Twenty-four Suffolk cross lambs, the progeny of three sires, were reared artificially under standardized conditions and slaughtered at 40 kg live weight.

The tritiated water technique as a means of estimating carcass composition in vivo was evaluated and carcass composition was established using both physical dissection and chemical analysis. Live-weight gain of the lambs from weaning was 389 g/day but the carcasses were lean. Dissected fat, lean and bone percentages were 20·5, 58·4 and 18·9 respectively. Differences between progeny groups were non-significant.

Fat percentage was the most variable body component, although lower than in many other reported studies. The CV for dissected fat was 15·2% and for chemically analysed fat 15·9%. The correlation between estimates for the two methods was high (r = 0·90) despite there being quantities of other constituents in the dissected fat. It was not possible to demonstrate any relationship between reciprocal of tritiated water count and fat percentage or any other measurement of the composition of the whole carcass. Other measurements made on the live animal, such as fasted live weight and ultrasonic determinations of fat thickness and area of m. longissimus dor si were also not related to carcass composition.

It is concluded that neither tritiated water count nor any of the other measurements of the live animal would be sufficiently accurate to be of value in performance testing.

The possible use of a pig's reaction to the anaesthetic halothane as a field test for Porcine Stress Syndrome in genetic improvement pro-grammes was investigated. A standard 3-min halothane test gave incidences of positive reaction of 20% in a composite Pietrain/Hampshire line, 5% in Norwegian Landrace, 1% in Hampshires and zero in Durocs, Large Whites and N. American Yorkshires. In the Pietrain/Hampshire population, two generations oftwo-way selection on the test gave a divergence in incidence of positive reaction of 85%, and the frequencies of affected progeny supported the hypothesis of monogenic recessive inheritance. From second tests made 20 days after the first, the probability of misclassifying a pig's reaction on one test was 5 ± 1%. Positive reactors had significantly shorter and leaner carcasses, fewer pigs born alive, poorer meat quality, higher mortality and greater plasma creatine phosphokinase activity than negative reactors.

Electrical conductivity was measured during the oestrous cycle of cows with electrodes implanted in the vaginal wall. Conductivity was considerably higher during oestrus than during the preceding or following cycle stage. Conductivity was also high in the fresh surgical wound, whereas the healing process was accompanied by a decrease.

Between July 1971 and June 1973 a flock of between 60 and 100 Finn-Dorset ewes were mated at 6-monthly intervals in July and January each year following oestrus synchronization. The conception rates at each mating were:

July 1971—51 from 67 mated (76%) using hand-mating with a follow-up of paddock mating (1 ram: 9 ewes);

January 1972—6 from 63 (10%) using artificial insemination only; July 1972—98 from 102 (97%) using paddock mating (1 ram: 10 ewes);

January 1973—28 from 80 (35%) using pen mating (1 ram: 10 ewes).

Satisfactory breeding performance was achieved at the July matings in both years, resulting in production of lambs for the early spring market. The very poor results of the January 1972 mating were associated with the problems of artificial insemination in the recently lambed ewe. The conception rate achieved at the January 1973 mating provided a clearer indication of the difficulty of achieving satisfactory remating within 40 days post partum, which is necessary to achieve a true 6-monthly lambing pattern.

The early initiation of the synchronization technique (7 days post partum) followed by mating only at the second oestrus in January 1973 appeared to offer some encouragement. While a number (48) of ewes were induced to lamb at least once at 6-monthly intervals, only one ewe lambed four times in 24 months.

An average of 60 Rambouillet and 60 Suffolk ewes was maintained under an intensive management system to lamb about every 7 months. Decreased daylength was used for oestrus induction in normally anoestrous periods. The experiment lasted 3·7 years, during which time six lamb crops were produced, three of them as a result of out-of-season mating. Ewes of each breed were subdivided into three experimental groups and each breed-group was maintained under one of three different light treatments before and during out-of-season mating. Imposed Treatment 1 consisted of a pre-mating period under natural daylight followed by a mating period of short daylength (8 h/day). Ewes under imposed Treatments 2 and 3 were exposed to 16 h of light during the pre-mating period and to 8 h of daylight during the mating period. This did not affect conception significantly in the Rambouillet but it did in the Suffolk. Different intensities and wavelengths of light during the long daylight period (16 h/day) were used in Treatments 2 and 3 but did not cause different responses.

In Rambouillet ewes the first mating (out-of-season) gave 73% conception. It was followed by two in-season matings with 72 and 85% conceptions. The last three matings (out-of-season, in-season, out-of-season) resulted in 57, 42, and 58% conceptions. In the Suffolk ewes, the conceptions were 30, 88, 77, 3, 77, and 10% in the same order as those for Rambouillet. The average production ofRambouil-lets on the three treatments was 166 lambs per 100 ewes per year (165, 177, 157) whereas Suffolks produced 132 lambs (120, 143, 135). Control Rambouillet and Suffolk ewes maintained under natural daylight year-round produced 139 and 117 lambs.

Two hundred and thirteen Suffolk × (Cadzow Improver × Scottish Blackface) young female sheep were mated either after the natural occurrence of puberty or at 140, 182 and 224 days of age in Year 1 and 140 and 182 days of age in Year 2 after treatment with progestagen (MAP) and 750 i.u. PMS; 90 to 100% of sheep ovulated after hormone treatment. Few sheep were found with embryos or live lambs in Year 1, possibly because of inadequacies in artificial insemination. In Year 2, after natural mating, the incidences of cleaved ova, live embryos 26 days after mating and live lambs born were 82, 33 and 23% respectively for sheep mated at 140 days; 100, 31 and 23% respectively for sheep mated at 182 days; and 100, 62 and 31% respectively for sheep mated after puberty. The occurrence of a second post-treatment ovulation in sheep without embryos at 26 days increased with age at treatment.

With deep frozen bull semen processed in an egg yolk – milk diluent and stored in plastic straws at — 196°C, a lowering of the dose rate from 25 million (3824 inseminations) to 12·5 million total sperm per insemination (3900 inseminations) resulted in a decline in conception rate (CR = 49-day non-return rate) of 6·5 % (60·1 v. 53·6). Development of a processing technique which allowed sperm to be stored at — 196°C at concentrations of 450 or 100 million sperm per ml prior to subsequent rapid thawing and redilution (RDF) allowed dose rates to be reduced to around 5 million total sperm per insemination without any significant reduction in CR. The re-diluted semen was used for inseminations made from 4 to 8 h after thawing and redilution. The use of RDF procedure could reduce semen storage costs, increase the number of inseminations per sire, and has potential application in oestrus synchronization programmes or in countries with developing insemination programmes.

Fifty-six young female Suffolk × (Cadzow Improver × Scottish Blackface) sheep were used in a 2 × 2 × 2 factorial experiment investigating: (i) change in daylength (constant C v. reduced R), (ii) level of feeding (to appetite, H, v. 75% of that allowance, L), and (iii) age at hormone treatment (20 v. 28 weeks). At the appropriate age, the sheep were treated with a progestagen (MAP) and 750 i.u. PMS, inseminated, and slaughtered 26 days later. In a second experiment, change in daylength and level of feeding only were investigated. Hormone treatment took place at 20 weeks of age. In both years, all sheep showed oestrous behaviour and ovulated. A greater number of sheep yielded embryos on C than on R treatments (P<0·05 in Year 2), but no effect of feed level or age was found. Of those sheep not yielding embryos, a greater number on R than on C treatments showed a second ovulation at 20 weeks but not at 28 weeks.

Direct injection of slurry into soil was tested as a means of avoiding the rejection of herbage by dairy cattle when slurry is spread on the surface. British Friesian dairy cows grazed paddocks that had been injected with slurry at 25 t/ha ( = 60 kg N/ha) 9 weeks previously, had slurry spread on the surface at the same rate and time, or received 60 kg N/ha as ammonium nitrate. There was less herbage dry matter available per cow on paddocks with slurry than on the control. The cattle on the surface slurry treatment consumed approximately 30% less herbage dry matter than those on the other two treatments.

Cattle on pasture with surface-spread slurry spent longer grazing, walked about more during grazing, appeared to take smaller bites of grass, engaged in competitive interactions more frequently and drank more often. Behaviour was less affected on injected paddocks. In a second experiment, paddocks which either received inorganic fertilizer throughout the season, or were injected at 25 t/ha in June and August instead of the fertilizer application, were grazed by the herd at intervals during the season. Injecting slurry had no effect on herbage intake or animal behaviour.

Karakul, Mehraban, Naeini and Bakhtiari sheep were checked twice a day for oestrus using aproned rams and were laparotomized within 5 to 16 h of the end of every second oestrous period. Oestrus was observed for 12 monthly periods commencing on 21 April.

The Mehraban breed with 1 -6 oestrous periods per month was less seasonal in its breeding activity (P<0·01) than the other breeds. Four-year-old ewes were more sexually active (P<0·01) than 3-year-old ewes (1·48 v. 1·28 oestrous periods per month). Seasonal variation in the sexual activity of the ewes was observed (P<001); the peak of activity in July to January was followed by a steady decline in February and March to a low in April and May, and then a steep recovery phase in June. There was only limited sexual activity for at least 4 months (March to June).

The overall mean cycle length was 17·8 days (14 to 23 days), and the means for the four breeds were 17·6, 17·8, 17·8 and 17·9. The oestrous cycle was longer (P<0·05) during the period from December t o February than during that from June to August.

The overall mean duration of the oestrous period was 36·9 h and the means for the four breeds were 35·2, 38·0, 37·4 and 37·1 h, respectively (P<0·05). The duration showed some monthly variation (P<0·01) but did not follow a special seasonal pattern. The ovulation rates for the four breeds were 1·07, 1·13,0·94 and 0·95 respectively, (P<0·01). There was a non-significant decline in the mean ovulation rate from March to June. Right ovaries were more active than left ovaries as judged by the observation of a higher average number of corpora lutea per ewe per laparotomy (0·58 v. 0·43, P<001).

The pre-weaning records (birth weight, weaning weight and gain from birth to weaning) of 291 male and female lambs and the post-weaning records (body weight, feedlot gain and food conversion) of 136 male lambs were used to study relationships between different traits. The lambs were derived from three fat-tailed Iranian sheep breeds (Karakul, Mehraban and Naeini) and their crosses with Corriedale and Targhee rams. All lambs were weaned at 75 + 5 days of age and the males were fed in a feedlot for 100 days after weaning. Feedlot measurements were taken at 20-day intervals.

Weaning weight and pre-weaning average daily gain showed positive and significant associations with birth weight. Birth weight, weaning weight and gain from birth to weaning were positively associated with body weight at subsequent ages in feedlot as well as with final weight (P<0·01). Birth weight, weaning weight and pre-weaning average daily gain were positively and significantly associated with total feedlot gain.

Of the different traits, total gain during the first 20 days in feedlot (adjust period) had the lowest and total gain during the second 20 days had the highest association with total feedlot daily gain. There was no evidence that the heavier lambs at weaning and those showing high growth rate before weaning, were more efficient in the feedlot. Gain during the second 20-day period in the feedlot had a significant negative association with the total food conversion (unit food/unit gain) and therefore was a good predictor for food conversion.

When the feedlot period was divided into two 40-day periods, it was found that gain during both had a significant negative association with the corresponding food conversion. A similar association was observed between total feedlot gain and food conversion, indicating that the rate and efficiency of gain improved simultaneously.

The coat of 16 Wiltshire × Wensleydale lambs was investigated and all were woolly, with no halo hairs on the back. The bulk of the coat consisted of curly-tip fibres, and most lambs had Valley (8) or Plain (6) fibre-type arrays, only two having Ravine arrays.

There was little difference in diameter between the primary and secondary fibres in the skin, and some evidence of ‘checking’ in the central primaries. The secondary/primary follicle ratio of 4·26 compared with a mid-parent value of 4·5. There was less latticed medullation in the crossbreds than in the Wiltshire.

The adult fleeces were visually similar to those of the Wensleydale and were intermediate in weight and staple length between the parent breeds. These findings could have practical application in the improvement of ‘hair’ sheep, in that a first cross with the Wensleydale would have a fleece of medium wool lacking hair or kemp.

1. British Friesian (F) and Hereford × British Friesian (H × F) male calves were raised from about 3 days to 8 weeks of age at air temperatures of 5, 10 or 15°C. They were given a milk replacer diet supplying 950 kJ metabolizable energy/kg M0·75.24 h.

2. There was no effect of environmental temperature on weight gain in calves of either type.

3. Total heat loss measured in a direct calorimeter, increased by about 5 kJ/kg M0·75.24 h per °C fall in air temperature. It was the same whether calves were penned singly or in pairs. Heat loss from F calves was slightly, but not significantly, greater at all temperatures than from H × F calves.

4. The proportion of heat lost by evaporation (a measure of environmental warmth) increased with increasing air temperature and was greater for H × F than for F calves at 15°C.

5. Tissue insulation and external insulation values were similar for H × F and F calves. The calculated lower critical temperatures of the F and H × F calves were 10 and 8°C respectively.

6. The results are discussed in relation to the housing requirements of young calves.

Thirty-five Assaf intact male lambs were divided into three groups and offered an all-concentrate pelleted diet based on barley and maize and supplemented with either toasted soya bean meal, herring meal or toasted soya bean meal plus methionine to contain 20% crude protein. The live-weight gains to a slaughter weight of 57 kg were 425, 440 and 394 g/day, and the feed conversion ratios were 3·12, 3·07 and 3·38 kg dry matter/kg gain, respectively. It is concluded that, with toasted soya bean meal as the protein supplement, it is possible to obtain high growth rates that do not diifer significantly from those obtained with herring meal.

Twenty-one mature ewes of each of two breeds, the Scottish Black-face and the Welsh Mountain, were allocated in equal numbers to three diets based on a complete cobbed feed with a 0, 5 and 15% inclusion of dried seaweed meal (Ascophyllum nodosum). All diets were made up to a Cu content of approximately 30 mg/kg by adding CuSO4 to the mix. Sheep were housed and fed individually for 15 weeks.

There was a significant breed difference in the Cu level of the liver dry matter; the Welsh increased by 316 mg/kg compared with 240 mg/kg in the Blackface and the amount of Cu accumulated in the liver per kg feed consumed was 0·66 mg in the Welsh and 0·46 in the Blackface. Diets also had a significant effect; the Cu levels in liver dry matter rose by 323, 293 and 220 mg/kg for the 0, 5 and 15% seaweed diets respectively and the Cu stored per kg feed consumed was 0·66, 0·61 and 0·41 mg respectively. There was no corresponding effect of diet on plasma Cu level, but there was a breed difference with Welsh higher than Blackface. Cu level in kidney dry matter showed a breed-by-diet interaction. Total food consumption did not differ among the treatments, and live-weight and carcass-weight data suggested no adverse effects from the inclusion of seaweed meal in the diet.

Newborn lambs were separated from their dams before they had an opportunity to suck. They were given bovine colostrum in a single feed and thereafter fed on a milk substitute. Their weight gain compared favourably with that of lambs fed on ovine colostrum followed by milk substitute or suckled naturally. It was concluded that bovine colostrum can be used successfully as an alternative source of immunoglobulin for rearing lambs.

The results of studies into penial, scrotal and testicular development of Icelandic male lambs indicate relatively early attainment of physiological puberty. This stage of sexual maturity is generally reached by 4 months of age, with marked variation in both puberal age and body weight. Testicular and epididymal weights were more closely associated with body and carcass weights than with age of the lamb. It is a common practice to use Icelandic male lambs for breeding at 7 months of age.

Trials were carried out over two winters to compare red clover and grass silage for cattle finishing.

The silages were mixed to give rations containing 0,25,50,75 or 100% red clover dry-matter and were offered ad libitum to individually fed British Friesian-type steers. Significant differences in dry-matter intake occurred but the effect of silage type on animal performance was not significant. Barley supplementation had a significant effect on both total dry-matter intake and daily live-weight gain.

The voluntary intake of two hays and one dried grass by 48 mature non-pregnant Blackface ewes was measured for 33 weeks. The apparent dry-matter digestibility coefficients of the diets in vitro were 59, 61 and 77% respectively for the hays and the dried grass. At the end of the first phase of the experiment each group of 16 ewes was split into two subgroups of five animals, each of which was subsequently given one of the other diets, and one subgroup of six animals which remained on the same diet. Food intake was measured for a further 8 weeks. Body fat was estimated at intervals from tritiated water space.

The amount of variation in voluntary food intake that could be attributed to variation in live weight and fatness of the animals and in apparent dry-matter digestibility and cell wall constituents of the diet was calculated for various periods.

The range of live weight and fatness increased during the experiment. Initially, and after the change in diets, variation in apparent dry-matter digestibility had an important positive effect on intake, but at the end of the 33-week phase its influence was negligible or, when fat weight was not considered, negative. The negative effect of fat weight on intake increased during the experiment.

Within individual diets during short periods of time (1 to 5 weeks) the highest proportions of the variation in intake that could be attributed to variation in live weight and fatness of the ewes were 50, 94 and 65% respectively for the hays and the dried grass. Taking all three diets together all the variables considered could explain 75% of the variation for a few weeks at a time, but for longer periods seasonal influences, and other factors not included among the independent variables, probably operated.

Eight British Friesian bulls and eight steers were compared in terms of performance and levels of metabolites and hormones in circulating blood. Under conditions of generous nutrition the bulls grew significantly more quickly, exhibited a superior feed conversion efficiency and had lower levels of serum albumin and plasma urea and higher levels of serum growth hormone and prolactin than the steers. Differences in levels of plasma glucose and free fatty acids and serum total protein and insulin were not significant. It is suggested that the superior growth performance of the bulls is due, at least partially, to hormonally mediated differences in nitrogen metabolism that result in a greater deposition of lean tissue and hence increased weight gain.