1. For 4 weeks before calving in December or January a group of 7 Ayrshire cows each received daily 6 lb. hay and silage to appetite, whilst a second group of 9 received the same roughages and 6–10 lb. concentrates. After calving, cows from both of the pre-calving treatments were placed in each of two post-calving groups of 8 cows. A High treatment received approximately 8 lb./day more concentrates at the same milk yield than the Low treatment. Both groups continued to receive 6 lb. hay/cow/day and silage to appetite. The cows were allowed to graze by day from 21 February and by day and night from 13 April. Hay, at 5 lb./cow/day and reducing rates of concentrates were offered until 8 May.
2. Individual feed intakes were estimated from faecal output and digestibility. Direct measures of the intakes of different treatment groups on indoor feeding agreed fairly closely with the mean individual estimates.
3. The digestible organic matter intake (DOMI) of 1,300 lb. cows in the last stages of pregnancy was increased from 10 up to 14–16 lb./day by giving 8–10 lb./day concentrates. Immediately after calving, the increases in DOMI compared with pre-calving levels were about 2.5 lb./day for cows which received concentrates before calving and 8.5 lb./day for cows which received no concentrates before calving.
4. When all cows had calved and were in full milk production there were no significant differences in DOMI, milk yield or rate of live-weight gain attributable to pre-calving treatment. Mean DOMI on the High and Low post-calving treatments were 23.8 and 19.4 lb./day, mean fat-corrected milk yields 44.5 and 38.8 lb./day and mean rates of live-weight gain 05 and nil lb./day, respectively.
5. DOMI increased by 0.7 and 4.9 lb./day for High and Low post-calving treatments when cows were turned out to night as well as day grazing, and milk yields increased by 1.0 and 2.2 lb./day respectively.
6. Regression equations relating animal production and feed intake, and substitution rates of concentrate usage were calculated. Faecal output and DOMI were closely related to milk yield. When additional concentrates were given the resulting increase in total DOMI was greater when the bulk feed was of low digestibility than when it was of high digestibility.