African
Journals Online
South African Journal of Animal Science
Volume 31, Issue 3, 2001
Abstracts
Variance component estimation on female fertility traits in
beef cattle
Rust, T.Groeneveld, E.
131-141
Abstract: The purpose of this review is to define possible
breeding objectives for Southern African beef cattle farmers and
to review different means of expressing genetic reproductive
merit. The breeding objective considered was to maximize the
number of calves born or weaned for a given number of cows in a
herd under prevailing environmental and management conditions.
This is a complex trait that has many components. While this
trait is clearly a function of the reproductive ability of each
cow, it is also affected by the age structure of the herd. A
number of auxiliary or index traits are used to assess this
objective and their merits, shortfalls and requirements in terms
of data collection are discussed. It was evident that the trait
of choice was influenced by the management system. Fewer
component traits can be measured and incorporated as variables in
a genetic model in more extensive systems. Since South African
beef cattle production systems tend to be semi-extensive or
extensive, traits to consider include calving rate, calving
success, calf survival, days to calving, age at first calving,
calving date, calving ease and calving interval.
Performance responses of lambs of various ages to Italian
ryegrass (Lolium multiflorum) fertilized
with various levels of nitrogen
De Villiers, J.F.Van Ryssen, J.B.J. 142-148
Abstract: Italian ryegrass (Lolium multiflorum cv.
Midmar) is often fertilized with high levels of nitrogen (N) in
order to ensure maximum dry matter (DM) yields. This practice
also increases the N content of herbage. This study was conducted
to determine whether differences in the nitrogen (N) content of
Italian ryegrass would have an effect on the performance of South
African Mutton Merino lambs. Fertilizer levels of 100, 200, 400,
600 or 800 kg N/ha were applied to the pastures in order to
produce herbage containing varying concentrations of N. Nitrogen
fertilization increased the total N and nitrate-N in the plant
material and decreased non-structural carbohydrate
concentrations. An increase in rumen ammonia-N concentration with
increasing pasture N concentration was observed in twelve and
four-month-old lambs. A quadratic relationship was found to exist
between the N content of ryegrass and DM intake for
twelve-month-old lambs, and a negative linear relationship was
observed for four-month-old lambs. A quadratic relationship was
observed between the N content of ryegrass and average daily gain
for lambs of both age groups. The equations derived in this study
illustrate the potentially negative effects of high
concentrations of N and nitrate-N in Italian ryegrass on intake
and growth rate of lambs.
Intake and rumen degradation in cattle fed napier grass (Pennisetum
purpureum) supplemented with various levels of Desmodium
intortum and Ipomoea batatus
vines
Kariuki, J.N.Tamminga, S.Gachuiri, C.K.Gitau, G.K.Muia,
J.M.K. 149-157
Abstract: This study was conducted to assess the effect of
greenleaf desmodium (Desmodium intortum) and sweet potato
vine (Ipomoea batatus) supplementation of napier grass on
dry matter intake, degradation and rumen fermentation in Friesian
steers. Four fistulated steers were offered napier grass diets
containing 0, 10, 20 or 30% desmodium or sweet potato vine in two
4 x 4 latin squares. Organic matter intake per kg metabolic body
weight increased linearly with increasing inclusion level of
desmodium (74-90 g/kg 0.75) and sweet potato vine
(78-94 g/kg 0.75). Crude protein intake also increased
linearly with the increase in inclusion level of desmodium
(7.6-13.0 g/kg 0.75) and sweet potato vine (7.9-12.9
g/kg 0.75). Supplementation improved DM degradation
but did not change rumen pH. Rumen fermentable organic matter
increased by up to 52% and 43% for desmodium and sweet potato
vine respectively at the highest levels of supplementation.
Ammonia nitrogen concentrations increased with increasing level
of desmodium (130-214 mg/l) and sweet potato vine 139-235 mg/l).
Inclusion of desmodium and sweet potato vine led to small
increases in concentrations of total and individual volatile
fatty acids. It was concluded that the two forage supplements
could play an important role in improving animal performance when
napier grass is fed as the basal diet.
Effect of dietary vitamin E on the performance of broilers
and quality of broiler meat during refrigerated and frozen
storage.
Coetzee, G.J.M.Hoffman, L.C.
158-173
Abstract: Experiment 1 was carried out with 220
one-day-old broiler chicks to evaluate the effect of 11 different
levels of vitamin E supplementation (viz. 0 to 200 mg
a-tocopheryl acetate/kg diet) on the production performance of
broilers and oxidative stability of frozen broiler carcasses. The
diets with vitamin E levels of 0 to 100 mg were fed from day-old
to 42 days of age, and the diets with vitamin E levels of 120 to
200 mg were fed from 21 to 42 days of age. The oxidative
stability, evaluated by thiobarbituric acid reactive substances
(TBARS), was determined after 30, 90, 120 and 150 days of storage
at -20 șC. There were no differences in weight gain (2.29 ±
0.397 kg) or feed conversion ratios (1.85 ± 0.111 kg feed/kg
gain) between dietary treatments. TBARS values increased with
increasing time of storage (basal diet: day 30 = 1.71 ± 0.51;
day 150 = 4.89 ± 0.51), but decreased with increasing vitamin E
levels (day 150: basal = 4.89 ± 0.51; 100 mg/kg = 1.09 ± 0.27).
Experiment 2 was carried out with day-old broiler chicks to
evaluate the effect of five levels of vitamin E supplementation (viz.
0 to 160 mg a-tocopheryl acetate/kg diet) on performance
parameters and the oxidative stability of refrigerated carcasses.
The experimental diets were fed from day-old to 42 days of age.
Oxidative stability, evaluated by TBARS, colour deterioration and
microbiological stability was determined after 0, 4, 8, 10 and 12
days of storage at 4 șC. Fatty acid analysis was done on samples
obtained on days 0 and 12. There were no differences in total
weight gain (2.37 ± 0.467 kg) or feed conversion ratio (1.88 ±
0.117 kg feed/kg gain) between dietary treatments. TBARS values
increased with increasing storage time, but decreased with
increasing vitamin E levels. There were no differences between
treatments for colour measurements for L* (44.97 ± 0.662), a*
(5.23 ± 0.315) or b* (12.76 ± 0.321) values. Microbiological
counts increased over time, but dietary vitamin E concentration
had no effect. There were no differences between dietary
treatments for any of the groups of fatty acids measured (SFA:
Day 0 = 26.1 ± 1.13 %, Day 12 = 26.1 ± 1.17 %; MUFA: Day 0 =
41.4 ± 1.46 %, Day 12 = 40.2 ± 2.28 %; PUFA: Day 0 = 32.4 ±
1.95 %, Day 12 = 33.8 ± 2.52 %). Similarly, fatty acid
proportions did not change over time. There were no differences
between dietary groups for mean muscle pH (6.01 ± 0.206).
Productive performance of naked neck, frizzle and dwarf
laying hens under various natural climates and two nutritional
treatments
Garces, A.Casey, N.H.Horst, P. 174-180
Abstract: The productive performance of major genes for
feather reduction (naked neck and frizzle) and body size
reduction (dwarf) in a dual-purpose layer strain was evaluated in
the subtropical coastal region of southeast Africa (Maputo,
Mozambique). The experimental material consisted of ight
different genetic groups, two diets (14.4 and 16.2% crude
protein) and two climatic seasons. Birds were caged individually
in a laying house with natural light and ventilation. Traits
measured were: temperature and relative humidity, body weight,
age at first egg, egg number and weight, feed intake and
mortality. The following were calculated: persistence, egg mass,
feed efficiency, feed conversion, biological efficiency (EMD/BW 0.75)
and productivity (EN/BW 0.75). The main results show
that: (1) none of the feather-reducing genes significantly
improved egg production or feed efficiency, although the naked
neck (Na) excelled in terms of biological efficiency and
productivity; (2) the dwarf gene (dw) was associated with
delayed sexual maturity, production of fewer and lighter eggs,
higher persistence, better feed conversion and higher
survivability; (3) elevated temperatures restrained voluntary
feed intake, egg number and weight, and body weight gain; (4) the
lower dietary protein content resulted in decreased body weight.
It was concluded that the genes were not equally responsive to
the environments, which offers the opportunity for selective
breeding.
Relationships between production and product traits in
subpopulations of Bonsmara and Nguni cattle
Strydom, P.E.Naude, R.T.Smith, M.F.Kotze, A.Scholtz,
M.M.Van Wyk, J.B. 181-194
Abstract: Ninety bull calves of five Bonsmara strains, viz.
Edelheer (E), T-49 (T), Wesselsvlei (W), Roodebos (R) and Belmont
Red (BR), and two Nguni sub-populations, viz. Bartlow (B)
and non-Bartlow (NB), were fattened under intensive feeding
conditions and serially slaughtered at four different slaughter
weights. Phylogenetic relationships between the five Bonsmara
strains and between the two Nguni subpopulations were determined
by means of blood typing. Growth performance, carcass
characteristics and meat quality characteristics were compared
between the sub-populations of each breed. Genetic distances
between the Bonsmara animals confirmed the existence of five
genetic subpopulations with variation in genetic distances
between them. The genetic distance between the two Nguni
subpopulations was very small, indicating genetic similarity.
Means for production and product characteristics were adjusted
for mean subcutaneous fat percentage by means of analysis of
covariance. T gained weight faster and more efficiently on a live
and carcass weight basis than the other Bonsmara groups, while B
gained carcass and muscle weight more efficiently than NB. T had
proportionally more meat in the high-priced cuts of the carcass
than W. Muscle of the W line had a higher ageing potential
(measured as myofibrillar fragmentation; MFI) than T, resulting
in higher tenderness scores for W. Similarly, B had higher MFI
for muscle aged for one or seven days, coupled with more tender
meat than NB. Pairwise correlations between growth and muscle
characteristics indicated that fast growing animals tend to
produce less tender meat.
Genetic and phenotypic variation of some reproductive
traits in Egyptian buffalo
Aziz, M.A.Schoeman, S.J.Jordaan, G.F.El-Chafie,
O.M.Mahdy, A.T.
195-199
Abstract: The objectives of this study were to determine
the effects of season, year of calving and parity on lactation
period, calving interval, number of days open and dry period in
Egyptian buffalo, and to estimate genetic and phenotypic
parameters for these traits using a multi-trait animal model.
Season of calving, year of calving and parity affected the traits
studied. Heritability estimates for lactation period, calving
interval, dry period and number of days open were 0.09, 0.07,
0.13 and 0.08 respectively and repeatability estimates were 0.27,
0.14, 0.27 and 0.19 respectively. Estimates of the permanent
environmental component (c2) were low. Genetic
correlations between these traits were low and positive, except
for that between lactation period and dry period, which was
negative. A similar pattern was observed for phenotypic
correlations, but these were higher than those observed for
genetic correlations.
A survey of small-scale cattle farming systems in the North
West Province of South Africa
Schwalbach, L.M.Groenewald, I.B.Marfo, C.B.
200-204
Abstract: A questionnaire-based survey was conducted among
a purposive sample of 60 small-scale cattle farmers in the
Mopeane Rustenburg district, all of whom owned five or more head
of cattle. Results showed that small-scale cattle farming is a
part-time activity for most farmers in this district, and a way
of investing or saving money in a form that is easily converted
to cash when needed. This activity also provides households with
a source of fresh milk. Contrary to the situation in most other
Southern African regions, social status and lobola (bridal dowry)
did not constitute the most important reasons for farming with
cattle. The poor economic return of these small-scale cattle
farming activities and the potential environmental degradation
associated with overstocking poses a serious risk to the
long-term sustainability of such farming systems.
The effect of calving season and age at calving on
production traits of South African dairy cattle
Mostert, B.E.Theron, H.E.Kanfer, F.H.J.
205-214
Abstract: Lactation records of South African Holstein and
Jersey cows were classified into six calving seasons and 18 age x
lactation classes using several trials involving analysis of
variance and estimation of fixed effects of calving age on
test-day as well as 305-day yields. Best Linear Unbiased
Estimates for the effect of season and age x lactation were
derived using an animal model following the prediction of daily
milk, butterfat and protein yields on fixed days-in-milk and of
cumulative 305-day yields by linear interpolation. For both
breeds, test-day and cumulative 305-day yields were higher for
cows calving in mid-winter (June/July) compared to cows calving
in mid-summer (December/January). Daily yields early in the
lactation were more influenced by calving age than daily yields
towards the end of the lactation. Cows that calved at younger
ages in lactations 1 and 2 produced less milk compared to cows
calving at older ages over the entire lactation. Second and later
parity cows had higher test-day yields than heifers for most
stages of the lactation. These estimates can be used to adjust
test-day and cumulative yields for the effect of season and age
class, thereby enabling the determination of herd levels and the
derivation of standard lactation curves and projection factors
for South African Holstein and Jersey cows.
Phenotypic and genetic relationships between lamb and ewe
traits for the Sabi sheep of Zimbabwe
Matika, O.Van Wyk, J.B.Erasmus, G.J.Baker, R.L.
215-222
Abstract: Genetic and phenotypic correlations were
estimated between lamb and ewe traits in a flock of Sabi sheep
reared at the Matopos Research Station. Direct additive estimates
of heritability were: 0.28 ± 0.04; 0.17 ± 0.00; 0.25 ± 0.01;
0.39 ± 0.01; 0.59 ± 0.01; 0.50 ± 0.01; 0.68 ± .03; 0.12 ±
0.003; 0.25 ± 0.01; 0.11 ± 0.00; 0.12 ± 0.00; for birth
weight, weaning weight (120 days), 12 month weight, 18 month
weight, ewe mating weight, post partum weight, ewe weight at
weaning of lamb, total weight of lamb weaned, slaughter weight,
hot and cold carcass weights respectively. Genetic correlations
between birth weight and other weights to 18 months were high
(0.75-0.85), whilst the relationship between weaning, 12 month
and 18 month weight was close to unity. The genetic correlation
between birth weight and ewe weights (mating, post-partum and dam
weight at weaning of lamb) were moderate viz. 0.51 ±
0.08, 0.40 ± 0.09, 0.49 ± 0.07 respectively and were close to
unity at 18 months of age viz. 0.96 ± 0.02, 0.92 ± 0.03,
and 0.84 ± 0.03 respectively. Total weight of lamb weaned was
moderately correlated to birth weight (rg = 0.46 ±
0.15) but tended to be highly correlated with 18 month weight
(0.92 ± 0.10) and ewe weights (0.75 ± 0.09-0.91 ± 0.07). The
genetic correlation between birth weight and slaughter and
carcass weight was moderate and was high at 18 months. The
heritability estimates from a univariate logit transformed
analysis for fertility, prolificacy and lamb survival were 0.08
± 0.04, 0.22 ± 0.03, and 0.01 ± 0.02 respectively. The genetic
correlation between fertility and lamb weight and ewe weights was
low (-0.08 ± 0.004, to 0.06 ± 0.02) and some estimates had
large standard errors. The genetic correlation between
prolificacy and birth weight was close to zero. The genetic
correlations between prolificacy and weaning weight, 12 month
weight, 18 month weight, ewe mating, post-partum and ewe weight
at weaning were 0.07 ± 0.02; 0.12 ± 0.00; 0.07 ± 0.02; 0.22 ±
0.00; 0.13 ± 0.00; 0.24 ± 0.00 respectively, and that between
fertility and prolificacy was negative (-0.17 ± 0.07). Genetic
correlations between lamb survival and birth weight, weaning
weight, 12 month weight, 18 month weight and total weight of lamb
weaned were 0.18 ± 0.00, 0.26 ± 0.00, 0.15 ± 0.00, 0.15 ±
0.00, 0.13 ± 0.00 respectively. Selection for birth weight and
total weight of lamb weaned have possible uses in a selection
index for the Sabi flock.
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