Eight multiparous Holstein±Friesian dairy cows in late lactation were used to investigate the potential of using perennial ryegrass with a high concentration of watersoluble carbohydrate (WSC) to increase the ef®ciency of milk production. After a pretreatment period on a common pasture, the cows were each given ad libitum access to one of two varieties of zero-grazed grass continuously for 3 weeks. Treatments were: high sugar (HS), an experimental perennial ryegrass variety bred to contain high concentrations of WSC; or control, a standard variety of perennial ryegrass (cv. AberElan) containing typical concentrations of WSC. The two grass varieties were matched in terms of heading date. All animals also received 4 kg day ±1 standard dairy concentrate. Grass dry matter (DM) intake was not signi®cantly different between treatments (11á6 vs. 10á7 kg DM day ±1 ; s.e.d. 0á95 for HS and control diets respectively), although DM digestibility was higher on the HS diet (0á71 vs. 0á64 g g ±1 DM; s.e.d. 0á23; P < 0á01) leading to higher digestible DM intakes for that diet. Milk yield from animals offered the HS diet was higher (15á3 vs. 12á6 kg day ±1 ; s.e.d. 0á87; P < 0á05) and, although milk constituent concentrations were unaffected by treatment, milk protein yields were signi®cantly increased on the HS diet. The partitioning of feed N was signi®cantly affected by diet, with more N from the HS diet being used for milk production (0á30 vs. 0á23 g milk N g ±1 feed N; s.e.d. 0á012; P < 0á01) and less being excreted in urine (0á25 vs. 0á35; s.e.d. 0á020; P < 0á01). In a separate experiment, using the same grasses harvested earlier in the season, the fractional rate of DM degradation, measured by in situ and gas production techniques, was higher for the HS grass than for the control. It is concluded that increased digestible DM intakes of the HS grass led to increased milk yields, whereas increased ef®ciency of utilization of the HS grass in the rumen resulted in the more ef®cient use of feed N for milk production and reduced N excretion.

Eight Hereford ✕ Friesian steers were used to investigate the effect of feeding Lolium perenne (L) forage containing elevated levels of water-soluble carbohydrate (WSC) on rumen metabolism and nitrogen (N) absorption from the small intestine. The steers were offered ad libitum access to one of two varieties with matched heading dates (Ba11353, high WSC, HS; AberElan, intermediate WSC, control) cut at different times of the day to accentuate WSC differentials, zero-grazed for 21 days. This was followed by a 14-day period where the animals were on grass silage to provide a covariate intake. Although the total N concentration was similar for the two grasses, all other measured values were significantly different. The dry matter (DM) concentration of HS was greater than that of the control (202 v. 167 g DM per kg; P 0·01). WSC and in-vitro dry matter digestibility (IVDMD) were 243 and 161 g/kg DM, and 0·61 and 0·56 for HS and control, respectively. In contrast, acid- and neutral-detergent fibre were 251 and 296 g/kg DM and 480 and 563 g/kg DM for HS compared with control, respectively. DM intake was increased (9·3 v. 6·7 kg/day; P 0·001) for HS animals and this contributed significantly towards higher flows of non-ammonia N to the duodenum as well as increased absorption of amino acids from the small intestine. This DM intake response was partly due to the elevation in DM concentration of HS. However fresh weight intake was increased proportionately by ca. 0·15 (P 0·05) in animals on HS compared with control. Rumen ammonia levels were lower (14·0 and 26·4 mg N per l; P 0·001) and concentrations of rumen propionate higher (P 0·01) and acetate lower (P 0·01; increasing the glucogenic: lipogenic volatile fatty acid ratio) in animals on HS compared with control. However, the efficiency of microbial protein synthesis (15·9 and 17·8 g microbial nitrogen per kg organic matter apparently digested) and flow of N to the duodenum per unit N intake (0·84 and 0·93) for HS and control, respectively, were similar across both diets.

Moorby, J. M., Evans, R. T., Scollan, N. D., MacRae, J. C., Theodorou, M. K. (2006).. Increased concentration of water-soluble carbohydrate in perennial ryegrass (Lolium perenne L.). Evaluation in dairy cows in early lactation. Grass and Forage Science, 61 (1), 52-59. Sponsorship: LINK Sustainable Livestock Production; Department for Environment, Food and Rural Affairs; Milk Development Council; Meat and Livestock Commission; Germinal Holdings LtdTwelve multiparous Holstein?Friesian dairy cows in early lactation were used to investigate the potential of using perennial ryegrass (Lolium perenne) with a high concentration of water-soluble carbohydrates (WSC) to increase the efficiency of milk production. Ad libitum access to one of two varieties of zero-grazed herbage was given continuously for 3 weeks: treatment High Sugar (HS), an experimental perennial ryegrass variety (Ba11353) bred to contain a high concentration of WSC, harvested in the afternoon; or Control, a standard variety of perennial ryegrass (cv. AberElan), harvested in the morning. All dairy cows also received 4 kg d?1 of a standard dairy concentrate. Dairy cows given the HS diet treatment consumed 2?8 kg dry matter (DM) d?1 more than Control dairy cows (P <0?01), and the DM digestibility of the diet on the HS treatment was significantly greater than that of the diet on the Control treatment (0?75 vs. 0?72; s.e.d. 0?010; P <0?05). Excretion of urinary purine derivatives (PD) tended (P <0?1) to be higher from dairy cows on the HS treatment, implying increased microbial protein flow to the duodenum, although there was no significant difference in the apparent efficiency of rumen fermentation of either dietary nitrogen (N) or DM expressed as a ratio to urinary PD. Milk yields and milk composition were not significantly affected by dietary treatment, although true protein yields of milk were higher (P <0?05) from dairy cows given the HS treatment. The proportion of dietary N excreted in urine was significantly lower from HS cows, although the values were low for both treatments (0?20 g g?1 vs. 0?27 g g?1; s.e.d. 0?020; P <0?05). It is concluded that increased DM intakes by dairy cows given the HS treatment led to increased milk protein outputs. With a proportional decrease in urinary N excretion, the use of perennial ryegrass with a high WSC concentration, in the context of the harvesting regime used in this study, may help to reduce N pollution from dairy systems into which it is incorporated.Peer reviewe

The aim of this study was to monitor amino acid (AA) exchange kinetics of the mammary gland in response to an imposed limitation on His supply for milk production. Lactating goats (n = 4, approximately 120 DIM) were fed a low protein ration that provided only 77% of metabolizable protein and 100% of energy requirements for milk production. The protein deficiency was alleviated by infusion into the abomasum of an AA mixture (67 g/d) including (+H; 4.4 g/d) or excluding (-H) His. Goats were assigned to treatments (6 to 7 d) according to a switchback design. On the last day of the first two periods, [U-13C]AA were continuously infused i.v. for 7 h and arterial and mammary vein blood was withdrawn to determine plasma AA concentration and enrichment. Flow probes monitored mammary blood flow. The secretion and enrichments of AA in milk casein were monitored each hour. A three-pool model of the gland was used to derive bi-directional rates of plasma AA exchange. Arterial plasma His concentration was lower during -H infusion (8 vs. 73 microM), but those of other AA changed little. Responses to low levels of plasma His were: 1) mammary blood flow increased by approximately 33%; 2) the gland's capacity to remove plasma His increased 43-fold, whereas the gland's capacity for other AA declined by two- to threefold; and 3) influx and efflux of His by the gland decreased. Thus, as the reduction in His efflux was insufficient to offset the reduced influx, milk protein yield decreased from 118 to 97 g/d.

I. Comparisons were made between castrated male Scottish Blackface sheep and red deer (Cervus eluphus) of voluntary forage intake (VFI), digestibility and the mean retention time (MRT) of a particulatephase markel ('OSRu-phenanthro1ine) in the alimentary tract, when a range of forages: dried-grass pellets, chopped dried grass, fIesh-frozen Agrosris-Festucu spp. and heather (Cullunu vulgaris, L. Hull) were given at different times of the year.2. On both the dried-grass-pellet and chopped dried-grass diets the red deer and sheep ate similar quantities. Both species had a higher VFI of dried-grass pellets in July than in November. The sheep digested the dried-grass-pellet diet better than the red deer and this was associated with a longer MRT of the particulate-phase marker in the alimentary tract.3. The VFI of Agrosfis-Festuca spp. and heather by the red deer was twice that of the sheep. The VFI of heather by the sheep increased by 32 % between January and April, and the VFI of both the AgrostisFestuco spp. and heather diets by the red deer increased by 65-70 %. The sheep digested the Agrostis-Fesfucu spp. better than the red deer but the red deer digested the heather slightly better than the sheep. MRT of the particulate-phase marker was greater for the sheep than for the red deer on both diets.The digestibility and MRT of both diets in the red deer did not decrease with the seasonal increase in VFI, suggesting a possible hypertrophy of the alimentary tract.Domesticated sheep and feral red deer (Cervus elaphus) are the principal producers of food for human consumption from a large proportion of the rough grazings of Scotland.In any study of land use or resource management it is necessary to know whether there are differences between the two species in the biological efficiency with which they use the resource. These can be brought about by differences between the species in their grazing behaviour, ability to consume more of a diet and digest it better, in their efficiency of utilization of the end-products of digestion and in their nutrient requirements. It is the second aspect which is examined in this paper. Sheep and red deer eat many similar plant species which range from highly digestible grasses in summer to poorly digested grasses and heather (Calluna vulgaris, L. Hull) in winter (Hobson, 1969), but seasonal fluctuations in voluntary intake by red deer (Simpson, 1976) and other Cervidae (Long, Cowan, Strawn, Wetzel & Miller, 1966;McEwan & Whitehead, 1970) would appear to be greater than those found with sheep (Gordon, 1964). Preliminary results of Kay & Goodall (1976) have indicated that with good-quality roughage diets there were only small differences between sheep and red deer in voluntary intake (VFI), digestibility and mean retention time of undigested residues in the gut. However, comparisons using poor quality roughages have not been made.The present experiments were designed to examine the differences between the sheep and the red deer in VFI, digestibility and mean retention time of a particulate...