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.

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.

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.

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.

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.

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.

Two experiments have been carried out to examine the interaction between animal size and the response in animal performance to an increase in the digestibility of grass silage. In experiment 1, grass silages harvested during July and August after regrowth intervals of 43 and 85 days were offered ad libitum both unsupplemented and supplemented with 2 kg of concentrates per head per day to British Friesian steers of (±s.e.) 170±1·9, 300±2·9 and 420±3·6 kg initial live weight. Earlier cutting did not affect silage dry-matter intake or live-weight gain but increased carcass gain by 0·12kg/day (P<0·01).

In experiment 2, early-cut grass silage, made from two regrowths of perennial ryegrass, which were harvested during July and August after regrowth intervals of 43 and 48 days, and late-cut silage, made from a single regrowth, which was harvested in August after a regrowth interval of 90 days, were offered ad libitum to 84 Hereford-cross steers of (±s.e.) 170±3·4, 300±4·4 and 420±5|·2kg initial live weight. Earlier cutting increased silage dry-matter intake by 340 g/kg, live-weight gain by 0·23 kg/day and carcass gain by 0·18 kg/day (P<0·001). It i s concluded that increasing the digestibility of grass silage by cutting grass at an earlier stage of growth is likely to produce a substantial increase in the daily carcass gain of beef cattle and that the response to higher digestibility is as great with mature cattle as with young, growing animals.

Twenty-four castrate male cattle were used in two nutritional balance and slaughter experiments to measure the effects of two implantations with 300 mg trenbolone acetate and 36 mg resorcylic acid lactone over the live-weight range 250 to 400 kg. Control and implanted animals were pair-fed barley-based diets of differing protein concentration in the first experiment and the lower protein diet at two levels of feeding in the second experiment.

Daily live-weight gain and nitrogen retention were significantly increased by implantation in both experiments. The carcasses of implanted animals contained significantly more lean meat and a higher proportion of meat in the forequarter. The edible portion of these carcasses contained significantly more protein and water and less fat.

Live-weight gain and carcass composition were not influenced by dietary protein intake. Increased feeding level improved live-weight gain, suggesting that a higher metabolizable energy intake would give an increased response to implantation.

Computer simulation was used to measure the effects of breeding management efficiency in block calving dairy herds and in those with a long mating season of 9 months. In particular, the effects of varying levels of oestrus detection and conception rates were assessed, and the product of these two parameters defined as the fertility factor. As the fertility factor increases from 20 to 50, where the mating season extends to 9 months, the mean calving index for the herd decreased linearly from 393·5 to 373·6 days and the culling rate for failure to conceive declines in curvilinear fashion from 0·196 to 0·006. Concurrent with the decrease in calving index, mean annual milk yield and margin over purchased food increase, with the herd commencing calving in January showing a more marked response than the herd commencing calving in October. When overall replacement rate is also taken into account, the margin over purchased food net of herd depreciation per cow, at 1979/80 prices, changes from £270·7 to £315·2 in the January herd compared with £275·9 to £315·8 in the October herd. For each day change in calving index associated with alteration in fertility factor, there is a change of £2·24 for the January herd and £2·01 for the October herd in margin over purchased food net of herd depreciation.

In the block calving herd, increases in fertility factor are reflected mainly in changes in culling rate for failure to conceive from 0·292 to 0·033, and not in margin over purchased food.

Two foods, distillers' wet draff and draff plus pot ale syrup, containing 207 and 256 g crude protein per kg dry matter respectively, were given as sole food at the maintenance level to four adult wether sheep. Two of the sheep were given draff and two draff plus syrup for a 28-day period; the treatments were then changed over for a second period. The copper contents of the foods were 17 and 30mg/kg dry matter for the draff and draff plus syrup respectively. Sheep are particularly susceptible to copper and care should be taken when feeding such by-products, but during these short-term trials there was no evidence of copper poisoning. Energy losses in the faeces and urine were measured for all sheep, and methane losses were measured in closed-circuit respiration chambers for two sheep on each treatment. The metabolizable energy values of the foods were 10·8 (s.e. 0·15) and 12·5 (s.e. 0·15) MJ/kg dry matter for the draff and draff plus syrup respectively. The proportions of gross energy intake lost as methane were 0·029 for the draff and 0·042 for the draff plus syrup; these were much lower than the values predicted by the commonly used equation.

The effects of pregnancy and lactation on growth were investigated in Ayrshire cattle, from data on 12 linear body measurements at 3-monthly intervals up to 4 years of age. In all, 9 888 sets of 12 measurements were obtained. There were 675 first and 518 second calvings.

When expressed as a percentage of the size of animals of the same age but in a non-pregnant, non-lactating state, the total set-back to normal growth due to pregancy and lactation ranged from 2% in withers height to 18% in forerib width in heifers, and from 1% to 3% for the same characters in cows.

All 12 measurements were affected significantly by first pregnancy (including parturition), the average retardation being 3%. For several measurements, a check to growth during pregnancy was largely obscured by progressive distention of the body, especially in measurements of width, until parturition had occurred. Thus a retardation of 9% in forerib width became apparent only after calving.

First lactation affected significantly most measurements, especially the later-maturing six, which were set-back in their normal growth over the lactation period by 3% to 9%. Thus, there was effectively zero- growth in width at forerib and only one-sixth of normal growth in foregirth, whilst growth rate in width at pins and hooks was approximately halved by lactation.

Calving at an earlier than average age affected growth adversely and thereby involved some increased risk of calving difficulties.

The time from birth to first suckling was recorded for 161 dairy calves. Of these calves, 0·32 failed to suckle within the first 6h of life. The most important factor determining the time to first suckling was the udder conformation of the dam but delays were also attributable to abnormal maternal behaviour, especially in heifers, and poor calf vigour, especially after difficult calvings. Delayed suckling was more common as the parity of the dam increased. Heifers' calves that were sired by a Sussex bull stood up earlier and suckled earlier than those sired by a Friesian bull. Offspring of different Friesian sires differed in the time to first standing and suckling. Delayed suckling became more common as the calving season progressed. Calves born within a group of animals suckled no later than calves born in individual calving pens but 0·15 of those calves first suckled from a cow other than their dam.

Two methods of estimating body fat in vivo in cattle, namely measurement of body water by dilution of deuterium oxide and subcutaneous adipose-cell size, were studied in mature cows and compared with a classical method based on dissection of a sample joint.

Total body fat, measured after complete dissection of 12 dry cows, varied between 64 and 185g/kg body weight. Rib fat and adipose-cell diameter were related positively, while body water was related negatively to total body fat. The equations for prediction of total body fat were sufficiently accurate (s.d. = 10·1 to 11·5 g total body fat per kg body weight) to warrant further examination, and adipose-cell diameter was as accurate as body water.

Groups of Hereford-cross steers weighing 283 kg were given 0·6 kg dry matter hay per head per day, and bruised barley supplemented with 40 g of a fully soluble liquid product per kg, containing urea, minerals and vitamins, ad libitum. Half the animals received 10 g limestone per kg diet as an additional supplement. Over a 105-day period the food intake of the limestone-supplemented animals was 0·20 higher than that of unsupplemented animals. The resultant daily live-weight gain was 1·22 kg compared with 0·92 kg for the animals receiving the diet containing no additional limestone. Food conversion ratios (kg/kg live-weight gain) were improved by limestone supplementation from 6·84 to 6·19. Limestone inclusion did not appear to influence the low concentrations of starch (ca. 15 g/kg) present in the faecal dry matter but there was a small significant difference in faecal pH.

Data from three comparative slaughter experiments involving a total of 73 ewes were used to study the influence of body fat content at the start of lactation (X1 kg) and of metabolizable energy intake (X2, MJ/day), on the rate of loss of body fat by lactating ewes over the first 6 weeks of lactation (Y, g/day). The relationship was described by the equation:

Thus the rate of fat loss was greater for ewes with higher initial fat contents, but the differential became less as metabolizable energy intake increased. Since increases in body fatness depress food intake it was not possible to prevent loss of body fat during early lactation in fat ewes given high concentrate diets ad libitum. The likely response in milk yield to increase in body fatness at parturition is therefore strongly dependent on the relative levels of body fatness and metabolizable energy intake. The value of any improvement in condition of the ewe at parturition may be considerable when metabolizable energy intake during lactation is low but much less when it is expected to be high.