A model is proposed to establish a functional relationship between food intake, weight gain and body composition during growth, based on the differential energy requirements for fat, fat-free tissues and contents of the digestive tract. If constant specific nutrient requirements are assumed for fat and fat-free tissues, these requirements can be directly estimated from changes in food intake and body composition during growth. By introducing an allometric function relating changes in fat-free tissue to changes in body weight, the model is extended to include situations where direct measures of body composition are not available. This enabled the model to be fitted to data on food intake, body weight and growth rate up to 2 years of age in Friesians and Jerseys fed ad libitum on a complete diet. The nonlinear model is contrasted with a linear relationship where food intake i s related to body weight and weight gain. The linear model was unable to account for the changes in food intake over the whole period of growth. The non-linear model allowed a gradual decline n i maintenance requirements per unit weight and indicated an increase in the net conversion coefficient of food into gain, consistent with an increase from early to late growth in proportion of fat deposited.

For the period studied the Jerseys were less efficient in transforming food into weight gain than Friesians. On the non-linear model, about half of the difference was attributable to the higher metabolic rate per unit weight of Jerseys, the remainder to poorer utilization of nutrients for weight gain. If, as the model indicated the conversion coefficients of food into body constituents were the same in the two breeds, the difference in efficiency may be attributable to a higher proportion of fat in the overall gain of Jerseys. The pattern of estimated fat deposition also differed in the two breeds with Jerseys appearing to be less mature in fat percentage at all stages.

Of 335 British Friesian bulls at AI centres progeny tested during the period 1960–65, 19% were retained for further use in the programme following selection.

A time trend towards more intense selection was observed, from an initial selection rate of 1 in 3 to a final rate of 1 in 7. This appeared to involve increased culling for both daughter type and daughter production.

At all stages of the programme approximately 50% of the selection practised was directed towards attributes other than milk yield.

A comparison of the mean contemporary comparison (c.c.) values of the selected bulls with the values obtained following selection solely for milk yield indicated that the inclusion of daughter type as a criterion of selection reduced the c.c. value of the stud by approximately 33%.

A drastic reduction in the c.c. value of the selected bulls was observed to coincide with the appearance of subsequent groups of daughters in the sire proofs.

Four experiments were carried out with calves offered pellets containing different ratios of cereal/protein concentrate and dried grass together with 10% chopped hay. Organic matter digestibility of total ration declined by 5·2 percentage units for each 25% increment of dried grass.

Dry matter (DM) intake of the total ration increased as dried grass content increased from 0 to 50% which led to similar intakes of digestible organic matter (DOM) and daily gain. When pellets contained 75% dried grass, total DM intakes were reduced in two experiments, leading to DOM intakes and daily gains similar to that of calves offered pellets of dried grass only. In the third experiment, DM intake of pellets containing 75 % dried grass was greater than the intake of pellets containing 50 to 100 % dried grass. When equal quantities of DM were offered, DOM intakes and daily gains tended to decline linearly as dried grass content in the pellet increased. The replacement value of the dried grass for concentrate at equal levels of live-weight gain was 1·36: 1.

The relationship was examined between the composition of carcasses from 30 castrated Hereford male cattle and their profile areas obtained from photographic negatives. The accuracy of this method n i determining fatness was compared with that of other methods including visual assessment.

Photographs were taken of a dorsal view of the intact carcass and lateral and medial views of the left side after splitting the carcass. A planimeter was used to measure the areas which were obtained from photographic negatives. Carcass lengths were recorded from the medial views. A panel of six judges assessed the sides for fatness on a seven-point scale with the aid of photographic standards.

Areas and carcass lengths, adjusted to dimensional parity, were used as independent variables in multiple regression analyses, with the weights of the dissected tissues as dependent variables. Explanation of variation in muscle weight was poor, but dorsal area and length were (very nearly) as good as visual score and side weight in predicting total fat weight.

The importance of the different adipose deposits with respect to the total dissectible fatty tissue in growing rabbits and lambs was studied. Development of the subcutaneous fat in the lamb is late and occurs after birth. In contrast, the internal types of fat, such as the perirenal and pelvic fat, represent at birth an important percentage of the total fat. They tend to lose part of their relative importance between 0 and 250 days after birth. In the rabbit the situation concerning the development of subcutaneous and perirenal fat is inverted. For both species the intermuscular fat remains almost constant in relative importance during the whole growth period.

After the period required for the establishment of the different fat deposits, we could observe in lambs, and to a smaller degree in rabbits, a relative growth which tends to become isometric with regard to the total fat deposits.

The relative performances of crossbred ewes sired by Finnish Landrace or by non-Finnish rams were measured in trials at 18 farms which yielded a total of about 2600 ewe lambing records. The dams of the crossbred ewes were Hill breeds (40%), Upland (22%), Long-wool x Hill (20%) and other breed types (18%). The non-Finnish sires were Longwool breeds (35 %), Down and Down crosses (33 %), Upland (22%) and other breeds (10%).

Finnish crossbred ewes were lighter at mating than the average of non-Finnish crossbreds by 10% at 7 months, increasing to 24% at 31 and 43 months, with an average difference of 18% for the first 4 years of life. Over the same period of 4 years Finnish crossbreds had a 27 % higher lambing percentage and 21 % higher weaning percentage than non-Finnish crossbreds.

Lambs born to Finnish crossbreds were, over the 4-year period, 16% lighter for singles and 20 % lighter for multiples at birth, and 11 % for single born and 12% for multiple born at 10 weeks, than those born to non-Finnish crossbreds. But the total litter weight of lamb reared to 10 weeks per 50-kg metabolic ewe weight (at mating) was 16% more for Finnish crossbreds than for non-Finnish crossbreds.

Sixteen Suffolk rams, 8 previously assessed as High libido and 8 as Medium libido, were mated to groups of 6, 12,18 and 30 ewes whose oestrous cycles had been synchronized using progestagen-impregnated vaginal sponges.

Observations over a 3-day mating period indicated that no differences occurred in mating behaviour between High and Medium libido rams. As number of ewes per ram increased, the rams achieved a greater mean total number of mounts and services, but mated a smaller mean percentage of ewes. Also the time taken and the number of services required to mate with all ewes served increased substantially.

As the number of ewes per ram increased the ewes had, on average, to wait longer for their first service and were served less often. There were no statistically significant differences between treatments in the ratio of ewes lambing to ewes served.

In two experiments carried out in the autumn of 1971 and 1972 (treatment prefixes 1 and 2 respectively), 84 Finn x Dorset ewes found by X-ray to carry from 1 to 4 foetuses were individually fed during the last 6 weeks of gestation either: 1A, ad libitum; 1H and 2H, 33 kcal M/kg ewe live weight+365 kcal per ME/kg foetus (anticipated birth weight); 1M, 80%; and 2L, 50% of the total energy fed to treatments 1H and 2H. The amounts given remained constant during the experimental period. The method of feeding according to foetal number within treatments, attempted to standardize the nutritional state within treatments.

All ewes (except those on 2L which remained constant) gained 6 to 8 kg live weight during the last 6 weeks of gestation and lost 8 to 10 kg at parturition. The birth weight of lambs was not affected by the range of energy (2·3 to 4·4 Meal ME/ewe per day) consumed during the last 6 weeks of gestation.

Plasma concentrations of free fatty acids (FFA), glucose and ketone bodies were determined weekly. The mean FFA levels were significantly higher in the low energy treatment groups than the high ones.

The present data indicated that if there is little change in body weight i n the early stages of pregnancy a 65 kg ewe bearing twin lambs, will require about 4 Meal ME/day during the last 50 days of gestation t o prevent a rise in plasma FFA concentration or loss of weight over the gestation period.

Forty litters were weaned from their Landrace × Landrace × Large White dams at 2-day intervals to give a range of lactation lengths from 4 to 42 days. A significant (P<0·001) negative curvilinear relationship was observed between lactation length and the interval from weaning to first oestrus. This period was increased by 4·2 days with the reduction of lactation from 42 to 4 days. The relationship between lactation length and the interval from farrowing to remating was significant (P<0·001) and positively linear over the whole range of observations. A decrease of 1 day in lactation length reduced this interval by 0·91 days. Very short lactations were associated with reduced litter size at the following farrowing; sows weaned after lactation lengths between 4 and 21 days had an average litter size of 9–6 piglets born per litter in the next parity, whereas sows weaned following lactation lengths between 21 and 42 days had an average of 12·7 piglets born in the next parity (P<0·01).

An experiment was conducted using 176 sows at three centres to investigate the effect of post-weaning feed level on reproductive performance. At two centres sows weaned 35 to 56 days after farrowing received 1·8, 2·3, 3·6 or 4·5 kg food/day from the day following weaning until the day following the last mating at the post-weaning oestrus.

At the third centre sows were rationed to 1·8, 2·3 or 3·6 kg food/day or given all they would consume in a single 1-hr feeding period each day. Reproductive performance of the sows was not significantly affected by post-weaning feed level.

The growth performance, carcass quality and digestive efficiency of growing pigs were used to compare sweet lupin seed meal (SLSM) to soya bean meal and meat meal as a source of supplementary protein to wheat in diets for pigs, and to study the influence of low levels of lysine and methionine, high levels of crude fibre and oil, and possible toxic factors in SLSM on the use of SLSM in such diets.

The growth rate and food utilization of pigs between 20 and 80 kg live weight were in the order soya bean meal > SLSM > meat meal, but only the difference between soya bean meal and meat meal was significant. These feeds did not differ significantly in their effects on the proportion of lean in the ham. Adding lysine to the SLSM diet improved growth performance but adding methionine did not. The digestibility of crude fibre in diets containing SLSM was greater than that in diets containing soya bean meal; the digestible energy contents of SLSM and soya bean meal were 4·13±0·05 and 4·16±0·08 Mcal/kg dry matter, respectively. Pigs fed on a diet containing 27·5% SLSM grew faster but utilized food as efficiently when fed ad libitum as on a restricted scale of feeding. The subcutaneous fat of pigs fed on SLSM had a higher iodine number than that of pigs fed on soya bean meal.

A study of the British Friesian Cattle Society's herdbook for 1961 showed that twin births were registered from 323 cows which had borne single calves the year before, and which had 2009 contemporaries of the same age calving single births in the same two seasons and in the same herds.

Least squares means of milk yield and fat percentage calculated from the truncated 305-day lactation showed that the twin mothers exceeded their contemporaries by 118±47 kg milk in lactations 2 days shorter. After correction for herd and year effects there was no difference between the twin birth lactation yield and the preceding single birth yield.

There was a reduction in fat percentage of 0±06% associated with the twin birth lactation.

The proportion of a sample of 194 twin mothers failing to calve again was 24±3% against 19±1% of the mothers of single calves, but no reasons for culling had been recorded.

In a series of feeding trials, measurements were made of silage drymatter (DM) content and pH, animal live weight and intake of DM other than silage. Silage intake has been related to these measurements by multiple regression. Subsequently, within the recorded ranges of the variables used, good predictions have been made of silage intake by large groups of cattle.

In the first of two trials, groups of 10 Chios lambs were fed on long or chopped straw for 13 weeks. They ate 0·61 and 0·65 kg per day, and lost a total of 7·6 and 8·5 kg body weight, respectively. Over the next 20 weeks, the supplementation of chopped straw with either 150 g of soya bean meal or a molasses-urea mixture given ad libitum increased straw intake. The decline in body weight was reversed and the lambs gained 0·04 kg/day on both treatments.

In Trial 2, the intakes of straw by non-lactating ewes were 0·78, 0·78 and 0·70 kg/day with supplements of molasses-urea, barley-urea and barley only, respectively. Ewes on the barley and the barley-urea supplements gained 5·3 and 4·6 kg respectively over the 16-week period whereas those given the molasses-urea supplement lost 2·6 kg.

The repeatability of ultrasonic backfat readings under field conditions was measured in a sample of 57 adult male (boars) and 77 young adult female (gilts) pigs. Repeatabilities of individual fat depths 6·5 cm off the mid-line at the shoulder, mid-back and loin ranged from 0·74 to 0·90. The repeatability of average backfat thickness was 0·92.