Regrouping dairy cows is a common feature of dairy farm management. Cows are grouped based on lactation stage, age, milk yield and other factors. Regrouping cows during the dry period (from far-off area to close up area and from close up area to the main herd) brings new challenges. This is especially true for heifers who, after being confirmed gravid, may be grouped into a new pen with dried off cows. The aims of this study were to determine how grouping affects activity, nearest neighbour relationships and aggression, and how heifers’ acclimatization to a new group differs from cows. Therefore, the hypotheses were that regrouping cows has less of an effect on older cows compared to heifers, and cows' individuality affects acclimatization to a new group. Aggression data were recorded using a video camera that was directed at the feed bunk, and activity was recorded with activity monitors that were attached around the right hind leg. Synchrony and distance to nearest neighbour were recorded, as was the cows' location on the first 3 d from the day they returned to the main herd. Motion index, mean number of steps and number of lying bouts were significantly higher after calving compared to the week before calving and the difference was higher amongst heifers compared to cows (P < 0.001). Both cows and heifers lay down more in the strawyard compared to cubicle housing (P < 0.01) and cows were more aggressive than heifers in both housing systems (P < 0.001 and P < 0.05, respectively). As hypothesized, heifers were more affected by regrouping and cows with more experience settled quicker to their new environment.

Previous work led to the proposal that the precision feeding of a high-concentrate diet may represent a potential method with which to enhance feed efficiency (FE) when rearing dairy heifers. However, the physiological and metabolic mechanisms underlying this approach remain unclear. This study used metabolomics analysis to investigate the changes in plasma metabolites of heifers precision-fed diets containing a wide range of forage to concentrate ratios. Twenty-four half-sib Holstein heifers, with a similar body condition, were randomly assigned into four groups and precision fed with diets containing different proportions of concentrate (20%, 40%, 60% and 80% based on DM). After 28 days of feeding, blood samples were collected 6 h after morning feeding and gas chromatography time-of-flight/MS was used to analyze the plasma samples. Parameters of oxidative status were also determined in the plasma. The FE (after being corrected for gut fill) increased linearly (P < 0.01) with increasing level of dietary concentrate. Significant changes were identified for 38 different metabolites in the plasma of heifers fed different dietary forage to concentrate ratios. The main pathways showing alterations were clustered into those relating to carbohydrate and amino acid metabolism; all of which have been previously associated with FE changes in ruminants. Heifers fed with a high-concentrate diet had higher (P < 0.01) plasma total antioxidant capacity and superoxide dismutase but lower (P ≤ 0.02) hydroxyl radical and hydrogen peroxide than heifers fed with a low-concentrate diet, which might indicate a lower plasma oxidative status in the heifers fed a high-concentrate diet. Thus, heifers fed with a high-concentrate diet had higher FE and antioxidant capacity but a lower plasma oxidative status as well as changed carbohydrate and amino acid metabolism. Our findings provide a better understanding of how forage to concentrate ratios affect FE and metabolism in the precision-fed growing heifers.

The aim of the present research was to assess factors associated with first-lactation milk yield in dairy heifers, including maternal and environmental factors, factors related to the development of the heifer and factors related to its offspring such as gender of the calf. In addition, the potential underlying mechanism, in particular metabolic adaptations, was further explored. Data on body growth, reproduction and milk yield of 74 Holstein Friesian heifers on three herds in Flanders (Belgium) were collected. At birth, body measurements of the heifers were recorded and blood samples were taken (in order) to determine basal glucose and insulin concentrations. Body measurements were assessed every 3 months until first calving, and gender and weight of their first calf were recorded. Information on fertility and milk yield of the heifer and its dam were collected from the herd databases. Daily temperature and photoperiod were recorded from the database of the Belgian Royal Meteorological Institute. Linear mixed models were run with herd as a random factor, to account for differences in herd management. Heifers grew 867±80.7 g/day during their first year of life and were inseminated at 14.8±1.34 months. First calving took place at 24.5±1.93 months, at a weight of 642±61.5 kg and heifers produced 8506±1064 kg energy corrected milk during their first 305-day lactation. Regression models revealed that none of the maternal factors such as milk yield and parity, nor the growth of the heifer during the 1st year of life were associated with milk yield during first lactation. Age, and to a lesser extent BW at first parturition were positively associated with first-lactation milk yield. In addition, the season of birth, but not calving, had a significant influence on milk yield, with winter-born heifers producing less than heifers born in any other season. The lower yielding winter-born heifers had higher insulin concentrations at birth, whereas glucose concentrations were similar, the latter being suggestive for lower insulin sensitivity of the peripheral tissues. Furthermore, environmental temperature at the end of gestation was negatively correlated with neonatal insulin concentrations. In conclusion, results of the present study suggest heifers born during the hotter months are born with a higher peripheral insulin sensitivity, finally leading to a higher first-lactation milk yield.

Rearing quality dairy heifers is essential to maintain herds by replacing culled cows. Information on the key factors influencing the cost of rearing under different management systems is, however, limited and many farmers are unaware of their true costs. This study determined the cost of rearing heifers from birth to first calving in Great Britain including the cost of mortality, investigated the main factors influencing these costs across differing farming systems and estimated how long it took heifers to repay the cost of rearing on individual farms. Primary data on heifer management from birth to calving was collected through a survey of 101 dairy farms during 2013. Univariate followed by multivariable linear regression was used to analyse the influence of farm factors and key rearing events on costs. An Excel spreadsheet model was developed to determine the time it took for heifers to repay the rearing cost. The mean±SD ages at weaning, conception and calving were 62±13, 509±60 and 784±60 days. The mean total cost of rearing was £1819±387/heifer with a mean daily cost of £2.31±0.41. This included the opportunity cost of the heifer and the mean cost of mortality, which ranged from £103.49 to £146.19/surviving heifer. The multivariable model predicted an increase in mean cost of rearing of £2.87 for each extra day of age at first calving and a decrease in mean cost of £6.06 for each percentile increase in time spent at grass. The model also predicted a decrease in the mean cost of rearing in autumn and spring calving herds of £273.20 and £288.56, respectively, compared with that in all-year-round calving herds. Farms with herd sizes⩾100 had lower mean costs of between £301.75 and £407.83 compared with farms with <100 milking cows. The mean gross margin per heifer was £441.66±304.56 (range £367.63 to £1120.08), with 11 farms experiencing negative gross margins. Most farms repaid the cost of heifer rearing in the first two lactations (range 1 to 6 lactations) with a mean time from first calving until breaking even of 530±293 days. The results of the economic analysis suggest that management decisions on key reproduction events and grazing policy significantly influence the cost of rearing and the time it takes for heifers to start making a profit for the farm.

This experiment compared growth, physiological, and reproductive responses of beef heifers with (MI) or without (CON) access to a creep-feeder, as a manner to stimulate metabolic imprinting while nursing their dams. On day 0, 60 Angus×Hereford heifers were ranked by BW and age (140±3 kg and 68±3 days), and assigned to pairs so all ranking criteria were similar between heifers within each pair. On day 1, pairs were randomly assigned to MI (n=15) or CON (n=15). From day 1 to 51, MI pairs and their dams were allocated to 15 drylot pens where heifers had ad libitum access to a corn-based supplement through a creep-feeder. The CON pairs and their dams were maintained in an adjacent single drylot pen. From day 52 to 111, treatments were managed as a single group on a semiarid range pasture. On day 111, heifers were weaned and allocated to two pastures (one pasture/treatment), receiving hay and a corn-based concentrate until day 326. Heifer BW was recorded before and at the end of the creep-feeding period (day 1 to 51), and on days 112 and 326. On days 0, 51, 111, 187, 261, and 325, jugular blood was collected and real-time ultrasonography for longissimus muscle depth and backfat thickness assessment was performed. Blood was also collected every 10 days from days 113 to 323 for puberty evaluation via plasma progesterone. Liver and subcutaneous fat biopsies were performed on days 51, 111, 261 and 325. Average daily gain was greater (P<0.01) for MI than CON from day 1 to 51, tended (P=0.09) to be greater for CON than MI from day 112 to 326, while BW on day 326 was similar between treatments. On day 51, MI had greater (P⩽0.01) plasma IGF-I and glucose concentrations, as well as mRNA expression of hepatic pyruvate carboxylase and adipose fatty acid synthase than CON. On days 261 and 325, plasma insulin concentrations were greater (P⩽0.03) in CON than MI. Mean mRNA expression of hepatic IGF-I and adipose peroxisome proliferator-activated receptor gamma were greater (P⩽0.05) in MI than CON. No treatment effects were detected for puberty attainment rate. In conclusion, supplementing nursing heifers via creep-feeding for 50 days altered physiological and biochemical variables suggestive of a metabolic imprinting effect, but did not hasten their puberty attainment.

This study was conducted to evaluate the development of the mammary gland in Holstein heifers subjected to different dietary metabolisable protein (MP): metabolisable energy (ME) ratios. Twenty-five Holstein heifers (initial body weight (BW) 213±13·5 kg and initial average age 7·8±0·5 months) were divided into five treatments. The treatments were designed to provide MP:ME ratios equal to 33, 38, 43, 48, and 53 g of MP per Mcal of ME. All diets were formulated to have the same energy content (2·6 Mcal ME/kg dry matter). Actual MP:ME ratios were 36·2, 40·2, 46·2, 47·1, and 50·8 g MP/Mcal ME. The experiment was conducted in a randomised block design, while considering initial BW as a blocking factor to evaluate pre- and post-pubertal periods. Block effect was not observed for all variables evaluated; hence it was considered that the diets had the same influence both on pre- and post-pubertal phases. Dry matter and nutrient intake did not change between treatments, excepting protein intake and digestibility. Serum concentrations of insulin-like growth factor 1 increased linearly across treatments. Changes in the pixel brightness of mammary gland ultrasound images, which are associated with lipid content, were significantly influenced by MP:ME ratios in the diet of heifers that were subjected to accelerated growth rates. It is not recommended to use diets of less than 38 g MP/Mcal ME in diets to heifers allowed to gain more than 1 kg/d.

The aim of this trial was to assess the effects of the administration of different combinations of mycotoxins in naturally contaminated maize grains on dairy heifer growth, blood measurements and puberty onset. A total of 35 Friesian female heifers were randomly allotted to three experimental groups from 18–21 to 42–45 weeks of age. During the 24-week experimental period (EP), heifers were fed the same diet, but with maize meal derived from three differently contaminated lots: very low contamination, as control (C); medium–low aflatoxin-contaminated (A); and mixed aflatoxin–fumonisin contaminated (A-F). At the end of the EP, they returned to a common diet without contaminated maize, and they were monitored for an additional period of 12 weeks (post-experimental period, PEP). BW, wither height, hip height, body length and heart girth were measured every 4 weeks from the beginning of EP to the end of PEP. At the same time, body condition score was evaluated and blood samples were taken from the jugular vein to be analysed for haematological, serum protein and metabolic profiles. Age at puberty was assessed by measuring weekly plasma progesterone levels from 40 to 52 weeks of age. Body growth measurements were processed both by ANOVA of average daily gain of EP and PEP separately, and by the analysis of growth curve parameters. Haematological, serum protein and metabolic profile were evaluated using a mixed model, taking into account the repeated measurements in time on each animal. Heifers’ growth was delayed both in A and A-F groups during EP, as evidenced by the different linear coefficients of the BW growth curve in the three groups. Differently contaminated diets did not affect the haematological profile, so that it can be concluded that these levels of mycotoxin contamination do not determine any specific effect on haematopoiesis and immunity in growing heifers. The main blood marker of mycotoxin chronic toxicity was the γ-glutamyl transferase activity level in plasma, which appeared to be altered even after the removal of mycotoxins. During EP, plasma glucose was lower in the groups fed contaminated diet compared with C. The joint actions of an altered nutritional status and a long-lasting liver damage were probably the causes of the delay in puberty attainment in A and, particularly, in the A-F group. The results from this trial evidenced that a chronic aflatoxin–fumonisin contamination in diets of dairy heifers can determine an important delay in the reproductive career of these animals.

The aim of this study was to evaluate nitric oxide (NOx) concentration in infected and non-infected mammary quarters of dairy heifers before and after calving. The relationship between bacterial species and NOx concentrations, as well as correlation between NOx concentrations and postpartum somatic cell count (SCC), was assessed. Coagulase-negative staphylococci, Staphylococcus aureus and Escherichia coli were the bacteria commonly isolated during the pre- and postpartum period. Infected quarters had greater NOx concentrations than non-infected quarters before (30.81 v. 22.83 μM/ml, P < 0.05) and after (9.56 v. 5.77 μM/ml, P < 0.0001) calving. It was determined that the interaction between sampling period and infectious status had no effect on NOx concentration (P < 0.16). Infected quarters had greater SCC (log10) than healthy quarters (4.95 v. 4.39; P < 0.0001). NOx concentrations, however, did not correlate with SCC (r = 0.02). In summary, changes in NOx concentration were mainly dependent on the infectious status of the quarters with variations among the bacterial species (P < 0.05).

The prevalence of intramammary infections (IMI) and subclinical mastitis (SCM) in 436 German Holstein heifers was put in relation with clinical findings of the udder and data regarding individual rearing and housing conditions of the animals. The clinical examination took place on the day of the livestock auction (at approximately 41 d in milk, DIM). On that day, 31% of the heifers had IMI in at least one quarter, and 18% of all quarters were infected. Coagulase-negative staphylococci were the most prevalent bacteria isolated, accounting for 68% of the positive samples. Data were analysed by logistic regression. Criteria such as ‘juvenile intersucking’, ‘teats shorter than 35 mm’, ‘teats with a diameter <18 mm’ and ‘udder oedema at the day of the auction’ were associated with IMI in heifers during the first 41 DIM. Loose-housing systems during pregnancy (as opposed to tie-stalls), juvenile intersucking, clinical mastitis during the first week after calving, teat diameters <18 mm, and employing organic bedding material in the stables before calving were associated with subclinical mastitis.

The aim of this study was to assess the influence of age, body weight (BW) and body condition score (BCS) of maiden Holstein–Friesian heifers before mating start date (MSD) on the rate of puberty, subsequent production and longevity and their implications with regard to farm profitability. Data were available on 871 Holstein–Friesian heifers from 48 herds. BW was recorded electronically and BCS was recorded by a single operator on a scale of 1 to 5. Heifer age was calculated as the number of days from birth to the day of visit. All of the independent variables of interest were grouped into three or four categories. Three age categories (thirtiles), four BW categories (quartiles) and four BCS categories (⩽2.75, 3.00, 3.25 and ⩾3.50) were formed. Heifers with an identifiable corpus lutuem (CL) in the presence or absence of large follicles and peri-ovulatory signs and with a plasma progesterone (P4) concentration ⩾1 ng/ml were classified as pubertal. In addition, heifers without an identifiable CL in the presence or absence of large follicles and peri-ovulatory signs but with a P4 concentration ⩾1 ng/ml were also classified as pubertal. Age, BW and BCS at MSD were all found to be significantly associated with pubertal rate (P < 0.05). Age was shown to have no practical implications on subsequent cow performance. BW at MSD was favourably associated with subsequent calving date (P < 0.05), subsequent cow BW (P < 0.001) and potential (305 days) milk fat plus protein yield (P < 0.001). BCS at MSD was found to be favourably associated with milk fat plus protein yield potential (P < 0.05) and BCS (P < 0.001) during lactation. The economic analysis undertaken indicated that larger, well-grown heifers will be more profitable because of superior production potential, all else being equal. However, because of the finding of poorer reproductive efficiency in heifers grown to more than 343 kg at MSD, heifers at ∼330 kg at MSD are deemed optimal. This will correspond to mature cow BW of ∼550 kg.

Wheat grain (WG) is unique in possessing extensive starch and nitrogen fermentation (i.e. >85% in ground and steam-processed WG), low cation–anion difference and high-intake properties, making it a potentially useful prepartal dietary choice. The objective was to determine the effects of WG provision to pre-partum first-calf heifers on metabolic, health and productive criteria during the transition period. WG replaced barley grain that was commonly used earlier. Fifteen Holstein heifers at 31 ± 6 days pre partum were blocked based on expected calving date and assigned to three treatments or feeding totally mixed rations containing either (i) barley grain (13.8%) and wheat bran (6.1%), (ii) 10% WG (WG10) or (iii) 18% WG (WG18; dry matter (DM) basis) from 31 days pre partum until calving. In replacing WG for barley grains, some changes in WG use and slight changes in soybean and cottonseed meals use were made to properly formulate balanced rations for net energy for lactation, CP, calcium and P. Prepartal diets contained no supplemental anionic salts. Cows were monitored until 21-day post partum and received the same early lactation diet. The prepartal provision of WG and related dietary changes reduced urine pH at 7-day pre partum, and elevated blood calcium and glucose at 7-day pre partum and at 3-day post partum. Milk fat and protein yields were increased during the 21 days post partum by prepartal WG provision and related diet changes. Blood albumin, globulins, total proteins and urea concentrations were similar among treatments. Feeding diets with WG did not affect body condition score, calving difficulty, calf weight, placenta weight and the time interval from calving to placenta expulsion. It is suggested that prepartal provision of WG with necessary dietary changes led to simultaneous improvements in energy and calcium status of the heifers experiencing their first periparturient phase without compromising parturition status.

Much research has been carried out and published on dairy replacement management, in order to rear heifers as efficiently as possible, from both a technical and economical point of view. In most cases, the aim is to rear the heifers at the lowest cost possible without any deleterious effects on future performances. However, the importance of dairy heifer husbandry is not sufficiently well recognized and probably mishandled by most farmers. The present review aims to give an actual overview of rearing procedures in dairy heifers and possible ways to achieve optimal goals. For many years, it has been well known that rapid rearing lowers the age of sexual maturity and consequently may be an efficient way to reduce the non-producing period prior to conception. But this may impair mammary development and consequently future milk production, at least during first lactation. In addition, a growth rate that is too low may not only be costly but also result in animals that are too fat at first calving, creating problems such as calving difficulties, dystocia, etc. Genetic considerations must also be factored, i.e. frame, size, body weight, etc. have changed during the last 20 years and there are differences between breeds. As a result, some time-honoured recommendations may not be appropriate. The present paper reviews factors and management practices that may affect rearing and subsequent performance of dairy heifers.

Wood-chip pads represent a low-cost alternative to housing for cattle during the winter. Considering the negative welfare implications associated with housing indoors on concrete, they may also offer welfare benefits to replacement dairy heifers. However, these animals may not be able to withstand winter weather conditions on a grass silage diet. The aim of this experiment was to evaluate behaviour, limb injuries, dirtiness scores, performance and climatic energy demand (CED) of yearling dairy heifers on two levels of nutrition kept outdoors on a wood-chip pad or indoors in cubicles during the winter. Ninety-six 10-month-old heifers were blocked and assigned in groups of eight, to one of the following four treatments in a 2 × 2 factorial design: (a) indoors, silage only; (b) indoors, silage plus concentrate; (c) outdoors, silage only; and (d) outdoors, silage plus concentrate. There were three replicate groups per treatment. All animals were inspected for skin lesions and were weighed and body condition scored (BCS) at the beginning and end of the trial. Instantaneous scan sampling and continuous all-occurrence behaviour sampling were used to collect behaviour data during two 24-h periods. Animals were also dirtiness scored and group feed intakes were recorded during the trial. Significantly more comfort, social and play behaviours were recorded outdoors (P < 0.05) while trips, slips and falls were only recorded indoors (P < 0.001). Groups outdoors had significantly lower limb lesion scores at the end of the experiment (P < 0.05) and fewer groups outdoors were affected by all categories of limb lesions. However, they were consistently dirtier than animals indoors (P < 0.001). Low-nutrition animals had lower feed intakes, smaller BCS changes and lower average daily weight gains than high-nutrition animals (P < 0.01). Heifers outdoors had significantly lower average daily weight gains and BCS changes (P < 0.05) explained by lower feed intakes (P < 0.01). However, outdoor heifers on both the high- and low-nutrition diets and indoor animals on the low-nutrition diet had lower UFL (feed unit for maintenance and lactation (Irish Republic)) intakes (−0.36, −0.35 and −0.22, respectively) than that required to meet the daily live-weight gains they achieved. Heifers indoors on the high-nutrition diet gained 0.98 kg per day but consumed 0.17 UFL more than what would be recommended to achieve a daily weight gain of 1.0 kg. The CED for outdoor heifers was higher than that of indoor heifers (6.18 v. 5.47 MJ/day per m2 body surface area; P < 0.001, s.e.d. 0.044). However, CED did not exceed heat production in any treatment. Although animal performance was reduced outdoors, the wood-chip pad was associated with welfare benefits compared with cubicle housing.

Sixty dairy heifers from seven Austrian herds, with high prevalence of Staphylococcus aureus mastitis, were used in this pilot study. Heifers were randomly allocated to two groups. The treatment group received at parturition intramuscularly 10 million i.u. of penethamate hydriodide and then 24 h later, 5 million i.u.; the control group received no treatment. Bacteriological examination was conducted on 7, 14, 21, 35 and 49 d post partum (pp) and milk yield data, fat and protein contents and SCC data were collected every 5th week for the first 200 d of lactation. Occurrence of retained placenta and endometritis were recorded, and the days open of both groups were compared. No effect was observed on the postparturient genital tract health and reproduction indicators. On day 7 pp, four intramammary infections (IMI; two severe clinical; one mild clinical; and one subclinical mastitis) were detected in the untreated control group, whereas there were no IMI in the antibiotic-treated group. At subsequent samplings, there were fewer IMI in the antibiotic-treated group, which were later in lactation, less severe and less persistent. Although SCC was numerically lower in the treatment group, significant differences in SCC between groups could not be detected. Antibiotic-treated heifers produced significantly more milk during the first 15 weeks of lactation than untreated heifers. Over the whole observation period (200 d), peripartum antibiotic-treated heifers produced 323 kg more milk than heifers in the untreated control. Periparturient antibiotic treatment of heifers with penethamate hydriodide prevented IMI during the first week after parturition and achieved a significant increase in milk yield, which was found to be economically beneficial.

A study was conducted to determine whether intramammary antibiotic treatment of heifer mammary glands following the first milking after calving was effective for reducing the percentage of mammary quarters infected during early lactation. Jersey and Holstein heifers from two research herds were assigned to one of three treatment groups: (1) no intramammary infusion following the first milking after parturition, (2) intramammary infusion of all quarters with pirlimycin hydrochloride following the first milking after parturition and (3) intramammary infusion of all quarters with novobiocin sodium plus penicillin G procaine following the first milking after parturition. Almost 93% of Jersey heifers (40/43) and 73·1% of quarters (125/171) were infected at the first milking. Almost 77% of quarters (33/43) were cured following treatment with pirlimycin, 61·8% (21/34) were cured following treatment with penicillin-novobiocin and 39·6% (19/48) of infections were eliminated spontaneously in the untreated control group. Significantly fewer infections were observed in pirlimycin or penicillin-novobiocin treated mammary glands of Jersey heifers during early lactation than in untreated control mammary glands. Almost 89% of Holstein heifers (32/36) and 52·8% of quarters (76/144) were infected at the first milking. About 57% (12/21) of quarters were cured following treatment with pirlimycin, 41·4% (12/29) were cured following treatment with penicillin-novobiocin and 23·1% (6/26) of infections were eliminated spontaneously in the untreated negative control group. Significantly fewer infections were observed in pirlimycin treated mammary glands of Holstein heifers during early lactation than in untreated control mammary glands. However, no significant differences were observed following penicillin-novobiocin treatment of Holstein heifers after the first milking of lactation compared with untreated control quarters. Coagulase-negative staphylococci, Streptococcus uberis and Streptococcus dysgalactiae subsp dysgalactiae were isolated most frequently in heifers from both herds.

Thirty-two 160 kg dairy heifers were used to measure the effects of increasing dietary protein content on growth and heat production. A basal diet containing (g/kg) 550 sodium hydroxide-treated straw, 220 barley, 220 sugarbeet pulp and 10 urea was offered with 0, 76 and 152 g fishmeal/kg dry matter of the basal diet (F0, F1 and F2 levels respectively). The three diets were each given at two levels of feeding (low, L; high, H): 57.6 g/d per kg metabolic body-weight (W0.75) for the LF0 diet and 74.7 g/d per kg W0.75 for the HFO diet. Apparent digestibility of the diets increased in response to the addition of fishmeal. Mean dry matter digestibility values were 0.67, 0.67, 0.69, 0.66, 0.68 and 0.69 and those for acid-detergent fibre digestibility were 0.60, 0.63, 0.66, 0.58, 0.60 and 0.65 for diets LF0, LF1, LF2, HF0, HF1 and HF2 respectively. Nitrogen retention increased in response to both fishmeal and feeding level. Live-weight gains were 170, 296, 434 g/d for the LF0, LF1 and LF2 diets and 468, 651 and 710 g/d for the HF0, HF1 and HF2 diets respectively. There were significant effects of increasing the plane of feeding and the level of fishmeal in the diet on live-weight gain. Dietary effects on live-weight gains were accompanied by increases in mean energy retention of 23, 45, 82, 94, 160 and 152 kJ/d per kg W0.75 for diets LF0, LF1, LF2, HF0, HF1 and HF2 respectively, but no definite evidence was obtained that dietary supplementation with fishmeal modified the efficiency of utilization of metabolizable energy for growth.