EVALUATION OF GENES ASSOCIATED WITH MASTITIS IN CROSSBRED DAIRY CATTLE

Mastitis is a detrimental disease that economically affects dairy farming by reducing milk quality and quantity produced, the sudden death of dairy cows, premature culling of dairy cows before attaining their maximum production ages, and the cost of disease prevention and treatments. In Sub-Sahara Africa, mastitis prevalence among smallholders’ dairy farmers have been recorded to exceed 50 percent, and it has continued to cause significant threats. In East Africa, subclinical mastitis prevalence varies between 16 and 80 percent among smallholders’ dairy farmers. Full udder quarters of 38 lactating crossbred dairy cows were cleaned with 75% alcohol and screened with the California mastitis test (CMT) kit for subclinical mastitis and somatic cell count (SCC). A total of 152 milk samples were collected aseptically from each quarter of 38 lactating dairy cows into screw-capped bottles `for direct microscopic somatic cell count analyses in the laboratory. Ninety-six blood samples from both lactating and non-lactating crossbred cattle were obtained for genomic DNA extractions. The genomic DNA was later run in polymerase chain reactions with two oligo primers of 252 bp (LGB) and 301bp (LTF) for beta-lactoglobulin lactoferrin genes, respectively. Results CMT scores carried out in the farm revealed that 55.01% of udder quarters were negative for subclinical mastitic, 43.99 % trace, and 1.32 % were positive for subclinical mastitis. The Least Square Difference (LSD) for pairwise comparison between CMT scores and lactation stage were significantly different between First and second lactation at 0.25±0.11, the second and third at 0.27±0.0118 at P≥0.05. The means of SCC among the breeds were significantly other at P≥0.05, for Ayshire and Friesian (68.055±18.82 cells/ml); Ayshire and Guernsey (71.976±23.844 cells/ml); Friesian and Jerseys (64.863±21.429 cells/ml); and Guernsey and Jersey (68.78±25.952 cells/ml). Results of PCR-DNA sequenced showed that there were several genetic variations in the nucleotide sequences. These were identified as Single Nucleotide Polymorphisms (SNPs) associated with mastitis resistance or tolerance. The genetic variations found among nucleotide sequences of both breeds positive for subclinical mastitis and those free from subclinical were oriented in either transitions or transversions models due to tautomeric shifts in the nucleotide sequences. They were either substituted or inserted, which eventually created variability among nucleotide base sequences. They could also be a result of point shift mutation in the nucleotide sequences. In conclusion, the study also found out that milk quality and somatic cell count were closely associated with the presence of beta-lactoglobulin and lactoferrin genes. The nucleotide sequences of genes have shown significant associations with milk quality and somatic cell counts.

Keyword: Crossbred, Gene, Somatic Cell Count, Mastitis resistant

 

 

 

 

 

 

 

Mastitis affects dairy production economically through its associated costs and production effects (Gupta et al., 2016; Martin et al., 2018). These costs may include: the price of drugs, reduced milk productions, and household income through the discarding of milk in times of treatment, sudden death, and premature dairy cows culling (Jingar et al., 2017). Mastitis is associated with declines in the quantity of milk produced due to high bacterial loads (Sharma et al., 2011; Jadhav et al., 2016) and the increase in milk somatic cells. These cells include; polymorphonuclear neutrophils, macrophages, lymphocytes, and mammary epithelial cells (Jadhav et al., 2016). The numbers of these cells in milk are used as an indicator to monitor mammary gland health, and their presence can be used to signal mastitic conditions in the udders of dairy cattle (Li et al., 2014; Jadhav et al., 2016).

In sub-Sahara Africa, the prevalence of mastitis among smallholder dairy farmers have been recorded to exceed 50 percent and continues to raise significant threats to dairy producers. In the great lakes region and western parts of Africa, milk production is mostly by smallholder dairy farmers (FAO, 2014). In East Africa, the prevalence of subclinical mastitis varies between 16 and 80 percent. To date, mastitis remains one of the significant factors limiting milk's maximum production by smallholder dairy farmers (FAO, 2014).

Mastitis prevalence has continued to increase despite practices adopted to manage it, such as continuous monitoring for subclinical mastitis, dry cow therapy, and culling of chronically infected cows. Udder health is a valuable trait in dairy cows that need to be maintained for high production of milk and better quality milk that meets consumers' demand in the market (Abebe et al., 2016). The udder health status of a dairy cow is a fundamental factor that boosts production outputs and increases the economic viability of a farm through income earned from the sales of dairy products and less money spent on disease control and prevention (Edwards et al., 2015). Immunity against mastitis is fundamental in addressing the economic challenges faced by smallholder dairy farmers (Fang et al., 2017). Traits associated with mastitis resistance may play a key role in improving milk quality and quantity. Information on systems that underlie these attributes is essential for smallholder dairy farmers' profitability and can be applied in designing selection criteria for dairy cows against mastitis (Peters et al., 2015; Ismail et al., 2018).

Generally, the presence of somatic cells in milk signifies deterioration in milk quality, and the SCCs are internationally used to evaluate milk quality (Sorensen et al., 2016). Breeds of dairy cattle with robust immune systems always produce significant amounts of somatic cells in the milk (Teresiah et al., 2016; Jadhav et al., 2016). However, in some instances, a high milk-producing breed of dairy cattle can produce many somatic cells due to inadequate milking and poor management (Gupta et al., 2016).

Beta-lactoglobulin and lactoferrin genes play significant roles concerning mastitis resistance and tolerance (Fang et al., 2017). The genes have a bactericidal and bacteriostatic action on pathogenic agents of mastitis. As compared to both SCC and SCS, mastitis has a low heritability making it a challenge to select mastitis resistance. Due to this, selective breeding can lower mastitis incidences in crossbred dairy cattle, where suitable candidate genes associated with mastitis resistance are identified (Cai et al., 2018).

Mastitis is a polygenic trait related to milk quality and production traits. These make it complicated for molecular markers to be used in selective breeding for mastitis resistance in dairy breeds of cattle (Tiezzil et al., 2015).

 

The low heritability of mastitis poses a significant challenge in selecting dairy cattle against the disease. Although traditional animal breeding and selection are broadly employed in the section for mastitis resistant dairy breeds, there has been no significant result (Curone et al., 2018). Smallholder dairy farmers make massive losses due to subclinical mastitis on their farms. Making dairy enterprises unprofitable (Fonseca et al., 2009; Cameron et al., 2015; Peters et al., 2015). Most of the losses are incurred due to the associated effects of the disease on the farm due to the challenge of diagnosing disease on farms. Inadequate awareness about the impact caused by the subclinical mastitis in dairy production is still a significant obstacle in smallholder dairy enterprise profitability

Mastitis is a disease of economic importance in dairy through its associated effects on dairy production. The condition causes enormous production challenges like the death of dairy cows before attaining their maximum production ages, increased production cost, and declined in production, which in turn affects the returns earned. The frequent use of antibiotic drugs in mastitis treatment and prevention results in their accumulation as residues in animal bodies. These residues find their way into milk, making it unfit for human consumption raising public health concerns (Jadhav et al., 2016). This study was undertaken to evaluate genes associated with mastitis in crossbred dairy cattle, with a view of determining the relationship between California mastitis test scores and somatic cell scores in a sampling population, associations between somatic cell count and lactation stages, and to evaluate the associations between genes and milk quality in different crossbred genotypes of dairy cows.