The relationship between milk fat to protein ratio and selected production traits of Polish Holstein-Friesian cows

The aim of this paper was to assess the relationship between the fat-protein ratio and selected characteristics of milk from Polish Holstein-Friesian (PHF) cows. Altogether, 891 milk samples from the first two months of lactation (60 days) were included in the analysis. Nine milk production traits were recorded: raw milk yield (kg), FCM - fat corrected milk yield (kg), FPCM - fat and protein corrected milk (kg), percentage of fat, protein, dry matter, and lactose, urea level (mg/L), and somatic cell number (thousand/mL). Cows were divided into four groups according to the fat to protein ratio (F/P ratio): <= 1.1 : 1 indicating rumen acidosis; 1.1-1.4 : 1 optimal; 1.4-1.7 : 1 indicating subclinical ketosis; >1.7 : 1 indicating clinical ketosis. The results demonstrated that ketosis and consequently the fat protein ratio affected milk production traits. A decrease in the ratio from 1.11.4 : 1 to >1.7 : 1 meant the daily milk yield lower by 3 kg, the lactation milk yield of 305 days lower by 649 kg, and lower protein and lactose content by 0.16 and 0.09%, respectively. The high daily milk yield loss was related to an increase in the F/P ratio in milk. Each additional 0.2 increase in the F/P ratio (beyond 1.0 : 1) resulted in a 1.52 kg milk loss for the first 60 DIM (days in milk) and 352 kg for 305 DIM. Similarly, in the first 60 DIM each 0.2 increase in the F/P ratio led to an increase in fat content in milk by 0.63% and a decrease in protein and lactose content by 0.05 and 0.02%, respectively. Generally, the results of this study show that the occurrence of ketosis in dairy herds leads to significant changes in the chemical composition of milk. Another effect is the reduction of milk yield in lactation.