African
Journals Online
South African Journal of Animal Science
Volume 30, Issue 2, 2000
Abstracts
Genetic relationships between three indigenous cattle
breeds in Mozambique
Kotze, A.Harun, M.Otto, F.Van der Bank, F.H.
92-97
Abstract: This study provides the first account of genetic
relationships between three indigenous cattle breeds from
Mozambique. Forty-two blood group factors and six blood proteins
revealed genetic variation of 84% (Angone), 88% (Bovine de Tete)
and 90% (Landim) at the loci studied. Average heterozygosity
values ranged from 33% for Angone and Bovine de Tete to 35% for
the Landim. The genetic distance was greatest between the Landim
and both the Bovine de Tete and the Angone breeds, whereas the
smallest genetic distance was observed between the Bovine de Tete
and the Angone. These results show the intermediate relationship
of Bovine de Tete with the Angone and Landim breeds and show that
the Bovine de Tete is an admixture of taurine and indicus genes.
The influence of proportion of Simmentaler breeding in a
multibreed synthetic beef cattle population on preweaning growth
traits
Schoeman, S.J.Jordaan, G.F.Skrypzeck, H.
98-109
Abstract: Data from a multibreed composite beef cattle
population managed under intensive irrigated grazing conditions
were used to estimate direct additive heritabilities (h 2a)
and maternal heritabilities (h2m) for birth
weight (BW) and weaning weight (WW) of the calf and cow
efficiency of the dam (CE; WW/dam weight 0.75). Calves
born between 1968 and 1993 (n = 52 628) had varying levels of
Simmentaler genes, ranging from 0% to 97%, with an average of
33.4%. Direct heritabilities fitting unitrait models were 0.66,
0.53 and 0.21 for BW, WW and CE respectively, with corresponding
estimates of h 2m being 0.22, 0.36 and
0.59. Genetic correlations between direct and maternal effects (ram)
were negative for all three traits, varying from -0.32 to -0.63.
Direct breeding values for BW and WW decreased and maternal
breeding values increased with increasing proportion of
Simmentaler. Cow efficiency was unaffected by an increase in the
proportion of Simmentaler.
The effect of choice-feeding from 7 weeks of age on the
production characteristics of laying hens
Olver, M.D.Malan, D.D.
110-114
Abstract: Day-old Amberlink pullets were fed chicken
starter mash for the first seven weeks of age. Group A was
choice-fed with pelleted protein concentrate, whole yellow maize
and limestone powder from seven to 16 weeks of age. Group B
received the same diet as group A, but the protein concentrate
was fed in mash form. Group C (control treatment) received a
pullet grower diet in mash form. The pullets were placed in
individual laying cages from 16-80 weeks of age. The choice-fed
groups received feedstuffs from three separate troughs (i.e.
whole maize, protein concentrate and limestone powder), and group
C received a layer diet in mash form. Hens offered the choice-fed
diets were heavier (P < 0.05) at 16 weeks and at first egg
than hens fed the control diet, even though they ate less food
(group A: 66.1 g/d; group B: 66.4 g/d) than the control group
(68.2 g/d). During the laying period (16-80 weeks), hens offered
the choice-fed diets laid significantly (P < 0.01) heavier
eggs, eggs with thicker shells, eggs with darker yolks and had
better food conversion ratios than those fed the control diet. No
significant differences between treatments were observed for eggs
laid per hen, food consumed per day or Haugh unit score. Choice
feeding was found to be beneficial for laying hens, and it
appeared that early commencement of the regime was necessary for
optimum output.
An evaluation of the use of blood metabolite concentrations
as indicators of nutritional status in free-ranging indigenous
goats
Pambu-Gollah, R.Cronje, P.B.Casey, N.H.
115-120
Abstract: The aim of this study was to determine whether
blood metabolite concentrations in free-ranging indigenous goats
are sensitive to expected variations in nutrient supply, and
whether they could be used to evaluate different kidding seasons
at two locations subject to similar seasonal variations in terms
of nutrient supply. Monthly blood samples were taken over a
period of one year. At Delftzyl farm, where a winter kidding
season (June) was practised, glucose concentrations decreased
from February onwards and reached their lowest levels just prior
to the kidding season. Plasma glucose concentrations increased
sharply after parturition and subsequently decreased until the
end of lactation. Glucose concentrations were lower in lactating
does than in non-lactating does during the first two months of
lactation. In contrast, glucose concentrations during lactation
in does at Loskop farm, where kidding took place during spring
(October), did not differ from those recorded during the four
months following weaning, and neither were there differences
between lactating and non-lactating does. Glucose concentrations
during lactation at Loskop farm were also higher than at Delftzyl
farm. The different responses can be attributed to the fact that
lactation at Loskop farm coincided with peak nutrient
availability during the summer period of vegetative growth,
whereas lactation at Delftzyl farm coincided with low nutrient
availability and quality during the winter period of plant
dormancy. Plasma urea concentrations were also elevated during
the last month of pregnancy and the first two months of lactation
at this location, and were higher during lactation than those
recorded at the summer kidding site, indicating that body protein
reserves may have been catabolized to support gluconeogenesis in
these animals. Plasma cholesterol concentrations were higher in
lactating goats than in non-lactating goats at Delftzyl farm but
not at Loskop farm. Cholesterol concentrations during lactation
were also higher at Delftzyl than at Loskop. This suggests that
body adipose tissue reserves were catabolized during the winter
lactation at Delftzyl farm. These results indicate that lactating
does at Delftzyl farm were unable to maintain glucose homeostasis
during pregnancy and lactation without significant catabolism of
body reserves, and suggests that the winter kidding practised
there was inappropriate in relation to the available nutrient
supply. It was concluded that the plasma concentrations of all
the blood metabolites studied were sensitive to seasonal changes
in nutrient supply, and that they could be of use as a management
tool in free-ranging farming systems in which conventional
methods of nutritional assessment are difficult to apply.
Growth parameters of Holstein-Friesland heifers reared on
complete diets containing different roughages
Muller, C.J.C.Botha, J.A.
121-127
Abstract: At two months of age, 48 Holstein-Friesland
heifers were randomly allocated to four treatments comprising
untreated wheat straw (WS), oven-ammoniated wheat straw (AWS),
lucerne hay (LH) or oat hay (OH). Least cost nutrient balanced
complete diets were formulated for heifers of different age
groups, i.e. 2–6, 6–10, 10–13, 13–18 months
and 18 months to first calving. Dry matter (DM) intakes of
individual heifers were determined twice weekly. Animals were
weighed once weekly, and girth circumference and wither height
were measured monthly. From 13 months of age, heifers were
observed daily for oestrus and inseminated provided that a
minimum live weight of 290 kg had been attained. At two months of
age, heifers weighed (mean ± s.e.) 69 ± 1.1 kg and wither
height and girth circumference measured 84.6 ± 0.4 and 94.1 ±
0.6 cm respectively. The average daily gain of heifers receiving
diets containing LH was higher (P < 0.001) from two months of
age to calving than that of heifers receiving diets containing
WS, AWS or OH (0.76 vs. 0.68, 0.64 and 0.68 kg/day
respectively). Heifers receiving LH diets were heavier (P <
0.001) at first calving than heifers fed diets containing other
roughages. Wither height at 22 months of age did not differ (P
> 0.05) between treatments, the overall mean being 129.3 ±
0.5 cm. Girth circumference of heifers fed diets containing WS,
AWS and OH was smaller (P < 0.001) than that of heifers fed LH
(179.2, 177.3 and 176.7 cm vs. 188.3 cm respectively).
Heifers fed diets containing LH also had higher (P < 0.01)
condition scores than heifers fed diets containing other
roughages. The lower feeding cost of AWS diets in comparison to
other diets should be utilized fully in the rearing of
replacement heifers.
Relationship between performance measurements and sale
price of Dorper rams in the Northern Cape Veld-Ram Club
Fourie, P.J.Neser, F.W.C.Van der Westhuizen, C.
128-132
Abstract: The sale prices of 1 609 Dorper rams sold
between 1990 and 1999 were compared with their measured
performances. An analysis of variance was carried out in order to
determine which variables influenced sale price. The most
importance factors were classification (stud vs.
commercial), auction weight and coat type (hair, wool or a
mixture). Buyers seem to show a preference for animals with hair
and a mixture of hair and wool over those with predominantly
woollen coats. Buyers recognise the importance of performance
data in the selection of breeding rams.
Meat quality attributes of night-cropped Impala (Aepyceros
melampus)
Hoffman, L.C. 133-137
Abstract: The aim of this experiment was to determine the
effect of using a heavy or a light calibre rifle for night
cropping of impala (Aepyceros melampus) on meat quality
(pH, colour, cooking and drip loss, tenderness). The effect of
gender on these parameters was also tested. Eight male and eight
female impala were shot at night using either a heavy or a light
calibre rifle. Sex and rifle calibre had an effect on some of the
parameters tested. An exponential function (y = a + b e (ct)
) was fitted to the rate of pH decline with time. Constants for
females were: a = 5.667 ± 0.0142, b = 2.097 ± 0.1777 and c =
-0.451 ± 0.0541, and constants for males were: a = 5.792 ±
0.0142, b = 3.055 ± 0.1777 and c = -0.711 ± 0.0541. These
constants differed (P < 0.05) between sexes. The impala showed
a mean pH45 of 7.17 ± 0.0674 and a mean pHf
of 5.70 ± 0.068. Mean drip and cooking loses were 2.55 ±
0.300%, 23.98 ± 0.367%, respectively, whilst a mean shear value
of 3.65 ± 0.293 kg / 1.27 cm diameter was also noted. The darker
colour of venison was reflected in the CIELAB values of the M.
longissimus thoracis (L* = 29.22 ± 0.590, a* = 11.26 ±
0.319, b* = 7.36 ± 0.266). One of the animals was stressed prior
to and during killing, and showed attributes associated with
ante-mortem stress: higher pHf, lower drip loss and
darker meat. The results indicate that the present method of
cropping ungulates does not have a negative effect on the meat
quality parameters tested.
A nonparametric Bayesian approach for genetic evaluation in
animal breeding
Pretorius, A.L.Van der Merwe, A.J.
138-148
Abstract: This article proposes the Bayesian approach to
solve problems arising in animal breeding theory. General
elements of Bayesian inferences, e.g. prior and posterior
distributions, likelihood functions, and the solving of the
random effects in the case of the mixed linear model are
discussed. Since the random effects are typically assumed to be
normally distributed in both the Bayesian and Classical models, a
Bayesian procedure is provided which allows these random effects
to have a nonparametric Dirichlet process prior distribution. In
the case of the Dirichlet process, the Gibbs sampler is
introduced to overcome some computational difficulties in solving
the genetic parameters of the mixed linear model. To illustrate
the application of these techniques, data from the Elsenburg
Dormer sheep stud and data from a simulation experiment are
utilized.
Factors affecting goat production in a communal farming
system in the Eastern Cape region of South Africa
Mahanjana, A.M.Cronje, P.B.
149-154
Abstract: The aim of this survey was to characterize the
economic, social and nutritional importance of goat farming in
the Mgwalana district of the Eastern Cape region of South Africa,
and to identify critical constraints and opportunities for use in
future development initiatives. The majority (68%) of de facto
heads of households were males, of which 66% were older than 50
years of age. The majority (60%) had received schooling for five
years or less. Most respondents (86%) kept goats. The mean flock
size was 16 head, of which 76.7% consisted of does, 15.8%
castrates and 7.5% bucks. The mean kidding percentage was 76% for
maiden does and 64% for older does.The annual mortality rate was
7%; adult does accounted for 47% of deaths, and abortions for
29%. The main reasons given for keeping goats were for slaughter
during traditional ceremonies (35%) and for cash sales (23%), and
only 15% kept goats for home meat consumption. The motivation for
the sale of goats was mainly to pay debts or save money (45%) and
to buy other foodstuffs (27%). The majority of sales (91%) took
place during the summer months, and buyers (possibly migrant
workers returning home during the Christmas vacation) used the
goats mainly for traditional ceremonies, funerals and weddings.
Only 10% of farmers indicated that they would invest in goat
farming if granted a loan that had to be paid back. This would
appear to be related to labour constraints, as 44% of goat owners
herded their flocks themselves and 37% relied on school-going
children for this purpose. Only 19% of respondents indicated that
they hired labour to herd their flocks. It would appear that
future expansion of goat farming in this area is severely
constrained by labour constraints and the fact that goat meat
ranked lowest on the scale of eating preferences. It was
concluded that initiatives aimed at improving the economic,
nutritional and health status of this community through increased
goat production are unlikely to be successful and that the
problem of bush encroachment is likely to increase to the
detriment of other ruminant species in the future.
The roles of the insulin-like growth factor system and
leptin as possible mediators of the effects of nutritional
restriction on age at puberty and compensatory growth in dairy
heifers
Luna-Pinto, G.Cronje, P.B.
155-163
Abstract: The aim of this experiment was to determine to
what extent changes in the blood concentrations of insulin-like
growth factor-1 (IGF-1), IGF binding proteins (IGFBPs), leptin
and glucose are associated with compensatory growth and age at
puberty in Friesian heifers. Twelve heifers (6 months old; 179.8
kg body weight) were allocated to one of two dietary treatments
for 30 weeks. Treatments were designed to result in two different
growth rates during the first 13 weeks of the experiment, viz.
0.3 kg/d (restriction treatment) or 0.6 kg/d (control treatment).
From week 14 to 30, the restricted group received the same amount
of feed per kg bodyweight as was fed to the control group
(compensatory phase). Heifers in the control treatment reached
puberty four weeks earlier than the restricted group. Mean body
weight at puberty was 256.3 kg and was not affected by treatment.
During the compensatory phase, the growth rate of the previously
restricted animals was greater, and feed conversion ratio
superior, compared to that of the control group. Plasma IGF-1 and
IGFBP-3 concentrations were higher in the restricted group than
in the control group during the early compensatory phase.
Concentrations of IGFBP-3 increased and peaked at puberty for
both treatments, even though puberty occurred at different ages.
In contrast, concentrations of IGF-1 peaked at the point of
maximum growth rate in the previously restricted animals, and in
neither treatment was there a clear relationship with the age of
puberty. Plasma leptin concentrations increased until puberty in
both treatments even though the date of puberty differed. Plasma
glucose concentration did not change at puberty for either
treatment; however, differences between treatments were found
after the restriction period. There were no differences in
IGFBP-2 concentrations between treatments or sampling periods. It
is concluded that concentrations of glucose, IGF-1 and IGFBP-3
are affected by nutritional restriction and repletion, and may
contribute in some measure to the endocrine regulation of
compensatory growth. It is suggested that the increased
concentrations of leptin and IGFBP-3 during pubertal development
may act as physiological signals for the onset of puberty.
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