Birth-weight data recorded between 1986 and 1991 on 3453 N'Dama calves from the village production systems of The Gambia were analysed to identify major factors influencing this trait and to quantify the relationship between birth weight and early calf mortality. Birth weights were measured over a range of time, from a few hours to 14 days after birth. Least-squares analysis of the fixed effects of site, year and season of birth, parity of dam, sex, age in days at which birth weight was recorded and random effects of herd and cow nested within site showed that all these factors significantly influenced this trait.

A subset of these data (no. = 2452) was used to derive adjustment factors which were applied to the larger data set to standardize birth weights to a common age measurement. Results from these adjustments showed that birth weights recorded between the 7th and 14th day after birth should be decreased by proportionately 0·12 to 0·14 to be comparable with those measured on day of birth.

Maximum likelihood analyis of cumulative calf mortality to 30, 60, 90 and 120 days of age using age-standardized data (no. = 3156), which excluded deaths of traumatic origin, showed that mortality was highly influenced by birth weight. Calves were grouped into three classes, namely below-average, average and above-average of sitemates' values. Mortality rates among the three groups during the first 30 days of life were 3·6, 0·9 and 0·3%. The corresponding values at day 120 were 13·8, 6·3 and 5·0%. The average age at death during the first 120 days in the three groups were 51, 58 and 73 days. Mortality rates among calves born in the wet season were higher than those born in the dry season (e.g. 9·9 v. 5·9% for mortality to day 120).

Examination of data on calving distribution and milk production patterns of the dams of the calves used in this study as well as the causes of deaths among the calves indicated that although dam effect was an important determinant of calf survival other factors such as the vigour of the calf at birth, weather conditions and disease environment at the tethering and grazing areas were important as well.

Multiparous cows were assigned before calving to three calving to first insemination intervals. Records of cows conceiving at first or second insemination, were used to construct a model of the lactation curve which incorporated peak production and the effect of progressing pregnancy. The model was used to simulate milk yield during a 4-year period for three production levels and five calving intervals. The model separated the descending part of the lactation curve into a linearly and an exponentially declining component, with the latter becoming distinct at about 20 weeks after conception. Peak yield was negatively correlated with the slope of the linear decline. Within a simulated 4-year period, cumulative milk yields at fixed time periods after calving depended upon the period chosen and the calving-to-conception interval of the cow. Late conceptions resulted in higher cumulative yields at the end of the 1st year, and in lower yields at the 2nd year end, with respect to early conceptions. Smaller differences were found between the intermediate calving intervals. During the 3rd and 4th years the early conceptions had a distinct advantage. Different rates of the linear decline, obtained for the different production levels, changed the magnitude of the yield differences between the calving intervals but not their relative ranking. The model presented offers a means for the suitable choice of the calving cycle according to the length of the period for which a cow is expected to remain in the herd.

Genetic variances were estimated from different types of relatives for a data set of 19038 first lactation fat yield (FY) and fat concentration (FC) records. For FY, h2 estimates were 0·377, 0·322 and 0·377 from an animal model, a sire model and a model using only female relationships. The corresponding estimates for FC were 0·632, 0·628 and 0·610. Regarding sires with most progeny in the data set as levels of a fixed effect slightly increased h2 estimates, most likely through accounting for selection of proven sires. Statistical models were presented to account for heterogeneous genetic variances for males and females in the prediction of breeding values or in estimating variance components. Simultaneously estimating genetic variances for FY from paternal half-sibs, maternal half-sibs, and daughter-dam comparisons, resulted in heterogeneous genetic variance estimates from male v. female comparisons and similar variance estimates from mhs and dd comparisons. For FC, h2 estimates from different types of relatives were similar.

Dam-daughter comparisons provide 0·75 to 0·80 of the information on heritability from female relationships and provide 0·42 to 0·55 of the total information on heritability.

The effects of heterogeneity among herds in phenotypic variance (σ2p) and in heritability (h2) on the accuracy of evaluation of dairy sires and cows are discussed with reference to estimates from field data. It is argued that heterogeneity of σ2P can be accounted for by using a (Bayesian) regression procedure. While the same procedure could be used to correct for heterogeneity of h2, in most practical situations the sampling errors of the h2 estimates for individual herds are likely to be so large that regressed estimates of h2 will differ little from each other, so constant values can be assumed.

Scarce and poor-quality food resources limit smallholder dairy production in the tropics. Food resources for zerograzing may be improved by intercropping Pennisetum purpureum (napier grass) with Leucaena leucocephala leguminous hedgerows. To evaluate dairy cow performance from this alley cropping system, 36 Ayrshire/Brown Swiss × Sahiwal cows in a 2×3 factorial design were individually fed from the 3rd week of lactation for 14 weeks on diets of napier fodder harvested at 1·0 m or 1·5 m and offered ad libitum, supplemented with 0, 4 or 8 kg fresh weight leucaena fodder. Average daily milk yield during the 2nd week of lactation was a covariate in the analyses of milk yield, and post-partum live weight a covariate in the analyses of dry matter (DM) intake and live-weight change.

Napier harvesting height and leucaena level had independent effects on performance. Napier height (1·0 m or 1·5 m) significantly (P < 0·01) affected daily napier DM intake (9·3 and 6·8 kg), total daily DM intake (10·5 and 7·9 kg), daily live-weight losses (165 and 490 g) and daily milk yield (8·6 and 6·9 kg respectively). Leucaena supplementation (0, 4 or 8 kg) significantly (P<0·01) increased total daily DM intake (7·8, 9·3 and 10·4 kg), reduced daily live-weight loss (560,235 and 175 g), and increased daily milk yield (7·3, 7·7 and 8·3 kg respectively). The results show that reasonable dairy performance can be achieved in the tropics by supplementing a napier fodder basal diet with leucaena forage, and highlight the importance of the stage of harvesting of the napier fodder. The results are discussed in relation to the nutrient requirements for milk production given by the Agricultural Research Council (1980 and 1984).

Changes in body composition of 54, second to fourth parity, autumn-calving Holstein-Friesian dairy cows offered grass silage ad libitum and 3(L), 6(M) or 9(H) kg concentrate dry matter per day were measured by serial slaughter at 0, 2, 5, 8, 11, 14, 19, 24 and 29 weeks post partum.

Concentrate level had a significant effect on the fresh weights of many of the body fractions with the differences generally being greater between L and M than between M and H. Increasing concentrate level generally reduced the extent of weight loss of body fractions in early lactation and enhanced subsequent repletion. Empty body weight decreased to week 8 and then increased steadily over the remaining 21 weeks, but within this pattern different organs were concomitantly increasing and decreasing. Carcass weight and the weights of the internal fat depots showed a decline over the first 8 weeks and a subsequent increase, udder weight declined throughout, weights of various sections of the digestive tract showed an initial increase then remained steady, whilst liver weight increased throughout.

In week 0 the carcass accounted for proportionately 0-61 of the total energy in the body (6278 MJ), of which fat and crude protein (CP) comprised proportionately 0·67 and 0·33, respectively. In early lactation mobilization of fat and CP in the carcass was reduced with increasing level of concentrate. In the non-carcass fraction increasing concentrate level led to a higher weight of CP in the metabolically active organs such as the digestive tract and udder but had little effect on the weight of fat. Nevertheless, there was generally a positive effect of concentrate level on energy content. Total weights of fat, CP and water in the body declined to week 8 then increased over the following 21 weeks. Although weight of CP in the liver increased throughout lactation and weight of fat was elevated in weeks 0 and 2, the energy content of the liver remained fairly constant.

Estimates of the change in net energy (NE) associated with live-weight loss and with live-weight gain showed a slight though non-significant difference between the two, despite evidence of a higher concentration of fat associated with gain than with loss, and CP concentration being the same in both cases. The mean value was 19·3 MJ/kg live-weight change.

Experiments were carried out in Nepal and Costa Rica to compare voluntary dry-matter intake (DMI) by oxen of diets based on poor quality hay (Costa Rica) and rice straw (Nepal) supplemented with different levels of concentrate foods when the animals were working and not working. Values for the apparent digestibility of the diets, rates of passage of solid and liquid phases ofdigesta and nitrogen balance are also reported.

Amounts of work calculated to raise daily energy expenditure to 1·3 to 1·6 × maintenance were associated with the following effects. (1) A depression of proportionately 0·11 and 0·14 in the DMI of oxen given a diet based on rice straw plus 18 and 27 g/kg live weight of concentrate respectively during work. No depression of DMI was seen with the hay diets which had slightly higher metabolizable energy but less nitrogen than the rice straw diets. (2) An increase in intake in the weeks following work on both the hay and rice straw diets. (3) Variable effects on apparent digestibility of food probably related more to the changes in DMI. (4) A tendency for gastro-intestinal mean retention time to be increased in working weeks particularly on the more fibrous diets.

The objective of the study was to assess the usefulness of providing shade for beef cows grazing summer dry Mediterranean -pasture and supplemented with a food high in non-protein nitrogen (poultry litter). Two groups of 30 cows each, in the last trimester of pregnancy, were placed on 1 June in two paddocks of similar grazing pressure, topography, vegetation cover and botanical composition. In one of the sub-units the cows had free access to a large shaded area, provided by 10 to 12 large eucalyptus trees, whereas in the second sub-unit, access to shade was denied until 31 August. Respiration rate, used as an index of heat stress, was much higher in the non-shaded cows (102 breaths per min) than in the cows with access to shade (62 breaths per min). In response to the much higher heat stress in the non-shaded cows, total body water and haematocrit value (an index of plasma volume) were higher than in the cows with access to shade. Metabolizable energy (ME) intake was apparently much lower in the non-shaded cows, as reflected in a much higher non-esterified fatty acid concentration in plasma. Consequently, large differences in live weight gradually developed during the course of the trial, the cows with access to shade becoming much heavier than those with no access to shade. An increase in the consumption of poultry litter by the non-shaded cows was interpreted as an effort to reduce internal heat load by avoiding grazing and by preferring food which induces a lower heat increment upon ingestion and digestion. Above-normal serum concentrations of cholesterol and alkaline phosphatase support previous results that the combination of low ME intake and high ammonia load induces a toxic effect on the liver. Although all the cows were pregnant at the onset of the study, successful parturition was recorded in 26 of the 30 cows having access to shade, and in only 20 of the 30 (F < 0·05 by t test) of the non-shaded cows. It is concluded that providing shade for beef cows under summer Mediterranean conditions will reduce the danger of embryonic loss. However, an interaction with metabolic burden, such as ammonia load and a negative energy balance, can make the situation much worse.

One hundred and twenty spring-born steers comprised of 40 Friesians (FR), 40 Canadian Hereford × Friesians (HF) and 40 Simmental × Friesians (SM) were reared together from shortly after birth to slaughter after a mean period of 740 days. During the finishing winter there was a 3 (breed types) × 2 (3 and 6 kg supplementary concentrates per head daily with grass silage ad libitum) × 2 (222- and 225-day finishing periods) factorial arrangement of treatments. One side from each of 96 carcasses (eight per treatment) was completely separated into bone, muscle, intermuscular fat and subcutaneous fat and a 10th rib sample of m. longissimus was chemically analysed.

Carcass weights per day of age and carcass weights were 404, 433 and 449 (s.e. 4·6) g and 301, 320 and 330 (s.e. 3·4) kg for FR, HF and SM, respectively. Corresponding proportions of carcass muscle were 602, 577 and 628 (s.e. 4·8) g/kg. FR and HF had similar proportions of their total muscle in the hindquarter, whereas SM had more of their muscle in the hindquarter. M. longissimus lipid concentrations for FR, HF and SM were 36, 39 and 26 (s.e. 1·96) g/kg. Increasing supplementary concentrate level from 3 to 6 kg/day increased side weight by 7 kg, of which proportionately 0·48 was fat. Extending the finishing period from 121 to 225 days increased side weight by 22 kg of which proportionately 0·45 was fat. Both the higher concentrate level and the longer finishing period reduced carcass muscle and bone proportions, and increased carcass fat proportion. Allometric regression coefficients for side muscle, bone and fat weights on side weight were 0·75, 0·51 and 2·13, respectively. It was calculated that FR, HF and SM would have similar carcass fat proportions at approximate carcass weights of 320, 290 and 380 kg, respectively.

Seventy-two, 4-month-old, British Friesian steers were used to investigate the effects of feeding a supplement of fish meal on the voluntary intake and live-weight gain by young growing cattle given a well preserved ryegrass silage. The silage was offered either alone or mixed with 50,100 or 150 g fish meal per kg silage dry matter (DM) and the diets were offered either ad libitum or intakes were restricted to 16, 19 or 22 g dietary DM per kg live weight (LW). Intakes were recorded daily, LW weekly and in vivo apparent digestibility over one 7-day period during the 132-day trial.

For animals fed ad libitum, the absolute intake of dietary DM increased linearly with an increase in the level of fish-meal supplementation such that intake when the highest level of fish meal was given was significantly higher (P < 0·01) than when silage was given alone. However, DM intake per unit LW (approx. 24 g DM per kg LW) was not affected significantly (P > 0·05).

Inclusion of fish meal in the diet did not affect the apparent digestibility of dietary DM, organic matter, acid-detergent or neutral-detergent fibre (NDF) although there was a trend for slightly higher (P > 0·05) gross energy apparent digestibility when fish meal was given. Increasing the level of feeding reduced NDF digestibility. The coefficients measured at the 22 g and ad libitum levels of intake were lower (P < 0·01 and P < 0·05 respectively) than that measured at the 16 g DM per kg LW level.

Animals given silage alone to appetite achieved LW gains of 0·6 kg/day. LW gains increased linearly with increasing level of feeding (P < 0·001) and increasing level offish-meal supplementation (P < 0·001).

Seven groups of five or six Holstein-Friesian male calves were transported to an experimental farm at 2 to 3 days of age. At 6 days of age, heat production (HP) and metabolizable energy (ME) intake were measured for an 8-day period. During this period, calves were exposed to various ambient temperatures: 6, 9, 12 and 15°C. Ambient temperature was constant within days, but changed between days. Calves were fed below (four groups) or near (three groups) the maintenance requirements (290 or 460 kJ ME per kg M0·75 per day).

From 6 to 14 days of age the lower critical temperature (Tc) was 12·5°C and HP increased by 8·4 kJ/kg M0·75 per day per °Cfall in ambient temperature below Tc. Both Tc and increase in HP below Tc were not affected by feeding level. Rectal temperature was lower at low ambient temperatures. The decrease in rectal temperature with ambient temperature was greatest at the low feeding level.

During the experimental period, calves were not in a steady-state regarding energy metabolism. Heat production decreased with time. This decrease was affected by feeding level and ambient temperature. After arrival, the influence of both ambient temperature and feeding level on the energy metabolism of young calves increased with time.

Four experiments examined the chemical composition, intake, dry matter (DDM) and organic matter (DOM) apparent digestibilities and rates of disappearance from nylon bags of hand-separated leaf and stem fractions of straw from four genotypes of barley: Arabi Abiad, Beecher, C63 and ER/Apam. In experiment 1, 900 g leaf from each genotype was offered to three or four wethers together with 200 g soya-bean meal (SBM), and in experiment 2 the leaf from the same four genotypes was offered ad libitum with 200 g SBM. In experiment 3, 500 g stem from Arabi Abiad and Beecher was offered with 100 g SBM to six wethers in two groups. Experiment 4 measured the rate and extent of disappearance of the leaf and stem fractions from nylon bags incubated in the rumen of wethers. The genotypes had widely contrasting morphological characteristics. Stems contained about half as much ash and crude protein as leaves and differences within fractions were small. The leaf and stem fractions of the two-rowed barleys Abiad and Apam contained less modified acid-detergent fibre than the six-rowed Beecher and C63 genotypes.

When leaf was offered with SBM, both restrictedly and ad libitum, the DDM and DOM of this fraction were similar between genotypes (P > 0·05) and in experiment 2 the intake of leaf was also similar between genotypes (P > 0·05). The apparent digestibility of stem differed significantly between Arabi Abiad and Beecher in experiment 3 (P < 0·05). Significant differences were apparent between genotypes in the extent and rate of disappearance of leaf and stem from nylon bags after 48 h incubation in the rumen.

Four sheep (live weight 39 to 42 kg) fitted with rumen cannulas were offered ammonia-treated barley straw alone (control) or supplemented with unmolassed sugar-beet pulp or rolled barley at 0·20 or 0·40 of the total diet on a fresh weight basis (SBP20, SBP40, B20 and B40, respectively) using a 4 × 5 randomized block design. Total diet intakes were 710, 873, 1054, 843 and 1021 g dry matter per day for control, SBP20, SBP40, B20 and B40 respectively. The intake of straw was depressed significantly with SBP40 and B40 (P < 0·05). Rumen pH and ammonia concentration decreased, and total volatile fatty acid concentrations increased (P < 0·05) with increasing level of supplementation for both supplements. Rumen liquid outflow rate was affected little by the supplementation although this measurement for B40 was significantly higher than that for the other treatments. Microbial protein supply, estimated from urinary excretion of purine derivatives, increased significantly with the increasing amounts of supplements (4·5, 6·7, 8·5, 7·1 and 9·0 (s.e.d. 0·73) g N per day for control, SBP20, SBP40, B20 and B40 respectively) (P < 0·05). The calculated efficiency of microbial protein production was 12·8, 14·2, 14·3, 15·7 and 14·5 (s.e.d. 1·45) g N per kg digestible organic matter intake (DOMI) for the five treatments. Although this value was lowest with the control, differences between treatments were not significant (P > 0·05). It seems that microbial protein yield per unit DOMI for a diet based on ammonia-treated straw could not be improved substantially by supplementation with sugar-beet pulp or barley.

Previous research has shown that piglets using the sow's more anterior teats tend to have greater average weight gains, but this difference is often slight in the first lactation and increases in subsequent lactations. In this study, 27 sows were used to determine whether this difference develops because of the piglets' preferential use of the anterior teats during the first lactation. In their first lactation, 14 sows had their anterior teats (pairs 1 to 3) and 13 sows had their posterior teats (pairs 4 to 7) covered so that the piglets could use only one end of the udder. In the second lactation, all the teats were left uncovered and the sucking positions and weight gains of the piglets were studied. Piglets in the second lactation showed the usual preference for anterior teats regardless of which teats had been used in the first lactation. Where the anterior teats had been covered in the first lactation, there was no difference in weight gain between anterior- and posterior-sucking piglets in the 1st week of the second lactation, but a degree of anterior superiority had developed by the 3rd week (P < 0·01). Where posterior teats had been covered in the first lactation, piglets using anterior teats showed substantially greater weight gains than those using posterior teats throughout the first 3 weeks of the second lactation (P < 0·001). Thus, non-use of a teat in the first lactation tended to reduce its productivity, at least in the early part of the next lactation. We conclude that previous non-use of posterior teats can contribute to their tendency for lower productivity, but the effect does not explain completely the greater piglet weight gains usually associated with using the anterior teats.

A total of 384 piglets from a three-way cross Yorkshire ♂ × (Finnish Landrace ♂ × Dutch Landrace♀) ♀ in the live-weight range of 11 to 25 kg were used in a feeding trial. The effect of supplementary microbial phytase from Aspergillus niger var. Van Tieghem on performance (average daily gain (ADG), average daily food intake (ADFI) and food conversion ratio (FCR)) and apparent digestibility of total phosphorus (P), in comparison with a non-supplemented basal diet or a diet supplemented with one or two levels of monocalcium phosphate (MCP), were studied.

The piglets were allotted to 12 blocks. Within each block, four experimental diets were offered ad libitum for a period of 4 weeks i.e. (1) basal diet; (2) basal diet + 1·0 g P, from MCP per kg diet; (3) basal diet + 1·9 g P, from MCP per kg diet; and (4) basal diet + 1450 phytase units (PTU) per kg diet. The diets, with added chromium III oxide as a marker, were cold pelleted without steam at a temperature not above 60°C to avoid a possible inactivation of the phytase. In all diets the ratio calcium: digestible P was intended to be constant.

Adding 1450 PTU of Aspergillus niger phytase enhanced the apparent digestibility of P by proportionately 0·216 when compared with diet 1 and by proportionately 0·100 compared with diet 3. In addition, significantly higher ADG and ADFI and better FCR were noted in pigs receiving supplementary microbial phytase than in pigs on any other treatment. The content of digestible P of the diet with added phytase, however, zvas between the two levels of the diets with added MCP.

The present paper discusses the results of a trial study, which was carried out to demonstrate the potential beneficial effects of virginiamycin (VM) on sow and litter performance. VM was added to the sow food at the levels of 0, 20 and 40 mg/kg, for a period of two breeding cycles, covering pregnancy and lactation. VM supplementation of the sow food improved sow performance by: (i) decreasing sow weight loss from farrowing to weaning (first period: 8·78 v. 3·54 v. 2·88 kg, P < 0·05; second period: 8·98 v. 3·93 v. 2·32 kg, P < 0·05), (ii) decreasing the duration of the reproductive cycle (first period: 154·5 v. 152·2 v. 151·2 days, P < 0·05; second period: 153·8 v. 151·5 v. 250·6 days, P < 0·05) and (in) increasing milk fat content (second period: 63·7 v. 81·3 v. 83·3 g/kg, P<0·05). Litter performance was also improved in terms of: (i) litter size at weaning (first period: 8·16 v. 8·88 v. 9·18, P < 0·05; second period: 8·98 v. 9·30 v. 9·76, P < 0·05), (ii) body weight at weaning (first period: 5·78 v. 6·29 v. 6·56 kg, P < 0·05; second period: 5·88 v. 6·38 v. 6·60 kg, P < 0·05), (Hi) average daily gain (first period: 172 v. 189 v. 197 g, P < 0·05; second period: 178 v. 292 v. 198 g, P < 0·05) and (iv) food conversion ratio (first period: 0·356 v. 0·331 v. 0·324, P < 0·05; second period: 0·363 v. 0·334 v. 0·325, P < 0·05). These beneficial effects of VM were more pronounced at the higher of the two inclusion levels.

The relationships between values for milk protein content (MP) and body condition score (BSC) were compared on a group of 30 farms in western Asturias, northern Spain during the autumn of1990. There was a marked positive relationship (P < 0·01) in between-farm variation in the two factors; a similar relationship has been reported from experiments in Scotland. It is suggested that an index based on the deviation of values for MP and BCS from normal or mean values might be useful, especially in advisory work, to indicate rapidly the dietary energy adequacy on individual frms. However, note would have to be taken of the known changes in MP and BCS with, for example, age of cow and stage of lactation

Effect of live yeast culture (Saccharomyces cerevisiae plus growth medium) inclusion in the diet of buffaloes (Bubalus bubalis) on milk yield and its composition was examined. Twenty buffaloes (Murrah breed) having an average daily milk yield of 8 to 10 I and in their early lactation stage were divided into two equal groups. The control group was given a basal production diet consisting of 35 to 40 kg green berseem and concentrate mixture (0·5 kg/kg milk produced) per day per animal and the yeast supplemented group the above diet supplemented with 10 g yeast culture (YC, 5 × 109 c.f.u. Saccharomyces cerevisiae strain 1026 per g). The feeding continued for 10 weeks and during this period milk samples collected at weekly intervals and milk yield recorded daily. During this period, average daily milk yield was increased by proportionately 0·135 and fat-corrected milk yield by 0·185 by inclusion of YC. Fat, protein, lactose and total solids in milk increased proportionately by 0·039, 0·051, 0·030 and 0·034 respectively. The corresponding proportional increases in the quantity of these constituents secreted in milk (kg/day) were 0·237, 0·200, 0·200 and 0·204.