Effect of dietary supplementation of pasture-based primiparous Holstein-Friesian cows with degummed crude canola oil on body condition score, liveweight, milk yield and composition

The main objective of this study was to investigate the effect of incremental levels of degummed crude canola oil (DCCO) supplementation to pasture-dominant diets of grazing, primiparous, Holstein-Friesian cows on lactation performance, milk composition and liveweight traits. We tested the hypothesis that supplementing primiparous Holstein-Friesian cows with DCCO in a pasture-based dairy system will increase milk yield, fat and protein contents, but decrease cow body condition score (BCS) and liveweight. A random allocation of 20 primiparous Holstein-Friesian cows into four treatments was utilized in an eight-week feeding trial after two weeks of adjustment. The experimental treatments included a wheat-based pellet without DCCO (control), wheat-based pellet with DCCO added at 25 mL/kg on dry matter (DM) basis (low), 35 mL/kg on DM basis (medium) and 50 mL/kg on DM basis (high). Treatment and week (duration) of supplementation were significant sources of variation influencing milk yield (P = 0.0042), fat (P = 0.0118) and protein (P = 0.0002). Cows in the high treatment group had the greatest milk yield (168.7 ± 3.5 kg/week) and lower fat (3.3 ± 0.1%) and protein (3.0 ± 0.09%) percentages than cows in the control group (milk yield of 157.1 ± 3.5 kg/week, 4.0 ± 0.2% fat and 3.1 ± 0.0% protein). With the exception of somatic cell count and yield, the week (duration) of supplementation significantly influenced all milk composition traits. We concluded that supplementation of grazing dairy cows with DCCO had no negative impact on BCS and body weight gain. DCCO can be used to enhance milk yield, but at the expense of milk fat and protein.