Ninety spring-calving cows grazing pasture produced milk with markedly different fatty acid (FA) profiles depending on breed — and the differences widened as lactation progressed, according to a study of the 2023–2024 lactation season.

The study compared Holstein-Friesian (F, n = 33), Friesian × Jersey crossbred (F × J, n = 31), and Jersey (J, n = 26) cows managed under a pasture-based system. Researchers analyzed 790 monthly herd test records to characterize milk yield and composition, collecting composite milk samples for fat, protein, and mid-infrared spectra determination. They predicted FA concentrations (g FA/100 g of milk) using partial least squares models calibrated against 120 samples with FA measured by gas chromatography. Random regression with orthogonal polynomial functions described lactation patterns.

The headline number for producers and processors: Jersey cows produced approximately 23% more saturated FA than Holstein-Friesian cows, a gap of +0.80 g FA/100 g of milk. Jersey cows also posted the highest total fat concentration at 6.29%, followed by F × J at 5.50% and F at 5.32%.

Stage of lactation drove most of the variation

Stage of lactation emerged as the dominant source of variation in milk FA composition. Short-chain, medium-chain, and saturated FA increased from early to late lactation, while preformed FA declined over the same period.

That pattern matters for milk payment schemes and processing. Late-lactation milk from Jersey-heavy herds will carry a different FA signature than early-lactation milk, and pooled herd averages can mask those shifts.

Crossbreds don't split the difference

When averaged across lactation, F × J cows generally resembled F cows for most FA groups. But the crossbred response was FA-specific: F × J was intermediate between the parent breeds for short-chain FA, yet resembled F for medium-chain FA.

The study's central conclusion follows directly: crossbred FA profiles are FA-specific and stage-dependent, and producers cannot predict them as simple parental averages.

Breed gaps widen across lactation

Breed differences were more pronounced within lactation stages than in pooled analyses. Breed × stage interactions reflected changes in the magnitude of breed differences rather than changes in ranking — Jerseys stayed ahead on saturated FA throughout, but the gap grew.

The saturated FA difference between J and F widened by about +0.11 g FA/100 g of milk from early to late lactation. In other words, the breed ranking held steady, but the spread between breeds did not.

What this changes at the farm gate

For pasture-based dairy operations weighing breed composition — particularly those supplying processors with FA-sensitive specifications or developing nutrition-forward milk products — the findings argue against assuming a crossbred herd will deliver a midpoint milk profile. They also argue for timing: stage-of-lactation effects on short-chain, medium-chain, saturated, and preformed FA are large enough that sampling month will shape any FA assessment.

The calibration approach itself offers a practical tool. With mid-infrared spectroscopy models calibrated against 120 gas chromatography samples, the study demonstrates a scalable method for monitoring FA profiles across herds without routine chromatographic analysis.

Future work building on these random regression models could refine breed-specific lactation curves for individual FA groups, giving processors and breeding programs finer control over milk composition than pooled herd averages allow.