A study of 1567 lactations of 336 Friesian cows in 10 herds has been undertaken to establish to what extent the shape of the lactation curve varies between parities, cows and herds, and to assess the importance of variations in seasonality from year to year, with particular reference to herd production forecasts.

In general, cows calving the same parity at the samé time of year showed similar curves, modified only by total yield and abnormal seasonality of production. Production forecasts based on month/parity subclasses are therefore adequate, provided due account is taken of extréme variations in weather conditions or forage growth.

1. Two experiments are described in which the consequences of variation in grazing intensity were studied during the subsequent period of winter feeding from 12 months of age to slaughter at 18 months. The cattle were loose-housed and fed on silage ad libitum, together with allowances of rolled barley. Individual organic-matter intake was measured periodically, chromic oxide being used to estimate faecal output. The digestibility of the diet was estimated with stall-fed steers.

2. Groups of 12 steers were grazed at different intensities over five-month periods, so that those grazed at the higher intensity were 38 and 16 kg lighter at the start of the 1966 and 1967 winter feeding periods respectively. They did not make significant compensatory growth over the subsequent winter feeding periods, although they had a significantly higher intake of feed organic matter per 100 kg live weight than the control steers.

3. With supplements of 3·63 and 1·81 kg/head per day of barley, live-weight gains were 0·77 and 0·50 kg/head per dayin the first half of the winter, but in the second half, when barley allowances were raised to 4.54 and 2·72 kg/head per day, both groups gained weight at the same rate (0·94 kg/head per day).

4. The higher level of barley feeding reduced silage intake by 0·4 kg OM/kg barley OM at all stages of the winter, and the additional 306 kg of barley was associated with the production of 21 kg more carcass weight at slaughter. This higher yield of carcass was reflected in a higher weight of fat in a three-rib sample joint.

A crossbreeding trial was conducted in the hot wet tropical zone of Ceylon at Karagoda-Uyangoda. Sinhala cows were mated to Jersey, Friesian and Sinhala bulls. A few reciprocal matings were done with the Jersey breed.

The milk yields of the Friesian crosses were higher than those of the corresponding Jersey crosses which were higher than those of the Sinhala. The ½ Sinhala ½ Friesian also had a longer lactation and larger body size than the Jersey cross or purebred Sinhala. A decline of about one-third of the milk yield of the F1 was evident in the F2 generation.

The liability to perinatal mortality increased from the F1 generation calves to F3 calves.

Studies of the social behaviour of a hill flock of sheep confirmed the existence of home range groups with each group having a definable territory. The groupings were not broken by a period of individual penning of the sheep.

Experiments were carried out with Clun Forest ewes to determine the effect on the onset of oestrus of applying the same abrupt decrease in daylength at two different times of the year. An abrupt decrease in daylength of 3·75 hr was applied to the ewes on 1 July 1968 and on 24 April 1969. The mean number of days from the commencement of the light treatment to the onset of oestrous activity was 59·5 and 87·0 days, respectively. It is concluded that the time of year at which the light treatments were applied, or the previous light treatment of the Clun Forest ewes, or both, significantly (P<0·001) affected the date of onset of oestrus.

Data on calves sired by Charolais bulls and their contemporaries in 22 commercial herds in Northern Ireland indicate that the Charolais calves were significantly heavier than their contemporaries at weaning as well as at birth. Although the weight of dam was also significantly greater for the Charolais calves, all the evidence indicated that this was not associated with calf weight and did not, therefore, invalidate the conclusion on calf weights.

The present results suggest that although interaction between breed of sire and sex is not statistically significant for calf weights neverthe-less the superiority of Charolais sires was much greater for males than for females. The interaction was significant for daily gain to weaning. Separate analyses for the two sexes indicated that the Charolais-cross males gained significantly better than their contemporaries whereas no significant difference in gain could be detected in the females.

The seasonal incidence of rumen and liver lesions is recorded in traditional and in intensively managed cattle, together with the vitamin A status of the two groups. Rumen lesions were observed to reach a peak in the late winter and early spring in traditional cattle, at which time the liver vitamin A levels fell to the lowest point; liver lesions reached a peak in the late summer. No specific trend was observable in rumen and liver lesions in the barley beef group. The mean levels of vitamin A were approximately one-third of those shown by the traditionally managed animals.

It did not prove possible using the agglutination test to identify the sera of animals showing active hepatic necrobacillosis at the time of slaughter.

Estimates of the heritability, the repeatability and the genetic cor-relation coefficients of litter performance traits were calculated from data on 38000 Large White litters farrowed in 146 British herds.

The repeatability estimates of number of live pigs per litter at birth, three weeks and eight weeks were 0·15, 0·14 and 0·14 respectively. The corresponding heritability estimates were 0·07±0·02, 0·07±0·02 and 0·09±0·03, respectively. The repeatability estimates of litter weight at three weeks and eight weeks were 0·15 and 0·04, while the corresponding heritabiUty estimates were 0·08±0·02 and 0·03±0·02. High positive genetic and phenotypic correlations were obtained between litter size and litter weight.

A number of model culling schemes were considered and it was found that even at relatively high culling levels the improvement in overall herd mean performance was very small. Direct selection for litter size may yield a useful rate of improvement if selection is con-fined to one trait and large selection differentials are achieved, but could not be economically justified.

Data from 22, 28, 36 and 41 pregnant cows in weeks 4, 3, 2 and 1 before calving respectively and 51, 65, 56 and 36 cows in weeks 1 to 4, 5 to 8, 9 to 12 and 13 to 16 of lactation respectively were used in multiple regression analyses to study the feasibility of predicting the daily total and the roughage organic matter and digestible organic matter intakes of cows given known weights of concentrates plus roughage ad libitum. The digestibility of the total intake and of the roughage component, the weight of concentrates eaten per day, the proportion of roughage in the total intake, age, milk yield, fat-corrected milk yield, live-weight gain and the 1·0, 0·73 and 0·66 exponents of live weight were used as independent variables.

The accuracy of the models was assessed from the significance of the partial regression coefficients, the size of the residual standard errors, and the population tolerance limits about predicted values, and by applying selected models to a set of data not included in the study. The results indicated that the precision likely to be achieved in the prediction of intake for individual cows was of limited practical application, but the mean intakes of groups of 30 similar cows could be predicted with an acceptable level of accuracy for practical application. In general, weight of concentrates offered and the digestibility of the roughage were the most effective independent variables in all cows, together with milk yield in lactating cows. The application of the results to conventional feeding systems and to complete diets offered ad libitum is discussed.

Animal Production: Volume 12, part 1, pp. 55–62: A number of arithmetical errors have been found in the paper entitled: The incidence, Repeatability and effect on dam performance of twinning in british friesian cattle

An estimate of the frequency of twin calvings was obtained from the analysis of over 38 000 calvings of Friesian cows in M.M.B, milkrecorded herds. The incidence of twinning increased from 0·54% in the first parity to 3·37 % in the fifth parity. A significant excess of cows above expected produced either more than one set of twins or no twins at all. Repeatability ranged from 0·028 for cows with three calvings to 0·063 for cows with five calvings.

Data on lactation yield and duration, butterfat percentage and calving interval showed some significant effects of twinning. Consistent trends were noted showing that dams which calve twins have longer subsequent lactations, higher whole lactation yields and lower fat percentages than contemporary dams with single calves. The possible causes for these trends are discussed and are considered to be the lower breeding efficiency and longer calving intervals of dams of twins.

Regression of litter weight of newborn lambs on the live weight of ewes at mating has been estimated from data on 15 breeds after conversion of group means of ewes and lambs to natural logarithms. Regression coefficients were estimated to be 0·721 for single lambs, 0·741 for twins and 0·773 for triplets. These values are not signi-ficantly different from each other. Data from ewes with single lambs and from ewes with twins are consistent with the hypothesis that litter weight at birth as a proportion of ewe weight at mating tends to dechne as ewe weight rises from small to large breeds. In a breed with ewes averaging 25 kg the expected birth weight of singles is 9·6% and of twins 15·2%, of ewe weight. For a breed with ewes of 100 kg the corresponding weights would be 6·5% and 10·6% of ewe weight. Since the estimated regression coefficient and the coefficient in the expression for metabolic weight (0·730) are alike, the regression equations can be interpreted as showing that single lambs were 22·6% and twin pairs 36·1% of ewes' metabolic weight.

Data from 38000 Large White litters farrowed in 146 British herds were analysed to investigate the relative importance of various sources of variation affecting litter productivity. The effects of the season and the year of farrowing were very small relative to the effect of the herd of farrowing which was particularly large on the litter and average pig weights at three weeks. There was a small increase in the size of gilt litters as the age of the gilt at first farrowing increased. Litter size increased progressively with parity up to around the fourth litter and then declined gradually at higher pari-ties. There was a suggestion that the sire of a litter may hve a very small effect on litter size at birth but not at three weeks or eight weeks.

A sample of 6846 Friesian heifers recorded in 672 herds during the year ending 30 September 1968, taken from two areas of England and Wales, has been used to estimate the effect of the calving month on total lactation yield. In both areas, the North and the South-West, a variation amounting to nearly 12% of the mean yield was estab-lished, with lactations resulting from October-December calvings the highest and those from May-June calvings the lowest. There was no evidence of association with particular levels of management, or management systems, as exemplified by a seasonal calving pattern.

Individual observations made in different weeks of lactation (WL) of live weight (LW, lb), milk yield (MY and FCM, lb/day), age (years) live-weight change (LWC, lb/day) and digestibility of the organic matter consumed (D, %) were used to produce models pre-dicting organic-matter intake (OMI, lb/day), digestibleorganic-matter intake (DOMI, lb/day) and faecal output (lb OM/day) in 72 grazing cows (Analysis A). Estimates of herbage availability (HA, lb dry matter/cow per day) applicable to 44 of the cows, together with the above variables were used in a similar manner (Analysis B). The multiple regression methods of analysis were applied solely to between-cow observations by selection of a single set of data from the many available for each cow.

FCM and LW0·73 gave better results than MY and LW, and together with age, were all significant variables for the prediction of the dependent variable. HA was not a significant source of variation, D was only effective in models of DOMI and faecal output, and stage of lactation was not considered a consistently useful variable. The application of the multiple regression technique to the problem of partition of nutrients and the prediction of intake is considered. Precision of prediction is discussed in terms of tolerance limits for predicted values, and it is concluded that the lack of accuracy of measurement of intake in the individual grazing cow is the major obstacle to the accurate prediction of intake in grazing cows.

In order to obtain a wide range of live weights, two Oxford Down, two Southdown, and two Soay rams of recent feral origin, were used to sire lambs from 169 crossbred ewes. These ewes had been bred from Blackface ewes mated to Border Leicester, Dorset Hora, Clun Forest, Finnish Landrace and Tasmanian Merino rams. Of the 282 lambs weaned by the crossbred ewes, 61 were singles, 166 twins, 51 triplets and 4 quadruplets. Carcass data were obtained from all but three of them.

Oxford Down cross lambs were, in terms of fitted values, 10 kg heavier and 4 days younger than Soay cross lambs and 6 kg heavier and 2 days younger than Southdown cross lambs when slaughtered. Twins and triplets were 1·4 and 2·1 kg, respectively, lighter than singles and were 37 and 58 days older than singles. Ewes of the heaviest groups produced heavier lambs in a shorter time than ewes of the lightest groups.

The Soay cross lambs showed a higher killing-out percentage, less tail fat, and more kidney fat, than the Southdown and Oxford Down cross lambs.

Carcass characters made little if any difference to the price paid for the lambs which depended mainly on weight. Receipts from lambs were highest when the most fertile ewes were mated to the largest rams.

The ruminal activity, daily live-weight gain and feed conversion efficiency of zebu calves inoculated with whole rumen contents from a mature cow were compared with those of calves maintained under the same conditions except that they were ciliate-free and isolated from other ruminants.

A thriving mixed population of ciliate protozoa became established in the rumen of calves two weeks after inoculation. Entodinium was the first genus to appear and was followed by Isotricha, Polyplastron, Ophryoscolex, Diplodinium and Dasytricha.

The ruminal volatile fatty acid and ammonia concentrations in the inoculated calves showed a pronounced rise above the values found in the uninoculated controls.

The inoculated calves grew faster and had a higher feed conversion efficiency than the uninoculated controls.

Three pelleted diets based on rolled barley, whole oats and ground oats respectively were offered ad libitum to mature wethers and growing lambs. With wethers, intakes on the whole oat diet were significantly greater than on the barley diet but digestible dry-matter intakes were not significantly different. On average, growing lambs ate significantly greater quantities of the ground oat diet and whereas digestible dry-matter intakes on the ground oat and barley diets were not significantly different, both were higher than on the whole oat diet. Examined at successive live weights, intakes on the whole oat diet were, at 15 kg, initially lower than on the barley diet but were ultimately higher at 60 kg, when there were no significant treatment differences in digestible drymatter intakes.