Research has addressed the issue of type of shade mainly on feedlots and high-producing dairy farms, but more studies are needed on the impact of shade on grazing beef cattle in a low-to-medium plane of nutrition. A 63-day grazing study using 24 British steers (268±4 kg) was undertaken in Uruguay (33°14'S, 54°15'W) to determine the effect of type of artificial shade on tympanic temperature (TT), behaviour and performance during summer. Cattle were allocated to six paddocks with an area of 2.5 ha each (four steers/paddock) continuously grazed. Treatments (two paddocks/treatment) were unshaded (US) and shaded with either 35% (35S) or 80% (80S) blockage of solar radiation. TT was recorded during 12 days placing an automatic device near the tympanic membrane inside the animal’s ear. Animal behaviours were measured by live observations of animals every 15 min from 1100 to 1600 h six times during the experimental period. According to the temperature–humidity index (THI), cattle was in the ‘normal’ category (THI<70, absence of heat stress) during 50% of the time, the rest being exposed to some degree of heat stress including 15% of the time with environmental conditions. Black globe temperature and surface soil temperature decreased as solar protection increased under the shade structure. Steers spent more time under the 80S structure than under the 35S between 1100 and 1600 h (83% and 49% of the time, respectively). Average 24-h TT did not differ among treatments (mean±s.e. 38.79±0.04ºC). Minimum TT was registered at 0700 h for all treatments (37.92±0.08ºC), whereas maximum TT was reached at 1700 h for both control group (39.73±0.18ºC) and 35% shade (39.48±0.12ºC) and at 1900 h for 80% shade (39.57±0.15ºC). Neither the provision nor the type of shade affected animal performance (0.622±0.060 kg/a per day), indicating the ability of cattle to acclimate and/or compensate for eventually short-term severe heat stress events. The results of this experiment suggest that the provision of shade with either 35% or 80% of blockage of solar radiation is recommended for the improvement of cattle well-being (expressed through changes in behaviour) without significantly affecting animal performance and TT. However, the overall results of the 63 days of the study can mask or dilute punctual effects of short heat stress events on cattle. More powerful experimental designs are required to address this issue in temperate regions.

Twenty-one 6-month-old Israeli Holstein heifers were used to determine the effect of three 6-month feeding regimes on growth, blood concentration of insulin, prolactin and insulin-like growth factor-1 (IGF-1), attainment of puberty and milk production during first lactation. Feeding regimes were as follows. (1) Restricted: the heifers were given food during months 1, 2 and 4, 5 of an experimental period, to support live-weight (LW) gain of 0·35 and 0·50 kg/day, respectively and during months 3 and 6 the heifers were given food to support compensatory growth. (2) Control: the heifers were given food to support LW gain of 1·0 kg/day. (3) Control + C: the heifers were given the same as the control, with a daily supplement of 0·05 mg/kg LW cimaterol (C) for 4 months. The total LW gain of the restricted heifers during the 6 months of the trial was significantly lower than that of the control heifers. Cimaterol improved growth rate only during the first 2 months of its application and its withdrawal was associated with severe LW gain retardation. The feeding regime employed in the restricted treatment was associated with a significant reduction in serum concentrations of insulin, prolactin and IGF-1 during the first restricted phase, followed by an elevation in the first compensatory phase. During the second restriction-compensation cycle, only the serum concentration of prolactin was significantly reduced. Cimaterol addition was also associated with a reduced blood concentration of the hormones. The animals in the restricted, control and control + C groups attained puberty at LW of 249·2, 277·6 and 304·9 kg (P <0·05), respectively. No effect of the treatments on milk yield was observed. The effect of the feeding regimes on skeletal growth and on metubolizable energy efficiency for growth is discussed.

More accurate definition of Angora rabbit breeding objectives has been investigated by considering multiple expression of different traits. Data on 9672 fleece harvests produced by 1343 Angora does which had at least one wool harvest were analysed in order to study genetic variability according to age. The animals of the French breed were defleeced and weighed at 8 and 21 weeks of age for the first and second time respectively. Thereafter, does were defleeced every 14 weeks and weighed 9 weeks before defleecing. Total fleece weight and live body weight were recorded at each harvest.

Direct heritability estimates of total fleece weight were similar accross ages and ranged from 0·31 to 0·42 . A significant maternal heritability was also observed at all ages of harvest. Maternal genetic estimates decreased with age from 0·44 at the first harvest to 0·10 for an adult harvest. Except for 8 weeks of age, genetic correlations between total fleece weight and live weight were generally not significantly different from zero. Genetic correlations of total fleece weight between the first and subsequent harvests were low (from 0·22 to 0·39) but genetic correlation estimates between consecutive harvests after the first were high, and ranged from 0·68 to 0·89 . The results suggest that the second harvest would be the first good predictor of breeding value for total fleece weight in the adult Angora rabbit.

Inbreeding leads to reduction of the additive variance, whereas inbreeding depression reduces the performance of milk producing cows in both the nucleus and the commercial population. In this study, the cumulative additive response to 30 years of selection corrected for variance reduction due to inbreeding and inbreeding depression in the commercial cow population (denoted as expected phenotypic level or P) was evaluated in a closed (1024 cows tested per year) dairy cattle nucleus scheme, assuming a large number of gametes available per female. No dominance effects were simulated nor estimated in the nucleus. Various hierarchical and factorial designs with fewer sires than dams, an equal number of sires and dams, or even a larger number of sires than dams were compared for P. The trait considered was overall economic merit for milk production with a heritability of the unselected base population of 0·30. Sires and dams were selected on their animal model estimated additive effect for the trait considered at either 15 or 27 months of age. All full-sibs were available for selection. In the absence of inbreeding depression, a complete factorial scheme with more sires than dams resulted in the highest P. With increasing inbreeding depression, the optimal number of sires increased relatively more than the optimal number of dams. Increasing the number of sires decreased inbreeding relatively more than increasing the number of dams, and resulted in a relatively higher P. This is due to the fact that correlations between estimated additive effects of male selection candidates are higher than between those of female selection candidates.

The objectives of this study were to evaluate effects of feeding propylene glycol (PG) on feed intake, milk yield and milk composition, blood metabolites and energy balance in Holstein dairy cows from 1 to 63 days in milk. Thirty-two multiparous cows, blocked by lactation number, previous 305-day milk production and expected calving date, were arranged into four groups in a randomized block design. Treatments were: control, low PG, medium PG and high PG with 0, 150, 300 and 450 ml PG per cow per day, respectively. The supplement of food grade PG (0.998 g/g PG) was hand-mixed into the top one-third of the daily ration. Cows were fed ad libitum a total mixed ration consisting of forage and concentrate (50 : 50, dry matter basis). Feed intake, milk yield and milk components were not affected (P > 0.05) by PG supplementation. Overall, body weight (BW) loss tended (P < 0.08) to be linearly reduced, and energy status was linearly improved with increasing PG supplementation. Concentrations of glucose in plasma were higher for cows fed PG relative to control (55.6 v. 58.9 mg/dl) and linearly increased (P < 0.01) with increasing PG supplementation. Plasma concentrations of non-esterified fatty acids and beta-hydroxybutyrate were linearly increased, but urine acetoacetate concentration was quadratically changed with the highest for control diet and the lowest for 450 ml/day of PG. These results indicated that supplementation of PG in the early lactating cow diets had minimal effects on feed intake and milk production, but may potentially reduce contents of milk fat and milk protein. Supplementation of early lactating dairy cow diets with PG is beneficial in terms of improving energy status and reducing BW loss.

Thirty-nine Hereford × Friesian autumn-calving cows (mean calving date 17 September) and their Charolais-cross calves were used in a 2 × 2 × 2 factorial experiment to assess the effects of feeding level in winter and sward height in summer on intake and performance. Mean estimated metabolizable energy intakes during winter (30 October to 6 May) were 63 (L) or 92 (H) MJ/day. Two sward heights, 4·8 (SI) or 7·6 (Tl) cm, were imposed from turn-out to weaning on 3 July, and a further two sward heights, 4·7 (S2) or 8·0 (T2) cm, from weaning to housing on 1 October. At turn-out the H cows were 17 kg heavier (P > 0·05) than the L cows and their calves were 30 kg heavier (P < 0·01). Cow herbage intakes were significantly higher on the Tl and T2 treatments compared with the SI and S2 treatments as were live-weight changes: 0·94 v. –0·01 kg/day (P < 0·001) for Tl and SI treatments and 0·96 v. –0·18 kg/day (P < 0·001) for T2 and S2 treatments respectively. Calves on the Tl treatment had higher live-weight gains than those on the SI treatment (1·40 v. 0·63 kg/day; P < 0·001). After weaning the SI cows had significantly higher herbage organic matter intakes than the Tl cows (P < 0·05) and had significantly higher live-weight gains (0·51 v. 0·28 kg/day; P < 0·05). Calving difficulty and calf birth weight were not affected by any of the treatments. The results demonstrate that both previous and current level of nutrition have an effect on cow performance. When cows are turned out to pasture at body condition scores of 2·25 to 2·5, the sward heights recommended for spring-calving cows are equally appropriate for autumn-calving cows.

Sirtuins are NAD+-dependent histone and protein deacetylases, which have been studied during the last decade with a focus on their role in lifespan extension and age-related diseases under normal and calorie-restricted or pathological conditions. However, sirtuins also have the ability to regulate energy homeostasis as they can sense the metabolic state of the cell through the NAD+/NADH ratio; hence, changes in the diet can modify the expression of these enzymes. Dietary manipulations are a common practice currently being used in livestock production with favorable results, probably due in part to the enhanced activity of sirtuins. Nevertheless, sirtuin expression in livestock species has not been a research target. For these reasons, the goal of this review is to awaken interest in these enzymes for future detailed characterization in livestock species by presenting a general introduction to what sirtuins are, how they work and what is known about their role in livestock.

Polymorphisms at codons 136, 154 and 171 of the gene encoding the prion protein (PrP) are associated with susceptibility to classical scrapie in sheep. Genetic selection for scrapie resistance based on PrP genotypes is central to the scrapie eradication programme in Great Britain but there are concerns about how this may affect other economically important traits. The objective of this study was to evaluate associations of PrP genotypes with live weight and slaughter traits in a hill sheep breed in Great Britain. Data used were from an experimental flock of Swaledale sheep in which the alleles ARR, ARQ, AHQ and VRQ were present. About 1450 genotyped lambs with birth, marking and weaning weights, and 620 with slaughter records were used for the study. Mixed models with various fixed effects and random direct genetic and maternal effects were tested to determine the appropriate model to use for each trait. None of the differences in lamb performance between PrP genotypes consistently reached significance. Therefore, this study does not support existence of significant relationships between PrP genotype and lamb performance traits in this breed.

The aim of this study was to test the hypotheses that differences in residual feed intake (RFI) of beef steers are related to diet sorting, diet nutrient composition, energy intake and apparent digestibility. To phenotype steers for RFI, 69 weaned Angus × Hereford steers were fed individually for 56 days. A finishing diet was fed twice daily on an ad libitum basis to maintain approximately 0.5 to 1.0 kg refusals. Diet offered and refused was measured daily, and DM intakes (DMI) were calculated by difference. Body weights were recorded at 14-day intervals following an 18-h solid feed withdrawal. The residual feed intake was determined as the residual of the regression of DMI versus mid-test metabolic BW (BW0.75) and average daily gain (ADG). Particle size distributions of diet and refusals were determined using the Penn State Particle Separator to quantify diet sorting. Sampling of diet, refusals and feces were repeated in four sampling periods which occurred during weeks 2, 4, 6 and 8 of the study. Particle size distributions of refusals and diet were analyzed in weeks 2, 4 and 6, and sampling for chemical analysis of refusals and feces occurred in all four periods. Indigestible neutral detergent fiber (288 h in situ) was used as an internal marker of apparent digestibility. We conclude that preference for the intakes of particles > 19 mm and 4 to 8 mm were negatively correlated to RFI and ADG, respectively. Although steers did sort to consume a different diet composition than offered, diet sorting did not impact intake energy, digestible energy or DM digestibility.

Enhancing the supply of arginine (Arg), a semi-essential amino acid, has positive effects on immune function in dairy cattle experiencing metabolic stress during early lactation. Our objective was to determine the effects of Arg supplementation on biomarkers of liver damage and inflammation in cows during early lactation. Six Chinese Holstein lactating cows with similar BW (508 ± 14 kg), body condition score (3.0), parity (4.0 ± 0), milk yield (30.6 ± 1.8 kg) and days in milk (20 ± days) were randomly assigned to three treatments in a replicated 3 × 3 Latin square design balanced for carryover effects. Each period was 21 days with 7 days for infusion and 14 days for washout. Treatments were (1) Control: saline; (2) Arg group: saline + 0.216 mol/day l-Arg; and (3) Alanine (Ala) group: saline + 0.868 mol/day l-Ala (iso-nitrogenous to the Arg group). Blood and milk samples from the experimental cows were collected on the last day of each infusion period and analyzed for indices of liver damage and inflammation, and the count and composition of somatic cells in milk. Compared with the Control, the infusion of Arg led to greater concentrations of total protein, immunoglobulin M and high density lipoprotein cholesterol coupled with lower concentrations of haptoglobin and tumor necrosis factor-α, and activity of aspartate aminotransferase in serum. Infusion of Ala had no effect on those biomarkers compared with the Control. Although milk somatic cell count was not affected, the concentration of granulocytes was lower in response to Arg infusion compared with the Control or Ala group. Overall, the biomarker analyses indicated that the supplementation of Arg via the jugular vein during early lactation alleviated inflammation and metabolic stress.

N-alkanes are long-chain saturated hydrocarbons occurring in plant cuticles that can be used as chemical markers for estimating the diet composition of herbivores. An important constraint of using n-alkanes to estimate diet composition with currently employed mathematical procedures is that the number of markers must be equal or larger than the number of diet components. This is a considerable limitation when dealing with free-ranging herbivores feeding on complex plant communities. We present a novel approach for the estimation of diet composition using n-alkanes which applies equally to cases where the number of markers is lower, equal or greater than the number of plant species in the diet. The model uses linear programming to estimate the minimum and maximum proportions of each plant in the diet, and avoids the need for grouping species in order to reduce the number of estimated dietary components. We illustrate the model with two data sets of n-alkane content of plants and faeces obtained from a sheep grazing experiment conducted in Australia and a red deer study in Portugal. Our results are consistent with previous studies on those data sets and provide additional information on the proportions of individual species in the diet. Results show that sheep included in the diet high proportions of white clover (from 0.25 to 0.37), and relatively high proportions of grasses (e.g. brome from 0.14 to 0.26) but tended to avoid Lotus spp. (always less than 0.04 of the diet). For red deer we found high proportions of legumes (e.g. Trifolium angustifolium and Vicia sativa reaching maximum proportions of 0.42 and 0.30 of the diet, respectively) with grasses being less important and Cistus ladanifer, a browse, also having relevance (from 0.21 to 0.42 of the diet).

Grain-rich diets often lead to subacute ruminal acidosis (SARA) impairing rumen and systemic cattle health. Recent data suggest beneficial effects of a clay mineral (CM)- based product on the rumen microbiome of cattle during SARA. This study sought to investigate whether the CM supplementation can counteract SARA-induced perturbations of the bovine systemic health. The study used an intermittent diet-induced SARA-model with eight dry Holstein cows receiving either no additive as control or CM via concentrates (n=8 per treatment). Cows received first a forage diet (Baseline) for 1 week, followed by a 1-week SARA-challenge (SARA 1), a 1-week recovery phase (Recovery) and finally a second SARA-challenge for 2 weeks (SARA 2). Cows were monitored for feed intake, reticular pH and chewing behavior. Blood samples were taken and analyzed for metabolites related to glucose and lipid metabolism as well as liver health biomarkers. In addition, a targeted electrospray ionization-liquid chromatography-MS-based metabolomics approach was carried out on the plasma samples obtained at the end of the Baseline and SARA 1 phase. Data showed that supplementing the cows’ diet with CM improved ruminating chews per regurgitated bolus by 16% in SARA 1 (P=0.01) and enhanced the dry matter intake during the Recovery phase (P=0.05). Moreover, the SARA-induced decreases in several amino acids and phosphatidylcholines were less pronounced in cows receiving CM (P≤0.10). The CM-supplemented cows also had lower concentrations of lactate (P=0.03) and biogenic amines such as histamine and spermine (P<0.01) in the blood. In contrast, the concentration of acylcarnitines with key metabolic functions was increased in the blood of treated cows (P≤0.05). In SARA 2, the CM-cows had lower concentrations of the liver enzymes aspartate aminotransferase and γ-glutamyltransferase (P<0.05). In conclusion, the data suggest that supplementation of CM holds the potential to alleviate the negative effects of high-grain feeding in cattle by counteracting multiple SARA-induced perturbations in the systemic metabolism and liver health.

Excess iodine intake by the pregnant dam reduces lamb serum antibody concentration, specifically immunoglobulin G (IgG). An experiment was conducted to investigate the mechanisms under pinning the reduced serum IgG concentration at 24 h postpartum in the progeny of iodine supplemented dams. Forty-five mature twin bearing ewes (n=15/treatment) were allocated to one of three dietary treatments as follows: basal diet (Control); basal diet plus 26.6 mg of iodine per ewe per day as calcium iodate (CaIO3); or potassium iodide (KI). Ewes were individually housed and fed from d 119 of gestation until parturition. All lambs received colostrum at 1, 10 and 18 h postpartum via stomach tube. At 1 h postpartum lambs from the control and an iodine supplemented treatment (n=10 per treatment from control and CaIO3) were euthanised before colostrum consumption and ileal segments isolated to determine the gene expression profile of a panel of genes identified as having a role in antibody transfer. Preceding euthanasia, lambs were blood sampled for determination of serum IgG, total thyroxine and free tri-iodothyronine concentrations. Progeny of CaIO3 supplemented dams had lower tri-iodothyronine concentrations (P<0.01) at 1 h postpartum and lower serum IgG concentrations (P<0.001) at 24 h postpartum when compared with the progeny of control dams. Iodine (CaIO3) supplementation of the dam increased the relative expression (P<0.05) of the B2M, PIGR and MYC genes in the ileum of the lamb, before colostrum consumption; while the expression of THRB declined when compared with the progeny of C dams (P<0.01). In conclusion, the results of this study show that it is the actual inclusion of excess iodine in the diet of the ewe, regardless of the carrier element, that negatively affects passive transfer in the newborn lamb. This study presents novel data describing the relationship between maternal iodine nutrition and its effect on the thyroid hormone status and subsequent gene expression in the newborn lamb; which results in a failure of passive transfer and a decline in serum IgG concentration.

Classification of pig carcasses in the European Community is based on the lean meat percentage of the carcass. The lean meat percentage is predicted from instrumental carcass measurements, such as fat and muscle depth measurements, obtained in the slaughter-line. The prediction formula employed is derived from the data of a dissection experiment and has to meet requirements for authorization as put down in EC regulations. Requirements involve the sampling procedure and sample size for the dissected carcasses and the accuracy of prediction. Formulae are often derived by linear regression. In this paper we look at a particular type of sampling scheme. This involves selection of carcasses on the basis of carcass measurements not all of which are intended to be used as prediction variables. This sampling scheme frequently appears in requests for authorization of carcass measurement instruments and accompanying prediction formulae, despite the fact that it lacks formal statistical justification when used in conjunction with linear regression. The objective of this work was to assess the performance of the prediction formula that follows from this potentially faulty combination of sampling scheme and linear regression in relation to the requirements in the EC regulations. We show that this sampling scheme may produce poor predictions for lean meat percentage compared with proper sampling procedures with selection on prediction variables only or random sampling. We do so by computer simulation. Initially, simulated data were based on recent and historic data from The Netherlands. Prediction variables are fat and muscle depth measurements. The additional variable involved in sampling, but not included in the regression, was carcass weight. We also show that due to this faulty sampling scheme there is a serious risk that a new measurement instrument may not be authorized because performance criteria in the EC-regulations are not met.

In each of 2 years, two groups of 25 British Friesian heifers were given, respectively, a moderate- and a low-energy diet for a 12-week period. Mean live-weight gains of 0·25 kg/day and 0·45 kg/day were recorded for the moderate-energy diet, and losses of 0·22 kg/day and 013 kg/day for the low-energy diet. Heifers were inseminated artificially at oestrus at approximately the mid-point of the 12-week period, this oestrus being the next observed after synchronized oestrus, which followed luteolysis induced by cloprostenol injections. With few exceptions, heifers that gained weight were in good or medium condition at insemination and those that lost weight were in medium or poor condition.

Highest pregnancy rate (0·78) was recorded for heifers that gained weight and were in medium condition at insemination. For heifers losing weight, pregnancy rate dropped to 0·46 (P < 0·05) due to reproductive failure occurring before the 25th day after insemination. Only in heifers in poor body condition was there a significantly higher proportion failing to ovulate normally (P < 0·001). Among heifers gaining weight, those failing to become pregnant to the first insemination were approximately lOOg/kg heavier than the pregnant ones (P<0·05).

Irrespective of gain or loss of weight, and of body condition at insemination, embryo losses did not occur later than the 25th day after insemination, except that five heifers that showed oestrus when pregnant (according to plasma progesterone levels) and were reinseminated then showed evidence of embryo loss.

Ileal digestibility in growing pigs fed starch-based diets with inclusion of four tropical leaves in a meal form was studied in a 5 × 5 Latin square design. Five diets were formulated with only casein as protein source in the basal diet (CAS), and casein plus dry cassava (CA) leaves, casein plus dry sweet potato (SP) leaves, casein plus dry cocoyam (CO) leaves and casein plus erythrina (ER) leaves in the other four diets. All diets contained the same amount of CP (14%), either provided by only CAS or a combination of casein and 250 g of leaf meal per kg of diet in the other diets. Leaves were separated manually from stems, and only the leaf part was used. A protein-free diet was fed during a sixth period in order to estimate the endogenous protein losses and calculate the CP- and amino-acid (AA)-standardized ileal digestibility (SID) values. The values for the foliages were calculated according to the difference method, assuming no interaction between the foliage and the casein. The ileal tract apparent digestibility of CP, organic matter and energy was higher in diet CAS than in the other diets (P < 0.05). The SID of CP and AA was close to 0.950 for casein, whereas the SID of AA was markedly lower in the foliages; the SID of indispensable and dispensable AA was highest in CO (0.500 and 0.352) and lowest in ER (0.170 and 0.195); intermediate values were obtained for SPs (0.367 and 0.349) and CA (0.232 and 0.242) leaves. Accordingly, the SID of lysine was highest (0.538) for CO leaves and lowest (0.126) in ER leaves; intermediate values were measured for CA and SP leaves. These low SID values in foliage meals must be related to the high levels of dietary fibre and the presence of secondary metabolites (tannins). These results suggest that it is only possible to replace a fraction of the conventional protein sources such as soyabean meal by tropical foliages in growing pig diets with a preference for CO leaves.

Traditionally, male pigs are surgically castrated without anaesthesia to avoid later occurrence of the sex odour of androstenone in the carcass. Active immunization against gonadotropin-releasing hormone (GnRH) is a painless alternative which inhibits LH and thus steroidogenesis in the Leydig cells. In a preceding study we clarified the return of Leydig cell function after the last dose of antigen by measuring hormones, and found a considerable variation (10 to 24 weeks) till return of their function (testosterone ⩾ 0.5 ng/ml blood plasma). The present paper analyses histological data on testes characteristics of the same six boars at an age of 52 weeks (26 weeks after last immunization). Data were compared to another four boars which were not immunized but slaughtered at the same age. Testis weight was related to the concentration of testosterone in blood. In boars, that first returned to testicular function, testis weight even exceeded those in controls probably due to rebound phenomena. Differences in testis weight were mainly due to differences of Leydig cell content of cytoplasm, and less to the size of nuclei. Additionally, the height of seminiferous epithelium was slightly dependent on testosterone concentrations and contributed moderately to differences in testis weight. Altogether, normalization of testicular function, even after return to steroidogenesis, requires another 13 weeks.

A study was carried out to determine if sheep could be used as a model for predicting the intakes of silages by cattle. Fifty ewes and 45 cows were offered five grass silages unsupplemented in two parallel randomized-block experiments over a 4-week period. Each silage had been made using the same equipment over a range of cutting dates (May, July, August 1991). The silages differed in fermentation characteristics, with lactic acid concentrations varying from 15·3 to 90·7 g/kg dry matter, and ammonia-nitrogen concentrations from 77 to 198 g/kg nitrogen. When expressed on a metabolic live-weight basis, the mean intakes of silages by cows were 2·25 times those of the sheep, with the mean intakes being 35·1 and 79·1 g/kg M0·75 for the sheep and cows respectively. However, there was no significant correlation between recorded intakes during the 4th week of the study by the two species (y (cows) = 0·62× (sheep) + 58·40; r2 = 0·03). It was concluded that sheep were not a useful model system to predict the intakes of a range of grass silages of similar chop length by dairy cows.

Ten Scottish male castrated cashmere-yielding (C) and 10 Angora (A) goats with initial live weights of 38·2 (C) and 32·1 (A) kg respectively were used in a 112-day study in the time period August to December. The goats were blocked within genotypes according to live weight and randomly assigned to one of two treatments: either no supplementation (O) or dietary supplementation (S) with 2·5 g/kg dry matter (DM) intake of rumen-protected intestinally available methionine (Smartamine™ M, Rhone Poulenc, Animal Nutrition, Antony 92164, France) in a 2 × 2 factorial arrangement.

The goats were offered a basal diet in the proportion of 0·6, grass hay and 0·4 concentrate according to their live weight. Diet metabolizable energy (ME) and crude protein (CP) concentration per kg DM were estimated as 9·9 MJ (ME) and 107 g (CP) and DM intake was restricted to 28 g/kg live weight daily. Apparent digestibility and nitrogen (N) balance studies were conducted from days 24 to 40 and 51 to 64. Measurements were made within three time periods of days 0 to 40, 41 to 75 and 76 to 112.

Angora goats excreted less urinary N than cashmere-yielding goats and had lower values for plasma urea and glucose and greater overall retention ofN, associated with a two- to three-fold greater total fibre yield. Cashmere as a proportion of total fibre by weight, (guard hair plus cashmere) varied from 0·27 to 0·43.

The main effects due to methionine supplementation were improvements in live-weight gain and food conversion ratio. Reductions in urinary N excretion and increases in N retention were recorded, which were generally greater for Angora than for cashmere-yielding goats, and were again associated with the larger responses in fibre production. Clear evidence was also obtained for methionine-induced increases in the weight of raw cashmere, although not guard hair up to day 58. This response was obtained in the absence of significant effects on cashmere diameter, although methionine supplementation consistently increased the average diameter of mohair fibres.

The work of the late Sir Joseph Barcroft and his collaborators (see Elsden & Phillipson, 1948) left little doubt that, in ruminants, the end products of the bacterial dissimilation of dietary carbohydrate included large amounts of the steam-volatile fatty acids—acetic, propionic and butyric acids. More recently, el Shazly (1952a, b) has shown that the steam-volatile fatty acids also arise together with ammonia during the bacterial breakdown of amino-acids in the rumen. Studies by Pfander & Phillipson (1953) and Schambye (1955) further indicate that the acids are absorbed from the digestive tract in amounts that suggest they make a major contribution to the energy requirement of the animal. Quantitative data relative to the amounts absorbed, however, are difficult to obtain. Carroll & Hungate (1954) have calculated that in cattle some 6,000-12,000 Cal. of energy are available from the acids produced by fermentation in the rumen. With sheep, Phillipson & Cuthbertson (1956) have calculated from the results of Schambye (1951a, b; 1955) that at least 600-1,200 Cal. of energy in the form of steam-volatile fatty acids could be absorbed every 24 hrs. Since the fasting heat production of the steer is about 6,500 Cal./24 hrs. and that of the sheep about 1,100 Cal./24 hrs. it is clear that if the fatty acids can be utilised efficiently by the body tissues, they could make a major contribution to the energy requirements, at least those for maintenance.