1. The heat production of four sows, approximately 17 months old at the start of the experiment, was measured at five ambient temperatures from 23° to 6°C. Food intake was controlled at different levels for different sows; one sow conceived during the experiment.

2. Heat production increased consistently as temperature decreased from 23° to 6°C; the relative effect on heat production of exposure to low temperatures was greater the lower the level of feeding.

3. Estimated values for whole body conductance decreased as ambient temperature decreased to minimum values of 73 to 77 kcal/m2. day. °C for three sows and 87 kcal/m2. day.°C for the fourth sow, which had a considerably thinner backfat than the others.

4. Estimated values for lower critical temperature varied from 10° to 20°C, with the lower values associated generally with the higher levels of feeding; nevertheless heat production was consistently lower at 23°C than at 18°C.

5. Differences in level of feeding were generally associated with differences in live weight, and it was difficult to obtain reliable estimates of metabolizable energy requirements for maintenance and of net efficiency of utilization of metabolizable energy above maintenance; however analysis on the basis of live weight0·75 produced values of 92 kcal/kg0·75 per day at 23°C and 106 kcal/kg0·75 per day at 18°C for maintenance and between 67 and 75% for the efficiency of utilization above maintenance.

Data from a random-bred population of mice were used to examine the sources of variation in litter size and 12-day body weight, and, the genetic relationships between these traits and post-weaning body weights and body-weight gain from 3 to 6 weeks of age (post-weaning gain). The genetic model included maternal genetic effects in addition to the usual direct (individual) genetic effects. Such maternal genetic effects may be important to an understanding of traits like 12-day body weight of mice, where the young depend to a large extent on the mother for early postnatal nutrition.

Analysis of litter size yielded a paternal half-sib heritability estimate of 0·34±0·19, while twice the daughter-dam regression was 0·23 ± 0·08. The repeatability of litter size was 0·51±0·07. The correlation between direct genetic effects on litter size and those on 3-, 6-, and 8- week body weights and post-weaning gain were –0·18,0·36,0-34 and 0·58 respectively. The correlation between direct genetic effects on litter size and 12-day weight was positive (0·41), while the genetic correlation between maternal effects on 12-day weight and direct effects on litter size was negative (–0·37).

Analysis of 12-day weight showed that direct and maternal genetic effects were important sources of variation, but there was a large negative correlation (-0·88) between these effects. The usual genetic correlations between 12-day weight and post-weaning body weights were positive while post-weaning gain yielded a negative estimate. However, there appears to be a general negative correlation between direct genetic and maternal genetic effects in this population, for all such correlations were negative except that between direct effects on 12-day weight and maternal effects on post-weaning gain.

The reproductive performance of a lowland flock of Clun Forest ewes is reported. During the period from 1955 to 1966, over 1300 ewes entered the flock and more than 4800 lambing records were obtained. The effects of culling and death on the records available were investigated and it was found that the reduction of the material caused by death was random, while that caused by culling was related to previous performance.

Barrenness decreased with age, and for ewes aged 1, 2 and more than 2 years was 44, 7 and 5%. Average litter sizes (ALS) over the same ages were 1·15, 1·55 and 1·75. Accordingly the number of lambs born per ewe mated and present at lambing also increased with age of ewe, and values for the same ages were 0·64, 1·44 and 1·68.

An analysis of over 170 ram mating groups, consisting of ewes older than 1 year, revealed no differences between rams on the ALS of their mates. The results of a similar smaller analysis of barrenness among 1-year-old ewes also showed no evidence of a ram effect.

Phenotypic and genetic parameters for reproductive performance in a flock of Clun Forest ewes have been estimated. Average litter size (ALS) appeared to be more repeatable than the number of lambs born per ewe mated and present at lambing (NLBEM), and the estimates obtained by regression (0·15 and 0·14) were slightly higher than those from the analyses of variance (0·12 and 0·09). The repeatability of barrenness was very low (0·05). It was concluded that little scope existed for the improvement of reproductive performance from a regular policy of culling.

Estimates of heritability by analysis of variance and a method for all-or-none traits were 0·12 and 0·11 for ALS, and 0·15 and 0·10 for NLBEM, whereas barrenness was less heritable (0·07). An estimate of 016 was found for the heritability of ALS performance over two years. The phenotypic correlation between body weight and reproductive performance were positive yet small (ALS:+0·16; NLBEM:+0·10), while at the genetic level ALS was more strongly related to body weight (+0·21) than NLBEM (-0·04). The genetic regressions indicated that an increase of 5 lambs per 100 ewes lambing would accompany genetic gain of 5 kg in ewe body weight, while an increase of 1 lamb per ewe lambing would lead to a correlated response in body weight of 5 kg.

Selection for ALS on the basis of dams' performance, within the flock studied, would be expected to yield a rate of progress of 2% per annum.

Body weight was studied from birth to 5½ years of age and six linear measures of body size from birth to 4¼ years for sheep of five breeds, Scottish Blackface, Cheviot, Welsh Mountain, Lincoln Longwool and Southdown, and of crosses of these breeds with each other and with the Tasmanian Merino, but not in all possible combinations. The sheep were run as a single flock. Numbers ranged from 753 at birth to 150 at the end of the experimental period.

There were marked differences among the breeds and crosses in all aspects of body size and some differences in rate of maturity. They also differed in conformation independently of body weight. Crosses of the hill breeds with the Lincoln and probably with the Southdown were heavier than the average of the parental breeds and larger in some linear body measurements from about weaning onwards. The weights of crosses of Blackface and Cheviot with Lincoln eventually exceeded those of the heavier parent of the cross. For the crosses among the three hill breeds only the Blackface Cheviot cross showed significant deviations from mid-parent values for weight and size.

Maternal effects were important for all traits studied from birth to weaning and for weight up to a year old. In relation to mature size, Welsh dams produced the biggest and Lincoln the smallest lambs. The data did not permit Southdown maternal effects to be estimated. The effects of birth type and rearing were apparent for late maturing body parts up to a year old and for weight up to 3 years. Males, measured only from birth to weaning, were heavier and generally larger than females.

Residual correlations between the various measures of size varied from 0·1 to 0·7.

Digestibility studies were carried out to establish the inter-relationship between crude fibre and total lipid digestibility in the presence of added calcium or non-ionic detergents. Three levels of calcium, corresponding to daily intakes of 2·3, 4·8 and 22·9 g per sheep, were used in a predominantly ground barley diet (65 to 73%) to which was added 8% beef tallow or maize oil. Two non-ionic detergents were used at 0·1% of the diet: nonyl phenol ethylene oxide and fatty alcohol combined with 3 molecules of ethylene oxide.

With a daily intake of 2·3 or 4·8 g calcium per sheep, supplementation with fat resulted in a reduced fibre digestibility. When the intake was increased to 22·9 g, there was a significant improvement (P<0·05) only for the maize-oil-supplemented diet. Increasing calcium intake, associated with increased calcium digestibility, significantly (P<0·05) depressed total lipid digestibility. Intake of 4·8 g calcium per day was associated with the highest calcium digestibility of 33% digestibility units and the total lipid digestibility of 94%. Maize oil was better digested than beef tallow with the lower level of calcium; the position was reversed with the higher level of calcium supplementation. No advantages were found for crude fibre and total lipid digestibility when detergents were added.

A possible mechanism by which the physical wetting of dietary lipids causes decreased digestibility of the fibre component is discussed.

1. Four groups of eight castrated male lambs, weighing initially about 37 kg, were fed ad libitum for 18 weeks on: C, chopped dried grass throughout; P, pelleted grass throughout; C/P (or P/C), the two forms alternated every 3 weeks; or C + P, both forms on offer.

2. Daily dry-matter intake (g/kg W0·75) was 58·2 for treatment C and 814 for treatment P; thus the long-term difference in intake was 40%. However, in the alternated sheep, dry-matter intake was 53·6 g/kg W0·75 for chopped grass and 86·5 g for pelleted; this short-term difference (61%) was significantly greater than the long-term difference. Dry-matter intake for treatment C+P was 84·9 g/kg W0·75; after the first week, chopped grass comprised only 10% of this. Dry-matter digestibility coefficients (%) were: C, 740; P, 61·4 and C+P, 62·0.

3. The sheep were killed in week 19 and the dimensions of digestive organs and their contents were adjusted to an animal of 50 kg empty body weight. The weight of the reticulo-rumen was greater for C (1·30 kg) than for P (0·94) or C+ P (1·05), C/P and P/C being inter-mediate (1·15). The water-filled volume of the rumen was proportional to weight, except that C/P (alternated sheep finishing on pelleted grass) had low volumes. Reticulo-rumen fill was greater for C (7·28 kg) than for P (3·97) or C+ P (4·53), P/C (5·90) and C/P (4·34) being intermediate. There were no other significant differences in organs or contents.

4. Gains in empty-body weight (g/day) were: C, 112; P, 181; C/P and P/C, 126; C + P, 195.

Silage made from a whole crop of barley was offered to sheep without neutralization or after partial neutralization to pH 5·4 to 5·5 with sodium bicarbonate or ammonia. In a further treatment the un-neutralized silage was supplemented with blood meal administered each day as a drench. Total organic-matter intake and nitrogen retention were significantly higher for the sheep receiving the blood meal supplement than for any of the other treatments, which did not differ significantly one from another. It is suggested that the intake of the un-supplemented silage was limited by a low uptake of amino acids from the intestine.

Ninety-six lamb carcasses drawn from six batches of lambs commercially consigned to an abattoir were analysed for characteristics which may affect their economic value. From each batch carcasses were selected in equal numbers into two classes of ‘good’ or ‘poor’ conformation according to traditional standards. Carcasses selected for ‘good’ conformation were heavier (P<0·05) and fatter (P<0·05), slightly shorter in carcass length and hind leg length (P<0·05), greater in circumference (P<0·001) and width (P<0·001) of the hind leg, slightly greater in muscle weight (P<0·05) but no greater in bone weight than those of poor conformation. The yield of prime retail joints was similar in the two conformation classes but the ‘good’ conformation class had a higher proportion of loin and rib joints and lower proportion of hind leg joint (P < 0·01) although these differences were not considered to be of commercial importance. There was a lower proportion of the carcass fatty tissue in the hind leg joint of the ‘good’ conformation class (P < 0·05). Muscle-to-bone ratio and area of ‘eye muscle’ (M. longissimus thoracis) appeared to be little affected by selecting for conformation differences. Depth of fleshing as indicated by the weight of muscle in the hind leg per 10 cm length, was 40 g (6%) heavier in the carcasses of the ‘good’ conformation class. This contrasted with the much greater differences, between batches, of 290 g (40 to 50%). Between batches there were significant differences for all the measures taken except the yield of preferred retail cuts. In the main the batch differences were greater and commercially more important than the conformation class differences.

The effect of the presence of rams upon the blood LH levels of ewes just at the start of the breeding season has been studied. It was found that there was a large and sudden increase in LH levels of ewes exposed to rams when compared to a control group. There were also small but non-significant effects on the mean date of the start of the breeding season and upon the number of lambs born.

An experiment was carried out in which equal amounts of concentrate were given to beef cattle once, twice or three times per day, with a basal hay diet. There were no significant differences between treatments in food and water intake, digestibility coefficients, nitrogen balance data or live-weight gain.

Selected sample joints from the right sides of twelve 18-month-old Friesian steers were used to compare their accuracy in predicting carcass composition. Results indicated that whilst the shin joint proved the more accurate predictor of carcass muscle and bone contents, the loin (ribs 11 to 13) or foreloin (ribs 9 to 10) proved more useful in predicting total carcass composition, provided carcass weight was included as an additional variate.

Two Pietrain/Hampshire crossbred males and two Large White males were mated in equal numbers to 24 Large White females. Breed of sire did not affect litter size or total weight at birth or weaning. After weaning, on ad libitum feeding over the live-weight range 25 to 88 kg, the crossbred pigs grew more slowly to slaughter (5%) but with equal efficiency of live-weight gain. Crossbreds had higher carcass yields (3%) shorter carcasses (3%) and larger ‘eye-muscle’ areas (18%). Fat depths, joint proportions and cut-out values were not affected. The ‘eye-muscles’ of crossbreds were paler in colour and had a lower water-binding capacity than those of the purebreds, but pH1 values and transmission percentages did not differ.

The present study investigated the intensity of the anoestrous period in 36 Hampshire and Suffolk ewes as influenced by the photoperiod and the presence of the ram. The study began on 4 April and terminated on 11 June. Ewes kept under natural light in the absence of the ram (Group I) exhibited a limited amount of ovarian activity as determined by cervical smear. Ewes kept under natural light, but in the presence of a ram (Group II) showed an increased amount of cycling (P < 0·05) when compared to that in Group I. Two ewes from Group II mated during the so-called anoestrous period and subse-quently lambed. Ten of 12 ewes, subjected to a decreased photoperiod (Group HI), increased ovarian activity within a few days of light reduction. Five ewes in this group lambed.