## Materials and Methods
### Experimental Design  
Sixty spring-calving Friesian and crossbred (Jersey x Friesian) cows were allocated to one of 4 groups (\(n=15\)) at the Teagasc Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland. The experiment was conducted over a seven-week period (23 July to 31 August 2018). Cows were selected and blocked of mean (\(\pm\)SE) for; calving date 6 February 2018 (\(\pm\)1.14), parity 2.2 (\(\pm\)0.04), milk yield 21.2 (\(\pm\)0.40) kg/day, milk fat 43.3 (\(\pm\)1.70) g/kg, milk protein 34.9 (\(\pm\)0.60) g/kg, daily milk solids 1.65 (\(\pm\)0.04) kg/day, and 159 (\(\pm\)21.4) days in milk. Four feeding systems were compared over the seven-week period (Table 1). Group 1 was fed 2 kg/cow per day of a 16% crude protein parlour concentrate (CONC), Group 2 was fed 4 kg/cow per day palm kernel expeller plus 2 kg/cow per day parlour concentrate (PALM), Group 3 was fed 4 kg/cow per day soya hulls plus 2 kg/cow per day parlour concentrate (SOYA), Group 4 was fed 4 kg/cow per day molassed beet pulp plus 2 kg/cow per day parlour concentrate (BEET). The parlour concentrate diet consisted of soybean meal (300 g/kg fresh weight), beet pulp/molasses (155 g/kg), barley (150 g/kg), maize (130 g/kg), maize distillers (120 g/kg), rapeseed meal (75 g/kg), Megalac (33 g/kg), maize/beet (25 g/kg), acid buff (7 g/kg), and salt (5 g/kg); the crude protein (CP) content was 160 g/kg fresh weight. The cows with additional supplementation (Groups 2, 3, and 4) were fed after morning milking (08:30) in individual feeders. Cows consumed \(\sim\)5 kg of dry matter per day (DM/d) (see Tables 2 and 3) of grazed grass, measured by pre- and post-grazing sward heights daily using the rising plate meter (Jenquip, Feilding, New Zealand), whereas pre-grazing herbage mass was measured with an Etesia mower (Etesia UK Ltd., Warwick, UK). Cows in Group 1 consumed \(\sim\)9 kg of DM/d and cows in groups 2, 3, and 4 consumed \(\sim\)5 kg of DM/d of grass silage measured by the difference between offered and refusal weights. Cows on the farm were milked at 07:30 and 15:30 daily, and milk yields were recorded using DairyMaster milk meters (DairyMaster, Kerry, Ireland). In week 6 and 7 of the experimental period, bulk milk samples were collected from the morning milking only from each of the feeding systems. To achieve this, cows in each of the 4 feeding systems were segregated in the milking parlour and were milked separately into designated refrigerated tanks. Bulk milk samples only were collected post morning milking on each of the sampling days (\(n=3\)) and stored at 4 \({}^{\circ}\)C before analysis; a subset of samples were also frozen at \(-20\)\({}^{\circ}\)C prior to analysis. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Feeding System**} & **Parlour Concentrate** & **Additional** & **Grass Silage** & **Grazed Grass** & **Total DM1** \\  & **(kg of DM/d)** & **(kg of DM/d)** & **(kg of DM/d)** & **(kg of DM/d)** & **(kg of DM/d)** \\ \hline
**Parlour Concentrate (CONC)** & 2.00 & 0.00 & 9.00 & 5.00 & 16.00 \\
**Palm Kernel Expeller (PALM)** & 2.00 & 4.00 & 5.00 & 5.00 & 16.00 \\
**Soya Hulls (SOYA)** & 2.00 & 4.00 & 5.00 & 5.00 & 16.00 \\
**Molasses Beet Pulp (BEET)** & 2.00 & 4.00 & 5.00 & 5.00 & 16.00 \\ \hline \multicolumn{5}{c}{\(\mathrm{DMI}^{1}=\mathrm{Dry\ matter\ intake; DM: Dry\ matter}\).} \\ \end{tabular}
\end{table} 
Table 1: Concentrate feed allocation and forage allowance (grazed grass and grass silage) offered daily throughout the experimental period.