This pilot study investigates dairy heifers' perception of ‘positive treatment’ by a human (stroking and brushing) through a test of appetitive motivation. The hypothesis was that positive treatment by a human results in heifers pursuing a human to seek further positive treatment. Thirty-seven dairy heifers were assigned to either minimal human contact or positive treatment during rearing for five minutes per week, for a total of four hours, between ages six to 24 months. Six months after treatment ceased, the heifers were tested in a suite of four sequential tests, conducted while free ranging in their home pen with a group of familiar conspecifics. The tests explored whether dairy heifers that received positive treatment had: 1) a lower flight distance than controls; 2) accepted initial positive treatment during the test; and (for those who voluntarily re-approached and interacted with the human after the human had retreated) whether this was due to 3) curiosity; or 4) motivation for further positive treatment. Positive treatment heifers had a lower flight distance in component 1 of the test and more of this group voluntarily approached the human compared to the control heifers. The positive treatment allowed more initial positive treatment (component 2) and sought further positive treatment in components 3 and 4. It is concluded that ‘positive’ treatment is rewarding for many heifers. It is suggested that positive treatment constitutes environmental enrichment of dairy cattle and can enhance cattle's quality of life and the human-animal relationship.

Biological control is a strategy to decrease parasitic populations, and the action takes place through natural antagonists in the environment. We studied the predatory activity of the fungus Duddingtonia flagrans in infective larvae (L3) of gastrointestinal nematodes after gastrointestinal transit. Ten heifers were divided into two groups: treated (animals received pellets containing fungus) and control (animals received pellets without fungus). Twelve hours after administration, faeces samples were collected for in vitro efficacy tests. The animals then remained for 7 h in the experimental pasture area. At the end of this period, 20 faecal pads (ten treated and ten control) were selected at random. Pasture, faecal pad and soil collections occurred with an interval of 7 days, totalling four assessments. In vitro activity demonstrated that fungi effectively preyed on L3, achieving a reduction percentage of 88%. In the faecal pad of the pasture area, there was a difference (P < 0.05) between collections 3 and 4 for both groups; in the treated group a reduction of 65% was obtained, while in the control group there was an increase of 217% in the number of L3. The recovery of L3 in the soil and in the pasture was similar in both groups. There was no influence (P = 0.87) of the passage time on the fungus predatory activity. Duddingtonia flagrans demonstrated the ability to survive gastrointestinal transit in the animals, reducing the number of L3 in the faeces, indicating that this biological control has great potential in the control of worm infections.

The aims of the research reported here were to identify potential risk factors associated with the presence of Staphylococcus aureus intramammary infection (IMI) in pre partum dairy heifers on 17 dairy farms from three provinces of Argentina and to characterize, at molecular level, isolates from those heifers and lactating cows from two selected herds. A total of 1474 heifers and 4878 lactating cows were studied. The prevalence of Staphylococcus aureus IMI in the heifers, heifers at quarter level and lactating cow mammary quarters was 14.41, 4.82, and 14.65%, respectively. Univariate analysis showed the key variables associated with S. aureus IMI presence in the heifers were: S. aureus IMI prevalence in cows of the lactating herd, the time calves stayed with their dam after birth, the calf rearing system, the place of rearing (own farm or other dairy farm) and fly control on the farm. None of the variables included in the multivariable analysis was associated with the presence of S. aureus IMI in the pre partum heifers, probably due to low variability among management practices used by the farms for rearing the heifer calves. At the molecular level, S. aureus isolates were grouped into three main PFGE clusters and several genotypes within the clusters. Isolates from mammary secretion of pre partum heifers and milk of lactating cows comprised different PFGE clusters in both herds, although two exceptions occurred. The absence of gene fnbpB, which codifies for a virulence factor protein involved in cell invasion by S. aureus, was significantly more frequent in pre partum heifer secretion isolates than in isolates from lactating cow milk. These results suggest that, under these management conditions, isolates from mammary secretions of pre partum heifers do not originate from the milk of lactating cows, but rather other sources to which the heifer is exposed.

Alpine transhumance or droving livestock to mountainous areas during summer months is highly relevant for Austrian agriculture but also for other countries in Alpine regions. Access of rearing stock to mountain pastures is often claimed to be beneficial with respect to health and longevity, but the robust evidence is scarce. Therefore, its effect was tested by including it in the routine genetic evaluation data set for longevity. Alpine transhumance records from 2004 to 2013 were used. After several plausibility checks and restriction to animals with sire and dam known, records of 871 287 dual-purpose Fleckvieh cows sired by 9953 bulls were available. Data were analysed by means of survival analysis accounting for the time-dependent fixed effects of region-year-season, relative performance within herd, change of herd size, and Alpine pasturing of cows, the fixed effects age at first calving and Alpine pasturing of rearing stock, the random time-dependent effect of herd-year and the random genetic effects of sire and maternal grandsire. Fleckvieh cows that had access to Alpine pasture during their rearing period at least once for a minimum of 60 days had functional longevity that was nearly 2 months prolonged compared with cows that had always stayed on the farms as calves or heifers. In a more detailed analysis, the lowest relative culling risk among the significant estimates was observed for cows that had been Alpine pastured in years 1 and 3; it was about 15% below that of cows that never had access to mountain grazing. Evidence for the beneficial effect of Alpine pasturing of rearing stock on the animals’ later fitness, indicated by longevity, could thus be provided.

The objective of this study was to validate an electronic system for monitoring individual feeding and drinking behaviour and intake developed for young cattle housed in group. A total of 35 Holstein–Gyr crossbred heifers (BW: 180±52 kg; age: 121.5±32.5 days), fitted with an ear tag containing a unique passive transponder, were distributed in three groups of 12, 12 and 11 animals per period and had free access to 12 electronic feed bins and two electronic water bins (Intergado® Ltd). The dimensions of feed and water bins, as well as the sensors position were appropriate for young cattle. The system documented the visit frequency and duration, as well as the feed and water intakes, by recording the animal’s identification tag, bin number, initial and final times of visits and the difference of feed/water weight at the start and end of each bin visit. Feed bins were monitored using time-lapse video recording over 4 days and the water bins were monitored over 6 days. For each feed bin, two feeding events were monitored using manual weighings with an external scale immediately before and after the animal’s visit and the difference between them was assumed as feed intake (n=24 observations). For the water bins, 60 manual weighings were made. Video and manual weighing data were regressed on the electronic feeding and drinking behaviour and intake data to evaluate the system’s precision and accuracy. The system showed high specificity (98.98% and 98.56% for the feed and water bins, respectively) and sensitivity (99.25% and 98.74%, respectively) for identifying an animal’s presence or absence. Duration of feed and water bin visits as well as feed and water consumption per visit estimated by the system were highly correlated and precise compared with the observed video and manual weighing data (r2=0.917, 0.963, 0.973 and 0.986, respectively). It was concluded that Intergado® system is a useful tool for monitoring feeding and drinking behaviour as well as water and feed intakes in young cattle housed in groups.

The objective of this research was to evaluate the survival rate of primiparous heifers within a large sample of herds across the United Kingdom and specifically to assess the association between age at first calving (AFC) on their survival. Data from 437 herds were re-structured for analysis. Descriptive statistics were calculated, and a multilevel logistic regression model was used to explore factors associated with the risk of first lactation culling. Potential explanatory variables included AFC, herd size, culling rate within the whole herd, calving season, herd mean 305-day yield and herd mean calving interval. The mean within-herd culling rate for the primiparous heifers was 15.9%. The mean within-herd AFC was 29.6 months, with 35.9% of heifers having an AFC >30 months of age. Multivariable analysis revealed a negative association between survival rate of primiparous heifers and increasing AFC, and also associations with herd culling rate in older cows and calving season. This study highlights the importance of AFC for survival of primiparous heifers, as well as the need to address heifer wastage in herds with high culling rates.

Domestic cattle have limited cardiopulmonary reserve for their body size and oxygen requirements. Therefore, it is plausible that impaired alveolar-arterial gas exchange may be detrimental to energetically expensive traits such as milk production which, like all aerobic processes, requires oxygen. The degree of alveolar-arterial oxygen transfer impairment can be determined by estimating the alveolar-arterial oxygen (A-a O2) pressure gradient from arterial blood-gas tensions. The degree of oxygen transfer impairment is proportional to the A-a O2 pressure gradient: the higher the A-a O2 pressure gradient the less oxygen is transferred to the blood for a given ventilation rate. In this study two cohorts of Holstein-Friesian heifers were followed on one northern Colorado dairy farm. Arterial blood-gas analyses were performed up to 9 d post-calving. Heifers were grouped into quartiles based on A-a O2 pressure gradient so that relative comparisons could be made. Heifers in the lowest (Q1) and highest (Q4) quartile had the least and greatest impairment of alveolar-arterial oxygen transfer, respectively. We hypothesised that milk yield over 60 d would be greatest for heifers in Q1 and would decrease with quartile increments. Hyperventilation, as indicated by hypocapnia, was notable. Despite hypoxia, haematocrit was low. Alveolar-arterial O2 pressure gradient was associated with milk production (P=0·03) when controlling for cohort, treatment for disease and calving difficulty score. Heifers in Q1 produced 1992 kg (95% CI=1858, 2127 kg) of milk when controlling for all other variables. Relative to heifers in Q1, heifers in Q2, Q3 and Q4 produced 130 kg (95% CI=313, −52 kg; P=0·45), 285 kg (95% CI=474, 96 kg; P=0·004) and 169 kg (95% CI=395, −57 kg; P=0.14) less milk, respectively. In conclusion, efficacy of alveolar-arterial oxygen transfer was associated with milk yield in dairy heifers on one farm at moderate altitude.

A reproductively efficient beef cow herd is fundamental to meeting the protein and specifically, red meat demand of an ever increasing global population. However, attaining a high level of reproductive efficiency is underpinned by producers being cognisant of and achieving many key targets throughout the production cycle and requires significant technical competency. The lifetime productivity of the beef bred female commences from the onset of puberty and will be dictated by subsequent critical events including age at first calving, duration of the postpartum interval for each successive calving, conception and pregnancy rate and ultimately manifested as length of intercalving intervals and number of calves weaned over her lifetime. Puberty in heifers is a consequence of the interactive effects of genetics and both pre- and post-weaning nutrition. Early onset of puberty is essential to achieving the first main reproductive target for beef cow herds; first calving at 2 years of age. In calved heifers and mature cows, the onset of ovarian activity, postpartum is a key event dictating the calving interval. Again, this will be the product mainly of prepartum nutrition, manifested through body condition and the strength of the maternal bond between cow and calf, though there is increasing evidence of a modest genetic influence on this trait. Following the initiation of postpartum ovarian cyclicity, conception and subsequent pregnancy rate is generally a function of bull fertility in natural service herds and heat detection and timing of insemination in herds bred through artificial insemination. Cows and heifers should be maintained on a steady plane of nutrition during the breeding season, but the contribution of significant excesses or deficiencies of nutrients including protein and trace elements is likely to be minor where adequate pasture is available. While, increased efforts are being made internationally to genetically identify and select for more reproductively efficient beef cows, this is a more long-term strategy and will not replace the need for a high level of technical efficiency and management practice at farm level.

Six experiments were conducted to investigate the effect of a feed supplement on the performance of grazing Belgian Blue double-muscled (BBDM) heifers with an initial weight and age of 195 ± 43 kg and 190 ± 52 days. Treatments included were: Exp. 1: supplementation with beet pulp (BP): 2 kg/day per head v.ad libitum intake; Exp. 2: supplementation ad libitum with BP v. a mixture of BP and soybean meal (SBM; BP/SBM ratio of 80/20; FW (fresh weight) basis); Exp. 3: supplementation with 4 kg/day per head of a mixture of BP/SBM (80/20; FW basis) v. BP/formaldehyde-treated SBM (BP/FSBM); Exp. 4: supplementation with 4 kg/day per head of a mixture with a similar protein content (125 g DVE per kg dry matter (DM)), consisting of 80/20 BP/SBM v. 92/8 BP/FSBM; Exp. 5: supplementation with 3 kg/day per head of a mixture of BP/SBM (80/20; FW basis) v. BP/DDGS (dried distillers grains and solubles; 70/30, FW basis); and Exp. 6: supplementation with 3 kg/day per head of 80/20 BP/SBM v. maize silage (MS) and SBM, on the basis of a similar protein concentration in the DM as the 80/20 BP/SBM supplement, and fed at a similar amount of DM as in the BP/SBM group. Supplementing BP ad libitum did not affect daily gain (0.54 v. 0.48 kg) and partial feed conversion (3.62 kg on average) compared with 2 kg/day. Supplying SBM besides BP increased growth rate compared with BP (0.87 v. 0.62 kg/day; P < 0.001), but partial feed conversion was similar. Supplying FSBM did not affect growth rate and partial feed conversion (P > 0.10), but blood urea levels were reduced by FSBM (P < 0.05). DDGS tended to increase growth rate (0.77 v. 0.59 kg/day; P < 0.10) compared with BP/SBM, without effect on partial feed conversion. Replacing BP by MS did not affect daily gain, but partial feed conversion tended to be higher (3.21 v. 3.60 kg/kg body weight (BW) gain; P = 0.062). Increasing the supplement (80/20 BP/SBM) level from 3 to 4 kg daily, corresponding to 1.02% and 1.18% of the mean BW, respectively, resulted in a tendency (P = 0.121) for an increased growth rate. Grazing BBDM heifers of <1 year of age necessitate extra protein besides an energy supplement to improve their performance. DDGS can replace SBM and BP can be replaced by MS.

The effect of propylene glycol drenching on ovarian and hormonal dynamics was studied in heifers. Five cycling heifers were used twice (as control and treatment) with crossover design. After the confirmation of ovulation (day 0), the heifers in the treatment group received propylene glycol on days 6, 7 and 8 as an oral drench (250 ml of 90% propylene glycol). On day 10, prostaglandin F2α (PGF2α), 15 mg per head of dinoprost, was administered intramuscularly to induce luteal regression followed by the follicular phase and then propylene glycol was again administered twice daily (500 ml/day) on days 10, 11 and 12. Palpation per rectum and ovarian ultrasonography were performed every other day from days 0 to 10, and daily after PGF2α administration until the subsequent ovulation (second ovulation) for analysis of follicular and luteal dynamics. Blood samples were also collected every other day from days 0 to 10, and then at 6 h intervals after PGF2α administration until the second ovulation. For the samples taken at 6-h intervals after PGF2α administration, the concentrations of glucose showed clear daily fluctuations in both groups. Changes in the plasma concentration of glucose in the treatment group were significantly (P < 0.05) higher than those of the control groups during the period between 0 and 72 h after PGF2α administration. No significant difference was detected in the growth of dominant follicles, maximum diameter of the ovulatory follicles and the changes in oestradiol and progesterone during the follicular phase between treatment and control groups. This study showed the clear daily fluctuations and stimulatory changes in the blood glucose concentrations at 24-h intervals during the short-term treatment of propylene glycol drenching in heifers. However, no significant changes in ovarian and hormonal dynamics were found under such metabolic conditions.

Two experiments were conducted to ascertain the effects of feeding an all-concentrate diet to growing heifers on performance, ruminal fermentation, behaviour and welfare. In experiment 1, eight tethered rumen fistulated Holstein heifers (143 ± 8.7 kg, initial BW) were used to study the effects of treatment on intake, ruminal changes and behaviour. In experiment 2, 48 Friesian female calves (initial BW = 84.5 ± 1.37 kg) were used to study the effects of treatment on performance, behaviour and welfare in feedlot conditions. In both experiments, treatments consisted of concentrate with barley straw (BS) or without barley straw (NBS) and feed was offered at 0830 h on an ad libitum basis. Experiment 1 was performed in four 42-day periods, and sampling was carried out in the last week of each period. Ruminal samples were collected over 3 days at 0, 4, 8 and 12 h post-feeding to measure pH, and volatile fatty acids (VFA) and NH3-N concentrations. Maintenance behaviour was video-recorded for 24 h over three consecutive days of each experimental period and feed intake pattern was studied by means of feed bunks mounted on digital platform scales. There were no statistical differences in average daily gain (ADG), concentrate dry matter (DM) intake or CP intake. In contrast, NDF intake and ADF intake were greater in heifers fed BS than NBS. Average ruminal pH was lower, whereas total VFA was greater, in heifers fed NBS diet. There were no differences in NH3-N, and in d- and l-lactate concentrations. Time spent in ruminating was shorter, and stereotypies were more frequent in heifers fed diet NBS compared with those fed BS. In experiment 2, nine 28-day periods were established, in which DM intake and ADG were measured, blood and faecal samples were taken for haptoglobin and glucocorticoid metabolites determination, respectively, as welfare indicators, and behaviour was monitored by video recording. Concentrate intake was similar in both treatments, but total feed intake was greater in heifers fed BS diet. As there were no differences in ADG between treatments, gain efficiency was lower in those fed BS than those fed NBS. Blood haptoglobin and faecal glucocorticoids metabolites were not different between treatments. In these competitive conditions, rumination was also reduced and stereotypic behaviour increased by straw exclusion. In conclusion, performance was either not affected or improved by straw exclusion, but animal behaviour was affected, suggesting a negative effect on animal welfare.

Early lactation parameters are difficult to estimate from commercial dairy records due to the small number of records available before the peak of production. A biological model of lactation was used with weekly milk records from a single Holstein herd to estimate these early lactation parameters and the secretion rate of milk from the average cell throughout lactation. A genetic analysis of the lactation curve parameters, calculated curve characteristics and secretion rate traits was undertaken. Early lactation traits were found to have little genetic variation and effectively zero heritability. Secretion rate traits for milk, protein, lactose and water were all moderately heritable and highly genetically correlated (>0.87) but fat secretion rate had lower genetic correlations with the other secretion rates. A similar pattern of correlations was seen between total lactation yield traits for fat, protein, lactose and water. The genetic correlations between the lactation curve traits and the secretion rate traits were calculated. Total milk yield, peak yield and maximum secretion potential were all highly correlated with milk, lactose and water secretion rates but less so with fat and protein secretion rates. In particular, fat secretion rate had a moderate to low genetic correlation with these lactation curve traits. Persistency of lactation was highly correlated with fat and protein secretion rates, more persistent lactations being associated with lower rates of secretion of these milk components. Similar levels of heritability were found, where trait genetic parameters were directly equivalent to those derived from the same dataset by random regression methods. However, by using a biological model of lactation to analyse lactation traits new insights into the biology of lactation are possible and ways to select cows on a range of lactation traits may be achieved.

Four ruminally fistulated Holstein heifers (BW = 264 ± 12 kg) were used in a 4 × 4 Latin square design experiment to determine the effect of increasing levels of sodium bicarbonate (BICARB; 0%, 1.25%, 2.50% and 5%, on concentrate dry matter (DM) basis) on DM intake (DMI), water consumption and ruminal fermentation. Sampling was carried out in the last week of each four 21-day experimental periods. Heifers were offered concentrate (13.4 ± 0.04% crude protein (CP), 13.3 ± 0.44% NDF, 51.7 ± 0.97% starch) and barley straw once daily at 0830 h ad libitum. There was a linear decrease in concentrate DMI and a linear increase in straw DMI with increasing buffer level in the diet, resulting in a tendency towards a linear decrease in total DMI. Intake of concentrate was 6.89, 7.66, 6.72 and 5.72 ± 0.83 kg/day, whereas straw intakes were 0.73, 0.84, 0.94 and 1.06 ± 0.14 kg/day, for the 0%, 1.25%, 2.5% and 5% BICARB, respectively. Water consumption was not affected by treatments when expressed as l/day or percentage of BW, but increased linearly when expressed as l/kg of DMI. The percentage of total daily water drunk in the morning (from 0830 to 1230 h) increased linearly with the level of buffer. Mean ruminal pH and total area under the pH curve were not affected with increasing buffer level. The lowest daily pH (5.65 ± 0.09) was not affected by treatments. A quadratic tendency (P ⩽ 0.10) was observed in the number of hours and the area under the pH curve in which ruminal pH was below 5.8, with high values only at the 0% BICARB. Additionally, increasing bicarbonate level caused a linear increase in the ruminal pH at 2 and 4 h after feeding. Daily average NH3 N (2.4 ± 0.9 mg N/100 ml) and total volatile fatty acids (VFA) (143 ± 12 mM) concentrations were not affected by treatments. Daily average molar proportion of propionate decreased linearly, and acetate proportion and the acetate-to-propionate ratio were increased with increasing buffer level in the diet. Molar percentage of butyrate, isobutyrate and isovalerate, and branched-chain VFA concentration increased linearly as the level of bicarbonate increased in the diet. Results indicate that high levels of BICARB to finishing heifers fed high-concentrate diets may result in a decreased DMI without significant effects on mean ruminal pH, which may affect animal performance. All individual VFA proportions, except valerate, were changed by the addition of bicarbonate.

The objective was to characterize the antibody isotype responses to vaccination with a commercial Staphylococcus aureus bacterin in dairy heifers. Twenty-five Holstein-Friesian dairy heifers were assigned at random to one of two groups, vaccinates (n=14) or controls (n=11). Vaccinates received two 5-ml doses of Lysigin 28 d apart in late gestation. Both groups were challenged with a heterologous serotype 5 strain of Staph. aureus by aseptic intramammary infusion on days 6, 7 and 8 of lactation. Samples for serum antibody isotype (IgG, IgG1, IgG2 and IgM) determinations were taken before each vaccination, immediately prior to challenge (6 d post-calving) and at the end of the study (28 d post-calving). Samples for milk antibody isotype determinations were taken immediately prior to challenge and at the end of the study. Antibody isotype sample-to-positive ratios (S[ratio ]P ratio=(mean test sample OD−mean within-plate negative control OD)/(mean within-plate positive control OD−mean within-plate negative control OD)) were determined in milk and serum using a series of ELISAs coated with different strains of Staph. aureus belonging to capsular polysaccharide (CP) serotype 5 or 8 or surface polysaccharide (SP) serotype 336. Vaccinates had higher mean serum IgG1 and IgG2 S[ratio ]P ratios than controls against all three strains of Staph. aureus (P[les ]0·023). Vaccinates had higher mean milk IgG S[ratio ]P ratios than controls against CP8 and SP336 strains of Staph. aureus (P[les ]0·030). Hence, a humoural immune response to the vaccine was detected in serum and milk, but responses varied according to strain and antibody isotype tested.

One hundred and eight high genetic merit Holstein-Friesian heifers were used to determine the effects of rearing regime on the development of the mammary gland and claw abnormalities. Heifers were allocated to one of four rearing regimes at 7 weeks of age and slaughtered at 18 (s.d.0.7) months of age; mating commenced at 14 months of age. Treatment 1 heifers were reared to calve at 540 kg and treatments 2, 3 and 4 heifers reared to calve at 620 kg. Treatment 1 and 2 heifers were offered grass silage-based diets during the winter and grass-based diets during the summer; treatment 2 heifers received additional concentrates. Treatment 3 heifers were offered a straw/concentrate diet during the winter and a grass-based diet during the summer. Treatment 4 heifers received the same winter diets as treatment 3 but were housed and offered a straw/concentrate diet in summer. Increasing plane of nutrition increased the weight of dissected udder fat (P < 0.01), but had no effect on the weight or chemical composition of dissected udder parenchyma. Offering straw- compared with silage-based diets reduced fat deposition in the udder (P < 0.01) and increased the proportion of parenchyma in the udder (P < 0.01). Keeping heifers housed during the first summer and offering straw-based diets relative to those turned out to grass had no effect on weight of fat although there was a tendency towards a reduction in the proportion of parenchyma in the udder (P < 0.06). Heifers reared on a low plane of nutrition had lower values for heel height (P < 0.001), lateral claw length (P < 0.001) and heel erosion scores (P < 0.01). A higher plane of nutrition also increased live weight/sole area although this was only significantly higher for treatment 3 (P < 0.05) compared with treatment 1 heifers. Housing heifers in the first summer increased the incidence of feet lesions in the white line area and solear area relative to turning heifers out to grass in the first summer (P < 0.05).

Twenty-nine Holstein-Friesian and 20 Norwegian dairy herd replacements were used to investigate the effect of habituating heifers to the milking parlour environment prior to calving on subsequent lactational performance. The heifers commenced the study at 3 weeks prior to calving when they were allocated on the basis of breed, genetic merit and live weight to either a habituation or no habituation (control) treatment. Heifers were housed together in cubicle accommodation with grass silage offered ad libitum along with 1 kg of concentrates per head per day offered in the feeding passage (control treatment) or in the food managers in the milking parlour (habituation treatment). Animals in the habituation treatment were exposed to the full milking parlour routine once daily (afternoon milking) in a 20-point rotary herringbone parlour. Holstein-Friesian heifers averaged 2.6 kg/day more milk than the Norwegian replacements. Holstein-Friesian heifers also had higher fat and protein yields than Norwegian heifers, however they also lost more body condition during the first 3 months of lactation. Habituated heifers yielded on average 1.3 kg/day more milk (P < 0.001) than the control group of heifers over the first 100 days of lactation (26.7 v. 25.4 (s.e.d. 0.38) kg/day), with the difference being greatest in the first 2 to 3 weeks of lactation. In early lactation, animals on the habituation treatment lost more live weight (0.16 v. 0.02 (s.e.d. 0.061) kg/day) (P < 0.05) and body condition than those on the control treatment. Duration of milking was longer (P < 0.001) (378.4 v. 340.5 (s.e.d. 6.53) s) and milk flow rate slower (P < 0.001) (2.20 v. 2.46 (s.e.d. 0.041) kg/min) respectively for the habituation compared with control group. Somatic cell counts (SCC) were lower (P < 0.001) for habituation group (1.66 v. 1.79 (s.e.d. 0.037) log10 SCC per ml), but there was no significant treatment effect on locomotion scores. Reproductive performance was lower for habituated heifers, with increased intervals to conception (P < 0.05) (102 v. 83 (s.e.d. 9.22) days). Habituating heifers to the milking parlour environment prior to calving increased milk production but appeared to have some detrimental effects on reproductive performance.

The plasma concentrations of cortisol and progesterone during reproductive maturation in the heifer calf were examined. Six beef heifer calves were handled and bled every 2 weeks (control), 30 were left unhandled (naive). At 13, 21, 30, 39 and 47 weeks of age, a different group of naive heifers and the control heifers were bled every day for 5 days (puberty seen at 57·4 (s.e. 1·3) weeks). Thirty-nine dairy heifer calves were allocated to seven groups to receive adrenocorticotropic hormone (ACTH) at either 4, 7, 9, 16, 26, 36 or 46 weeks of age (puberty expected around 43 weeks of age). Plasma concentrations of cortisol increased at 21, 30 and 39 weeks of age in frequently handled and naive beef heifers; the increase was greater at these ages in the naive beef heifers (age and treatment P < 0·01). No age trend was apparent for plasma concentrations of cortisol and progesterone prior to ACTH injections (t = 0) in frequently handled dairy heifers. Adrenal progesterone secretion did not change with age in beef heifers, but naive beef heifers had greater plasma concentrations than frequently handled beef heifers. ACTH induced cortisol release in dairy heifers as early as 4 weeks of age (P < 0·05), but the response was greater in dairy heifers 16 weeks old and older (P < 0·05). A progesterone response to ACTH in dairy heifers was not seen until animals were 9 weeks old. It is concluded that as heifers mature reproductively, there is a parallel increase in the sensitivity of the adrenal gland to ACTH and handling stress.

One hundred and thirteen high genetic merit Holstein-Friesian heifers were used in a study to determine the effect of rearing regime, in terms of diet offered and target calving weight, on body size, reproductive performance and milk production in high genetic merit heifers. Eighty of the heifers were supplied from 11 commercial farms, the remainder were supplied from the herd at the Agricultural Research Institute of Northern Ireland. The heifers commenced the experiment at 7 weeks of age when they were allocated on the basis of source, live weight and genetic merit to one of four rearing regimes. The target weights at calving were 540 kg (treatment 1) and 620 kg (treatments 2, 3 and 4). Treatment 1 heifers were offered grass silage-based diets during the winter and grass-based diets during the summer. Treatment 2 heifers were offered the same forage base plus additional concentrate supplementation. Treatment 3 heifers were offered a straw/concentrate diet during the winter and grass-based diets during the summer. Treatment 4 heifers received the same diets as treatment 3, except for the first summer period when they remained housed and were offered a straw/concentrate diet. The heifers were mated at 14 months of age and were returned to the 11 source farms one month prior to calving. Heifers reared on treatment 1 had a lower withers height (P < 0·001) and were of a lower condition score (P < 0·001) before calving than heifers reared on treatments 2, 3 and 4. During early lactation (3 months post calving) heifers reared on treatment 1 lost less weight and condition score than the heifers reared on the other treatments. Thus at the end of the first lactation live weights did not differ significantly between the treatments. However, body length remained shorter (P < 0·01) in treatment 1 compared with treatments 2, 3 and 4. First lactation milk yield (305 days) was lower for heifers reared on treatment 1 (7222 l) compared with heifers reared on treatment 2 (8020 l) (P < 0·01), 3 (7956 l) (P < 0·01) and 4 (7901 l) (P < 0·05). Similarly, milk fat plus protein yield was lower (P < 0·05) for heifers reared on treatment 1 (511 kg) compared with treatments 2 (544 kg), 3 (544 kg) and 4 (554 kg). The interval from calving to first recorded oestrus was shorter in treatment 1 compared with treatments 2 and 3 (P < 0·05). There was a tendency (P < 0·10) for heifers reared on treatment 1 to have a shorter calving interval (394 days) compared with treatments 2 (426 days), 3 (435 days) and 4 (458 days). In conclusion increasing the live weight of Holstein-Friesian heifers at first calving from 540 to 620 kg pre-calving increased milk yield proportionally by 0·11 but tended to increase the calving interval. Diet type during the rearing period had no effect on milk fat plus protein yield or reproductive performance.

The objectives of this study were to investigate reproductive performance and the influence of maternal environment on reproductive performance in two genetic lines of maiden heifers. These were given food and managed in the same way at the Langhill Dairy Cattle Research Centre. The two genetic lines were established in 1973; one has been selected for high combined yield of fat plus protein (selection line; S) and the other has been maintained at around the UK average for genetic merit of yield of fat plus protein (control line; C). Analysis of the reproductive performance of 988 heifers born between 1981 and 1998 showed that S heifers were poorer (all P < 0·05) than C heifers for all reproductive measures: conception at first service (S: 0·64, s.e. 0·02; C: 0·71, s.e. 0·03), interval between first and last service (S: 18·2 days, s.e. 2·2; C: 13·4 days, s.e. 2·2) and number of services per conception (S: 1·49 services, s.e. 0·06; C: 1·39 services, s.e. 0·06). S heifers were also younger at first service than C heifers (474·9 days v. 480·1 days, s.e. 1·9, for S and C respectively; P • 01). Fertility of service sires may have had some influence on these results, but this could not be investigated here, as S heifers were mated only to high merit bulls and C heifers to average merit bulls. However, within genetic line, the yearly downward trend in the average number of services per conception of heifers was significantly different from zero for the S line, but not the C line. There were no statistically significant relationships between conception rates in maiden heifers and their subsequent reproductive performance in first lactation. The effect of maternal environment on the reproductive performance of daughters as maiden heifers was investigated. There were no statistically significant relationships between daughter reproductive performance and dam parity or the feeding system of the dam (either a high or low level of concentrates). Within the limited range of nutritional status of dams during the periods post calving and in early pregnancy, there was no statistically significant effect of maternal nutrition on daughter reproductive performance.

A series of laboratory and animal studies examined the use of chemical and biological agents to enhance the digestibility of Rhodes grass (grass) cut at 60 (young) and 100 (mature) days of regrowth and ensiled as big round bales. The treatments included an untreated control (C), a microbial inoculant (I), NaOH, CaO and NaOH plus inoculant (NaOH + I). Inoculant was grown anaerobically, using a starter culture of rumen fluid from cattle given Rhodes grass. Treatments C, I, NaOH, NaOH + I, were offered separately to twelve dairy heifers, in a 3 ✕ 4 randomized complete block design, repeated twice for each grass silage. C and I had substantial mould growth, compared with no visible mould in NaOH or NaOH + I. CaO treatment was effective in preventing mould growth, but had little effect on the chemical composition and in sacco digestibility of mature grass silage. NaOH reduced NDF content and increased in sacco digestibility (P < 0·05) but not the in vivo digestibility (P > 0·05) of both mature- and young-grass silage. The effects of other treatments on nutritive value were non-significant at both stages of maturity. NaOH increased the intake of mature-grass silage by 24-26% (P < 0·05), but had little effect on the intake of young-grass silage (P > 0·05). Treatment I consistently reduced grass silage intake (P < 0·05) for young-grass silage. The findings of these studies show that treating mature Rhodes grass with NaOH will improve its nutritive value and reduce mould growth in conserved herbage. However none of the treatments in this study had any consistently positive effects on the in vivo nutritive value or storage quality of young-grass silage.