The n‐alkane technique for estimating herbage intake and diet selection in dairy cows fed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) herbages was evaluated. Pairs of animals were offered either 8, 10, 12 or 14 kg dry matter (DM) d−1 of herbage alone or with 2 kg DM d−1 of barley. Fresh herbage was cut daily from a perennial ryegrass/white clover sward and the appropriate amount was fed in four feeds during the day. Individual intakes and the white clover proportion of the diet were estimated during a 12‐d period using the n‐alkane technique. Animals were dosed twice daily with paper pellets containing dotriacontane (C32‐alkane). Faecal grab samples were collected after the morning and afternoon milking. Three least‐squares optimization methods were compared in calculating the white clover proportion in the diet; then, total DM intake was calculated. The different least‐squares optimization methods gave similar predictions of the white clover content of the forage consumed. No significant (P < 0.05) effects of sampling routine, concentrate (barley) fed or interactions between the two were detected with respect to the difference between calculated and actual intake, the difference as a proportion of the total intake and estimated white clover content of the diet. The difference between the calculated and actual intake ranged from 139 to 366 g DM d −1, which resulted in a proportional difference ranging from 0.004 to 0.02 depending on sampling routine. The actual white clover content of the herbage mixture fed was 0.42 ± 0.008, whereas the estimated white clover content ranged from 0.41 ± 0.006 to 0.43 ± 0.008. The results suggest that accurate herbage intake estimates can be achieved in dairy cows grazing perennial ryegrass/white clover swards if representative samples from herbage consumed can be collected.

Sixteen multiparous Holstein/Friesian cows were used to examine the effect on food intake and milk production of replacing 40% of the dry matter (DM) of first cut perennial ryegrass silage (G) with either maize silage (M), fermented (F) or urea‐treated (U) wheat whole crop silage. In addition to the forage mixtures, the animals received 5.25 kg DM d −1 of a standard concentrate and 1.75 kg DM d −1 of soya bean meal. The experiment consisted of four periods, each of 4 weeks duration, in a Latin square design. The grass silage used was of high quality with an estimated metabolizable energy (ME) content of 11.4 MJ kg −1 DM and in vitro digestibility of 748 g kg −1 DM. DM intake was significantly increased (s.e.d. = 0.364, P < 0.01) with the inclusion of M, F and U. The resulting total DM intakes were 17.6, 18.4, 19.2 and 20.1 kg d −1 for treatments G, M, F and U respectively. None of the animal production variables was significantly affected by the treatments. Milk yield was 27.4, 26.4, 27.1 and 26.9 kg d −1 for treatments G, M, F and U respectively. Milk fat content was 48.9, 46.9, 49.0 and 48.1 g kg −1, and milk protein content was 34.1, 33.6, 34.0 and 34.3 g kg −1 for treatments G, M, F and U respectively. The results show that partly (40%) replacing a high‐quality grass silage with forage maize, fermented whole crop wheat or urea‐treated whole crop wheat will increase DM intake in dairy cows but is not accompanied by an increase in animal performance and therefore will result in decreased efficiency of forage DM utilization.

The effects of the level of energy intake (high E and low E) offered before and after calving on body condition score at calving, production performance, and energy status in the first 250 d of lactation were evaluated in a 2 × 2 factorial design experiment involving 80 Holstein-Friesian dairy animals (40 primiparous and 40 multiparous). From d 80 until d 21 precalving, primiparous animals were offered either high or low pasture allowances. Thereafter, these animals were housed and had ad libitum access to a high energy density diet (high E) or restricted access [6 kg of dry matter (DM) per d] to a low energy density diet (low E), respectively, until calving. From d 100 until d 42 precalving, multiparous animals were offered either ad libitum or restricted (10 kg of DM/d) access to a late lactation diet, and thereafter, had ad libitum access to a high E diet or restricted access (7 kg of DM complete diet/d) to a low E diet, respectively, until calving. The forage to concentrate (F:C) ratios (DM basis) of these high E and low E diets [d 42 (d 21 in primiparous animals) until calving] were 64:36 and 83:17, respectively. Cows offered high E and low E precalving diets were allocated to either a high E or low E postcalving diet [F:C ratio (DM basis) of 30:70 and 70:30, respectively] and remained on these diets until d 250 of lactation. Multiparous animals offered a high E diet precalving had a significantly higher body condition score at calving than those offered the low E diet precalving. This effect was not evident in primiparous animals. Precalving diet had no significant effect on plasma nonesterified fatty acid concentrations during the last 3 wk precalving in primi- or multiparous animals. Primiparous animals offered a high E diet precalving had significantly higher postcalving plasma concentrations of nonesterified fatty acid, suggesting greater mobilization of body reserves. Primi- and multiparous animals offered a high E diet postcalving had a significantly higher dry matter intake, milk yield, and energy status postcalving compared with animals offered a low E diet postcalving. Milk yields of primiparous animals offered high E and low E diets postcalving were 29.7 and 24.8 kg/d, respectively, and milk yield of multiparous animals offered high E and low E diets postcalving were 33.5 and 28.2 kg/d, respectively. It is concluded that altering body condition score during the dry period is difficult but that specific dietary regimens applied precalving can have a significant influence on postcalving production and energy-related parameters.

Forage maize grown in areas where spring temperatures are low and accumulated heat is limited will be restricted in terms of maturity and thus nutritional value. A stagnant growth phase is commonly caused by low temperatures between germination and the five‐leaf stage, which could be caused by reduced mineral availability. The effects on maize plant development and harvest characteristics of supplying phosphorus and zinc to young plants in a foliar spray were investigated. Three different application dates, between the four‐leaf and the seven‐leaf stage, were compared. Applying the phosphorus and zinc foliar spray at the four‐leaf stage resulted in a significant (P < 0·05) increase in starch content at harvest. Cob index [proportion of plant dry matter (DM) in the cob] was increased (P < 0·05) by applying the nutrient spray at the four‐, five‐ and seven‐leaf stages. However, there was no effect on DM yield, suggesting some alteration in partitioning within the plant.

A grazing experiment was carried out using 18 Holstein/Friesian dairy cows at the Scottish Agricultural College, Crichton Royal Farm in 1991, to investigate the use of n-alkanes for estimating supplementary grass silage intake by grazing dairy cows. Two groups of animals grazed perennial ryegrass swards and were offered a supplement, consisting of a perennial ryegrass silage, twice daily after milking. Mean group silage intakes were measured daily during the last 5 days of a 12-day experimental period and individual silage intakes were estimated using n-alkanes. Animals were dosed twice daily with paper pellets containing dotriacontane (C32). The silage was marked with hexatriacontane (C36). The mean silage intake, estimated by weighing, was 6·8 kg DM per day. The mean estimated silage intakes were 6·9, 8·7 and 8·3 kg DM per day respectively using odd-chain n-alkanes in the C27−C35 range of naturally occurring alkanes, the odd-chain n-alkanes in the C27−C35 range with C36, and C36 by itself. No significant differences were found due to sampling routine (morning or afternoon) when using the naturally occurring n-alkanes but significant differences did exist when using the C36 alkane in the calculation of supplement intake. The results indicate that the n-alkane technique can be used to estimate the supplementary silage intake of grazing dairy cows using naturally occurring n-alkane patterns.

The present experiment examined the effect of offering either a high-(H) or low-(L) energy-density diet in late gestation and early lactation on physiological parameters, body condition score (BCS) and milk production in early lactation. In all, 40 multiparous Holstein cows were randomly allocated to one of four treatments in a 2 3 2 factorial design, where the factors were H-or L-energy density in a total mixed ration (TMR) both pre-and post-calving. Consequently, there were four treatment groups: HH, HL, LL and LH. The pre-calving treatment was initiated 100 days prior to expected calving; the H TMR was fed ad libitum whereas the L TMR was restricted to 10 kg dry matter/day during late lactation, and to approximately 75% of energy requirements from drying off until calving. Both diets were offered ad libitum post-calving. Feeding diet H compared to L precalving led to higher BCS at calving (2.68 v. 2.34, P , 0.01). Energy corrected milk yield and energy-intake post-calving were not affected by pre-calving diets. Changes in BCS and blood concentrations of non-esterified fatty acids, beta-hydroxybutyrate and glucose in early lactation showed that cows offered diet H pre-calving generally mobilised more body reserves compared to cows offered diet L pre-calving. An interaction between pre-and post-calving diets showed that cows offered diet H pre-calving had lower body tissue mobilisation when offered diet H post-calving compared to diet L. Cows offered diet L pre-calving, did not mobilise differently whether they were offered diet H or L post-calving. The pre-and post-calving diets had no effect on liver triacylglycerol, whereas liver glycogen was higher in cows on treatment HH compared to the other three treatments. Collectively, these results indicate that overfeeding should be avoided in late gestation and that a high-energy-density diet is desirable in early lactation in order to obtain a more favourable metabolic profile.

Environmental pressures on the agricultural industry to reduce the use of nitrogenous mineral fertiliser combined with a trend to more extensive systems of production has led to renewed interest in white clover for dairy systems. An EEC funded research project was initiated to investigate whole systems implications with regard to nitrogen efficiency. As part of the project the potential of barley grain or fodder beet as home-grown concentrates to supplement grass/clover silage was investigated.Thirty early lactation muciparous Holstein Friesian cows were used in a 16 week continuous design experiment lasting from 13 December 1993 to 3 April 1994. The animals were allocated to three treatments on the basis of milk yield, liveweight and days calved. The treatments consisted of ad-libgrass/clover silage supplemented with 5 kg DMd-1 barley grain (B), 2.5 kg DM d-1 of barley grain and 2.5 kg DMd-1 of fodder beet (B/FB) or 5 kg DMd-l fodder beet (FB) daily. All animals received additionally a protein supplement consisting of 3 kg DMd-1 of soya bean meal. The silage was made from the primary growth of grass/white clover sward containing 12% white clover in the DM. The grass/clover herbage, barley and fodder beet were all produced without the use of nitrogenous mineral fertiliser.

Grass/clover swards vary in nitrogen (N) content throughout the season. This is mainly due to the changing proportion of clover in the sward, being low in spring and increasing throughout the grazing season as shown by Søegaard (1993). This could have major implications for efficiency of the grazing animal as demonstrated by Beever et al(1986). Season specific supplementation could be necessary in order to maximise utilisation and N-efficiency.Two grazing experiments were carried out with 30 multiparous Holstein Friesian cows on a spring (1) and summer (2) growth of a grass clover pasture containing 7.1 and 38.2% clover in the DM respectively. The three supplementation treatments (Al, Bl, CI) on the spring (1) sward consisted on 0.7, 3.1 and 3.1 kg DM day-1 of a concentrate with an analysis of ME and CP of 10.4, 12.2, 12.3 MJ kg DM-1 and 276, 230 and 204 g kg DM-1 respectively for treatment Al, Bl and CI aiming to supply 90, 100 and 90% of ERDP requirements.