Data from 5270 lactation records of 1380 cows sired by 132 bulls and recorded from 1962 to 1977 were analysed. Statistical analyses, using least squares and maximum likelihood methods, showed significant effects for genetic group, age of cow, month and year of calving, and lactation length. Overall mean milk yield was 2780 kg (CV = 0·31) with mean lactation length of 281 days. Maximum production occurred in the fifth lactation (104 or 105 months of age at calving) with a yield of 1·3 times that of the first lactation. Repeatability estimated by intraclass correlation was 0·40 (s.e. 0·03). Heritability estimated from paternal half-sib correlation was 0·16 (s.e. 0·06). Overall results were very similar to those obtained from research with European breeds in temperate areas.

A study of 1514 lactations that occurred between 1977 and 1982 in 790 Friesian, Ayrshire and Holstein crossbred cows was undertaken. One thousand and eighty-four of these lactations were used to consider the association between the occurrence of clinical mastitis and changes in milk yield, and to illustrate a technique that enables the previous lactation history of a cow to be used for estimating changes associated with the disease.

The lactation curves were described using the model y(n) = anbe−cn from which values for peak yield, persistency, rate of decline at week 25, and recorded and extrapolated 305-day yield were calculated. A significant correlation between successive lactations of the same animal was observed for each of these variables. Pairs of successive lactations free from clinical mastitis were then compared by regression analysis with lactations in which the preceding lactation was free from the disease whilst the second lactation of the pair was infected.

Significant reductions in peak yield, recorded and extrapolated 305-day yield were found when mastitis occurred before the week of peak yield. A reduction in recorded 305-day yield was also observed when the disease occurred between peak and 10 weeks after peak. Mastitis later in the lactation had no significant effect.

The mean reduction in recorded 305-day yield of 540 kg when mastitis occurred before peak for a cow with a mean yield of 4830 kg, was higher than previous estimates. No evidence of recovery was observed in subsequent lactations that were free of clinical infection, indicating that once a cow has contracted mastitis it may not achieve its full milk-yield potential in the next lactation.

Comparative slaughter was used to assess the body composition of Shorthorn-Hereford (SH), Africander cross (A×), Brahman cross (B×), and late castrated Brahman cross (B×(late)) steers of the F, generation with respect to their yield of carcass, gross carcass composition and offal composition. Animals were slaughtered at pre-determined weights of 315, 355, 399, 449 and 505 kg.

The B× animals had the highest carcass yield (expressed either as dressed carcass weight at the same fasted body weight or at the same empty body weight), while the A×, B×(late) and SH animals had similar carcass yield. Within a breed, rate of growth affected carcass yield, with faster growing animals having the lower carcass yield, particularly with respect to fasted body weight.

The breeds were different in carcass composition but this was dependent on both size and growth rate. Brahman cross animals had a lower proportion of bone than A× and SH animals, particularly at the higher body weights. Faster growing animals tended to contain more muscle and bone and less fat, with the exception of the SH animals.

The breeds were also significantly different in the composition of the offal components. A× were notable for high head weights and low tail weights, B× having high blood weights and low total gut tissue weights, and Bx(late) having high hide weights and low abdominal fat weights.

Rate of growth had some effect on offal composition, the general trend being that the faster growing animals were characterized by a lower proportion of heart, blood and pancreas. However there was also evidence that the rate of growth differentially affected the offal composition with respect to breeds. This effect mainly arose because the faster growing B×(late) animals had lower weights of abdominal fat. Within the other breeds, the opposite trend was observed.

The response to avoparcin in cattle diets was examined in two trials. In trial 1 compound diets containing 0, 15, 30 or 60 mg/kg avoparcin were given to 32 British Friesian bulls from 231 kg body weight to slaughter at a mean body weight of 422 kg. In trial 2 diets containing 0, 15, 30 or 45 mg/kg avoparcin and composed of equal portions of dry matter (DM) from grass silage and compound food were given to 64 British Friesian steers over a 12-week period from 258 kg body weight to 340 kg body weight.

There was a significant growth response of 120 g per head daily in trial 1 and 80 g per head daily in trial 2 to inclusion of 15 mg/kg avoparcin in the diet compared to the control diet without avoparcin. Food conversion efficiency of diets with 15 mg/kg avoparcin was improved by a reduction of 0·52 and 0·61 kg DM per kg live-weight gain respectively in the two trials. There was no further growth response or improvement in food conversion with higher levels of avoparcin with the diets used, the type of cattle employed and the management which applied in these trials. These findings are in good agreement with those previously published.

Two experiments were conducted to investigate the effect of the composition and particle size of the basal diet on the outflow of chromium-treated fish meal from the rumen of lactating British Friesian dairy cows, using Cr-concentrations in faeces. A 4 × 4 Latin square design was used and the cows were fed at twice the estimated energy requirements for maintenance in two equal meals.

Fractional outflow rates per h were, 0·079, 0·088, 0·086 and 0·064 for the 1·00 hay: 0·00 concentrate, 0·75 hay: 0·25 concentrate, 0·50 hay: 0·50 concentrate and 0·25 hay: 0·75 concentrate respectively. The difference between 0·75 and 0·50 concentrate was significant (P < 0·05).

Grinding of long dried grass through 40 or 20 mm screens had no significant effect on the outflow of Cr-treated fish meal from the rumen, however fine grinding (5 mm) and pelleting significantly reduced the outflow from rumen (P < 0·05). Fractional outflow rates per h were 0·080, 0·086, 0·088 and 0·047 for the long, 40, 20 mm and the 5 mm and pelleted diets respectively.

The relative importance of the breed of lamb and the breed of dam in determining the copper status of the lamb until 24 weeks of age was investigated by transferring embryos within and reciprocally between Scottish Blackface and Welsh Mountain ewes. A diet low in Cu (2·4 mg/kg dry matter (DM) was fed both to the ewes from mating onward and subsequently to their lambs.

At birth, lambs with Welsh dams had greater concentrations of Cu in their livers than lambs with Blackface dams. This difference, although reduced, still remained at 9 weeks of age (weaning), when lambs with Welsh dams also had greater concentrations of Cu in plasma.

By 24 weeks of age, Welsh lambs, irrespective of their dams' breed, had greater concentrations of Cu in both liver and plasma than Blackface lambs, although the average Cu concentration in the liver was below 10 mg/kg DM in both breeds.

Results are also given for concentrations of Cu in kidney, brain and milk.

The experiment suggests the importance of maternal breed in determining the susceptibility, both of the foetus and of the young lamb to problems associated with Cu deficiency.

The relative importance of the breed of dam and the breed of lamb in determining the copper status of the lamb was investigated by transferring embryos reciprocally between Scottish Blackface and Welsh Mountain ewes. A diet moderately high in Cu (8 mg/kg dry matter (DM)) was fed both to the ewes from mating onward and subsequently to their lambs.

At birth, 9 and 24 weeks of age the concentration of Cu in the liver of lambs was the same for the two maternal breeds but within breed groups there was correspondence between full sibs when they were born to the same dam.

By 9 weeks and at 24 weeks of age Welsh lambs, irrespective of their dam's breed, had greater concentrations of Cu in liver than Blackface lambs. The average concentration at 9 weeks was 190 and 130 mg/kg DM respectively for the two breeds of lamb.

Results are also given for concentrations of Cu in plasma, kidney, brain, milk and faeces.

The results differ from those found in the previous paper under a regime of low dietary Cu where the maternal breed affected concentration of Cu in the liver of lambs up to 9 weeks of age.

An experiment was designed to compare saline, prostaglandin F2α tham salt and progestagen pessaries as agents for oestrous synchronization in mature cyclic ewes maintained under normal husbandry conditions. The effect of these agents on ewe fertility and lambing performance was also assessed.

One hundred and sixty Clun Forest ewes were allocated to one of four equal-sized treatment groups and received either two injections of saline given 9 days apart (group A), two injections of 10 mg (group C) or 20 mg (group D) postaglandin F2α tham salt given 9 days apart, or progestagen pessaries left in situ for 12 days (group B). Oestrous response, fertility and lambing performance were monitored thereafter. Oestrus occurred within 3 days of the end of treatment in 0·28, 0·98, 0·58 and 0·83 of ewes in groups A to D respectively, with return rates after a single mating of 0·15, 0·13, 0·25 and 0·33 respectively. There was no difference between treatments in lambing performance. These results indicate that two injections of either 10 or 20 mg prostaglandin F2α given 9 days apart is a less effective means of synchronizing oestrus in sheep than progestagen pessaries.

In two experiments over 2 years, 181 Scottish Blackface ewes were differentially group-fed indoors to achieve moderately-good (score 2·5), moderate (score 2) or poor (score 1·5) body condition. Over 5 weeks prior to mating, ewes in moderately-good condition were either maintained or brought down to moderate condition by restricted feeding and ewes in moderate and poor condition were raised, respectively, to moderately-good and moderate condition by a high level of feeding. After mating, ewes were maintained in condition until slaughtered for a count of corpora lutea relating to first service. Ovulation rate was positively and significantly related to the level of pre-mating food intake at the moderate level of condition but not significantly so at the moderately-good level. It is postulated that ewes of this breed are more sensitive to the level of pre-mating food intake when in moderate condition at mating than they are when condition has risen to a moderately-good level.

A contemporary comparison of crossbred ewes from five crossing sire breeds was made on a research farm from 1976 to 1981. The breeds involved were the traditional Border Leicester, three imported breeds — the East Friesian, the Oldenburg and the Texel, and a new prolific composite breed — the Cambridge. Rams from these breeds were group mated (2 to 3 rams per breed per year) to Scottish Blackface ewes on an upland farm in Scotland. Crossbred ewes derived from these matings were compared over three lamb crops on a lowland farm in England. The ewes were run together with the same husbandry conditions for all types. Results were available on some 120 to 150 ewes (300 to 450 lambings) per crossbred type. The Oldenburg and Texel crossbred ewes were appreciably poorer in most aspects of lowland lamb production. The Cambridge crosses were prolific but had high lamb mortality and lower litter weights at weaning than the traditional Border Leicester crosses. The East Friesian crosses were appreciably superior in several production traits. These results were combined with those from three other trials, involving crosses from the Bluefaced Leicester and Animal Breeding Research Organisation Damline to provide a ranking for UK crossing sire breeds.

Maturing patterns of carcass muscle, fat and bone and of body organs were established relative to live weight, using data from 20 Dorset Horn rams and 20 Dorset Horn wethers. The sheep were fed a pelleted ration from soon after weaning and individual sheep of both groups slaughtered at 6-kg increments in live weight from 18 kg to maturity at approx. 100 and 96 kg for the rams and wethers, respectively. This small difference in mature weight was mostly due to the weight of the testes and the increased weight of the head in mature rams.

As proportions of live weight, the mature rams had more carcass muscle and bone and less carcass fat than the mature wethers. In the mature animals the body organs in general comprised similar proportions of live weight in the two groups. However the head, hide and blood were proportionately heavier in the mature rams. The liver and alimentary tract were heavier in the mature wethers.

The maturing patterns for the three carcass tissues were not different for the two groups. However, many of the body organs matured on different patterns in the rams and wethers.

As the mature live weights and the maturing patterns for carcass tissues and some body organs were not different for the two groups, comparisons of the proportions of these tissues in rams and wethers would yield similar conclusions on an equal weight basis, as on the basis of the same proportion of maturity. However, comparisons of the proportions comprised by some body organs need to take account of different maturing patterns, as comparisons at different stages of maturity will each give different answers.

Maturity patterns have been established for 93 individual carcass muscles and nine standard muscle groups using dissection data from 20 Dorset Horn rams and 20 Dorset Horn wethers. A very high proportion, 81/93, of the individual muscles and all the muscle groups had maturity patterns which were not different for the rams and wethers.

Maturity patterns of some muscle groups varied from those previously demonstrated in Merino rams, in that the abdominal wall group was later maturing and the neck to forelimb and neck and thorax groups were earlier maturing in the Dorset Horns.

Comparison of the distribution of muscle weight of the Dorset Horn rams and wethers at the mean total muscle weight resulted in different conclusions to comparison at the mean proportion of maturity. It is concluded that comparisons of muscle weight distribution of entire and castrated male sheep, in which mature muscle weight varies, will be most meaningful if carried out at the same proportion of maturity, since comparisons at the same weight of total muscle will embrace components of difference due to stage of maturity.

In a 2 × 2 factorial experiment, the effect of implants of the growth promoter Zeranol, with and without supplementary food, on the growth rate, blood metabolite and hormone profiles of lambs finished at pasture was examined. For lambs fed no supplement, Zeranol implants increased growth rates from 166 to 185 g/day (s.e. of difference = 11·4) whereas for animals fed supplement the response to Zeranol was much greater, the growth rates being 167 and 234 g/day (s.e. of difference = 12·8). Supplement given to lambs not treated with Zeranol replaced a proportion of the herbage intake while, in lambs given supplement and treated with Zeranol, herbage intake was greatly increased (P < 0·001). Plasma glucose and urea concentrations were not affected by treatment but non-esterified fatty acids (NEFA) were depressed and albumin levels increased by Zeranol implants, while supplementary food caused reductions in plasma NEFA and urea concentrations. It is suggested that Zeranol treatment and supplementary food acted synergistically through changes in insulin and growth hormone concentrations to induce a much larger increase in growth rate in the treated animals given supplementary food than in those given either Zeranol or supplement alone. The response to Zeranol may also have been altered by differences in thyroid hormone status associated with supplementary food.

Forty Landrace × (Landrace × Large White) gilts were randomly assigned at 70 days of age to each of two rearing treatments. The two treatments were: (1) gilts reared with gilts but kept in complete isolation from other pigs, and (2) gilts reared with visual, aural, olfactory and limited tactile contact with a mature boar. At 160 days of age, all gilts were subjected to a pen change and housed adjacent to either a mature boar for the first time, or to a different mature boar from that with which they had contact during the rearing phase. In addition, gilts were exposed to a mature, vasectomized boar for 30 min each day. They were served twice at second oestrus and the reproductive tracts were examined at slaughter 21 days later to determine ovulation rate and embryo survival. The presence of a mature male during the rearing phase had no effect on the attainment of puberty. There were no significant differences between treatments 1 and 2 for age at puberty (168·1 and 166·9 days respectively), weight at puberty (74·0 and 75·7 kg respectively) and the interval from movement and boar introduction to puberty (8·3 and 7·4 days respectively). The rearing treatments also had no effect on ovulation rate or embryo survival.

In two separate experiments pigs were weaned at 14 or 28 days and heat production was determined in an open-circuit respiration chamber at temperatures above and below the lower critical temperature (Tcl) at intervals during the post-weaning period.

With 14-day weaned pigs the mean 24 h heat production above Tc1 averaged 267, 328, 474 and 554 kJ/h per m2 at 3, 9, 15 and 21 days post weaning respectively. The mean thermal conductance (H/AT, kJ/h per m2 per °ΔT, where H is total heat production, m2 is the surface area calculated as 0·097 M kg0·633 and °Δ is the difference between rectal temperature, taken at 39°, and air temperature) below TC1 was calculated as 20·5, 20·1, 23·1 and 24·2 at 17, 23, 29 and 35 days of age respectively and the corresponding values for Tc1 were 25·9, 23·0, 18·4 and 16·0°C.

With 28-day weaned pigs the mean 24 h heat production above Tc1 averaged 280, 361 and 445 kJ/h per m2 at 3, 9 and 15 days post weaning. The calculated values for H/ΔT were 19·7, 20·8 and 21·6 and the corresponding values of Tcl were 24·8, 21·7, and 18·8°C at 31, 37 and 43 days of age respectively.

The results are discussed in relation to previous studies on 10-day and 28-day weaned pigs and in relation to the practical implications for pigs weaned into controlled-environment accommodation.

In two experiments, the first with 96 pigs from 5 weeks of age and the second with 384 pigs from 3 weeks of age, high nutrient dense diets (HND) or conventional diets (CONV) were given with (50 g/kg diet) or without fish meal, up to slaughter at 90 kg live weight. Diets were unmedicated. In both experiments pigs were given food according to scales which equalized digestible energy intakes for the HND and the CONV diets. In experiment 1 pigs were individually fed; in experiment 2 group feeding was practised with pens of 16 pigs either floor or trough fed.

There was no mortality in experiment 1, but the mortality was high in experiment 2, particularly amongst those pigs receiving the CONV diet without fish meal. In experiment 1, in the first 56 days, inclusion of fish meal in the CONV and HND diets significantly improved growth rate but food conversion efficiency was significantly improved in the CONV diet only. Overall, up to slaughter, growth rate and food conversion efficiency were significantly poorer in pigs given the CONV diet without fish meal (cf. the three other diets) but the HND diets were significantly better than the CONV diet with fish meal. In experiment 2, overall there were no significant differences in performance between floor- and trough- feeding methods, CONV diets without fish meal gave significantly poorer growth rates in the first 56 days and overall than the other three diets, between which there were no significant differences. In both periods, for food conversion efficiency, fish meal inclusion was without significant effect in the HND diets but significantly improved the CONV diets, both of which were significantly inferior to the HND diets.

Effects of the period of pre-slaughter lairage and diet on responses to post-mortem electrical stimulation (ES) were observed in 113 bulls and 18 cows. The efficiency of ES was assessed by the rate of the decrease of muscle pH. Stimulation was made at 80 V for 45 s. ES significantly decreased pH values at 1 h after slaughter. The effect was greater for animals on a normal diet than for those on a reduced diet. ES was also more effective for animals killed within 2 h after transportation to the meat processing plant than for animals slaughtered 24 h after transportation. There were no significant differences in the effect of ES between sexes. The basic requirement for effective ES is a good condition of animals at slaughter.

Mature Angus (A), Hereford (H) and Simmental (S) cows (16 each) that had been randomly assigned and fed a maize silage-based diet at different levels of intake during lactation were selected.

Lean and fat A, H and S cows were fed the maize silage-based diet individually to provide metabolizable energy (ME) intakes of 542, 506; 476, 437; and 624, 597 kj/kg0.75 per day respectively for 84 days. Daily weight gains of lean cows were greater than those of fat cows (0·40 v. 0·11 kg/day) even though daily ME intakes were less (55·2 v. 62·4 MJ/day). Theoretical estimates of ME requirements for maintenance were less for lean than for fat cows, and maintenance of A and H cows tended to be less than those of S cows.

These results suggest that cow maintenance requirements increased in association with fatness that resulted from the previously imposed nutritional regimes and tended to differ among cow breeds.

The occurrence of melanin pigmented wool fibres in the skirted white fleece wool from 1-year-old Corriedale ewes, having either least (group 1), most (group 3) or an intermediate level (group 2) of black nose skin pigmentation, was investigated. Thirteen of the 87 fleeces analysed had the equivalent of 10 to 389 isolated pigmented fibres per 100 g of scoured wool. The mean diameter of the pigmented fibres was similar to that of the fleece specimens analysed and they occurred singly or in small groups within individual staples. Large numbers of isolated pigmented fibres in fleeces were widely distributed, and constitute a serious problem of identification by visual inspection. Fibre darkness and the number of fleeces found with pigmented wool fibres were two measurements which showed a significant association (P < 0·001 and P < 0·05, respectively) with nose skin pigment group. With one exception from group 2 the results support the suggestion that the usual selection for dark nose skin in this breed may be antagonistic to selection for a white fleece. The pigmented lengths of fibres were found to be independent of nose skin pigment group.