What does a bull’s daughter profile reveal? A description of how the daughters are expected to perform in an intensive barn-housed environment. That works for temperate climates where there is winter, machinery for harvesting forages and cheap fossil fuels. However, what about areas, where only grasses can be grown? Are today’s dairy genetics suited for heat, new bugs and grazing?

The World is Changing

Our dairy cows, developed in north central Europe, operate best in temperatures -20C to +22C ( -5F to 72F). In the 21^st century, there are many new factors at play as we breed cows for a variety of environments. Some of these factors include:

• Climate Change: Predictions are that North America will be 5F warmer by 2050. Dairy cows, like humans, will need to be able to operate optimally at higher temperatures. It will be a significant added cost to keep cows cool for more than half the year. Heat resistance in cattle will be an important characteristic in the future.
• Land Use: Around the world land for cities is gobbling up vegetable, grains and fruit lands. In turn those crops will push forages for livestock on to land only suitable for grasses or pasture.
• Regions of Population Increase: The next 2B people, bringing the world to 9B, will be in Asia. Dairy cows there will need to be able to pasture the hillsides and floodplains.
• Diseases / Insects Resistance: Hot climate and non-temperate climate diseases and insects will add stress to a cow’s life.
• Fossil Fuel Usage, Machinery and Technology: All of these will become costlier. This will have a significant effect on farms without high cow/heifer numbers. The current trend to replace the cost of labor with technology will continue. Many producers will have cows harvest the forage instead of machinery doing it.
• Consumer Opinion / Support: The world is no longer about farmers producing food and consumers accepting what is in the store. Consumers are making their needs and requirements known and, in the future, will put many more stipulations on the food they buy. Sure, the milk will be wholesome, but animal welfare, use of drugs on animals, feeds fed to cows, natural environments and many more items will be dictated by consumer understanding. The customer is always right, and they will only buy products that meet their specifications.

As with all things, it comes down to economics. The need to include and the relative importance of these and other factors in genetic indexing and breeding schemes will take time to become a reality. Cows will need to take care of their needs by themselves as much as possible. That also includes nutrition, health, welfare, … and intelligent robots everywhere.

Breeding Must be Ready

Our one-size-fits-all dairy cows are not ready for coping with and prospering under some of the above and other factors. It will take planning and implementation for dairy cattle breeders to be ready with adapted breeds or blood lines. It is hard to look long term when the current cost of production (COP) is not being exceeded by farm gate price in many dairy countries, but the future COP on dairy farms must be addressed by both progressive breeders and breeding organization. First come the ideas, then the research, then the development and finally the application.

A Breeding Goal – A Cow that Manages to Her Own Needs.

We already are breeding for the cow that, on her own, visits the milking machine. Now can we breed the cow that harvests her forage, resists diseases and infections and does it at optimal levels when the thermometer reads 90+F (32+C). Oh yes and she needs to do all that and get back in calf within 80-100 days after her previous calving.

Currently we do not have farm data to use in developing genomic ratings for sires and cows for their ability to forage and exist in tomorrow’s hotter world. So, it will be some time before we can rate and select animals genetically for the traits associated with grazing and a warmer planet.

Some genetic matters that are being worked on include: Slick hair gene, where animals with that gene cope better in hot climates; Tick resistance has yet to be successfully introduced into dairy cattle; Fertility (cow and heifer) is presently receiving much research study; Calf livability and scour resistance is being worked on but with only very limited farm data it is almost impossible to genetically rank sires for these matters.  Without devices that attach to cows it is not possible to measure intake for pastured animals. Information on feed conversion efficiency genetic indexing for animals consuming harvested forages was covered by the Bullvine (reference) but that is for machine harvested forage not for grazing animals.

Information Currently Available to Breeders

Health and wellness genetic ratings have become available for milk cows in the past 3-4 years and for calves and heifer in the past year. More health and disease will be added in the future.

That still leaves research into which sires are genetically the best in terms of heat resistance and forage intake from pasture.

Regarding the ability to cope with tropical temperatures relatively little new information has been found to help breeders. Some breeders rely on their understanding of added body capacity for lungs, solid red color, crossbreeding (i.e. using the Gyr breed from India) and raising heifers at higher altitudes to develop larger lungs. There are no sire indexes for breeders to use. Research needs to be done and field data captured so that more is known on the genetics of dairy cattle coping with tropical conditions.

On the matter of which sires produce daughters more suited to grazing, there are currently three indexes provided by organizations. These indexes are:

• GM$ (Grazing Merit is published by CDCB) – it includes the same traits as NM$ (Net Merit) but puts 253% as much emphasis on fertility, 85% as much emphasis on production traits and 59% as much emphasis on PL and LIV as NM$ does. The AIPL-USDA research shows that grazed cows need to calve annually, do not need to produce as much fat and protein volume and have fewer longevity and livability problems as compared to housed cows. As in NM$, higher milk volume, higher SCS and higher body weight all receive a negative weighting in GM$. The trait emphasis for GM$(2018) follows:

GM$ = 38% Yield* + 24.5% Fertility* + 16% Type* + 13.5% PL/LIV/Health* + 3.5% SCS + 4.5% CA*

                (* indicates that a number of traits are combined to create the category.  Calving Ability is 4 traits related to calving.)

Table 1: Top Ranking US Holstein Sires for GM$ (Grazing Merit)

• GrazingPRO™ (Published by Select Sires Inc.) – SSI designates their sires as GrazingPRO™ based in their GM$ rating and requiring that the DPR is >+3.0, Stature is <+0.5, Fat% is positive and Protein% is positive.
• GrazingPro™ (Published by Semex) – Semex designates their sires as GrazingPro™ and thereby Pasture Perfect for sires that will maximize component yield and put a focus on health and reproductive traits to ensure highly profitable, long-lasting animals with limited problems. These sires will also produce easier calvings and darker colored calves.
• Outside of North America both Ireland and New Zealand prove their sires on grass-based feeding systems so their EBI (Ireland) and BW (New Zealand) indexes rank sires with consideration of grazing.

The Bullvine Bottom Line

Dairy cattle being fed on grazing systems and living in warmer and warmer climates will be part of our industry’s future. To date there is only limited genetic information, based on assumed trait emphasis, available for breeders to use if they choose to graze their cattle or farm in regions having heat and humidity. Research and genetic evaluation centers need to address these topics.

Get original “Bullvine” content sent straight to your email inbox for free.

Feeding dairy animals has gone from least cost to balanced rations to now where Income Over Feed Costs is king on a herd basis. Producers are now wanting to know which animals are the more efficient at converting feed to growth or milk. Since feed intake in dairy cattle has been considered to be too costly to measure, progeny testing programs have not provided sire daughter feed efficiency indexes.

Breeders want more for less. More growth and more milk from less feed. In this article, The Bullvine do an overview on where the genetics of feed efficiency is at.

Why is Feed Efficiency Important?

With feed costs being 50-60% of the total cost for the milking herd and an even higher percentage for calves, heifers and dry cows, it means that the managers of tomorrow need answers on the genetic side of feed efficiency to help attain future success. The margins in dairy farming are narrow and are likely to remain so into the future. Genetics, along with other disciplines, need to advance efficiencies.  Of course, this not just a “cow” issue, it is also a crop production, harvest, storage and processing issue.

 In other livestock industries, poultry, swine and beef, the genetics of feed efficiency has become a must-have. Dairy is behind in using genetics to advance feed conversion efficiency.

In dollars, saving $0.25 in feed costs per animal per day without reducing income, amounts to $83,500 per year for a 600-cow herd, that milks 500, has up to 100 dry cows and raises their own heifers as herd replacements. That’s not pocket change and if by genetic selection that $83,500 can be achieved – that’s significant.

Tracking Feed Efficiency

Many ways of tracking feed intake have been tried by researchers and companies to monitor animals. They include dry matter intake (DMI), residual feed intake (RFI), feed saved, time at the feed bunk, head movements during feeding, rumination activity and the use of novel electronic devices. But none, as yet, have been found to be the answer to the question – “Which sires produce the daughters that take less feed to produce the same milk revenue?”

Current State of Public Research Results

Dr. Kent Weigel (University of Wisconsin-Madison) on March 24, 2018 presented a very comprehensive report to the Northeast (Cornell) Dairy Production Medicine Symposium on a three-country dairy feed efficiency project (eleven research institutions with nine from the United States, one from Canada and one from The Netherlands) that analyzed numerous research projects and in each project the cows’ intake and performance.  A synopsis of the facts that he reported include:

• The RFI data available, on approximately 8,000 cows, is not enough to provide accurate sire proofs. Heritability was found to be 19%, but the reliability of sire indexes is only 20-25%. Many, many more cow feed intake records are needed to go along with production and other data.
• DMI information is closely associated with level of production and cow size but it is not a good indicator of the genetic ability of a sire’s daughters for saving feed costs without altering yield.
• The ‘feed saved’ research results from Australia provide an interesting concept but, there again, much more data is needed, in order to provide sire genetic indexes.
• To get to the point of sire genomic indexes for feed efficiency will take time. First of all, a broad-based reference population is needed. Breeders are accustomed to genomic indexes being 65%-75% REL, so the current 20-25% REL for feed efficiency is not high enough.
• Currently high and low feed efficient cow families have been identified with some level of confidence. So there is progress being made in arriving at useful information.
• The three country international project, studying dairy cow feed efficiency, will continue including trying out new measurements and devices but breeders cannot expect answers any time soon.

General Recommendation by A. I. for Selecting Sires for Feed Efficiency

The general recommendation from A.I. for breeders who want to move their herds forward, genetically, for feed efficiency has been that they place emphasis on sires with higher fat and protein yield indexes but that also only have average to below average size/frames proofs. National total merit indexes and A.I. stud composite indexes (TPI, NM$, JPI, LPI, Pro$, ICC$, …) usually only place about 50% of their emphasis on those three traits, so changing a herd genetically for feed efficiency will not occur quickly. And it will only occur if the top-ranked sires for those three traits are used extensively to sire the next generation.

Four Organization are Stepping Out and Publishing Feed Efficiency Sire Ratings

There are four organizations that are publishing sire ratings for feed efficiency. A closer look at their information, currently available to breeders, follows:

Holstein US Predicts Feed Efficiency by Using Other Genetic Indexes

All sires on Holstein US various sire listings contain a ‘FE’ (feed efficiency) column. It is an estimate of the net profit a milk producer can expect to receive. Factors included in ’FE’ are: dollar value of extra milk produced, feed costs of the extra milk and extra maintenance costs for large cows. This is the formula that Holstein US uses:

FE = (-0.0187 x Milk) + (1.28 x Fat) + (1.95 x Protein) – (12.4 x Body Weight Composite)

Table 1 – Top FE Proven Holstein Sires

* Data Source – Holstein US Official Top 100 TPI List of Proven Sires (April ’18)
** Top 15 sires for FE and TPI differ significantly in averages for fat yield (Fat) and fertility (FI). FE sire are superior for fat yeild but inferior for fertilty. As well TPI sires have somewhat higher type (PTAT).

In Table 1 the only points of difference between the Top 15 FE and TPI sires are in the traits FE, Fat Yield, and FI (fertility index). The FE sires are inferior to the TPI sires for fertility (FI), but superior for FE and Fat Yield.

It is worth noting that a feed efficiency index in this context has no direct measurement of feed intake.

Select Sires Uses Indexes and Designates Sires as FeedPRO®

Select Sires identifies the top 20% of their sire lineups as FeedPRO® Sires. The purpose of this selection tool is to highlight sires for producers who are concerned about feed costs and want to improve overall profitability. FeedPRO® is based on US and UK research that found that production, body traits, body condition score and daughter fertility accounted for 90% of the difference in feed intake between animals. Sires that qualify are designated as FeedPRO® Sires but are not assigned an independent index.

Third party researcher reviews were sought by Select Sires in FeedPRO®’s development. Dr Chad Dechow (Penn State) in his analysis found the “FeedPRO® Sires have an advantage, on average, of $0.13 to $0.18 (USA$) per day in income over feed cost when compared to the average active A.I. sire”.

Table 2 – Top SSI FeedPRO® Holstein & Jersey Sires ranked by NM$

* Only the top 20% of SSI sires according to more income from less feed, high production, moderate size, long-term fitness and productivity are designated FeedPRO® 
** Note: These FeedPRO® sires always high high production and longevity but are variable for fertility and type.

The sires listed in Table 2 are among the current top sires that Select Sires has available based on the TPI and NM$ ranking systems.

Table 3 – Correlation of FeedPRO® and Other Indexes.

* Data Source – Select Sires Inc Program Description for FeedPRO®

These correlations are moderately high. They show that FeedPRO® is aggressively selecting for increased production, but still, it identifies a noticeably different group of sires at the very top of the lists.

CRV Uses Genetic Indexes and Feed Intakes to Predict Lifetime Efficiency, and Feed Saved

CRV partnered with Wageningen Livestock Research to develop a large dataset of genotyped cows with individual feed intake measurements and then conducted the genetic analysis. From the results of this work CRV has developed two indexes relating to efficiency:

1. a) ‘Better Life Efficiency’ – Its main components included the breeding values for fat yield, protein yield, longevity and feed intake. CRV has determined that, across a genotyped cow population of >60,000 cows, the top 25% of cows for life efficiency produced over 13,000 kgs. more milk per lifetime than the poorest 25% of cows. Ratings are published for every bull of every breed.  and
2. b) ‘Saved Feed for Maintenance’ – Cows with a positive breeding value for Saved Feed for Maintenance need less than an average amount of feed for their body maintenance and therefore convert feed into milk more efficiently. This breeding value indicates how much feed (in kg dry matter per day) is saved because the cow is more efficient than average. It has been added to the Dutch/Flemish total merit index, NVI.

Table 4 – Top BLE (and SFM) Sires

* Feed Efficiency has two indexes composing it – Beter Life  Efficiency and Saved Feed for Maintenance
** Better Life Efficiency uses the genetic indexes for fat yield, protein yield, longevity andfeed intake.
*** Saved Feed for Mantenance is the feed saved expressed in kg dry matter pe day
Longevity is expressed in days of productive life
Fertility has average value of 100 and STD Dev of 5.

The CRV sires in Table 4 give breeders a variety of pedigrees to choose from and are high production rated.

STgenetics Conducts Progeny Tests for Feed Intake and Performance to Predict Feed Efficiency

STgenetics has been capturing individual animal feed intake information for the extensive group of heifers and cows they own or control. From that feed intake data, along with all genetic indexes and DNA profiles, they have developed a program called ‘EcoFeed™’.

EcoFeed™ is more than simple feed efficiency for milking cows. It is a continuously growing database that monitors the animal’s growth and productivity throughout its entire lifetime from calves, to heifers, to milking cows. Feed efficient animals are expected to use fewer feed resources and convert feed more efficiently while creating less waste, manure, methane and CO2 per unit of production. All of these outcomes should greatly assist in making future dairying more viable, more sustainable and an environmentally friendly industry.

Some of the key components of EcoFeed™ sire indexing include: 1) it is a multi-factor efficiency index that encompasses the entire lifespan of a cow; 2) it is based on modern technology that measures daily individual animal consumption; 3) it includes a progeny testing program, the gold standard of dairy cattle genetic indexing; and 4) once proven, STgenetics sires reach high levels of reliability for EcoFeed™.

STgenetics reports that “To qualify as an EcoFeed™ sire, a bull’s progeny must be genomically tested and complete feed efficiency testing.  Ecofeed™ rankings are based on a 100 base system where every five points, over 100, equals one pound less feed that a sire’s progeny can be expected to consume each day while producing the same amount of milk as their peers.”

Table 5 –  Top Six ST genetics EcoFeed™ Progeny Tested Holstein Sires

Note:
1. EcoFeed™ reliabilities are only moderate compared to other traits but they are double the reliabilities for other FE rating systems. As more research is conducted and more animal data is captured, the reliabilitites will increase.
2. Production and longevity focused dairy breeders want productive, fertile, longer lived and moderate sized cows.  The averages for fat, protein, BWC, SCS , PL and FI of the EcoFeed™ sires all should assist in achieving breeders needs.

In Table 5 full brothers, Charismatic and Comanche, stand out ahead of other STgenetics sires for EcoFeed™. Both have good reliabilities with considerable daughter information included, and neither is yet four years old. It appears that the story has just begun for EcoFeed™ sire indexing given that, every week,  STgenetics captures more feed intake and performance data on milking first lactation cows.

Table 6 ST’s correlations table

* Data Source – ST Genetics information materials

Table 6 reports no correlations between EcoFeed™ and other traits. We would not have expected that as Table 3 shows moderate to high correlations for FeedPRO® with other traits. But when we consider that EcoFeed™is more than just feed efficiency, it may not be as surprising as it first appears. Definitely, breeders will be following the research that STgenetics is doing on lifetime efficiency. It should be noted that the concept of lifetime efficiency is also what CRV bases its ‘Better Life Efficiency’ index on.

 The Bullvine Bottom Line

It is very encouraging to see that organizations have recognized the need to put weight on feed efficiency in their genetic programs.  The potential for increased profit is thereby using genetic indexes to save on feed costs.

 Now is the time for all dairy breeders to study the matter of feed efficiency sire indexing and decide how they will incorporate it into their breeding program. Dairy cattle breeders must use feed efficiency sire ratings now (2018-2019) for milk producers to be able to benefit tomorrow.

Get original “Bullvine” content sent straight to your email inbox for free.

The Bullvine seldom talks about the processing of milk into product when it comes to writing about the breeding of dairy cattle. We expect it happens even less frequently that dairy cattle breeders consider the yield their processor obtains in products from the milk they ship. The different kappa casein genotypes found in today’s dairy cattle can have a significant effect on the volume and quality of cheese produced from milk. Here are some interesting details that we found from our research on this subject.

The Situation

Dairy cattle are evaluated for their ability to produce the percentage of protein in milk and the total protein yield.  Milk processors find that: 1) some milks clot quickly, its cheese is firm and produces the most cheese per unit of milk; 2) some milks clot, but not quickly, and have varying degrees of firmness and produces 10%-15% less cheese, and 3) some milks do not clot. Cheese makers are not prepared to buy milk that fits into the latter category. Studies from Europe and North America have found a strong association between the kappa casein genotype BB and milk that clots quickly, produces firm cheese and has a high volume of cheese yield.

The situation of poor or non-clotting milk came to international attention in the 1970’s when Italian cheese makers were no longer able to make their cheeses from the milk from certain farms. After studying the situation, it was determined that some daughters from North American Holstein sires produced milk that was not desirable for cheese making.  In-depth study identified the problem to be with the kappa casein produced by these non-Italian sires’ daughters.

Kappa Casein Alleles

At least nine alleles have been identified for kappa casein. Specifically, three alleles, A, B, and E, dominate in global dairy cattle populations. Initially, it was thought that two alleles, A and B, were the main ones present in dairy cattle. However, a third allele, E, was found to exist approximately 10% of the time. E is the allele associated with the milk that does not clot to make cheese.

Cheese Yield by Genotype

A synopsis of the published findings on kappa casein genotypes follows:

• Cheese from the milk of BB cows’ clots 25% faster and is twice as firm as cheese made from AA cow’s milk.
• Milk from BB cows produces 1.0- 1.5 lbs (about 10%) more cheese per cwt of milk than milk from AA cows.
• Milk from AB cows is about midway between BB and AA cows for clotting speed, firmness, and yield.
• Milk from EE cows does not clot and is not suitable for cheese making
• Milk from AE cows is also considered by most cheese makers to be unsuitable.
• The literature is not informative on the properties of milk from BE cows. There are suggestions that it may be similar to milk from AA cows when it comes to cheese making.
• A 1985 study by Okigbo, Richardson, Brown and Ernstrom found that milk with impaired clotting properties was not improved by mixing it with an equal amount of well-clotting milk.

General Stat’s with respect to Kappa Casein

Initially, our focus was on kappa casein relative to North American dairy cows. However, we found interesting information from published studies in Italy, France, Estonia, The Netherlands, Scandinavia, and Turkey.  Milk for cheesemaking is important in these countries because from 40% to 75% (Italy) of the national milk is used to make cheese. Some additional facts include:

• About 10% of North American Holsteins are BB.
• North American Jerseys have a significantly higher percent BB than do Holsteins. Likely the result heavy use of two BB Jersey sires from twenty years ago.
• Globally Brown Swiss are reported to be 35% BB.
• Holsteins in Europe have between 15% and 23% BB
• Water Buffalo are almost 100% BB. India, the world’s largest milk producing country, gets half its milk from Water Buffalo.

What About Current Holstein Sires?

Table 1 is the frequency of occurrence for the kappa casein genotypes for the top North American proven or most used Holstein sires.

Table 1 – Kappa Casein Genotype Profiles for North American Holstein Sires

* For time period two weeks prior to April 03, 2017
** Based on registrations in 2016
*** April 2017 Proofs

Some points that should be noted from this table include:

• The sires in Table 1 have a higher occurrence of BB (17%) than in the general cow population (10%).
• There are no EE sires but the 16% level of AE should concern breeders and A.I studs when it comes to cheese firmness and lost potential yield in the future.
• The frequency of BB & AB is higher in the Canadian sire proof groupings than in other groupings.
• The overall 38% gene frequency of the B allele gives hope that genetic progress to eliminating E and reducing the A allele should be possible in the not too distant future.

Some BB daughter proven sires that topped or were near the top of the groupings in Table 1 are listed in Table 2.

Table 2 –  Leading BB Daughter Proven Sires

One BB genomically evaluated sire is in the top registered USA sire grouping in Table 1:

• Jedi                       (7HO13250)                             (Montross x Supersire x Bookem)                #8 US Registered

What About Genomic Sires?

With over half of the semen being used coming from genomically evaluated sires it is important to consider this category. In some herds, only genomic sires are used. However, to summarize the kappa casein genotype frequency for this group is not reasonable as many of the top sires on the April 2017 listings are too young to have semen available yet. As well the usual cautions that The Bullvine gives apply do not overuse any one genomically evaluated sire as their indexes range from 55% to 75% REL. Moreover, take into consideration the future inbreeding coefficient of these sires as a breeder may already have those sires close up in their animals’ sire stacks.

Some genomically evaluated Holstein and Jersey sires that are BB for kappa casein that are worthy of breeder consideration include:

Table 3 – High Ranking BB Genomic Evaluated Sires

Take Home Ideas

The Bullvine offers the following ideas for breeders and breeding industry people to consider:

• Cheese Making: In the future, it is entirely possible that cheese processors will not buy milk from Holstein herds that cannot guarantee that their cows are at least a high percentage are BB. Jersey herds and totally BB Holstein herds are likely to be paid a premium for this milk.
• Niche or Mainstream: In the next five years breeding to increase the percent of BB females will be niche. However, as more and more milk is used to make cheese selection for the B allele and away from the E allele is likely to be mainstream. Selecting sires on total protein without regards to the kappa casein profile of those sires should become a practice from the past.
• Breeding Animals: Breeders and breeding organizations would be well advised to commence selecting for the B allele when it comes to sire and ET donor selection. An achievable objective would be for A.I. studs to only enter BB and AB bulls into stud starting in 2019. Breeders are advised not to flush any females that are EE, AE and perhaps even BE starting in 2019 or before. Breeders need to ask their semen sales reps for a sire’s kappa casein profile before buying semen. Bull kappa casein profiles are not included in CDCB or CDN files but are most often included in A.I. stud electronic bull files or hard copy catalogs.
• Research: More research is taking place in many countries of the impact of kappa casein genotype on cheese production. At the University of California (Davis) there are major projects underway on how to use genetic engineering to eliminate the E allele and to fast track changing Holsteins into being BB.

The Bullvine Bottom Line

One characteristic, like kappa casein, cannot rule the breeding, milk production and milk processing industries. However, with a higher and higher percentage of dairy cows’ milk being used to make cheese, breeding for animals with the BB kappa casein genotype can no longer be ignored or thought not to be important. Breeders are advised to ask their semen suppliers for the kappa casein profiles of sires before they purchase semen. Starting immediately sires with EE and AE profiles should be avoided and if the semen is already in the tank then even throwing it out may make good business sense. Because producing females that are EE or AE will delay when premiums may be possible for milk sold for making cheese.

Get original “Bullvine” content sent straight to your email inbox for free.

Dairy breeders spend considerable time choosing the next round of bulls to use. That’s important because improvements in genetics has a significant influence on the generations that follow.  Nevertheless, future performance will depend on how epigenetics regulates the DNA acquired through breeding.  When epigenetics enters the picture,  breeders will need to re-consider how they breed and manage their dairy cattle.

What’s Epigenetics?

Epigenetics underlies processes that affect health, ­ fertility, longevity and many traits of dairy cattle. Epigenetic effects differ from direct genetic effects because the animal’s DNA sequence is not changed by epigenetic processes. Rather, epigenetic processes act by regulating whether genes within DNA sequences are “turned on” or “turned off” without any change in the DNA sequence. (Read more: FORGET GENOMICS – EPIGENOMICS & NUTRIGENOMICS ARE THE FUTURE)

Genetic and Epigenetic Differences

Traits such as milk yield, milk protein, conception rate, somatic cell count and udder conformation are heritable, meaning that differences among animals in these traits can be accounted for by family relationships among sires, dams and ancestors. Heritability ranges from around 3% to over 50% for various traits, therefore 3 to 50% of differences among animals are accounted for by differences in their DNA sequences.

The non-genetic variation in traits is included in what we refer to as environmental effects. Weather, feed, facilities, management practices and everything else that cattle are affected by in a herd fits into environmental effects.  Many responses of cattle to environmental effects are regulated by epigenetic or closely-related processes at the cellular level in animals.

Epigenetic effects do not change an animal’s DNA sequence (genome). Instead, epigenetic effects alter how individual genes or groups of genes are controlled or as geneticists say “silenced or differentially regulated” throughout an animal’s life. Originally, epigenetic effects were thought to represent only alterations that could be passed to the next generation without changing in the animal’s genetic code. More recently it seems that epigenetic effects may impact various tissues and organs during certain periods in the animal’s life, without being passed to the next generation.

Epigenetic Triggers

Animal scientists are using the term “developmental programming” to define practices that may trigger epigenetic effects. Developmental programming may act through epigenetic or similar pathways to influence almost any trait of interest in dairy cattle. For dairy farmers, it matters little whether the action occurs through one mechanism or another, as long as responses are predictable and repeatable.

Repeatability means that there is a fairly predictable pattern of an action causing a specific or response separated by weeks, months, years or generations. That makes it challenging to determine cause and effect, without careful observations, good records and repeated verification.

Epigenetic effects may be triggered by conditions associated with natural biological process or by adverse conditions such as negative energy balance, heat stress, exposure to toxins or other disturbances. Epigenetic effects can be either positive or negative, so as we learn more it will be useful to incorporate management practices that stimulate positive effects and limit negative ones.

Epigenetic Effect #1        Calf Feeding and Future Performance

One epigenetic or epigenetic-like effect is the latent response to feeding higher levels of milk or replacer to heifer calves. Calves fed at higher levels produce more milk in first lactation about 2 years later, so the response occurs beginning about 700 days after the action. Preliminary data suggest that heifers fed more milk develop more mammary epithelial cells that become milk-secreting cells when first lactation begins. This is the kind of epigenetic effect that one would see for stem cells that are dividing rapidly when the milk is being fed. The exact regulatory mechanism for this effect is yet to be determined.

Epigenetic Effect #2        Milking Frequency Immediately After Calving

Similar to the situation in calves fed more milk, it has been demonstrated that cows milked 4X daily during the first 3 weeks of lactation and then 2X daily thereafter produce considerably more milk than cows milked 2X from freshening. The 4X milking early in lactation apparently stimulates development of more milk-secreting cells and these then remain throughout lactation, even when milking frequency drops to 2X.

Epigenetic Effect #3        Embryo Survival

It is highly probable that negative epigenetic effects occur when eggs (oocytes) are developing within the ovary when a cow is under stressful conditions. Such can be the case for the egg ovulated by an energy and/or health stressed cow that comes into heat 80 days post calving. The egg ovulated at day eighty actually started growing as an oocyte within her ovary about 3 weeks before calving.

 Oocytes that develop under these stressful conditions have low survivability as embryos. Their fertilization rate is normal, but they degenerate and die at a higher rate in the first week after fertilization. This is a classical example of an adverse epigenetic effect. Our North Carolina State research team published the first report of this effect in 1992. It is referred to as the Britt Hypothesis and it has taken about 25 years for scientists to begin to understand this phenomenon at the DNA level.

Stay Tuned As We Learn More

There is a strong interest in understanding how epigenetics affect the developing fetus and how management of the pregnant cow influences the future long-term responses of the calf she is carrying. During fetal stages, tissues that will form muscles, mammary tissue, the immune system and all other systems undergo development.  We will see a lot of new discoveries about epigenetics in these areas in the years ahead and this will give us tools to support development of better calves during pregnancy.

Husbandry practices trigger many of the epigenetic effects, both good and bad.  Understanding how such effects are mediated will give us husbandry tools to improve both DNA-based genetics and ways to regulate the DNA in a beneficial manner.

The Bullvine Bottom Line

The Bullvine found that this information shared by Jack Britt assisted us in better understanding the topic of epigenetics.  Yes, epigenetics is yet one more piece of the puzzle that progressive breeders are likely to use in the future to both breed and manage their dairy herds.

Get original “Bullvine” content sent straight to your email inbox for free.