First-lactation milk fat-to-protein ratio in tropically-raised dairy cows: environmental and genetic influences

The objective of this research was to determine factors influencing to fat-to-protein ratio (FPR) in the first-lactation of dairy cows raised in tropical climate. The dataset included fat percentage, protein percentage, and FPR values from 160,506 records representing 23,201 first-lactation cows that calved between 1993 and 2017. These cows originated from 508 farms in all regions of Thailand. The data were analyzed using the general linear model procedure in the R program. The models included herd-year-season of records, and breed group as fixed effects, and age at calving and days in milk as covariates. The result showed that the average fat percentage, protein percentage, and FPR were 3.560±0.960, 3.130±0.390 and 1.150±0.330, respectively. Effects of herd-year-season of records, breed group, age at calving, and days in milk were highly significant for all traits (P<0.05). Cows containing less than 87.50% Holstein Friesian (HF) blood gave fat percentage, protein percentage and FPR higher than 93.75%HF and 87.50-93.74%HF. The FPR was highest in the winter and lowest in the summer. In conclusion, present results indicated that fat percentage, protein percentage and FPR are clearly influenced by both genetic and non-genetic factors. Therefore, development of different breed, feeding systems, according to season and herd is needed to produce quality of fat and protein percentage.