Dr Chad Dechow – The Dairy Cow: Beyond Mass Production
As dairy farmers struggle to make ends meet, economic efficiency often forces the health and wellbeing of cattle to take a back seat. Dr Chad Dechow and his team at Pennsylvania State University have set about tackling this problem, providing a means for producing healthy, fertile cows, without compromising on productivity.
As the global human population continues to soar and multinational economics drive our societies, dairy farming is witnessing an era of tremendous growth and change. An increased demand for dairy products coupled with tight financial margins has resulted in the large-scale expansion and intensification of the farming industry. That quaint, family farm you used to visit at the bottom of the village is struggling to stay in business, as we make way for high-yield, intensive production systems – with each cow representing a single cog in this vast network of mass-production.
Cattle farmers across the globe strive to stay on top, encouraging their herds to metamorphose through selective breeding to achieve the highest productive efficiencies of milk, fat, and protein. ‘We have made a lot of changes to dairy cows over the last half-century – milk production levels have doubled for instance, largely because of genetic change,’ says Dr Chad Dechow of Pennsylvania State University. ‘This has many benefits as we are able to feed a growing population more efficiently.’
However, with this emphasis on improving economic efficiency, breeders weren’t always encouraged to select traits relating to the health and fertility of cattle. Although some anticipated adverse effects on cattle fitness and mortality, a look back at historic trends can be eye opening. Since selective breeding accelerated with the widespread adoption of artificial insemination in the 1970s, declines in cattle health and fertility, with increasing incidences of premature death and lameness, have been observed. Not all, or even most, unfavourable trends are due to genetic changes in our cows.
Mastitis and pneumonia are two examples of common diseases in dairy cattle, and both have a huge effect on the annual yields of dairy farms around the world. Mastitis-induced inflammation of the udders leads to milk that is low in potassium, calcium, and casein – the main protein found in milk. Not only does mastitis result in low-quality liquid that is unfit for sale, but the resultant infections cause udder damage and are occasionally fatal. Mastitis is still the most costly disease to the dairy industry, but through better herd management and selection for traits such as udder conformation and disease resistance, mastitis is one disease that is actually less prevalent now despite higher milk yield.
Rising concern for animal welfare is one factor that has led to growing success in the organic farming industry. These dairy farmers, however, have their own unique challenges – although providing a more natural environment appears to benefit their cows’ health and wellbeing, the lack of antibiotics means that many easily treatable conditions cannot be kept at bay. While conventional farmers use antibiotics to treat infectious disease, their organic counterparts must instead be proactive, adopting preventative measures to avoid contracting the bug in the first place. Pneumonia can be a particularly big challenge – it is highly contagious in young calves and without the help of antibiotics, a calf’s lungs can be permanently damaged.
Dr Dechow, who actually grew up on a dairy farm, leads studies that are focused on remedying this problem. His team aims to provide a means to monitor and overcome prolific diseases for organic and non-organic farmers alike. He tackles the problem from a genomics approach, arguing that, ‘genetic selection can be part of the solution’.
With the consumption of organic produce becoming more popular, and greater pressures on conventional farmers to decrease the prophylactic use of antibiotics, providing cattle with superior all-round genetics is key for farmers of the future.
Genetics and Genotyping
As international champions of milk production, the Dutch-built Holstein Friesians are the most prevalent breed of dairy cattle. Dr Dechow tells us that he and his team are ‘beginning to evaluate genetic selection and crossbreeding options to improve calf and cow health in organic dairy herds’, in collaboration with researchers from the University of Minnesota, Alfred State College and USDA – ARS.
Much of this work focuses on a mix of Holstein and crossbred herds. The researchers have access to commercial organic dairy farms throughout the US, which they can compare to two experimental herds. On the commercial farms there are pure Holsteins and crosses with various breeds including Jersey, Norwegian Red, Normande, Swedish Reds and Montbeliardes.
In this ongoing project, Dr Dechow and his colleagues are currently analysing the health and welfare of cattle on all farms, and aim to compile this information on a standardised database. Although measuring animal welfare can prove difficult, as there are no obvious quantitative measures, the team is implementing the following methods.
They individually genotype (analyse the genomes of) each cow and calf on the farms, using hair samples as genetic material. By analysing genetic variants known as single-nucleotide polymorphisms (SNPs), they are able to predict genetic merit for specific traits, such as resistance to pneumonia. SNPs are points on the genome that vary between individuals, and these differences can provide the team with information regarding the expected health and behaviour of the cows.
Further, Dr Dechow and his colleagues use their genotyping data to distinguish between cows that possess genes coding for the protein A1 beta-casein and those with genes for A2 beta-casein. These two forms of the predominant protein in milk may have different effects on human health, with A1 beta-casein thought by some to have a negative effect on human gastrointestinal health. Research has not yet been extended to explore the effect of this protein on calves during weaning – if the team finds an association between A1 beta-casein genes in cows and their calves’ gastrointestinal health, they can then select against this trait when breeding.
To measure calf health and wellbeing, the team weigh each individual, assign a respiratory score relating to presence of a cough or nasal discharge, and also assign a score related to the calf’s faeces. Cow examination, on the other hand, involves scoring their body condition, movement, hygiene, lesions, and stature. The researchers also record the cows’ white blood cell counts and how low their udders hang, as these factors correlate directly to mastitis.
The Tale of the Telomere
In another research direction, Dr Dechow and his team have been focusing on genetic components known as ‘telomeres’. Every living organism on Earth possesses a genome, which consists of a number of pairs of large genetic bundles known as chromosomes (humans possess 23 pairs of chromosomes, while cows have 30). Chromosomes are rod-like structures that contain many thousands of individual genes. The tips of these rods, however, are particularly susceptible to becoming degraded every time they are replicated during cell division.
To avoid our genomes being eaten away over time, we have structures called ‘telomeres’ at either end of each chromosomal rod, to protect the vital genetic information within. When telomeres become degraded beyond a specific threshold, the cell they exist in dies – a process that occurs more commonly as we age.
Previous studies have shown that, in humans, the original length of our telomeres is inherited – and inherent short telomeres have been associated with diseases such as diabetes, renal failure and neurodegeneration. The degradation of human telomeres over time has also been shown to occur more rapidly under stress and disease.
Although little relevant research exists concerning telomeres in livestock, Dr Dechow’s team showed an association between telomere length and cow health and premature death in a study they published in 2012. Since then, there have also been a few studies reporting a correlation between telomere length and milk yield in Holstein cattle.
Based on this previous research in both humans and cattle, the research team believes that the degradation rate of telomeres in cattle might offer some insight into animal welfare, providing them with a quantifiable element to measure. Genetic evaluation of telomere length in Holsteins could also provide a marker to help the team select for inherently healthy cattle with higher stress-coping abilities.
In one of their ongoing research projects, Dr Dechow’s team implements a routine genetic procedure called qPCR to accurately measure telomere length. To scientifically quantify animal welfare, the team considers the health and stress levels of individual cows. When considering health, they examine blood samples, white blood cell counts, and activity levels, while the cortisol concentration in the cows’ hair is used as a measure of stress. Cortisol is a well-studied stress hormone that can be easily extracted from hair, saliva and faeces – with hair providing a better indicator of more long-term stress.
Using these techniques, the research team aims to prove that telomere length is heritable and is an indicator of disease susceptibility and productivity levels, by comparing calves’ telomeres with those from their mothers. This information will provide an invaluable guide for genetic selection. Furthermore, if they find a link between stress and disease levels and telomere degradation rates, the team will be able to confirm their hypothesis that telomere length is an indicator of cow health and wellbeing.
A Moove Towards Diversity
Intense genetic selection can also compromise the genetic diversity of cattle worldwide. Breeders have focused on artificial insemination from bulls of limited genetic lineages, based largely on the productivity and appearance of their daughters. Inbreeding levels have consequently risen, while bulls with unique lineages but lower daughter performance are cast aside, unable to pass their genes on to future generations. Rising inbreeding means that cattle become increasingly susceptible to genetic defects over time.
Dr Dechow is part of a research effort, in partnership with Dr Harvey Blackburn from the National Animal Germplasm Program repository, and Dr Wansheng Liu from Penn State University, to bring back the genetic variation that has been lost from cattle breeds such as Holstein and Jersey.
The research team has already determined that most Holstein bulls worldwide can be traced to one of two ancestral lineages, each dating back to 1880. Jersey bulls follow an even more drastic trend, with every individual originating from a single bull from 1898. This lack of genetic diversity is thought to be due to the boom in popularity of artificial insemination over the last 50 years, allowing thousands of progeny from a single bull, coupled with intensive selection for high-yield traits. These intensive, selective breeding programs have neglected any conservation of genetic diversity, particularly on the Y chromosome (the part of the genome exclusively passed from father to son).
Dr Dechow, Dr Blackburn and Dr Liu’s most recent accomplishment includes the regeneration of two male genetic lineage of Holstein cattle, which had previously been lost from dairy farming altogether.
The team aims to generate a method for assessing the variation and fertility of each bull’s Y chromosome, as well as checking whether regenerating genes that have been lost is actually beneficial in the first place. Not only is their work anticipated to provide valuable information about a rare lineage found in the National Animal Germplasm Program repository, but potential long-term prospects include the reintroduction of genetic variation back into commercially farmed cattle.
Dr Dechow and his team seek to improve the welfare of farmed cattle, by using their acquired information to develop best genetic selection and crossbreeding strategies. By enhancing traits such as disease resistance, organic farmers will benefit from this research, but conventional farmers will reap the rewards too. As Dr Dechow points out: ‘Pressure to reduce antibiotic usage on conventional dairy farms is increasing, so the development of cattle with higher innate disease resistance is relevant to all farmers.’
Through their research and outreach efforts, Dr Dechow’s team is on track to make serious advancements regarding the sustainability of dairy farms, and the health and happiness of dairy herds across the globe. Dairy cattle genetics researchers around the world, including Dr Dechow and his team at the Pennsylvania State University, have set about tackling this problem, providing a means for producing healthy, fertile cows, without compromising on productivity. Long gone are the days of selecting cows entirely for their milk production capacity.
Meet the researcher
Dr Chad Dechow
Department of Animal Science
Pennsylvania State University
Dr Dechow grew up on a small dairy farm in New York State that milked Friesians and a few Brown Swiss. After receiving a BSc at Cornell University and an MSc at Pennsylvania State University, he went on to achieve his PhD in Animal Science from the University of Tennessee in 2003. After this, he moved back to Pennsylvania State University, where he is currently an Associate Professor of dairy cattle genetics. Here, his research involves improving the health and wellbeing of dairy cattle, with a particular focus on organic farms. Dr Dechow’s mission involves optimising the productivity and yield on these farms, whilst also maintaining a very high standard of animal welfare. Dr Dechow also teaches in the areas of animal genetics, dairy cattle selection, dairy herd management and the use of dairy management software. He also co-advises Penn State’s Dairy Science Club and is the coach of Pennsylvania’s 4-H Dairy Judging team.
CD Dechow, CR Baumrucker, RM Bruckmaier and JW Blum, Blood plasma traits associated with genetic merit for feed utilization in Holstein cows, Journal of Dairy Science, 2017, 100, 8232–8238.
DE Brown, CD Dechow, WS Liu , KJ Harvatine and TL Ott, Association of telomere length with age, herd, and culling in lactating Holsteins, Journal of Dairy Science, 2012, 95, 6384–6387
CD Dechow, EA Smith and RC Goodling, The effect of management system on mortality and other welfare indicators in Pennsylvania dairy herds, Animal Welfare, 2011, 20, 145–158.