Individually recorded milk yields, yields and concentrations of milk components, food intakes and live weights of multiparous dairy cows given silage ad libitum and concentrates at a flat rate in weeks 4 to 13 of lactation and data for silage and concentrate composition from experiments conducted at four sites, were used to obtain simple correlations and multiple linear regressions of yields and concentrations of milk constituents on other variables.

Simple correlations between yields and concentrations and other variables were low. Yield terms were most highly correlated with intake terms. Milk fat concentration was most highly correlated with silage fibre concentration. Milk protein concentration was most highly correlated with digestible energy intake. The best multiple regression models including time effects accounted proportionately for 0·35 of the variation in fat yield, 0·51 in protein yield, 0·55 in lactose yield, 0·39 in total milk yield, 0·19 in fat concentration, 043 in protein concentration and 0·19 in lactose concentration. Most of these models included terms for silage intake and cow live weight which are not generally available on farms. More practical models including fewer independent variates were therefore produced. These models accounted proportionately for 0·33 of the variation in fat yield, 048 in protein yield, 0·50 in lactose yield, 0·32 in total milk yield, 0·19 in fat concentration, 0·40 in protein concentration and 0·17 in lactose concentration.

Eighteen multiparous Holstein-Friesian cows were offered grass silage ad libitum and 3,6 or 9 kg dry matter per day of concentrates. Triplicate milk samples were taken at each of two daily milkings over a 28-day period and analysed for fat protein and lactose concentration. Milk yield and fat concentration were more variable than protein and lactose concentrations both between animals and between days. Sampling variation was small for all component concentrations. The main source of variation for all traits was time of milking (morning or afternoon) followed by variation between cows and by day-to-day variation. There was little linear trend with time in the data due to cows being close to peak yield. There was no evidence of cyclical variation over time for any trait. Mean weekly or monthly yields and concentrations were better predicted using samples from four rather than from two consecutive milkings but there was no further advantage from using six samples.

Both milk production (MP) and conception rate (CR) of primi- and multiparous cows (P+M) in Israel are characterized by the same summer-autumn trough and winter-spring peak. Although there is no causal link between CR and MP (a simulation-model study explained the connection), monthly CR determines the number of dry cows 7 months later, at 2 months pre-calving. Inevitably, when the number of dry cows is low, MP is high, and vice versa.

Replacement heifers (RH) in Israel have a consistently high (64%) CR throughout the year. The same simulation model was used to investigate the effect of manipulated RH breeding on the herd MP pattern. When RH breeding was confined to the 3-month July to September (J-S) period during which CR is lowest for post-partum P+Ms, the monthly MP pattern in an otherwise year-round breeding dairy herd was the diametric opposite of the one produced by all-year RH breeding. When a uniform monthly quota was set for RH and P+M conceptions, and monthly RH conceptions were restricted to complement monthly P+M conceptions, the herd MP pattern became almost level. There did not appear to be any economic penalty attached to the planned RH conception system.

In practice it will not be possible to adhere to a strict monthly quota of conceptions, since there is a 1 to 2 month lag between insemination and confirmed conception. Estimates of individual farm monthly CR could be used, where available. Alternatively, if 40% of all RH inseminations were performed in J-S, the MP curve would be much flatter than under the present non-planned system of RH insemination.

Lactating Holstein-Friesian cows from two calving groups (no. = 90) were studied during the early post-partum period to determine the effect of dry-matter intake (DM1), 40 g/kg fat-corrected milk (FCM) production, energy balance (EB), parity, and food additives (calcium salts of long-chain fatty acids [CaLCFA] and niacin) on the recrudescence of ovarian function and establishment of pregnancy. Cows that ovulated early during the post-partum period (15 to 21 days after calving) consumed more food and tended to produce more FCM compared with cows ovulating later (22 to 42 days or after 42 days). Primiparous cows had lower EB and tended to have longer intervals to first ovulation compared with multiparous cows but the average interval to pregnancy was similar for primiparous and multiparous cows. Feeding CaLCFA tended to extend the interval to first service and decreased pregnancy rate. Production characteristics (including DMI and FCM production) seem to determine interval from calving to first ovulation as well as interval from calving to pregnancy (days open). Fertility was affected negatively by feeding CaLCFA.

Twenty-four Friesian dairy cows were divided into two groups of 12 between 12 and 18 weeks prior to calving and fed to achieve condition scores at calving of 3·2 (F) or 2·3 (T). For the first 11 weeks of lactation, six cows from each group (H) were given daily 9 kg of a high-fat compound (acid ether extract (AEE) 96 g/kg dry matter (DM)), 3 kg molassed sugar-beet pulp and hay ad libitum. The other six cows in each group (L) were given 10 kg of a low-fat compound (AEE 29 g/kg DM), 2 kg sugar-beet pulp and hay ad libitum. Allowances of compound and sugar-beet pulp were designed to provide equal amounts of energy, neutral-detergent fibre and protein. The fat source used in compound H was a calcium salt of palm acid oil (Megalac®).

DM intake was not affected by treatment but fat intake was significantly higher on diet H (P < 0·001). Group TH had higher intakes of digestible energy (DE) than group FH (249 v. 229 MJ/day; P < 0·05), but condition at calving did not affect DE intake with diet L (FL = 230, TL = 233 MJ/day). Milk yield was not significantly affected by treatment, although cows in group TL tended to yield less milk than other groups (28·3, 27·3, 28·0 and 24·3 kg/day for FH, FL, TH and TL respectively). The concentration of milk fat was higher and of milk protein lower with diet H compared with diet L (milk fat 48·1, 42·2, 42·9 and 39·6; milk protein 28·0, 31·0, 28·4 and 30·5 g/kg for FH, FL, TH and TL respectively). Loss of condition score was greater for cows in group F (0·65 units) than for those in group T (0·04 units). Within group F, loss of condition tended to be greater with diet L.

It is concluded that the increased intake of fat with diet H tended to decrease loss of condition in cows that were fat at calving but increase milk yield in cows that were thin at calving. It also tended to increase milk fat concentration but decreased milk protein concentration.

Eighty calves of both sexes, 4 months of age, of two lines, differing in genetic merit for fat plus protein production by 70 kg per 305-day lactation, were given one of four diets differing in protein content to give an estimated range of protein intakes from 299 to 530 g/day. After 21 days the calves were fasted for 72 h. Samples of blood were taken before and after feeding in the morning and afternoon prior to fasting, seven further samples were taken throughout the fast and five samples were taken ranging from 0·5 to 7·5 h after food was re-introduced. The samples were analysed for concentrations of urea, free fatty acids (FFA), glucose, triglyceride and f5-hydroxybutyrate.

No association between metabolite concentrations and predicted breeding value (PBV) were found at any stage of the trial except for the effect of feeding on FFA concentration, the rate of increase of FFA during the fast and its ultimate concentration. These associations with FFA depended on the sex of the calf and were either absent or less marked in males. The results strengthen the possibility that FFA concentrations during fasting are related to PBV in females, and that sexual dimorphism may explain differing conclusions amongst previous trials.

The magnitude of the estimate of coheritability of urea concentration during fasting with PBV, pooled across experiments, is reduced from -0·193 to -0·066 (s.e. 0·037) by inclusion of these results. However, heterogeneity between experiments is evident and remains to be explained. This suggests that urea concentrations are not consistent predictors of genetic merit and cannot be considered to be reliable for use in practice.

An experiment was carried out to evaluate the effects of forage type and level of concentrate supplementation on forage intake, diet digestibility and milk production. Twenty-four crossbred cows (Bos taurus × Bos indicus), in early lactation, were allocated to the following six dietary treatments: native grass hay (H) or oat-vetch hay (OV), offered ad libitum, and supplemented with either 0, 2·5 or 5·0 kg per cow per day of a wheat-middling-based concentrate. A four-period, partially balanced, change-over design was used and the treatments were arranged as a 2 × 3 factorial.

The daily dry-matter (DM) intake was 640 g (P < 0·001) higher with cows on (H) diets compared with those on OV diets. However, OV diets were more digestible (0·675 v. 0·566, P < 0·001) resulting in 800 g higher (P < 0·05) daily intake of digestible DM. The daily milk yield was 1·24 kg higher (P < 0·001) for cows on OV diets compared with H diets. Milk fat concentration was higher (P < 0·05), but milk protein concentration was lower (P < 0·001) with H diets. The rates of rumen degradation of DM and nitrogen of OV were higher than of H for all incubation periods; similarly the values of the rate constant of DM and nitrogen were greater for OV than for H.

The daily DM intake increased by 3·72 kg/day (P < 0·001), when the amount of concentrate increased from 0 to 5·0 kg/day, indicating a minor substitution of basal forage by concentrate. The apparent DM digestibilities of the diets were higher when the diets were supplemented with concentrates. The milk yield increased linearly (P < 0·001), when the level of concentrate supplement increased from 0 to 5 kg, resulting in 0·52 kg more milk per day per kg additional concentrate given.

Two experiments were carried out to evaluate extracted soya-bean meal, fish meal and maize gluten feed as protein supplements for calves offered grass silage ad libitum. The five treatments used in experiment 1 consisted of 1·4 kg per head daily of concentrate dry matter (DM) consisting of (g/kg) 50 molasses and 25 minerals and vitamins plus (1) 925 barley (B), (2) 700 B and 225 extracted soya-bean meal (SBM), (3) 785 B and 140 fish meal (FM), (4) 925 maize gluten feed (MGF) and (5) 2·25 kg DM per head daily of concentrate (1). Those used in experiment 2 consisted of 1·4 kg per head daily of concentrate DM consisting of (g/kg) (1) 1000 B, (2) 800 B and 200 SBM, (3) 860 B and 140 FM, (4) 1000 MGF and (5) 2·25 kg DM per head daily of B. In each experiment the diets were offered to 70 calves which were initially 131 and 130 kg live weight, for periods of 14 and 13 weeks in experiments 1 and 2 respectively. The silages contained 155 and 154 g crude protein (CP) per kg DM; 45 and 77 g ammonia-nitrogen per kg total nitrogen and 698 and 726 g digestible organic matter per kg DM in experiments 1 and 2. Concentrates 1 and 5 contained 104 to 110 g CP per kg DM and concentrates 2, 3 and 4 contained 195 to 204 g CP per kg DM in both experiments. For diets 1 to 5 respectively silage DM intakes were 2·31,2·50,2·53,2·59 and 1 -61 (s.e. 0·097) kg/day; live-weight gains were 0·84,0·98,1 -01, 0·88 and 0·95 (s.e. 0·032) kg/day in experiment 1 and 2·38, 2·53, 2·54, 2·82 and 1·77 (s.e. 0·045) kg/day and 0·90,1·04,1·03,1·05 and 0·99 (s.e. 0·038) kg/day for experiment 2. It is concluded that the use of soya-bean meal rather than fish meal did not affect silage intake or animal performance. Replacing mixtures of barley and soya-bean meal or barley and fish meal with an equal quantity of isonitrogenous maize gluten feed did not affect animal performance in one experiment but significantly reduced it in the other experiment.

Daily partial milk yield of Sanga cows in 13 smallholder agropastoralist herds at two locations on the Accra Plains was recorded through monthly sampling. Estimates of mean daily partial milk yield and milk composition were computed from 1266 observations. The unadjusted mean daily partial milk yield was 875 (s.e. 11) g. The composition of milk: total solids (TS), fat (F) and solid-not-fat (SNF) were 131 (s.e. 14), 41 (s.e. 11) and 90 (s.e. 7) g/kg respectively. Least squares estimate of mean daily partial milk yield were 808·2 and 462·4 g with average s.e. of 41·8 for wet and dry season respectively. The wet and dry season differences in daily partial milk yield, TS and F were highly significant (P < 0·01). Seasonal difference in SNF was not significant.

Herd difference in partial milk yield, TS, F and SNF were highly significant (P < 0·02). There were no significant effects of location on daily partial milk yield and SNF, although location effects on F and TS were significant (P < 0·05). The highest milk yield was observed in cows in third lactation and the lowest in cows in seventh lactation (P < 0·01). Daily partial milk yield peaked in the 3rd month of lactation. On average, lactation length was 210 to 240 days. Both linear and quadratic effects of stage of lactation were highly significant (P < 0·01). Lactation curve parameters for partially milked cows were also estimated. The implications of the results for milk production in sub-Saharan Africa were discussed.

Forty-five Friesian × zebu crossbred calves (4 days old) were used to evaluate the effect of feeding different levels of whole milk and weaning at different ages. A total of 252 I whole milk offered over 12 weeks was compared with a feeding level of 134 I milk offered over 8 weeks. Water given ad libitum was also compared with allowing access to water once daily. The calves were penned and fed individually. The average daily gain of the calves weaned at 12 weeks was 464 g compared with 378 g for the calves weaned at 8 weeks of age and allowed access to water once daily and 422 g for the calves weaned at 8 weeks and given water a d libitum. Feeding extra milk and weaning at 12 weeks decreased the intake of concentrates and significantly (P < 0·05) increased live-weight gain. Allowing ad libitum access to water was associated with an increase in concentrate intake but this was not reflected in a significant increase in animal performance.

The performance of Hereford × Friesian calves sired by Hereford bulls selected for either lean growth rate (LGR) or lean food conversion ratio (LFCR), or by unselected Hereford bulls, was evaluated on 327 calves on three farms over 2 years. Animals started test at 130 days of age on average and remained on test for approximately 300 days, whereupon all animals were slaughtered and carcass dissections were undertaken. Individual food intake was measured on tioo of the farms (189 animals), but only intake per pen of animals was measured on the third farm and individual food intake had to be estimated. LGR, LFCR and other traits describing performance were calculated from the growth, food intake and carcass composition data.

If no breed or environment interactions exist it is expected that proportionately 0-5 of the genetic differences between selected and control line bulls would be transmitted to their offspring. For the LGR and LFCR line bulls these values were 0·38 and 0·44, respectively, however the LGR value had a much smaller confidence interval. Genetic correlations derived from regressing breeding values predicted from offspring performance on breeding values predicted from the bulk's own performance in the selection experiment were 0·62 (s.e. 0·28) and 0·96 (s.e. 0·28) for LGR and LFCR, respectively. Heritabilities were: live-weight gain on test, 0·27; daily gain, 0·48; food intake, 0·06; food conversion ratio, 0·46; predicted carcass lean content, 0·10; killing-out proportion, 0·10; LGR, 0·36 and LFCR, 0·48.

This paper addresses the rescaling controversy in the estimation of economic weights for livestock improvement programmes. A model of genetic improvement based on the neoclassical theory of the firm and incorporating genetic improvement is proposed for the estimation of economic weights. Disparities between estimates of economic weights calculated per animal as opposed to per unit of product, per breeding female or per enterprise disappear when economic weights are calculated using this model. Equivalences of economic weights at the different bases of evaluation, previously obtained by rescaling the production enterprise to a fixed input, output or profit are compared with this model. The conventional approach to the derivation of economic weights is characterized as implicitly making unreasonable assumptions about the behaviour offarm firms.

Extension of the proposed model to the level of the farm product market allows assessment of the distribution of gains from genetic improvement between producers and consumers using the economic surplus approach. In an illustrative example, the distribution of benefits among producers and consumers from genetic improvement in the Ontario cow-calf sector is shown to depend on the elasticity of demand for beef products in the North American market. When the demand for farm output is elastic, a significant proportion of the benefits from genetic improvement would accrue to producers. Conversely, when demand is inelastic, the majority of benefits would accrue to consumers. Economic weights calculated from the perspective of all producers could thus be different from those calculated from the perspective of an individual farmer or society as a whole. Finally, the market level model is used to compare the effects of genetic improvement which enhance product quality with cost-reducing genetic improvements.

An experiment was conducted to measure the response of spring-born suckled calves to supplementary feeding when they grazed, with their dams, on swards of different heights in the autumn. Two swards were maintained at mean heights of either 5·8 cm or 9·0 cm, and calves were offered 0, 0·76 or 1 -51 kg organic matter (OM) per day of a commercially available supplement for a period of 60 days until weaning. Supplement intakes by the calves grazing the taller sward increased throughout the 60-day period, but did not exceed 0·75 kg OM per day. There was no response in terms of calf live-weight gain to the provision of supplement on the sward maintained at 9·0 cm. On the shorter sward, intake of supplement increased at a greater rate and reached 0·75 kg OM within 3 weeks. Maximum intake by those calves offered 1·51 kg supplement OM per day was 1·25 kg OM per day. The provision of supplementary feeding when mean sward height was 5·8 cm resulted in a significant increase in calf live-weight gain (P < 0·05), although supplementary feeding did not fully compensate for the reduction in milk and herbage intakes because of partial substitution of supplement for herbage. During the winter after weaning the calves that had previously grazed the shorter sward showed increased live-weight gain compared with those that had previously grazed the taller sward but prior supplementary feeding was without significant effect in this group.

Two trials, involving a total of 1006 Mule ewes and 1862 Suffolk-× ewes, were conducted to investigate the ability of implantation with melatonin to induce early breeding in lowland sheep flocks. Dates of implantation ranged from mid May to late June for Suffolk-× flocks and mid May to early July for Mule flocks.

From the mating patterns obtained it is suggested that the optimum implantation date is mid May to mid June for Suffolk-× ewes and mid June to mid July for Mule-type ewes.

Melatonin treatment also significantly increased the mean litter size per ewe exposed to the ram (resulting from a 6-week mating period) when the data were pooled across flocks, but the magnitude of this effect varied across flocks. Part of this overall mean increase in Mule ewes (+0·84 and +0·50 extra lambs per ewe in trials 1 and 2 respectively) was due to an increase in the proportion of ewes mating and lambing and part of it (+0·13 and +0·17 extra lambs per ewe, respectively) was due to an increase in litter size per ewe pregnant. In the Suffolk-× ewes there was evidence that the overall mean benefit following implantation with two implants (+0·31 extra lambs per ewe) was greater than that following implantation with one implant (+0·14 extra lambs per ewe), with all of the increase at the lower dose level and +0·21 extra lambs per ewe at the higher dose being due to an increase in litter size per ewe pregnant.

Formulas were derived to predict asymptotic response to selection on best linear unbiased predictors (BLUP) of breeding values that account for selection-induced gametic phase disequilibrium, also known as the ‘Bulmer’ effect. Breeding programmes in populations of infinite size and with discrete generations were considered. For two-path breeding programmes with equal male and female accuracy of selection, relative reductions in response due to gametic phase disequilibrium were independent of heritability. Reductions in response depended only on intensities of selection and ranged from 0·22 to 0·27 when selected proportions were less than 04 for both males and females. With unequal accuracy of males and females, relative reductions in response depended on the ratio of accuracies, in addition to selection intensities. For given selection intensities, reductions were up to proportionately 0·08 larger with unequal accuracies than reductions obtained for equal accuracies. Relative reductions in response for breeding programmes with four paths of selection depended on intensity and accuracy of selection in each path, but were within a range similar to that observed for two-path programmes. Gametic phase disequilibrium will, therefore, not greatly affect ranking and relative differences among alternative breeding programmes.

Gametic phase disequilibrium had a larger effect on response with selection on BLUP than on phenotype, which is largely due to larger relative reductions in accuracy of selection with BLUP. Despite larger relative reductions, asymptotic response to selection on BLUP is expected to be larger than selection on phenotype.

During clinical investigation of a commercial herd it was found that intake of supplemented poultry litter (PL) by beef cows at >10 kg/day, was associated with severe cachexia and a mortality rate of between 10 and 20% of cows. Postmortem analysis of 40 fresh carcasses and elevated serum levels of cholesterol, bilirubin, alkaline phosphatase, glutamic oxaloacetic transaminase and sorbitol dehydrogenase in cachetic cows indicated that the cows suffered severe liver damage. The interrelationship between liver damage and PL intake was subsequently investigated in three groups of 20 beef cows each, consuming 0, 3 and 10 kg PL respectively. As determined by the serum indices, intake of 3 kg PL seemed to be sufficient to cause liver damage, although these cows appeared healthy.

In another experiment, six beef cows were stall-fed a diet giving separate access to PL and wheat straw. PL intakes were 3·1,4·7 and 6·0 kg/day. Ruminal ammonia concentration was three to five times higher than the estimate of that required for maximal fermentation in the rumen. The high pH values (6·81 to 6·97) found are optimal for absorption of ammonia from the rumen. The combination of excess absorption of ammonia from the gut and low metabolizable energy intake might have been the cause of liver damage.

Maternal behaviour and lamb vigour are both considered major variables affecting lamb survival, but there are few data to describe their relative importance. To investigate the relationship between lamb vigour and maternal behaviour this study compared the behaviour of pure Scottish Blackface lambs with Mule (Bluefaced Leicester ♀. × Scottish Blackface ♂) lambs, all born indoors. Anecdotal accounts suggested a significant reduction in lamb vigour in Mule lambs, a matter also of significant practical importance given the current incease in Mule numbers. Observations on the grooming behaviour of 32 single or twin-bearing ewes, and on the general activity and udder-seeking behaviour of their lambs were made at parturition. In this study, neither ewe grooming behaviour nor general lamb activity were directly related to lamb sucking success. It was shown that, although Mule lambs had high birth weights and stood as quickly as Blackface lambs, they showed significantly fewer sucking attempts (P < 0·01) and took longer to suck successfully (28 min for Blackface v. 55 min for Mules). The inability of Mule lambs to suck successfully was due to their failure to show proper udder-directed behaviour. These results indicate the importance of considering the behaviour of both ewes and lambs as it would seem that it is not ‘poor’ maternal behaviour but inappropriate lamb behaviour that is a limiting factor in lamb survival in the Mule breed.

An experiment was conducted to investigate the effects of the length of the interval between implantation with melatonin and ram introduction on mating patterns, and to investigate the effects of melatonin on ovulation rate and litter size in Mule ewes.

Increasing the interval from treatment to ram introduction from 4 to 6 weeks was associated with a progressive and significant reduction in the time from ram introduction to mating as well as a reduction in the spread of mating across the group.

Melatonin resulted in a significant and consistent increase in ovulation rate at first oestrus (+0·44 to +0·48 ovulations per ewe) across the three treated groups, although the increase in litter size (+0·19 to +0·36) was more variable.

It is concluded that melatonin influences the pattern of mating and increases litter size in ewes and that the increase in litter size is accounted for by an induced increase in ovulation rate.

Friesian steer calves born in August were reared from 3 to 7 months of age on silage alone (S) or on silage and concentrates to supply metabolizable energy (ME) in the proportion of 0·5: 0·5 (55) or 0·1: 0·9 (19). The mixed diets were either offered to appetite (55A and 19A) or restricted to provide the same energy intake as the S group (55R and 19R). The cattle were then grazed for a 6-month period as a single group. During the winter the S, 55R and 19R groups had similar live-weight gains. Despite having the highest nitrogen intakes the S group deposited less protein, but more fat than the other two groups. There were no significant differences within A or R groups, but the A groups had higher live weights, empty-body weights and carcass weights than the R groups and had more fat and less protein per kg empty body weight at turn-out to grazing.

Compensatory growth was exhibited by the S, 55R and 19R groups during the grazing season. It arose because of differences in intake and not because of differences in the energy content of the gain. Intake was inversely related to the level of fat per kg empty body weight at the start of grazing. There was no evidence that the nature of the diet in winter had an effect on subsequent herbage intake.

It was concluded that diet per se in winter had no residual effect on intake at grazing, but that it did have direct and residual effects on the relative deposition of fat and protein which could lead to an association between the level of fat in the empty body and intake. Inefficient use of nitrogen from silages with moderate fermentation characteristics was also demonstrated.

A divergent selection experiment for carcass leanness in Texel-Oxford sheep was established to examine the differences between genetically lean and fat animals derived from the same base population. The selection criterion was designed to change body composition without a corresponding change in live weight, using an index of ultrasonic backfat depth and live weight at 20 weeks of age. The index was constructed using estimates of genetic and phenotypic parameters, which were available at the start of the experiment in 1985. The difference between the high and low lines, after 3 years of selection, for the selection index, live weight at 20 weeks of age, ultrasonic backfat and muscle depths was 0·59,1·30 kg, -0·76 mm and 0·88 mm respectively. The estimated difference for carcass lean and fat weight was 0·72 kg and -0·04 kg respectively with 13·5 g/kg and -13·8 g/kg for carcass lean and fat proportion. The realized heritability for the selection index, estimated from the regression of cumulative response on cumulative selection differential was 0·42, with a standard error of 0·25, after taking account of genetic drift. The selection index heritability, estimated with residual maximum likelihood (REML) methodology, was 0·46 (s.e. 0·14). REML heritability estimates for live weight at 20 weeks of age, ultrasonic backfat and muscle depths were 0·20 (s.e. 0·13), 0·35 (s.e. 0·14) and 0·43 (s.e. 0·14) respectively.