Groups of six single- and six twin-rearing ewes were continuously stocked on five pastures with sward surface heights (SSHs) of 3·5, 5·0, 6·0, 7·0 and 8·5 cm from week l until week ll of lactation. Herbage intake, estimated from faecal chromium concentrations and the in vitro digestibility of herbage samples collected from oesophageal-fistulated wethers, was lowest on the 3·5 cm sward but was not significantly different between SSH treatments during weeks 5, 8 and 9 of lactation. Twin-rearing ewes consumed 0·9–17·6% more herbage than single-rearing ewes did. By week ll, ewe liveweights showed increases of 2–4 kg/ewe on all except the 3·5 cm sward, where the ewes lost a similar amount of liveweight. From week 4 of lactation, twin-rearing ewes had a lower body condition than ewes raising a single lamb on all except the 3·5 cm sward, where the body condition of both rearing ranks was similar. Lamb growth rates during the first 6 weeks were similar for each SSH treatment but from days 46–76 of lactation, lambs on the 5·0 cm and longer swards grew faster (240 g/day) than those on the 3·5 cm sward (197 g/day). Lamb weight on day 76 ranged from 21·5 kg on the 3·5 cm sward to 23·0 kg on the 5·0 cm sward, but was not significantly affected by SSH. Similarly, midside wool growth of ewes and lambs was not significantly influenced by SSH during the period of continuous stocking. The results indicate that farmers should aim to provide swards of 5–7 cm height during lactation to maximize production in both single- and twin-rearing ewes.

Simulating changes in the distribution of the particle marker between particle-phase and fluid-phase dry matter by ±40% resulted in calculated flows of dry matter to the duodenum that differed from the ideal of uniform distribution by 1 to 2%; true digesta flow values were virtually unaffected. These errors are small and can probably be ignored.

The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Modelling Approaches to the Control of Agricultural Pollution’ on 12 November 1991 at Silsoe Research Institute. The group promotes the use of the scientific method in solving management problems. The aim of the meeting was to look at different ways in which modelling could contribute to the understanding and hence control of different types of pollution. Contrasts were the order of the day, with the first talk being a complex mass of differential equations and the second talk describing an expert system with a few simple design equations. Model dimensions ranged from point sources for silage effluent to several farms for invertebrate populations. A common theme was the difficulty of validating models faced with the extremely variable and difficult-to-obtain experimental data.

Lactating ewes, ewes that had lambed but subsequently lost their lambs (dry) and weaners were either artificially infested with 2000–3000 third-stage Haemonchus contortus larvae (parasitized) or drenched with levamisole (treated) and run under extensive grazing conditions in north-west Queensland. Worm egg counts in parasitized lactating, dry and weaner sheep ranged from 860–2830 eggs per gram of faeces. These levels of infestation significantly (P < 0·01) reduced liveweight gain of all three sheep classes, milk yield of ewes and wool growth of weaners compared to their treated counterparts. The lower milk yield of the parasitized ewes significantly (P < 0·01) reduced lamb growth rate. Survival of lambs to weaning was 26% higher in the treated group. The experiments showed that moderate levels of H. contortus, that did not produce clinical signs of infestation, reduce productivity of sheep in this semi-arid environment.

Twenty-four lambs (equally representing males and females), born in December 1986, were obtained from each of the Najdi, Awassi and Hejazi sheep breeds kept at the Experimental Station of King Faisal University in Saudi Arabia. The lambs were reared on their dams and fed after weaning on the same diet up to slaughter at 9 months of age. Slaughter and carcass data were analysed for breed and sex differences using the degree of body maturity and growth rate as covariates. After the effects of differences in body maturity and growth rate were removed, significant breed but not sex effects were recorded in skin, feet, carcass and carcass to bone proportions. In Najdi lambs the feet and bone nproportions (g/kg empty body weight) were higher than in Awassi or Hejazi lambs, whereas Awassi lambs possessed lower carcass but higher skin proportions than the other two native breeds.

Breed but not sex affected fat distribution. Awassi lambs had higher tail but lower intermuscular fat content (g/kg total body fat) than Najdi or Hejazi lambs. Most body components were significantly related to the degree of body maturity but not to growth rate.

Five cross-bred Suffolk lambs (liveweight 24–29 kg) were fed lucerne silage and made acidotic or offered supplemental protein with the objective of determining the effects of acidosis and amino acid undersupply on food intake from silage. In this study, at McGill University, Quebec, Canada in January 1989, lucerne silage (25% DM) was supplemented with equimolar amounts (450 mmol/kg DM) of ammonium chloride, ammonium bicarbonate and sodium bicarbonate; fishmeal was added at 100 g/kg silage DM. The lambs were fed ad libitum according to a 5 × 5 Latin square with 21-day periods.

Digestibility of organic matter (OM) from silage ranged from 78 to 82% and was not significantly affected by diet (P > 0·05). Voluntary intake of digestible organic matter (DOM) from silage was . Fishmeal supplementation of lucerne silage improved nitrogen retention (P > 0·05) but not intake of DOM. The addition of ammonium chloride to silage reduced blood concentration (p < 0·05) and urinary output of HCO3, increased ammonia excretion in urine (P < 0·05), and depressed intake of DOM (P < 0·05). Ammonium bicarbonate also reduced voluntary intake of DOM (P < 0·05) but had no significant effect (P > 0·05) on the acid-base status of the lambs. Sodium bicarbonate depressed food intake but had no significant effect on measures of acid-base balance.

The results suggest that metabolic acidosis is not an underlying mechanism restricting food intake by sheep and that neither acid-base imbalance nor inadequate protein status is likely to explain the limitation in food intake from ensiled lucerne.

The effect of maternal undernutrition between the 30th and 96th day of pregnancy on placental growth in single-bearing ewes was determined separately in two experiments in consecutive years (1986 and 1987) at Mount Derrimut Field Station, Deer Park, Australia. In the first experiment, placental growth measured on the 96th day of pregnancy was reduced (473 v. 596 g) by maternal undernutrition, while in the second, placental growth was increased (600 v. 496 g). Foetal weight and its linear dimensions on the 96th day of pregnancy were not significantly affected by maternal u dernutrition in either experiment. The only significant difference in the animals and experimental conditions between the two studies was the liveweight of the ewes at mating, which was c. 10 kg higher in the second experiment compared with the first (P < 0·01). Body condition score and the change in condition score during the respective nutritional treatments were not significantly different between the two experiments. The results suggest that maternal liveweight, possibly body reserves not quantifiable by condition score, protects and even enhances placental growth during a period of maternal undernutrition.

The hatchability of layers' eggs stored and incubated in different positions was examined at the Defence Agricultural Research Laboratory, Almora, India (5500' above sea level) in 1990. Hatchability was found to be highest in the eggs stored and incubated with their narrow end up and lowest in eggs stored and incubated horizontally.