Sixty-four lactating dairy cows (Ayrshire, British Friesian and Shorthorn × Ayrshire) were offered grass silage with a dry-matter content of 258 g/kg, and containing 75 g/kg digestible crude protein and 64·6% digestible organic matter in the dry matter for an average period of 16·7 weeks. The control and supplemented groups, each of 32 cows, received concentrates containing on a fresh basis 14% and 18% crude protein respectively which were offered at the rate of 0·4 kg/kg milk for yields above 2·3 kg/day. The mean daily yields of milk were 17·4 and 19·5 kg/cow, silage dry-matter intake 8·16 and 9·00 kg/cow per day and concentrate dry-matter intake 5·36 and 5·94 kg/cow per day on the control and supplemented treatments respectively and these differences were highly significant. The treatments had no significant effects on milk yield and composition in the post-experimental grazing period.

A computerized mathematical model was used to test the economic effect of changing calving intervals under typical high-yielding (63701 per 305 days for mature cows) herd conditions at 1976 prices. The effect of month of first calving was also tested in a herd where four lactations are assumed to follow at equal calving intervals.

Under the prescribed conditions, cows should calve at 320-day to 360-day intervals (with two exceptions) to maximize the annual margins over concentrates, but the month of the initial calving affects the absolute level of margins over concentrates markedly (maximum £382·10 for 365-day interval for November calving, minimum £318·10 for April). This means that complete knowledge of the main input-output factors is required before recommendations can be made for an individual cow. The change in margin over concentrates for each day's delay in conception varies widely, with rates of loss as high as £1·80 per day's delay occurring.

1. Thirty lactating British Friesian heifers and cows were individually given maize silage ad libitum containing 331 g dry matter/kg, 13 g nitrogen and 11·2 MJ of metabolizable energy per kg dry matter. Urea or aqueous ammonia was mixed in at the time of feeding to give 7·0 g nitrogen per kg silage dry matter. Urea-treated silage was given with concentrates at a high (mean 6·6 kg dry matter/day: treatment HU) or a low (mean 3·3 kg:treatment LU) level of feeding; the lower level only was given with ammonia-treated silage (treatment LA).

2. The addition of ammonia raised silage pH values from 3·9 to 4·4. Silage dry-matter intakes in lactation weeks 7 to 22 for treatments HU, LU and LA were 8·8, 11·1 and 10·7 kg/day.

3. Digestible organic matter content in the dry matter of the diets measured in vivo was not significantly affected by treatment. However, digestible organic matter intakes were significantly greater for treatment HU than for LU in weeks 7 to 10, and for LU than for LA in weeks 11 to 22.

4. The yields of milk and the contents of protein, lactose and energy did not differ between treatments. The milk yields for treatments HU, LU and LA in weeks 7 to 22 were 20·2,19·2, 18·8 kg/day respectively. Fat content of milk was significantly depressed with the HU treatment for heifers in weeks 7 to 10. The live-weight changes of the cows in weeks 7 to 22 for treatments HU, LU and LA were +0·10, −0·07 and −0·37 kg/day; the live-weight loss by cows given treatment LA was significantly greater than for LU. The live-weight change of the heifers was not affected by treatment.

Measurements of the m. longissimus and overlying fat at the last rib were taken on the live pig using ultrasonic machines of differing complexity: Sonatest (simple A-mode machine), Scanogram and His Observer (modified linear scanners), and Danscanner (‘real time’ scanner). These measurements were examined as predictors of the corresponding carcass measurements and percentage lean in the carcass.

Sonatest and Scanogram were compared using 143 purebred and crossbred pigs of different types. The analysis was pooled within breed-type and sex. The standard deviation for percentage lean was 3·94. Residual standard deviations for predicting percentage lean from live weight and best fat thickness were 2·72 (Sonatest) and 2·56 (Scanogram). Addition of m. longissimus depth (Sonatest) and m. longissimus area (Scanogram) reduced these to 2·69 and 2·29 respectively. The use of two or more fat measurements provided no extra precision over a single fat measurement.

Scanogram and His Observer were compared using a subset of 38 pigs. Scanogram was a better predictor of percentage lean using a single fat measurement but when a combination of measurements was used, there was little difference between the machines.

Scanogram and Danscanner were compared using a subset of 27 pigs. The standard deviation of percentage lean was 3·57. Residual standard deviations for predicting percentage lean from live weight, best fat depth and m. longissimus area were 2·18 (Scanogram), and 2·03 (Danscanner). Fat areas had similar predictive precision to fat thickness measurements.

Observations were made on a pig herd where sow service in lactation had been practised for 2 years. Sows and their litters were grouped and a boar later introduced. Of the 49% of sows mated in lactation 78% conceived. Sow and litter data were subjected to multiple regression analyses which indicated that lactational oestrus was more likely to occur for sows farrowing at the end of the calendar year, and for sows with smaller litter sizes. Sows mated in lactation showed a smaller weight change from the end of the previous pregnancy to weaning than those first showing oestrus after weaning. It is suggested that these weight changes in lactation and the seasonal relationship to lactation oestrus may be related to weight gain achieved by the sow in the previous pregnancy. Sows mated early in lactation had piglets with lower weaning weights and sows mated in late lactation had greater weaning weights than piglets whose dams showed oestrus after weaning.

Failure to recycle after weaning and the interval from weaning to oestrus were studied using sows representing 28 crosses from eight breeds at three stations. Of the sows farrowing their first litter, 12·9% failed to recycle within 50 days. The least squares mean for weaning to oestrus interval for all crosses was 13·5 days. Hampshire × Landrace, followed by Hampshire × Yorkshire sows had the shortest intervals (8·0 and 8·7 days respectively) whereas Large Black × Lacombe sows had the longest interval (22·1 days). Crosses involving the Yorkshire, Hampshire, Berkshire and Tamworth breeds had shorter intervals than those involving Landrace, Duroc, Large Black and Lacombe. Season of farrowing had significant effect (P < 0·05), with the shortest interval (11·4 days) occurring in autumn and the longest (15·1 days) in spring and summer. Weaning to oestrus interval increased with the increase in litter size. The interval was longer (15·7 days) at Lennoxville but similar at the other stations. There was a steady increase in size in the following litter with the increase in the weaning-oestrus interval. The heritability estimate (full-sib analysis) for the weaning-oestrus interval was 0·25 ± 0·10. Repeatability based on limited data was calculated at 0·28.

To investigate possible pre-test environmental effects on testing station performance, pigs from a total of 107 litters from two breed types were weaned on one of three treatments: weaning at 3, 5 or 8 weeks of age, with a different creep-feeding regime on each. At 8 to 10 weeks of age, litter groups (usually consisting of two boars, one male castrate and one gilt) were sent to a Meat and Livestock Commission testing station and performance-tested from 27 to 85 kg live weight on twice daily to-appetite feeding.

Weaning treatment significantly affected live weight at 50 days and boar growth rate and feed efficiency on test, but carcass traits were largely unaffected. Boars weaned on the 8-week treatment showed a significant advantage in index score of two-thirds of a standard deviation over those weaned at 3 weeks. A smaller number on the 5-week treatment were intermediate but did not differ significantly from those on the other two. It is concluded that wide variation in the weaning methods of herds sending pigs to a testing station could affect selection decisions. Ways of removing any bias by standardizing weaning methods or by statistical adjustment are discussed.

Three experiments, involving a total of 84 pigs of approximately 90 kg live weight, were undertaken to determine the effects of feeding sugar solutions immediately prior to slaughter on carcass yield, liver weights, ultimate pH of the musculature and some chemical characteristics of muscle and liver. In the first, where water-only (14 h) prior to slaughter, or access to a solution of either glucose syrup (12 h) or sucrose (12 h) followed by water-only (2 h) were the treatments, sugar feeding did not influence carcass yield. Liver weight was increased with glucose (39%) and markedly so with sucrose (77%). Livers from sugar-fed pigs had higher glycogen and lower protein concentrations. Glucose reduced muscle ultimate pH (0·2 to 0·4 units) but sucrose had little effect. In the second study various sugars were tested (pure glucose, glucose syrup, sucrose and fructose) and pigs had access to solutions of them for 4 h and water-only thereafter for 10 h prior to slaughter. All sugar treatments increased liver weight and reduced muscle ultimate pH relative to water-only before slaughter. The final experiment involved access to varying amounts of a glucose syrup solution for 4 h followed by water-only (10 h). In comparison with ‘water-only’ prior to slaughter, an intake of some 250 g hexose equivalent reduced muscle ultimate pH (0·2 to 0·3 units) and increased liver weight but a response in carcass yield required in excess of 1000 g hexose equivalent.

Three field trials were undertaken to determine the influence of feeding sugar solutions to pigs immediately prior to slaughter on carcass yield, liver weight and muscle quality. In the first, which involved 168 pigs of 85 to 95 kg live weight, provision of a glucose syrup solution in lairage (4 h) followed by water (12 h), compared with water-only (16 h) increased carcass yield (3%) and liver weight (27%) and reduced muscle ultimate pH (0·1 to 0·4 unit). When water was not made available after consumption of the sugar there was no response in carcass yield. In the second trial conducted with 169 pigs of 110 to 125 kg live weight, and involving the same treatments as in Trial I, except that sugar was provided for a longer period (6 h), corresponding responses in carcass yield, liver weight and muscle ultimate pH were +2·7%, +24% and a decrease of 0·2 to 0·3 units. In both trials responses to sugar feeding were less when compared with pigs slaughtered shortly after arrival at the abattoir. In the final trial, which also involved heavy pigs (88), access to a glucose syrup solution (9 h), but not a sucrose one, followed by water (8 h), relative to water-only in lairage, improved carcass yield (1·1%). Liver weight was increased with glucose (34·2%) and markedly so with sucrose (49·7%) and both sugars reduced muscle ultimate pH (0·1 to 0·6 units).

Thirty-six Large White × (Large White × Landrace) young female pigs (gilts) were allocated to one of nine treatments. These were 30 min daily boar contact from 125, 132, 139, 146, 153, 160, 167, 174 or 181 days of age. Gilts were fed so as to maintain them on a pre-determined growth curve, gaining 0·45 kg per day. Once puberty had been detected, gilts were mated at the next (second) oestrous period and subsequently slaughtered 20 days post coitum.

The interval from first boar contact to puberty was significantly longer (P<0·05) amongst gilts first exposed to a boar at ages below 139 days. Amongst gilts older than this the interval was similar. Though the 174- and 181-day groups were significantly older at puberty (P<0·05) no significant differences were observed amongst the younger age groups. Synchronization of pubertal oestrus appeared to be better for the 160- and 167-day groups, with three out of four gilts reaching puberty within an 8-day period. There was no indication that weight at puberty, ovulation rate, percentage embryo survivval, or number of viable embryos at 20 days post coitum were affected by treatment.

From the results it appears that the optimal gilt age at which to commence boar contact, in terms of age at puberty, interval from first boar contact to puberty and synchronization of the pubertal oestrus, is in the age range 160 to 170 days.

The effect of fermentation on cassava meal diets supplemented with 0, 2, 4 and 6% levels of palm oil on the performance, carcass characteristics and economic value of broiler chickens was studied. During the growing phase, fermentation had no influence on growth rate, but resulted in reduced mortality and improved efficiency of feed utilization in the chickens. However, there were greater intakes of fermented cassava meal diets, higher efficiency of feed utilization, better growth rate and reduced mortality during the finishing phase. Abdominal fat was lower during both phases in chickens given the fermented cassava meal diets than those given the cassava meal diets. There was evidence of economic benefits in reduced feed cost, increased gross revenue and higher revenue less feed cost values in fermented cassava meal than in cassava meal diets. There were non-significant reductions in feed intake, mortality rate, daily rate of gain, final body weight and carcass quality, but significant economic benefits during both growing and finishing phases as the level of supplementary palm oil increased in the diets. The results suggest that while about 2% palm oil might be required in fermented cassava meal diets, 2 to 4% would be needed in cassava meal diets by broiler chickens for comparable performance.

A primary growth crop of perennial ryegrass (cv. S24), containing 17% crude protein and 9·9 MJ metabolizable energy/kg dry matter, was artificially dried, ground through a 3·0 mm screen and pelleted either without further treatment (C), or after the application of formaldehyde (T) at a rate of 1 g/100 g crude protein. The C and T diets were each fed to 20 lambs for 77 days. Diets C and T were given ad libitum and at three lower planes of nutrition. Similar amounts of dry matter, nitrogen and digestible energy were consumed at each of the four planes of nutrition by lambs fed diets C and T. Carcass energy, fat and protein retention, and total body energy retention were measured by the comparative slaughter technique and did not differ between the diets (P> 0·05). Metabolizable energy intake was calculated from digestible energy intake using the factor 0·81. The efficiency of utilization of the metabolizable energy for growth and fattening (kf) and the net energy value were calculated by linear regression analysis from the total body energy retention, the calculated metabolizable energy intake and dry-matter intake data scaled to M0·75. They did not differ between the diets (P > 0·05), and were 0·370 (C) and 0·431 (T) for kf, and 2·09 (C) and 1·97 MJ/kg dry matter (T) for net energy.

Four experiments were made during early lactation on individually penned Finnish Landrace × Dorset Horn ewes, each suckling two lambs. In Experiment 1, 14 ewes of mean body weight 74 ± 2·4 kg received daily, 1·9 kg dry matter, 20 MJ of metabolizable energy and 300 g of crude protein from a diet (H) containing hay, barley and fish meal. Reduction of the daily crude protein intake of half the ewes to 225 g by replacing fish meal with barley (diet L) in week 2 of lactation resulted in a decrease (P< 0·01) in daily milk yield of 0·53 kg (17%) compared with no change for ewes remaining on diet H. The effect was reversed by returning the ewes to diet H at the end of week 3. In Experiment 2 the use of four ewes fitted with abomasal cannulae showed that the additional non-ammonia nitrogen reaching the abomasum when fish meal was given was used with an efficiency of 0·51 for the production of milk nitrogen. In Experiment 3, involving 20 ewes, a restriction in protein intake for more than 10 days in early lactation by replacing the fish meal with barley depressed subsequent milk yield. In Experiment 4, 24 ewes were given either fish meal, soya bean meal or groundnut meal as protein supplements. In early lactation fish meal was superior by 0·40 and 0·43 kg of milk per day to soya bean meal and groundnut meal respectively, and this was attributed to the greater quantity of non-ammonia nitrogen reaching the abomasum in the fish meal compared with the soya bean meal and groundnut meal supplements. The commercial significance of the results is discussed.

The effect of haemoglobin types A and B on reproductive performance of ewes grazing oestrogenic pastures was studied in four commercial flocks in 1973 and in an additional five in 1974 (a total of nine flocks). The number of ewes lambing per ewe mated differed significantly (P< 0·05) between mating types (male AA × female AA, male AA × female AB, male BB × female AB and male BB × female BB). Differences between mating types in the number of lambs born per ewe exposed to the ram and in the number of lambs weaned per ewe exposed to the ram bordered on significance (0·05<P<0·1). Matings involving BB sires were superior to matings involving AA sires. This finding differs from previously published evidence on this topic. There were no significant differences in lamb mortality or in the number of lambs born per parturition. Reproductive performance did not differ amongst ewe genotypes. Age of dam, farm and year had significant effects on most of the reproductive characteristics studied. Three significant interactions (P<0·05) involving mating type were found: mating type × age on number of ewes lambing per ewe exposed to the ram, mating type × farm on number of lambs born per parturition and mating type × year on lamb mortality. Due to the relatively small differences observed in reproductive performance between mating types it is concluded that selection for haemoglobin type is unlikely to overcome the problem of low reproductive performance in sheep grazing oestrogenic pastures.

Over 2 years, 104 Greyface ewes were mated at a synchronized oestrus either in early October or early November. From late September until slaughter at return to service or between 4 and 7 weeks after mating, ewes were fed to maintain their body condition score as previously adjusted by differential group feeding on grass. Ovulation rate and potential lambing rate were derived from counts of corpora lutea and viable embryos at slaughter. Both rates were higher in the early-mated ewes in comparable body condition. Stress factors were implicated as contributing to the decline in ovulation rate with time, while ewes which failed to hold to first mating were largely responsible for the decline in potential lambing rate.