Optimum designs of three-tier open nucleus breeding schemes are evaluated deterministically by maximizing the equilibrium rate of genetic gain for two methods of selection. Methodology is developed for both restricted and unrestricted migration between tiers and incorporates the loss of variance due to selection. A formula is derived for calculating the asymptotic rate of inbreeding. In the extensive livestock industries, proportional improvements in the equilibrium rate of genetic gain of between 0·12 and 0·22 are possible over a closed nucleus if no restrictions are imposed on male and female migration between tiers. The value of the extra tier in an optimized three-tier open nucleus scheme is approximately 0-45 of the maximum proportional improvement of a two-tier open nucleus over a closed nucleus scheme. The optimum structure is to have approximately 1% and 10% of the population in the nucleus and multiplier respectively. With this optimum structure the asymptotic rate of inbreeding will be reduced to one-sixth of that in a closed nucleus. The effects of various factors on the optimum structure, genetic gain and inbreeding are examined. The advantage of a three-tier open nucleus scheme over a closed nucleus scheme can be reduced substantially if thesefactors are operating.

Two groups of 16 cubicle-housed Holstein-Friesian cattle from weeks 3 to 27 of lactation were offered either a proprietary protein supplement of animal origin (P) or soya-bean meal (S) as the protein source in the concentrate in a continuous design experiment. Concentrates were offered mixed with grass silage as complete diets to give a forage: concentrate ratio of 41: 59 and a crude protein content of 213 and 210 g/kg dry matter (DM) and a metabolizable energy content (MJ/kg DM) of 11·9 and 12·0 for P and S respectively. There was no significant difference due to diet for mean locomotion score (1·75 v. 1·66 (s.e. 0·15)), prevalence (0·1 v. 0·09 per cow per week) or incidence of lameness (0·04 v. 0·04) for P and S respectively. Similarly there was no effect on hoof growth, wear, hardness or conformation. Sole haemorrhages, indicative of subclinical laminitis, were observed throughout the experiment but were most severe at approximately 16 weeks after calving. Levels of heel erosion remained constant throughout. There was no significant effect of treatment on either heel or sole lesion formation. No significant differences were observed between treatments for milk yield, live weight, condition score or blood metabolites. The conclusions from this study were that source of dietary protein has no effect on dairy cow lameness or the development of sole lesions indicative of subclinical laminitis.

According to animal breeding theory, profit after, say, 10 generations of selection is maximized when the usually non-linear profit function is approximated by a linear breeding goal where the linearization is at the population mean in generation 10 and the linear breeding goal is subsequently predicted by a linear index for which the animals are selected. The prediction of the population mean at generation 10 requires linear relationships among the traits that constitute the non-linear profit, because otherwise this prediction becomes very complicated.

A non-linear index is proposed that simply estimates the non-linear goal H =f(u) by Ĥ =f(û), where u = vector of genetic values for the traits and u is its (BLUP) estimate. This non-linear index does not require predictions of (future) population means and does not require linearly related traits.

To test these indices a simple meat production example was constructed where the non-linearity between the traits was due to the competition between weight and probability of survival for the same resources from food intake. In the model selection for weight and, in particular, for weight over costs (mainly food) led to reduced profits due to large reductions of survival rates. Although, the example was oversimplified, this should provide a warning for the use of oversimplified breeding goals, e.g. fitness traits may reduce by more than expected from base population genetic parameters.

When probability of survival and weight were measured, a non-linear index of these non-linear traits gave the greatest genetic gains. Failure to update genetic parameters each generation severely reduced genetic gain and, if linear indices were used, it was also important to update the economic weights. When probability of survival was measured, profit could be calculated on each animal and included as a trait in the calculation of estimated breeding value. This yielded high genetic gain and did not require updating of genetic parameters or economic weights.

This paper presents the economic perspectives applied when either using or not using opportunity costs of postponed replacement in deriving the economic value of herd life. Results show the equivalence of the rescaling method and the correction for opportunity costs. In economic terms, using rescaling or correction for opportunity costs forces the value of genetic improvement to change from revenues of increased output to reduction of costs per unit of (fixed) ouput. Under the zero profit theory, the economic value of herd life is equal when either using or not using correction for opportunity costs. In deriving economic values to define breeding goals, the choice of a method and price parameters will have to depend on foreseen future production circumstances for the system under study.

The relationship between the interval to post-partum (PP) commencement of luteal activity (CLA) and traditional measures of fertility was studied in 1733 lactations of British Friesian cows. Milk progesterone (P4) concentrations were used to determine the interval to PP ovulation and to confirm pregnancy. Milk samples were taken thrice weekly from cows in 20 commercial herds and daily in the University of Nottingham research herd. Commencement of luteal activity was defined as the day of first PP occurrence ofP4 levels >3 μg/l which was then maintained for at least two consecutive readings in the commercial herds and for 4 days in the university herd. Records from animals with retained placenta, uterine infection or those treated with reproductive hormone preparations for reproductive disorders were excluded for this analysis from the original database of cows during 2503 lactations. The interval to PP CLA averaged 27·0 (s.d. 12·1) days (no. = 1733), interval to first service 71·2 (s.d. 19·9) days (no. = 1646), interval to conception 87·2 (s.d. 35·0) days (no. = 1510), number of services per conception 1·50 (s.d. 0·83, no. = 1510) and conception to first service was 0·65. Linear models were then fitted to subsets of the data with complete information to assess the influences of lactation number, season and herd (at least 1243 observations in all analyses). The interval to PP CLA was favourably correlated with measures of fertility such that for every day delay in the interval to CLA there was an average delay of 0·24 and 0·41 days (P < 0·001) in the interval to first service and conception, respectively. The number of services per conception was reduced by 0·11 for each additional 21 days in the interval between PP CLA and first service (P < 0·001). Furthermore, conception rate was influenced by the interval from the onset of luteal activity to first insemination (P < 0·01) such that each additional 21 days progressively reduced the probability of failure at a given insemination number to 0·89 of its previous value. There were significant effects of parity and season (P < 0·05) on the interval to first PP service while the variation among herds in the interval to PP service and days open was significant (P < 0·01). The regressions of measures of fertility on milk yield were not significant. This extensive database on the hormone profiles of PP cows shows that the early re-establishment of PP ovarian activity is an important prerequisite for high fertility.

The effects of experimental Trypanosoma congolense infection on the digestive physiology and nutrient utilization in Gobra zebu and N'Dama cattle were examined in a 16-week trial. A pair-feeding procedure permitted examination of the effects of both food intake and trypanosomosis infection. Twenty Gobra and 16 N'dama bulls aged between 1 and 2 years were paired on a live-weight basis within each breed. One of each pair was chosen at random to serve as an uninfected control while the other was inoculated intradermally with 104 T. congolense in mice blood in the 6th week of the experiment. Packed cell volume and parasitaemia data were collected weekly throughout the trial. Total dry-matter intake (TDMI) and live-weight changes were measured weekly in all animals during the 16-week trial. Rate of passage (RoP) and dry matter digestibility were evaluated before and after infection.

While infection significantly depressed TDMI in both breeds (P < 0·05), neither infection nor breed affected the RoP and the apparent digestibility of the dry matter. Significant changes in live weight attributable solely to the infection were observed in both breeds. Loss of body weight was more severe (P < 0·05) in infected Gobra bulls compared with N'dama bulls possibly implying a superior efficiency of nutrient utilization by the N'dama during infection. In the course of the trial, one N'dama and three Gobra bulls that presented severe clinical symptoms of trypanosomosis were treated and withdrawn from the experiment along with their pair-fed controls.

In conclusion, the RoP and the digestive efficiency were not affected by infection and breed differences. Also, the trypanotolerance mechanism does not seem to be affected by anorexia but rather by the ability to conserve body reserves during infection.

Forty-five Bos indicus (zebu) cows were blocked by body condition (BC) score at calving and allocated by body weight (BW) to three treatments: untreated controls (CON), and progesterone-releasing intra-vaginal device (PRID)-treated at either 45 (T45) or 60 days (T60) post partum. Cows were given food individually and blood-sampled three times a week for progesterone. Calves sucked twice a day and were weighed weekly. PRIDs resulted in only 21% of cows responding at 60 days and they did not reduce anoestrus (PPI) or calving interval (CI) (P > 0·05). Dry matter (DM) and metabolizable energy (ME) intake were 7·1 (s.e. 0·6) kg and 54·3 (s.e. 4·6) MJ/day, respectively. BC score and BW at calving, and ME intake influenced cow and calf average daily gain ranging from −580 to 625 and 331 to 868 g/day, respectively. Milk yield during the first 4 months was 507 (s.e. 97) l. Cows gained 25 kg per unit increase in condition but lost 50 kg for a unit decline. CI (mean 14·2, range 10 to 24 months) was inversely related to BC score at calving (r = −0·31) and was delayed by a long PPI (r = 0·51), ranging from 38 to 297 days. Most (95%) cows experienced one or more ‘silent ovulations’ before first oestrus, the number extending PPI length (r = 0·49, P < 0·001). Efficiency of ME utilization was higher for smaller cows of 240 (s.e. 28) kg at calving. It is concluded that: (1) PRID treatment before 60 days post partum is unlikely to reduce anoestrus in Boran zebu cattle; (2) given adequate energy intake zebu cattle in thin condition at calving initially replenish body reserves at the cost of lactation and experience more ‘silent’ ovarian activity before returning to oestrus; (3) cows in good condition at calving express maximum lactation potential, mobilizing their own body reserves to support milk production, yet resume oestrous activity earlier despite weight losses to support higher milk yields.

Six Holstein-Friesian cows in mid lactation were used to examine the effects of replacing increasing proportions of grass silage (GS) by whole-crop wheat (WCW) in the diet of lactating dairy cows. Grass silage was a first-cut perennial ryegrass. The WCW was harvested at 645 g dry matter (DM) per kg and was preserved with either 20 (WCW-20) or 40 (WCW-40) kg urea per t DM. The diets were 6 kg DM dairy concentrate daily with one of six forage treatments offered ad libitum. The forage treatments were GS alone, GS with either WCW-20 or WCW-40 in a 2:1 DM ratio, GS with either WCW-20 or WCW-40 in a 1:2 DM ratio, or WCW-40 alone. The experiment consisted of an incomplete change-over design with three 4-week periods. DM intakes were highest with the mixtures (P < 0·05) but milk yield was not significantly affected by the treatments although it tended to be highest with the 1:2 ratio. Milk composition responses were generally small and non-significant, but yields of fat and protein were highest with the mixtures (P < 0·05). The apparent digestibility of DM and organic matter (OM) decreased linearly (P · 0·01) with increasing WCW inclusion but digestible DM and OM intakes were not significantly affected. Apparent digestibility of neutral-detergent fibre tended to be lower with the forage mixtures (quadratic P < 0·20). Apparent digestibility of starch was higher with GS than with diets containing WCW and decreased linearly with diets containing increasing proportions of WCW (P < 0·01). Intakes of starch and digestible starch rose with increasing WCW inclusion but so also did faecal starch output such that 0·75 kg starch per day was excreted on WCW-40 alone. Water intake from food and water excretion in urine decreased linearly with increasing WCW inclusion but water excretion in faeces and milk was not significantly affected by diet. The difference between measured water intake and output (water deficit) increased from 38 kg/day on GS alone to 58 kg/day on WCW-40 alone (linear P < 0·001). The only effects of level of urea treatment were to increase milk urea concentration (P < 0·05). It is concluded that the small size of the milk yield response to the increased forage intake obtained when up to two-thirds of the GS is replaced by WCW is due to the reduced digestibility of the OM and particularly of the starch component resulting from the egestion of whole wheat grains in the faeces.

The effect of water restriction on rumen degradability and outflow rate of low quality veld hay and dry-matter apparent digestibility was investigated in four rumen cannulated Tuli × Friesian steers (mean weight 329 (s.d. 36·6) kg) given food at maintenance (metabolizable energy allowance (maintenance) (MJ) = 8·3 + 0·091 M). Two diets with 20: 80 (low, L) and 80:20 (high, H) roughage to concentrate ratios were used in combination with free access to water for 2·5 h once daily or once every 3rd day. A 4 × 4 Latin-square design with a 2 (diets) × 2 (watering frequencies) factorial arrangement of treatments was used.

The degradation pattern of veld hay was not affected by the type of diet and the watering frequency. Although the effective degradabilities of hay in steers given the two diets were low (177 and 258 g/kg for L and H, respectively), they were significantly different (P < 0·05) from each other. However, watering frequency did not affect the effective degradability of hay (218 and 217 g/kg). While the low roughage diet had a higher rumen outflow rate for Crmordanted hay than the high roughage diet (0·047 per h and 0·031 per h), this was not statistically significant. The same outflow rate was obtained for the two watering frequencies (0·039 per h).

Milk temperature was measured automatically during milking with a view to detecting silent oestrus in dairy cows. A total of 38 silent oestrous periods were studied, based mainly on ovulation and milk progesterone levels together with visual observation.

In 78·9% of silent oestrous periods, a significant increase in milk temperature amounting to a mean of 0·6 (s.e. 0·07)°C was found, and this was highly correlated (r = 0·90) with an increased body temperature. In most silent oestrous periods increases in milk and body temperatures and ovulation with milk progesterone levels below 2 μg/l were found, the oestrous cycles being characterized by typical progesterone profiles. In some cows increases in milk and body temperatures and ovulation during a silent oestrous period were associated with non-typical progesterone profiles although most of these occurred shortly after parturition.

The purpose of this study was to estimate genetic parameters for measures offertility and several health disorders in dairy cows. Data consisted of 33732 records, of which 9163 were on heifers, on 305-day milk yield, health disorders and inseminations. Measures offertility were calculated from calving and insemination dates and included calving interval, days to first service and conception to first service. Health disorders included milk fever, mastitis and lameness. Genetic and phenotypic (co)variances were estimated using restricted maximum likelihood. Heritability estimates for both health disorders and fertility traits were low, ranging from 0·003 to 0·080. All genetic correlations between 305-day milk yield and health and fertility traits, in cows and heifers together, were antagonistic implying that selection for milk yield may have caused a deterioration in health and fertility. The unfavourable correlation between milk yield and health and fertility traits, plus the economic importance of the latter, suggests that future breeding goals should be expanded to include some health disorders and fertility.

The effects of day length, of the daily change in day length and of heat load, together with age effect, on live-weight gain of Holstein-Friesian bull calves, were studied using 8205 gain records of 1019 calves that were maintained in the experimental herd at Newe Ya'ar during a 5-year period (1991 to 1995). The age range of the calves was 150 to 450 days. Effects of day length (h) and of day length change (min/day) were assumed to be linear and effect of age was assumed to be quadratic. Three heat load indexes were calculated, accounting for day temperatures above 27°C, or night temperatures above 18°C, or both, and their effect was assumed to be linear also. Random effect of calf and fixed effect of the year were also accounted for by the regression analysis. The mean gain was 1·274 kg/day. The effect of day length was 0·027 (s.e. 0·003) kg/day per h, and effect of day length change was 0·042 (s.e. 0·003) kg/ay per min/day both effects being highly significant (P < 0·0001). The effects of heat load according to each of the three indexes were either not significant, or tended to be positive, which implies increased gain with increasing heat load. Effect of age was positive (P = 0·0005), and of age2 was negative (P < 0·0001). Based on the regression model that did not include heat load effect, the peak gain was obtained on 19 May, 33 days before the longest day and the trough was obtained on 18 November, with a difference of 0·206 kg/day (proportionately 0·15 of the peak gain) between peak and trough gains. It was calculated by the regression coefficients for the photoperiod effects, that a calf that enters the feedlot at the age of 150 days and a live weight of 180 kg on 1 January, will be 23 kg heavier at the age of 350 days than a calf that enters the feedlot at the same age and weight on 1 July. This difference is reduced to 10 kg at the age of 450 days.

The herd life of dairy cows was approximated by a single lifespan value based on the geometric distribution and accounting for the number of lactations each cow had completed or, if still in the herd, was expected to complete. For cows which had completed lactation n, but had not had time to complete lactation n + 1, the probability of survival from lactation n to complete lactation n + 1, from n + 1 to n + 2 etc. was incorporated, utilizing average population survival probabilities.

Formulae for the genetic variance in lifespan, its heritability and the genetic regression of breeding value on phenotype, the latter found to be independent of the amount of information included in the phenotype, are derived and checked by simulation.

From an analysis of 25227 dairy cows, each with the opportunity to complete five lactations, the heritability of lifespan was 0·06 and its genetic correlation with survival to complete three, four and five lactations ranged from 0·90 to 0·96, for both complete and incomplete survival information, showing that the lifespan trait appears to account adequately for missing observations. Genetic correlations between lifespan and first lactation yield traits were around 0·50, whilst the corresponding phenotypic correlations were approximately 0·13.

Charolais cows were individually given hay ad libitum around calving for two successive winters (no. = 40 and no. = 43). Profiles of hay intake are defined for each cow as the evolution of individual daily intake level around calving.

The aim of this work was to build a typology of these profiles, using multivariate analysis. Four and three groups of cows were distinguished respectively for a 2-month and a 4-month period around calving (PI and PI). These groups corresponded to different kinetics of intake level around calving which were defined as follows: group 1 — plane profiles, with a low difference of intake level between pregnancy and lactation; group 2 — profiles characterized by a marked decrease in intake level just before calving followed by a long and regular increase after calving; group 3 — profiles with no decrease before calving but an early break in the increase in intake after calving; group 4 — intake profiles with a large difference in intake level between pregnancy and lactation. Groups 2 and 3 were pooled for P2.

Cows from groups 2 and 4 increased intake after calving fast enough to prevent the use of their body reserves even with a high milk-production level. Their calculated energy balance became positive very quickly, only 1 week after calving. At the other extreme, a decrease in body reserves was observed for cows which needed at least 1 month after calving to reach their maximum intake capacity and then recover a positive energy balance.

In two experiments the growth, body composition and behaviour of steers and heifers kept in a building with natural day length only (average 9·7 h/day, treatment N) were compared with similar groups of animals kept in identical housing with the day length artificially extended to 16 h/day, (treatment L). The effects were recorded for 126 days in steers and 180 days in heifers, with both groups of animals being slaughtered in March when the two experiments ended. There were no effects over the entire experiment on the growth rate or food intake of either steers or heifers. The growth of the steers was reduced in the first 2 weeks after the lights were switched on but they gained more weight to compensate over the next 8 weeks. Over the whole experiment there was no treatment effect on food conversion ratio for either steers or heifers but it was reduced for steers on treatment L over the first 10 weeks. Steers in treatment N produced fatter carcasses than those on treatment L. Ultrasonic scanning of the heifers showed that those on treatment N deposited more fatty tissue between autumn and winter and less between winter and spring compared with those on treatment L.

The behaviour of steers on treatment L did not vary over the experiment but steers on treatment N changed their behaviour with season. They slept for more time in winter and less in spring. Over the whole experiment steers on treatment L slept less and spent more time lying ruminating than those on treatment N but the total time spent lying was not affected by treatment. In contrast, the heifers on treatment L lay down for longer than those on treatment N, suggesting that the effect of supplementary light on lying time, which has been observed previously with dairy cows, is confined to female cattle. Heifers on treatment L started mounting each other earlier than heifers on treatment N and, like the steers, they spent less time sleeping It is concluded that extending the photoperiod for cattle in winter reduced body fatness in both steers and heifers and increased the time heifers spend lying down but that there were no major effects on growth rate or food intake.

This work was designed to study the influence of parity (multiparous (MP, no. = 9) or primiparous (PP, no. = 10)) and feeding level (control diet (CD; 1·00) or restricted diet (RD; proportionately 0·70 of requirements) in a 2×2 factorial design on the utilization of exogenous glucose in the suckler anoestrous Charolais beef cow. Lack of ovarian activity was confirmed by low circulating progesterone concentrations measured in weekly blood samples taken after parturition. An injection of glucose (1·5 mmol/kg live weight) lasting 20 min was given 30 days and 50 days post partum. Blood samples were collected before and for 120 min after the start of the injection and plasma insulin, glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate and urea were measured. Although plasma glucose concentrations were not significantly different between treatment groups in the period immediately after the injection of glucose, CD PP animals had higher plasma insulin levels than CD MP animals (at 25 min: 596·4, 283·8, 435·1 and 309·6 pmol/l, P < 0·05 for groups PP CD, MP CD, PP RD and MP RD respectively). Plasma NEFA concentrations were initially higher in the RD groups compared with the CD groups but were reduced by the glucose injection (P < 0·001). However, the PP RD cows took longer to respond to the exogenous glucose compared with the MP RD cows (at 25 min: PP RD: 133·2 and MP RD: 57·5 eq/l, P < 0·05). In conclusion, suckler anoestrous PP cows appear to require higher plasma insulin levels than MP cows to metabolize exogenous glucose and underfed PP cows were slower to reduce plasma NEFA after glucose injection than underfed MP cows.

To determine a best measure for predicting genetic merit for milking and nursing ability in beef cattle, restricted maximum likelihood (REML) estimates of variances and covariances for direct and maternal effect were obtained by using pre-weaning growth records of calves at various stages after parturition until weaning in Japanese Black cattle. Data used in this study were pre-weaning growth records of 1892 Japanese Black calves obtained from the Tottori National Livestock Breeding Station covering the period from 1960 to 1985. Traits analysed were adjusted monthly weights, adjusted monthly heights and cumulative daily gains (DGs) from birth to 1, 2, 3, 4, 5 and 6 months of age. Estimates of variances and covariances were obtained by REML using the DFREML program of Meyer. Results indicate that: (1) the direct effects on pre-weaning growth of calves are the smallest at birth to 1 month of age and then increase; (2) the maternal effects of the dams are the largest for the first 2 months, and then decrease; (3) the contribution of these two effects on calf growth is reversed at 3 or 4 months of age; (4) the non-additive maternal effects exist but are small; and (5) the genetic correlations between direct and maternal effects are low for weight and cumulative DG, whereas those for height are relatively high. These results suggest that DGfrom birth to 2 months of age (DGO-2) is most influenced by the additive maternal effect. Thus, DGO-2 is concluded to be the best measure for predicting genetic merit for milking and nursing ability in beef cattle.

The purpose of this work was to investigate the relationship between individual animal performance and production per unit area of land of steers of different potential growth rate under different grazing stocking rates (SR). The analysis involved 160 steers divided equally between two breeds, over 2 years at four SRfor each breed and two replicates for each SR. Thus there werefive steers per replicate. The breeds were purebred Aberdeen Angus (Angus) and 4 Limousin (Limousin). After weaning steers were grazed for 251 days on a pasture dominated by Festuca arundinacea. Given that equal SR does not equate to equal treament for breeds characterized to be of different size and rate of growth at a given age, the analysis was undertaken on the basis of three categories of metabolic body size per ha (S). The variables analysed were individual live-weight gain (final minus initial weight, kg), relative individual live-weight gain (logefinal weight - loge initial weight) and production (kg/ha). A mixed model was used to examine effects of breed, S, year and the interactions between these variables. In general significant (P < 0·05) differences were found for all factors of classification and interactions. Independent linear regressions were calculated for each breed between absolute live-weight gain, relative live-weight gain, and production on S. It was concluded that there was a genotype × environment interaction, with the Angus breed tending to show a higher production per unit area than the Limousin, especially at high levels of S when scarcity of forage was apparent. Nevertheless Limousin steers had higher absolute individual performance than the Angus. The higher production of the smaller breed may be explained by a higher SR at a given S level and also by its higher relative individual live-weight gain in relation to that of the larger breed. The data were coded to use Mott's model to study the relationship between absolute performance (kg) and production (kg/ha). However this model ignores the existing interaction involving breeds.

The aim of the current study was to investigate the effects of level of feeding and level offish-meal supplementation on the carcass composition of young steers and in doing so, to assess the potential for employing near infrared reflectance spectroscopy (NIRS) in such studies. In addition to wet chemical techniques, NIRS was used to examine carcass samples from animals offered silage-based diets at one of four levels of feeding ranging from near maintenance to ad libitum and with one of four levels offish meal (0, 50,100 or 150 g/kg silage dry matter).

Wet chemical data indicated an increase in fat concentration (P < 0·001) and decrease in crude protein concentration (P < 0·05) in the fresh carcass in response to increasing level of feeding but no statistically significant effect of level of fish meal. Ash concentration was not affected significantly by either level of feeding or level of fish-meal supplementation. Ground, freeze-dried samples were scanned in the wavelength range 1100 to 2498 nm. Calibration equations for ash, fat and crude protein concentration (g/kg carcass) were derived using a modified partial least-squares regression technique. Equations were found to be superior for fat compared with those for crude protein and ash. Standard errors of calibration (g/kg carcass) and multiple correlation coefficients of 6·96 and 0·42, 6·61 and 0·95 and 4·36 and 0·61 were obtained for ash, fat and crude protein respectively with corresponding standard errors of cross validation of 7·71, 7·82 and 4·96 g/kg carcass respectively. Qualitative analysis of spectral information using multivariate techniques and difference spectra clearly showed differences in carcass composition resulting from the different levels of feeding and less so the different levels offish-meal supplementation.

It is shown, that NIRS can be used both quantitatively and qualitatively to study the effects of nutrition on carcass composition.

A method is described for assigning beef cattle performance records to within-herd management effects (contemporary groups) retrospectively, using information on the recording date and herd. This method takes account of the within-herd calving pattern. The objective of developing a method of assigning records to contemporary groups was to maximize the contemporary group size while ensuring as far as possible that records in any contemporary group were subject to the same management.

A simple method for assessing the effectiveness of different strategies for assigning records to contemporary groups is proposed, based on investigating the balance between the effects of contemporary group size upon the heritability and the accuracy of mass selection.

The results of a study of different contemporary grouping strategies in the Simmental breed are reported.