels of urea had no affect on either the rumen NH3N concentration (P=0.3508) or pH (P= 0.0810). According to the results of both studies it seems that urea can supply all the supplemental RDP to steers on low quality roughage. From the results it was concluded that further research is needed on the RDP-requirements of ruminants consuming different types of low quality roughages.