To determine the genetic variability and population structure of the β-lactoglobulin (LGB) locus in the Argentinian Holstein breed, milk samples from 12 herds at four locations in Córdoba, Argentina, were analysed. Allelic and genotypic frequencies of LGB variants were compared by contingency tables. A G-test was applied to detect Hardy–Weinberg equilibrium. LGB A allele frequency was 0·43 and B allele frequency was 0·57. Allelic and genotypic frequencies indicated great homogeneity among populations. Most of the populations were in Hardy–Weinberg equilibrium. According to the fixation index, populations were panmictics. The partition of the F-statistic demonstrated that mating was at random, although there was a slight excess of heterozygotes, and there were no genetic differences among populations. The Shannon–Weaver index showed that more than 96% of the total genetic diversity for this locus is attributable to the differences within each herd. The diversity among herds within locations and among locations accounted for <4% of the total variation. Phenograms obtained by the Nei procedure for genetic distances disclosed the separation of the herds into two groups, one with an average frequency of LGB B of 0·61 and the other with an LGB B frequency of 0·53. Locations defined two clusters, but the divergence among populations was not important. These results indicated that the Argentinian Holstein breed from Córdoba constitutes one population.

Metabolizable energy intake and heat production were measured in a series of calorimetry experiments carried out at the Agricultural Research Institute of Northern Ireland, Hillsborough, between 1993 and 1996 with beef cattle and sheep. A total of 75 estimates were made with cattle: 23 with Charolais cross steers; 16 with Simmental cross steers and 36 with Angus cross steers (450–628 kg liveweight). Fifty-six estimates were made with lambs: 24 with Blackface cross, eight with Suffolk cross and 24 with Texel cross (23–53 kg liveweight). The diets offered to both cattle and sheep contained proportionately 0·0–0·8 cereal-based concentrates, the remainder being grass silage. Linear regressions of energy retention (measured by calorimetry) against metabolizable energy intake were produced for the cattle and sheep studies. From these linear regressions an estimate of metabolizable energy required for maintenance (MEm) was obtained. For cattle, the derived MEm was 0·614 MJ/kg LW0·75 per day, and for sheep the derived MEm was 0·460 MJ/kg LW/kg LW0·75 per day. The estimates were proportionately 0·34 higher in cattle and 0·32 higher in sheep than the 1990 values of the UK Agricultural and Food Research Council.

A study on the energy expenditure of sheep was carried out at the Central Sheep and Wool Research Institute, India during August 1995 to July 1996 by conducting two experiments: one on tracheal cannulated rams maintained on stall-feeding in autumn 1995 (Expt 1) followed by year-round grazing on silvipasture (Cenchrus ciliaris pasture interspersed with fodder trees) over three seasons: monsoon, winter and summer, 1995/96 (Expt 2). Physiological responses and energy expenditure measurement of housed and grazing sheep were recorded at 06.00, 14.00 and 22.00 h for 5 consecutive days in each season. Tracheostomized sheep harness with meteorological balloon were used for collection of expired air and measurement of energy expenditure. Rectal temperature (RT) of sheep at 06.00 h was similar in all the seasons except for a significant (P<0·05) lower value in monsoon. The rise of RT from 06.00 to 14.00 h in grazing animals was 1·6 °C, higher than that in housed sheep (0·9 °C). Skin temperature (ST) was least in winter and highest at 14.00 h in the monsoon and autumn seasons. Respiration rate (RR) showed a marked rise at 14.00 h in all the seasons. The heart rate (HR) of grazing sheep was higher, irrespective of season, at 14.00 h. At 06.00 and 22.00 h, the heart rate was higher in winter and summer than in the monsoon season. Overall energy expenditure (EE) was 4·85 MJ/24 h during winter which increased to 5·85 MJ/24 h in summer and 6·70 MJ/24 h in the monsoon. The mean rise in energy expenditure per °C rectal temperature in all the seasons was 338 kJ/kg W0·75. Comparable mean values per 10 °C ambient temperature and 10 °C black globe temperature were 404 and 173. The increase in energy expenditure of grazing compared to housed sheep in monsoon, winter and summer was 78, 15 and 33 % respectively. The mean value was +43%.

Granular calcined magnesites originating from Spain, China and Greece and magnesium hydroxide powder were evaluated in a series of balance experiments conducted with wether sheep (c. 42 kg liveweight) given a basal ration of dried grass at Glasgow University Veterinary School between 1989 and 1994. Four Spanish ‘Agma’ products and three Spanish ‘Navarras’ products contained less material (0–104 g/kg)>1000 μm diameter than four Chinese and four Greek materials 178–483 g/kg). The Spanish products had lower (18–45 g/kg) losses on ignition compared with the Chinese and Greek materials (53–112 g/kg). A fifth Greek product contained only 4 g/kg>1000 μm diameter. In three experiments comparing supplementation of the basal diet with 2·0 g Mg as either magnesium hydroxide or as one of the three separate purchases of the commercial calcined magnesite sources, the powdered magnesium hydroxide had the highest mean apparent availability coefficient (0·30) (faecal increase method). The corresponding values were 0·24 (Agma and Navarras), 0·20 (Chinese) and 0·15 (Greek) (pooled s.e. 0·014, d.f. 10). Powdered magnesium hydroxide also had the highest (0·18) mean availability coefficient (urinary increase method) compared with 0·12 (Agma), 0·13 (Navarras), 0·14 (Chinese), 0·10 (Greek) (pooled s.e. 0·005, d.f. 10). In two subsequent experiments, Agma had a superior apparent availability coefficient (0·26) (faecal method) than either the Chinese (0·14) or the Greek materials (0·19). A finer grade of Greek calcined magnesite (0·25) was equivalent to Agma. For the 12 calcined magnesites evaluated in the three main experiments, significant (P<0·05) correlations (r) were found between the magnesium availability coefficient (faecal method) and loss on ignition (−0·65); particle size proportions (<250 μm, 0·59; and >1000 μm, −0·65) and tended towards significance for rumen solubility in 24 μm nylon bags in hay-fed cows over two days (r=0·54, P=0·07) and rate of reaction with citric acid (0·57, P=0·055). No correlations were found with magnesium availability coefficients (urinary increase method). This confirms the limitations of both in vitro predictions and in vivo (faecal) estimates of magnesium availability for different calcined magnesites. The mean magnesium availability coefficient (faeces) of the 17 calcined magnesites was 0·21 (s.d. 0·05). If this were to be confirmed by other observations, it would have implications for the amounts of dietary calcined magnesite required to meet recommended dietary magnesium allowances for ruminants.

Spring postpartum reproductive performance was investigated in 19 Awassi and 15 Finn×Texel×Awassi (FTA) crossbred ewes, weaned at 2 months postpartum and simultaneously exposed to rams for a period of 48 days. The study was conducted in 1991/92 in the Bekaa Valley of Lebanon.

Postpartum FTA ewes tended to have higher fecundity and prolificacy than those of Awassi ewes. Forty percent of the FTA ewes conceived and gave birth to 1·3 lambs per lambing, while 31·4% of the Awassi ewes conceived and lambed (1·1 lambs per lambing). Lambing to lambing and ram introduction to lambing intervals were similar in both genotypes and confirmed that a sizeable proportion (30–40%) of Awassi ewes and their crosses may rebreed during spring postpartum anoestrus and lamb at c. 8 months interval. Furthermore, relative progesterone values revealed continuous ovarian activity in 16% of Awassi ewes and 40% of FTA ewes and confirmed estimates of conception in ewes. All ewes with continuous ovulation mated and lambed. Weekly estimates of milk production over a 2-month period, starting the second week of lactation, showed that daily milk yields were almost twice as much in Awassi as in FTA ewes (P<0·01). These results indicate the potential for Awassi ewes and their crosses to be incorporated into frequent lambing systems. Reproductive efficiency in these ewes could be monitored efficiently by measuring progesterone at 2-weekly intervals.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The thirtieth meeting of the group, chaired by G. J. S. Ross of the Institute of Arable Crops Research, Rothamsted, was held in the Wellcome Meeting Room at the Royal Society, 6 Carlton House Terrace, London on Friday, 3 April 1998, when the following papers were read.

A set of four silages, comprising unwilted and wilted silages, both with and without bacterial inoculation, was prepared from perennial ryegrass swards on each of eight harvesting occasions during the 1994 growing season. The four silages, within a single harvest, were offered as the total diet at the maintenance level of feeding to 16 wether sheep in an 8-period change-over study with experimental periods of 3 weeks duration, in order to determine whole tract digestibility and urinary excretion of purine derivatives (PD). Silage dry matter (DM) and nitrogen (N) degradabilities were also examined in the rumen of four rumen-fistulated steers offered a medium quality silage and a concentrate supplement at a ratio of 60[ratio ]40 (silage[ratio ]concentrate) on a DM basis. The data presented are the mean results obtained across the eight harvests.

There were no significant effects of inoculation on silage pH and ammonia-N/total-N across the unwilted and wilted materials. Inoculation of either the unwilted or wilted silages had no significant effect on microbial activity in the rumen of sheep, as indicated from excretion of urinary PD, or on silage DM or N degradability assessed with rumen-fistulated steers. However, inoculation significantly increased the digestibility of organic matter (1·7%, P<0·01), N (4·6%, P<0·001), energy (2·3%, P<0·01), neutral detergent fibre (1·5%, P<0·05) and acid detergent fibre (2·8%, P<0·001) in the silage. These increases in digestibility following inoculation, in general derived equally from both the unwilted and wilted silages. The results indicate that the increase in silage nutrient digestibility following inoculation probably reflects a more extensive digestion in the abomasum and intestine, rather than in the rumen.

Wilting of grass prior to ensiling resulted in silages with significantly lower pH (5·4%, P<0·05) and ammonia-N/total-N (42·7%, P<0·001) across the untreated and inoculant-treated materials. Wilting also significantly increased (P<0·05) urinary PD-N output of sheep by 6·9% and silage DM degradability by steers by 1·6–2·4% across the untreated and inoculant-treated silages. However, there were no significant effects of wilting on silage N degradability and silage nutrient digestibility.

Of 41 male kids, 14 were killed immediately after birth (3·3 kg BW); the remainder were either fed on goat milk to satiation or weaned at 10 kg BW. After achieving 15·7 kg BW, weaned kids were fed on complete diets including either 20 or 40% straw. Milk-fed kids were slaughtered at 16·8 or 26·7 kg BW, weaned kids at 15·7 or 29–30 kg BW, respectively (at least four kids per treatment). Empty BW as a proportion of final live BW was 0·91±0·02 in milk-fed kids compared to 0·85±0·04 and 0·76±0·04 in kids given complete feeds including 20 or 40% straw, respectively. Empty BW of kids in the heaviest groups were c. 24 kg for milk-fed or weaned kids. Energy and crude protein contents per kg empty BW increased from 4·5 MJ and 158 g in newborn kids to 12·2 MJ and 163 g in milk-fed kids or 10·4 MJ and 194 g in weaned kids, respectively. No influence of the feeding system was found on mineral contents of empty BW. Ca, P and K remained constant at 12·6, 7·7 and 1·9 g/kg, Mg increased from 0·32 to 0·46 g/kg and Na decreased from 2·0 to 1·3 g/kg. Differences in composition of live BW gain are mainly caused by differences in gut-fill. Efficiency of utilization of ME for growth was c. 0·75 in milk-fed kids even at high BW, but only 0·31 in weaned kids. Proportions retained of dietary N, Ca, P, Mg, Na and K were highest in milk-fed kids between birth and 16·8 kg BW: 0·57, 0·88, 0·78, 0·40, 0·37 and 0·10, respectively. They were lowest in kids fed on complete feed including 40% straw from 15·7 to 30·3 kg BW: 0·25, 0·26, 0·32, 0·04, 0·11 and 0·04, respectively. Weaning seems to be of greater influence on composition of BW gain and efficiency of utilization than the increase in empty BW.

Four grass silages, namely unwilted and wilted silages each with and without bacterial inoculation, were prepared on each of eight harvesting occasions during the 1994 growing season (Yan et al. 1998). The four silages, made at each harvest, were offered ad libitum to 48 lactating dairy cows in a 2 (control v. additive)×2 (unwilted v. wilted)×8 (harvest (period)) change-over design experiment with 3-week experimental periods. The animals also received 6·9 kg dry matter (DM) of a concentrate supplement daily during the first period and then the allowance of the supplement was reduced by 0·43 kg DM at the start of each subsequent period. The supplement was based on barley, molasses and soyabean meal. The data presented are the mean results obtained across the eight harvests.

No significant interactions were found between inoculation and wilting for silage intake, performance and silage eating behaviour. Inoculation significantly increased milk yield (2·4%, P<0·05) and lactose output in milk (2·3%, P<0·05) across the unwilted and wilted silages. These increases following inoculation in general arose equally from both the unwilted and wilted silages. However, inoculation of either the unwilted or wilted silages had no significant effects on silage DM intake, milk composition, or silage eating behaviour. Wilting significantly increased silage DM intake (20·1%, P<0·001), milk yield (2·8%, P<0·05) and the concentrations (P<0·001) and yields (P<0·01) of both fat and protein across the untreated and inoculant-treated silages. The increases following wilting derived equally from both the untreated and inoculant-treated silages. Wilting also significantly influenced silage eating behaviour with a significant decrease following wilting in number of meals per day (6·5%, P<0·05) and an increase in eating rate (kg DM per eating hour) (29·7%, P<0·001) across the untreated and inoculant-treated silages. These results indicate that inoculation of the unwilted and wilted silages produced similar increases in milk production. Large positive responses in silage DM intake and performance were recorded following wilting with both the untreated and inoculant-treated silages.

Five grazing trials using Suffolk wethers were carried out at Obihiro, Japan from June to July of 1989 and 1990. New methodology was developed to investigate bite weight and bite selection using hand-constructed swards, which were composed of 128 points of plant units spaced 4 cm apart. Leaves and reproductive culms of orchardgrass (Dactylis glomerata) and timothy (Phleum pratense) were used in five kinds of artificial swards (three pure leaf mixtures and two leaf/culm mixtures).

In the leaf/culm mixture, sheep definitely selected leaf units. The inclusion of reproductive culms decreased the number of prehending bites and the total distance of travel between bites. Mean distance of travel between bites was 8·6–10·6 cm. Mean travelling speed was 7·2 cm/s and was not influenced by the inclusion of culms. Total distance of travel between bites was 3·8–4·1 m/min in pure leaf mixtures and 3·4–3·5 m/min in leaf/culm mixtures.

The actual area covered by one prehending bite, estimated from direct measurement, was 21–27 cm2 in pure leaf mixtures and 15–16 cm2 in leaf/culm mixtures. Decreased bite area in leaf/culm mixtures resulted in decreased bite weight and intake rate. Experimental errors observed were discussed with respect to the biting behaviour of sheep and flexibility of grass leaves.

The influence of dietary nutrient concentration on performance and the growth of fat depots, breast meat and leg muscles was examined in five groups of male broiler chickens fed ad libitum with combinations of high (H), commercial (C) or low (L) energy and nutrient concentration in starter and finisher diets. Diets were changed from starter to finisher at 3 weeks of age giving 200 birds on each of five treatments: HH, HL, CC, LH and LL. Ten birds per treatment were slaughtered at weekly intervals from 0 to 70 days. Five of these were dissected into component lean tissues of breast muscles (white meat) and thigh+leg muscles (dark meat) and fat depots, and the other five carcasses were minced for chemical analyses. Data were analysed by fitting Gompertz functions to each component.

Analysis of body weight, carcass components and feed intake revealed that at 70 days birds on LH approached similar liveweights to those on HH with lower overall food intakes, comparable feed conversion ratios but slightly greater fat depots. The HL birds had less fat but achieved specific weights over longer periods of time with greater feed intakes and poorer feed conversion ratios. Content of white and dark meat was always greater in HH birds, with differences between treatments being greater for white meat.

Decisions on which conditions are most appropriate will be influenced by time taken to reach specific liveweights if whole birds are marketed, or the rate of growth of individual portions if further processing is considered, together with feed conversion efficiency and the relative costs of diets varying in energy and nutrient concentration.