Evolution of milk composition in cow's milk during the time course of milking

Catherine Hurtaud (1) , Élise Vanbergue (1) , Clément Cirot (1) , Lucile Herve (1) , Marion Boutinaud (1)

1 PEGASE - Physiologie, Environnement et Génétique pour l'Animal et les Systèmes d'Elevage [Rennes]

Our objective was to study the evolution of milk composition during the time course of milking. We used 9 dairy cows averaging 56±6 days in milk. Yield, composition (fat, protein, calcium) and free fatty acids (determined by copper soap method) were measured on milk samples collected every min during morning milking (on one day per dairy cow). Statistical analysis was carried out using the Proc Mixed procedure in SAS software with repeated statement. Milk fat content increased during milking (from 6.9 to 62.6 g/ kg). Lactose and protein contents slightly but significantly decreased during milking (from 51.8 to 47.7 g/ kg and from 28.1 to 26.4 g/kg respectively). Milk free fatty acids (Meq/100 g fat) measured after milking decreased during the first 3 minutes and after reached a plateau. Milk free fatty acids measured after 24 hours of storage at 4 °C followed the same trend. Milk lipolysis remained unchanged during milking in our trial. Milk fat globule diameter measured as d4,3 increased at the beginning of milking, but reached a plateau very quickly. Measured as d3,2, it also increased at the beginning of milking and decreased at the end of milking that could suggest a reduction in milk fat globule membrane availability towards the end of milking. Milk calcium decreased during milking (from 1,205 to 1,147 mg/kg). Intra animal, there was a strong curvilinear relationship between milk fat content and milk fat globule diameter, d4,3 (R2 from 0.67 to 0.98), a positive linear relationship between milk protein content and milk calcium and lactose contents (R2 from 0.32 to 0.95 and from 0.50 to 0.99, respectively) and a negative linear relationship between milk fat globule diameter and milk free fatty acids measured after 24 hours of storage at 4 °C (R2 from 0.13 to 0.97). In conclusion, there was a great change in milk composition during milking and a complete milking is necessary to obtain a representative picture of the secreted milk.

Domaines: Sciences du Vivant [q-bio]

Catherine Hurtaud, Élise Vanbergue, Clément Cirot, Lucile Herve, Marion Boutinaud. Evolution of milk composition in cow's milk during the time course of milking. 67. Annual Meeting of the European Federation of Animal Science (EAAP), Aug 2016, Belfast, United Kingdom. Wageningen Academic Publishers, Annual Meeting of the European Association for Animal Production, 22, 2016, Annual Meeting of the European Association for Animal Production. ⟨hal-01455939⟩