In two consecutive lactations in 1985/86 and 1986/87, 60 cows were injected with 500 mg of Sometribove, methionyl bovine somatotropin (BST), or a placebo at day 60±3 post partum; injections were repeated fortnightly for the remainder of each lactation. All cows received the same complete diet (metabolizable energy (ME) 11·5 MJ/kg dry matter; crude protein 169 g/kg dry matter) ad libitum for the first 20 weeks of lactation, after which, energy concentration of the diet was reduced as yield declined.

The administration of BST significantly increased milk yield by 4·3 (P < 0·001) and 3·1 kg/day (P < 0·05) in the first and second lactations, respectively. The mean dry matter (DM) intake of 16·3 kg/day in lactation 1 for the treated group was significantly (P < 0·01) higher than the 14·7 kg/day recorded for the control group. The response in intake was not significant until 6 weeks after treatment started. However, in the pretreatment period of the subseque1t lactation, the DM intake of the cows in the treated group was already significantly (P < 0·01) higher (+ 1·2 kg/day) than that of the control group. Although the DM intake in the treatment period of lactation 2 was also higher for the treated group, the difference from the control group was not significant.

With the exception of a significant (P < 0·01) increase in milk protein (control 35·3 g/kg v. treated 36·3 g/kg) in lactation 1, overall milk composition was unaffected by BST treatment. The administration of BST increased apparent feed efficiency (kg 4% fat-corrected milk (FCM)/kg DM intake) by 6 and 10% and gross feed efficiency (kg FCM/MJ ME) by 8 and 6% in lactations 1 and 2, respectively.

Animals treated with BST had significantly (P < 0·05) lower scores for body condition during the treatment period in lactation 1. This was, however, recouped during the dry period so that both groups had similar body conditions before the start of the next treatment period.

BST administered every 14 days in a prolonged-release formulation increased the yields of milk and milk constituents and apparent and gross feed efficiency during two consecutive lactations of treatment.

Between weeks 3 and 18 of lactation, 141 British Friesians all received concentrate (metabolizable energy (ME) 12·9 MJ/kg dry matter (DM), 202 g crude protein (CP)/kg DM) at 8·0 kg fresh weight/day. In addition, cows received ad libitum either grass silage (ME 11·7 MJ/kg toluene DM; 219 gCP/kg DM) or a mixture containing grass silage and 15, 25 or 40% (DM basis) of winter barley straw (cv. Igri) either untreated (UTS) or treated (TS) with 4% NaOH. Forage treatments were imposed at either week 3 or week 9 of lactation.

The mean forage DM intake of cows receiving grass silage only was 8·60 kg/day. When 15, 25 and 40% UTS was introduced into the rations at week 3 or 9 of lactation, forage DM intakes were 884, 8·43, 7·62 and 8·63, 8·83, 819 kg/day, respectively; the corresponding values for TS were 8·88, 855, 8·99 and 8·97, 8·98, 9·35 kg7sol;day. The milk yield of cows receiving grass silage only was 22·1 kg/day. When 15, 25 and 40% UTS was introduced into the rations at week 3 or 9 of lactation, milk yields were 21·1 kg/3, 20·1 kg/1, 20·1 kg/5 and 20·1 kg/1, 21·4, 20·5 kg/day, respectively; the corresponding values for TS were 21·8, 22·1, 21·3 and 22·5, 21·4, 22·6 kg/day. When averaged across the three inclusion rates, TS significantly increased forage intake (P < 0·05) and milk yield (P < 0·01) compared with UTS. Intermediate values were recorded for the diet with grass silage alone. The inclusion of TS in the ration did not affect milk yield compared with grass silage alone. No major changes in milk composition were recorded by the inclusion of either TS or UTS. However, the yields of milk fat, protein and lactose for the TS treatments were higher than for UTS and were significant for protein (P < 0·01) and lactose (P < 0·001). Cows with UTS in their ration tended to have lower live weight gains than either the control group or treatments with TS.

When compared with grass silage only, the inclusion of TS or UTS decreased digestibility coefficients and ME contents, determined in vivo using wether sheep fed at maintenance. However, the treatment of straw with NaOH (4%) increased its digestibility coefficients of dry matter from 0·-393 to 0·668, of organic matter from 0·445 to 0·686, of acid detergent fibre from 0·442 to 0·713, gross energy from 0·438 to 0·640 and ME content from 7·0 to 9·4 MJ/kg DM.

Direct-cut silage was made in mid-October 1985 from established swards of predominantly hybrid ryegrass (Lolium perenne x Lolium multiflorum). The crop contained 161 g dry matter/kg and 94 g soluble carbohydrate/kg and was ensiled in bunker silos with (i) no additive (control), (ii), formic acid (5 litres/t) or (iii) addition of 45 kg rolled barley per tonne of grass in silo.

The inclusion of barley reduced effluent production to 27 litres/t of ensiled grass compared with 51 litres for the control and 60 litres for the formic acid treatment. Losses of DM in effluent were small but total in-silo DM loss was reduced from 25 % for the control to 11% by formic acid and to 13% by inclusion of barley.

DM content of the silage containing barley was 30 g/kg higher than that of the other silages. Silage treated with formic acid contained least ammonia-N, 6% of the total N, compared with 9% in the barley-added silage and 11% in the control. In vivo assessment in sheep gave metabolizable energy values of 98, 10·9 and 11middot;2 MJ/kg for the control, formic and barley silages, respectively; N retention was higher in the formic acid and barley-added silages.

The silages were fed ad libitum to beef cattle for 8 weeks, with a daily feed supplement to the control and formic acid groups to equate barley intakes. Silage DM intake was higher for the barley silage, daily live weight gain per animal was similar for the barley-added and formic acid silages (c. 1 kg), both being higher than the control (0·8 kg).

It was concluded that barley inclusion achieved similar improvements in silage quality, in-silo losses and cattle performance to formic acid treatment but with the additional benefit of markedly reducing effluent production.

There were 45 cows in each of the control and treated groups in the first lactation of the study and, of these, 30 cows in each group received the same treatment for a second lactation. The study was conducted during the winters of 1985/86 and 1986/87. Injections of either bovine somatotropin (BST) or a placebo were started at day 60±3 post partum and repeated at fortnightly intervals for the remainder of each lactation.

Body temperature and heart and respiration rates were unaffected by the administration of BST. Minor abnormalities were noted in individual animals in both groups, hygromata of the tarsus or carpus being most common. However, no health problems could be related to treatment. There was no evidence that the administration of BST increased the incidence of metabolic disorders. Ketosis was not observed in either lactation.

Acetyl-CoA hydrolase which is stimulated by adenosine-5′-triphosphate is present in the cytoplasm of ovine liver and, unlike in certain others species, is not inactivated by cold. It is suggested that this enzyme is involved in a substrate cycle between acetate and acetyl-CoA. The heat produced as a result of such cycling may be as much as 2·5% of basal heat production and may be partly responsible for the increased heat increment that often follows the ingestion of diets that provide large quantities of acetate.

The study was carried out in northern Kenya in 1984–87. Forestomach volumes and digesta retention times were measured using Cr-EDTA or Co-EDTA as fluid markers and Ce-labelled particles or Cr-mordanted particles as paniculate phase markers.

Mean retention times of fluid and of particles were longer in the dry season than in the green season in all four animal species. The increase of particle mean retention time, as a percentage of the values in the green season, was highest in sheep (46%), followed by cattle (27%), goats (22%) and camels(18%). Forestomach volumes were also greater in the dry than in the green season; the increase was again highest in sheep (55%), followed by cattle (31%), goats (29%) and camels (28%). Outflow rates of fluid from the forestomach and the selectivity factor, by which small particles were retained longer in the forestomach than fluid, did not differ significantly between the seasons.

It is suggested that the increase of forestomach volumes is an effective adaptation to dry-season pasture conditions. It enables the animals to retain feed particles longer in the forestomach and so improve fibre digestion when feed quality is low. Cattle and sheep, which depend on a poor quality diet, improve fibre digestion in this way in the dry season more effectively than camels and goats. Camels and goats, on the other hand, were able to select a diet of such quality, even in the dry season, that their need to augment fibre digestion was reduced.

Manufacturing properties and quality of Cheddar, Wensleydale and Cheshire cheeses made either with milk from cows treated with Sometribove, methionyl bovine somatotropin (BST), or with milk from untreated control cows were compared.

The source of milk did not affect manufacturing properties in terms of processing time. Renneting times for Cheddar cheese made from control milk and that made from milk produced by cows treated with BST were 57 and 55 min, respectively. Corresponding values for Wensleydale and Cheshire cheeses were 50 and 53 min and 49 and 46 min, respectively. The source of milk did not influence cheese composition in terms of moisture, fat, protein and salt. When cheeses were submitted to the National Grading Service, those made from milk produced by BST-treated cows were indistinguishable from those made from control milk. The total points scored (maximum 100) for Cheddar, Wensleydale and Cheshire cheeses made with milk from control and BST-treated cows were 89 and 88, 85 and 85, and 86 and 86, respectively.

A feeding trial was performed during 1986, in Townsville, Australia, to describe alterations in nutrient metabolism, and the coincident gross changes in rumen microbiology, when a sulphurdeficient diet was supplemented with inorganic sulphur. Eight Merino sheep were fed ad libitum a spear grass (Heteropogon contortus) hay of low sulphur content (0·4 g/kg DM), supplemented with all other essential minerals. Upon supplementation, daily sulphur intake was increased to c. 0·75 g and four animals continued to be fed ad libitum (group A) whilst the remaining animals were restricted in feed intake (group B). Sulphur supplementation caused a twofold increase in the feed intake of group A (P < 0·05). In both groups of animals, sulphur supplementation increased the fermentation of cotton thread cellulose (P < 0·05), as well as of ground plant dry matter (P < 0·05), suspended in the rumen in nylon bags for 24 and 48 h. The apparent digestibility of organic matter (AOMD) was also increased by sulphur supplementation; from 30·6 to 39·3% in group A (P < 0·05) and from 35·1 to 41·5% in group B (P > 0·05). The difference in AOMD between groups with sulphur supplementation was not significant, despite group B maintaining a longer retention of fluid digesta in the rumen (20·7 v. 25·3 h) with a significantly lowered rumen volume (4·68 v 3·67 litres, P < 0·05) and outflow of fluid digesta from this site (5·31 v 3·58 litres/day, P < 0·05). Sulphur supplementation increased the molar proportion of acetic acid in rumen fluid (P < 0·05) but lowered propionic and butyric acids in group A (P < 0·05). Only the molar proportion of propionic acid in rumen fluid was significantly lowered in group B (P < 0·05). In both groups of animals, counts of fluid-borne rumen bacteria, protozoa and sporangia of rumen anaerobic fungi (RAF) all increased significantly with sulphur supplementation (P < 0·05 in all instances), but no significant differences were observed between groups in microbial counts, despite the different feeding regimes. The increase in sporangial forms of RAF was most marked; no sporangial forms were detectable until the diet was supplemented with sulphate and measurable concentrations of rumen sulphide were observed. This is the first account of nondetectable concentrations of RAF brought about by the nutritional status of the diet.

Muscle metabolism was studied in pregnant sheep over the final 4 weeks of pregnancy, between January and March 1985 and between December and March 1986, to investigate the effect of (i) chronic cold exposure, induced by shearing pregnant ewes 8 weeks before lambing and (ii) undernutrition in shorn and unshorn ewes. This was achieved by measuring hind-limb tissue metabolism using a combination of isotopic and arterio–venous difference techniques.

The rates of blood flow, oxygen uptake, carbon dioxide production and calculated heat production were all significantly higher across the hind-limb tissues in shorn than in unshorn ewes. The increase in hind-limb energy metabolism in the shorn group was such that 65% of the difference in wholebody heat production between shorn and unshorn groups could be attributed to muscle tissue. Following underfeeding, all of the difference in whole-body heat production between the two groups was completely attributable to muscle tissue.

Nonesterified fatty acid (NEFA) oxidation by muscle accounted for 46% of the difference in whole-body NEFA oxidation rate between fed shorn and unshorn groups. Underfeeding significantly increased the mean arterial plasma concentration of NEFA in shorn and unshorn ewes and the rate of NEFA oxidation across the hind-limb tissues in shorn ewes. The difference in whole-body NEFA oxidation between shorn and unshorn groups could, therefore, be completely accounted for by muscle. No significant differences in the arterial plasma concentrations of glucose, lactate or 3-hydroxybutyrate were recorded between shorn and unshorn ewes, although the rate of glucose uptake across the hind-limb tissued was significantly higher in the shorn group. Calculation of the maximum potential contribution of these substrates to hind-limb metabolism demonstrated that NEFA were the predominant energy source in all experimental conditions studied in all ewes. When data from fed and underfed shorn ewes were pooled, regression analysis revealed a significant negative correlation between the arterial plasma concentrations of glucose and 3-hydroxybutyrate, and significant positive relationships between the arterial concentrations of both glucose and 3-hydroxybutyrate and their rate of uptake across the hind-limb tissues. These relationsips were not observed in unshorn ewes.

It is concluded that the muscle mass plays a major role in the nonshivering thermogenic adaptation to chronic cold exposure in shorn pregnant sheep and that NEFA are the major substrate utilized for oxidative metabolism in this tissue.

Estimates of dry matter intake reported by Barlow el al. in this journal in 1988 appeared low for grazing beef cows during early lactation. Further estimates for 144 crossbred and Hereford cows at Grafton, NSW, support the contention that the previous estimates for early lactation were biased downward. This appears to have been simply a scale effect as rankings of pastures and cow genotypes remained unchanged, although the magnitude of differences did alter.

Five sheep were fitted with rumen cannulas and fed once daily ad libitumat 09.00 h with a low-quality mixed-grass hay or a good-quality lucerne hay. The effects of a second amount of the same hay or of the second hay distributed at the end of the large meal following the morning distribution, when rumen fill reaches its daily maximum, were investigated for feed intake, alimentary behaviour and rumen fill. The second distribution induced a true meal (200–400 g dry matter intake), except in the case of mixed grass offered after lucerne. On the basis of initial eating rate and the amount ingested, the highest palatability was for lucerne offered after mixed grass, and the lowest for mixed grass offered after lucerne. Diet selection was more pronounced with lucerne than with mixed grass, as indicated by the larger decrease in the neutral detergent fibre content of the fraction ingested. The true meals following the second distribution were associated with an increase in rumen fill up to 10% of the daily maximum observed without the second distribution. However, rumen fill with lucerne remained 1 kg lower than with mixed-grass hay, even after a second meal. It is concluded that the sensory response induced by a distribution of a sufficiently palatable hay is able to override the satiety signals due to rumen fill, and that there is a permanent balance between the stimuli related to the characteristics of the food available and those related to reticulo-ruminal digesta.

The in vivo digestibility of soyabean integuments, rape integuments and dehydrated beet pulp was determined in sheep in the Centre de Recherches de Clermont-Ferrand-Theix, in 1985. Organic matter digestibility was 83·5, 59·6 and 85·0%, respectively, for the three feeds. The nylon bag method was used to determine the disappearance of dry matter (DM) in the rumen. After 72 h, 89 and 96% DM had disappeared for soyabean integuments and beet pulp, respectively, but only 61% for rape integuments. The DM disappearance rate was slowest (P < 0·05) for soyabean integuments. Microscopic examination showed that the different layers of the soyabean integument could be ranked in increasing order of resistance to microbial degradation as follows: parenchyma, aleurone layer, column cell layer, palisade layer and epidermis. The hilum area was the most resistant and the only one lignified. The cell layers of the rape integument could be ranked in increasing order of resistance as follows: epidermis, aleurone layer and palisade layer. The last was highly lignified and not degradable. Degradation of beet pulp was fast, occurring first in the parenchyma. The vessels resisted degradation but were only a small part of the feed. This study shows why beet pulp has a low fill value and allows high intake. The soyabean integument is very digestible and is degraded slowly, whereas almost half of the rape integument is made up of a cell layer that is not degradable.

Ionophores and inhibitors of bacterial energy metabolism were added to mixed rumen bacteria prepared from sheep receiving grass hay plus concentrate diets, and their influence on the rate of metabolism of alanine (Ala) peptides was determined. Dicyclohexylcarbodiimide (DCCD) had no influence on the rate of breakdown of Ala2, Ala3, Ala4 or Ala5, indicating that the metabolism of these peptides did not require ATP. The protonophores tetrachlorosalicylanilide (TCS) and carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) inhibited peptide breakdown to a minor extent (< 15%), whereas the ionophores monensin and tetronasin had greater, but still small (12–31%), inhibitory effects. Toluene stimulated peptide breakdown, consistent with a permeability barrier having been removed. Thus, at least some peptide metabolism depends on transport into bacteria; transport appears not to be ATP-linked, and may well be coupled to the uptake of mineral cations rather than protons. Rumen fluid from sheep receiving a similar diet with added monensin (33 mg/kg) or tetronasin (10 mg/kg) hydrolysed Ala3 and Ala4 at rates that did not differ significantly from controls. Nevertheless, the peak concentration of free peptides in rumen fluid after feeding was more than doubled in ionophore-fed sheep, and peptides persisted for longer than in control animals.

Six Brahman (Bos indicus) steers implanted with 300 mg trenbolone acetate and six similar nonimplanted steers were fed a low-quality, low-protein roughage diet at 10 g dry matter/kg live weight. They were housed in individual pens for 27 days in 1987 before being placed in metabolism crates for measurement of digestibility, nitrogen retention, and the rate of protein synthesis in the whole body and fractional rate in three muscles and hide.

The rate of weight loss of steers treated with trenbolone acetate was significantly (P < 0·05) less than that of controls (–0·34 v. –0·56 kg/day). Treated steers excreted significantly (P < 0·05) less 3-methylhistidine (128 v. 202 μmol) and urea N (0·5 v. 1·6 g/day) in urine. There was a more favourable nitrogen retention in animals implanted with trenbolone acetate (–10 v. –12g/day) but this difference was not significant.

Whole-body protein synthesis, calculated from plasma leucine flux, was 511 and 508 g/day in treated and control steers, respectively. Treatment also had no significant effect on the fractional rate of protein synthesis, in skeletal muscle or in hide. The fractional rate of synthesis in muscle was < 1%/day and in hide < 2%/day. These results are discussed in relation to the protein and energy metabolism of undernourished cattle.

Silage effluents with pH values of 4·1, 4·7 and 5·1 (normal (N), high (H) and very high (VH), respectively) were treated with hydrochloric acid to bring the pH of each effluent to 40. The effluents were offered to finishing pigs in a randomized block experiment (November 1983 to February 1984 at the Agricultural Research Institute of Northern Ireland) with dietary treatments which comprised a control diet in which meal was given to a standard scale of feeding, or effluent diets N, H and VH, in which the effluent was substituted on a dry matter basis for 150g/kg of the standard scale of feeding. In a negative control diet, meal was offered at 850 g/kg of the control diet. Water or effluent as appropriate was given on the meal, and water was also available ad libitum. A total of 60 pigs was used with mean initial and final live weights (LW) of 37·1 and 86·4 kg, respectively.

Effluents H and VH had higher ammonia N: total N and lower amino acid N: total N and lactic acid contents than effluent N. The rates of LW gain, feed conversion ratios, backfat thicknesses and the proportions of lean and fat in the ham joint were similar for the control diet and effluent diets N and H, indicating a similar nutritive value for all three. Effluent diet VH gave a significantly (P < 0·01) reduced rate of LW gain and poorer feed conversion ratio than diets N and H. While diet VH was consumed reluctantly with widespread refusals (mean refusal 28 g DM/kg DM offered), the feed refusals together with the lower lysine and threonine contents of the effluent would not have produced the observed degree of deterioration in growth and feed conversion. Possible reasons for the lower nutritive value are undetectable wastage of feed or the presence of an antinutritional factor in effluent VHG, or a combination of both factors.

The effect of 200, 400 and 600 mg dietary copper sulphate/kg was studied in 64 Japanese quail (Coturnix coturnix japonica) in 1987. The results indicated that addition of 200 or 400 mg/kg to conventional diets of quail 7–42 days old significantly increased (P < 0·05) body weight gain and significantly decreased (P < 0·05) feed intake. There were significant (P < 0·05) increases in carcass, breast and leg weights in some cases; the first two characters had the highest values in the quail fed the diet containing 200 mg Cu/kg. The addition of 600 mg Cu/kg to the diet had an adverse effect on liver weight compared with the addition of 200 and 400 mg/kg. Copper concentration in the liver was not influenced by any rate of copper supplementation.

Male and female New Zealand White rabbits were exposed for 3h to 34 °C and 36 °C (both at 40% r.h.) when hydrated and dehydrated. Females had lower rectal and skin temperatures and respiratory rates than males (P < 0·001). Differences between the sexes in rectal temperature were greater at 36 °C than at 34 °C. Withholding water for 24h significantly increased the responses in rectal temperature; the differentials between hydrated and dehydrated males and females being 0·3 °C and 0·2 °C, respectively. In contrast, respiratory rates were lower in dehydrated than in hydrated rabbits, suggesting that the former were attempting water homeostatis at the expense of thermoregulation.

The results suggest that the performance of rabbits in the tropics is likely to be maximized when drinking water is available at all times, and that of males, particularly breeding bucks, might be improved simply by housing them in the coolest available location. Significant individual differences in observed responses point to the need for genetic studies of heat tolerance and the possibility of developing better adapted genotypes.

Water and energy metabolism were measured in six growing female New Zealand White rabbits placed individually in metabolism cages within chambers at 20 or 30 °C and offered a diet high (H) or low (L) in roughage. For water balance measurements, feed intake was higher at 20 °C than at 30 °C; mean water balance of rabbits on diet L was 7 g/day at 20 °C and 36 g/day at 30 °C. Total daily water consumption was 84–96 g/kg body weight (W), and the ratio of free water to feed intake was 1·6:1 at 20 °C and 2·3:1 at 30 °C.

Calorimetric measurements showed no differences in energy metabolism of rabbits due to diet or temperature. Metabolizable energy needed for maintenance was 357 kJ/kg W0·75 per day and was used with an efficiency of 0·44 for weight gain.