Friesian Heifer Calves Research Articles

Effect of ad libitum feeding of Holstein Friesian calves on immunological parameters and molecular stress on a transcriptional level

Our aim was to compare the health and performance of ad libitum (ADLIB) and restrictedly fed Holstein Friesian heifer calves. Calves were selected to ADLIB (n = 13) and control (n = 13) groups randomly. The period of ADLIB feeding lasted for 3 weeks after colostrum supplementation. The calves in the control group received the same milk replacer, which was supplied according to the restrained feeding schedule of the farm. There was no difference between the two groups in weight, weight gain or movement activity, furthermore in the values of glucose, albumin, total protein, BHB, AST, oxidant and antioxidant status incl. dROM, PAT and OSI. The IL8 gene had higher levels (non significant, p > 0.05) of expression in the ADLIB group during the first 20 days of life, which indicates that ADLIB feeding might potentiate a stronger immune response to environmental stress. The IGF1 gene showed increased expression in the ADLIB fed group at almost all time points, however the difference was already detected on the first day of the study, indicating the importance of individual differences even within the same breed. During the first 10 days INS expression was higher in the restricted group, followed by a shift by day 20 and after, when the ADLIB group showed a higher relative expression level. The observed values describe a trend that, although not significant (p > 0.05), would seem to indicate that ADLIB feeding might potentiate a stronger immune response to environmental stress.

Influence of teat flow rate in commercial milk feeding systems on calf digestion and performance

SummarySeventy two, one day old Friesian heifer calves were fed whole milk either via regular or slow release teats on commercial calfeteria systems (Milkbar, McInnes Manufacturing Limited, Waipu, New Zealand) for 42 days. For the entire period, the consumption time for the calves fed on the regular flow rate teat calfeterias was twice as fast as for those fed using the slow teats. Meal intake was numerically higher for the calves fed milk using the slow teats. At day 42, calves on the slow teats had a strong trend towards higher daily gain. At 14 days of age, visual differences in curding were seen in the abomasum of culled calves, with the fast teat-fed animals having large lumps of curded milk surrounded by watery liquid, whereas the slow teat-fed calves had much smaller particle sized curding in thicker fluid. Lactose digestion in the stomach was significantly higher for the calves fed using the slow teats, and there was a strong trend for higher levels of free protein in the ileum. Using slow flow rate teats to feed calves from day old to weaning appears to have an important impact on digestive processes in the immature gut. Such improvements in digestion and rumen development in young calves may assist in the digestion of milk and other feeds, leading to improved growth performance. Under farm conditions, slow release teat systems may reduce scours and other digestive problems in young calves during peak milk intake (up to 15 d of age), due to increased ileal digestion of nutrients, preventing undigested nutrient flow to the hind gut. It may also reduce cross-sucking behaviour in calves, which is undesirable.

Growth pattern of crossbred Holstein Friesian heifer calves in an organized farm

Growth pattern of crossbred Holstein Friesian heifer calves in an organized farm

The benzodiazepine brotizolam reduces fear in calves exposed to a novel object test

The present study examined the effects of the intravenous administration of the anxiolytic drug brotizolam on the behavioral and physiological responsiveness of calves to novelty in a dose response fashion. Holstein Friesian heifer calves (39–41 weeks of age; body weight 200–300 kg) received an intravenous injection of either a vehicle control (12 calves) or one of four doses of brotizolam (8 calves per dose): 0.0125, 0.05, 0.2 and 0.8 mg/100 kg body weight. They were then individually subjected to a ‘combined’ test involving exposure to a novel environment (open field, OF) for 5 min followed by the sudden introduction of a novel object (NO) that remained in place for a further 10 min. Behavioral, heart rate and plasma cortisol responses were recorded in all animals. Compared to vehicle treatment, the highest dose of brotizolam dose-dependently and significantly increased the time spent in locomotion and the distance travelled near the NO, as well as the time spent in contact with the NO. In addition, post-test plasma cortisol concentrations changed in a dose-dependent manner over time: they decreased between 0 and 10 min after the test in calves that had received the two highest doses of brotizolam, whereas they increased in vehicle-treated and low-dosage calves. There were no effects of brotizolam on vocalization or locomotion during the OF phase of the test or on vocalization following introduction of the NO. These findings strongly support the notion that interaction with a novel object in a novel arena represents a behavioral index of fear and fearfulness in calves, and that vocalization and locomotion in an OF reflect other independent characteristics.

Responses of calves to acute stress: Individual consistency and relations between behavioral and physiological measures

The present study examined the consistency over time of individual differences in behavioral and physiological responsiveness of calves to intuitively alarming test situations as well as the relationships between behavioral and physiological measures. Twenty Holstein Friesian heifer calves were individually subjected to the same series of two behavioral and two hypothalamo–pituitary–adrenocortical (HPA) axis reactivity tests at 3, 13 and 26 weeks of age. Novel environment (open field, OF) and novel object (NO) tests involved measurement of behavioral, plasma cortisol and heart rate responses. Plasma ACTH and/or cortisol response profiles were determined after administration of exogenous CRH and ACTH, respectively, in the HPA axis reactivity tests. Principal component analysis (PCA) was used to condense correlated measures within ages into principal components reflecting independent dimensions underlying the calves' reactivity. Cortisol responses to the OF and NO tests were positively associated with the latency to contact and negatively related to the time spent in contact with the NO. Individual differences in scores of a principal component summarizing this pattern of inter-correlations, as well as differences in separate measures of adrenocortical and behavioral reactivity in the OF and NO tests proved highly consistent over time. The cardiac response to confinement in a start box prior to the OF test was positively associated with the cortisol responses to the OF and NO tests at 26 weeks of age. HPA axis reactivity to ACTH or CRH was unrelated to adrenocortical and behavioral responses to novelty. These findings strongly suggest that the responsiveness of calves was mediated by stable individual characteristics. Correlated adrenocortical and behavioral responses to novelty may reflect underlying fearfulness, defining the individual's susceptibility to the elicitation of fear. Other independent characteristics mediating reactivity may include activity or coping style (related to locomotion) and underlying sociality (associated with vocalization).

Drying times of umbilical cords of dairy calves

To determine the distribution of drying times of umbilical cords of dairy calves and to determine if cord dryness is a reliable indicator of age. An observational study was undertaken in a spring calving herd in Victoria, of the umbilical cords of 188 calves (82 Friesian bulls, 82 Friesian heifers, 24 crossbreds). Umbilical cords were examined daily, visually and by palpation, until the cord to the junction of the skin on the abdomen of the calf was dry, shrivelled and inflexible. Drying times ranged from 1 to 8 days. By the fifth day of life, the umbilical cords of 96.7% of all calves, 97.5% Friesian heifer calves, 87.5% of Friesian bull calves and 100% of cross-bred calves were dry. If cord dryness only was used to select calves for sale, 91.3% of all calves, 86.4% of Friesian bull calves and 100% of cross bred calves could have been sold before their fifth day of life. If calves were selected on age only, 3.3% of all calves, 2.5% of Friesian heifer calves and 12.5% of Friesian bull calves would have been sold before their umbilical cord was dry. The dairy industry cannot rely on cord dryness alone as an indicator of age for selection of calves for sale and transportation. Cord dryness is a poor indicator of age.

Behavioural reactivity of heifer calves in potentially alarming test situations: a multivariate and correlational analysis

The aim of the present study was to determine the degree of consistency of individual differences in behavioural responses of heifer calves over time and across different situations. Twenty-five Holstein Friesian heifer calves were individually subjected to the same set of four behavioural tests at 3, 16 and 29 weeks of age. The tests involved measuring the calves’ responses to a stationary human, a novel object, an open field (novel environment), and to tethering restraint. Principal component analysis (PCA) of measures recorded at each age was used to identify independent dimensions underlying the calves’ reactivity to these situations. The consistency of individual differences was established by ranking the behavioural scores and the scores of factors extracted by PCA and then estimating the correlations between the ranks of each individual calf at each of the test ages. At each age, PCA revealed four factors that could be labelled: “locomotion”, “vocalisation”, “interaction with a novel object”, and “interaction with a human”. Individual differences in 7 of 13 behavioural measures and in scores of all factors except “interaction with a human” were consistent between 16 and 29 weeks of age. Rank orders for scores of the factor labelled “interaction with a novel object” were significantly correlated across all three ages. Our results support the existence in calves of stable characteristics mediating reactivity to challenge. Multiple behavioural dimensions obtained with PCA suggest that behavioural responsiveness of calves to challenge is governed by a number of underlying factors rather than univariate phenomena, such as fearfulness or coping style.

Effects of growth hormone and feeding level on endocrine measurements, hormone receptors, muscle growth and performance of prepubertal heifers.

Prepubertal Friesian heifer calves (n = 24, initial BW = 195 +/- 5 kg) were assigned to a 2 x 2 factorial block design and used to evaluate the effects of daily GH treatment (0 or 15 mg/d) at either a low or a high feeding level in a 5-wk treatment period on endocrine measurements, hormone receptors, muscle growth, and overall performance. In the pretreatment period, a low feeding level was employed for all calves. During the treatment period, animals at the low feeding level had free access to a roughage-based mixture, whereas animals at the high feeding level had free access to a concentrate mixture and were offered 2 kg/d of the roughage-based mixture. Blood samples were collected weekly starting 3 wk before treatment. Longissimus (LM) and supraspinatus (SS) muscles were obtained at slaughter. Metabolizable energy intake was 81% higher, digestible CP intake was 140% higher, and ADG was 115% higher (all P < 0.001) at the high vs. low feeding level. Feed (DMI, ME, and protein) intake was not affected by GH treatment, but ADG was 18% higher (P < 0.13) in GH-treated than in control heifers at both feeding levels. Although of different magnitudes, the muscle anabolic effects of GH treatment and high vs. low feeding level were additive, and both treatments increased carcass weights (P < 0.02 and P < 0.001, respectively), LM (P < 0.05 and P < 0.001), and SS (P < 0.06 and P < 0.003). The anabolic effect of GH treatment was similar in both muscles, whereas the effect of feeding level was most pronounced in LM. Overall, GH treatment increased plasma GH, IGF-I (both P < 0.001), and IGFBP-3 (P < 0.02); however, GH treatment increased total IGF-I, free IGF-I, and IGFBP-3, and decreased IGFBP-2 mainly at the high feeding level (GH x feeding level interaction; P < 0.02, 0.01, 0.03, and 0.10, respectively). The high feeding level increased insulin, free and total IGF-I, and IGFBP-3 (all P < 0.001), but decreased GH and IGFBP-2 (both P < 0.001). High feeding increased type-1 IGF receptor density (P < 0.02), mainly in LM, in accordance with the largest anabolic response in this muscle, whereas GH treatment had no effect on type-1 IGF receptors. The results suggest that in skeletal muscle, the anabolic effects of exogenous GH are related to endocrine changes in the GH-IGF axis, whereas the effects of feeding level also seem to rely on IGF receptor density in the muscles.

Effect of Forage Type on Claw Horn Lesion Development in Dairy Heifers

In a continuous design study the claw health of 54 Holstein–Friesian heifer calves was recorded from three months of age until six months after first calving (30 months of age). Pre-calving heifers were either fed a wet, fermented grass silage-based diet (WF) or a dry, unfermented straw and concentrate based diet (DU), apart from grazing during their first summer. Approximately one month before calving both groups were fed a silage-based diet and afterwards all received a silage and concentrate lactation ration. Claws were examined four times during rearing, once pre-calving, and four times during lactation. Both white line and sole lesions were significantly worse for WF than DU both during rearing and throughout first lactation although the effect was not as consistent over time for white line lesions. It is concluded that for optimal claw health youngstock diets should not be heavily based on wet grass silage (less than 25% DM).

Effect of growth rate on tenderness development and final tenderness of meat from Friesian calves

AbstractThe present study was conducted to determine the effect of growth rate of calves on the activity of the calpain system post mortem, post mortem desmin degradation, myofibrillar fragmentation index and meat tenderness of m. longissimus lumborum (LL) and m. supraspinatus (SS). Twenty-four Friesian heifer calves were allocated to two treatment groups: MM and HH. The MM calves were given food to achieve a moderate growth rate (678 g/day from 5 days of age to 90 kg body weight (BW) (period I) and 770 g/day from 90 kg BW to slaughter at 250 kg BW (period II)) and the HH calves were given food to achieve a high growth rate (period I: 895 g/day and period II: 1204 g/day). The myofibril fragmentation index (MFI), desmin degradation and the activity of µ-calpain, m-calpain and calpastatin were measured in LL and SS at slaughter, and 1 and 7 days post mortem. Shear force was measured in LL and SS after 1 and 7 days of ageing and a sensory panel evaluated the eating quality of the loin aged 7 days. MFI (P &lt; 0·01) and tenderness (P &lt; 0·01) were higher and shear force was lower (P &lt; 0·001) in meat from HH calves compared with meat from MM calves. However, growth rate did not affect the activity of µ-calpain, m-calpain or calpastatin or the degradation pattern of desmin at any time post mortem. Besides growth rate and MFI at day 7 post mortem, which both correlated positively with meat tenderness (P &lt; 0·001 and P &lt; 0·01, respectively), fibre type traits and DNA or RNA concentrations were not generally related to final tenderness. Thus, it was concluded that increased growth rate of calves before slaughter increased the ease of fragmentation (MFI) of the meat and improved the tenderness but these findings could not be related to any changes in the activity of the calpain system.

Influence of growth rate and muscle type on muscle fibre type characteristics, protein synthesis capacity and activity of the calpain system in Friesian calves

AbstractThe objective of this study was to determine the effect of growth rate on muscle fibre characteristics, concentration of nucleic acids (RNA and DNA) as indicators of muscle protein synthesis capacity and activity of the calpain system at time of slaughter in m. longissimus lumborum (LL) and m. supraspinatus (SS) from calves, in order to elucidate the effect of growth rate on muscle protein turn-over at time of slaughter. Twenty-four Friesian heifer calves were allocated to two different feeding regimens that allowed for a moderate/moderate (MM) or high/high (HH) growth rate from 5 days of age to 90 kg body weight (BW) (period I) and from 90 kg BW to slaughter at 250 kg BW (period II), respectively. The growth rates in the two periods and the weight of LL and SS at slaughter were recorded. Within 30 min after exsanguination, samples were removed from LL and SS, snap-frozen, and later analysed for muscle fibre type frequency and cross-sectional area, DNA and RNA concentration and the activity of the calpain system. High growth rate (i.e. 895 g/day and 1204 g/day in periods I and II, respectively), compared with moderate growth rate (678 g/day and 770 g/day in periods I and II, respectively) had a marked effect on muscle weight and muscle characteristics. High compared with moderate growth rate resulted in hypertrophic growth of type I, IIA and IIB fibres in LL and of type IIA and type IIB fibres in SS, but had no effect on the muscle fibre type frequency in either of the muscles. High growth rate increased total DNA and RNA content and the RNA: DNA ratio in LL, indicating a greater potential for protein synthesis in this muscle, whereas the effect of growth rate was smaller in SS. The activity of µ-calpain, m-calpain and calpastatin was higher in the red SS muscle compared with the whiter LL muscle. However, these enzyme activities were not affected by growth rate, and thus, did not indicate a higher myofibrillar proteolysis in vivo in calves exhibiting high growth rate compared with moderate growth rate. Overall the results showed that different types of muscles react differently to high versus moderate growth rate. High growth rate induced muscle hypertrophy and increased protein synthesis capacity especially in LL and less in SS, but the activities of the enzymes in the calpain system did not show any concomitant increase in muscle protein degradation that would be in favour of improved meat tenderness.

Immunity in calves against Dictyocaulus viviparus following a low primary infection.

Thirty Holstein Friesian heifer calves, 3 months of age, were used to evaluate whether a low primary infection with Dictyocaulus viviparus would result in immunity against challenge infection 5 or 12 weeks later. Fifteen calves were experimentally infected with 30 larvae at day 0, while the other calves remained as uninfected controls. On day thirty-five 6 primary infected (G1) and 6 non-infected calves (G2) were challenged with 2000 larvae. These groups were necropsied on day 70. On day 84 the remaining 9 primary infected (G3) and 9 non-infected (G4) calves were similarly challenged and necropsied on day 119. Respiratory signs developed in most calves from approximately 2 weeks after challenge, but signs were more severe in G2 and G4 than in G1 and G3. The low primary infection resulted in significantly reduced faecal larval excretion (> 80%) and worm burdens (> 70%). In the primary infected groups the proportion of female worms in the worm burden was increased, suggesting that part of the developed immunity affected survival of the worms after their establishment in the host. Worm lengths and worm fecundity were also significantly reduced. All observed effects were stronger following challenge on day 84 than on day 35, but the effect of the duration of a primary infection (contrast between G1 and G3) was only statistically significant in the case of mean faecal larval excretion on the day of necropsy (P < 0.05) and fecundity (P < 0.05).

Control of gastrointestinal parasitism in calves with albendazole delivered via an intraruminal controlled-release device

The efficacy of albendazole in an intraruminal controlled-release device against gastrointestinal nematodes in calves was evaluated under field conditions. Calf productivity was monitored during the first and second grazing seasons. Two groups of parasite-naive Holstein Friesian heifer calves were grazed from May to October on adjacent, similarly contaminated paddocks. One group was given a Captec bolus at turnout, the other group was left untreated. Pasture larval counts peaked on the paddock grazed by the untreated calves at 23 000 1 kg −1 dry matter in October. This precipitated clinical parasitic gastro-enteritis in the untreated calves with a mean peak faecal egg count of 335 epg, high blood pepsinogen and gastrin concentrations and a mean worm burden of 79 614 at 100 days post-turnout. Pasture larval counts on the paddock grazed by the treated calves remained less than 3000 1 kg −1 DM and the mean faecal egg count was zero until mid-August, peaking at 146 eggs per gram of faeces (epg) in October. The treated calves had body liveweight advantage of 19 kg at the end of September. During the second grazing season the first season untreated calves were refractory to infection. The first season treated calves showed signs of parasitic gastro-enteritis, although not to the extent exhibited by a group of first season parasite-naive tracer calves which were grazed on the same paddock.

Influence of Early Season Moxidectin Treatments on Acquisition of Immunity to Ostertagia ostertagi in Calves

Moxidectin, a newly developed endectocide, has previously been demonstrated to have a high efficacy against gastrointestinal nematodes in cattle (Ranjan et al. 1992, Scholl et al. 1992). In a field trial (Yang, Satrija and Nansen, unpublished data) matched groups of 8 first-season Black Pied Friesian heifer calves, 6-8 months of age, were turned out in early May 1992 on a permanent pasture contaminated with trichostrongyles. The groups were grazed separately on comparable plots until they were housed in mid October 1992. Group Β was treated with moxidectin at turnout, and group C was treated at turnout and again 8 weeks after turnout. A third group served as non-treated controls (group A). The results showed that the 2 early season prophylactic treatments (group C) reduced the late season herbage trichostrongyle larval infectivity with 80 to 90%, whereas the reduction accomplished by only 1 treatment at turnout (group B) was much less. Group C excreted significantly lower numbers of strongyle eggs than groups A and B. The non-treated controls showed clinical signs of trichostrongylosis in late September, which coincided with a steep rise in serum pepsinogen levels reaching an average peak level of 3.5 IU tyrosine litre-1. A few animals in group Β showed softening of faeces particularly in the very late season. In contrast, animals receiving 2 moxidectin treatments remained in a clinically good condition throughout the season.

Conditioning calves to accept high Na feeds

In saline areas livestock are often offered food and water with high sodium contents and there is evidence for major effects of the sodium content of feeds on their palatability, ingestive behaviour and the performance of ruminants (Youssef et al 1993). The aim in this experiment was to examine whether calves could be conditioned to accept high sodium feeds by early experience.Sixteen dairy Friesian heifer calves, aged 7 days, were allocated to receive their ad libitum concentrate feed with or without 27g added Na/calf/day, up to weaning at 6 weeks. The daily concentrate and water intakes were recorded for each calf until weaning time. The behaviour of calves was also observed for 12 hours per week at 8 min-intervals throughout the weaning period. At 6 months of age, calves were offered silage with added sodium, to give 0.1, 0.3, 0.5, 0.7, 0.8, 1.1, 1.3 and 1.5% sodium content in the DM. The daily silage intake for each calf was recorded for 2 weeks, beside observing the ingestive behaviour of calves for 24 hours at 3 min - intervals.

The development of behaviour patterns and temperament in dairy heifers

Observations were carried out on a group of twenty autumn born Friesian heifer calves from birth until calving at about 25 months of age. During rearing they experienced several rearing conditions; (I) Calf house, where from 48 hrs of age they were individually penned. (II) Group housed Indoors. At weaning they were housed in pens in groups of 10–20 animals and fed hay or silage ad libitum plus some concentrate food. (III) Grazing out doors (HGI) from spring to autumn in groups of 15–30 animals and moved to fresh pastures at about 2 week intervals. (IV) Housed indoors in large groups of 70–80 animals in a yard with access to covered or indoor cubicles, and fed silage ad lib. During this period they were artificially inseminated. (V) Second grazing period. In the following spring they were kept in large groups for grazing. Focal animal sampling to allow sequence analysis of behaviour was performed and a time base was used to estimate time budgets. In addition the temperament of each animal was assessed by recording its reaction to being touched. The development of behaviour was strongly influenced by changes between rearing conditions but generally stabilized rapidly within a particular husbandry condition. The time spent resting was greater when the animals were in the fields than indoors. Ruminating increased over the first 20 weeks and then stabilized. In the calf house the time spent in investigation increased up to 4–5 weeks and then decreased while the frequency of investigation increased. Grooming generally decreased over the study period. In the calf house calf licking increased but after grouping this decreased and rubbing of the body increased. Social encounters tended to decrease with age. The development of temperament as defined later in the text here appears to be determined at an early age and to be stable thereafter. Sequence analysis showed that behavioural sequences became shorter and less variable in content and that as the animal matured fewer behavioural activities were associated in any sequence and that these showed an increase in their degree of association.

The Effect of Extended Photoperiod in Winter on the Growth and Coat Characteristics of Heifer Calves

Additional daily artificial illumination during winter has been reported to increase growth rates in both cattle and sheep.In an experiment conducted at Seale-Hayne College between September 22, 1982 and March 29, 1983, 20 Hereford x Friesian heifer calves (approximately 7 days of age at the start of the trial) were randomly allocated to either a natural daylength treatment or an artificially supplemented 16L:8D photoperiod. Animals were weaned at 5 weeks of age and then fed on a restricted concentrate ration (2.5 kg/head/day) with hay provided ad libitum. Body weight, girth and height at shoulder measurements were taken at 2-week intervals. Hair samples (4 cm2) were taken from the mid-flank on January 13.

The effect of age at which spring-born calves are introduced to pasture

SummarySpring-born Friesian heifer calves were turned out to grass at either 3 or 4 months of age. In the summer of 1976 the experiment had 20 calves per treatment and in 1977 there were 22 calves per treatment. The calves remained outside for both day and night. They were the leaders in a leader–follower rotational grazing system based on nine paddocks. The followers were yearling heifers and sheep. Each calf was offered a daily grazing supplement of 1·8 kg concentrates. Housing was in mid-September.There were no management problems and summer growth rates were within the range 0·55–0·74 kg/day. Calves turned out at 3 months of age grew slightly better than calves turned out at 4 months. This difference was not statistically significant, but it does suggest there is no harm in turning calves out at an early age. From a practical viewpoint the result indicates that all spring-born calves could be turned out in one batch in early summer.

The effects of implanting prepuberal dairy heifers with anabolic steroids on live-weight gain, blood and urine composition and milk yield

SUMMARYTwenty-seven British Friesian heifer calves were housed as a group but fed individually barley-lucerne pellets according to a scale related to body weight. At 16 weeks and again at 31 weeks of age nine calves were implanted subcutaneously at the base of the ear with 300 mg trenbolone acetate (group T), nine calves were similarly implanted with 140 mg trenbolone acetate and 20 mg oestradiol-17/? (group TE) and the remaining nine calves were sham implanted (group C).As a result of increased feed conversion ratios, body-weight gains were significantly greater in group T (0–80 kg/day) and group TE (0–87 kg/day) than in group C (0–72 kg/ day) during the 15 weeks following the second implant, but there was no significant difference between groups following the first implant.Following both implants in groups T and TE the mean concentrations of urea and albumin in serum decreased, and that of globulin increased. The mean urea: creatinine ratio in the urine of animals in groups T and TE relative to that in group C also decreased.The heifers were served by an Aberdeen Angus bull at the first and, when they occurred, subsequent oestruses. Following calving the mean milk yields in the first lactation in group T (641 kg in 96 days) and group TE (1993 in 212 days) was considerably lower than in group C (3636 kg in 293 days). The udder size in both groups of animals treated with the anabolic steroids was markedly reduced. It is concluded that despite an improvement in feed conversion ratios and body-weight gains, trenbolone acetate should not be administered to prepuberal heifers which will be retained for breeding and milk production.

The effects of rapid rearing and early calving on the subsequent performance of dairy heifers

ABSTRACT1. One-hundred-and-ten British Friesian, British Friesian × Ayrshire or successive backcrosses to British Friesian heifer calves were allocated to three groups. Groups A and B were rapidly reared and fed a barley-beef diet which resulted in mean body-weight gains exceeding 1 kg/day (13 to 39 weeks) and group C was normally reared on summer grazing and hay plus concentrates in winter at a mean body-weight gain never exceeding 0·74 kg/day. Animals in group A were first mated at an average age of 42·9 weeks (body weight, 302 kg). Groups B and C were mated later at average ages of 78·4 and 78·1 weeks (average body weights, 443 and 353 kg respectively). After the first calving all animals were fed and managed as a single group.2. There were no significant differences between the proportion of heifers conceiving at first service in groups A (55·5%), B (66·7%) and C (72·4%).3. There were no differences in the incidence of dystocia at first calving in heifers served by an Aberdeen Angus bull but 12 out of 19 heifers in group A served by a British Friesian bull had dystocia.4. Average 305-day fat-corrected milk yields in the first four lactations in group A (18 animals) were 1959, 2918, 3545 and 3210 kg and in the first three lactations in group B were2450,3216and3310kgand in group C 3863,4694 and 4813 kg. Thus milk yield was significantly lower in all lactations for rapidly-reared animals irrespective of the age at breeding and was further significantly lowered in the first lactation of animals mated early.5. There was a high incidence of laminitis and bloat in heifers reared on the barley-beef diet, but during lactation, there was a lower incidence of mastitis in the lower-yielding, rapidly-reared groups.