The n-alkane and chromium/in vitro procedures for estimating herbage intake were compared in grazing ewes during late pregnancy, early lactation, and mid-lactation. To ensure differences in herbage intake, the ewes were grazed in 4 plots of phalaris-dominant pasture at 2 levels of stocking: 17.1 ewes/ha and 30.8 ewes/ha. To investigate whether either procedure for estimating herbage intake was influenced by supplement consumption, half of the ewes at each stocking level received 500 g/day air-dry of a pelletted supplement (1 : 1 milled oat grain : sunflower meal). Supplement intakes were estimated using tritiated gypsum as a marker. During intake measurement periods, ewes were dosed twice daily with both alkane capsules and capsules containing chromium sesquioxide. For the last 6 days of the 12-day dosing period, rectal faecal samples were taken twice daily, immediately before the dosing. Over these same periods, wether sheep fitted with faecal collection harnesses were similarly dosed and sampled, and their total faecal output collected to establish the faecal recovery of chromium and the alkanes. Herbage intakes were estimated using the C27/C28, C29/C28, C31/C32, and C33/C32 alkane pairs. Estimates of intake based on the shorter alkane pairs were lower than those estimated with the C33/C32 alkane pair, by amounts which differed between the periods. Evidence is presented that estimates based on the last pair of alkanes (C33/C32) are the most accurate and are also more accurate than those based on the chromium/in vitro procedure. The relationship between these 2 methods for estimating intake was different in mid-pregnancy compared with either stage of lactation. The consumption of supplement did not interfere with any of the methods for estimating herbage intake. Estimates of faecal output based on the use of chromium, C28 alkane, or C32 as an external marker were statistically identical, indicating that the difference between the 2 methods for estimating herbage intake was not related to a failure to accommodate the incomplete recovery of any of the markers used or to the failure of rectal grab samples to be representative of total faeces. Our results indicate that herbage collected by oesophageally fistulated (OF) sheep was representative of that grazed by the ewes and could thus be used to provide the herbage alkane data needed to estimate herbage intake by the alkane method. However, the in vitro digestibility values obtained from the OF samples did not represent the digestibilities actually occurring in vivo. This was the main cause of the observed difference between the 2 methods for estimating intake. Possible reasons for the differences between the in vitro and in vivo estimates of digestibility are discussed.

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Forty-eight approximately 18-month-old Scottish Blackface ewes were used to study the effects of two levels of nutrition during mid-pregnancy (30-98 days of gestation) on the birth weight of lambs from ewes varying in weight, size and condition at first mating. The mean live weight (42-4 kg), size index (31-9) and condition score (2-4) at mating of the 26 ewes from flock A were all less than those of the 22 ewes from flock B (54-5, 39-4 and 2-9 respectively). Mean intakes of the low and high nutritional treatment ewes during mid-pregnancy were 10-6 and 22-0 g/kg/day respectively of a pelleted diet supplying 8-81 MJ metabolizable energy and 125-5 g crude protein/kg. These intakes produced estimated changes in net maternal weight of approximately -5 and 0 kg respectively.Mean lamb birth weights from ewes on the low and high nutritional treatments were: flock A, 3-32 and 3-83 kg; flock B, 4-96 and 4-23 kg respectively. Analyses showed intake during mid-pregnancy to have a positive effect on lamb birth weight in the flock A ewes, and a negative effect in flock B ewes. Mating weight accounted for 78% of the variance in birth weight in the low nutritional treatment ewes but had little effect in those on the higher level of feeding.The practical implications of the results are discussed in relation to levels of juvenile nutrition.

There have been few successful programmes to select forage plants with improved nutritive value for dairy cattle, despite the implications of improved forage quality for dairy production. Part of this lack of progress has been attributed to differences in opinion on the relative importance of improving individual traits relating to nutritive value. This paper reports the use of the Delphi survey technique to obtain an estimate of the priority for improvement of individual nutritive value traits among a large group of respondents. The Delphi technique has been used previously to rank nutritive value traits in forages for liveweight gain and wool production (Wheeler and Corbett, 1989, Grass and Forage Science, 44, 77-83). Increasing dry-matter digestibility (DMD) was ranked as the most important goal for grasses; increased non-structural carbohydrate (WSC) and improved rate of digestion were ranked second and third in importance. The absence of anti-quality factors, and an 'optimal ratio' of rumen degradable protein to undegradable protein (RDP/UDP) were ranked most highly for legumes, with increased DMD and WSC following closely behind. Increased magnesium and increased lipid content were ranked lowest for both grasses and legumes. Similar rankings were achieved when mean rankings from Australian and New Zealand scientists were compared with those from US and European scientists. Rankings were also similar when results from nutrition scientists were compared with those from plant breeders/ agronomists.

I . The use of deuterium oxide dilution to obtain an indirect estimate of body water in pregnant ewes was examined and the value of such an estimate in predicting body fat was investigated.2. Deuterium oxide was infused intravenously into fourteen twin-bearing Blackface ewes and blood samples were taken 6-7 h later. The animals were subsequently slaughtered.3. Deuterium oxide concentration was estimated by infrared spectroscopy and the deuterium oxide space was calculated. Studies on dose rates and equilibration times were made with the Blackface ewes and some non-pregnant Dorset ewes.4. The amount of body fat in each ewe was estimated from the deuterium oxide space using a prediction equation relating body fat to body water in twenty-five pregnant and non-pregnant ewes which had been slaughtered.5. Once satisfactory measurement of deuterium oxide concentration had been achieved, body fat predicted from deuterium oxide space differed from values obtained by analysis of the slaughtered animals by -0.8 to + 1.7 kg in seven ewes containing 52-21.4 kg fat.6. The standard deviation from regression of percentage of body fat estimated from deuterium oxide space on percentage of body fat measured after slaughter was 1.2 percentage units. Thus deuterium oxide space was used to provide a useful measure of body fat in pregnant ewes.In order to study the changes taking place in the body composition of pregnant ewes, we required a routine indirect method for making serial measurements of total body fat. Body fat can be estimated as the difference between total body-weight and lean body mass, and lean body mass can be predicted from measurements of body water. Relationships between total body water and lean body mass may be complicated in ruminants by the large proportion of body water held in the alimentary tract, and in pregnant animals by the proportion held in the uterus (Flanagan, 1964). Reid, Bensadoun, Bull, Burton, Gleeson, Han, Joo, Johnson, McManus, Paladines, Stroud, Tyrrell, VanNiekerk, Wellington & Wood (1968), who studied interrelationships between body components in 330 sheep and 256 cattle, expressed their results in terms of empty (i.e. digesta-free) body-weight, but Panaretto (1963) found that total bodyweight and total body water were as satisfactory as the empty body values for predicting body fat in sheep and goats. With regard to the effect of pregnancy, we showed earlier (Foot, 1969) that relationships between the water and fat contents of the body were substantially the same in pregnant and non-pregnant ewes. It appeared, therefore, that if body water could be estimated, it would be feasible to predict body fat in pregnant animals.Of the marker substances used in the indirect estimation of body water, hydrogen isotopes appear the most promising since water containing these isotopes is not, in the * Present address: Hill Farming Research Organization, 29 Lauder Road, Edinburgh EH9 z JQ.https://www.cambridge.org/core/terms. https://doi