1. Two experiments each with 3 dry cows, 3 heifers and 3 calves were carried out in 1959 and 1960 under uniform continuous grazing conditions on a ryegrass-white clover sward to measure individual feed intake by the chromic oxide-faecal nitrogen method.2. Estimates of digestibility were high (70–82% in organic matter) and there was evidence that calves selected a diet of higher digestibility than cows.3. Mean daily estimates of organic matter intake were for cows (1300 lb. live-weight) 23·5 lb., for heifers (790 lb. live-weight) 20·8 lb. and for calves (450 lb. live-weight) 14·3 lb. Corresponding digestible organic matter intakes were 17·4, 15·3 and 11·0 lb.4. Relationships between digestible organic matter intake and liveweight were calculated and the merits of the exponents 0·62 and 0·73 of liveweight discussed.5. The results were compared with accepted cow equivalent standards and, regardless of the exponent chosen, agreed with the system which adopts higher values for young grazing cattle.

SUMMARY1. 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.

SUMMARY1. The feed intakes of 18 Ayrshire cows continuously grazing a timothy-meadow fescue-white clover sward were estimated by the chromic oxide-faecal nitrogen method for two 6-weekly periods, one in 1960 and one in 1961. The cows consisted of (1) 6 lactating cows, 6–7 months post partum (Low yield), (2) 6 lactating cows, 2 months post partum (High yield) and (3) 6 dry cows; their live-weights, milk yields and milk composition were recorded.2. The mean organic matter digestibility of the herbage consumed in the two experiments was 78·2 and 76·2%. The mean digestible organic matter intakes (DOMI) were 23·3, 24·7 and 17·6 Ib./day for low yield, high yield and dry cows respectively.3. The mean daily fat-corrected milk (FCM) yields of the low and high yield cows were 29·1 and 34·3 lb. in the first experiment, and 26·8 and 42·8 lb. in the second. The mean live-weights of the lactating groups were 1036 lb. and 1106 lb. in the two experiments and did not differ between yield levels.4. DOMI was partitioned between maintenance, live-weight gain and FCM yield by regression analysis. Significant partial regression coefficients of DOMI on FCM varying between 0·221 and 0·272 were obtained. It was concluded that milk production accounted for about 0·24 lb. DOMI per lb. FCM.5. The results are discussed with particular regard to other estimates of the effect of milk production on the DOMI of the grazing cow and to the estimation of the maintenance requirement for DOM by the grazing animal.