ALBERT

Description: SummaryDigestibility trials were conducted at two stages of lactation with each of 107 Friesian cows using three diets (60:40, 75:25, 90:10 proportions of compound feed to medium quality hay fed long). Each cow received throughout lactation fixed daily allowances of one of these diets at either 2·26 or 2·63 times average maintenance requirements (MM), or was fed ad libitum, average intake equalling 3·07 MM. The digestibilities of the diets were also measured on immature cattle at 0·76 and 1·33 MM and sheep at 0·65 and 1·27 MM.For all classes of stock the digestibility of dry matter increased linearly and that of fibre decreased curvilinearly with increasing proportion of compound in the diet. There was no interaction of effects of diet composition and amount consumed on digestibility of feed. The digestibility of both dietary components declined for the young cattle and sheep with increased intake. The digestibilities for lactating cows were lower than for other stock but did not change with amount consumed or milk yield. Digestibility was slightly higher for first and second calf cows than for adult cows; and was higher for organic matter in mid lactation compared with early lactation for adult cows.These results for dairy cows conflict with the generally accepted interpretation that a linear decline in digestibility occurs from once to five times maintenance intake, embracing all classes of stock.

Description: SummarySeventy-six first-calf cows (heifers), 32 second·calf cows and 39 adult cows participated in a trial in which three diets composed of 60:40, 75:25, 90:10 proportions of compound to hay (hay dry-matter digestibility 0·6) were given for the first 36 weeks of lactation in amounts to provide daily an estimated 125, 156 MJ and ad libitum digestible energy (DE) for heifers, and 156, 187 MJ and ad libitum DE for the other parities. The ad libitum intakes were 150 and 200 MJ DE daily for heifers and for older cows respectively. Greater compound content of the diet and larger daily allowance of DE were associated with increased occurrence of mastitis and lameness but not digestive upsets. Dry·matter (D.M.) digestibility was increased with a greater proportion of compound in the diet but was not affected by the amount consumed or stage of lactation. Milk yield and live·weight change were increased linearly and additively by a greater intake of digestible dry matter and by a greater proportion of compound in the diet, throughout the lactation save for no effect of diet composition on live·weight change in early lactation. On equal feed intakes older cows gave more milk and lost more live weight than heifers in early lactation but not thereafter; responses to additional feed were equal for all parities studied. Milk fat concentration was reduced both by increased allowance and by the high compound diet. Milk solids·not·fat (SNF) concentration was not affected by the treatments. Yield of milk fat was not affected by amount eaten and was reduced by the 90:10 diet. Yields of SNF and milk energy were increased by amount eaten and by increased compound in the diet. Thirty-two primiparous cows continued on their experimental treatments without interruption to the end of the second lactation. In the second lactation the effects on yields of milk, milk energy, and SNF were magnified indicating a cumulative effect from lactation to lactation. Little cumulative effect was observed on either milk fat yield, or concentrations of fat and SNF in milk. More generous feeding was associated with reduced milk output/unit D.M. consumed in the first but not the second lactation. More generous feeding improved live·weight change less in the second than in the first lactation. No cumulative effects over two lactations were observed consequent upon variation in diet composition.

Description: This report presents data describing convection in a rotating cylindrical Benard cell filled with He I. In particular, convection modes are observed at Rayleigh numbers substantially below those predicted by linear stability analyses for a horizontally infinite layer. Both the Rayleigh numbers associated with the convective onset and the initial-slope measure of heat transport of these modes are found to depend on the rotation rate Ω and the aspect ratio ⌈ of the cell. A discussion of the relevant literature reveals that these convective modes are probably the same as those observed by Rossby (1969) and are reasonably well characterized by the recent analysis of Buell & Catton (1983) assuming asymmetric modes. © 1987, Cambridge University Press. All rights reserved.

Description: SummaryTwenty-four Friesian cows were allocated to one of four diets for weeks 3–14 of lactation following 2 weeks on a common diet. The diets (kg air-dry feed/day) were 7–2 kg hay and 10·8 kg either starchy or fibrous concentrates (60S and 60F) or 3·5 kg hay and 14·0 kg either starchy or fibrous concentrates (80S and 80F). Rumen samples were taken by stomach tube in weeks 10 and 12 of lactation and the digestibility of the diets was measured with four cows per treatment during weeks 13 and 14. The digestibility of the same feeds was also measured in sheep at maintenance.The principal carbohydrate constituents of the concentrates were barley, wheat and cassava in the starchy concentrates and citrus pulp, sugar-beet pulp and wheat feed in the fibrous concentrates. The concentrates were designed to have similar concentrations of metabolizable energy (ME) and the diets were planned to provide similar intakes of digestible energy and crude protein.Milk yield and composition were very similar for treatments 60S and 60F. With the higher proportion of starchy concentrates (80S), milk yield was about 20% greater than on 60S, fat concentration fell severely but protein and lactose concentrations were unaffected. With the higher proportion of fibrous concentrates (80F), milk yield and the protein and lactose concentration were similar to values on 60F but fat concentration was lower, though not nearly so low as on 80S. Milk energy yield was reduced by the higher proportion of concentrates but was unaffected by type of carbohydrates. Live-weight changes were small.In both the sheep, consuming at maintenance, and the lactating cows consuming at about 3 times maintenance, digestibility of dry matter, organic matter and energy was higher with the higher concentrate diets but was unaffected by type of concentrate. The digestibility of fibre was greater with the fibrous concentrates but the effect of level of concentrate inclusion was inconsistent. Digestibility coefficients were consistently lower for the lactating cows than for the sheep.The proportion of acetic acid in the rumen volatile fatty acids in the cows was higher and the proportion of propionic acid was lower with the fibrous concentrates. The differences were much greater with the higher proportion of concentrates.During weeks 15–22 of lactation the cows were reallocated to concentrate treatments and given hay ad libitum. Hay intake was about 1 kg/day higher with the fibrous concentrates but the difference was not significant. Hay intake fell by about 0·6 kg/kg concentrate intake for both concentrate types. No significant differences in milk yield or composition were established, probably because of incomplete adaptation even after 8 weeks.It is concluded that at concentrate intakes of about 10 kg/day, the source of carbohydrate in the concentrates has little effect on milk production when the concentrates are of similar ME concentration. However, at higher levels of concentrate inclusion, although the diets may have similar ME concentrations, important differences in the yields of fat, protein and lactose occur due to carbohydrate source and these can be related to differences in rumen fermentation.

Description: SummaryMean digestible energy (DE) intakes of 147 cows of three parities receiving three levels of DE including one ad libitum (about 2·2, 2·6 and 3·3 multiples of maintenance (MM)) drawn from three mixed diets containing hay and 60, 75 or 90% compound were calculated.Rumen samples were taken from three-quarters of the cows at monthly intervals throughout the experiment. Molar proportions of volatile fatty acids (VFA) in the rumen were not affected by stage of lactation over the 36 weeks of the experiment. The proportion of acetic acid decreased and that of propionic acid increased with greater intakes and with higher proportions of compound in the diet. The proportion of n-butyric acid was little affected by level of intake but decreased with increasing proportions of compound. In young, non-lactating cattle given the same diets but at lower levels of intake, VFA proportions were unaffected by diet composition at intakes of about 0·7 MM but at intakes of about 1·3 MM the proportion of acetate decreased and that of propionate increased when the proportion of compound was increased from 75 to 90%.The efficiency of milk energy production in relation to DE or metabolizable energy (ME) above maintenance decreased with increasing level of intake but was little affected by the proportion of compound. Partition towards live weight increased with level of intake in early lactation but not in late lactation. It also increased with higher proportions of compound in mid and late lactation but not in early lactation.Estimates of the ME requirement for live-weight change (LWC) were in reasonable agreement with recently published standards in early lactation when live weight was decreasing, but later in lactation when live-weight gain was occurring, a much higher value was calculated which is difficult to reconcile with these standards.Rumen VFA proportions were related to dietary fibre concentration and level of intake additively. The relationship to VFA proportions was close for milk fat concentration, but less so for energy partition towards live weight and none was apparent for the efficiency of ME utilization for milk energy production. It is suggested that both the reduction in milk fat concentration and the increase in milk yield in response to reductions in the fibre content of diets may be independently related to the increase in the proportion of propionate in the rumen VFA.It is concluded that further progress in studies of the dietary factors affecting the efficiency of milk production will require measurements of nutrient uptake from the digestive tract and description of milk production and LWC in terms of their chemical composition rather than energy alone.

Description: SummaryThere has been little study on the growth and morphology of individual plants constituting the population of white clover in mixed swards under grazing. Such information is required if the mechanisms governing plant productivity and persistence are to be understood.Intact white clover plants were sampled from intensively sheep-grazed pastures under set stocking, rotational grazing, and a combination of both systems, by taking turves (250 × 250 mm), and washing out the plants, every month for a year. Characters measured for every stolon of each plant were: presence of a growing point; numbers of leaves, roots and axillary buds; stolon length. Total plant leaf and stolon dry weight were also recorded. Plants were classified according to degree of branching, and the contribution of each branching order to the population determined.There were strong seasonal variations in plant size (leaf and stolon dry weight, stolon length, and numbers of stolons and leaves per plant) which showed a significant decrease in spring with recovery over the following summer. This was paralleled by a rapid increase in the proportion of less branched plants (1st and 2nd branching order) in the population from 60 to 80% in spring, as higher-order plants broke up into smaller- and lower-ordered plants at this time. Numbers of roots per plant increased over winter to peak in early spring then declined in the following summer-autumn. While system of grazing management had no significant effect on branching structure of plants, it had a large effect on plant dry weight; rotationally grazed plants were 2·5 times larger than set stocked plants (0·182 cf. 0·073 g respectively).Other general features of plant morphology were that each successive order of branch stolons was shorter and length before branching was less than that of their preceding parent stolon. The highest branching order observed was 6th order. There was no relationship between branching and numbers of roots; in branched plants only 55% of stolons were rooted regardless of plant order, but rooted stolons accounted for 85% of total stolon length and carried 62, 48 and 90% of the leaves, growing points and axillary buds per plant, respectively.Comparison with other studies suggests that the processes outlined in this report may be common to white clover growth under grazing over a wide range of favourable environments.

Description: SUMMARYSilastic implants of different lengths (0·5–4 cm) containing oestradiol were implanted in wether or ewe lambs, which were slaughtered at 14 or 23 weeks of age. Live weight gain and carcass weight of lambs was increased marginally by oestradiol treatment. Oestradiol decreased the percentage of fat in the carcass, while increasing the percentage of carcass water. Older lambs had a greater response to oestradiol treatment for the weights of the carcass protein and ash. The female reproductive system was affected by oestradiol with the ovarian weights being depressed and the uterine weights increasing. The uterus was especially sensitive to oestradiol at 14 weeks of age. Oestradiol increased the weight of protein in lamb carcasses, especially in the older lambs of this study.

Description: SummaryIn an experiment, carried out over 3 years, two groups of dairy cows offered ad libitum access to grass silage received 8 kg/day concentrate differing only in phosphorus content (low P concentrate: 4·0–4·5 g/kg dry matter (D.M.); high P concentrate: 6·0–6·5 g/kg D.M.) during the winter feeding period of approximately 6 months. During the summer period all animals were grazed together on perennial ryegrass pastures. There were no consistent significant effects of P content on any of the variables measured. The mean calving indices were 371 (S.E. = 3·71, n = 122) and 379 (S.E. = 4·28, n = 95) days and overall conception rates were 0·70 and 0·68 for the low and high P treatments, respectively. Mean plasma P concentrations during the winter period were significantly reduced (P 〉 0·01 or greater) in years 2 and 3 of the study on the low P treatment. In 1 year milk yield was significantly higher (P 〉 0·01) on the low P treatment although the fat content was significantly reduced (P 〉 0·05) but these effects were not recorded in the other 2 years.

Description: J. agric. Sci., Camb. (1988), 110, 261–270The authors regret that there is an error in Fig. 1 of this paper. The values on the x-axis should be reversed to read from left to right: 200, 150, 100 g ADF/kg diet D. M.

Description: Potassium–argon dating of 44 samples of basalt lavas and pantelleritic ignimbrites provides a provisional chronology for the 1900-metre thick Cenozoic succession of the Suregei–Asille district, northeast of Lake Turkana. Volcanic rocks of the Asille Group range in age from late Oligocene (Chattian) to late Miocene (Tortonian). Data obtained from conventional K–Ar total-rock analysis of basalt samples are appraised statistically to indicate the presence of three periods of enhanced volcanism centred around 27, 17 and 11.5 Ma. Equivalent ages obtained from the pyroclastic pantellerites by conventional K–Ar total-rock analysis and 40Ar/39Ar analysis of sanidine concentrates indicate that basic and acid eruptions were closely spaced in time. Continental tholeiite flood lavas belonging to the Gombe Group are of Pliocene age, but are difficult to date precisely because of their young ages and relatively high atmospheric contamination occurring as a result of the secondary alteration in the ubiquitous glass mesostasis. Those ages involving least atmospheric correction are considered most reliable, and are closely similar for the Chen Alia and Harr formations at around 4.85 Ma, although later flood eruptions may have occurred to the south and west of the Suregei–Asille district at about 3.85 Ma.