MPG treats ketosis in grazing cows but fails where it counts: milk & reproduction. Are we treating the wrong problem?

EDITOR’S NOTE: This article challenges conventional ketosis treatment wisdom based on groundbreaking New Zealand pasture-based dairies research. What works in the barn may not work on pasture, and it’s time we face this reality.

The Sacred Cow of Ketosis Treatment Gets Tipped Over

You’ve seen it a hundred times. Fresh cow tests high for ketones. Your veterinarian or nutritionist insists you grab the propylene glycol. Drench. Repeat daily until resolved. It’s practically gospel in dairy farming.

But what if this well-established practice – swallowed hook, line, and sinker by dairy farmers worldwide – isn’t delivering the goods where it counts?

A bombshell study published in the Journal of Dairy Science (The effect of monopropylene glycol on milk production, uterine health, and reproductive performance in cows diagnosed with hyperketonemia on 3 pasture-based dairy farms) from New Zealand dropped a truth bomb that might force you to rethink your approach to ketosis management in pasture-based dairy systems. The findings? While propylene glycol fixes your ketone meter’s numbers, it does little to improve the metrics that pay the bills – milk production and reproduction.

This isn’t just another academic paper to file and ignore. This research directly challenges what we’ve been taught about ketosis treatment, especially for those managing grazing dairy operations. And it raises the uncomfortable question: Have we been wasting money treating a condition that, at moderate levels, might not be harming our cows as much as we thought?

What The Study Found

Before you throw away your ketone meter, let’s look at what the researchers discovered. This wasn’t some small-scale experiment – it was a massive undertaking across three New Zealand dairy farms involving 980 cows that underwent intensive ketone testing (three times weekly for 35 days post-calving).

Here’s what happened:

• A staggering 76% of cows had at least one positive test for hyperketonemia (BHB ≥1.2 mmol/L)
• Cows that tested positive were randomly assigned to either receive propylene glycol treatment (300ml daily until resolved) or serve as untreated controls
• MPG treatment worked perfectly at the biochemical level – treated cows resolved ketosis faster (2.5 vs 3.1 days) and were 69% less likely to develop severe ketosis

So far, so good. The treatment did exactly what the product label promised. But here’s where conventional wisdom gets flipped on its head.

Despite successfully fixing the ketones, MPG treatment:

• Did NOT improve milk production (in fact, energy-corrected milk was slightly LOWER in treated cows)
• Did NOT improve reproductive performance (no better submission rates, conception rates, or pregnancy rates)
• Only reduced severe uterine discharge (affecting just 4.3% of cows), with no effect on milder cases

The researchers’ blunt conclusion? “There would be little benefit to routine administration of MPG to hyperketonemia cows on pasture-based dairy farms based on a blood BHB threshold of ≥1.2 mmol/L.”

Are We Using the Wrong Threshold for Treatment?

Here’s a provocative thought that challenges decades of ketosis management: What if 1.2 mmol/L is the wrong threshold for treatment in grazing cows?

Think about it. This widely accepted cutoff for what constitutes “subclinical ketosis” comes primarily from research on high-producing, TMR-fed, housed dairy cows. These animals have completely different metabolic demands, consumption patterns, and environmental stresses compared to cows harvesting their feed on pasture.

Consider these mind-blowing numbers from the New Zealand study:

• Over 76% of healthy, grazing cows had at least one BHB test ≥1.2 mmol/L in early lactation
• Untreated control cows with “ketosis” (left untreated) performed just as well as MPG-treated cows in terms of milk production and reproduction
• The incidence of severe clinical symptoms was relatively low, even in untreated cows

These observations suggest that rather than asking, “Does this cow have ketosis?” we should perhaps be asking, “Is this level of ketosis harmful to this specific cow in this specific production system?”

The Folly of One-Size-Fits-All Ketosis Management

Let’s call out the elephant in the room: We’ve been blindly applying research from one production system to another without questioning whether it makes sense.

The uncomfortable truth is that what works in a Wisconsin free-stall barn might be useless – or counterproductive – in a New Zealand pasture system. Think about the fundamental differences:

• Different energy intake patterns: Grazing cows consume their energy in discrete meals throughout the day, with higher intake during daylight hours versus TMR-fed cows with constant feed access
• Different diet composition: Pasture contains more rapidly fermentable carbohydrates and typically has a higher ratio of glucogenic to lipogenic nutrients compared to many TMRs
• Different levels of physical activity: Grazing cows might walk kilometers daily to harvest their feed, creating different energy dynamics
• Different milk production levels: Grazing cows typically produce less milk than their TMR-fed counterparts, potentially altering the severity and impact of negative energy balance

Have we been so obsessed with “fixing” ketone levels that we’ve forgotten to ask whether they need fixing at all?

The Economic Reality Check

Let’s put some dollars and cents into this discussion.

The cost of treating ketosis includes:

• Labor for testing and treatment ($2-5 per cow tested)
• Propylene glycol ($1-2 per treatment)
• Equipment and supplies ($0.50-1 per cow)

For a 300-cow grazing herd with 75% testing positive for ketosis and requiring an average of 2 treatment bouts each, this quickly adds up to $1,500-4,000 indirect costs – not counting the opportunity cost of labor that could be directed elsewhere.

What are you getting for this investment? According to this research:

• No improvement in milk yield
• No improvement in reproductive performance
• A reduction in severe endometritis cases (about 3.7 fewer cases per 100 treated cows)
• Peace of mind that fewer cows will progress to severe ketosis

Is that worth $1,500-4,000 to your operation? Only you can answer that question, but the data suggests the ROI might be questionable at best for grazing operations.

When MPG Treatment Still Makes Sense

Before you completely throw the baby out with the bathwater, let’s acknowledge situations where treatment likely remains beneficial:

Severe hyperketonemia: Cows with BHB ≥3.0 mmol/L still benefit from treatment. The study showed MPG effectively prevents progression to this severe state, which likely does impact performance.

Clinical ketosis: Cows showing clinical signs (decreased appetite, dramatic milk drop, neurological symptoms) should be treated, regardless of system.

High-risk individuals: Cows with other risk factors (very high BCS, history of ketosis, twin births, difficult calving) may benefit from treatment at lower thresholds.

TMR/confinement operations: This study doesn’t invalidate the research showing the benefits of ketosis treatment in housed systems – it simply highlights system-specific differences.

Rethinking Our Approach: A Better Way Forward

So, where do we go from here? This research doesn’t provide all the answers, but it certainly points us toward some important questions and considerations:

1. Consider raising your treatment threshold to 1.8 or 2.0 mmol/L for pasture-based cows, focusing treatment efforts on more severe cases.
2. Test your approach: Split your hyperketonemic cows into treated/untreated groups and track subsequent performance. What works on your neighbor’s farm might not work on yours (or vice versa).
3. Focus on prevention first: Double down on transition cow management to prevent severe ketosis, which still showed negative effects even in this study.
4. Challenge the “treat the number” mentality: Are you treating to fix a lab value or to improve cow performance? If the latter is your goal, the evidence suggests you might need to rethink your approach to grazing systems.

Here’s a radical thought: What if we’re making ketosis management more complicated than it needs to be in grazing systems? What if we focused on excellent transition management and only treated the truly problematic cases?

A Challenge to Veterinarians and Nutritionists

Let’s be brutally honest: How many recommendations about ketosis are based on actual evidence in the production system where they’re being applied?

Vets and nutritionists advising pasture-based dairies must reconsider whether they’re simply importing protocols developed for housed systems without critical evaluation. The days of universally recommending treatment for every cow above 1.2 mmol/L BHB should be over.

If you’re a dairy professional, ask yourself: Am I recommending this treatment because I have evidence it works in this specific system or because it’s what I learned in school based on research from completely different production environments?

Take Action: What You Should Do Tomorrow Morning

1. Evaluate your current ketosis testing and treatment protocol. Calculate the actual costs, including labor, supplies, and MPG.
2. Based on this research, if you operate a pasture-based system, consider raising your treatment threshold to 1.8-2.0 mmol/L BHB.
3. Track outcomes that matter – not just ketone levels but milk production, reproduction, and overall health.
4. Discuss system-specific evidence for ketosis treatment recommendations with your veterinarian or nutritionist.
5. Consider reallocating resources from routine treatment of moderate ketosis to preventing it through optimal transition management.

The Bottom Line: Evidence Trumps Tradition

This New Zealand research delivers a wake-up call to the dairy industry. It challenges us to question whether our current approaches to diagnosing and treating hyperketonemia in pasture-based systems make economic and biological sense.

The next time you reach for that drench gun to treat a cow with moderately elevated ketones, ask yourself: Is this intervention improving this cow’s performance, or am I just treating a number on a meter?

The best dairy producers have always been those willing to question conventional wisdom when evidence suggests a different approach might be better. This research gives us that opportunity.

Perhaps the most valuable outcome isn’t a new treatment protocol but a new way of thinking about metabolic health that recognizes the unique characteristics of different production systems. After all, the goal isn’t to have perfect blood tests – it’s to have healthy, productive, profitable cows.

BOTTOM LINE: For pasture-based operations, treating moderate hyperketonemia (BHB 1.2-2.9 mmol/L) with propylene glycol resolves ketosis faster but doesn’t improve milk production or reproduction. Consider raising your treatment threshold, focusing on prevention, and developing protocols specific to your system rather than blindly applying confinement research to grazing operations.

Key Takeaways:

• MPG works biochemically (1.5x faster HYK resolution, 69% lower severe ketosis risk) but fails economically (no milk/reproduction gains).
• Treated cows had lower fat yields and marginally reduced ECM (-0.4 kg/day) vs controls.
• No fertility boost: Identical 42-day pregnancy rates (60% vs 65%) and submission rates across groups.
• Threshold debate: 76% of grazing cows hit BHB ≥1.2 mmol/L – possibly an adaptive norm, not a crisis.
• Farm variability: MPG reduced first-service conception by 35% on one farm – context matters.

Executive Summary:

A New Zealand study of 980 pasture-based dairy cows found that while monopropylene glycol (MPG) effectively resolves hyperketonemia (blood BHB ≥1.2 mmol/L) and reduces severe cases by 69%, it delivered no meaningful milk yield gains, marginally lowered fat production, and showed no reproductive benefits. Despite biochemical success, treated cows had identical pregnancy rates and slightly worse energy-corrected milk yields than untreated controls. The research challenges the economic rationale for routine MPG use in grazing herds, suggesting moderate ketosis at this threshold may not impair performance as previously assumed. System-specific thresholds and prevention strategies may offer better ROI.

Learn more:

• The Vital Role of Ketones in Dairy Cow Lactation
  Explore how ketones support energy balance in fresh cows, the difference between healthy hyperketonemia and pathological ketosis, and why not all elevated ketones are bad news.
• Shorter or No Dry Periods: A New Frontier in Dairy Cow Management
  Discover how adjusting dry period length and glucogenic diets can improve energy balance, reduce metabolic disorders like ketosis, and enhance reproductive outcomes.
• Mastering Dry Cow Management: Essential Strategies for Healthier Cows and Higher Milk Yields
  Learn proven dry cow nutrition and management tactics that set the stage for metabolic health, optimal milk production, and improved transition success.

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