Amino acid concentrations in uterine fluid during early pregnancy differ in fertile and subfertile dairy cow strains.

The objective of this study was to determine if free AA concentrations in uterine luminal fluid (ULF) and plasma differed between dairy cow strains that differ phenotypically for fertility and to evaluate the effect of the presence of a conceptus on ULF AA concentrations. Uterine luminal fluid was obtained postmortem from cows characterized on the basis of genetic ancestry as fertile (n=11) or subfertile (n=11) strains. At slaughter, cows were at a similar stage of lactation (fertile, 85 ± 1 d and subfertile, 87 ± 1 d postpartum, respectively). Cows were slaughtered on either d 17 of the estrous cycle [nonpregnant (n=10): fertile n=5; subfertile n=5] or d 17 of pregnancy [10d after embryo transfer, which was undertaken 7d after estrus (n=12, pregnant): fertile n=6, subfertile n=6]. Uterine luminal fluid was collected from each uterine horn of the pregnant (gravid and nongravid horns) and nonpregnant (horn ipsilateral and contralateral to the corpus luteum) cows. Plasma harvested on the day of slaughter and ULF samples were analyzed for AA determination using HPLC. The main effects of genetic strain, reproductive status, and their interactions on ULF and plasma AA content were tested. Additionally, the effect of uterine horn on ULF AA was tested for the pregnant and nonpregnant cows. Reproductive status had the greatest effect on AA concentrations in ULF. The concentrations of Leu, Met, Phe, Val, 1-methyhistidine, Asp, essential, ketogenic, and branched-chain AA, and those AA classified as both glucogenic and ketogenic were greater in the ULF collected from pregnant cows, with taurine being lower. Additionally, we observed effects of uterine horn and genetic strain × uterine horn interaction for ULF AA concentrations. Concentrations of the essential AA plus Met and Phe were greater in the ULF from the gravid horn, irrespective of strain. The ULF from the gravid horn of fertile cows contained the greatest concentrations of nonessential, glucogenic, branched-chain AA, and Leu, Thr, Ala, Ser, and Asp. With the exception of Asp, plasma AA profiles were not different in fertile and subfertile strains. These data support the hypothesis that reproductive status modifies the AA profiles of the ULF and that these profiles differ in fertile and subfertile genetic strains. Successful pregnancy depends on the complex interactions between the developing conceptus and uterine environment. Understanding the mechanisms contributing to maternal-conceptus communication using models with divergent fertility phenotypes could provide information regarding novel mechanisms to improve dairy cow fertility.

Applying additive logistic regression to data derived from sensors monitoring behavioral and physiological characteristics of dairy cows to detect lameness.

The hypothesis was that sensors currently available on farm that monitor behavioral and physiological characteristics have potential for the detection of lameness in dairy cows. This was tested by applying additive logistic regression to variables derived from sensor data. Data were collected between November 2010 and June 2012 on 5 commercial pasture-based dairy farms. Sensor data from weigh scales (liveweight), pedometers (activity), and milk meters (milking order, unadjusted and adjusted milk yield in the first 2 min of milking, total milk yield, and milking duration) were collected at every milking from 4,904 cows. Lameness events were recorded by farmers who were trained in detecting lameness before the study commenced. A total of 318 lameness events affecting 292 cows were available for statistical analyses. For each lameness event, the lame cow's sensor data for a time period of 14 d before observation date were randomly matched by farm and date to 10 healthy cows (i.e., cows that were not lame and had no other health event recorded for the matched time period). Sensor data relating to the 14-d time periods were used for developing univariable (using one source of sensor data) and multivariable (using multiple sources of sensor data) models. Model development involved the use of additive logistic regression by applying the LogitBoost algorithm with a regression tree as base learner. The model's output was a probability estimate for lameness, given the sensor data collected during the 14-d time period. Models were validated using leave-one-farm-out cross-validation and, as a result of this validation, each cow in the data set (318 lame and 3,180 nonlame cows) received a probability estimate for lameness. Based on the area under the curve (AUC), results indicated that univariable models had low predictive potential, with the highest AUC values found for liveweight (AUC=0.66), activity (AUC=0.60), and milking order (AUC=0.65). Combining these 3 sensors improved AUC to 0.74. Detection performance of this combined model varied between farms but it consistently and significantly outperformed univariable models across farms at a fixed specificity of 80%. Still, detection performance was not high enough to be implemented in practice on large, pasture-based dairy farms. Future research may improve performance by developing variables based on sensor data of liveweight, activity, and milking order, but that better describe changes in sensor data patterns when cows go lame.

Calving body condition score affects indicators of health in grazing dairy cows.

The objectives of this study were to determine the effect of calving body condition score (BCS) on cow health during the transition period in a pasture-based dairying system. Feed inputs were managed during the second half of the previous lactation so that BCS differed at drying off (BCS 5.0, 4.0, and 3.0 for high, medium, and low treatments, respectively: a 10-point scale); feed allowance was managed after cows were dried off, such that the BCS differences established during lactation remained at the subsequent calving (BCS 5.5, 4.5, and 3.5; n=20, 18, and 19, for high, medium, and low treatments, respectively). After calving, cows were allocated pasture and pasture silage to ensure grazing residuals >1,600 kg of DM/ha. Milk production was measured weekly; blood was sampled regularly pre- and postpartum to measure indicators of health, and udder and uterine health were evaluated during the 6 wk after calving. Milk weight, fat, protein, and lactose yields, and fat content increased with calving BCS during the first 6 wk of lactation. The effect of calving BCS on the metabolic profile was nonlinear. Before calving, cows in the low group had lower mean plasma ß-hydroxybutyrate and serum Mg concentrations and greater mean serum urea than cows in the medium and high BCS groups, which did not differ from each other. During the 6 wk after calving, cows in the low group had lower serum albumin and fructosamine concentrations than cows in the other 2 treatment groups, whereas cows in the low- and medium-BCS groups had proportionately more polymorphonucleated cells in their uterine secretions at 3 and 5 wk postpartum than high-BCS cows. In comparison, plasma ß-hydroxybutyrate and nonesterified fatty acid concentrations increased linearly in early lactation with calving BCS, consistent with a greater negative energy balance in these cows. Many of the parameters measured did not vary with BCS. The results highlight that calving BCS and, therefore, BCS through early lactation are not effective indicators of functional welfare, with the analyses presented indicating that both low and high BCS at calving will increase the risk of disease: cows in the low group were more prone to reproductive compromise and fatter cows had an increased risk of metabolic diseases. These results are important in defining the welfare consequences of cow BCS.

Behavioral and physiological effects of a short-term feed restriction in lactating dairy cattle with different body condition scores at calving.

Body condition score (BCS) around calving, and the typical BCS loss for up to 100 d after parturition, is associated with both production and reproductive performance of dairy cattle. In addition, there is public concern that thin cows may have impaired welfare, particularly in early lactation where feed demand exceeds pasture growth, and a lag exists between peak milk energy requirements and intake. The aim of this experiment was to determine how BCS at calving influences behavioral and physiological responses to a short-term feed restriction at 47 DIM. Body condition score (on a 10-point scale) at calving was manipulated by modifying the diets in the previous lactation of healthy dairy cattle to generate 3 treatment groups: low BCS (3.4; n=17), medium BCS (4.6; n=18), or high BCS (5.4; n=20). Cows were tested in 4 groups for 8 consecutive days; testing consisted of different levels of feed allocation (d 1 and 2: 100%; d 3 and 4: 75%; d 5: 50%; d 6 to 8: 125%), where 100% was 15kg of DM/cow per day. All BCS groups had similar and marked behavioral and physiological responses to feed restriction. For example, they increased vocalization, time spent eating silage and grazing, aggressive behavior, and fat metabolism (as measured by concentrations of ß-hydroxybutyrate and nonesterified fatty acids), and reduced milk production. Body condition affected some of these responses. Fewer cows with low BCS engaged in aggressive interactions in a feed competition test (trough filled with silage that could be consumed in 15 min) on the first day of feed restriction (low: 32%; medium: 74%; high: 64%; standard error of difference=15.4%). High BCS cows had greater concentrations of ß-hydroxybutyrate and nonesterified fatty acids throughout the experimental period, which suggests more fat mobilization; however, plasma leptin and fecal glucocorticosteroid metabolite concentrations were unaffected by BCS. Whereas cows demonstrated marked responses to feed restriction, the results suggest that a BCS of 3.4, 4.6, or 5.4 in healthy cows at calving does not overwhelmingly influence this response at 47 DIM.

Technical note: Effects of an epinephrine infusion on eye temperature and heart rate variability in bull calves.

Changes in autonomic nervous system (ANS) activity are one of the first phases of a stress response, but they are rarely used to assess the welfare of farm animals. Eye temperature measured using infrared thermography (IRT) is proposed as an indicator of ANS activity because it may reflect changes in blood flow in the capillary beds of the conjunctiva. The aim was to determine whether epinephrine infusion would initiate eye temperature changes in calves. Sixteen 4-mo-old Friesian calves (124±5 kg) were assigned randomly to receive a jugular infusion of either epinephrine (4 µg/kg per min for 5 min) or saline. Eye temperature (°C), heart rate (HR), and HR variability (HRV) were recorded from 15 min before infusion until 10 min after it was completed. Blood samples collected via jugular catheter were assayed for epinephrine, norepinephrine, and cortisol concentrations, and packed cell volume (PCV) was measured. No changes in any variable were observed with the saline infusion. Plasma epinephrine concentrations increased 90-fold with epinephrine infusion, which was associated with a decrease in eye temperature of 1.4±0.05°C. During epinephrine infusion, plasma norepinephrine concentrations decreased by half and HR decreased by 9.3±3.3 beats/min. The HRV measure, the root mean square of successive differences, increased by 49.7±9.2 ms, indicating a compensatory increase in parasympathetic activity. After epinephrine infusion, plasma cortisol concentrations increased by 10.4±1.7 ng/mL and PCV was higher (38 vs. 31±0.1%, epinephrine vs. saline, respectively). These results support the hypothesis that changes in eye temperature are mediated by the sympathetic component of the ANS. Infrared thermography is a noninvasive method to assess ANS activity for evaluating welfare of cattle.

Noninvasive assessment of autonomic activity for evaluation of pain in calves, using surgical castration as a model.

The role of the autonomic nervous system (ANS) in mediating eye temperature responses during painful procedures was examined in thirty 4-mo-old bull calves randomly assigned to 4 treatments: 1) sham handling control (C; n=8), 2) surgical castration (SC; n=6), 3) local anesthesia with sham handling (LAC; n=8), and 4) local anesthesia with surgical castration (LASC; n=8). Maximum eye temperature ( degrees C), measured by infrared thermography, heart rate (HR), and heart rate variability (HRV) were recorded continuously from 25 min before to 20 min after castration. The HRV was analyzed by examining segments of 512 interbeat intervals before and after treatments and comparing the root mean square of successive differences (RMSSD), high and low frequency (HF and LF, respectively) power, and the ratio of LF and HF powers (LF:HF). Jugular blood samples were analyzed for norepinephrine and epinephrine in C and SC treatments and for cortisol during all treatments. There was an immediate increase in HR following castration in SC (+15.3+/-2.8 beats/min) and LASC (+6.3+/-2.4 beats/min) calves. Eye temperature increased during the 20-min observation period in SC and LASC calves (+0.47+/-0.05 degrees C and +0.28+/-0.05 degrees C, respectively), and there was a small increase in C calves (+0.10+/-0.05 degrees C). Following castration in SC calves, there was an increase in RMSSD (+25.8+/-6.4) and HF power (+11.0+/-6.5) and LF:HF decreased (-2.1+/-0.7). Following castration in LASC, there was an increase in RMSSD (+18.1+/-4.9) and a decrease in LF power (-10.2+/-5.0). Cortisol increased above baseline within 15 min following treatment in both castrated groups, but was greater for SC calves (+18.4+/-2.3 ng/mL) than for LASC calves (+11.1+/-1.9 ng/mL). After castration, norepinephrine increased 3-fold and epinephrine increased by half in SC calves but not in C calves. There were no changes in HR, HRV, or cortisol responses to C or LAC treatments. Local anesthetic reduced, but did not eliminate, responses to surgical castration. The synchronized increase in catecholamine and HR responses immediately following SC treatment suggests the initial response was mediated by the sympathetic branch of the ANS. The subsequent changes in RMSSD, HF power, and LF:HF ratio indicated this was followed by an increase in parasympathetic activity. The use of HR, HRV, and infrared thermography measurements together provide a noninvasive means to assess ANS responses as indicators of acute pain in cattle.

The development of reproductive management practices in New Zealand: what will the future hold in a consumer-focused, environmentally-conscious, export-driven marketplace?

The New Zealand (NZ) economy and its dairy industry are sensitive to global consumer perception of farming practices used to generate milk products because milk exports account for > 25% of national export earnings and > 90% of milk produced is exported as products. Astute management of product image and market risk is, therefore, important for the viability of the industry and country. More than 95% of milk produced in NZ comes from strictly seasonal, pasture-based systems, with associated constraints on reproductive performance. Increasing herd sizes, operational changes and genetic selection priorities have further challenged dairy farmers to achieve optimal levels of herd fertility. Reproductive management practices have developed to address the need to maintain a 365-day inter-calving interval, essentially through maximizing the number of cyclic cows during the breeding period and minimizing the duration of the seasonal calving period. Aspects of the hormonal interventions developed and routinely used to achieve these objectives have been the subject of product quality and market risk concerns forcing the industry to explore alternative ways of achieving reproductive performance goals. One approach has been to exploit the inherently high level of fertility in NZ dairy herds. This approach has seen the inclusion of fertility-related traits in the national genetic evaluation system to prevent further decline in genetic fertility. More recently, a nationally coordinated extension program has been adopted to support farmers and their advisors to identify, prioritize and improve on key management areas for incremental gains in herd reproductive performance. Advances in automation and bio-sensing are yet to make a significant impact, but remain potentially valuable additions in supporting the dairy farmer to manage the areas having the largest effects on reproductive performance.

Effects of reduced frequency of milk removal on gene expression in the bovine mammary gland.

Regulation of milk synthesis and secretion is controlled mostly through local (intramammary) mechanisms. To gain insight into the molecular pathways comprising this response, an analysis of mammary gene expression was conducted in 12 lactating cows shifted from twice daily to once daily milking. Tissues were sampled by biopsy from adjacent mammary quarters of these animals during the two milking frequencies, allowing changes in gene expression to be assessed within each animal. Using bovine-specific, oligonucleotide arrays representing 21,495 unique transcripts, a range of differentially expressed genes were found as a result of less frequent milk removal, constituting transcripts and pathways related to apoptotic signaling (NF-kappaB, JUN, ATF3, IGFBP5, TNFSF12A) mechanical stress and epithelial tight junction synthesis (CYR61, CTGF, THBS1, CLDN4, CLDN8), and downregulated milk synthesis (LALBA, B4GALT1, UGP2, CSN2, GPAM, LPL). Quantitative real-time PCR was used to assess the expression of 13 genes in the study, and all 13 of these were correlated (P < 0.05) with values derived from array analysis. It can be concluded that the physiological changes that occur in the bovine mammary gland as a result of reduced milk removal frequency likely comprise the earliest stages of the involution response and that mechano-signal transduction cascades associated with udder distension may play a role in triggering these events.

Comparing subpopulations of plasma progesterone using cluster analyses.

The production of progesterone during the luteal phase of the estrous cycle regulates early embryonic development, uterine function, and luteal function. Plasma progesterone concentrations were measured during a spontaneous estrous cycle in lactating Holstein-Friesian cows of New Zealand or North American ancestry, fed either fresh pasture or a total mixed ration. Subpopulations of profiles were identified using 2 approaches: 1) shape-based clustering and 2) trait-based clustering. Subpopulations of profiles were compared using key progesterone profile components, which described the early and late luteal phase of the estrous cycle. The application of resistant nonlinear smoothing functions across raw progesterone profiles resulted in a high degree of agreement between the raw data and smoothed estimates (R(2) = 0.93). Both clustering techniques resulted in the identification of 3 similar subpopulations of progesterone profiles. The distribution of animals in these defined subpopulations and the association with cow strain and diet were examined. The early luteal phase was similar for the shape-based categories, but differed in the trait-based analyses. Differences in the late luteal phase and the onset of functional luteal regression in the different clusters were evident for both the shape- and trait-based analyses. The distribution of animals across the subpopulations identified by shape-based clustering was not associated with either cow strain or diet. However, within the 3 subpopulations identified using trait-based clustering, cow strain affected the shape of the progesterone profile. Isolation of 3 subpopulations within a small data set showed that otherwise normal progesterone profiles exhibit significant variation. The differences in the luteal phase of these subpopulations, in particular progesterone early in the luteal phase and the early onset of functional luteal regression, may provide an insight into factors associated with subfertility.

Effects of local anesthetic and a nonsteroidal antiinflammatory drug on pain responses of dairy calves to hot-iron dehorning.

This study examined the effects of a nonsteroidal antiinflammatory agent (NSAID) on physiological responses of calves immediately after hot-iron dehorning (DH) and during the time that local anesthetic (LA) wears off (2 to 3 h) after this procedure. Forty-six calves (33 +/- 0.3 d of age) were randomly assigned to 6 treatments: hot-iron DH versus sham DH with either no pain mitigation, LA alone, or LA with NSAID (i.v. Meloxicam). Eye temperature (measured using infrared thermography) was recorded every 5 min for 3 h after treatments. Heart rate (HR) and heart rate variability (HRV) were recorded continuously; for analysis of HRV, short segments of 512 interbeat intervals were examined. After DH without LA or NSAID, HR increased by 35 +/- 3.0 beats/min in the first 5 min and remained elevated above baseline for 3 h. The HRV around the time of DH did not differ between treatments; however, the root mean square of successive differences decreased from 68 to 41 +/- 12.6 ms immediately following DH without pain relief, suggesting a decrease in vagal tone at this time. Between 2 and 3 h following DH with LA, there was a decrease in eye temperature (-0.6 +/- 0.1 degrees C), an increase in HR (8 +/- 3.0 beats per min) and changes in HRV. Changes in HRV at this time included a decreased high-frequency power and an increase in the low-frequency power and low-frequency/high-frequency ratio, indicating a change in sympatho-vagal balance. The changes in eye temperature, HR, and HRV between 2 and 3 h following DH with LA indicated the onset of pain coinciding with the time that the LA effects wear off. In addition, this study demonstrated that the combination of LA and NSAID mitigated the onset of pain responses when the LA wanes.

Somatotropic axis components and nutrient partitioning in genetically diverse dairy cows managed under different feed allowances in a pasture system.

The somatotropic axis [including growth hormone (GH), GH receptor, and insulin-like growth factor (IGF)-I] is uncoupled in high-producing cows in early lactation so that the liver fails to respond to GH and produces less IGF-I. This uncoupling was implicated in the process of nutrient partitioning, enabling high milk production. Different genetic selection goals may affect functional components of the somatotropic axis. Thus, the somatotropic axis was examined in diverse genetic strains of dairy cows [North American Holstein 1990 (NA90), New Zealand Holstein-Friesian 1990 (NZ90), and New Zealand Holstein-Friesian 1970 (NZ70)] that were managed similarly within a pasture-based system but were offered feed allowances commensurate with their genetic ability to produce milk. The NA90 cows produced more milk (26.2 +/- 0.3, 24.1 +/- 0.3, and 20.1 +/- 0.4 kg/d, for NA90, NZ90, and NZ70, respectively), but had lower milk fat percentages (4.28 +/- 0.03, 4.69 +/- 0.03, and 4.58 +/- 0.04 kg/d for NA90, NZ90, and NZ70, respectively) compared with both NZ strains. Milk protein percentages (3.38 +/- 0.02, 3.52 +/- 0.02, and 3.29 +/- 0.03 kg/d for NA90, NZ90, and NZ70, respectively) were greater for NZ90 cows. During early lactation (wk 2 to 6), the total net energy produced in milk was greater in NA90 compared with NZ90 or NZ70 cows, but total net energy in milk after wk 6 was equivalent for NA90 and NZ90 cows. The greater milk production in early lactation in NA90 cows was associated with lower body condition scores (BCS; 1 to 10 scale; 4.0 +/- 0.1) elevated blood GH concentrations (1.6 +/- 0.1 ng/mL), and low blood IGF-I concentrations (14.8 +/- 1.1 ng/mL), indicating an uncoupled somatotropic axis. In comparison, the NZ70 cows retained a coupled somatotropic axis during early lactation, maintaining greater BCS (4.6 +/- 0.1), lower blood GH (0.7 +/- 0.1 ng/mL), and greater blood IGF-I (21.9 +/- 1.2 ng/mL). The degree of uncoupling in NZ90 cows was intermediate between the other 2 strains. Additional feed allowance failed to change blood IGF-I concentrations in NA90 cows but increased IGF-I concentrations in NZ90 cows (20.9 +/- 1.4 and 13.2 +/- 1.4 ng/mL for the high and low feed allowance, respectively). Furthermore, additional feed allowance in NZ90 cows lessened BCS loss in early lactation, but did not affect BCS loss in NA90 cows. Functional components of the somatotropic axis differed for the respective strains and were consistent with strain differences in milk production, BCS, and feed allowance.

A comparison of three strains of holstein-friesian grazed on pasture and managed under different feed allowances.

This experiment compared Holstein-Friesian (HF) cows of New Zealand (NZ) origin representative of genetics present in the 1970s (NZ70; n = 45) and 1990s (NZ90; n = 60), and a group of HF cows of North American origin with 1990s genetics (NA90; n = 60), which were managed in grazing systems with a range of feeding allowances (4.5 to 7.0 t/cow per yr) over 3 yr. The NZ70 cows had the lowest Breeding Worth genetic index and the lowest breeding values for yields of fat, protein, and milk volume; the NZ90 and NA90 cows were selected to have similar breeding values for milk traits and were representative of cows of high genetic merit in the 1990s. The NZ90 cows had a higher milk protein concentration (3.71%) than either the NA90 (3.43%) or the NZ70 cows (3.41%), and a higher milk fat concentration (4.86%) than the NA90 cows (4.26%) with a level similar to the NZ70 cows (4.65%). The NZ90 cows produced significantly greater yields of fat, protein, and lactose than the NA90 and NZ70 cows. The NZ70 cows had the lowest mean annual body weight (473 kg) but the highest body condition score (BCS; 5.06). Days in milk were the same for the 2 NZ strains (286 d in milk), both of which were greater than the NA90 cows (252 d in milk). There was no genotype x environment interaction for combined milk fat and protein yield (milksolids), with NZ90 producing 52 kg/cow more than the NA90 at all feeding levels. The NZ70 strain had the highest seasonal average BCS (5.06), followed by the NZ90 (4.51) and the NA90 (4.13) strains on a 1 to 10 scale. Body condition score increased with higher feeding levels in the 2 NZ strains, but not in the NA strain. The first-parity cows commenced luteal activity 11 d later than older cows (parities 2 and 3), and the NA90 cows commenced luteal activity 4 and 10 d earlier than the NZ70 and NZ90 cows. Earlier estrus activity did not result in a higher in-calf rate. The NZ70 and NZ90 cows had similar in-calf rates (pregnancy diagnosed to 6 wk; 69%), which were higher than those achieved by NA90 cows (54%). Results showed that the NA90 strain used in this experiment was not suitable for traditional NZ grazing systems. Grazing systems need to be modified if the NA90 strain is to be successfully farmed in NZ. The data reported here show that the NA90 cows require large amounts of feed, but this will not prevent them from having a lower BCS than the NZ strains. Combined with poor reproductive performance, this means that NA90 cows are less productive than NZ HF in pasture-based seasonal calving systems with low levels of supplementation.

Metabolic adaptations associated with irreversible glucose loss are different to those observed during under-nutrition.

In this study the hypothesis that irreversible glucose loss results in an 'uncoupling' of the somatotrophic axis (increasing plasma GH levels and decreasing plasma IGF-I) was tested. During periods of negative energy balance the somatotrophic axis respond by increasing plasma GH and decreasing plasma IGF-I levels. In turn, elevated GH repartitions nutrient by increasing lipolysis and protein synthesis, and decreases protein degradation. Irreversible glucose loss was induced using sub-cutaneous injections of phloridizin. Seven non-lactating cows were treated with 8g/day phloridizin (PHZ) and seven control animals (CTRL, 0g/day), while being restricted to a diet of 80% maintenance. PHZ treatment increased urinary glucose excretion (P<0.001), resulting in hypoglycemia (P<0.001). As a response to this glucose loss, the PHZ treated animals had elevated plasma NEFA (P<0.005) and BHBA (P<0.001) levels. Average plasma insulin concentrations were not altered with PHZ treatment (P=0.059). Plasma GH was not different between the two groups (P>0.1), whereas plasma IGF-I levels decreased significantly (P<0.001) with PHZ treatment. The decline in plasma IGF-I concentrations was mirrored by a decrease in the abundance of hepatic IGF-I mRNA (P=0.005), in addition the abundance of hepatic mRNA for both growth hormone receptors (GHR(tot) and GHR(1A)) was also decreased (P<0.05). Therefore, the irreversible glucose loss resulted in a partial 'uncoupling' of the somatotrophic axis, as no increase in plasma GH levels occurred although plasma IGF-I levels, hepatic IGF-I mRNA declined, and the abundance of liver GH receptor mRNA declined.

Sprinklers and shade cool cows and reduce insect-avoidance behavior in pasture-based dairy systems.

The body temperature of dairy cows in pastoral systems during summer reaches a peak during and following the p.m. milking. Shade and sprinklers can be used separately or in combination at the milking parlor to reduce heat load. Farmers anecdotally report that the use of sprinklers reduces irritation from insects that occurs while cows are waiting for milking. Once daily, we assessed the effectiveness of short-term exposure to shade and sprinklers for cooling cows [via respiration rate and body (vaginal) temperature] and reducing insect-avoidance behaviors before the p.m. milking in a pasture-based dairy system. Head position was measured as an indicator of whether cattle were avoiding water from the sprinklers. Forty-eight Holstein-Friesian dairy cows were divided into 12 groups (4 cows per group, n = 3 groups/treatment) and were exposed to 1 of 4 treatments for 90 min before the p.m. milking: 1) shade, 2) sprinklers, 3) shade and sprinklers, or 4) uncooled control. Respiration rate was reduced by 30% with shade alone compared with controls [54 vs. 78 +/- 2.3 ( +/- SED) breaths/min, respectively]. Sprinklers alone (30 +/- 2.3 breaths/min) and the combined effects of shade and sprinklers (24 +/- 2.3 breaths/min) reduced the respiration rate by 60 and 67%, respectively, compared with controls. Shaded cows had lower body temperatures during the 90-min treatment period compared with controls (shade: 38.6 degrees C; shade and sprinklers: 38.6 degrees C; control: 38.9 +/- 0.09 degrees C). The decrease in body temperature of cows under sprinklers was more marked than for shade alone and remained lower for at least 4 h after milking (sprinklers: 38.7 degrees C; shade and sprinklers: 38.6 degrees C; shade: 38.9 degrees C; control: 39.2 +/- 0.10 degrees C). The sprinkler treatment reduced the number of tail flicks (control: 12.6 vs. sprinklers: 6.6 +/- 2.4 flicks/min) and hoof stamps (control: 4.4 vs. sprinkler: 2.2 +/- 0.5 stamps/min). Cows exposed to sprinklers spent more time with their heads lowered compared with cows in the shaded and control treatments. The reductions in body temperature and respiration rate attributable to shade and sprinklers were greatest when the temperature-humidity index and heat-load index were > or = 69 and 77, respectively, and cows benefited from cooling when these levels were exceeded.

A comparison of three strains of Holstein-Friesian cows grazed on pasture: growth, development, and puberty.

With the introduction of a protein milk payment system in New Zealand in 1988, there was an influx of North American (NA) Holstein-Friesian (HF) genetics into New Zealand (NZ) dairy herds, leading to an increase in the average percentage of NA genetics in NZ HF cows--from 2% in 1980 to 38% in 1999. Of interest has been the effect this change has had on farm profitability and on the management required for these animals, as well as the phenotypic changes that have occurred within the national herd under the breeding programs operated in NZ from 1970 to 1990. The objective of this study was to quantify differences in body dimensions, body weights, and puberty-related parameters among 3 strains of HF, representing animals of NZ origin representative of the genetics present in 1970 and 1990 and of NA origin with 1990s genetics. A total of 172 animals born in 1999 were compared. The strains were 1) NZ70, a strain of NZ Friesian (average 7% NA genetics) equivalent to high-genetic-merit (high Breeding Worth) cows farmed in the 1970s; 2) NZ90, a strain of HF of NZ origin (average 24% NA genetics) typical of the animals present in the 1990s; and 3) NA90, a strain of HF of NA origin (average of 91% NA genetics) typical of animals present in the 1990s. The differences in BW among all strains were significant at 6 and 12 mo of age. At 15 and 24 mo, the 2 NZ strains were significantly lighter than the NA90 animals. At 24 mo of age (i.e., prior to first calving), the NA90 strain animals (BW = 515 kg) were 22 and 34 kg heavier than the NZ90 and NZ70 strains. The body length of the NA90 strain was greater than either of the 2 NZ strains; the differences among the NA90 strain and the 2 NZ strains varied from 2 to 6 cm, with the differences generally being greater at older ages. The trend in heart girth difference among strains was similar to that observed for body length. The wither height of the NA90 animals was greater than that of the NZ strains by 1 to 7 cm, although there was no significant difference between the NA90 and NZ90 strains at birth. At puberty the NA90 heifers were 20 d older and 20 kg heavier than the NZ90 heifers, which in turn were 25 kg and 25 d older than the NZ70 heifers. The NA90 strain had a heavier mature body weight, and their older age at puberty suggested either that they mature later or that, under pastoral conditions, their growth rate is limited by their inability to consume sufficient metabolizable energy as grazed pasture, with a consequent delay in puberty. Results from this study will be useful in revising target BW in growing heifers of different germplasm.

Non-invasive measurement of stress in dairy cows using infrared thermography.

The possibility that changes in eye temperature, measured using infrared thermography (IRT), can detect stress in dairy cattle was examined by six different stimulations of the stress axis. Six cows were given six treatments in a random Latin-square design: 1) Control (saline) 2) ACTH (0.05 mg Synacthen) 3) bCRH (20 mug) 4) bCRH (40 mug) 5) epinephrine (1.4 mug /kg liveweight) and 6) social isolation. Treatments were administered at time 0 and blood samples were taken at -30, -15, 0, 5, 10, 15, 20, 30, 40, 50, 60, 75, 90, 120, 180 and 240 min except for epinephrine which was sampled at -30, -15, -10, -5, 0, 2, 5, 10, 15, 20, 30, 45, 60, 90 and 120 min. Core body temperature was recorded every 10 min and eye images collected every 2 min. Eye temperature and cortisol increased following catheterization (P<0.05). ACTH increased following bCRH, cortisol increased following ACTH and bCRH (P<0.001) and NEFA increased following epinephrine (P<0.001). Core body temperature was unaffected by treatments. Eye temperature was unaffected by CRH and epinephrine but was higher 30 and 60 min following control and ACTH (P<0.001). Our results provide evidence that exogenous HPA stimulation does not increase eye temperature. The increases in eye temperature following catheterization however raise the possibility that a cognitive component may be required for an eye temperature response to occur.

Effect of monopropylene glycol on luteinizing hormone, metabolites, and postpartum anovulatory intervals in primiparous dairy cows.

This study examined the effect of monopropylene glycol (MPG) supplementation on LH secretion, postpartum interval to first ovulation, and milk production in heifers calving with poor body condition score (BCS). Forty-seven heifers were allocated to 3 treatments: 1) heifers with high BCS (BCH; n = 13) that calved at a BCS of 3.4 (BCS scale of 1 to 5); 2) heifers with low BCS (BCL; n = 17) that calved at a BCS of 2.8; and 3) heifers with low BCS that calved at a BCS of 2.8 and were assigned to receive MPG supplementation (BCL + MPG; n = 17) and grazed pasture ad libitum. Monopropylene glycol was drenched (250 mL) twice daily for 16 wk after calving. Patterns of change in plasma LH were measured at 2 and 5 wk after calving. Pulsatile release of LH at 2 and 5 wk was greater in BCL + MPG and BCH cows compared with the BCL control cows. The BCL + MPG cows had lower NEFA concentrations than did the BCL cows during wk 1 to 6 after calving. At 12 wk postpartum, the proportion of cows cycling was 77, 82, and 28% for the BCH, BCL + MPG, and BCL treatments, respectively. Mean milk fat yield was greater for the BCH treatment during the first 12 wk postpartum compared with the BCL + MPG or BCL treatments, which did not differ from each other. Results of this study indicate that MPG supplementation reduced the interval from calving to first ovulation in heifers having poor body condition at calving.

Precalving effects on metabolic responses and postpartum anestrus in grazing primiparous dairy cows.

The effect of increased access to pasture feeding during the last 6 wk of gestation on metabolic responses and postpartum anestrous interval was investigated. Heifers with a body condition score (BCS) of 5.0 (BC5+FF; on a 1-to-10 scale, US = 1.5 + 0.32 x New Zealand) were offered unrestricted pasture, and those with BCS 4.0 were fed either pasture unrestricted (BC4+FF) or restricted (BC4+RES) for the last 6 wk of gestation. After calving, all groups were offered unrestricted pasture. Mean BCS at calving for BC5+FF, BC4+FF, and BC4+RES were 4.7 +/- 0.1, 4.3 +/- 0.1, and 3.5 +/- 0.1, respectively. At 35 d postpartum, LH pulse frequency was lower in BC4+RES than in BC4+FF and BC5+FF, which were similar. At 77 d after calving, 8% of BC4+RES cows had ovulated compared with 75% of BC4+FF and 69% of BC5+FF cows. Metabolic hormonal differences between BC4+FF and BC4+RES were not reflected in the differences between BC4+FF and BC5+FF for LH pulse frequency or ovulation. Unrestricted access to pasture during the final 6 wk of gestation for BC4 heifers reduced the risk of prolonged postpartum anestrus. Systemic factors, tissue sensitivity, and critical developmental set points are probably involved in the integrated control of ovulation by body condition.

Invited review: Treatment of cows with an extended postpartum anestrous interval.

Cows with an extended interval from calving to first ovulation (PPI) have increased intervals from calving to conception and are more likely to be culled compared with cows with a short PPI. In year-round calving dairy herds, between 11 and 38% of cows are reported as anestrus by 50 or 60 d after calving. In seasonally calving dairy herds, between 13 and 48% of cows are diagnosed as anovulatory anestrus at the start of the breeding period. Ovulation and estrus after calving are delayed when the positive feedback effects of estradiol on release of LH from the pituitary, and circulating concentrations of metabolic hormones such as insulin and insulin-like growth factor-I, are reduced by a variety of environmental factors. The main factors are limited energy intake, lower body reserves, increased partitioning of energy to milk production, suckling, and peripartum disease. Treatment options for cows with an extended PPI include hormonal and management strategies. Hormonal treatments that include a period of progesterone supplementation result in the majority of treated animals displaying estrus with a subsequent luteal phase of normal duration and improved pregnancy rates compared with untreated controls. Hormonal interventions also tend to have more predictable outcomes compared with management changes, such as manipulating body condition or dietary intakes after calving, and usually have some estrous synchronization effect, thus facilitating the use of artificial insemination. However, responses to any treatment are variable and are related to those factors that influence duration of the PPI, such as body condition and parity.

Effect of dietary intake on steroid feedback on release of luteinizing hormone in ovariectomized cows.

This study tested the hypothesis that the decline in pulsatile release of luteinizing hormone (LH), resulting from steroid negative feedback, is greater in animals fed a low, compared with a high, plane of nutrition. Two-year-old cows were ovariectomized and six days later were fed diets to provide 1.5 x maintenance requirements (n = 6, supplemented) or 0.5 x maintenance requirements (n = 6, restricted) (Round 1). Pulsatile release of LH was measured over a 14-h period on the fifth day of feeding these diets (Day 1); at 6 h, all animals were treated with an intravaginal insert containing 1.38 g progesterone, which remained in place until the end of Day 3. Pulsatile release of LH was again measured for 14 h on Day 3; at 6 h, all animals were injected intramuscularly with oestradiol benzoate (ODB; 1 mg per 500 kg live weight). Three days later, this protocol was repeated, in a cross-over design, with cows that were previously restricted now being supplemented and those cows previously supplemented, now restricted (Round 2). Plasma concentrations of progesterone after intravaginal progesterone treatment were 1.01 ng mL(-1) higher in restricted cows compared with supplemented cows (P < 0.001) and were also higher in Round 1 than in Round 2 and on Day 1 than on Day 3 (P < 0.001). Plasma concentrations of oestradiol following injection with ODB did not differ between supplemented and restricted cows (P > 0.1). Dietary intake did not affect mean concentrations of LH, pulse frequency or amplitude during the 6-h period before steroid treatment or the change in these variables following steroid treatment; however, the slope of the decline in concentrations of LH following progesterone treatment was significantly more negative in cows fed restricted diets compared with those fed supplemented diets. In Round 2, mean concentrations of LH were higher preceding, and decreased more following, progesterone treatment compared with the decrease after ODB treatment. In conclusion, acute dietary restriction resulted in a more rapid decline in the release of LH following treatment with intravaginal progesterone, and was associated with higher concentrations of progesterone in plasma.