The incidence, heritability and effects on lactation performance of twinning in 185 000 calvings in Israeli-Friesian dairy herds are presented. The incidence of twinning in heifer and cow calvings (parities 2 to 6 inclusive) was 0·7 and 5·4% respectively in the large Kibbutz herds and 0·7 and 3·5% in smallholders' herds. The heritability estimate for 144 sires each with over 200 calvings of daughters of parity 2 to 6 was 0·024 ± 0·002. The range of incidence of twinning in these parities among sire progeny groups each with more than 1000 calvings was 2·8 to 7·8 %, apart from one sire, whose daughters had 12·2% twins. His progeny excelled in five characters and as an explanation it is suggested that a rare gene is segregating in the breed with a major effect on the endocrine system and associated pleiotropic effects.

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.

1. Six experiments each with 2 groups of 9 pigs (9 castrated males and 9 females), 26 to 31 kg initial weight, were kept in a large indirect calorimeter equipped with two identical pig pens. In each pen nine animals were housed for periods of 6 to 8 weeks. The floors tested were: asphalt, straw bedding on asphalt (25 mm straw on asphalt), and concrete slats. Two experiments, each of four periods, were performed on each of the floors. The temperature in the calorimeter was changed in stepwise fashion by 2 to 3°C at intervals of 2 to 3 days. In periods 1 and 3 the temperature was decreased stepwise from 20·23°C to 5·8°C, and in periods 2 and 4 in the reverse order. Gaseous exchange was measured at each of the temperatures for 48 hr. Feeding level was kept constant at about 1160 kJ meta-bolizable energy/kg0·75.day.

2. Heat production and energy balance per unit of feed intake were similar on all floors in the zone of thermoneutrality and the derived maintenance requirements were also similar with a mean value 438 kJ/kg0·75.

3. The effective critical temperature of animals weighing 40 kg was 11*5 to 13°C on straw bedding, 14 to 15°C on asphalt and 19 to 20°C on concrete slats.

4. At temperatures below the critical temperature heat production was increased. The increase in extra thermoregulatory heat production was on average 8·9 kJ/kg0·75 per °C below the effective critical temperature. Between the various floor types differences in this increase were noticed, but were not significant.

5. Body-weight gains on asphalt and straw bedding were similar; on concrete slats the body-weight gain was significantly reduced.

In a population in which generations overlap the improvement in performance in successive years resulting from a single year of selection is not constant, for the genes from a group of selected individuals may take many years to pass through the population. A formal method is developed for predicting responses and discounted returns from improvement in populations with overlapping generations including, if necessary, generations of multiplication of breeding stock.

The method is based on a matrix which specifies the passage of genes between the different age groups and sexes. Simple matrix operations can be used to compute the proportion of genes in animals of both sexes and each age in the population at any time which derive from a group of selected animals at an earlier time. The response produced by these selected animals equals the product of their genetic selection differential and the proportion of genes deriving from them. Comparisons are made between responses predicted using this theory and the classical theory of uniform rates of response, and a method is given for computing the time lag of genes passing through the population.

The results are extended to enable computation of discounted returns from improvement.

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.

1. Twenty-six shorn Scottish Blackface sheep received nine daily cold shocks (down to −10°C) each lasting 1 hr. This treatment reduced the metabolic response to cold (lower heart rates) and caused passive body cooling—defined as habituation. Eight selected sheep showing maximum habituation and 16 untreated controls then received blocking treatment (re-shorn and cooled for 2 hr at 18°C or 8°C) before being heat-stressed (at 42°C) to elicit panting.

2. Thermal panting, delayed as expected by blocking treatment, was further delayed by previous cold habituation. Habituated sheep blocked at 18°C panted 30 min later than blocked controls. In habituated sheep blocked at 8°C, panting was completely inhibited even after 90 min heat stress; their final mean respiration rate was 19/min v. 220/min in blocked controls and 250/min in unblocked controls. Rectal temperatures of habituated sheep were lower than controls during blocking treatment.

3. Habituation, by restraining the normal metabolic response to cold, increased the heat debt during blocking treatment and lessened the heat load during subsequent heat stress. This apparently reduced the drive for panting. Habituation may also have favoured a direct inhibitory effect of cold on the respiratory centres.

Observations have been carried out on the effect of social environment on the behaviour and growth rates of British Friesian male calves artificially reared on an automatic Nursette milk dispenser. The observations were made during two watches of 3 hr duration per week for the first 9 weeks of the calves' stay in the rearing unit. The calves appeared to be in a high state of anxiety on arrival and showed a vigorous following response to each other and the stockman. Although the lighter subordinate calves spent less time in sucking the Nursette than the heavier dominant calves, and had a lower pre-weaning growth rate, they spent more time ingesting dry feed. Consequently they suffered a less severe check in growth rate at abrupt weaning after 6 weeks than the dominant calves. Non-nutritive cross-sucking of the ear, scrotum or prepuce of others in the group occurred in some calves. The aetiology of cross-sucking is discussed and interpreted in terms of an oral deprivation hypothesis.

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.

Blood groups were determined for eight loci in a total of 742 sheep and for the Tf (transferrin) locus of 512 sheep comprising the Scottish Blackface, the Cheviot and the Welsh Mountain breeds and their crosses. Each breed and cross was represented by a non-inbred F2 generation and by three stages of inbreeding (25, 37½ and 50%). The loci for which all genotypes were distinguished were Hb, M, and Tf, and those for which partial description (including the recessive homozygote) was made were A, B, C, D, R and i.

There were large differences among the three pure breeds only for the frequencies at the Hb and Tf loci. The homozygote frequencies of the Blackface-Welsh and Cheviot-Welsh crosses were approximately half-way between their respective pure breeds. For the Blackface-Cheviot cross the homozygote frequency was considerably lower than either parental breed, suggesting that over all loci there were greater differences in gene frequencies between these two breeds than between the Blackface and Welsh or Cheviot and Welsh.

On average over all loci (except Tf) inbreeding had the effect of decreasing heterozygosity roughly in relation to expectation. Individually this effect was statistically significant only for ii, MbMb, HbAHbA and HbbHbb. For the Tf locus there was no average decrease in heterozygosity as a result of 25% inbreeding but thereafter there was a greater decrease in the purebreds than in the crosses.

There were small (< 0·20) but significant residual correlations between R-O-ii blood types and genotypes at several other loci, and between dd and the M system genotypes.

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.

Sows which had lactated for 2 days were allocated either to a control group or to a group in which oestrus was delayed by the administration of 75 mg methallibure per day for 12 consecutive days, followed by an intramuscular injection of 1000 IU pregnant mare serum gonadotrophin. All sows were mated whenever they were receptive to a boar. The mean time to first mating for the control group of 12 sows was 7·3 days but the mean time to conception was 22·3 days. The corresponding figures for the 9 treated sows were 17·0 and 22·2 days. The treated sows had significantly (P < 0·025) larger litters than the control sows (11·7 v. 8·5). For those sows which conceived at the first post-weaning service, the delayed oestrus treatment increased litter size on average by more than four pigs per litter.

In a 15-year period (1956-1970) data were available from 192 Brahman cows exposed to bulls on 1409 occasions (1199 calvings) and from 155 Santa Gertrudis cows exposed 907 times (847 calvings). All were mated by natural service in the same herd in Cuba. Calving percentage and net calf crop significantly favoured the Santa Gertrudis with overall means of 92·7 and 85·3% for the two traits respectively. Parity, lactation status and year of calving significantly affected calving percentage with significant year × breed and status × parity interactions. Lactation status, year of calving, breed × year and status × parity interactions also affected net calf crop. Calf mortality was 6·41% in Brahmans and 5·64% in Santa Gertrudis but more of the latter breed were stillborn (41·7 v. 16·9% of all deaths). There were no breed effects on age at first or last calving, age at culling or calves per cow which were 38·5 months, 117·1 months, 130·1 months and 6·62 calves in Brahmans and 39·3, 111·5, 123·2 and 6·58 respectively in Santa Gertrudis. Twinning percentage was low (under 0·4%) and male births high (53·54%) in both breeds. Some 30% of cows lost at least one calf prior to weaning during their lifetime.

The onset and duration of oestrous and ovulatory activity in 26 Greyface ewes receiving natural daylength changes were determined. Precise ovulation data were obtained by endoscopy and repeated observations of the ovaries of all ewes were made on 10 occasions from 15 July 1971 to 27 June 1972. The natural breeding season for these Greyface ewes was, on average, 22 September 1971 to 18 February 1972. There were significant seasonal changes in the mean ovulation rate of the ewes which appeared to be inversely related to seasonal changes in natural daylength.

An abrupt decrease in artificial daylength of 11 -43 hr applied on 22 June 1971 to 28 similar Greyface ewes advanced their mean onset of oestrous activity by 23 days. The decrease in artificial daylength also advanced the occurrence of ovulation in these ewes. The highest mean ovulation rate of the ewes receiving the decrease in artificial daylength was at least as high as the peak mean ovulation rate measured in the control ewes.

At most stages of the experiment, the plane of nutrition had no significant effect on either oestrous or ovulatory activity in the ewes.

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.

Over a 15-year period 1011 calving intervals from 187 Brahman (B) cows and 687 calving intervals from 146 Santa Gertrudis (SG) were examined. Year of calving significantly affected intervals in both breeds. Season of calving and parity of dam were both important in SG. Longer intervals were seen in B than SG (437 v. 406 days). Repeatability of calving interval was low (< 0·02). The average life-time calving interval was significantly related to total calf production in that cows with shorter mean intervals had more calves in their lifetime.

Fleece and skin samples were taken at intervals from birth to 86 days from Scottish Blackface lambs born into one line selected for hairiness, another for fineness and an unselected control line. The birthcoats in the Hairy line were longer than those in the Fine line, and had a predominance of Plateauo and Pi fibre type arrays, whereas P2 and P3 arrays predominated in the Fine line. The Hairy group had significantly more halo hairs and hairy-tip curly-tip fibres, but significantly fewer histerotrichs.

Most secondary follicles had fibres by 56 days, and development appeared to be faster in the Control than in the other two groups. The Hairy and Control groups had consistently high percentages of primary medullation, whereas the Fine group had a peak at 14 days. The Fine group had consistently low secondary medullation, whereas it increased in the Hairy and Control lambs, apart from a set-back at 28 days.

Up to 56 days the Fine group had no fibre shedding in the skin, and the Hairy group had most, although the incidence in any sample was less than 2%. There was more follicle inactivity at 86 days, and the Fine group then had most.

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%.

Complete diets each containing (1) 0%, (2) 20%, (3) 40%, (4) 60% high-quality, (5) 20% and (6) 40% low-quality dried grass were given ad libitum to 48 British Friesian calves.

The performance of the animals was studied over the stages of growth from 50 to 100 kg and 150 to 200 kg live weight. At each stage of growth the live-weight gain was similar on all treatments while the daily intake of dry matter was significantly affected by the treatments. Over the stage of growth from 50 to 100 kg live weight the intake of metabolizable energy was greatest on treatment 2 and lowest on treatment 4. The conversion ratio of metabolizable energy decreased with increasing levels and with both qualities of dried grass over the weight range 50 to 100 kg.

When the calves reached 100 kg live weight, digestibility and N balance studies were carried out. The metabolizable energy (ME) expressed as a percentage of the gross energy decreased with increasing levels and with the lower quality of dried grass. Nitrogen retention was not significantly affected by treatment differences.

The relationships of the voluntary intake of dry matter, ME intake and the conversion ratio of ME with the ME expressed as a percentage of gross energy over the lower live-weight range are also presented.

The Israeli procedure for measuring sire breeding values and genetic progress due to selection is described. The estimate of sire breeding value has two components, the current contemporary comparison (CC) and an adjustment for the average genetic deviation of the contemporaries from the original base population. The combined value is called the cumulative difference (CD). For practical purposes the CD was found to be free of the time trends observed for CC, and the residual variances of the two measures were approximately equal. The relative genetic level in any given time interval was measured by the average CD of all sires used during the period October 1964 o t January 1971 in Israel. The analysis indicates that essentially all of the progress in 122-day FCM yields was due to sire selection, whereas 60% of the progress in 305-day FCM yields was due to selection and 40% to improved management.

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.