Genetic and Genomic Studies on Production, Composition and Processability Characteristics of Dairy Sheep Milk Ana Carolina Marshall (PhD Student at Massey University)
The New Zealand dairy sheep industry has had significant growth over the last seven years and is an alternative to traditional dairy cow farming. The high nutritional value of sheep milk is mainly attributed to the high content of unsaturated fatty acids, minerals, and protein. The higher content of milk solids (fat, protein, and lactose) in sheep milk also makes it ideal for processing into dairy products such as cheese. The lower carbon footprint and the smaller nitrogen leaching effect produced by dairy sheep when compared to that of dairy cows are also important aspects to consider as New Zealand aims to market environmentally sustainable farming systems. The characteristics of milk prior to processing is determined by several factors such as the animals` feed and genetics, farm management, and animal health. However, there has been very limited research done on the molecular genetics (identification of genes that determine traits of economic interest) in dairy sheep milk. Most dairy sheep breeding programmes have focused mainly on improving milk yield, leaving aside other traits of economic relevance such as milk composition, milk processing value, ewe udder morphology, milk somatic cell count, ewe machine milking ability, and ewe resistance to diseases. Selection of dairy sheep solely for milk yield can indirectly result in reduced fertility, impaired udder morphology and reduced milk solids. Udder characteristics must be considered in the breeding programme as selection of dairy ewes for high milk yield has been related to pendulous udders, which is not a desirable trait for machine milking nor for suckling lambs. Furthermore, udder scores were reported to have high heritability and can affect coagulation traits which can be exploited in selection indexes. Milk processability traits have not yet been included in selection schemes (for most ruminant species) although heritability of coagulation traits (important indices of product yield and quality i.e., cheese yield and quality) in sheep milk has been reported to be moderate and could be included in selection schemes. Heritability of somatic cell counts, lactose content and milk pH were moderate and were significantly correlated with coagulation traits in sheep milk, so there is also potential in including these traits.
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Goat & Sheep Milk NZ - Issue 4 | December 2021
Black ewe and her lamb in the yards at Kingsmeade.
PhD student Ana Carolina at the Food Characteristics Lab, Massey University, for analysis of milk coagulation traits.
Overall, the New Zealand dairy sheep industry needs a breeding program for selection of genetically superior animals for production and for milk characteristics. Although application of molecular genetics is costly and recording of production data/traits is time demanding, using genes to assist in selection for traits in a small number of animals (nucleus) for further expansion of genetics through breeding and transfer to commercial flocks can result in faster genetic gain, which is attractive for the industry. Therefore, the aim of this study is to develop a model for genomic selection of dairy sheep for milk production, composition and processability. This study will also investigate a faster and cheaper method to achieve coagulation traits for inclusion in genetic schemes. The calibration of the spectra generated by infrared spectroscopy equipment could enable indirect measurements of coagulation traits and of fatty acid profiles from individual milk samples. It is also important to enhance the need for more accurate and efficient milk sampling and recording systems at the farm level as most milk meters designed for sheep or goats collect a very small percentage of the daily milk volume which is insufficient for research purposes that usually require 100-200 mls of milk.
