First lactation records from 971 daughters of 93 Red Danish Milk-breed bulls exported as pregnant heifers from Denmark to 4 Bulgarian and 21 Czechoslovakian herds were analysed and compared to results from corresponding half-sib groups under Danish field progeny tests. Average butterfat production in East European tests was 75% of that in Danish tests.

The results indicate that the true genetic variance and the heritabilities for milk yield, fat content and butterfat yield are higher under the Danish conditions than under the corresponding East European conditions. The genetic correlations between the two environments are estimated to be 0·91, 0·97 and 0·79 for milk yield, fat content and butterfat yield, respectively. Because of insufficient correction for environmental effects, these estimates are considered to be lower than the true parameters.

It is concluded that selection of proven sires in the Danish main population for use in the small East European subpopulations will result in a higher genetic improvement rate than will sire testing and selection within the subpopulations.

With the object of comparing the energy requirements of cattle of different breeds a total of 108 animals, representing three maturity types, were individually fed at two levels of intake over three 12-week periods commencing at 250, 375 and 500 kg live weight in a co-ordinated experiment. The three breeds compared were Aberdeen Angus cross, Hereford × British Friesian and British Friesian. Animals were offered a 50:50 hay: concentrate ration at two levels of feeding; one level was designed to give 0·7 kg gain daily and the other 75 to 80% of this intake.

Though the relative performance of breeds differed at the three centres, overall average live-weight gain did not differ significantly between breeds. Feed conversion efficiency dropped from 8·55 kg dry matter per kg gain in the first period to 16·95 kg in the third period, but differences in conversion ratio between breeds were not significant.

Carcass measurements taken at slaughter immediately after the third test period indicated higher killing-out percentages and higher fat percentages in the Angus cross than in the British Friesian with Hereford × Friesian intermediate. Differences in energy needs for gain among the three breeds, predicted by apportioning ME intake to maintenance and gain using a multiple regression technique, were greater than differences calculated from carcass composition and published energy requirements for fat and protein deposition. The limitations of the use of the multiple regression technique for this purpose are discussed.

Correlations and regressions between estimated breeding values for 122 day part-lactation, 1st and 2nd lactation yield (part, 1st, 2nd) were estimated from 106 sire progeny groups, each with at least 60 effective daughters.

The genetic correlations between part, 1st and 2nd kg milk were 1·0 and 0·84 respectively, and the regressions of 1st on part and of 2nd on 1st test were 2·40 and 0·82 kg/kg milk, respectively. Selection by one standard deviation between sires on part-lactation tests would improve 1st lactation yields by an average of 204 kg milk with a standard deviation of 84 kg. Selection on 1st lactation yields by one standard deviation would increase 2nd lactation yields by an average of 183 kg milk with a standard deviation of 156 kg, indicating that some bulls so selected could have below average 2nd lactation yields.

Two sire selection models were simulated differing in the selection criterion; 1 st yield in model 1, and 1 st followed by 2nd yields in model 2. The contribution of proven sires to the rate of genetic improvement in lifetime production was greater from model 2 than from model 1 by about 15% without any additional costs for bull maintenance.

An attempt to evaluate a group of 72 beef carcasses, in retail terms, is described, resulting in a comparative measure of retail value that takes account of saleable fat and of the distribution of lean amongst the different cuts. Changes in the general level of beef prices can be discounted, provided the ratios of the prices of different joints remain the same. It was found that the index of retail value was poorly correlated with the commonly used ratio of high-priced to low-priced parts, but highly correlated with total proportion of lean. The index could best be predicted from a multiple regression on side weight and proportional area of muscle determined from photographs of the cut surface after quartering.

Three changeover experiments, each with 16 milking cows, were conducted to evaluate the effects of stage of growth of lucerne, level of feeding of lucerne or ryegrass and level of inclusion of barley. The artificially dried and processed forages were in the form of cobs and given to cows in addition to a basal ration of hay. Late-cut lucerne (organic matter digestibility, OMD, 55%) promoted significantly lower milk yields than early-cut lucerne (68% OMD). When offered ad libitum in two meals each day both forages were eaten in quantities of about 13 kg dry matter. Ryegrass cobs (79% OMD) produced more milk than lucerne cobs (59% OMD) but gave similar milk yields per unit of digestible organic matter. Production rations supplying similar amounts of digestible organic matter and composed of different proportions of lucerne cobs and rolled barley gave similar milk yields. It is concluded that the relative milk-producing value of processed forages depends on their content of digestible organic matter. However, their bulk may limit their value and the inclusion of cereal with the dried forage may be worth while.

Three groups each of 14 cows, balanced for stage of lactation and potential milk yield, were kept either on a control treatment C, grazing within a rigid rotational grazing system, or on a leader (L) and follower (F) grazing system operated within a similar system. The stocking rate of treatment C was 5·76 cows/ha, the same as the overall stocking rate of treatments L and F. In Experiment 1, a 10-week continuous-type randomized block experiment was preceded by a 4-week uniformity period; in Experiment 2, a 3 × 3 Latin square design was adopted with periods of 4 weeks. Herbage intake and milk yield were only slightly, and not significantly (P > 0·05), higher in the leader than control cows, whilst the performance of cows on treatment F fell significantly (P< 0·001) below the other treatments. In treatment L, cows in early lactation responded to the extra opportunity for herbage selection with significantly (P< 0·01) more milk than those in late lactation. The mean milk production of the leader and follower cows was similar to that of the control cows. It is suggested that the potential value of a ‘leader and follower’ grazing system is unlikely to be greater than that of a conventional rotational grazing system.

A rigid system of grazing management was examined for 2 years using rotations of fixed length. Rotations of 21 and 35 days were compared at low (3 calves+ 3 heifers/ha) and high (4 calves+ 4 heifers/ha) stocking rates. The calves and heifers grazed the paddocks on a leader/follower basis.

Average growth rates for the 21- and 35-day rotations were respectively 0·75 and 0·78 for calves and 0·78 and 0·83 kg/day for heifers, but these differences were not significant. The 35-day rotation produced 6% more live-weight gain and 4% more herbage dry matter/ha than the 21-day rotation. The high stocking rate produced 14% more live-weight gain but 3% less herbage dry matter/ha than the low stocking rate. The total percentage utilization of herbage dry matter for the whole season was similar for 35- and 21-day rotations, averaging 90%. There were no significant interactions between length of rotation and stocking rate.

Suffolk and Rambouillet female sheep (ewes) were kept in pens where daylight was gradually reduced and were treated, or not treated, with hormones to obtain four lambing cycles in 2·5 years. Oestrus in May, June and July was induced more easily (P<0·01) in Rambouillet than the Suffolk ewes. The advantage of higher conception rates in the Rambouillet ewes during anoestrus was offset by the higher prolificacy rates in the Suffolk in the other three lambing cycles. On average, each breed produced 128 lambs per 100 ewes exposed per lambing cycle. This corresponds to 5·1 lambs per ewe in four lambings, which is equivalent to 2·04 lambs per ewe per year. Under the conditions of the experiment, the addition of Syncro-Mate pessaries (20 mg fluorogestone acetate) and pregnant mare serum gonadotrophin (PMSG, 5 ml/ewe, 50 IU/ml) to the treatment of reduced daylight did not affect the ovulation or conception rates.

Weaning increased forage intake and depressed live weight; differences in intakes and growth rates of lambs born to South Australian and Fine wool Merinos were small. At 21 days, sucking lambs received less than 2% of their digestible organic matter from pasture and half the lambs weaned at this age died but the survivors consumed twice as much forage as unweaned sheep in the 14 days following weaning. At 49 days, unweaned lambs obtained approximately 41% of their digestible organic matter from pasture, and weaning resulted in less mortality and a proportionally smaller increase in forage consumption.

Fifty-three Landrace × (Landrace × Large White) young female pigs (gilts) were fed ad libitum from selection at 20 kg live weight until mating at the second oestrous period. All gilts were subjected to a change of environment at 55 kg live weight, and the male was introduced daily from 64 kg live weight. Gilts were mated twice at second heat, and slaughtered on the 20th day of gestation. There was a range in age at puberty from 135 to 235 days (mean 178·9 ± 3·4 days), and in weight at puberty from 70 to 125 kg (mean 90·5 ±2·3 kg), indicating that there is a potential in some animals, at least, to attain sexual maturity at a very young age. Neither gilt age norweight at puberty significantly affected ovulation rate at second oestrus, conception rate or embryo survival during the first 20 days of gestation.

Gilts sired by one boar reached puberty significantly earlier (P < 0·05) than did the offspring of three other boars.

The intake and digestibility of diets containing dried grass supplemented with either molasses or tapioca was studied with 12 Friesian steers in two experiments, using a Latin square design. Three periods were used, each containing 3 weeks preliminary followed by a 10-day collection period. In both experiments long, artificially dried grass was given to appetite (treatment A). The other treatments in Experiment 1 were 25% molasses plus 75% dried grass (B) and 50% molasses plus 50% dried grass (C). In Experiment 2 the treatments were 21% tapioca plus 79% dried grass (D) and 42% tapioca plus 58% dried grass (E). There was no significant difference in dry matter or organic matter intake between the diets, though the intakes in both experiments tended to be lower when the dried grass was supplemented with either molasses or tapioca than when it was given alone. Nor were there any significant differences in the digestibility of dry matter or organic matter between the diets in either experiment. In both experiments the digestibility of crude fibre was significantly lower (P<0·05) when either molasses or tapioca was given with the dried grass than when the grass was offered alone.

The densities of about 1000 limb bones, excised from 110 carcasses of four breeds of cattle ranging in age from 6 to 36 months, were measured by the method of weighing in water. The density of individual bones varied considerably ranging from 1·24 to 1·71 gcm-3 Some of this variation was due to differences between the various bone types within a limb, the cannon bones being more dense than the tibia and radius/ulna which in turn were more dense than either the humerus or femur. Age and breed also influenced density; the older the animal the more dense were its bones and the bones of Jersey cattle were more dense than those of Herefords of the same age. These findings conflict with an assumption that has been made hither to in theoretical analyses of the densitometric method of estimating the composition of carcasses, where skeletal density has been generally taken as constant.