Review: Perspective on high-performing dairy cows and herds.

Milk and dairy products provide highly sustainable concentrations of essential amino acids and other required nutrients for humans; however, amount of milk currently produced per dairy cow globally is inadequate to meet future needs. Higher performing dairy cows and herds produce more milk with less environmental impact per kg than lower performing cows and herds. In 2018, 15.4% of the world's dairy cows produced 45.4% of the world's dairy cow milk, reflecting the global contribution of high-performing cows and herds. In high-performing herds, genomic evaluations are utilized for multiple trait selection, welfare is monitored by remote sensing, rations are formulated at micronutrient levels, health care is focused on prevention and reproduction is managed with precision. Higher performing herds require more inputs and generate more waste products per cow, thus innovations in environmental management on such farms are essential for lowering environmental impacts. Our focus is to provide perspectives on technologies and practices that contribute most to sustainable production of milk from high-performing dairy cows and herds.

Short communication: Chronology of different sexual behaviors and motion activity during estrus in dairy cows.

In studying the efficiency of a variety of methods for estrus detection in a large dairy herd, we suspected a definite sequence of estrus signs. Consequently, we observed a subset of animals continuously between 0400 and 2400 h, making a note of the precise timing and frequency of each sexual behavior. Sixteen Holstein-Friesian cows, >20 d postpartum, were equipped with motion activity-sensing neck collars and had milk progesterone profiles monitored simultaneously. The duration between the first and last observed estrus behavior was (mean ± SE) 14.0 ± 1.9 h, with a range 8.5 to 28.75 h. The duration of standing to be mounted (STBM) was 4.68 ± 1.49 h, with a range of 0.25 to 18.25 h. Sniffing the vulva of another cow occurred on average 5.5 ± 1.3 h (range = 0.25-18.25 h) before the first STBM. By ranking the first appearance of each behavior, we established that sniffing was followed by the active behaviors of mounting another cow and not accepting a mount, as well as the passive behaviors of being sniffed and STBM by another cow. Chin resting occurred before not accepting a mount and STBM. All these behaviors were observed in the reverse order after the last STBM. The mean profile of motion activity revealed an increase in motion activity with the onset of exploratory behaviors, and highest values occurred within the period of STBM. Such distinct behavioral sequences may be controlled by changes in peripheral progesterone and estradiol concentrations, as well as by subtle independent mechanisms via pheromones in differing concentrations or divergent composition.

Association of production diseases with motor activity-sensing devices and milk progesterone concentrations in dairy cows.

We have previously established that the efficiency of identifying oestrus with activity-sensing devices can be compromised by common production diseases; the present study was undertaken to determine how these diseases may affect device readings. A total of 67 Holstein-Friesian cows, >20 days postpartum, were equipped with activity-sensing neck collars and pedometers, and simultaneous milk progesterone profiles were also monitored twice a week. The influences of common production stressors on maximum activity and progesterone values were analysed. Approximately 30% potential oestrus events (low progesterone value between two high values) remained unrecognised by both activity methods, and progesterone values in these animals were higher on the potential day of oestrus when both activity methods did not detect an event (0.043 ±â€¯0.004 versus 0.029 ±â€¯0.004 ng/mL; P = 0.03). Data from a subset of 45 cows (two events each) were subjected to mixed models and multiple regression modelling to investigate associations with production diseases. Cow motor activity was lower in lame cows. Maximum progesterone concentrations prior to oestrus increased as time postpartum and body condition score (BCS) increased. There were also fewer days of low progesterone prior to oestrus associated with increases in BCS and maximum progesterone concentrations prior to oestrus. In conclusion, lameness was associated with lower activity values, but this suppression was insufficient to account for lowered oestrus detection efficiency of either device. However, associations were identified between production diseases and progesterone profiles.

Invited review: Learning from the future-A vision for dairy farms and cows in 2067.

The world's population will reach 10.4 billion in 2067, with 81% residing in Africa or Asia. Arable land available for food production will decrease to 0.15 ha per person. Temperature will increase in tropical and temperate zones, especially in the Northern Hemisphere, and this will push growing seasons and dairy farming away from arid areas and into more northern latitudes. Dairy consumption will increase because it provides essential nutrients more efficiently than many other agricultural systems. Dairy farming will become modernized in developing countries and milk production per cow will increase, doubling in countries with advanced dairying systems. Profitability of dairy farms will be the key to their sustainability. Genetic improvements will include emphasis on the coding genome and associated noncoding epigenome of cattle, and on microbiomes of dairy cattle and farmsteads. Farm sizes will increase and there will be greater lateral integration of housing and management of dairy cattle of different ages and production stages. Integrated sensors, robotics, and automation will replace much of the manual labor on farms. Managing the epigenome and microbiome will become part of routine herd management. Innovations in dairy facilities will improve the health of cows and permit expression of natural behaviors. Herds will be viewed as superorganisms, and studies of herds as observational units will lead to improvements in productivity, health, and well-being of dairy cattle, and improve the agroecology and sustainability of dairy farms. Dairy farmers in 2067 will meet the world's needs for essential nutrients by adopting technologies and practices that provide improved cow health and longevity, profitable dairy farms, and sustainable agriculture.

KNDy neurone activation prior to the LH surge of the ewe is disrupted by LPS.

In the ewe, steroid hormones act on the hypothalamic arcuate nucleus (ARC) to initiate the GnRH/LH surge. Within the ARC, steroid signal transduction may be mediated by estrogen receptive dopamine-, ß-endorphin- or neuropeptide Y (NPY)-expressing cells, as well as those co-localising kisspeptin, neurokinin B (NKB) and dynorphin (termed KNDy). We investigated the time during the follicular phase when these cells become activated (i.e., co-localise c-Fos) relative to the timing of the LH surge onset and may therefore be involved in the surge generating mechanism. Furthermore, we aimed to elucidate whether these activation patterns are altered after lipopolysaccharide (LPS) administration, which is known to inhibit the LH surge. Follicular phases of ewes were synchronised by progesterone withdrawal and blood samples were collected every 2 h. Hypothalamic tissue was retrieved at various times during the follicular phase with or without the administration of LPS (100 ng/kg). The percentage of activated dopamine cells decreased before the onset of sexual behaviour, whereas activation of ß-endorphin decreased and NPY activation tended to increase during the LH surge. These patterns were not disturbed by LPS administration. Maximal co-expression of c-Fos in dynorphin immunoreactive neurons was observed earlier during the follicular phase, compared to kisspeptin and NKB, which were maximally activated during the surge. This indicates a distinct role for ARC dynorphin in the LH surge generation mechanism. Acute LPS decreased the percentage of activated dynorphin and kisspeptin immunoreactive cells. Thus, in the ovary-intact ewe, KNDy neurones are activated prior to the LH surge onset and this pattern is inhibited by the administration of LPS.

Upgrade of ductal carcinoma in situ on core biopsies to invasive disease at final surgery: a retrospective review across the Scottish Breast Screening Programme.

AIM: To identify factors affecting upgrade rates from B5a (non-invasive) preoperative core biopsies to invasive disease at surgery and ways to improve screening performance. MATERIAL AND METHODS: This was a retrospective analysis of 1252 cases of B5a biopsies across all six Scottish Breast Screening Programmes (BSPs), ranging between 2004 and 2012. Final surgical histopathology was correlated with radiological and biopsy factors. Data were analysed using basic Microsoft Excel and standard Chi-squared test used for evaluating statistical significance. RESULTS: B5a upgrade rates for the units ranged from 19.2% to 29.2%, with an average of 23.6%. Mean sizes of invasive tumours were small (3-11 mm). The upgrade rate was significantly higher for cases where the main mammographic abnormality was mass, distortion, or asymmetry, compared with micro-calcification alone (33.2% versus 21.7%, p = 0.0004). The upgrade rate was significantly lower with the use of large-volume vacuum-assisted biopsy (VAB) devices than 14 G core needles (19.9% versus 26%, p = 0.013); in stereotactic than ultrasound-guided biopsies (21.2% versus 36.1%, p < 0.001). Heterogeneity of data from different centres limited evaluation of other potential factors. CONCLUSION: Upgrade rates are lower for cases with micro-calcification as the sole mammographic feature with the use of VAB devices. Nevertheless, there is variation in practice across Scottish BSPs, including first-line biopsy technique and/or device; and it is of interest that a few centres maintain low upgrade rates despite not using VAB routinely for biopsy of micro-calcification.

Effect of signs of oestrus, disease stressors and cow activity on pregnancy rate following artificial insemination.

The objective was to examine (a) how pregnancy rate on one farm (500 cows) was affected by signs of oestrus and disease stressors and (b) whether pregnancy rate could be maximised by considering cow activity. The signs of oestrus and timings were recorded at artificial insemination (AI), and cow activity was monitored by neck collars. Pregnancy rate tended to be higher in animals that displayed standing oestrus (35 v 26 per cent; P=0.06) but was 10 per cent lower in those cows with an elevated somatic cell count (SCC; >200,000 cells/ml milk) within 0-4 or 4-8 weeks prior to AI (P=0.01 and 0.05, respectively), irrespective of the incidence of clinical mastitis prior to AI. Cow activity data were available for 525 inseminations (from a total of 1299). The mean interval from increased activity to AI in all cows (11 hours 32 minutes; 95 per cent CI 10 hours 40 minutes to 12 hours 24 minutes) was not different for cows that did or did not establish a pregnancy (P=0.90). The pregnancy rate improved to the average of unaffected cows if AI was delayed by about eight hours in animals with an elevated SCC 0-4 weeks prior to AI (P=0.025), indicating that, in cows with prior elevated SCC, AI could be repeated approximately eight hours later to achieve maximum pregnancy rates.

Incidence of palmar process fractures of the distal phalanx and association with front hoof conformation in foals.

REASONS FOR PERFORMING STUDY: Recent studies indicate a high prevalence of fractures of the palmar processes (PP) of the distal phalanx in foals. However, information on the prevalence of such fractures in different breeds and the effect of predisposing factors, such as hoof conformation, is limited. OBJECTIVES: To examine the prevalence of distal phalanx PP fractures in foals and report the relationship of distal limb and hoof conformation with the prevalence of fracture. STUDY DESIGN: Longitudinal study. METHODS: Front hooves of 19 Thoroughbred, Quarter Horse and Arabian foals were examined. Digital radiographic and photographic images of the distal aspect of the forelimbs were taken at ∼2.5 month intervals. Five radiographic projections of each limb were as follows: lateromedial; horizontal beam dorsopalmar; dorso60°proximal-palmarodistal oblique; dorso60°proximo45°lateral-palmarodistomedial oblique; and dorso60°proximo45°medial-palmarodistolateral oblique. The relationship between measurements and the prevalence of fractures was assessed by 3-way ANOVA. RESULTS: Fractures were found in 74% (n = 14) of the foals during the study period. The prevalences of lateral PP and medial PP fractures were not significantly different. Several hoof measurements were associated with PP fractures. Longer dorsal length of the distal phalanx was associated with medial PP fractures, while smaller lateral angle and shorter lateral palmar length were associated with a higher prevalence of lateral PP fractures. CONCLUSIONS: This study revealed a high prevalence of PP fractures in young foals, particularly in Thoroughbred foals. The hoof conformation may be one of the contributory factors to PP fractures in foals.

Co-expression of c-Fos with oestradiol receptor α or somatostatin in the arcuate nucleus, ventromedial nucleus and medial preoptic area in the follicular phase of intact ewes: alteration after insulin-induced hypoglycaemia.

The aim of this study was to investigate how acute insulin-induced hypoglycaemia (IIH) alters the activity of cells containing oestradiol receptor α (ERα) or somatostatin (SST) in the arcuate nucleus (ARC) and ventromedial nucleus (VMN), and ERα cells in the medial preoptic area (mPOA) of intact ewes. Follicular phases were synchronized with progesterone vaginal pessaries. Control animals were killed at 0 h or 31 h (n = 5 and 6, respectively) after progesterone withdrawal (PW; time zero). At 28 h, five other animals received insulin (INS; 4 iu/kg) and were subsequently killed at 31 h. Hypothalamic sections were immunostained for ERα or SST each with c-Fos, a marker of neuronal transcriptional activation. Insulin did not alter the percentage of activated ERα cells in the ARC; however, it appeared visually that two insulin-treated animals (INS responders, with no LH surge) had an increase in the VMN (from 32 to 78%) and a decrease in the mPOA (from 40 to 12%) compared to no increase in the two INS non-responders (with an LH surge). The percentage of activated SST cells in the ARC was greater in all four insulin-treated animals (from 10 to 60%), whereas it was visually estimated that activated SST cells in the VMN increased only in the two insulin responders (from 10 to 70%). From these results, we suggest that IIH stimulates SST activation in the ARC as part of the glucose-sensing mechanism but ERα activation is unaffected in this region. We present evidence to support a hypothesis that disruption of the GnRH/LH surge may occur in insulin responders via a mechanism that involves, at least in part, SST cell activation in the VMN along with decreased ERα cell activation in the mPOA.

Herd monitoring to optimise fertility in the dairy cow: making the most of herd records, metabolic profiling and ultrasonography (research into practice).

Fertility performance is intrinsically linked to the quality of the animal environment, overall management and nutrition. This review describes the use of dairy herd records, metabolic profiles and ultrasonographic findings at veterinary fertility examinations to monitor and manage dairy herd fertility. After calving, a cow has to overcome a series of physiological hurdles before establishing a pregnancy. The selection of timely key performance indicators (KPIs) that monitor specific events in the postpartum and service periods is vital to correctly identify problems and their potential causes that hopefully can be rectified. Cumulative sum charts are the timeliest monitors of efficiency of detection of oestrus, insemination outcome and relationship between postpartum events and fertility, with the point of inflection indicating when a change took place. Other KPIs use data from specific cohorts, adding an inherent delay to when change is indicated. Metabolic profiles and milk constituent data allow monitoring of nutritional adequacy and developments to offer new possibilities of on-farm systems for regular measurements of milk constituents (including progesterone) and energy status. Examination of the reproductive tract can be used to indicate individual and herd fertility status but the currently available detail is under used. Recent advances in ultrasonography can improve the diagnosis of reproductive tract pathophysiology still further but the clinical use of these methods in veterinary practice needs further evaluation. Development of new KPIs to exploit research findings are needed to ensure this knowledge is used to improve on-farm performance.

Kisspeptin, c-Fos and CRFR type 2 co-expression in the hypothalamus after insulin-induced hypoglycaemia.

Normal reproductive function is dependent upon availability of glucose and insulin-induced hypoglycaemia is a metabolic stressor known to disrupt the ovine oestrous cycle. We have recently shown that IIH has the ability to delay the LH surge of intact ewes. In the present study, we examined brain tissue to determine: (i) which hypothalamic regions are activated with respect to IIH and (ii) the effect of IIH on kisspeptin cell activation and CRFR type 2 immunoreactivity, all of which may be involved in disruptive mechanisms. Follicular phases were synchronized with progesterone vaginal pessaries and at 28 h after progesterone withdrawal (PW), animals received saline (n = 6) or insulin (4 IU/kg; n = 5) and were subsequently killed at 31 h after PW (i.e., 3 h after insulin administration). Peripheral hormone concentrations were evaluated, and hypothalamic sections were immunostained for either kisspeptin and c-Fos (a marker of neuronal activation) or CRFR type 2. Within 3 h of treatment, cortisol concentrations had increased whereas plasma oestradiol concentrations decreased in peripheral plasma (p < 0.05 for both). In the arcuate nucleus (ARC), insulin-treated ewes had an increased expression of c-Fos. Furthermore, the percentage of kisspeptin cells co-expressing c-Fos increased in the ARC (from 11 to 51%; p < 0.05), but there was no change in the medial pre-optic area (mPOA; 14 vs 19%). CRFR type 2 expression in the lower part of the ARC and the median eminence was not altered by insulin treatment. Thus, disruption of the LH surge after IIH in the follicular phase is not associated with decreased kisspeptin cell activation or an increase in CRFR type 2 in the ARC but may involve other cell types located in the ARC nucleus which are activated in response to IIH.

Identification of inadequate maternal progesterone concentrations in nulliparous dairy heifers and treatment with human chorionic gonadotrophin.

Plasma progesterone concentrations were estimated for 381 nulliparous dairy heifers from eight farms on days 4-6 after insemination. Heifers were synchronised using two treatments of prostaglandin F2α (PGF2α) 11 days apart. Alternate heifers were treated with 1500 IU human chorionic gonadotrophin (hCG) at the time of sampling, and the pregnancy status assessed ~35 days after insemination. Heifers with no corpus luteum (CL; n-30) at the second PGF2α had lower progesterone concentrations (P<0.001) and pregnancy rates (PR; P=0.001) compared with heifers with CL (n=351, defined as cyclic). The risk of no CL increased in heifers <15 months of age (OR=7.5, P<0.001) and with body condition score <2.5 (OR=4.5, P=0.001). Those with no CL were removed from further analysis. The 20 per cent cyclic control heifers with progesterone concentrations ≤2 ng/ml on days 4-6 had lower PRs compared with those with higher concentrations (42 per cent vs 64 per cent, OR=0.3, P=0.01). There was no overall effect of hCG on PR compared with controls (51 per cent vs 60 per cent, P=0.10). However, heifers with high progesterone on days 4-6 (>2 ng/ml) had a lower PR after treatment (51 per cent vs 64 per cent, OR=0.6, P=0.02). Heifers inseminated with sexed (n=18) compared with conventional (n=333) semen had a decreased PR (33 per cent vs 57 per cent, OR=0.2, P=0.01). This study demonstrates that higher plasma progesterone concentrations as early as days 4-6 after insemination have a positive effect on first insemination PR, but there was no beneficial effect of hCG treatment on these days in dairy heifers.

Effects of high somatic cell counts in milk on reproductive hormones and oestrus behaviour in dairy cows with special reference to those with concurrent lameness.

The present investigation aims to establish the reason(s) why dairy cows with high somatic cell counts (SCCs; >100,000 cells/ml) are less fertile than cows with low SCCs alone. The objective of Study One was to determine whether differences in steroid hormone profiles could explain the low incidence of ovulation in cows with combined High SCC and lameness. Between 30 and 80 days post-partum, animals were scored for SCC and lameness and three groups were formed: Healthy (n=22), High SCC alone (n=12) or High SCC + Lame (n=9). The ovarian follicular phases of all cows were synchronised by administering gonadotrophin releasing hormone (GnRH) followed seven days later by prostaglandin F2alpha (PG). Milk samples were collected daily throughout the entire study period; twice daily during the follicular phase, blood samples were taken and the ovaries were monitored using ultrasonography. Progesterone concentrations were similar in all three groups during each of five specific time periods, i.e. throughout the five days before PG injection, the peri-ovulatory period, on Day 5 and on Day 7, and during the mid luteal phase 12-17 days after ovulation (P>0.13). Mean plasma oestradiol concentrations monitored every 12h during the 36h period before ovulation were similar in all groups (Healthy, 2.80±0.30pg/ml; High SCC alone, 3.82±0.48pg/ml; High SCC+Lame 2.94±0.51pg/ml; P=0.175). The objective of Study Two was to establish whether cows with High SCC (scored and synchronised as above) display different behaviours, especially the intensity and timing of oestrus. Intervals from PG to the onset of oestrus or to the first stand-to-be-mounted (STBM) were longer for the High SCC cows than the Low SCC animals (n=8 and 20; P=0.011 and 0.002, respectively). Also, cows with High SCC tended to have a less intense oestrus and a lower maximum oestrus score per 30-min period than Low SCC cows (P=0.063 and 0.066, respectively). In conclusion, High SCC±lameness did not affect progesterone or twice daily oestradiol profiles but the onset of oestrus was delayed and oestrus tended to be less intense in cows with High SCC. These factors could explain low fertility associated with High SCC.

Kisspeptin, c-Fos and CRFR type 2 expression in the preoptic area and mediobasal hypothalamus during the follicular phase of intact ewes, and alteration after LPS.

Increasing estradiol concentrations during the late follicular phase stimulate sexual behavior and the GnRH/LH surge, and it is known that kisspeptin signaling is essential for the latter. Administration of LPS can block these events, but the mechanism involved is unclear. We examined brain tissue from intact ewes to determine: i) which regions are activated with respect to sexual behavior, the LH surge and LPS administration, ii) the location and activation pattern of kisspeptin cells in control and LPS treated animals, and iii) whether CRFR type 2 is involved in such disruptive mechanisms. Follicular phases were synchronized with progesterone vaginal pessaries and control animals were killed at 0 h, 16 h, 31 h or 40 h (n=4-6/group) after progesterone withdrawal (time zero). At 28 h, other animals received endotoxin (LPS; 100 ng/kg) and were subsequently killed at 31 h or 40 h (n=5/group). LH surges only occurred in control ewes, during which there was a marked increase in c-Fos expression within the ventromedial nucleus (VMN), arcuate nucleus (ARC), and medial preoptic area (mPOA), as well as an increase in the percentage of kisspeptin cells co-expressing c-Fos in the ARC and mPOA compared to animals sacrificed at all other times. Expression of c-Fos also increased in the bed nucleus of the stria terminalis (BNST) in animals just before the expected onset of sexual behavior. However, LPS treatment increased c-Fos expression within the VMN, ARC, mPOA and diagonal band of broca (dBb), along with CRFR type 2 immunoreactivity in the lower part of the ARC and median eminence (ME), compared to controls. Furthermore, the percentage of kisspeptin cells co-expressing c-Fos was lower in the ARC and mPOA. Thus, we hypothesize that in intact ewes, the BNST is involved in the initiation of sexual behavior while the VMN, ARC, and mPOA as well as kisspeptin cells located in the latter two areas are involved in estradiol positive feedback only during the LH surge. By contrast, disruption of sexual behavior and the LH surge after LPS involves cells located in the VMN, ARC, mPOA and dBb, as well as cells containing CRFR type 2 in the lower part of the ARC and ME, and is accompanied by inhibition of kisspeptin cell activation in both the ARC and mPOA.

Effects of periparturient events on subsequent culling and fertility in eight UK dairy herds.

The occurrence of five periparturient events and their effects on subsequent culling and fertility was recorded in eight herds in the UK. Combining data from all 2105 calvings, the proportion affected by assisted calving, dead calf, retained fetal membranes (RFM), milk fever or twins was 5.9, 8.2, 5.3, 5.0 or 3.3 per cent, respectively. Compared with unaffected herdmates, cows with an assisted calving or a dead calf had higher early (but not late) culling rates, (assisted calving: 8.8 per cent being culled before 100 days after calving compared with 5.7 per cent; P=0.05; dead calf: 12.2 per cent culled compared with 5.3 per cent; P=0.001). Compared with unaffected animals, cows with milk fever were four times more likely to be culled before 100 days after calving (16.2 per cent compared with 5.3 per cent; P=0.001), whereas those with RFM were twice as likely to be culled between 100 and 200 days (14.3 per cent compared with 7.6 per cent; P=0.003), and both groups were twice as likely to not be pregnant by 200 days. Cows with RFM or milk fever also had markedly reduced subsequent fertility: both conditions extended calving to pregnancy intervals (by 20 days; P=0.001, or by 13 days; P=0.03, respectively), lowered 100-day in-calf rates (by 24.5 per cent; P=0.001, or by 17.8 per cent; P=0.008, respectively) and lowered 200-day in-calf rates (by 20 per cent; P=0.001, or by 15 per cent; P=0.002, respectively). The birth of twins had no effect on subsequent culling or fertility.

Effects of stress on reproduction in ewes.

Stressors, such as poor body condition, adverse temperatures or even common management procedures (e.g., transport or shearing) suppress normal oestrus behaviour and reduce ewe fertility. All these events are co-ordinated by endocrine interactions, which are disrupted in stressful situations. This disruption is usually temporary in adult ewes, so that, when prevailing conditions improve, normal fertility would resume. Imposition of an experimental stressor (shearing, transport, isolation from other sheep, injection of endotoxin or insulin or cortisol infusion) suppresses GnRH/LH pulse frequency and amplitude. Part of the cause is at the pituitary, but effects on GnRH/LH pulse frequency and the GnRH/LH surge are mediated via the hypothalamus. It is not yet clear whether delays in the surge are caused by interruption of the oestradiol signal-reading phase, the signal transmission phase or GnRH surge release. Stressors also delay the onset of behaviour, sometimes distancing this from the onset of the pre-ovulatory LH surge. This could have deleterious consequences for fertility.

Estrous behavior, luteinizing hormone and estradiol profiles of intact ewes treated with insulin or endotoxin.

Acute insulin administration causes a disparity between the onset of estrous behavior and the LH surge in ovary-intact ewes. To examine the considerable variation in responses, in the present study we used a large number of animals to confirm findings with insulin, and examine whether endotoxin has the same effect. During the breeding season, follicular phases of intact ewes were synchronized with progesterone vaginal pessaries and received saline vehicle (n=22; controls), insulin (4 IU/kg; n=21 ewes) or endotoxin (LPS; 100 ng/kg; n=10) at 28 h after progesterone withdrawal (time zero). In controls, the LH surge onset occurred at 36.5±5.7 h and were first mounted by a ram at 38.2±1.8 h, but there was a delay of 17.6 h (P<0.001) and 7.2 h (P<0.05), respectively, in half the insulin-treated animals ('insulin-delayed') but not in the other half; and a delay of 22.5 h (P<0.001) and 20.7h (P<0.001), respectively, in all LPS-treated animals. Plasma estradiol concentrations decreased after both stressors, and remained low for a period of time equivalent to the LH surge delay (P<0.001; Rs-q=78%). Cortisol increased for 12h after treatment in both insulin subgroups and the LPS group (P<0.05); whereas progesterone increased in the insulin-delayed and LPS groups from 4.0±0.5 ng/ml and 5.3±1.0 ng/ml to a maximum of 5.7±0.3 ng/ml and 8.8±1.6 ng/ml, respectively (P<0.05 for both comparisons). Plasma triglycerides were measured to assess insulin resistance, but concentrations were similar before and after treatment (0.25±0.01 mmol/l versus 0.21±0.01 and 0.25±0.01 mmol/l versus 0.26±0.01 mmol/l in the insulin-non delayed and insulin delayed subgroups, respectively). Therefore, we hypothesize that a) when an acute stressor is applied during the late follicular phase, the duration of the LH surge delay is related to the duration of estradiol signal disruption b) cortisol is not the key disruptor of the LH surge after insulin, c) insulin (but not LPS) can separate the onsets of LH surge and estrus by approximately 10h, providing a model to identify the specific neuronal systems that control behavior distinct from those initiating the GnRH surge.

Comparison of oestrus detection methods in dairy cattle.

Sixty-seven Holstein-Friesian cows, from 20 days postpartum, were recruited into the study and fitted with both a pedometer (SAE Afikim) and a Heatime neck collar (SCR Engineers) and allocated a heat mount detector (either scratchcard [Dairymac] or KaMaR [KaMaR]) or left with none, relying only on farm staff observation. Common production stressors and other factors were assessed to determine their impact on the ability of each method to accurately detect oestrus and to investigate effects on the frequency of false-positive detections. Only 74 per cent of all potential oestrus periods (episodes of low progesterone) were identified by combining information from all methods. There was no difference between the methods in terms of sensitivity for detecting 'true oestrus events' (approximately 60 per cent), with the exception of scratchcards, which were less efficient (36 per cent). Pedometers and KaMaRs had higher numbers of false-positive identifications. No production stressors had any consequence on false-positives. The positive predictive values for neck collars or observation by farm staff were higher than those of other methods, and combining these two methods yielded the best results. Neck collars did not detect any of the nine oestrus events occurring in three cows with a body condition score (BCS) of less than 2, and the efficiency of correctly identifying oestrus was also reduced by high milk yield (odds ratio [OR]=0.34). Pedometer efficiency was reduced by lameness, low BCS or high milk yield (OR=0.42, 0.15 or 0.30, respectively).

Influence of lameness on follicular growth, ovulation, reproductive hormone concentrations and estrus behavior in dairy cows.

The objective of this study was to examine the effect of a chronic stressor, lameness, on reproductive parameters. Seventy cows 30-80 days post-partum were scored for lameness and follicular phases synchronized with GnRH followed seven days later by prostaglandin (PG). Fifteen Lame animals did not respond to GnRH ovarian stimulation. Milk progesterone for 5 days prior to PG was lower in the remaining Lame cows than Healthy herdmates. Fewer Lame cows ovulated (26/37 versus 17/18; P = 0.04) and the interval from PG to ovulation was shorter in Lame cows. In Subset 1 (20 animals), the LH pulse frequency was similar in ovulating animals (Lame and Healthy) but lower in Lame non-ovulators. An LH surge always preceded ovulation but lameness did not affect the interval from PG to LH surge onset or LH surge concentrations. Before the LH surge, estradiol was lower in non-ovulating cows compared to those that ovulated and estradiol concentrations were positively correlated with LH pulse frequency. In Subset 2 (45 cows), Lame ovulating cows had a less intense estrus than Healthy cows, although Lame cows began estrus and stood-to-be-mounted earlier than Healthy cows. In conclusion, we have identified several parameters to explain poor fertility in some chronically stressed animals. From 30 to 80 days post-partum, there was a graded effect that ranged from 29% Lame cows with absence of ovarian activity, whereas another 21% Lame cows failed to express estrus or ovulate a low estrogenic follicle; in 50% cows, many reproductive parameters were unaffected by lameness.