Investigation of leptin genotypes and economically important dairy traits in jersey cows.
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Date
2005
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Abstract
Dairy farming is one of the most important agricultural industries in South
Africa, and thus improving the performance of dairy cows, with respect to
economically important dairy traits, would be beneficial. Selection of dairy
cows has traditionally been phenotypic, but new molecular techniques have
made it possible to evaluate phenotypic dairy traits at the DNA level, providing
the possibility of more accurate selection. The economically important dairy
traits, milk production and reproductive performance, are quantitative traits,
and are therefore controlled by many genes and the environment. A number
of genes have been identified that have been shown to influence economically
important dairy traits, including the lep gene. This gene encodes the hormone
leptin, which has been proven to regulate feed intake, energy balance, fertility
and immune function. A polymorphism has been identified in the lep gene,
which may be associated with economically important dairy traits. This study
on a South African Jersey herd investigated the possible association of the
polymorphism, RFLP-Kpn 21, with milk production and reproductive
performance. The lactation records of fifty Jersey cows that completed their
first lactation between 1997 and 2004 were collected, and these cows were
genotyped for the RFLP-Kpn 21 polymorphism, located at exon 2 of the lep
gene. This involved the extraction of DNA from venous blood, using a salting
out technique. The extracted DNA was amplified using PCR primers; the
reverse primer included a purposeful mismatch. The role of the purposeful
mismatch was to create a recognition site for a restriction enzyme (Kpn 21),
thus allowing the alleles of the polymorphism to be identified through a
restriction digestion protocol. Two alleles were identified, the C- and the Tallele.
The genotype of each cow was identified using PAGE. The
significance of the genotype effects on the milk production traits and the
reproductive performance traits were estimated using the F-statistic provided
by a GLM Univariate analysis. In conclusion, no significant effect of the
RFLP-Kpn 21 polymorphism was found for milk yield, butterfat and protein
percentage, ICP and SPC (p > 0.05), but a possible association with lactose
percentage was suggested by the statistical analysis (p < 0.05). Further
investigation of South African Jersey cows will be necessary in order for
conclusive results to be obtained.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Dairy cattle--Economic aspects--South Africa., Milk yield., Cattle--Reproduction., Dairy cattle--Genetics., Leptin., Jersey cattle--South Africa--Genetics., Lactation., Jersey cattle--Breeding--South Africa., Genotype., Theses--Genetics.