Seasonal variation in milk composition and somatic cell count of crossbred dairy cattle

Abstract:

Dairy processors picking up bulk tanker milk from collection centres in Chiang Mai note a recurring pattern fat and protein percentages drift down through April and May, climb back through October and November, and somatic cell count readings move roughly inversely. This research set out to quantify that seasonal pattern. Individual-cow milk samples (n = 2 880) were collected across a complete calendar year (January to December 2023) from 120 crossbred dairy cattle 72 Holstein-Friesian × Thai Native and 48 Jersey × Brahman managed under loose-housing at the institutional farm and two commercial cooperative farms in Chiang Mai district. Samples were analysed for fat, protein, lactose, solids-not-fat, urea, somatic cell count and microbiological quality on a monthly schedule. Compositional parameters showed clear seasonal signatures: fat percentage rose from 3.54 in monsoon to 4.24 in winter, protein from 3.04 to 3.46 and SNF from 8.13 to 8.64. Somatic cell count followed the opposite trajectory, peaking at 521 × 10³ cells/mL in July and falling to 218 × 10³ cells/mL in January. Daily milk yield for HF crossbreds averaged 9.6 kg per animal in summer and 14.8 kg in winter, with Jersey crossbreds running 1.2 to 2.4 kg lower throughout. Temperature-humidity index explained 76 percent of the yield variance and 64 percent of the SCC variance across the twelve months. The findings quantify the seasonal envelope that northern Thailand dairy processors plan against and argue for heat-stress mitigation as the primary leverage point for narrowing the variation.