The length of productive life is of major economic importance in dairy cattle production.
Simple breeding objectives such as selection for increased production in dairy cattle have led to a
significant decline in fitness traits. A multi-purpose breeding objective that includes other traits
such as length of productive life should be considered. Herd life reflects the ability of a cow to
avoid being culled for low production, low fertility, or illness. Herd life can be used in breeding
programs if genetic parameters are known. The objectives of the study were to: (1) estimate
genetic parameters for functional herd life for the South African Jersey breed using a multiple
trait linear model, (2) develop a prototype breeding value for functional herd life for the South
African Jersey breed, (3) estimate genetic relationships between functional herd life and
conformation traits in the South African Jersey breed and (4) assess inbreeding depression for
functional herd life in the South African Jersey breed based on level and rate of inbreeding. A
measure of herd life called functional herd life was considered in the current study. Functional
herd life refers to herd life adjusted for milk production in the first lactation. In this study
functional herd life was defined as survival in each of the first three lactations. Functional herd
life was denoted by a 1 if a cow survived and 0 otherwise.
Analyses to estimate genetic parameters for functional herd life were carried out as
follows. Data and pedigree records on purebred Jersey cows that participated in National Milk
Recording and Improvement Scheme were analyzed. Data before editing comprised test-day and
lactation yields on milk, fat and protein yields from 252 629 Jersey cows born between 1968 and
2005. After editing, 181 269 cow records from 636 herds recorded over 16 years were available
for analysis. Estimates of genetic parameters for herd life were obtained using REML procedures
fitting a multiple-trait linear animal and sire models. Heritability estimates (0.02 to 0.03) from
the two models were somewhat similar for all lactations. However, heritability estimates for
lactations 2 and 3 were slightly higher with the sire model compared to the animal model. The
genetic correlation between lactations 1 and 2 from both the sire and animal models was higher
than that between lactations 2 and 3. Genetic correlations from the sire model ranged from 0.68 to 0.99 and corresponding estimates from the animal model ranged from 0.76 to 0.99. Genetic
parameters obtained in the current study suggest that sufficient genetic variation exist for herd
life to allow for genetic improvement and that early selection for functional herd life is feasible.
The development of a prototype breeding value for functional herd life for the South
African Jersey breed was carried out as follows. Test-day and lactation data on cows that
participated in the National Dairy Cattle Improvement Scheme were considered. A multiple-trait
linear animal model was used to estimate breeding values using Parameter ESTimation (PEST)
software package. A complete (co)variance structure for the additive genetic and residual effects
for the three traits were used. These (co)variances were estimated in the first objective.
Reliabilities were approximated using the effective number of daughters. Estimated breeding
values were scaled so that the average breeding value was a 100. Estimated breeding values for
sires ranged from 79 to 114. The rate of genetic progress per year for the period 1985 to 2002
was statistically non-significant (b = 0.02±0.05 per year). The mean reliability was 33.43% and
reflective of the low heritability of functional herd life. However, it should be noted that while
direct selection for functional herd life could lead to genetic progress, this genetic response could
be relatively slow due to the low heritability.
The genetic relationship between conformation traits and functional herd life of the South
African Jersey population was investigated. Data on conformation traits (n = 46 238) and
functional herd life (n = 90 530) on registered South African Jersey cows calving between 1989
and 2008 were obtained from the Integrated Registration and Genetic Information System.
Conformation traits were scored using a subjective linear scoring system ranging from 1 to 9,
except for foot angle with a maximum score of 8. Conformation traits included stature, chest
width, body depth, dairy strength, rump angle, thurl width, rear leg side view, foot angle, fore
udder attachment, rear udder height, rear udder width, udder support, udder depth, front teat
placement, rear teat placement and front teat length. Genetic correlations between conformation
traits and functional herd life were estimated using a series of bivariate analyses. The highest
correlations were estimated for udder traits. Significant moderate to high positive genetic
correlations between most udder traits and functional herd life (0.23 to 0.63) were estimated. The
most important udder traits related to functional herd life were fore udder attachment, rear udder height, and udder depth. Correlations between the majority of body structure and functional herd
life were variable. Most of the body structure traits had a low to moderate negative correlation
with functional herd life (-0.04 to -0.27). The structural body traits of rump angle and foot angle
were estimated to have a moderate positive genetic correlation with functional herd life. The
genetic relationships between functional herd life and conformation traits in the South African
Jersey breed indicate that conformation traits could be used to enhance the accuracy of genetic
evaluation for functional herd life.
The effect of inbreeding depression on functional herd life in the South African Jersey
population based on individual level and rate of inbreeding was investigated. A pedigree file of
the South African Jersey breed (n = 912 638) was obtained from the Integrated Registration and
Genetic Information System (INTERGIS). The data included registered, grade and imported
animals. The percentages of animals in the pedigree file with two, one and zero parents unknown
were 22%, 18% and 60%, respectively. The inbreeding coefficient for each animal (Fi) and the
rate of individual inbreeding (ÎFi), as an alternative measure of inbreeding which is adjusted for
the depth of known pedigree, were calculated. The effect of inbreeding on functional herd life in
each of the first three lactations was estimated using a single trait sire model on data collected
from 1985 to 2003. Three analyses for survival in each of the first three lactations were
conducted. In the first analysis, in addition to fixed and random effects, an individual inbreeding
coefficient (Fi) was fitted as a linear covariate. In the second analysis, the inbreeding coefficient
was included as a discrete variable with the following classes of inbreeding: 0 < F ⤠3.125, 3.125
< F ⤠6.25, 6.25 < F ⤠12.5 and F > 12.5. In the third analysis, the individual rate of inbreeding
(ÎFi) was included in the model as a linear covariate. The level of inbreeding in the SA Jersey
population showed a gradual increase for the period 1985 to 1994, while the period 1995 to 2009
showed a rapid increase. The current mean level of inbreeding (for the year 2010) is 4.85% with
a minimum and maximum of 0 and 31.34%, respectively. The rate of inbreeding showed a
gradual increase from 0.36% to 0.43% between 1985 and 2003. The average rate of inbreeding is
currently (for the year 2010) at 0.55%. There was a significant (P<0.05) unfavourable
relationship between inbreeding and functional herd life in the first and second lactation. The
effect of inbreeding was more pronounced in the second lactation for both measures of inbreeding. Based on the current level of inbreeding, the reduction in functional herd life in the
first lactation can be estimated to be 0.68%. The corresponding estimate for the second lactation
is 1.70%. These results indicate that the current level or rate of inbreeding has reached levels that
are detrimental to functional herd life. Therefore, individual inbreeding coefficient should be
considered when breeding decisions are made by the Jersey breeders in addition to genetic merit.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-08142012-155827 |
| Date | 14 August 2012 |
| Creators | du Toit, Jacobus |
| Contributors | Dr A Maiwashe, Prof JB van Wyk |
| 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-08142012-155827/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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