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Composition and processability of bovine milk from herds with different calving patterns

  • B. O’Brien (a1)

Abstract

The chemical composition and processing characteristics of milks from spring and autumn calving herds were investigated to establish if an autumn/winter milk supply would overcome the variation in composition and quality which is characteristic of a seasonal milk supply. Three herds of 26 cows were established with mean calving dates of 22 February, 28 September and a 50:50 combination of both. The experimental period was from 5 August to 22 December. Bulk milks were collected separately from each of the three herds at one consecutive am and pm milking each week. Spring and autumn milks were also bulked in proportions of 70:30, 50:50 and 30:70, respectively. All milks were analysed for gross composition, protein fractions, renneting properties (rennet coagulation time [RCT], rate of curd aggregation [K20] and curd firmness [A60]), free fatty acids (FFA) and somatic cell count (SCC). Total protein and casein of spring milk were reduced (P<0.001) from 38.1 and 28.7 g/kg, respectively in the period 14 October-24 November to 33.8 and 25.9 g/kg in the period 25 November-22 December. This was accompanied by a deterioration (minimum P<0.01) in RCT from 21.7 to 33.3 min, in K20 from 8.2 to 15.2 min and in A60 from 43.8 to 30.8 mm. Autumn milk had higher fat (P<0.01) and lactose (P<0.001) concentrations, lower FFA levels (P<0.001), improved (P<0.001) RCT, K20 and A60 values compared to spring milk in the period 25 November-22 December. During this period, the 70:30 milk had improved RCT (P<0.01) and K20 (P<0.05) values and reduced (P<0.01) FFA levels compared to spring milk. It is concluded that the composition and processing characteristics of spring milk deteriorated after 275 days in milk. Changes in total protein and casein were closely associated with changes in renneting properties. Blending of autumn milk with spring milk improved the processing characteristics of the mix compared to those of spring milk. Thus, the introduction of early lactation autumn milk at the end of the spring lactation would maintain good milk processability and allow continuous product manufacture.

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