Abstract. Leptin is mainly secreted by white adipose tissue in animals. Leptin acts by stimulating or inhibiting the release of a neurotransmitter, which eventually results in a decrease in food/feed intake and an increase in energy expenditure. In this investigation, the polymerase chain reaction (PCR) coupled with single-strand conformation polymorphism (SSCP) analysis was used to reveal nucleotide sequence variations in bovine leptin gene (LEP) in 338 cattle of a variety of breeds farmed in New Zealand (NZ) and Nigeria. These included NZ Hereford, Angus, Shorthorn, and crossbred Holstein-Friesian × Jersey cattle and the Nigerian Sokoto Gudali, Red Bororo, White Fulani, and crossbred Holstein-Friesian × White Fulani cattle. Sequence analysis of three regions of bovine LEP that encompassed selected coding and non-coding regions, revealed a total of 12 nucleotide sequence variations (six in exons and six in introns). Of these, three are reported here for the first time, whereas nine have been previously described. Some of the variations identified were common in both the NZ and Nigerian cattle breeds, while others were peculiar to particular breeds from a specific region. The sharing of common variants across different breeds irrespective of geography may indicate an evolutionary relationship, just as the differences within a breed might be attributable to either selective pressure for specific traits or random genetic drift. The detection of both new and previously documented variations in bovine LEP suggests that the gene is highly variable.

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Animal production is a booming industry with the improvement of economically desirable traits as its primary concern. Markerassisted selection utilizes genetic variations within candidate genes that influence production traits as a means of guiding animal breeding and improving the traits of interest. Growth hormone (GH) plays a crucial role in pre-natal muscular and bone growth and development. GH brings about various physiological functions either directly by binding its receptor or indirectly by stimulating the release of insulin growth factor 1 (IGF1). Insulin growth factor 1 receptor (IGF1R) mediates its function on metabolism, homeostasis and development upon the binding of IGF1. The POU-domain class 1 transcription factor 1 (POU1F1) regulates the pre-natal development of cells of the anterior pituitary, including somatotrophs that produce GH. Reports have demonstrated associations between polymorphisms in these genes and animal production traits. This novel study examined the polymorphisms in the coding regions of candidate genes, GH2Z, IGF1R and POU1F1, in New Zealand (NZ) sheep. The sheep breeds investigated were NZ Romney and Merino, two commercially sought-after breeds. The results revealed two variants, AA and AB, for the exon 3 of POU1F1. The AA and AB genotypes had frequencies of 78% and 22% for Romney sheep, and 64% and 36% for Merino sheep respectively. All frequencies were in accordance with the Hardy-Weinberg Equilibrium (P > 0.05). The exon 2 of GH2Z revealed multiple variations while no variation was detected for the exon 15 of IGF1R..

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Having the ability to control litter size is important for sheep farmers and breeders worldwide. However, making genetic gain in key livestock traits like reproductive performance needs typically a lot of time, and both the fecundity and fertility traits have a great economic importance. Attention has therefore turned to better understanding the genes that control reproductive performance. Of these genes, research has focussed on the growth differentiation growth factor 9 (GDF9) gene (GDF9). In this study, a PCR-single strand conformation polymorphism (PCR-SSCP) approach was used to investigate variation in this gene in separate groups of purebred Finnish Landrace sheep, Finnish Landrace × Texel-cross sheep and composite sheep of undefined breed background, but based on New Zealand Romney-type genetics. Three GDF9 variants (named A, B and C) were found, and upon DNA sequencing, the nucleotide substitutions c.978A>G, c.994G>A and c.1111G>A were revealed. The frequency of variant A (containing nucleotides c.978A, c.994G and c.1111G) in the Finnish Landrace, Finnish Landrace × Texel-cross and composite sheep was 0.86, 0.78 and 0.76, respectively. In these three sheep groups, the frequency of B (defined by the presence of nucleotides c.978G and c.994A) was 0.01, 0.03 and 0.23 and for C (containing c.1111A) was 0.13, 0.18 and 0.01, respectively. An animal model was used to estimate the additive effect of fertility data for Finnish Landrace × Texel-cross sheep and revealed an association between litter size and the c.1111G>A variation (p = .036), but this was not observed for the Finnish Landrace sheep (p = .27) or the composite sheep (p = .17). When all the sheep were analysed together, the presence of c.1111A was associated (p < .05) with increased litter size, when compared to ewes that had c.1111G. Litter size did not differ between sheep with and without c.994A in all three groups of sheep investigated. This study suggests that c.1111A could be a useful genetic marker for improving fecundity in New Zealand sheep breeds and that it could be introgressed into other breeds, but analysis of more sheep will be required to confirm the associations that have been observed here.