Ranking trait was used as a selection criterion for competition horses to estimate racing performance. In the literature the most common approaches to estimate breeding values are the linear or threshold statistical models. However, recent studies have shown that a Thurstonian approach was able to fix the race effect (competitive level of the horses that participate in the same race), thus suggesting a better prediction accuracy of breeding values for ranking trait. The aim of this study was to compare the predictability of linear, threshold and Thurstonian approaches for genetic evaluation of ranking in endurance horses. For this purpose, eight genetic models were used for each approach with different combinations of random effects: rider, rider–horse interaction and environmental permanent effect. All genetic models included gender, age and race as systematic effects. The database that was used contained 4065 ranking records from 966 horses and that for the pedigree contained 8733 animals (47% Arabian horses), with an estimated heritability around 0.10 for the ranking trait. The prediction ability of the models for racing performance was evaluated using a cross-validation approach. The average correlation between real and predicted performances across genetic models was around 0.25 for threshold, 0.58 for linear and 0.60 for Thurstonian approaches. Although no significant differences were found between models within approaches, the best genetic model included: the rider and rider–horse random effects for threshold, only rider and environmental permanent effects for linear approach and all random effects for Thurstonian approach. The absolute correlations of predicted breeding values among models were higher between threshold and Thurstonian: 0.90, 0.91 and 0.88 for all animals, top 20% and top 5% best animals. For rank correlations these figures were 0.85, 0.84 and 0.86. The lower values were those between linear and threshold approaches (0.65, 0.62 and 0.51). In conclusion, the Thurstonian approach is recommended for the routine genetic evaluations for ranking in endurance horses.

For Swedish Warmblood sport horses, breeding values (BVs) are predicted using a multiple-trait animal model with results from competitions and young horse performance tests. Data go back to the beginning of the 1970s, and earlier studies have indicated that some of the recorded traits have changed through the years. The objective of this study was to investigate the effects of including all performance data or excluding the older ones compared to a bivariate model (BM) considering performance traits in early and late periods as separate traits. The bivariate approach was assumed to give the most correct BVs for the actual breeding population. Competition results in dressage and show jumping for almost 40 000 horses until 2006 were available. For riding horse quality test (RHQT), data of 14 000 horses judged between 1973 and 2007 were used. Genetic correlations of 0.69 to 1.00 were estimated between traits recorded at different time periods (RHQT data) or different birth year groups (competition data). A cross-validation study and comparison of BVs using different sets of data showed that most accurate and similar results were obtained when BVs were predicted from either the BM or the univariate model including all data from the beginning of the recording. We recommend using all data and applying the univariate model to minimise the computational efforts for genetic evaluations and for provision of reliable BVs for as many horses as possible.

The effect of recombinantly derived bovine somatotropin (bST) treatment on milk production and pasture intake was examined in 16 New Zealand Friesian cows from low or high genetic merit (breeding index) selection lines. Recombinantly derived bST was administered by 2-weekly injection of a controlled release formulation for a period of 4 weeks (weeks 16 to 19 of lactation) at a dose rate equivalent to 50 mg/day. During this period the animals were housed for 18 days with food intake being measured over the last 8 days. Treatment with bST resulted in significantly higher yields of milk, fat and protein compared with the controls. Cows from the low breeding index (LBI) line were more responsive to exogenous bST than cows of the high breeding index (HBI) line in both milk and fat yield. Milk composition was not affected by bST treatment. There was a significant increase of proportionately 0·108 in intake of freshly cut pasture between bST-treated and untreated animals during days 16 to 23 of treatment. Thus, no significant difference in calculated energy balance was observed between the bSTtreated and untreated cows. This study indicates that the genetic background of cows may be an important determinant of their response to bST treatment and that such treatment rapidly alters voluntary intake in pasture-fed cows.

Metabolic adaptation includes an array of concerted metabolic and endocrine events that enable dairy cows bridging the period of energy deficit at the onset of lactation. The present study evaluated metabolic, endocrine and reticuloruminal pH changes in 30 (25 Holstein and five Simmental) periparturient dairy cows experiencing variable lipolysis early postpartum. Cows were fed the same close-up and fresh lactation diets and kept in the same management conditions. Blood samples were collected at day 14, and day 4, relative to expected parturition, and at day 2, and day 21 postpartum, and serum metabolites and hormones related to glucose and lipid metabolism, as well as concentrations of several liver enzymes and acute phase proteins were determined. Additionally, reticuloruminal pH was monitored every 10 min over the last 3 days of the observation period. BW and milk yields were recorded and balances of energy and protein were assessed. Based on serum concentration of non-esterified fatty acids (NEFA) postpartum, cows were retrospectively classified into low (n=8), medium (n=11), and high (n=11) lipolysis groups, with NEFA levels of <0.4 mmol/l, between 0.4 and 0.7 mmol/l, and >0.7 mmol/l, respectively. Overall, elevated NEFA concentrations in the High group went along with a higher ratio of NEFA to cholesterol and reduced insulin sensitivity. While serum glucose, energy deficit and BW loss did not differ, cows of the High group exhibited increased lactate concentrations in the serum, compared with the Medium group. No differences in liver enzymes and acute phase proteins were evidenced among fat mobilization groups, whereas concentration of serum billirubin was lowest in the Low group after parturition. Data of milk yield and milk energy output showed no differences among groups, despite divergences in calculated energy balance and BW change postpartum. Cows of the Low group tended to increase dry matter intake but also showed longer time duration of pH below 6.0 in the reticulorumen (on average 299 min/day compared with 99 and 91 min/day for Medium and High groups, respectively). Differences in metabolic, endocrine and reticuloruminal pH responses indicate diverse metabolic adaptation strategies of early-lactation cows to cope with energy deficit postpartum.

Groups of Friesian bull calves were reared on a high intake of milk substitute for either 21 or 28 days, and were then weaned over 7 or 14 days. Dried grass cubes were offered, as the only source of solid food, for 6 weeks from the start of weaning.

The rate of increase of solid food intake of calves weaned from 28 days was considerably greater than that of calves weaned from 21 days, and the later weaned groups were less severely affected by weaning. There was little difference in either the development of solid food intake, or in the severity of the weaning check, between groups weaned at different rates, though the slower rate of weaning tended to delay the intake of solid food temporarily.

The severity of the post-weaning check was inversely related to age at weaning, but was not affected by weaning weight. Growth after weaning was not related to either weight or age at weaning.

There were significant correlations between weight or age at weaning and solid food intake 5 weeks later, and a close correlation between the level of liquid intake established before weaning, and subsequent solid food intake. It was not possible to evaluate the effect of each of these variables, in isolation, on food intake after weaning.

Whole-body amino acid composition was determined in six male and six female 53-day-old New Zealand White rabbits. There were no significant sex differences in whole-body amino acid compositition except for arginine and glycine where whole-body concentrations (g/16 g N) were significantly lower in the females (P < 0·05). Overall mean whole-body essential amino acid levels (relative to lysine = 100 units) were methionine = 20; cystine = 41; histidine = 50; phenylalanine = 65; tyrosine = 50; threonine = 64; leucine = 112; isoleucine = 51; valine = 62; arginine = 109. The lysine concentration of rabbit whole-body tissue was 6·12 g/16 g N. There was close agreement between rabbit whole-body amino acid composition and corresponding published values for the rat and pig, although the rabbit whole-body cystine was high and methionine concentration low compared with the rat or pig. The rabbit whole-body amino acid pattern can be regarded as approximating an ideal balance of dietary amino acids and as such indicates discrepancies in current recommendations on the essential amino acid requirements for growth in the meat rabbit.

The rumen dry-matter degradation of straw from nine varieties of barley, nine varieties of wheat and seven varieties of hard wheat was studied to provide further information on varietal differences and their relationships with agronomic characteristics.

In all the cereals there were significant differences in in situ dry-matter disappearance between varieties. The range of differences was lower in hard wheat varieties compared with the other cereals. There were no significant correlations between straw degradability and plant height, days from sowing to heading and grain production and quality. Lignin concentration was significantly correlated to straw degradability (r = −0·937 in barley, −0·675 in wheat and −0·987 in hard wheat).

Leaf had lower concentrations of lignin and higher degradability than stem in barley and wheat but the two fractions were similar in hard wheat straws. The differences in degradation between the most and the least degradable straw varieties of each cereal species were mainly due to differences in degradability of both the fractions whereas the role of leaf and stem proportions was of minor importance.

Twenty-four sows from three nutritional regimes imposed until weaning of their third litters were used to investigate the influence of weight and body condition on ovulation rate.

For low-, medium- and high-plane sows respectively, mean corpora lutea numbers at 3 to 6 days post coitus were 13·8±0·78, 16·4±0·87 and 15·2±1·01 (not significantly different); conception rates at first service were 50, 87·5 and 100% percentages prenatal mortality were 36·1±7·95, 67·2±7·26 and 41·7±7·26, and mean numbers of pigs born alive were 9·0±1·19, 5·2±1·09 and 8·8±1·09.

Pooled data indicated no significant effect of body weight but a significant effect of weight loss during the preceding lactation on ovulation rate (P<0–01).

The effect of slaughter weight and breed on the composition of intramuscular fat (IMF) of seven Spanish cattle breeds was studied. Lipid classes and fatty acids were evaluated in young bulls of seven local Spanish cattle breeds, Asturiana, Avileña, Morucha, Parda Alpina, Pirenaica, Retinta and Rubia Gallega, slaughtered at a live weight of 320 kg (veal type) and 550 kg (yearling bull type). Higher slaughter weight and early maturating breeds produced higher IMF content in the longissimus muscle (P < 0.001), which was linked to a reduction in phospholipids, monoglycerides, diglycerides, cholesterol and free-fatty acids content, but an increase in triacylglycerols. Besides, heavier animals displayed a higher percentage of saturated and monounsaturated fatty acids (MUFA), but a lower polyunsaturated fatty acids (PUFA) percentage (P < 0.001). The increase in triglycerides (TG), saturated fatty acids (SFA) and MUFA illustrates the increasing importance of lipid storage as fattening proceeds and the acquisition of ruminal functionality. The feeding system based on cereals had a strong influence on the fatty acid profile, giving the studied beef a relatively high PUFA/SFA and n-6/n-3 ratios.

Two groups of suckling Charolais cows were fed at different levels of nutrition from 70 days before the estimated date of calving until 45 days after calving, to study the effects of reduced dietary intake on pre-partum plasma levels of progesterone and total oestrogens (conjugated + unconjugated) and post-partum plasma levels of luteinizing hormone and follicle stimulating hormone. Eight control cows received a ration containing the Institut National de la Recherche Agronomique's recommendations for all nutrients, while 10 cows received a restricted diet which supplied approximately three-quarters of the recommended amounts for energy and nitrogen.

The mean weight of the two groups of cows was similar at the beginning of the experiment but the restricted group had a significantly lower weight just before calving than the control group (678 v. 766 kg; P < 0·05).

After calving, cows ont he low diet had a weight loss of 600 g/day, while those on the control diet gained 300 g/day. During the last 45 days of pregnancy underfeeding did not significantly affect oestrogen levels, but progesterone levels increased proportionally by 0·24 (P < 0·01).

During the first 45 days of lactation underfeeding decreased the number of cows showing oestrus (0/10 v. 4/8) and significantly decreased both luteinizing hormone and follicle stimulating hormone levels at 5, 15 and 30 days post partum.

Furthermore, the correlation between mean daily gain (0 to 45 days post partum) and luteinizing hormone concentration on day 30 was highly significant (r = 0·58; P < 0·01; no. = 19). These results suggest that the delay of the first post-partum ovulation in the underfed cow is due to low gonadotropin levels.

Nutrient requirements in cattle are dependent on physiological stage, breed and environmental conditions. In Holstein × Gyr crossbred dairy heifers, the lack of data remains a limiting factor for estimating energy and protein requirements. Thus, we aimed to estimate the energy and protein requirements of Holstein × Gyr crossbred heifers raised under tropical conditions. Twenty-two crossbred (½ Holstein × ½ Gyr) heifers with an average initial BW of 102.2 ± 3.4 kg and 3 to 4 months of age were used. To estimate requirements, the comparative slaughter technique was used: four animals were assigned to the reference group, slaughtered at the beginning of the experiment to estimate the initial empty BW (EBW) and composition of the animals that remained in the experiment. The remaining animals were randomized into three treatments based on targeted rates of BW gain: high (1.0 kg/day), low (0.5 kg/day) and close to maintenance (0.1 kg/day). At the end of the experiment, all animals were slaughtered to determine EBW, empty body gain (EBG) and body energy and protein contents. The linear regression parameters were estimated using PROC MIXED of SAS (version 9.4). Estimates of the parameters of non-linear regressions were adjusted through PROC NLIN of SAS using the Gauss–Newton method for parameter fit. The net requirements of energy for maintenance (NEm) and metabolizable energy for maintenance (MEm) were 0.303 and 0.469 MJ/EBW0.75 per day, respectively. The efficiency of use of MEm was 64.5%. The estimated equation to predict the net energy requirement for gain (NEg) was: NEg (MJ/day) = 0.299 × EBW0.75 × EBG0.601. The efficiency of use of ME for gain (kg) was 30.7%. The requirement of metabolizable protein for maintenance was 3.52 g/EBW0.75 per day. The equation to predict net protein requirement for gain (NPg) was: NPg (g/day) = 243.65 × EBW−0.091 × EBG. The efficiency of use of metabolizable protein for gain (k) was 50.8%. We observed noteworthy differences when comparing to ME and protein requirements of Holstein × Gyr crossbred heifers with other systems. In addition, we also observed differences in estimates for NEm, NEg, NPg, kg and k. Therefore, we propose that the equations generated in the present study should be used to estimate energy and protein requirements for Holstein × Gyr crossbred dairy heifers raised in tropical conditions in the post-weaning phase up to 185 kg of BW.

Improvement of reproduction in dairy cows has become a major challenge in dairy production. We have recently shown that dairy cows carrying the ‘fertil−’ haplotype for one quantitative trait locus (QTL), affecting female fertility and located on the bovine chromosome 3, had a significantly lower conception rate after the first artificial insemination than cows carrying the ‘fertil+’ haplotype. The objective of this paper was to study other phenotypic modifications linked to this QTL. In the present study, 23 ‘fertil+’ and 18 ‘fertil−’ cows were characterized for live weight, milk production, food intake, eating behaviour and plasma metabolites. These parameters were measured during the first lactation, from calving to 40 weeks postpartum (wkpp). In the first 7 weeks of lactation, ‘fertil+’ primiparous cows had a significantly higher live BW and milk production than ‘fertil−’ cows. Dry matter intake tended to be slightly higher for ‘fertil+’ than for ‘fertil−’ primiparous cows in this period. However, energy balance was similar for the two haplotypes in the whole lactation, except in the first wkpp, and consequently, could not explain their different fertility. The major observation concerned the eating behaviour. ‘Fertil+’ primiparous cows had a significantly lower eating rate than ‘fertil−’ cows during the 40 weeks of lactation. In parallel, ‘fertil+’ cows spent significantly more time at the feeder for a similar number of visits than ‘fertil−’ cows. Furthermore, no differences in plasma concentrations of non-esterified fatty acids and insulin were observed between the two haplotypes. Plasma glucose was significantly lower in ‘fertil+’ than in ‘fertil−’ cows in the second wkpp. Taken together, our results show that ‘fertil+’ and ‘fertil−’ dairy cows, with different fertility, have also different eating behaviour without any variation in energy balance, except in the first week of lactation.

Growth hormone (GH) and β agonists increase muscle mass, but the mechanisms for this response are unclear and the magnitude of response is thought to vary with age of animal. To investigate the mechanisms driving the muscle response to these agents, we examined the effects of short-term (6 day) administration of GH or cimaterol (a β2-adrenergic agonist, BA) on skeletal muscle phenotype in both young (day 60) and mature (day 120) lambs. Expression of myosin heavy chain (MyHC) isoforms were measured in Longissimus dorsi (LD), Semitendinosus (ST) and Supraspinatus (SS) muscles as markers of fibre type and metabolic enzyme activities were measured in LD. To investigate potential mechanisms regulating the changes in fibre type/metabolism, expression or activity of a number of signalling molecules were examined in LD. There were no effects of GH administration on MyHC isoform expression at either the mRNA or protein level in any of the muscles. However, BA treatment induced a proportional change in MyHC mRNA expression at both ages, with the %MyHCI and/or IIA mRNA being significantly decreased in all three muscles and %MyHCIIX/IIB mRNA significantly increased in the LD and ST. BA treatment induced de novo expression of MyHCIIB mRNA in LD, the fastest isoform not normally expressed in sheep LD, as well as increasing expression in the other two muscles. In the LD, the increased expression of the fastest MyHC isoforms (IIX and IIB) was associated with a decrease in isocitrate dehydrogenase activity, but no change in lactate dehydrogenase activity, indicating a reduced capacity for oxidative metabolism. In both young and mature lambs, changes in expression of metabolic regulatory factors were observed that might induce these changes in muscle metabolism/fibre type. In particular, BA treatment decreased PPAR-γ coactivator-1β mRNA and increased receptor-interacting protein 140 mRNA. The results suggest that the two agents work via different mechanisms or over different timescales, with only BA inducing changes in muscle mass and transitions to a faster, less oxidative fibre type after a 6-day treatment.

Determining welfare status in a population is the first step in efforts to improve welfare. The primary objective of this study was to explore a new epidemiological approach for analysis of data from official competent authorities that pertain to compliance with animal welfare legislation. We reviewed data already routinely collected as part of Swedish official animal welfare inspections for 2010–13, using a checklist containing 45 checkpoints (CPs). These covered animal-, resource- and management-based measures of equine welfare. The animal-based CPs were measures that directly related to the animal and included social contact, body condition, hoof condition and cleanliness. Non-compliance with one or more of the animal-based CPs was used as a binary outcome of poor equine welfare; 95% confidence intervals (CI) were estimated using the exact binomial distribution. Associations were determined using multivariable logistic regression, adjusting for clustering on premises. Resource- and management-based CPs (model inputs) were reduced by principal component analysis. Other input factors included premises characteristics (e.g. size, location) and inspection characteristics (e.g. type of inspection). There were 30 053 premises with horses from 21 counties registered by the Swedish Board of Agriculture. In total 13 321 inspections of premises were conducted at 28.4% (n=8532) of all registered premises. For random inspections, the premises-prevalence of poor equine welfare was 9.5% (95% CI 7.5, 11.9). Factors associated with poor equine welfare were non-compliance with requirements for supervision, care or feeding of horses, facility design, personnel, stable hygiene, pasture and exercise area maintenance, as well as the owner not being notified of the inspection, a previous complaint or deficiency, spring compared with autumn, and not operating as a professional equine business. Horses at premises compliant with stabling and shelter requirements had significantly better welfare if they also complied with documentation requirements. We present a novel approach for analysis of equine welfare data from regulatory inspections by the official competent authorities, and propose on-going analyses and benchmarking of trends in animal-based measures over time. We also suggest how such a database could be further improved to facilitate future epidemiological analyses of risk factors associated with poor equine welfare. The study has implications for other competent authorities and researchers collaborating in the area of animal welfare epidemiology.

1. The voluntary dry-matter intake, water intake and rate of live-weight gain of indigenous, exotic and crossbred cattle on low- and medium-roughage diets have been compared under similar conditions of management.

2. At similar live weights and on similar diets exotic cattle usually have a higher food intake than indigenous animals.

3. When roughage was freely available the voluntary dry-matter intake of both types of cattle increased.

4. Water intake was closely related to dry-matter intake and varied with the nature of the diet. The ratio of water to dry-matter intake was not affected by live weight and varied only slightly between the different types of cattle.

5. Exotic cattle were generally more efficient than indigenous cattle of comparable live weight in converting food into live-weight gain; crossbred animals were intermediate. It is suggested that this largely reflects their higher intake of food relative to their maintenance requirement.

6. One group of indigenous animals that were initially mature but under weight gained weight as quickly, and converted their food as efficiently, as did exotic animals.

Three aspects of body condition scoring in commercial sheep flocks were examined. Ewes in 44 flocks were condition scored when the rams were introduced to the flock and their subsequent lambing performance was recorded. The pooled regression coefficient obtained for the relationship between individual ewe condition score and litter size was 0·29±0·0243 with a squared correlation coefficient of 1·96%.

Between flock differences accounted for 57% of the variation in ewe condition score. Within the breeds recorded average flock condition score at mating was related to the number of live lambs born per 100 ewes mated. This relationship is shown for several breeds of ewe. A further 27 flocks were involved in a trial to evaluate the effectiveness of a specific use of condition scoring. Ewes were scored 6 to 8 weeks before mating and in 12 flocks the ewes in poor condition were given an improved plane of nutrition. These ewes showed an improvement of 12 lambs born per 100 ewes mated over ewes not given better nutrition.

1. Scottish Blackface and Tasmanian Merino one-year-old males were exposed to cold in climate chambers. The environmental temperature fell slowly from +10°C to −15°C in the first experiment when the sheep were in full fleece and from +30°C to −5°C in the second experiment when the same sheep were closely shorn. In the second experiment each sheep received two identical exposures separated by one day spent in a cool environment. Rectal temperatures and skin temperatures on the body and the extremities were recorded.

2. In experiment 1 skin temperatures on the feet and ears generally fell sharply due to vasoconstriction, especially in the Blackface sheep. The Blackface sheep showed earlier and more intense vasoconstriction than the Merinos.

3. In experiment 2 foot and ear skin temperatures fell smoothly with gradual vasoconstriction. In contrast to experiment 1, both breeds were similar in the time of onset of vasoconstriction. Foot temperatures, however, were significantly higher and vasoconstriction correspondingly later during the second exposure of experiment 2 than during the first exposure.

4. The skin temperature at which vasoconstriction occurred remained similar irrespective of breed, shearing or exposure occasion. But the ambient temperature at vasoconstriction was significantly influenced by all these variables.

5. Cold-induced vasodilatations were more frequent in experiment 1 than in experiment 2.

6. Retarded vasoconstriction among the Merinos in experiment 1 could, except for two sheep, be accounted for by their superior fleece cover. In experiment 2, the delayed foot vasoconstriction on second exposure was attributed to increased blood flow resulting from acclimatization.

As a part of a study investigating the extent to which ad libitum feeding of a high fibre diet could mitigate behavioural problems associated with food restriction, the performance of sows given food at restricted or ad libitum levels was compared. Ten subgroups of five were allocated to each of the restricted (R) and ad libitum (A) feeding regimes. Five weeks after service, subgroups were introduced into one of two dynamic groups of sows housed in adjacent straw-bedded pens. R sows received a fixed daily ration (parity 1: 2·2 kg; parity 2: 2·4 kg) of a conventional pregnancy diet (13·1 MJ digestible energy per kg) from an electronic sow feeder. Sows on the A regime had unrestricted access to five single-space hoppers dispensing a high fibre diet (containing 600 g unmolassed sugar beet pulp per kg). Subgroups were maintained on these gestation feeding regimes for two consecutive parities. During both parities, A sows were heavier by day 50 of gestation (parity 1: P < 0·05; parity 2: P < 0·01) and at farrowing (parity 1: P < 0·001; parity 2: P < 0·001) than R sows. No difference was found between feeding regime in sow weight at weaning, due to a greater weight loss during lactation of A (parity 1: P < 0·001; parity 2: P < 0·001) than R sows. No difference was found between feeding regime in sow backfat thickness, sow reproductive performance or litter performance in either parity. This suggests that unmolassed sugar beet pulp diets may be used to feed sows on an ad libitum basis during gestation without compromising productivity. However, food intakes may be too high (estimated at 4·1 kg per sow per day) to make ad libitum feeding of pregnant sows an attractive option for producers.

Lactational performance was measured in Large White gilts from lines that had been divergently selected over seven generations for daily food intake (DFI), lean food conversion ratio (LFC), lean growth rate with ad-libitum (LGA) or restricted (LGS) feeding during performance test. Control line gilts were included in the study. During the lactation period of 21 days, gilts were given to appetite five isoenergetic diets differing in ileal digestible lysine: energy (0·40, 0·58, 0·76, 0·94 and 1·12 g/MJ digestible energy). The study consisted of 223 gilts with a similar number of animals in each selection line.

Live-weight loss was greater in the low LFC and LGA lines than in the high lines and food intake was significantly lower in the low LGA line than in the high line. Litter-weight gain of the low LFC and high LGA lines were greater than in the complementary selection lines. Prediction equations for nutrient utilization were used to express the effect of diet and selection line in terms of energy and protein inputs and outputs. Selection on DFI or LGS resulted in gilts that did not mobilize lipid during lactation as sufficient energy for milk and maintenance was provided by dietary intake. In contrast, there was insufficient dietary energy with selection on LFC or on low LGA so lipid mobilization was required to achieve energy balance. The energy required to excrete excess protein and energy from lipid mobilization increased as the dietary lysine energy ratio increased, but there were no other dietary effects on energy and protein utilization. Genotype with nutrition interactions were detected for energy intake and lipid mobilization, which were due to the lines selected for low DFI and LGA. The general absence of genotype with nutrition interactions for lactational performance in gilts selected for components of efficient lean growth and the lack of significant dietary effects on energy utilization indicated that the consequences of changing nutritional inputs will be broadly similar for genotypes within the set of genotypes studied. Selection strategies which result in reduced food intake during lactation should be avoided if lipid mobilization is then required to attain energy balance and there are resultant negative effects on subsequent reproductive performance.

1. A growth trial and nitrogen balance studies were carried out on 32 early-weaned calves fed on a basal diet containing fish meal or diets in which the fish meal nitrogen was partially replaced by urea or ammonium acetate or totally replaced by urea.

2. Growth rate and feed conversion efficiency were highest on the fish meal diet and fell as urea replaced the fish meal.

3. Rumen ammonia levels and urinary nitrogen excretion were highest, and nitrogen retention lowest, in the calves receiving the diet in which fish meal nitrogen was completely replaced by urea nitrogen.