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The Effect of Compositional Changes Due to Seasonal Variation on Milk Density and the Determination of Season-Based Density Conversion Factors for Use in the Dairy Industry
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2020-07-27
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Parmar, P.; Lopez-Villalobos, N.; Tobin, J.T.; Murphy, E.; McDonagh, A.; Crowley, S.V.; Kelly, A.L.; Shalloo, L. The Effect of Compositional Changes Due to Seasonal Variation on Milk Density and the Determination of Season-Based Density Conversion Factors for Use in the Dairy Industry. Foods 2020, 9, 1004. https://doi.org/10.3390/foods9081004
Abstract
The objective of this study was to determine the effect of seasonal variation on milk
composition and establish an algorithm to predict density based on milk composition to enable
the calculation of season-based density conversion calculations. A total of 1035 raw whole milk
samples were collected from morning and evening milking of 60 spring-calving individual cows
of different genetic groups, namely Jersey, Elite HF (Holstein–Friesian) and National Average HF,
once every two weeks for a period of 9 months (March–November, 2018). The average mean and
standard deviation for milk compositional traits were 4.72 ± 1.30% fat, 3.85 ± 0.61% protein and
4.69 ± 0.30% lactose and density was estimated at 1.0308 ± 0.002 g/cm3
. The density of the milk
samples was evaluated using three methods: a portable density meter, DMA 35; a standard desktop
version, DMA 4500M; and an Association of Official Agricultural Chemists (AOAC) method using
100-mL glass pycnometers. Statistical analysis using a linear mixed model showed a significant
difference in density of milk samples (p < 0.05) across seasonal and compositional variations adjusted
for the effects of days in milk, parity, the feeding treatment, the genetic group and the measurement
technique. The mean density values and standard error of mean estimated for milk samples in each
season, i.e., spring, summer and autumn were 1.0304 ± 0.00008 g/cm3
, 1.0314 ± 0.00005 g/cm3 and
1.0309 ± 0.00007 g/cm3
, respectively.