title: Assessing the effect of pregnancy stage on milk composition of dairy cows using mid-infrared spectra.
abstract: Changes in milk production traits (i.e., milk yield, fat, and protein contents) with the pregnancy stage are well documented. To our knowledge, the effect of pregnancy on the detailed milk composition has not been studied so far. The mid-infrared (MIR) spectrum reflects the detailed composition of a milk sample and is obtained by a nonexhaustive and widely used method for milk analysis. Therefore, this study aimed to investigate the effect of pregnancy on milk MIR spectrum in addition to milk production traits (milk yield, fat, and protein contents). A model including regression on the number of days pregnant was applied on milk production traits (milk yield, fat, and protein contents) and on 212 spectral points from the MIR spectra of 9,757 primiparous Holstein cows from Walloon herds. Effects of pregnancy stage were expressed on a relative scale (effect divided by the squared root of the phenotypic variance); this allowed comparisons between effects on milk traits and on 212 spectral points. Effect of pregnancy stage on production traits were in line with previous studies indicating that the model accounted well for the pregnancy effect. Trends of the relative effect of the pregnancy stage on the 212 spectral points were consistent with known and observed effect on milk traits. The highest effect of the pregnancy was observed in the MIR spectral region from 968 to 1,577 cm-1. For some specific wavenumbers, the effect was higher than for fat and protein contents in the beginning of the pregnancy (from 30 to 90 or 120 d pregnant). In conclusion, the effect of early pregnancy can be observed in the detailed milk composition through the analysis of the MIR spectrum of bovine milk. Further analyses are warranted to explore deeply the use of MIR spectra of bovine milk for breeding and management of dairy cow pregnancy.
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Lainé
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Bastin
authors.affiliation: Walloon Agricultural Research Center (CRA-W), Valorization of Agricultural Products Department, B-5030 Gembloux, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Grelet
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Hammami
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
authors.forename: F G
authors.initials: FG
authors.lastname: Colinet
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
authors.forename: L M
authors.initials: LM
authors.lastname: Dale
authors.affiliation: Walloon Breeding Association (awé), B-5530 Ciney, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Gillon
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium; National Fund for Scientific Research, B-1000 Brussels, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Vandenplas
authors.affiliation: Walloon Agricultural Research Center (CRA-W), Valorization of Agricultural Products Department, B-5030 Gembloux, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Dehareng
authors.affiliation: Agriculture, Bio-engineering and Chemistry Department, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium. Electronic address: nicolas.gengler@ulg.ac.be.
authors.forename: N
authors.initials: N
authors.lastname: Gengler
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle; D005260:Female; D007774:Lactation; D008892:Milk; D010298:Parity; D010641:Phenotype; D011247:Pregnancy
keywords: dairy cow; milk mid-infrared spectrum; pregnancy