The objective of this study was to infer direct and maternal additive effects and direct and
maternal heterosis effects for growth, fitness and carcass traits in beef cattle using least
squares means estimated from crossbreeding studies by Els (1988) and De Bruyn (1991).
The dataset was formed by recording each least squares mean along with the breed
composition, maternal breed composition and direct and maternal heterozygosity. Each trait
was analyzed using a single trait fixed effect model which included source of data as a fixed
effect and breed composition and heterozygosity as covariates. Breed solutions were
relative to the Afrikaner breed. Heterosis results were also obtained for crosses not made.
Among breed groups, crossbred calves showed higher average values for almost all traits
than purebred calves.
The average direct heterosis contributions to weight traits in ten two-breed genotypes, which
involved the Afrikaner (A) as dam line and the Simmentaler (S), Brahman (B), Charolais (C)
and Herefords (H) as sire lines were 3.5, 7.9, 8.2 and 4.3% for birth weight (BW), weaning
weight (WW), 19-month heifer weight (HW) and cow weight at partus (CW) respectively.
Similarly, the average maternal heterosis effects for the weight traits in the four A crossbred
dam genotypes (BA, CA, HA and SA) were 1.5, 8.8, 4.9 and 2.9% for the growth traits
respectively. Due to additive and non-additive effects of C and B purebreds on BW these
sires should only be bred to mature cows. For a weaner calf production system, the C
genotype had the highest direct breed effect of +64.1 kg or 34.8% for WW. The combined
additive effect of the C dam line was however, exceeded by the S dam line (+38.4 kg or
+20.9% versus +50.0 kg or +27.2%). The total combined heterosis effect of the CA dam line
was +32.5 kg versus the +19.2 kg effect of the SA dam line. The average expected
phenotypic values for WW for the SA dam line was thus larger than the CA dam line (233.3
versus 230.7 kg). The maternal heterosis effect of the HA dam was the second largest
(+22.1 kg) of the four two-breed combinations of A. The B genotype used in the study did not have a true superior ability to increase the
expected WW in the A breed. The direct and maternal heterosis effects of the breed were -
0.5 kg or -0.3% and +22.1 kg or 12.0% respectively. The H breed had the lowest direct
breed effects of +24.7 kg or +13.4% on WW out of the four purebred sire lines that were
bred to the A dam line and a small negative direct heterosis effect (-0.5 kg or -0.3%).
Furthermore, the maternal additive effect was negative (-29.6 kg or -16.1%). The maternal
heterosis effect however, was positive (+22.1 kg or +12.0%).
The A sire line had the lowest expected phenotypic values for HW and CW (323.9 and 434.3
kg respectively), indicating that these heifers would probably reach puberty earlier and that
these cows would be smaller compared to genotypes from S, B, C and H genotypes. On
average two-breed genotypes had 48.9 and 40.6 kg expected increase in HW and CW
respectively, and an additional 21.9 kg and 20.4 kg for the two traits respectively in threebreed
genotypes (backcrossing excluded). The H sire line did not have a true ability to
increase expected CW in the A breed. The C genotypes had the lowest average individual
heterosis effect of -17.6 kg (-4.0%) on CW of all four sire lines which were involved in the ten
different two-breed combinations of the study. However, the CA dam line was responsible
for the highest maternal heterosis effect of +54.8 kg or +12.6% out of the four crossbred A
dam lines.
By utilizing genotypic differences the opportunity for high productivity and profitability can be
maximized, especially through cumulative traits such as the calf/cow weight ratio. All
crossbred genotypes, except the BA genotype, increased the calf/cow weight ratio. Results
indicated that the A breed should constitute 75% of the genetic make up of B and C
crossbred genotypes and 25% of H and S crossbred genotypes to maximize calf/cow weight
ratios. The HSA, HBA and BSA, genotypes had the largest calf/cow weight ratios of 0.509,
0.506 and 0.495 respectively, mainly due to the large direct heterosis effects of +22.7
(+12.3%), +28.0 (+15.2%) and +36.7 kg (+19.9%) of the HS, HB and BS genotypes for WW
respectively. This gives opportunity for direct paternal heterosis to be used in crossbreeding
systems with purebred A dams. Alternatively, since the B breed had a true ability to increase
the expected BW in the A dam, it is suggested that a specific or rotational crossbreeding
system which involves S and A dams that are mated with either H or B (only on mature
dams) sires for the production of weaner calves under sweet veld conditions, be used.
The data were also used to estimate the additive and non-additive effects for fitness traits in
the two- and three-breed crosses. The average direct heterosis contributions were +14.9,
+109.1, -162.7, +21.0 and 15.4% respectively for CR, MB, MP, WP and WR for ten two breed genotypes. Similarly, the average maternal heterosis effects in four A crossbred dam
genotypes were 0.0, -87.5, +97.7, -1.9 and -7.4% for the fitness traits respectively. The HA
genotype had the highest expected F of 83.1% in two-breed genotypes. The direct heterosis
contributions in the HA genotype were +21.7, -2.3, -5.8, +28.3 and +30.1% percentage units
respectively and the maternal contributions were -8.2, -2.4, +1.6, -6.4 and -11.6 for the traits
respectively. The expected phenotypic values for improved traits in the HA and AHA
genotypes were 94.9 versus 96.4% for CR, 92.2 versus 96.3% for WP and 83.1 versus
86.8% for WR (MB and MW remained unchanged). Crossbreeding the A dam line with the B
sire line resulted in improved expected WR: 66.7 versus 80.2% in BA. Backcrossing the BA
genotype decreased WR. This could mainly be explained by the increased expected MW;
3.3% in the A versus 6.0 and 15.6% in the BA and ABA genotypes respectively and the
lower expected WR of 72.8 and 74.5% in the ABA and BBA genotypes respectively. While
the SA genotype had an improved expected WR of 78.4% compared to the A genotype
(66.7%), the WR in the ASA progeny was the lowest of all genotypes (60.4%). The low
expected WR of the SA genotype could be explained by the increased expected MB of 5.3
versus 2.2% and MW 5.7 versus 3.3% of the A breed. The poor performance of the SSA
genotype could be ascribed to an increase in MB and MW which was 7.3 and 4.3%
respectively. The ACA, AHA and BHA genotypes had the highest expected WR of 86.9,
86.8 and 83.0% respectively. A specific crossbreeding combined with a terminal sire system
is suggested to increase fertility in the A breed. Rotational systems will not have the same
advantage since backcrossing the CA or HA dams to their respective sire lines would
decrease the WR to 64.2 and 73.1% respectively. Alternatively, CA, HA or CH crossbred
sires could be used on purebred A dams in a specific crossbreeding system. These
genotypes had the largest direct heterosis effect on WR of all ten two-breed genotypes
(36.5, 30.1 and 30.8% percentage units respectively). In a specific two-breed system the HA
genotype would maximize WR.
Although the average direct heterosis effects were unfavourable (-2.1 and -13.0 g/day
respectively) for feedlot gain (FG) and carcass gain CG), feed conversion ratio (FCR) was
-2.3% (a desirable effect). The average maternal heterosis effects for the feedlot traits were
undesirable in the four A crossbred dam genotypes (-1.3, -7.4, and +0.9% respectively) for
all the traits. Although these average heterosis effects suggest that feedlot traits do not
benefit from crossbreeding, selected genotypes offer opportunity to increase feedlot
production efficiency.
As purebred the A compared less favourably in feedlot traits with Bos taurus breeds.
However, it was evident that the A dam in two-breed crossbreeding could outperform the purebred S and Bos taurus crossbred dam lines in most of the these traits. The average
direct heterosis contributions to feedlot traits in ten two-breed genotypes for the S, B, C and
H as sire lines were -2.1, -13.0 (undesirable) and -2.3% (desirable) for feedlot gain (FG),
carcass gain (CG) and feed conversion rate (FCR) respectively. Similarly, the average
maternal heterosis effects for the feedlot traits in the four A crossbred dam genotypes were
-1.3, -7.4, and +0.9% (undesirable) for FG, CG and FCR respectively. However, the A dam
could be utilized in two-way crossbreeding systems with a terminal sire such as the C. The
CCA genotype had expected average FG, CG and FCR of 1376.8 g/day, 781.2 g/day and
6.0 kg/kg respectively. Alternatively, the paternal heterosis contributions from BA, HA, SA,
BH, BS and HS sire lines were also favourable. The aforementioned genotypes could thus
be used as sire lines on purebred A dams to improve feedlot traits.
It should however be noted that the data did not take cogniance of the genetic trends in the
traits and the effects on heterosis parameters in any of the breeds since the conduction of
the crossbreeding experiments. Heterosis units are therefore not directly applicable.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08162012-105748 |
| Date | 16 August 2012 |
| Creators | Theunissen, Anette |
| Contributors | Dr MD MacNeil, Prof FWC Neser, Prof MM Scholtz |
| 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-08162012-105748/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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