SUMMARYBritish Friesian dairy female calves were offered once daily either 320 or 480 g of milk substitute reconstituted in warm water. Weaning took place when calves were consistently eating 400, 650 or 900 g/day of concentrates. The number of days taken to reach weaning was greater with calves offered 480 g than with calves offered 320 g of milk substitute per day. Calves with a high initial live weight achieved the required concentrate intake and were therefore weaned sooner than smaller calves. A fall in energy intake occurred immediately after weaning and this was greatest in calves previously offered 480 g/day of milk substitute. The treatments had no significant effect on the total intake of concentrates and hay over the 8 weeks of the experiment. Increasing the amount of milk substitute from 320 to 480 g/day increased total feed costs, and feed costs per kg live-weight gain. Increasing the required level of concentrate intake at weaning also increased total feed costs and feed costs/kg live-weight gain, but to a lesser extent. The results suggest that it is preferable to feed dairy replacement calves only 320 g of milk substitute in a once-daily feeding system. Weaning can be successfully under-taken when the calves are consistently eating 400 g/day of concentrates.

SUMMARYOne-hundred-and-seventy British Friesian heifers were individually fed from 6 weeks before to 6 weeks after artificial insemination on a diet of 90% maize silage and 10% decorticated groundnut in the dry matter. Three levels of nutrition were compared: 48, 55 and 62 g/day of digestible organic matter/kg live weight0·73, which gave mean growth rates of 0·34, 0·50 and 0·68 kg/day respectively. Pregnancy rates to first service were not significantly different, averaging 67, 69 and 65%. Heifers were given a body condition score at the time of insemination, and pregnancy rates corrected for level of nutrition were 42,72, 70 and 63% for heifers in poor, moderate, good or very good condition. For heifers in poor/moderate condition increasing the level of nutrition increased pregnancy rates and for those in good/very good condition pregnancy rates declined, but these effects were not significant.

Link to this article: http://journals.cambridge.org/ abstract_S0003356100030269How to cite this article: J. D. Leaver (1973). Rearing of dairy cattle. 4. Effect of concentrate supplementation on the live-weight gain and feed intake of calves offered roughages ad libitum. SUMMARYThe effects of three levels of concentrate supplementation on the liveweight gain and intake of roughages of 12-week-old British Friesian female calves were examined. Each supplement was offered for 12 weeks to two replicates of five calves which were group fed. The following six roughages were studied; high quality hay, dried grass wafers, grass silage, barley straw, poor quality hay and maize silage. The digestibility of the roughages was measured with sheep by total collection of faeces. Increasing the level of concentrate supplementation gave linear increases in live-weight gains of calves with all roughages, the greatest response occurring with roughages of low digestibility. The intake of roughage was depressed by increasing the level of concentrate supplementation, the greatest depressions occurring with roughages of high digestibility. Live-weight gains and roughage intakes were higher with dried grass wafers and lower with maize silage than would be expected from their respective digestibility coefficients. Multiple regression equations were calculated to relate live-weight gains or roughage intakes to concentrate intake and roughage digestibility. These equations predict from the digestibility of a roughage, the amount of concentrates required daily to produce a given live-weight gain, and the amount of roughage which is eaten under these circumstances.

Grassland plots were dressed with different amounts of cow slurry in January or March and grazed hy dairy heifers at interrals from late April to August. In the first experiment slurry was applied at levels up to 56 tonnes/ha (22-4 tons/ac) in March. Total herbage DM production was directly proportional to the amount of slurry applied. There was no effect of treatment on percentage herbage utilization. In the second experiment slurry was applied at levels up to 100 t/ha (40 tons/ac) in January or in March. There was no significant effect of time or level of slurry application on herbage production or on animal intake, but the behaviour of the heifers was modified during the first eight weeks after plots had been dressed with 75 or 100 t/ha (30 or 40 tons/ac).

In each of 2 years, two groups of 25 British Friesian heifers were given, respectively, a moderate-and a low-energy diet for a 12-week period. Mean live-weight gains of 0-25 kg/day and 0-45 kg/day were recorded for the moderate-energy diet, and losses of 0-22 kg/day and 013 kg/day for the low-energy diet. Heifers were inseminated artificially at oestrus at approximately the mid-point of the 12-week period, this oestrus being the next observed after synchronized oestrus, which followed luteolysis induced by cloprostenol injections. With few exceptions, heifers that gained weight were in good or medium condition at insemination and those that lost weight were in medium or poor condition.Highest pregnancy rate (0-78) was recorded for heifers that gained weight and were in medium condition at insemination. For heifers losing weight, pregnancy rate dropped to 0-46 (P < 0-05) due to reproductive failure occurring before the 25th day after insemination. Only in heifers in poor body condition was there a significantly higher proportion failing to ovulate normally (P < 0-001). Among heifers gaining weight, those failing to become pregnant to the first insemination were approximately lOOg/kg heavier than the pregnant ones (P<0-05).Irrespective of gain or loss of weight, and of body condition at insemination, embryo losses did not occur later than the 25th day after insemination, except that five heifers that showed oestrus when pregnant (according to plasma progesterone levels) and were reinseminated then showed evidence of embryo loss.