A new model is proposed to describe the lactation curve of a dairy cow. It uses the fact that milk yield at a given stage of lactation is largely determined by the yield in the preceding stage. The model is written as: yt = λ(m0 – m1t) + (1 – λ)yt–1. t ≥ 1, 0 ≤ λ ≤ 1, where y1, and yt–1 are the current and preceding milk yields in kg/week, and the constant × estimates the fraction (1–λ) by which milk yield adjusts to the level at the next stage. The fraction (1–λ) by which the milk yield persists at the preceding level is used to define a measure of persistency, P = (1–λ)m0/m1 weeks, where m1 is the rate of decline in kg/week and m0 is a constant.

Thirty-six male pigs weaned at 28 days of age were used to study the effects of methyl-3-(2- quinoxalinylmethylene) carbazate-N1, N4-dioxide (carbadox) in high- and low-protein diets on the performance of pigs growing between 7 and 32 kg live weight, and on carcass characteristics at the latter weight.

The inclusion of carbadox (55 mg/kg) in a high-protein diet containing 195 g crude protein per kg and 10·2 g lysine per kg had no effect on performance or on carcass characteristics. Pigs offered the high-protein diets grew more rapidly, had a lower food conversion ratio and were leaner at 32 kg live weight than those offered a lowprotein diet containing 146g crude protein per kg and 6·0 g lysine per kg. Supplementation of the low-protein diet with lysine (4·2 g/kg) had no effect on performance or carcass characteristics but the inclusion of carbadox in the low-protein diet increased growth performance and reduced carcass backfat measurements at 32 kg. However, the performance was inferior, and the backfat thickness greater, compared with the high-protein diets. On the other hand, supplementation of the low-protein diet with lysine plus carbadox raised growth performance and reduced carcass backfat measurements to the levels exhibited on the high protein diets.

Eight dietary levels of threonine ranging from 4·8 to 6·6 g/kg air-dry diet were given to 64 growing female pigs from 25 to 55 kg live weight. Results for daily live-weight gain and food conversion ratio indicated a requirement value for dietary threonine of 5·6 g/kg. The pattern of response exhibited by blood urea suggested a requirement of 5·4 g/kg. No clear trends were found for carcass composition or plasma free amino acids

Scans of the m. longissimus and overlying fat at the 12th rib were taken, just prior to slaughter, on 254 lambs using the Scanogram and Danscanner ultrasonic machines. The lambs were from a ram breed trial and comprised six sire breed × five dam breed groups. Mean live weight at slaughter was 44·5 kg.

The precision with which scan measurements predicted comparable carcass measurements and carcass lean content (g/kg lean) was examined within groups with variation in live weight eliminated.

Residual s.d. for the prediction of carcass m. longissimus area from the corresponding scan measurement was 141 and 158 mm2 for the Scanogram and Danscanner respectively (s.d. of carcass m. longissimus area was 162mm2). Residual s.d. for the prediction of lean from the best combination of fat measurements was 32·0 for the Scanogram and 35·8 for the Danscanner (s.d. of lean was 38·5). M. longissimus did not increase the precision of lean prediction.

In a comparable evaluation of the Scanogram, involving 147 lambs, the residual s.d. for the prediction of lean was 24·0 (s.d. = 28·9).

The levels of precision obtained were low and it is debatable whether the ultrasonic techniques examined would be of value for carcass lean prediction in practical applications. They might be of use in selection programmes within nucleus flocks of the more important meat sire breeds or as an aid in experiments for differentiating between animals of widely differing composition.

Seventy-two pigs between 7 and 28 days of age were given diets containing milk, fish or soya bean proteins in two separate experiments. In the first experiment, the weight gains of pigs given casein, isolated soya bean protein, fish meal and soya bean meal were 211,180,200 and 191 g/day, respectively, and the food conversion ratios were 0·84, 1·16, 0·93 and 1·10, respectively.

In the second experiment, the protein sources were skim milk, casein, isolated soya bean protein, soya bean concentrate and soya bean meal; weight gains of the pigs on these respective diets were 205, 180, 154, 133 and 169 g/day, and the food conversion ratios were 0·81, 0·92, 0·97, 1·07 and 1·05.

Apparent digestibilities of the soya bean and fish protein diets were less than those of milk protein diets. Apparent digestibilities of all diets increased between the collection periods at 9 to 14 days and 23 to 28 days of age.

Nineteen field trials were conducted in eight 1 uropean countries to examine the effects of tylosin, administered in the food at a level of 20mg/kg to healthy pigs under good management conditions. Average daily gain and food conversion ratio were improved by 33 g and 0·17 respectively over untreated control animals, with no change in average daily food consumption. These improvements in growth performance were similar in the grower and finisher phases, and the response to tylosin was not affected by sex, initial weight or year. Absolute responses in average daily gain and efficiency of food utilization were constant, whatever the level of performance in the controls.

The distribution of lean tissue between eight standard joints was examined in 956 crossbred lambs slaughtered at constant live weights of either 35 or 40 kg. The sire breeds used were the Dorset Down, Ile-de-France, Oldenburg, Oxford, Suffolk and Texel. Sire breed did not have a significant effect on the proportion of total carcass lean found in the higher-priced joints but did show significant differences in the proportion of total carcass lean found in individual joints, with a maximum difference of 7·7 g total lean per kg joint being recorded. Similarly, small but significant effects due to ewe age (1 to 3 years), rearing type (single, twin, triplet), sex (male castrate, female) and weight of total lean were reported for the proportion of total carcass lean found in different joints.

Heritability estimates ranged from 0·07 (s.e. 008) to 0·65 (s.e. 0·16) for the proportion of total lean in the best-end neck and higher-priced joints respectively. Phenotypic standard deviations of 5·8g/kg and 17·9g/kg were reported for the proportion of total lean found in the best-end neck and the higher-priced joints respectively. The genetic correlations between the proportion of total lean in each of the higher-priced joints and the proportion of total lean in the higher-priced joints combined were positive. A genetic correlation of 017 (s.e. 0·20) was found for the relationship between average daily gain from birth to slaughter and the proportion of total lean in the higher-priced joints.

Seventy-four Yorkshire gilts, mated at puberty, were used in three experiments to study the effect of severe food restriction, 0·45 kg/day for either the last 15 or 30 days of gestation, on reproductive performance, body-weight change, and carcass quality and meat acceptability. The objective of the experiments was to assess the feasibility of limiting weight gain during gestation to produce an acceptable carcass post-partum, within the market weight range of 55 to 90 kg. Age and weight at puberty averaged 170·3 days and 99·1 kg respectively. Litter size averaged 9·3 liveborn piglets at an average weight of 1·13 kg. The necessary reduction in weight gain during gestation to bring final carcass weight within the acceptable range was associated with a significant reduction in mean individual birth weight to below 1·0 kg. Sensory evaluation of loin and ham joints from mated and unmated gilts of market weight revealed no differences in juiciness or flavour but both loin and ham joints from maiden gilts were significantly more tender than those from gilts that had farrowed and from unmated controls of the same age as those that had farrowed

Ewes with body condition scores of 2·6 (T) and 3·3 (F) on day 90 of pregnancy were allocated to one of two feeding regimes calculated either to maintain ewe body reserves (H) or to mobilize body reserves and produce a daily loss of 150 g in ewe body weight (L) during the last 8 weeks of pregnancy. Eight ewes with twin lambs from treatments TL, TH, FL and FH, and six ewes with single lambs from treatment TH, were grazed for the first 10 weeks of lactation at a mean daily herbage dry matter allowance of lOOg/kg live weight.

Feeding treatments applied during pregnancy produced differences in ewe live weights and body condition scores at lambing (68·6, 72·4, 76·7, 831 (s.e. 2·40) kg and 1·9, 2·9, 2·8, 31 (s.e. 011) for treatments TL, TH, FL and FH respectively) that persisted through lactation, but had no effect on herbage organic matter intake by ewes (mean 21 (s.e. 0·05) kg/day) milk yield (2·4 (s.e. 0·13) kg/day), lamb growth rate (mean 245 (s.e. 4·7) g/day) or herbage intake by lambs in weeks 7, 8 and 10 (mean 0·23, 0·28 and 0·36 (s.e. 0·007) kg/day).

Ewes with single lambs, when compared with ewes with twins, had similar intakes of herbage organic matter (mean 2·2 (s.e. 0·14) kg/day), produced 0·28 less milk (mean 1·7 (s.e. 010) kg/day) and increased in weight (mean 5·0 (s.e. 1·96) kg). Single lambs had significantly higher growth rates (322 (s.e. 13·1) g/day) overall but had similar intakes of herbage organic matter in weeks 7, 8 and 10 (means 0·25, 0·29 and 0·39 (s.e. 0·03) kg/day).

The range of ewe body condition and feeding in late pregnancy examined in this experiment had little subsequent effect on milk production by the ewes suckling twin lambs, given a plentiful supply of herbage.

Individually penned Finnish Landrace × Dorset Horn and Suffolk × Scottish Halfbred ewes were used to study the effects of supplementing diets based on ad libitum swedes. Supplementing a pregnancy diet of ad libitum swedes plus 225 g of hay with 454 g of a barley/soya bean meal supplement per day had no effect on swede intake or ewe performance in terms of the birth weight and survival of lambs born. Level of swede intake during late pregnancy was constant.

In early lactation, ewes offered ad libitum swedes plus 225 g hay per day were supplemented with 454 g of either barley or soya bean meal daily. Soya bean meal supplementation resulted in a 014 increase in swede intake to give a daily intake of 113g dry matter per kgM 0·7·5 and a total live-weight gain of 218kg in early lactation compared with a loss of 2·53 kg by barley-supplemented ewes. Lamb daily gain increased by 54g per day. The results are discussed in relation to trends towards the housing of ewes and current feeding practices for lactating ewes.

1. In two experiments. Scottish Blackface and Finnish Landrace ♂ × Dorset Horn ♀ rams were housed in light-proof buildings and subjected to a constant 10-h light: 14-h dark photoperiod 70 days before and during the experiment. In experiment 1, four rams from each breed type were given either 750kJ/MJ(L) or 1250 to 1500 kJ/MJ(H) of their maintenance requirement for 20 weeks. In experiment 2, four rams of each breed were given either 750kJ/MJ(T) or 2000 kJ/MJ(F) of their maintenance requirement for 20 weeks, and were then fed to maintain live weight for a further 10 weeks. Daily sperm output in the urine and scrotal circumference were measured in both experiments. Various characteristics of ejaculated semen were measured in experiment 1. Sequential blood samples were collected from the rams on both experiments and assayed for follicle stimulating hormone and luteinizing hormone. At the end of each experiment the rams were slaughtered, and their testes, epididymides and anterior pituitary glands recovered.

2. In Experiment 1, the L feeding level depressed progressively the numbers of sperm voided in the urine, scrotal circumference, and the concentration and total numbers of sperm in ejaculated semen. The testes and epididymides of L rams were lighter (P<0·01) and fewer sperm were recovered from the reproductive tract than i n H rams (P<0·01). The pituitary glands were lighter (P<0·05) and contained less luteinizing hormone (P<0·01) but amounts of follicle stimulating hormone similar to the H rams. Plasma luteinizing hormone levels were lower in L than in H rams at 20 weeks (P<0·05).

3. In experiment 2, the T rams showed a progressive depression of numbers of sperm in the urine and scrotal circumference, such that at 20 weeks differences between F and T treatments were statistically significant (P<0·05 and 001 respectively). Subsequently, some recovery occurred which, with a reduction in these measures on F treatments, led to there being no statistically significant difference at 30 weeks. There were no statistically significant differences between F and T treatments in testes and epididymes weights, total number of sperm in the tract, and anterior pituitary weight, follicle stimulating hormone and luteinizing hormone content.

Individually penned Finnish Landrace × Dorset Horn ewes in early lactation, and each suckling two lambs, were used to test the effects on milk yield, milk composition and the concentrations of some plasma constituents of supplementing a basal diet with either urea, groundnut, soya bean, linseed, fish, meat and bone, or blood meal. The basal diet contained 94 g crude protein and 10 MJ of metabolizable energy per kg dry matter and supplied daily 0·3 MJ of metabolizable energy per kg body weight. Except for urea, which was tested at an inclusion rate that increased the protein (nitrogen × 6·25) content of the basal diet by 43 g/kg, the remaining sources were tested at three levels, corresponding to increases in protein content of 34,60 and 86 g/kg. Daily milk yields were 1·92 and 2·08 kg for ewes given the basal diet and the basal diet supplemented with urea. For the high inclusion rates of each protein source the following daily yields were obtained (kg): groundnut, 2·26; soya bean, 2·45; meat and bone, 2·49; linseed, 2·68; fish, 2·84; and blood meal, 2·91. The daily yields of true protein in milk were (g): basal diet, 76; basal diet plus urea, 80; groundnut, 104; soya bean, 107; meat and bone, 105; linseed, 112; fish, 136; and blood meal, 125. Plasma concentrations of free fatty acids did not appear to support the hypothesis that the milk yield response to protein is accomplished solely by increases in tissue energy loss.

The increment in the amount of non-ammonia nitrogen reaching the abomasum as a result of the low levels of inclusion of the protein sources in the basal diet was used for the production of true protein-nitrogen in milk with an efficiency of 0·58.

Progesterone, oestradiol-I7β and luleinizing hormone were measured by radioimmunoassay in plasma samples collected daily or on alternate days following insemination in six ‘repeat breeder’ buffaloes. The endocrine profiles in these animals demonstrated that a variety of temporary disturbances in behaviour of these circulating hormones resulted in reproductive failure.

Two hundred and forty Suffolk × (Cadzow Improver × Scottish Blackface) female sheep were housed at 4 months of age and average live weight (± s.d.) of 30·6 ± 501 kg, and divided into four equal treatment groups: HH, HL, LH and LL. They were group-fed such that HH and HL sheep were 39·7 ± 5·27 kg, and LH and LL were 35·6 ± 4·64 kg, at puberty, which was recorded in all sheep. There were no differences in average date at puberty.

After puberty the sheep were gradually transferred to different levels of feeding by the time of mating with fertile rams at the second oestrus such that HH and LH were group-fed 1·50, and HL and LL 0·75 of maintenance requirement. The sheep were slaughtered at return or 25 ± 3 days after mating.

The proportion of sheep with live embryos was 0·48,0·40,0·50 and 0·41 for HH, HL, LH and LL groups respectively (NS). Ova wastage was 0·59, 0·68, 0·51 and 0·59 for the treatments, with statistically significant differences in losses between treatments in sheep with two corpora lutea (P<0·05). Ovulation rate also differed between treatments (HH > HL, P < 0·01; HH > LH and LL, P < 0·05). Differences occurred between treatments in the proportion of multiple cycles between first and second oestrus (P<0·05), and HL sheep had a greater proportion of sheep failing to return to service but without embryos (HH>HL, P<0·05). The pooled results showed that pregnant sheep were heavier at 4 months of age (P < 0·05), but not at mating, than non-pregnant sheep. Sheep with two corpora lutea were more likely to be pregnant than sheep with one corpus luteum (P < 0·05).

Two hundred Landrace × Large White sows were used to evaluate the influence of mating to Landrace or hybrid boars, at different intervals and with different frequencies, on subsequent reproductive performance. Sows were allocated at random to either a mating on each of the first 2 days of oestrus (double mating), two matings on the 1st day and one on the 2nd, one on the 1st day and two on the 2nd or single matings on each of the first 3 days of oestrus. All triple mating systems increased number of piglets born and born alive, with mating on 3 consecutive days significantly influencing these parameters compared with double mating (P < 0·05). Number of piglets weaned and mean piglet weaning weight were not affected significantly by treatment. Breed of boar used did not influence significantly any of the factors measured.

An unselected, non-inbred population of laboratory mice has been propagated for 25 generations by 20 pairs (families) of mice, each leaving one son and one daughter selected at random from the litter. The daughter was given the family number of her dam, while her mate came from another family varying systematically in different generations. The breeding plan precluded any possibility of common ancestry for five generations. In later generations the inbreeding coefficient rose at an average rate expected from a population with an effective number of approximately 80, to approximately 0·13 in generation 25. The rise occurred in cycles, repeating every five generations. Data are presented to demonstrate that overall reproduction (total weight of young produced at 9 weeks of age, per female mated) and the components of survival from birth to 9 weeks, survival from sexing (3 weeks) to 9 weeks separately for males and females, and 9-week weight of males and females, were each sensitive to changes in inbreeding coefficient. In contrast, conception rate, litter size (live young born) and sex ratio did not reflect changes in the inbreeding coefficient. The magnitude of the depression in overall reproduction was substantially greater than that in any of the affected components.

Progesterone concentration was measured in milk samples collected twice or three times weekly from 157 suckling beef cows in three herds during the period from parturition until the resumption of ovarian cycles. The length of the post partum acyclic period varied between cows from 11 to 125 days. The length of the acyclic period did not differ between cows suckling one or two calves or between the two breeds of cow studied. There were significant negative correlations between the length of the acyclic period and 1. body weight at calving (r = −0·394; P<0·001) and 2. days from calving to the next longest day of the year (r=−0·782; P<0·001). Cows calving between February and April were acyclic significantly longer (83 days) than those calving between August and December (44 days; s.e. of difference = 3·5; P < 0·001). In one herd there was a significant negative correlation between the length of the acyclic period and order of calving both in spring (r=−0·379; P<0·05)- and autumn/winter (r=− 0·349; P < 0·05)-calving cows. Of the 40 spring-calving cows in the same herd, 17 were served naturally prior to any rise in milk progesterone concentrations and 11 of these conceived to this service.

A 2×2×2 factorial experiment investigated the effect on lactational oestrus in sows of housing system (group or singly housed; G v. S), boar presence (boar present or absent; B v. N) and feeding level (ad libitum or restricted; A v. R). All treatments were imposed from day 20 post partum until weaning at day 42. A total of 183 Camborough hybrid female pigs were used, providing between 21 and 24 animals within each cell in the experimental design.

The occurrence of oestrus during lactation was observed as: 0·40 for G compared with 0·10 for S (P<0·01); 0·36 for B compared with 0·14 for N (P<0·05); and 0·28 for A compared with 0·21 for R (NS). The only treatment in which a high proportion of sows (0·78) showed oestrus was the combination G-B-A. Oestrus occurred during lactation on average 11 -4 days after imposing treatments, on average at day 20 post partum and 31·6 days after farrowing, and no significant differences were apparent between treatments. Individual piglet and overall litter weight gains were significantly reduced on G compared with S treatments (P < 0·01).

Sow food intake was greater for the S compared with G, for N compared with B, and A compared with R treatments (P<0·001). Sows on the R treatment lost significantly more live weight than the A sows between days 20 and 42 (P<0·001). Singly-housed sows also lost more weight than group-housed sows between farrowing and day 42 (P<0·001), mainly because of losses occurring before day 20.

A study was undertaken to determine the magnitude of any financial loss incurred in the utilization of pale, soft exudative (PSE) pigmeat. Twenty pairs of first-grade bacon-weight carcasses were selected on the slaughter line. Members of each pair were of the same sex and weight but one had an m. longissimus dorsi pH at 45 min post mortem (pH1) of 5·4 to 5·8 (PSE) and the other a pH, of 6·2 to 6·5 (normal). One side of each carcass was processed for Wiltshire bacon and the other was cut into retail joints, which were packaged, placed in a refrigerated cabinet and measured for drip loss 72 h later. PSE, compared with normal carcasses, had a lower bacon yield (16g/kg) and drip loss from fresh PSE meat was more than double (17·0 v. 7·0g/kg trimmed carcass weight). In shop testing, the sales of bacon from the two types of carcass were similar; with the fresh meat fewer PSE cuts were sold (0·23) but mainly during the final test day. It would appear that an economic assessment of PSE meat in Wiltshire curing need consider a reduced bacon yield only (= £1·13 per carcass at the present difference of 0·8 kg). The reduced financial return on a PSE carcass of similar weight for fresh meat was calculated to be zero to £8·74, depending upon the type of retailing operation and effort devoted to ensuring an early sale of PSE cuts.

The live-weight gain and efficiency of food utilization of purebred British Friesian steers and of crossbred steers out of British Friesian dams by Aberdeen-Angus, Charolais, Devon, Hereford, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One system was similar to the commercial 18-month grass/cereal system (16-month system) and the other to a commercial 2-year system (24-month system). The cattle were slaughtered at a standard level of fatness, determined by the use of the Scanogram ultrasonic machine.

The trial extended over 3 years and a total of 579 cattle were involved.

Data for the two production systems were analysed separately. Adjustment was made to equal age at the beginning of the test and to equal carcass subcutaneous fat concentration.

There were important differences between sire breeds in daily live-weight gain (P < 0.05), the order of performance for the different sire breeds being similar in the two systems. Charolais and Simmental crosses grew fastest, followed by South Devon crosses, and then by the purebred British Friesian and the other native breed crosses. Faster growing sire-breed crosses were generally heavier and older at slaughter; they ate more, and there was no obvious relationship between sire-breed means for growth rate and efficiency. The range in efficiency between sire breeds was 27 g and 17 g live-weight gain per kg digestible organic matter intake for the 16- and 24- month systems respectively. In both systems, Hereford crosses ranked highest and the purebred British Friesian among the lowest. Probability levels for sire breed differences were P < 0.1 (16 month) and P < 0.01 (24 month).