Immediately following parturition, physiological demands for calcium increase substantially to support the onset of milk production. As a result, transitioning dairy cows may experi­ence subclinical hypocalcemia (SCH) at some point during early lactation. Cows respond to this homeostatic challenge dynamically, such that serum total calcium concentrations (tCa) at 1 and 4 days in milk (DIM) can be used to classify cows into 4 calcium dynamic groups: normocalcemic (NC: SCH at no DIM), transient (tSCH: SCH at 1 DIM only), delayed (dSCH: SCH at 4 DIM only) and persistent (pSCH: SCH at both 1 and 4 DIM). Identifying cows in the pSCH and dSCH groups is important clinically because these groups are at greater risk of adverse health events compared to the NC and tSCH cows. Our objective was to describe the temporal patterns of milk constituents for cows in each calcium group using Fourier-transform infrared (FTIR) spectroscopic analysis of milk samples. Additionally, we hoped to ascertain whether these methods might be valuable as a diagnostic tool for grouping cows based on calcium dynamics at a clinically useful timepoint.

Post-parturient subclinical hypocalcemia (SCH) in dairy cows, a common metabolic disease which arises from the increased calcium demands of early lactation, has been associated with decreased milk production and negative health outcomes. Our objective was to determine how postpartum calcium supple­mentation methods, and the timing of their administration, affect blood calcium concentrations and regulators of calcium homeostasis, specifically parathyroid hormone and calcitonin.

Cows undergo immense physiological stress to produce milk during early lactation. Monitoring early lactation milk through Fourier-transform infrared (FTIR) spectroscopy might offer an understanding of which cows transition successfully. Daily patterns of milk constituents in early lactation have yet to be reported continuously, and the study objective was to initially describe these patterns for cows of varying parity groups from 3 through 10 d postpartum, piloted on a single dairy. We enrolled 1,024 Holstein cows from a commercial dairy farm in Cayuga County, New York, in an observational study, with a total of 306 parity 1 cows, 274 parity 2 cows, and 444 parity ≥3 cows. Cows were sampled once daily, Monday through Friday, via proportional milk samplers, and milk was stored at 4°C until analysis using FTIR. Estimated constituents included anhydrous lactose, true protein, and fat (g/100 g of milk); relative % (rel%) of total fatty acids (FA) and concentration (g/100 g of milk) of de novo, mixed, and preformed FA; individual fatty acids C16:0, C18:0, and C18:1 cis -9 (g/100 g of milk); milk urea nitrogen (MUN; mg/100 g of milk); and milk acetone (mACE), milk β-hydroxybutyrate (mBHB), and milk-predicted blood nonesterified fatty acids (mpbNEFA) (all expressed in mmol/L). Differences between parity groups were assessed using repeated-measures ANOVA. Milk yield per milking differed over time between 3 and 10 DIM and averaged 8.7, 13.3, and 13.3 kg for parity 1, 2, and ≥3 cows, respectively. Parity differences were found for % anhydrous lactose, % fat, and preformed FA (g/100 g of milk). Parity differed across DIM for % true protein, de novo FA (rel% and g/100 g of milk), mixed FA (rel% and g/100 g of milk), preformed FA rel%, C16:0, C18:0, C18:1 cis -9, MUN, mACE, mBHB, and mpbNEFA. Parity 1 cows had less true protein and greater fat percentages than parity 2 and ≥3 cows (% true protein: 3.52, 3.76, 3.81; % fat: 5.55, 4.69, 4.95, for parity 1, 2, ≥3, respectively). De novo and mixed FA rel% were reduced and preformed FA rel% were increased in primiparous compared with parity 2 and ≥3 cows. The increase in preformed FA rel% in primiparous cows agreed with milk markers of energy deficit, such that mpbNEFA, mBHB, and mACE were greatest in parity 1 cows followed by parity ≥3 cows, with parity 2 cows having the lowest concentrations. When measuring milk constituents with FTIR, these results suggest it is critical to account for parity for the majority of estimated milk constituents. We acknowledge the limitation that this study was conducted on a single farm; however, if FTIR technology is to be used as a method of identifying cows maladapted to lactation, understanding variations in early lactation milk constituents is a crucial first step in the practical adoption of this technology.