Physical and financial performance predictors for the dairy herd frequently take little or no account of current management practices, notably in respect of rebreeding. They do not anticipate the influence of unforeseen change or of increased beef bull use on the dairy herd in the longer term. The results of rebreeding management recording in 35 large dairy herds were reported at this meeting in 1983. These, and subsequent results, indicated that a decline in rebreeding management was most likely to influence annual milk sales and therefore income within no less than a 2 year period. The consequences of rebreeding management practices are long term and therefore it is essential to have the ability to look ahead to predict the likely outcome of change whether planned or unplanned. Rebreeding management influences calving pattern and any change influences feed requirements, both forage and other feeds. In addition, forage quality and quantity influence intake, the requirement for other feeds and therefore the financial performance. To take account of possible combinations of unplanned changes the computer program was developed as an extension to a program developed initially for the purpose of improving rebreeding and health management.

Hereford x Friesian (HF) and Limousin x Friesian (LF) heifers purchased at two weeks of age were artificially reared under the same conditions. They were first bred to calve at two years using one Aberdeen-Angus bull. One Simmental sire was used for the second and fourth calvings and one Charolais sire was used for the third calving. Data are presented for the cow herd up to the date of fifth calving and on their progeny to weaning for each of the first four calving seasons. Calving was in the period March/June. Animals were put to pasture in April. Weaning was in October/November when all animals were housed. Cows were fed grass silage in winter. Information was available for 36, 35, 27 and 24 calvings in seasons 1, 2, 3 and 4 respectively. The corresponding figures for calves available at weaning were 26, 35, 25 and 22.

Seasonality payments for milk are intended to encourage milk production in the months July to September, and to discourage production from April to June. Summer calving to match this pattern of production is not popular as the margins achieved on farms are generally poorer than for cows calving in autumn and winter. The reasons for the poor margins appear to be lower lactation yields due to late season grazing coinciding with peak yields, and high concentrate intakes due to the long feeding period from summer to the following spring. This study aimed to develop profitable systems of calving in the summer.

Sires from British breeds are less likely to cause calving difficulties than sires from Continental breeds. Consequently, heifers have usually been mated to Aberdeen-Angus, Beef Shorthorn or Hereford sires although Continental sires produce bigger, faster growing calves which mature at heavier weights. However, information is available on calving difficulties for sires used in AI and this enables easy calving Continental sires to be selected.

A group of 70 Hereford x British Friesian heifers were allocated at random to be mated, using AI, to a progeny tested high performance easy calving Aberdeen-Angus or to an easy calving sire of the Blonde d'Aquitaine, Limousin and Simmental breeds.

Only one sire from each breed was involved. The heifers were mated to commence calving in mid August 1985. A combined PRID/PG (PRID, CEVA; prostaglandin ICI Estrumate) technique was used to synchronise oestrus in the heifers and they were served by AI at 72 and 96 hours after the PG injection.

The Agricultural Research Council (1980, 1984) protein recommendation for dairy cows was designed to ensure that total amino acid nitrogen (TAA-N) entering the duodenum is sufficient to provide TAA-N for production. Essential amino acid (EAA) supply and demand, although recognised as important, was not an integral part of the scheme.

These trials were designed to test the feasibility and efficacy of formulating compound feeds to complement and improve the duodenal EAA supply from the basal diet of lactating cows.

The experimental aim was to formulate compound feeds on the basis of undegradable EAA (UEAA), to compare the performance of dairy cows fed these rations and to relate performance to measurements of nutrient supply to the duodenum. The trials took the form of two production trials (years 1 and 2) and one digestibility trial (year 2). Estimates of the supply of EAA to the duodenum were obtained by in vivo measurements in cannulated cows (year 2).

The trials described were designed to examine the effect of a protected lipid supplement (FPl; Unilever pic.) on the production of milk and milk constituents, under a range of feeding conditions. The supplement was protein-based, and had a high content of undegradable, digestible protein (UDP); the composition of the supplement is given in Table 1.

Fodder beet is a high yielding crop with a yield of up to 12 t DM ha-1 from the roots and 2 to 5 t DM ha-1 from the tops. The root has a high metabolisable energy (ME) content, and can be used in dairy cow diets as a substitute for silage or concentrate. Pearce (1983) reported that fodder beet can be included in rations at between 10 and 25 kg cow-1 d-1 but there have been few controlled feeding experiments with modern varieties of beet under UK conditions.

Food additives are used to increase growth rate by young growing cattle in their first winter before being turned out to graze. Evidence indicates that increased gains may not be retained through the grazing season. A trial was made to measure the effect of food additives on the performance of young growing cattle during winter and subsequently through the grazing season. Sixty British Friesian castrated male calves were offered grass silage ad libitum (DM 198g/kg; ME l0.0MJ/kg DM; CP 130g/kg DM) supplemented with either bruised barley or dried, molassed sugar beet pulp.

The use of an effective silage additive to help achieve a good preservation is recommended in poor silage-making conditions. At present over 70 additives are available, varying widely in content, application rate, cost and effectiveness. This trial was conducted to assess the effectiveness of three silage additives in improving silage fermentation quality, enhancing animal production and reducing dry matter (DM) losses in silo. Additives studied were the bacterial inoculant Ecosyl, the sulphuric acid based Scotsil and the formic acid product Add-F.

Trials were undertaken with 320 heifers in 13 groups on nine farms. Within each group heifers were allocated within matched weight pairs to treatment sub-groups at yarding. One sub-group was treated with an implant containing 200 mg Testosterone Propionate and 20 mg Oestradiol Benzoate (Synovex-H, Syntex). The two sub-groups were then reared together until slaughter or disbandonment of the group. Seven groups were sold deadweight, five of which had liveweights just prior to slaughter. Four farms sold to live auctions and weighed cattle on the day of sale. Two groups were grass finished but were weighed at turnout (Table 1).

Animal performance from grassland is dependant both on the grass growth achieved and the efficiency of utilisation. The Grassland Research Institute and ADAS conducted a series of trials (GM 20) which showed grass growth to be mainly influenced by the available water capacity of the soil, summer rainfall and altitude. This gives a site class which together with the fertilizer used determines the quantity of herbage grown.

Less is known of the variation in utilisation of the grass grown. This analysis has been undertaken to assess the levels of grassland utilisation found on dairy farms of England and Wales.

The gross energy (GE) of a feed represents its total energy content and is measured by burning the material in an atmosphere of oxygen in a bomb calorimeter. The GE of many feeds is often taken to be 18.4 MJ/kg dry matter (DM) (MAFF et al, 1984). This assumption is likely to be doubtful for feeds which are for example high in lipid or which contain products of fermentation. The gross energy content of grass silages in particular has recently been reviewed by Edwards (1986).

The GE content of grass silage can account for some 50% of the variability in metabolisable energy (ME). It is however ignored in present laboratory methods used for the prediction of ME which largely depend on using fibre fractions (Givens, 1986) which are more closely related to digestibility. This paper presents the results of GE determinations made on 109 grass silages made in clamps and since GE cannot be measured routinely, examines a number of factors which may be helpful in its prediction.

Cane molasses (CM) a by-product of sugar production, provides a relatively cheap means of increasing the energy content of ruminant diets. It is commonly thought that dietary concentrations of CM above about 200g/kg of the dry matter (DM) intake will lead to a reduction in rumen pH and hence have a depressant effect on forage digestibility. Recent work in vivo at the FEU and in vitro (ref 1) has suggested that there is an interaction between forage and CM, and indeed the in vitro experiment found evidence that increasing the proportion of CM actually enhanced the digestibility of the mixture. A further experiment was therefore conducted to monitor rumen pH and measure the degradability of hay DM in sheep fed increasing levels of molasses.

The measurement of the degradability of a roughage by means of the nylon bag technique usually requires the preparation of the sample by grinding with a laboratory hammer mill. There is a wide range of screen sizes available which produce samples which range from a fine flour to coarser materials containing particles several millimeters in length. The objective of this experiment was to examine the effect of fineness of grinding on the degradation of roughages as measured by the nylon bag technique.

Samples of hay and barley straw were ground through a 1 mm screen (fine) or through a bar screen with 3-5 by 33 mm slots (coarse). Two grammes contained in nylon bags were incubated in the rumen of each of four sheep fed on a good quality roughage, giving four observations per sample. All bags were introduced into the rumen at the same time relative to feeding. Zero-time losses were determined by washing bags without incubation. Water soluble material by filtration through a Whatman No. 1 filter paper. The particle size distribution of the hay used in Expt 1 is shown by Fig 1.

Increasing the crude protein (CP) concentrations of dairy concentrates in mixed diets has been found to increase milk yield and forage intake in a curvilinear manner in lactating dairy cows. In an experiment with lactating goats, linear increases in milk yield were observed as the CP in the concentrates was increased from 117 to 185 gAg DM. The purpose of the present experiment was to see if increases in hay intake and milk yield could be established to still higher levels of CP in the concentrates and to measure various associated aspects of digestion.

The problem of gizzard erosion in poultry has been linked with the presence in some fishmeal samples of a contaminant, gizzerosine, which stimulates the secretion of acid by the proventriculus. In 1985, a severe outbreak of gizzard erosion in a broiler unit in Devon was associated with the inclusion of Chilean fishmeal at 90g/kg. When the inclusion rate was reduced to 30g/kg the symptoms disappeared. This experiment used fishmeal from the same batch as that which had apparently caused gizzard erosion, and the same rates of inclusion, to examine the potential of NaHCO. to buffer the effects of increased acid secretion.