Factors affecting survival to first and second calving and successful completion of a > 168-day first lactation were assessed in 3075 purebred and crossbred dairy heifer calves. Growth, disease, frequency, reproduction, calving, udder and lactation traits were examined in females of a breeding project conducted jointly at five research stations (herds) of Agriculture Canada. Losses included mortalities and non-discretionary culling. About 0·23 of potential heifers were culled or died before first calving, and 0·25 of those calving once did not calve a second time. Results from retrospective selection index and stepwise linear logistic analyses showed that predictability of culling prior to 308 days post partum was poor. With few exceptions, survival rates from birth to 82 weeks varied among herds (P < 0·001) and among lines (P < 0·05). Heterosis for the probability of completing a lactation and of survival to second calving was significant (P < 0·05) and positive (0·05 to 0·09). Heavier heifers were more likely to survive to first calving. Sire's estimated breeding values (SEBV) for milk yield and fat, protein and lactose concentration were not important in predicting survival to first calving. SEBV lactose was negatively associated with survival after first calving as predicted from data available at most preceding stages of life. An age greater than 82 weeks at last insemination was associated with a lower probability of survival to first and second calving (P < 0·001). Cows which conceived for a second gestation and subsequently aborted had a lower probability of survival to second calving than cows which did not abort (0·57 v. 0·76, P < 0·01). The only continuous traits with large effects on survival or the probability of completing a first lactation were days to last insemination (a measure of fertility) and milk yield. It was concluded that (1) there is considerable scope for improved management to increase survival in early life by prevention of calfhood diseases; (2) losses in early life do not bias sire evaluation on first lactation records; (3) improved reproductive success would greatly enhance overall survival rates; and (4) crossbreeding could have a large impact on overall herd profitability through increased survival.

Twenty bulls of three different breeds were tethered individually from 5 months until slaughter at 21 months. On the day of slaughter, the bulls were divided into groups of five animals, transported and then released in a pen. The first bull of the group was slaughtered 60 or 110 min after regrouping. Subsequent bulls were slaughtered individually at 50-min intervals. Social interactions among the bulls were recorded. Muscle pH, light reflectance values and water-holding capacity were measured in samples of m. longissimus dorsi. These characteristics showed correlations with the amount of non-agonistic social activity in which a bull had been involved before slaughter. The characteristics were also correlated with the number of agonistic interactions. Whether a bull was behaving as a dominant or a submissive animal did not influence the incidence of dark-cutting meat as judged by pH values. On the other hand, light reflectance values and water-holding capacity were correlated with the number of passive agonistic interactions (i.e. how many times a bull was attacked) and considerably less with the number of active interactions (number of attacks by the bull). The incidence of butting was not significantly related to muscle characteristics but mounting was significantly correlated with them.

The study indicates that dark-cutting beef is primarily caused by physically exhausting activities such as mounting, and further modified by stress-inducing social interactions.

There is increasing interest in how the raw material make-up of concentrates can influence the milk performance of dairy cows. Thus, over two consecutive winters, 54 dairy cows were used to investigate the effects on dry matter (DM) intake, milk yield and its composition of feeding concentrates of diverse energy source (LNDF — 131 g neutral-detergent fibre per kg DM, 492 g starch plus sugars per kg DM; HNDF — 244 g neutral-detergent fibre per kg DM, 293 g starch plus sugar per kg DM) at two formulated crude protein (CP) levels (157 v. 187 g/kg DM) and three levels of concentrate allowance (9, 11, 13 kg DM). The concentrates were formulated to be of equivalent metabolizable energy concentration (MJ/kg DM) and were offered with silage ad libitum for a 10-week period (weeks 4 to 13 of lactation).

Silage intakes were variable but not significantly influenced by concentrate energy source or formulated CP level, except in the 1st year where animals consuming the high CP concentrate ate more silage. Silage DM intake decreased as concentrate allowance was increased with the substitution rate (kg silage DM per kg concentrate DM) increasing as concentrate allowance was increased.

Increasing the concentrate allowance effected the expected increases in milk yield. Concentrate energy source did not influence milk yield but the higher CP levels effected a 2-kg increase in milk yield. Feeding of LNDF concentrates depressed milk fat concentration and its yield, the depression being accentuated with each increase in concentrate allowance. The depression in milk fat concentration was negatively correlated with the forage: concentrate ratio of the diet consumed. Furthermore, dietary NDF proportion was shown to account for greater than half of the variation in milk fat concentration. In contrast to the observations made for milk fat, feeding the LNDF concentrates effected an increase in milk protein concentration but only at the lower CP level of the concentrate.

The value of indicator traits (7), such as physiological or biochemical traits in the genetic improvement of dairy cattle for milk yield (M) was studied. First, some corrections were made to the base rates of genetic change possible by improvement systems based on progeny testing and on multiple ovulation and embryo transfer (MOET), and on combinations of these. Efficient field progeny-testing systems can be competitive with current adult MOET nucleus herd schemes but juvenile MOET nucleus herd schemes offer substantial increases in rates of response. With high co-heritability, selection for the T alone may allow greater rates of response than those currently considered feasible using progeny testing. However, faster rates are obtained with combined selection. When breeding values are accurately measured by pedigree and performance records on M, as in the progeny test, the extra rates of response with combined selection may be small. Where breeding values are less accurately assessed, as in juvenile MOET nucleus schemes, the extra rates of response can be appreciable. For T with co-heritability (hMrGhT) of 0·27 and the CV for M from 0·15 to 0·20, response rates of 2·0 to 2·7% of the mean per year possible by traditional methods could be increased to 2·2 to 2·9% in progeny testing schemes, 2·3 to 3·1% and to 4·3 to 5·7% for adult and juvenile MOET nucleus schemes respectively.

A possible useful indicator trait is blood urea nitrogen (BUN) measured in young animals after a short fast. Results from four experiments with calves having high or low genetic merit for M were summarized. The pooled co-heritability estimate was —0·27 (s.e. 0·05). With this, or even a more modest effect, BUN would be a useful indicator trait in selection for milk production. Its use in practice in high and low selection lines or in a section of the industry, would allow assessment of the merit of the method.

Following a 3-week covariance period, 30 group-housed dairy cows were individually given one of three diets from week 4 to week 13 of lactation to determine any possible advantage in milk yield and production of feeding levels of undegradable protein (+UDP) or rumen-degradable protein (+RDP) above the minimum levels (control) proposed by the Agricultural Research Council (ARC, 1984). The three concentrates given were formulated to be of equivalent metabolizable energy (ME, 13·5 MJ/kg dry matter (DM)) concentration and each consisted of rolled barley plus a protein supplement: control (crude protein (CP), 129 g/kg DM) 0·35 kg DM fish meal per day; +UDP (CP, 167 g7kg DM) 1·0 kg DM fish meal per day; and +RDP (CP, 167 g/kg DM) 1+5 kg DM soya per day. For each group the total ‘concentrate’ allowance per animal per day was 11·6 kg fresh weight and was given in three equal feeds. Grass silage (CP 122 g/kg DM, ME 106 MJ/kg DM) was given ad libitum. For the control, +UDP and +RDP treatments, respectively, mean grass silage intakes were 8·29, 8·62 and 8·65 kg/day and mean milk yields were 26·6, 26·3 and 26·1 kg/day. These were not significantly different (P > 0·05). Milk fat concentration was lower (P < 0·05) for the +UDP treatment (36·4 g/kg) in comparison with the control (38·6 g/kg) or the +RDP treatment (39·7 g/kg) but no other milk constituent was significantly influenced by treatment. There was a trend for a greater live-weight gain with treatment +UDP (0·81 kg/day) compared with the other two treatments (control 0·50, +RDP 0·51 kg/day) but there were no differences in condition-score change between treatments. In this trial there was no advantage to feeding formulated levels of UDP or RDP above those proposed by ARC (1984).

This study was carried out to investigate: (1) changes in plasma oestradiol-17β and progesterone concentrations in six pre-pubertal beef heifers, 9 months old, subjected to a superovulatory treatment, consisting of a single dose of PMSG followed 120 h later by a single injection of human chorionic gonadotrophin (HCG); and (2) the ability of this treatment to trigger cyclic gonadal activity. After PMSG administration, oestradiol-17β levels increased from 11·8 (s.d. 10·78) to 92·9 (s.d. 38·15) ng/1 just before HCG injection. The oestradiol-17β increase during the superovulatory treatment and numbe r of ovulations were correlated (r = 0·83; P < 0·05). After HCG injection, progesterone concentrations rose significantly reaching values which in some cases were higher than 60 [μg/1. The progesterone peak on days 9 and 10 post HCG was strongly correlated with the number of corpora lutea (r = 0·95; P < 0·01 and r = 0·92; P < 0·01, respectively). Progesterone determinations were performed for a period of 90 days after HCG administration. No evidence was found for the induction of permanent cyclic ovarian activity since all heifers returned, after the induced luteal phase, to their pre-pubertal condition.

Equations for the prediction of forage dry-matter intake, metabolizable energy (ME), rumen degradable protein and undegraded protein, based on those in the current Agricultural Research Council system, were incorporated into a computer program designed to be used by livestock advisors for on-farm rationing of beef cattle. The predictions of silage intake and live-weight gain are compared with experimental data.

Voluntary intake of grass silage was generally over-estimated by the program by proportionately at least 0·06, with a root mean square error of ±0·18 of the mean observed silage intake for the all-silage rations. The prediction of ME requirement for observed production had an error of +0·15 of average ME intake but the calculations of ME intake were themselves dependent on the predictions of the ME concentrations of the silages and supplements. Similarly the comparison of protein supply with requirement was highly dependent on the value assigned to N-degradability. However, the program can be used to assess how changes in the input values would affect ration formulation.

The mathematical basis of the program is described in the Appendix.

Thirty-two Friesian cows in early lactation were given one of tour completely mixed diets based on equal proportions of barley straw and concentrate. Two varieties of barley straws had been identified as varying in degradation characteristics (Corgi and Gerbel) and the straws were either given untreated or treated with anhydrous ammonia. The ad libitum intake for 10 weeks closely reflected degradation characteristics. For Corgi, treated and untreated and Gerbel, treated and untreated the 48·h degradabilities were 71·9, 66·8, 61·9 and 52·2 (g/100 g) respectively. The voluntary intakes of dry matter were 17·1, 14·8, 15·0 and 13·1 (s.e. 0·51) kg/day and average yields of fat-corrected milk for 10 weeks were 26·7, 21·5, 22·6 and 22·4 (s.e. 1·0) kg/day respectively.

It was calculated that the differences between actual digestibility and potential degradability were greatest for ammonia-treated straws. Also it was observed that the degradability of faecal dry matter was greater from animals given ammonia-treated straws.

Two varieties of rice straw, long variety — no. 370 Basmati traditional (L) and short variety — no. PR106 hybrid (S) were separated into botanical fractions giving the proportion of leaf plus leaf sheath, internode, node and chaff (g/kg dry matter) as 633, 247, 83 and 37 for L and 680, 156, 76 and 88 for S, respectively. Samples of whole plants, leaves plus leaf sheaths and internodes were subjected to ammonia treatment. The chemical composition and the rumen degradability of dry matter and organic matter determined by the nylon bag technique were ascertained for treated and untreated samples of whole plants and botanical fractions of plants from both varieties. The ash and silica content were higher in leaf plus leaf sheath, 211 and 102 g/kg for the L and 190 and 67 g/kg for the S, than in internodes, 160 and 29 g/kg for L and 184 and 29 g/kg S, respectively.

The potential degradability (a + b) value from the formula p = a + b(−e−ct) for dry-matter loss (DML), organic-matter loss (OML) and degradability of organic matter in dry matter (DOMD) were significantly higher for the S being 622, 659 and 544 g/kg, than for the L being 561, 586 and 500 g/kg, respectively (P < 0·01). The degradation rate too was significantly higher for the S than for the L for DML, OML and DOMD (P < 0·01). The ammonia treatment significantly improved the potential degradability for DML, OML and DOMD for both the varieties and their fractions (P < 0·01).

The ability of the protein nutrition scheme proposed by the Agricultural Research Council (ARC, 1980, 1984) to predict responses to protein supply was examined in two experiments. In experiment 1, groups of nine British Friesian steers implanted with oestradiol-17β and nine non-implanted steers were fed from 133 to 300 kg live weight on each of four all-concentrate diets (metabolizable energy (ME) = 12 MJ/kg dry matter (DM)) containing ratios of soya-bean meal and formaldehyde-treated soya-bean meal such that undegradable protein (UDP) concentration was 19, 25, 32 or 42 g/kg DM. Rumen degradable protein (RDP) concentration was relatively constant (111 to 116 g/kg DM). Implantation did not affect DM intake (DMI, g/kg M0·75). Both live-weight gain (LWG) and food conversion efficiency (FCE) (LWG/DMI) were greater (P < 0·05) for the implanted cattle (LWG = 1·41 (s.e. 0·04) kg/day; FCE = 0·24 (s.e. 0·02)) than for the non-implanted cattle (LWG = 1·23 (s.e. 0·05) kg/day; FCE = 0·22 (s.e. 0·02)). There were no dietary effects on either DMI or FCE. In the non-implanted steers, UDP did not affect LWG but, for the implanted steers, there were positive, linear responses in LWG to both UDP concentration (P = 0·048) and UDP intake (P = 0·026). In experiment 2, groups of eight implanted steers were fed from 132 to 300 kg live weight on each of six diets (ME = 12 MJ/kg DM, soya-bean meal and formaldehyde-treated soya-bean meal as chief protein sources) supplying 17, 26, 34, 39, 54 and 82 g UDP per kg DM and concentrations of RDP up to 1·5 times ARC recommendations. There was no effect of UDP on either DMI or FCE but positive, linear responses in LWG to both UDP concentration (P = 0·019) and UDP intake (P = 0·010). In both experiments, mean DMI exceeded that predicted by ARC (1980) (P < 0·05). LWG predicted by the ME system and the ARC protein scheme was not significantly different from observed LWG for non-implanted steers, but was an underestimate of observed LWG for implanted steers (P = 0·002 in experiment 1, P < 0·001 in experiment 2). Observed responses in LWG to UDP concentration were also poorly predicted (regressions of observed on predicted LWG: experiment 1, r2 = 0·12, residual s.d. = 0·126; experiment 2, r2 = 0·004, residual s.d. = 0·119). It was concluded that oestradiol-17p has significant effects on responses in LWG to UDP, which are not predicted by the current ARC (1980, 1984) protein nutrition scheme.

Five different straws consisting of two varieties of winter barley, two varieties of spring barley and one variety of winter wheat were chosen due to differences in degradation characteristics determined by using nylon bags incubated in the rumen of cattle and describing the straw using the equation: p = a + b (1 – e–ct). To increase variation in degradability, batches of the same straws were also treated with anhydrous ammonia in a sealed oven.

The straws were subsequently offered ad libitum to groups of steers given a daily supplement of 1·5 kg concentrate and untreated straws were supplemented with urea. The dry-matter intake (DMI) of the straws varied from 3·4 to 5·7 kg/day, the digestible DMI from 1·4 to 3·5 kg/day and growth rate from 106 to 608 g/day.

By using multiple regression of a, b, c from the exponential equations characterizing degradability of the straw, the correlation coefficients with DMI, digestible DMI and growth rate were 0·88, 0·96 and 0·95 respectively.

The live-weight gain (LWG) and efficiency of food utilization of purebred British Friesian and Canadian Holstein steers and of crossbred steers out of British Friesian dams by Charolais, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One was similar to the commercial 18-month grass/cereal system (16-month) and the other to a commercial 2-year system (24-month). The cattle were serially slaughtered at three levels of fatness covering the commercial range and determined by the use of the Scanogram ultrasonic machine. The trial extended over 4 years and involved a total of 650 cattle. Data for the two production systems were analysed separately. Changes in growth performance were examined relative to estimated carcass subcutaneous fat content (g/kg; SFC) and sire breed crosses compared at the mean fatness level within system: 65 g/kg SFe for 16-month and 74 g/kg SFe for 24-month.

Sire breed differences were not detected (P > 0·05) in the regressions on SFe of age and live weight at slaughter, overall daily LWG and overall efficiency of weight gain. Pooled within sire breed, live at slaughter and age at slaughter increased by 2·5 kg and 2·8 days (16-month) and 2·2 kg and 2·1 days (24-month) for each g/kg increase in SFe.

Charolais crosses and Canadian Holsteins were heaviest at equal SFC in both systems, but the latter were 63 days older (16-month) and 42 days older (24-month): Hereford, Lincoln Red and Sussex crosses were lightest and among the youngest in both systems.

Sire breed crosses differed significantly in daily LWG: Charolais crosses grew fastest in both systems; the relative growth rate of other sire breed crosses was less consistent between the two although the Hereford crosses and British Friesians grew slowly in both systems. Overall efficiency of LWG (g gain per kg digestible organic matter intake) ranged from 164 to 205 (16-month) and 146 to 171 (24-month). Canadian Holsteins and British Friesians had the lowest efficiency of LWG in both systems of production; differences between the other breeds were not statistically significant (P > 0·05).

In the present study, a commercially available anabolic implant containing trenbolone acetate and oestradiol-17p was investigated in intact and castrated bulls. Measurements of growth rate, serum hormones and metabolites in both phenotypes, and testicular development and function in bulls, were obtained. The experimental objectives were realized in a 2 × 2 factorially designed experiment utilizing eight Angus-sired crossbred bulls and eight similar steers castrated at 7 months of age. Half of each group were implanted with 140 mg trenbolone acetate plus 28 mg oestradiol-17β. Body weights were monitored every 7 days and plasma samples were obtained at 28-day intervals from 9 to 15 months of age. In the implanted groups, mean concentrations of plasma trenbolone and oestradiol-17p were 380 ng/1 and 31 ng/1, respectively. Trenbolone concentrations were undetectable in both non-implanted groups, and plasma oestradiol-17β was less than half that in implanted animals. While plasma GH concentrations were stratified according to implant treatment, they did not differ among the groups. Cortisol levels showed phenotype × implant interaction; implanted steers and non-implanted bulls had lower concentrations than non-implanted steers and implanted bulls. The implant resulted in no significant changes in gross testicular measures in the bulls but did affect the testosterone response to a GnRH challenge and basal plasma concentrations of testosterone were reduced. Plasma urea concentrations were reduced by the implant, but sex phenotype had no effect. Over the 175-day trial, implantation did not significantly improve the growth rate of bulls, except during the first third of the experiment. In contrast, implantation improved the growth rate of steers over the entire experiment, although implanted steers still grew more slowly than either implanted or non-implanted bulls. It can be concluded that the endocrine status of the young bull is set for a fast growth rate, making improvements via an anabolic implant marginal, except in the immature animal.

Eighteen mature (3 to 6 years) Debouillet × Rambouillet ewes (mean weight 79·2 (s.e. 21) kg) producing and nursing single offspring were randomly allotted to one of three groups to examine the influence of ovine growth hormone (oGH) on reproductive, hormonal and lactational responses of springlambing ewes. Each ewe received a daily subcutaneous injection of either 0, 5 or 10 mg oGH from day 11 through to day 20 post partum (day 0 = parturition). Treatment groups were subdivided into two pens (three ewes per pen) and food intake was monitored from day 1 through to day 20 post partum. On days 11 and 20 post partum, jugular blood samples were collected before and hourly for 8 h after treatment. Blood samples were also collected daily from day 10 through to day 21 post partum and on alternate days through to day 40 post partum. Milk production (oxytocin-induced hand milking) and fat and protein concentrations were determined 21 days post partum. Food intake did not differ before or during the treatment period (P > 0·05). Likewise, ewe and lamb weights were similar among treatment groups through to day 60 post partum (P > 0·05). Serum insulin did not differ before or after treatment on day 11 (P > 0·05); however, on day 20 before treatment, serum insulin was significantly higher in ewes receiving 5 (2·3 (s.e. 0·3) μg/I) and 10 (2·4 (s.e. 0·3) μg/1) mg oGH than in controls (1·2 (s.e. 0·3) μg/1) (P < 0·05). After treatment, no differences were detected in serum insulin among treatments on day 20 post partum (P > 0·05). Serum growth hormone (GH) was similar among groups before treatment on day 11 post partum; but by 8 h after treatment, serum GH was significantly elevated in ewes receiving 10 mg oGH (32·4 (s.e. 1·9) μg/1) compared with ewes receiving 5 (13·9 (s.e. 1·9) μg/1) or 0 (4·5 (s.e. 1·9) μg/1) mg oGH (P < 0·01). By 20 days after lambing, serum GH differed significantly among groups both before and after administration of exogenous oGH (P < 0·01). Ewes receiving 5 or 10 mg oGH produced 2·3 (s.e. 0·2) kg milk per day compared with 1·9 (s.e. 0·2) kg/day for controls (P < 0·10). Milk fat and protein concentrations did not differ significantly among treatments (P > 0·05), but total fat yield was higher in ewes receiving either dose of oGH (206 (s.e. 20) g/day) compared with control ewes (141 (s.e. 20) g/day) (P < 005). Serum progesterone remained less than 0·5 μg/1 in ewes through to day 40 post partum. A linear decrease was observed in interval from parturition to first observed oestrus as dosage of oGH increased (116, 108 and 102 (s.e. 6) days for ewes receiving 0, 5 and 10 mg oGH, respectively; P = 0·10). Administration of exogenous oGH to lactating. anoestrous ewes between days 11 and 20 post partum enhances milk production and may influence the interval to oestrus.

Carcass characteristics, and the rate and efficiency of lean gain of purebred British Friesian and Canadian Holstein steers and of crossbred steers out of British Friesian dams by Charolais, Hereford, Limousin, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One was similar to the commercial 18-month grass/cereal system (16-month) and the other to a commercial 2-year system (24-month). The cattle were serially slaughtered at three pre-determined fatness levels, estimated by the Scanogram ultrasonic machine. The trial extended over 4 years and involved a total of 650 cattle, 398 of which had their left sides separated into tissues. Breeds were compared at equal carcass subcutaneous fat proportion determined by visual carcass assessment (SFe). Data for the two production systems were analysed separately.

Sire breed differences were not detected in the regression on SFe for most characteristics (P > 0·05). Sire breeds differed in killing out and visual conformation score in both production systems (P < 0·001): Charolais and Limousin crosses had the highest values and purebred Canadian Holsteins the lowest. The overall range between sire breeds was 30 g carcass weight per kg live weight and five points on a 15-point conformation scale.

Breeds with the higher conformation scores generally had higher carcass lean proportions and higher lean: bone ratios. Canadian Holsteins had a 20 g/kg lower carcass lean proportion than the British Friesians (P < 0·05).

Breed crosses with larger adult body size tended to have higher lean tissue growth rates: the difference between mean values for Charolais crosses and Hereford crosses was 49 g/day (16-month) and 38 g/day (24-month). The lean tissue growth rates of the British Friesians and especially the Canadian Holsteins were low in relation to their adult body size.

Limousin and Charolais crosses had the highest efficiency of lean gain (g lean per kg digestible organic matter intake). These and the other crosses were significantly more efficient than the purebred Canadian Holsteins (P < 0·05). The overall range between breeds was 20 g/kg.

A series of experiments was conducted to examine the potential of using ammonia released from the hydrolysis of urea for alkali treatment of straw.

In an initial experiment (1) the effect on urea hydrolysis of adding either hydrochloric acid (HC1) or the surfactant alkyl phenyl ethylene oxide to straw of differing dry matter (DM) concentration was examined. The inclusion of HC1 or surfactant failed to improve the proportion of urea hydrolysed at straw DM concentrations of 450, 600 or 750 g/kg.

In experiment 2, straw was prepared and treated with urea, at a level of 20 (U2), 50 (U5), 70 (U7) g/kg straw DM and ammonia 40 (A4) g/kg straw DM to compare with untreated straw (S). Samples of the straws were milled and degradability at 60 h was estimated using the nylon bag technique. DM loss was significantly higher for all treated straws compared with untreated straw (P < 0·001). However, the proportion of added nitrogen retained from all urea treatments was less than 0·33 but U7 and U5 were approximately double that obtained from A4.

In experiment 3, 3-t batches of straw equivalent to treatments U2, U7, A4 and S were treated during September and later offered to steers in digestibility and food intake trials. Straws were ground through a 40-mm screen and offered to steers in digestibility stalls, in a balanced incomplete-block design. There were increases in the digestibility of DM (+0·08 g/kg), organic matter (+0·08 g/kg), and acid-detergent fibre (+0·09) of U7 and A4 straw compared with values for untreated straw (P < 0·01).

In a subsequent food intake trial treatment of long straw, with 20 g urea per kg straw DM (U2) failed to prevent moulding, however digestible organic matter intake (DOMI) of U7 and A4 straws increased by 0·42 and 0·27 kg/day respectively compared with intakes of untreated straw (P < 0·01). The application of 70 g urea per kg straw DM gave results comparable with treatment with 40 g ammonia per kg straw DM in improving digestibility of ground straw and the DOMI and preservation of long straw.

Two experiments have been carried out to examine the effects on the intake and performance of finishing beef cattle of supplementing grass silages (perennial ryegrass) of medium and high digestibility (MD and HD respectively) with either extracted soya-bean meal or fish meal. In each experiment, the two silages were supplemented with (1) barley (107 g crude protein (CP) per kg dry matter (DM)), (2) a mixture of barley and soya-bean meal (187 g CP per kg DM) and (3) a mixture of barley and fish meal (182 g CP per kg DM) in a 2 × 3 factorial design. The MD silages were supplemented with 4·5 kg concentrates per head daily in each experiment and the HD silages with 2·75 and 2·5 kg per head daily in experiments 1 and 2 respectively. In experiments 1 and 2 respectively the diets were offered to 72 and 60 castrated male cattle of late maturing breed type which were initially 455 (s.e. 3·6) and 484 (s.e. 3·2) kg live weight; the MD silages contained 642 and 652 g digestible organic matter (DOM) per kg DM, 119 and 114 g CP per kg DM, 72 and 68 g NH3N per kg total N, and the HD silages contained 698 and 724 g DOM per kg DM, 158 and 148 g CP per kg DM, 58 and 51 g NH3N per kg DM. In experiment 1 for the MD silages supplemented with concentrates 1, 2 and 3 and the HD silages supplemented with concentrates 1, 2 and 3 respectively silage DM intakes were 5·47, 5·29, 5·24, 6·86, 6·77 and 6·76 (s.e. 0·129) kg/day; carcass gains 0·76, 0·74, 0·72, 0·75, 0·75 and 0·79 (s.e. 0·011) kg/day; subcutaneous fat depths 6·8, 7·8, 8·0, 9·2, 7·2 and 7·1 (s.e. 0·59) mm and areas of m. longissimus 21·5, 21·7, 23·2, 21·5, 22·4 and 21·9 (s.e. 0·78) mm2/kg carcass weight. Corresponding values for experiment 2 were 6·12, 6·05, 6·18, 7·65, 7·53 and 7·36 (s.e. 0·235) kg/day; 0·82, 0·88, 0·83, 0·85, 0·89 and 0·83 (s.e. 0·042) kg/day; 8·1, 7·8, 7·5, 9·1, 8·3 and 7·4 (s.e. 0·77) mm; 22·8, 21·9, 21·9, 21·0, 21·9 and 21·7 (s.e. 0·79) mm2/kg carcass weight. It is concluded that supplementation of MD or HD grass silages with soya-bean or fish meals did not significantly affect the intake, performance or carcass fatness of finishing beef cattle although the carcasses of animals offered HD silage supplemented with barley tended to be fatter than those from the other treatments.

Observations were made of the behaviour of a home-range group of Scottish Blackface ewes. The group, including replacement ewe lambs, remained on the hill throughout winter and was offered supplemental feedblocks from December to April. Sheep were individually identified and data collected on ranging behaviour between 06.00 and 18.00 h GMT in autumn and winter. Additionally in winter, records were made of time spent eating from the feedblock or standing within 3 m of it.

Age was found to have a strong effect on time spent eating from the feedblock, with older ewes (4 years and over) eating more than younger animals. This was partly attributable to the ewe lambs forming peer groups in winter that were uninfluenced by the movements of mature ewes to the feedblock. Consequently, the majority (0·82) of ewe lambs did not eat feedblock in their first winter. Two- and 3-year-old ewes, although not eating significantly more often from the feedblock than ewe lambs, spent significantly more time standing within 3 m of it and were prevented from eating from it by the competitive behaviour of older ewes. The increased gregariousness of hill sheep in winter appears to be an important factor in preventing the younger ewes taking advantage of the continuous availability of feedblocks. The feedblocks were also found to reduce significantly the size of ewes' home ranges.

The results indicate that the social behaviour of hill sheep limits the use of feedblocks to the older and stronger animals in the group. In addition, feedblocks may reduce the utilization by sheep of available winter forage. Alternative strategies for more effective deployment of feedblocks are discussed.

The effect of castration on the cellular characteristics of dissected fat partitions was examined in 20 Dorset Horn rams and 20 Dorset Horn wethers. Cellular characteristics of dissected carcass (subcutaneous and intermuscular partitions) and non-carcass (kidney fat, omental and mesenteric partitions) fat partitions were examined in 13 mature animals, and the rate of change in adipocyte volume relative to the change in chemical-fat weight in that partition, examined in 27 immature animals.

Mature wethers had a greater concentration of chemical fat in the subcutaneous fat partition than mature rams (917 v. 885 g/kg, respectively). This, in combination with a greater weight of dissected subcutaneous fat, resulted in a greater weight of chemical fat in the subcutaneous partition of wethers compared with rams. Mature wethers had larger adipocytes than mature rams in all dissected fat partitions, with the largest increase in the subcutaneous and omental fat partitions. The increased adipocyte volume in the dissected fat partitions in mature wethers resulted in a smaller total estimated number of adipocytes in all carcass and non-carcass fat partitions compared with mature rams.

Standardized allometric coefficients for adipocyte volume relative to chemical-fat weight in that partition showed that increases in chemical-fat weight were due to a combination of hypertrophy and hyperplasia. In the omental and kidney fat partitions, hypertrophy contributed more to the increase in chemical-fat weight in wethers compared with rams.

Twenty-eight inbred (I, inbreeding coefficient 0-375 and 0-5) and 28 matching outbred (O) sheep, aged 26 weeks, were housed and allocated in equal number to two planes of nutrition, a high plane (H), involving ad libitum feeding on a pelleted diet, the other a low plane (L), restricted to an amount of the same diet which would maintain live weight. Food consumption, live weight, linear body dimensions and wool growth were recorded for 19 weeks, and for 4 weeks later in the experiment when L as well H animals received ad libitum feeding. Observations were also made for a final 9 weeks when the sheep were at grass.

The I sheep were substantially smaller in weight and body dimensions than the O sheep throughout the experiment. On ad libitum feeding, the I and O lambs grew in parallel and by the same amount per unit of food consumed. There was also no difference between I and O sheep in the amount of food per kg metabolic live weight (M0·73) required to maintain the live weight of the sheep on the restricted intake. The two types of sheep were therefore similar in efficiency.

During the 4-week period when L sheep were fed ad libitum they showed some compensatory growth relative to the H group, but I and O groups behaved similarly. At grass, a tendency for slightly faster growth continued for the O group formerly on a low plane, but there were no significant interactions between plane of nutrition (as originally allocated) and inbreeding.

Wool growth mirrored the results on body growth, with substantial effects of plane of nutrition, but wool growth per unit area of skin did not differ between I and O groups.