In two changeover design experiments, fifteen early‐ and sixteen late‐lactation cows were used to investigate the effects of offering food beet with ad libitum grass silage and concentrates with different CP content on milk yield and quality. In Experiment 1 (early lactation) cows were offered no fodder beet (0) or 4 kg DM d−1 (4) in conjunction with one of three concentrates containing 159, 191 or 244g CP kg−1 DM (L.M.H.). Treatments were therefore 1L/0, 1L/4, 1M/0, 1M/4, 1H/0 and 1H/4. In Experiment 2 (late lactation) cows were offered the same level of fodder beet in conjunction with two concentrates containing 129 and 229 (L,H) g CP kg−1 DM. Treatments were therefore 2L/0, 2L/4, 2H/0 and 2H/4. In both experiments feeding fodder beet reduced silage DM intakes (P < 0·001) and increased total DM intake (P < 0·05 to P < 0·001). The substitution rate (r) ranged from 0·46 to 0·59kg of silage DM (kg−1 fodder beet DM). In Experiment 1, fodder beet tended to increase milk yield, composition and yield of constituents, but the effect was statistically significant for milk protein content only (P < 0·01). In Experiment 2, milk yields for 2L/0, 2L/4, 2H/0 and 2H/4 were 11·3, 12·1, 11·7 and 12·5 kg d−1 respectively (s.e.d. 0·43, non‐significant), fat contents were 44·4, 47·3, 44·3 and 46·8g fat kg−1 respectively (s.e.d. 0·73, P < 0·001), protein contents were 34·3, 35·6, 35·3 and 36·2 g protein kg−1 respectively (s.e.d. 0·28, P < 0·001), fat yields were 494, 574, 512 and 579 g fat d−1 respectively (s.e.d. 20, P < 0·001) and protein yields were 385, 426, 407 and 442 g protein d−1 (s.e.d. 13, P < 0·01) respectively. Increasing CP in the concentrate significantly increased milk yield in Experiment 1 (23·9, 22·5, 23·5, 23·8, 26·2, 26·5kg d−1 for 1L/0, 1L/4, 1M/0, 1M/4, 1H/0 and 1H/4 respectively, P < 0·05). Higher CP in concentrate also resulted in significantly increased milk protein yield in early‐lactation (P < 0·001) and milk protein content in late‐lactation (P < 0·01) cows. There was a significant interaction between fodder beet and concentrate CP content for milk protein yield (P < 0·001) in Experiment 1.

Twelve cows were used in a cyclic changeover design experiment to examine the effects of feeding fodder beet (variety Kyros) at three levels (0, 2 and 4 kg dry matter (DM) d"') with two levels of concentrate feeding (4 and 8 kg DM~'). Silage was offered ad libitum. At the start of the experiment the mean number of days after calving was 46 and the mean live weight 516 kg. The experiment consisted of four 3-week periods with intake and performance measurements during the last week of each period.An in vitro analysis of the feeds for the silage, fodder beet and concentrate respectively was: DM (g kg-') 189, 163, 860; crude protein (g kg DM -') 143,76,201; metabolizable energy (M J kg DM-') 104, 13 3, 13-5.Silage DM intake decreased but total DM intake increased when fodder beet was fed. The DM intakes (kg d-') for treatments (fodder beet/ concentrate) 0/4, 2/4, 4/4, 0/8, 2/8, 4/8 respectively were: silage DM 91, 7 9, 7 8, 8 3, 7 0 and 6 8 (s.e.d.=O 31); and total DM 13 0, 13 8, 15 6, 16 2, 16 6, 18 3 (s.e.d. = 0 36). Feeding fodder beet had no significant effects on milk yield or milk composition, but there was a significant increase in milk protein yield when fodder beet was included in the ration. There were no significant interactions between level of fodder beet feeding and concentrate level. Increasing the level of concentrate feeding led to a highly significant increase in milk yield, milk protein content and yield of milk constituents. The yields for treatments 0/4, 2/4,4/4,0/8, 2/8,4/8 respectively were: milk yield (kgd-') 20 6,20 4,21 8,241,23 5,24 4 (s.e.d. = 0-58); fat yield (g d"') 827, 793, 885, 954, 936, 954 (s.e.d. = 39 4); and protein yield (g d-') 622, 628, 679, 774, 777, 814 (s.e.d. = 17 9). There were no significant differences in milk yield and milk composition when fodder beet was included in the diet which may have been due to the low crude protein content of the diet.

Two experiments were carried out with sheep, to characterize fodder beet in terms of its effects on rumen function. In experiment A, a study was made of the effects of supplementing hay with fodder beet (FB) on rumen pH and volatile fatty acid (VFA) concentration compared with two control supplements of either barley/maize (BM) or molassed sugar-beet shreds (SBP). Hay was offered with all three supplements in a 50 : 50 ratio on a dry matter (DM) basis. The mean rumen pH for the fodder beet diet was 6-34 and intermediate between two controls (BM 6-20 and SBP 6-38). There was no significant difference in rumen concentration of total VFA for the three different diets (FB, SBP and BM) but there were highly significant effects due to diet for acetic and propionic acid molar proportions (P < 0-001). Molar proportion of propionic acid for diets FB, BM and SBP were 0-2064, 0-2221 and 01880 respectively. The loss of DM from nylon bags incubated in the rumen of sheep given the test diets was 471, 447 and 486 g/kg for FB, BM and SBP respectively. In experiment B, the rate of in sacco organic matter (OM) disappearance of the three supplements were compared in sheep given a constant high forage diet (900 g/day hay DM + 200 g/day compound food DM). There were highly significant differences in rates of OM disappearances for the supplements (P < 0-001). The losses of OM measured after 3 h incubation in the rumen were 767, 608, 378 and 236 g/kg for fodder beet, barley/maize, molassed sugar-beet shreds and hay respectively.

Six castrated male sheep were used to measure the apparent digestibility of fodder beet roots when included at two concentrations (610 and 490 glkg) in a feeding regimen in which the only other component was a standard complete diet of known digestibility. Mean digestibility coefficients for organic matter and gross energy for the beet were calculated to be 0·962 and 0·953 respectively. Digestible and metabolizable energy values (MJIkg DM) were calculated to be 16·0 and 13·1 respectively.

Fodder beet is a high yielding crop in terms of dry matter (DM) per hectare with yields of up to 12 t DM ha-1 from the roots and 2 to 5 t DM ha-1 from the tops. The root has a high metabolizable energy (ME) content and the average utilized metabolizable energy (UME) per hectare is 150% of average grass silage UME production (Heppel, 1985). The roots are highly digestible and can be used in dairy cow diets as a substitute for silage or concentrates. Most research work has shown an increase in total dry matter intake when fodder beet is included in a dairy cow ration (Roberts, 1987). The effect on animal performance, particularly milk fat content, is however more variable (Sabri, 1987). One reason for the differences may be the level of protein supplementatio in the fodder beet rations.This experiment evaluated the interactions between the feeding of fodder beet and level of protein supplementation in the concentrate on feed intake and cow performance.