The test proofs of 29 Holstein-Friesian sires (12 Canadian and 17 US) with milking daughters in both Canada and the USA were compared. The mean test rating of the Canadian and US sires respectively was 125±74 kg and 265±57 kg higher in Canada than in the United States.

These results were supported by others obtained in milking trials in Denmark and West Germany.

The fat percentage of US Holstein progeny was higher in Canada and Europe than in the USA, suggesting that the low fat percentage of the US Holstein in its country of origin cannot be attributed simply to lack of genetic potential.

It is suggested that the US Holstein be considered as a substitute for the Canadian for the improvement of milking performance in European Friesian populations.

Birth weights of 568 Santa Gertrudis calves by 15 sires out of 111 different dams over a 14-year period were obtained from a herd in Cuba. Year of birth, season of birth, sex of calf, sire and dam all had highly significant influences upon birth weight but there was no effect of dam age or parity. Calf inbreeding ranged from 0 to 25% and led to a decrease of 012 kg in weight for each 1% increase in inbreeding. Calves surviving to weaning or dying between birth and weaning were of similar mean weight. Calves dying at birth were some 4·53 kg above the overall average of 38·59 kg. Sire effects covered a range of some 9·85 kg in birth weight. Heritability of birth weight estimated from an intra-class correlation between paternal half-sib groups was 0·67. Repeatability estimates were of the order of 0·22 from intra-class correlation and 0-24 on the basis of regression of later on earlier records. The overall least squares mean weight of 38-59 kg was several kg higher than previous estimates in the literature.

The selection objective in choosing dual-purpose bulls for use in artificial insemination should be the economic benefit conferred on the population with each insemination. The value of a unit of genetic superiority in the bull for a beef or a dairy trait, as realized through one insemination, depends on two factors—the economic value per unit of superiority and the number of times that superiority is expressed. The economic values are easily established. A standard unit of expression for a trait is defined to be one progeny expression in the year in which the insemination is carried out. A method is developed for summarizing the total genetic consequences of an insemination in these standard units. It takes account of the timing of the insemination, the number of years over which the evaluation is carried out, a discount factor, the dilution of the bull's genotype in his descendants, the female replacement rate, the calf survival rate, and the probability that a surviving calf becomes a dairy cow. The method is independent of the full testing procedures, the intensity of selection, and the level of bull usage. It applies, equally, to selection of bulls for general use and for use in planned matings to produce young sires for testing.

In an egg-transfer experiment, seven breeds of sheep differing widely in mean mature ewe weight were used: Oxford Down, 96 kg; Borderm Leicester, 77; Finnish Landrace, 55; Southdown, 52; Tasmanian Merino, 42; Welsh Mountain, 34; and Soay, 22. Body weight and gestation length of recipient ewes are briefly examined. Of 60 recipient ewes, 95% became pregnant. Embryo survival averaged 69% and appeared to be independent of breed of embryo. Litter size of Welsh Mountain, Border Leicester and Finnish Landrace ewes each given four eggs averaged 2·6, 2·9 and 2·9 respectively so that most of the normally observed breed differences are mainly due to differences in ovulation rate. Observed birth weights were in general agreement with those predicted from litter size and donor and recipient ewe weights. The maternal capacity of Finnish ewes was close to average. Litter size affected survival mainly through its effect on birth weight. For Oxford lambs in litters of 3 to 5 from Finnish recipients, birth weight was 42% that of normal single-born Oxfords and only 42% survived. For Soays the corresponding values were 59% for birth weight and 85% for survival. Finnish lambs were exceptionally small at birth but had the highest viability of all breeds. Lamb mortality was higher for males (18%) than females (9%) especially in large litters (26 v. 11%) but about the same in both sexes for Finnish lambs.

Litter size (number of lambs born per female lambing) of adult female Finnish Landrace and Tasmanian Merino sheep mated to males of either breed was 2·9 and 1·0 respectively. Breed of ram had a direct effect on the conception rate of the ewes to which they were mated—22% of ewes mated to Merino rams returned to oestrus but only 10% of those mated to Finn rams—but not on their litter size.

A comparison of the reproductive performance of crossbred females with that of purebred contemporaries indicated that there was very little or no heterosis for litter size, the crossbreds being almost exactly intermediate between the parents. The proportion of females showing oestrus during the mating period, however, was lower in the Merinos than in the Finns and crossbreds. This was particularly noticeable in females put to the ram at around 6 months of age. Whereas 35 of 36 Finnish Landrace females and 46 of 49 crossbreds showed oestrus, only one of the 20 Merinos did so. At about 6 months of age therefore the crossbred females showed heterosis in the incidence of oestrus.

A rotational system of grazing, in which Friesian calves grazed the paddock immediately in front of a group consisting of pregnant and non-pregnant young female cattle (heifers), was examined at stocking rates initially of 3·0, 3·5 and 4·0 replacement units per ha (a replacement unit = one calf + one heifer). The stocking rates were reduced towards the end of the season by removing pregnant heifers. Measurements were made of live-weight gains and herbage production and utilization. Increasing the stocking rate from 3·0 to 4·0 units/ha depressed live-weight gain in calves by 18% on average and in heifers by 32%. The stocking rate of 3·5 replacement units/ha produced the greatest amount of live-weight gain per ha. There was a progressive decline in herbage production and consequently live-weight gain from early to late season. Herbage production was also depressed by the increased stocking rate. Although the average utilization of herbage at each grazing was low, ranging from 27 to 37% in calves and 35 to 48% in heifers, the total utilization of herbage over the whole season was high, ranging from 88 to 96%.

Muturu (Bos taunts) cattle had a higher density of sweat glands in the skin (2208/cm2) than N'Dama (Bos taurus) (1776/cm2) and White Fulani (Bos indicus) (1584/cm2) cattle. Mean gland volume was 10·46,4·95 and 3·06 × 106 μ3 and length/diameter ratio (shape) of the glands was 3·97, 3·85 and 3·15 in N'Dama, Muturu and White Fulani cattle respectively.

Results of similar studies with German Friesian cattle in the same environment gave a gland count of 1968/cm2, a mean gland volume of 14·1 × 106 μm3 and a length/diameter ratio of 5·73.

Sweat gland measurements were generally higher for Friesian cattle than for zebu cattle and cattle of indigenous Bos taurus breeds.

Regional differences in the parameters were generally significant. The relevance of the results to the adaptability of the various breeds of cattle to the tropical environment are discussed.

Ninety-nine ewes, 33 from each of the Cyprus fat-tailed, Chios and Awassi breeds, were used to compare the effects of three suckling regimes on lactation. These consisted of weaning the lambs at birth (W0), 2 days (W2) and 35 days (W35). The 35-day, 150-day and total milk yields, as well as lactation length, were measured for each group. The lambs weaned from the ewes at birth and 2 days were reared on ewe-milk replacer. The growth rate of these lambs was compared with that of the lambs being suckled by their dams, before and after weaning.

In all cases the milk yields of the Chios and Awassi breeds of sheep were significantly higher (P<0·01) than those of the Cyprus fat-tailed. Within each breed the 35-day milk yields of the ewes suckling one lamb were significantly higher (P<0·01) than those of the ewes on the W0 or W2 treatments, which themselves did not differ significantly. While the 150-day milk yields of the W35 treatment were significantly higher than those of the W0 or W2 treatments, the differences between suckling regimes in terms of total milk yield and lactation length were not significant. It is concluded that differences in milk yield obtained on different suckling regimes are attributable solely to the length of time that the lambs are suckled by their dams.

Prior to weaning the growth rate of the lambs given the ewe-milk replacer was significantly lower than that of the lambs suckled by their dams. There were no differences in the growth rates of these groups of lambs when both were fattened on a creep feed after weaning.

Two feeding trials involving 105 pigs weighing approximately 14·5 kg were carried out to investigate the effects of palm oil, groundnut oil, locally produced lard, and beef tallow at 2·5% and 5% of the diet, on performance characteristics and carcass quality. The pigs were of the Yorkshire and Yorkshire × Landrace crosses, and of both sexes. The 23% protein basal diet had no oil added, and the other eight diets were made from the basal diet by the weight-for-weight substitution of the maize with the 2·5% or 5% levels of the four oil types. The results of the two trials were combined and considered as a 2 × 4 factorial experiment (2 levels and 4 types of oil) with the basal diet serving as the control. Only the pigs in the second trial were slaughtered and their carcasses graded at the average live weight of 57±1 kg. Correlation and regression analyses were made on some performance and carcass characteristics, on the average daily digestible energy intake. Results showed no significant treatment differences in the average daily gains, average daily feed intake, and average daily digestible energy intake, but there were highly significant treatment differences in feed consumed/kg of gain and average digestible energy (DE) consumed/kg of gain (P<0·01). None of the carcass quality parameters showed any significant treatment differences. Both the correlation and the regression coefficients for the average daily gain on DE intake were highly significant for all the oil types and levels, but the relationships were low and non-significant when the feed/gain ratio, average backfat thickness and the average percentage of lean cuts were regressed on the daily DE intake.

Changes in the level of aggression in a restricted feeding situation were examined in a herd of goats with a stable dominance hierarchy. It was found that the number of butts occurring (the level of aggression) depended on both the nature and novelty of the various feeds presented. In general the highest number of butts and the lowest consumption were recorded on the first occasion that each feed was presented. The introduction of unfamiliar or highly desirable feeds to livestock may require special precautions if increased aggression is to be avoided.

The results of earlier work by Breirem have been reanalysed, and some recent results are presented. Breirem's results indicated that for pigs of 16 to 96 kg live weight and fasted for 4 to 9 days, heat production (HP) was related to live weight (LW) according to:

HP = 229 LW0·512

which could be converted to:

HP = 185 LW0·569

This equation gives values for fasting heat production which are about 20% higher than those usually estimated from Breirem's results on pigs of 16 to 196 kg. The recent results, for pigs fasted for 24 hr, were slightly higher than would be indicated by the latter equation. If the values derived from the reanalysis of Breirem's data are related to several estimates of the energy required for maintenance by pigs, values for km% between 87 to 103% are obtained.

The experiment compared the performance of pigs from 11 to 56 days of age when given diets based on maize which had been rolled, or ground through coarse, medium or fine screens, or which were made with maize which had been ground through a medium screen and which were then pelleted or pelleted and crumbled. All diets were given ad libitum.

From 11 days to weaning at 28 days, little feed was eaten and there were no significant effects of the treatments. From 29 to 35 days, daily gain and feed conversion were best on the fine, medium and pelleted diets. From 36 to 56 days, pellets and crumble gave the best performance. There were no significant differences between treatments in the incidence of scouring.