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It’s not easy getting older: Heifers versus lactating dairy cows as they transition

Yasmin Schuermann and Raj Duggavathi for Progressive Dairyman Published on 29 September 2017

The dairy cow is quite an extraordinary creature. Time and time again the record for highest milk production is broken, most recently by My Gold from Ever-Green-View Farms in Wisconsin with a mind-boggling 77,480 pounds (35,144 kilograms) of milk produced in a 365-day period.

Without a doubt, the biological limit for milk production by our dairy cows has not been reached, and we can look forward to this record being challenged sooner rather than later. However, not as easily broken is another record, one which honours the cow producing the greatest amount of milk over her lifetime.

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To this day, Gillette Emperor Smurf from Ontario holds on to this title, whereby she produced 478,163 pounds (216,891 kilograms) of milk by the time she reached 15 years of age, a record which has stood since 2012. Although fascinating, it is simultaneously unfortunate that no dairy cow could dethrone Smurf in the past five years.

In a nutshell, this tells us that cows might be producing astonishing volumes of milk, but they are simply unable to realize their full potential of the number of lactations. In addition to economics, this also raises important ethical questions.

Do modern dairy cows achieve their full potential of lifetime calf and milk production? Is it reasonable to propose that cow longevity is the key factor that deserves attention when it comes to running a sustainable and profitable dairy operation? Table 1 provides a summary of our typical Canadian dairy farms.

What is happening on our dairy farms?
Does this table represent an ideal scenario? Well, not exactly, and for that reason, the focus of research is directed toward decreasing age at first calving, increasing the number of cows making it to subsequent lactations and decreasing the percentage of cows leaving the herd due to poor reproductive performance, all without drastically affecting their production performance.

We need to address these parameters if we wish to see our cows last just a little bit longer.

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At McGill University’s annual Centre for Research in Reproduction and Development Research Day, held in May, a guest speaker said, “Life is short, but fertility is shorter.” This is obviously and undeniably true, but when it comes to cows we must modify this quote to: “Life is shorter because fertility is short.”

Overall, fertility is viewed as a hot topic, especially considering that issues in reproductive performance are the predominant reasons cows are being culled.

It is no secret that the transition period, defined as three weeks pre-calving to three weeks post-calving, is viewed as a challenging time for both the cow and the producer.

The producer will do his or her best to get the cow off to a solid start at the onset of lactation and get her ready for breeding within 80 to 100 days in milk. Nonetheless, this period comes with numerous challenges.

It is well-established that transition into early lactation is characterized by drastic physiological changes leading to negative energy balance, often followed by metabolic stress.

In severe cases, cows will go on to suffer from diseases such as ketosis, displaced abomasum and milk fever, all of which can result in costly losses in milk production or even death.

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Often at the onset of lactation, a cow can easily be the victim of abnormally decreased dry matter intake, increased fat mobilization, disease, a weakened immune system or liver damage, which can have a snowball effect and take a toll on subsequent reproductive performance.

Of course, a plethora of studies have and continue to investigate vitamin, mineral and protein supplementation, energy formulation, modifications of the dry period length and the body condition score around calving, among others. So far, there is no one silver bullet to increase cow longevity.

Ultimately, enhancing our understanding beyond the current knowledge of physiology during the transition period will help us formulate right hypotheses to test by scientific experiments and eventually develop more strategies to manage metabolic imbalance of lactating dairy cows.

On that note, we must remember that the extent of transition period and metabolic alterations do change as cows get older. Simply put, heifers and cows differ greatly from a metabolic standpoint when it comes to the period leading up to breeding.

Our heifers rarely give us breeding troubles, while our older cows come with some added challenges, especially depending on their success during the transition period. As they say, “little kids, little problems; big kids, big problems.”

I suppose one analogy we can use is to compare our dairy cattle to car brands. First, we have our 13- to 15-month-old heifers, these are our Honda Civic models, a nice car for first time drivers; it works well and can tolerate a small fender bender here and there.

But as soon as these heifers enter their first transition period, makes and models start to change. Of course, you will have some cows that will maintain their trouble-free status, but the spectrum of makes increases.

Now you will start dealing with the Fords, Volkswagens, Mercedes, Audis, Ferraris, Teslas, Porsches and Lamborghinis. With so many different makes in the barn, producers have quite the task ahead of them to meet everybody’s individualized needs. Therefore, it is important to clarify different but specific types of metabolic alterations that occur during the transition period.

Blood chemistry has been used for decades to analyze the health status of cows, where a wide range of metabolites and hormones can be measured to assess immune function, liver health and energy status.

Ketone bodies, most notably, beta-hydroxybutyric acid (BHBA), can easily be measured on-farm and provide producers with the likelihood of ketosis, where elevated levels (greater than 1.2mmol/L) report a sign that cows are using their body fat stores as an energy source instead of obtaining energy from their diet.

Our group in the animal science department at McGill University has compared the metabolic profile from the blood of cattle at different stages of production: heifers (13 to 15 months old) versus cows entering their first lactation versus cows entering their second or greater lactation.

This paints a colourful picture of animals experiencing the transition period versus “nonstressed” heifers. If we compare the BHBA levels three weeks pre-calving to 12 weeks post-calving, overall, older cows have higher levels of BHBA during this time when compared to cows entering their first lactation (Figure 1).

A look at ketones at different stages of production-BHBA beta-hydroxybutryic acid

Furthermore, if we look at seven weeks post-calving, a time right before breeding these cows, and compare to heifers (blood collected at a time right before they are to be bred by about 15 months of age), we can see that overall the BHBA levels for older cows are still very high even past the transition period, when heifers have significantly lower levels of BHBA.

As cows get older, milk production increases, which would suggest they have an increased need for energy in the form of feed or lipid mobilization (Figure 2).

Changes of milk production among lactations

Heifers are not investing any energy other than for maintenance and breeding and will therefore not depend on mobilizing fat tissue. If cows are not experiencing any drastic health issues during the transition period that can severely hinder milk production, it is well-established that mature cows will produce more milk than first-lactation cows and will really shine and be most profitable by the fourth lactation.

This is a solid reason for keeping our cows around for more than one lactation, especially considering that the Canadian dairy cow only starts making a profit during the second lactation.

However, this means we must make sure our cows are getting the most out of their diet, especially in the form of optimal dry matter intake and energy to decrease fat mobilization and improve energy used for milk production and subsequent reproduction.

Energy in the form of glucose levels (Figure 3) provides a striking example of differences between lactating cows and heifers during the weeks leading up to the breeding period.

The changing glucose levels over time

Glucose requirements are elevated in lactating cows for milk synthesis and very low levels are associated with metabolic stress. Energy in the form of glucose is a component for immune regulation and helps in maintaining an important population of immune cells necessary for overall “body cleanup.”

Moreover, it has been suggested that high levels of BHBA, which represent an alternate source of energy, can be used by cows, but can simultaneously alter normal glucose metabolism.

Ultimately, cows are at an automatic disadvantage in terms of energy in the form of glucose for immune function when compared to heifers, perhaps influencing overall physiological preparation for the onset of breeding. Therefore, our management must be altered depending on the stage of production.

It is good to consider the metabolic parameters in blood circulation as they are reflected in the ovarian follicular fluid. The latter is an environment that supports growth of the healthy egg (oocyte) with adequate developmental potential, which can have implications well beyond fertilization, including the development of the fetus and its eventual production performance as an adult.

In fact, the follicle that will be ovulating (releasing the egg into the uterus for fertilization) at the first attempted breeding requires approximately 11 to 14 weeks to grow.

If we backtrack, the ovulating follicle would be developing during the transition period when metabolites are severely altered; this is not the case for heifers.

It comes to show the importance of adapting overall management of our cows, depending on their age and stage of production to increase overall longevity, by providing a smooth transition period.

More fundamental and applied research is necessary so that we can develop individualized approaches to take good care of our Ferraris and give Smurf a run for her money.  end mark

Acknowledgements: Figures included in this article are from the research program of Dr. Duggavathi, which is supported by NSERC and FQRNT. Yasmin Schuermann is supported by RQR and FQRNT.  

Raj Duggavathi is also with the animal science department of McGill University.

References omitted but are available upon request. Click here to email an editor. 

Yasmin Schuermann
  • Yasmin Schuermann

  • Animal Science Department
  • McGill University
  • Email Yasmin Schuermann

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