An experiment was conducted using two batches of 40 purchased male Hereford x Friesian calves, reared conventionally with weaning after 5 weeks. Five diets were offered ad libitum for 9 weeks: a basic concentrate pellet A offered alone, or with additional chopped or long straw; a diet incorporating 35 g sodium bicarbonate per kg in the basic pellet; and a complete diet with the inclusion of 176g chopped straw (20 mm) per kg in the concentrate pellet.Concentrate intakes and live-weight gains tended to increase with voluntary intake of roughage and the inclusion of buffer in the diet; giving a complete diet, however, gave the best results, with total intake increased to 1 -6 of that for diet A and also significantly increased weight gains.Rumen acidity was decreased by roughage consumption or by buffer inclusion in the diet. Increasing roughage consumption tended to promote an increase in the molar proportions of acetic and butyric acids in the rumen liquor, and a decrease in the molar proportion of propionic acid.Results suggested that chopping the roughage into 20-mm lengths did not obviously alter the rumen-buffering characteristics of long roughage, provided that a greater quantity was included in chopped form.

1. Herbage was ensiled, fresh at 17% DM or wilted to 32% DM, with and without the addition of formic acid (19-2 kg/tonne DM). The silages were fed individually ad libitum to 36 fifteen-month-old British Friesian steers of about 280 kg initial live weight (nine animals per treatment). 2. Wilting and the application of formic acid both inhibited fermentation, resulting in silages with higher levels of water-soluble carbohydrates, lower concentrations of volatile nitrogen and lower organic acid contents. 3. There were no significant dry matter x formic acid interactions in dry-matter intake or daily live-weight gain. 4. Treatment with formic acid did not enhance significantly either dry-matter intake or daily live-weight gain. Furthermore, it had little effect on digestibility, nitrogen retention or metabolizable energy (ME) concentration. 5. Wilting before ensiling increased dry-matter intake from 5-0 to 8-3 kg/head per day with consequent marked increases in ME intake, nitrogen retention and live-weight gain. Wilting, however, had little effect on digestibility, ME concentration, or the efficiency with which dietary nitrogen intake was retained.

In a lifetime study of spring-born cattle in a 20-month beef system the effects of production factors on carcass characteristics were examined using 302 serially slaughtered animals born in three consecutive years. A multifactorial design was used with three animal factors — maturity (early maturing Hereford crosses v. late maturing Charolais crosses), sex (heifer v. steer) and method of rearing (suckled calves v. bucket-reared calves). After an initial rearing period, feeding treatments were imposed during the subsequent winter period, followed by the imposition of two sward heights (low 6 to 8 cm and high 8 to 10 cm) during the subsequent grazing season. An initial representative group of 16 cattle was slaughtered at the start of the grazing season and most of the remaining cattle were subsequently slaughtered off grass at three randomly allocated slaughter times, on average 67, 110 and 154 days post turn-out. Interactions between the main production factors were not significant with the exception of slaughter date with winter feeding levels for fat in rib joint and weight of saleable meat, and slaughter date and sex for live weight, carcass weight and weight of saleable meat. Breed type, sex and method of rearing affected the weight of saleable meat off grass by 14·7, 14·8 and 5·6 kg respectively. The influence of the winter feeding treatments on the weight of saleable meat was small by the time the final group were slaughtered. Sward height had a transient effect on weight, condition and carcass composition, the effects becoming less evident as the grazing season progressed. The effect of delaying slaughter had the largest and most significant influence on carcass composition of all the production factors studied, although changes in body composition between slaughter dates were relatively slow.

In a lifetime study of spring born cattle managed in a 20-month beef system, four feeding treatments were imposed during the 5-month winter period and two grass heights (low 6 to 8 cm, high 8 to 10 cm) during the subsequent grazing period. Three slaughter weights were imposed over the grazing period, early, mid and late, at an average of 67,110 and 154 days post turn-out. A multi-factorial design was used with three animal factors — maturity (early maturing Hereford crosses v. late maturing Charolais crosses), sex (heifer v. steer) and method of rearing (suckled calves v. bucket-reared calves). There were significant differences in growth rate for both sex and maturity (P < 0·001) and a highly significant negative effect of winter food level on summer growth rate (P < 0·001), the growth rate of food treatment 4 being proportionately 0·61 of that treatment 1.Sward height significantly influenced summer growth rate (P < 0·001) but showed no interaction with winter food level in any of the three grazing periods. Growth rates increased over the summer but differences between winter food treatments decreased with daily gains for food treatment 4 being proportionately 0·44, 0·81 and 0·84 of food treatment 1 as the grazing season progressed.Eliminating winter feeding treatment as a factor and including condition score at turn-out as a co-variate improved the variation explained and reduced differences in growth rate for the main effects with only the main effect of grass height remaining significant. This suggests that the condition of animals at turn-out in conjunction with the subsequent grazing sward height provides a simple practical guide to subsequent animal performance.

SUMMARYSelected sample joints from the right sides of twelve 18-month-old Friesian steers were used to compare their accuracy in predicting carcass composition. Results indicated that whilst the shin joint proved the more accurate predictor of carcass muscle and bone contents, the loin (ribs 11 to 13) or foreloin (ribs 9 to 10) proved more useful in predicting total carcass composition, provided carcass weight was included as an additional variate.