A scheme is described for the genetic improvement of milk yield in a large population of dairy cows, based on half-sister selection of young bulls, as an alternative to the normal procedure of progeny testing. The results indicate that the suggested scheme would lead t o an eventual rate of genetic progress very similar to the progeny testing scheme. However, the annual cost of the new scheme is less than a progeny testing scheme, largely because the ‘laying off’ of candidate bulls, to await selection, is completely eliminated. In addition, improvement of the dairy cows shows up sooner in the new scheme; by the 10th year from the start the cumulative genetic improvement is four times greater than for progeny testing.

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.

Twenty-eight lactating cows were used in an experiment of changeover design with four periods to evaluate concentrates containing 0, 16, 32, 49, 65, 81 and 97% dried grass. The dry matter of the dried grass was 63% digestible. The concentrates also contained barley, together with groundnut meal to equalize their protein content at approximately 16-5% of dry matter. All animals had grass silage ad libitum and all concentrates were given at the rate of 0·4 kg/kg milk. Milk yield, milk composition and liveweight change were not affected by including dried grass in the concentrate. No significant effect of concentrate on silage intake was obtained. Ration digestibility and nitrogen utilization were measured with four animals per treatment. The digestibility of dry matter, organic matter and nitrogen was not reduced by increasing the proportion of dried grass in the concentrate. The efficiency of utilization of apparently digested nitrogen for total productive purposes (body retention and milk nitrogen) was also not affected by the proportion of dried grass.

Thirty one-year-old Charolais × Holstein-Friesian (CH) and Hereford × Holstein-Friesian (HH) steers averaging about 268 kg live weight were used to study the effect of increasing slaughterweight from the traditional 454 kg (1000 lb) to 544 and 635 kg (1200 and 1400 lb) live weight. The steers were fed a growing ration of grain, silage and hay until they weighed 68 kg (150 lb) below the assigned slaughter weight, followed by a finishing ration of grain mixture and maize silage given ad libitum. Average daily gain on the growing ration was 0·91 kg in CH, 14% higher than that in HH steers, while on the finishing ration HH steers, finished at 544 and 635 kg, made higher gains. CH steers were 7·9% more efficient than HH steers in feed conversion. Feed conversion efficiency (total dig. nutrients (kg) per kg live-weight gain) decreased by 10% and 19% respectively as slaughter weight increased to 544 and 635 kg. Live measurements showed that CH steers were generally longer, taller and wider at the hip, whereas HH steers had a greater depth of chest and width of shoulder. CH steers, slaughtered at different weights, had a higher percentage of round and shank, while HH steers had a higher percentage of all other wholesale cuts. Carcass measurements were generally higher in CH than in HH steers. CH steers had a higher percentage of muscle and bone, and lower fat, in the 12th rib. They also had larger areas of m. longissimus thoracis. Fat deposition over and in that muscle was much higher in HH than in CH steers. Under the conditions of this study, 544 kg was found to be the optimum slaughter weight for both groups. Slaughtering steers at 635 kg was found to be economically disadvantageous.

The intake of drinking water of lactating British Friesian cows in 14 herds with a total of 840 animals was measured monthly from November to April inclusive. The intake of food, the air temperature and relative humidity were also recorded. The herds which mainly contained autumn-calved cows were managed under controlled commercial conditions.

The average daily intake of drinking water was 49·9 (range 20·1 to 87·1) kg/cow for animals yielding an average of 16·8 kg milk/day in an environment with a mean temperature of 8·2°C and a relative humidity of 84·8%. The amount of water drunk daily was positively and significantly related to the mean daily milk yield and the drymatter content of the ration, but not significantly related to either the mean air temperature or the relative humidity. The average intake of water was 3·70 kg per kg of dry matter consumed after subtracting the amount of water in the milk. On average, 40·0% of the total daily intake of water was drunk between 15·00 and 21·00 hr.

Behaviour studies of 24 hr duration on five herds showed that drinking time ranged from 2·0 to 7·8 min/cow per day, and the rate of drinking varied from 4·5 to 14·9 kg/min.

Recommendations are made for the provision of drinking water for dairy cows being offered a wide range of forages under modern conditions of housing.

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.

Five measures of persistency of milk yield were compared by means of apparent heritabilities and repeatabilities using 598 first lactation records from the Danish progeny testing stations and 354 records of all parities from Red Danish cows at a state experimental farm. Unbiased estimates of heritabilities could not be obtained because of common environmental effects. Results indicate that measures of persistency giving equal weight to single milk records are superior to measures giving different weight to single records.

Correlations between persistency, expressed as the absolute decrease of yield, and maximum daily yield were —0·46 to —0·52 (phenotypic) and —0·22 (genetic). Correlations between persistency and 305-day yield were —0·06 to —0·10 (phenotypic) and 0·02 (genetic).Correlations between persistency, expressed as the decrease of yield relative to level of yield in early lactation, and maximum daily yield were —0·06 to —0·13 (phenotypic) and 0·17 to 0·42 (genetic). Correlations between the measure of persistency and 305-day yield were 0·12 to 0·45 (phenotypic) and 0·45 to 0·69 (genetic).

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.

Maternal performance of female sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds has been studied in terms of lifetime production and some of its components. The data are based on 193 ewes, which were given the opportunity of having four annual lamb crops, and their lambs.

There was no significant variation among the breeds and crosses in ewe survival or in the proportion of barren ewes at each lambing. There was significant variation among the breeds and crosses in the number of lambs born per ewe lambing, in lamb survival and in weights of lamb at birth and at weaning. Crossbred ewes (producing crossbred lambs) had more and heavier lambs than expected from the average of the pure breeds contributing to each cross, but the three crossbred types differed in the amount of heterosis shown. Over their lifetime in the flock there were significant breed differences in the total weight of lambs weaned, with crossbred ewes producing about 9% more than the average of the parent breeds involved. The crossbred ewes produced more weight of lambs over their lifetime than pure Cheviot or pure Welsh Mountain ewes, but not as much as pure Scottish Blackface.

Effects of parity of dam and of sex, birth type, and type of rearing of lamb are given.

The effects of roughage level (15 and 35% of the ration) and of slaughter weight (400,450 and 500 kg) were studied in an experiment of 2 x 3 factorial design. Daily live-weight gains and carcass gains were significantly higher on the lower roughage levels, but there was no difference in degree of fatness of the carcass. Dry-matter intake expressed as a percentage of body weight was 2·91 on 35% roughage compared with 2·53 and 15% roughage, i.e. 15% higher on the highroughage diet. This compensated the animals on the high-roughage diet for the lower energy content of their feed. Rate of gain increased with an increase in slaughter weight. The percentage of fat trim and of saleable meat increased, while that of bone decreased significantly with an increase in slaughter weight. The animals on the lowroughage diet were approximately 11% more efficient than the others in converting metabolizable energy into live weight.

Data werfe analysed of litters from Large White and Landrace herds which were tested at central stations in Great Britain for growth and carcass traits. Information on reproductive performance of young females was combined with data on their relatives at central stations in order to calculate genetic relationships of reproduction with growth and with carcass traits. Progeny testing of boars for both sets of traits was the most efficient of the methods considered for this analysis.

In general, the estimated genetic correlations of reproductive performance with growth and with carcass traits were alike in sign for the two breeds, and the signs of the matrix of values were internally consistent. For example, combining data for litter sizes in the Large White breed, genetic correlations were −0·15 (food conversion ratio), 0·06 (daily gain), −0·18 (average backfat depth), −0·63 (killing-out percentage) and −0·41 (hind quarter percentage). When the growth and carcass traits were combined as total points score in a selection index, the genetic correlation between this score and reproductive performance was very small, with a range from −0·04 to 0·02. Calculations showed that inclusion of reproductive performance in the index would increase the rate of genetic improvement by only 0·55%.

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.

Mortality to one year of age was studied in artificially-reared calves of Tharparkar, Sahiwal and Red Sindhi breeds together with Murrah buffaloes and Brown Swiss x Sahiwal and Brown Swiss x Red Sindhi. Data covered 6267 animals over the period 1952–71. There were significant breed differences with the Brown Swiss crosses and buffaloes suffering higher losses than the Zebu breeds. Age effects (0 to 1, 1 to 3, 3 to 6 and 6 to 12 months) showed that losses were greatest in the first month of life and declined thereafter. There were significant year effects but seasons (summer, monsoon and winter) showed no significant effects although a tendency to higher losses in winter did exist. Sex effects showed no differences. Pneumonia was the major cause of loss to 6 months accounting for 30 to 40% of deaths with scours and enteritis being the second most serious factor (15 to 35% of losses).

Half carcasses of 18 Pietrain and 18 Large White female pigs were dissected into 10 bone units. An allometric analysis of the weights of these units relative to total bone revealed increasing craniocaudal and distoproximal growth gradients. No differences in bone distribution were observed between the two breeds. Because of a difference in muscle distribution, the muscle: bone ratio in the femoral region of the Pietrain was greater than that of the Large White breed.

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.

One hundred and four Damascus goats with their kids were used study the effects of early weaning on the lactation of the goats and the growth rate of the kids. The treatments studied were: 2-day suckling (S2) where the kids were suckled by their dams for 2 days a d then reared artificially on milk replacer; 35-day suckling (S35) where the dams suckled their kids for 35 days; 70-day suckling (S70) where the dams suckled their kids for 70 days.

The differences among treatments in 150-day and total milk yield and lactation length were not significant. Conversely, the differences in the yield of milk available for marketing were highly significant. The goats on S2 produced more marketable milk than those on S35 and S70, and the goats on S35 produced more than those on S70. The growth rate of the kids weaned at 35 days of age was significantly lower than that of those weaned at 70 days. The differences between kids reared artificially and those suckled by their dams to 70 days of age were not significant. It was concluded that early weaning does not materially affect lactation performance and that it can increase the milk available for marketing.

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.

1. Pig growth hormone (PGH) concentrations were measured in plasma samples from piglets of 3–4 to 7–8 weeks of age.

2. Plasma PGH concentrations decreased significantly with age. No difference was observed between the hormone concentrations of gilts and barrows.

3. Correlation coefficients were calculated between mean plasma growth hormone concentration over a 4-week period and several carcass characteristics and measures of growth rate. Plasma PGH over this period showed significant negative correlations with several measures of carcass backfat thickness at bacon weight. In barrows only, PGH concentrations showed a significant direct correlation with relative growth rate from 3 to 7 weeks.

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.

The rate of cutaneous evaporation was highest in the White Fulani (Bos indicus) followed by the N'Dama and German Friesian (Bos taunts). The lowest rate of evaporation was recorded in the Muturu (Bos taurus brachyceros). In all breeds, the rate at 15.00 hr was significantly higher than at 18.00 hr.

For the sites sampled, evaporation rate was highest on the hump and mid-side, followed by the neck and lateral thigh and lowest on the dewlap and navel flap.

The possible correlation of these results with the size and distribution of the sweat glands on various sites of different cattle breeds is discussed.