Feedlot performance of Dorper lambs on Opunti: based diets with different nitrogen sources
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Date
2009-11
Authors
Shiningavamwe, Katrina Lugambo
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Three feedlot diets were evaluated with Dorper wether lambs at Bergvlug Experimental
Farm, Khomas Region, Namibia. Bergvlug is located about 35 km east of Windhoek. The
three treatment diets consisted of a conventional feedlot diet (treatment diet T0) and two
Opuntia-based treatment diets (T1 and T2) containing different additional nitrogen sources,
namely a non-protein nitrogen (NPN; feed grade urea) or natural protein (sunflower oilcake
meal). Treatment diet T0 was based on coarsely ground lucerne hay, yellow maize meal, feed
grade urea and molasses meal. The Opuntia-based treatment diets (T1 and T2) were
reformulated and part of the lucerne was replaced by sun-dried and coarsely ground Opuntia
cladodes at levels of 330 or 300 g/kg. In treatment diet T1 additional nitrogen was included
as feed grade urea (non-protein nitrogen; NPN) and for treatment diet T2 the additional
nitrogen was included as sunflower oilcake meal (a natural protein).
The feed intake and water intake, the growth performance and carcass characteristics of the
Dorper wether lambs were evaluated in the feedlot. Forty-five newly weaned Dorper wether lambs, weighing on average about 22 kg, were randomly allocated to the three treatment
diets. The 15 Dorper wether lambs per treatment diet were further subdivided into three
subgroups or replicates of five lambs each. For the duration of the trial the lambs were kept in
small pens in a shaded area (open-sided roofed shed). The Dorper wether lambs were fed the
treatment diets until a target average slaughter weight of 35 kg per treatment diet was
reached.
During the feeding period in the feedlot, one replicate of five Dorper wether lambs per
treatment diet was moved from the feedlot pens to metabolism cages for a week every third
week to determine their individual daily feed and water intake and apparent digestibility of
the three treatment diets. The daily urine and faecal excretions were also monitored.
Chemical analysis of the three treatment diets used in this study showed that acid-detergent
fibre (ADF), neutral-detergent fibre (NDF), organic matter (OM) and gross energy (GE) have
decreased with inclusion of sun-dried and coarsely ground Opuntia cladodes, which is
ascribed to the lower ADF, NDF, OM and GE content of the Opuntia cladodes. On the other
hand, the ash and lipids increased with inclusion of sun-dried and coarsely ground Opuntia
cladodes in the treatment diets.
The inclusion of sun-dried and coarsely ground Opuntia cladodes at 330 or 300 g/kg in the
treatment diets in general had little or no effect on the feed intake and digestibility of the
treatment diets by Dorper wether lambs. Exceptions were observed for the intake and
apparent digestibility of ADF and NDF as a result of the difference in fibre content of the
treatment diets. Similar water intake and urine excretion were observed for Dorper wether
lambs fed any one of the treatment diets during the three cage feeding periods.
The results of the study confirmed that the feed intake and apparent digestibility of the
treatment diets for Dorper wether lambs were not affected by: (1) the inclusion of sun-dried
and coarsely ground Opuntia cladodes at 330 and 300 g/kg; or (2) two nitrogen sources used
(NPN or natural protein) in the Opuntia-based diets.
Considering the results of the Cage Periods 1 to 3, it can be summarised that the daily intake
and apparent digestibility of DM and other chemical constituents of the Dorper wether lambs
increased as the trial progressed, regardless of the treatment diets. It suggests that the reticulo-rumen of Dorper wether lambs were getting better adapted over time to the diets and
consequently digestibility improved.
The average daily gain and feed conversion efficiency of Dorper wether lambs fed the
Opuntia-based diet supplemented with natural protein were comparable to those fed the
conventional feedlot diet. The Dorper wether lambs fed the Opuntia-based diet supplemented
with NPN had a lower growth rate than those fed the conventional feedlot diet and the
Opuntia-based diet supplemented with natural protein. Thus, although feed conversion
efficiency was not significantly (P>0.05) different among treatment diets, Dorper wether
lambs fed the conventional diet and the Opuntia-based diet supplemented with natural protein
required less feed to gain weight than those fed the Opuntia-based diet supplemented with
NPN. This suggests that supplementing an Opuntia-based feedlot diet with a natural protein
source will markedly improve feed efficiency and average daily gain of lambs. This may
reduce the feeding period required to reach the target slaughter weight and increase the
economic benefit associated with the use of sun-dried and coarsely ground Opuntia cladodes
in feedlot diets.
Most of the carcass characteristics considered were not significantly different (P>0.05)
among treatments. It suggests that carcass quality or grading is not markedly affected by
inclusion of sun-dried and coarsely ground Opuntia cladodes in feedlot diets (up to 330 or
300 g/kg) for Dorper wether lambs or by the nitrogen source used to balance the diets. The
carcasses of the Dorper wether lambs fed the three different treatment diets fetched very
similar prices per kg. However, the Dorper wether lambs fed treatment diet T1, the Opuntiabased
diet with the inclusion of feed grade urea (an NPN source), did not reach the average
target slaughter weight of 35 kg, even after 91 days in the feedlot. Therefore, their lighter
carcasses and poorer carcass grading at slaughter fetched a lower total price per carcass.
The results of this study, the fourth study under the auspices of the UFS, opened the prospect
of formulating affordable Opuntia-based diets for specific application to ruminant species of
different ages and production classes. However, more research is needed to evaluate the
growth performance, carcass characteristics and profitability of other small stock breeds and
ruminant species fed sun-dried and coarsely ground Opuntia cladodes in feedlot diets,
balanced with different nitrogen sources.
Description
Keywords
Dorper Sheep -- Feeding and Feeds, Sheep -- Feed utilization efficiency, Lambs -- Feeding and feeds, Dissertation (M.Sc.Agric. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2009