Changes in Milk Yield and Quality During Lactation in Polish Red and White-Backed Cows Included in the Genetic Resources Conservation Programme in Comparison with the Simmental Breed

Milk yield and quality was assessed in cows raised on low-input farms (traditional feeding), i.e. two breeds covered by genetic resources conservation (RP and BG) and the SM breed. The reference group was PHF HO cows from an intensive milk production system (PMR feeding). A total of 1,212 milk samples were collected from three periods of lactation: I (up to 120 days), II (121–200) and II (over 200). The milk was analysed for content of fat, protein, casein, lactose, dry matter, non-fat dry matter and the protein-to-fat ratio, coagulation time, heat stability and the percentage of fat globules in different size ranges. Fatty acid profile and cholesterol content were determined in a representative number of 180 milk samples. Daily yield in the native breeds in the third phase of lactation was 9.6 and 8.7 kg, which was slightly over 55% of their yield in phase I, compared to 66% in the SM and 73.4% in the reference group (PHF HO). The increase in fat and protein (including casein) in the milk during lactation was much higher in the native breeds, so its energy value in phase II of lactation was 11% higher in the BG cows and 9% higher in RP, but only 4% higher in the SM with regard to phase I of lactation. The milk fat from the Polish Red cows had the highest proportion of PUFA in each phase of lactation, including CLA, and the highest PUFA/SFA ratio. Over the course of lactation the percentage of large fat globules in the milk decreased, particularly in the native breeds (P≤0.01), while in the SM the differences were much smaller and statistically insignificant. Lactation persistency in both native breeds raised in a low-input system was worse than in the SM, but the increase in basic components during lactation was markedly higher, while that of cholesterol was lower.