Journal Articles
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Item Teat and udder morphology and pathology of New Zealand dairy ewes.(Taylor and Francis Group, 2025-02-12) Chambers G; Lawrence KE; Ridler AL; Laven RAAIMS: To describe the morphology and prevalence of teat and udder pathology of New Zealand dairy ewes. METHODS: A repeated cross-sectional study was conducted on 20 commercial New Zealand dairy sheep farms over the 2022-2023 season. Approximately 15 randomly selected ewes were examined on each farm in early, mid, and late lactation. Four udder morphology measures were scored on a 5-point scale: depth (1 = pendulous, 5 = compact udder), suspension (ratio of width at abdominal attachment to height, 1 = low, 5 = high), gland separation (1 = zero, 5 = maximum separation), and teat placement (1 = distally located, vertically oriented, 5 = laterally located, horizontally oriented teats). Teat length and width were measured, and the presence of supernumerary teats, asymmetry, visible teat/udder inflammation, and lesions were recorded. Teats and glands were palpated for consistency, gland-nodules, teat canal thickening, and patency, and teat ends scored for hyperkeratosis. Teat and gland-level pathological variables were converted to ewe-level scores. The presence of involuted, non- or minimally lactating glands was recorded. Data were analysed using descriptive statistics. RESULTS: Across the three visits, 893 observations were made on 882 unique ewes. Mean teat length and width were 27.5 (95% CI = 27.2-27.7) and 15.8 (95% CI = 15.7-15.9) mm. Udder depth, separation, suspension, and teat placement had modal scores of 4, 3, 3, and 3 respectively, and varied across visits and age groups. Asymmetrical udder prevalence was 39% (95% CI = 35.5-42%) overall and increased with age (27% for 1-year-olds, 38% for two-year-olds, 43% for mixed age ewes). Supernumerary teats were observed in 15% (95% CI = 13-17.9%) of ewes. There was between-farm variation in all udder morphology variables. Ewe-level prevalences of teat end hyperkeratosis (any degree of severity), gland/teat inflammation, lesions, palpable defects, and involuted glands were all < 6%. CONCLUSIONS: Morphological observations resembled those from overseas dairy sheep. Teat dimensions, udder depth, separation, suspension, teat placement, and presence of supernumerary teats varied between farms. Udder depth, separation, and suspension scores decreased with age, while teat placement score and the prevalence of asymmetry increased with age. Teat and udder pathology were rare. CLINICAL RELEVANCE: This is the first systematic study of teat and udder morphology and pathology in New Zealand dairy ewes. The data will be useful for farmers and industry partners, providing a comparison with their own flocks, identifying areas for improvement, and informing and contrasting with future studies.Item Pathophysiology of Penetrating Captive Bolt Stunning in Horned and Polled Sheep and Factors Determining Incomplete Concussion.(MDPI (Basel, Switzerland), 2025-01-13) Gibson TJ; Ridler AL; Limon G; Lamb C; Williams A; Gregory NG; Bø-Granquist EGPenetrating captive bolt (PCB) is widely used for stunning and on-farm dispatch of livestock, yet its efficacy can vary, with the potential for animal welfare compromise. This study investigated the pathophysiology of PCB-induced trauma in horned and polled sheep (Ovis aries), focusing on factors contributing to incomplete concussion. Thirty-seven (n = 18 horned Scottish blackface and n = 19 polled North Country mule) mature ewes (aged 4-10 years) were shot with PCB with varying cartridge power and PCB modifications, followed by clinical assessment and post-mortem analysis using magnetic resonance imagining (MRI) and gross pathology. The results indicated that damage to the reticular activating system, bolt velocity and penetration depth are crucial for inducing irreversible unconsciousness, with depths less than 37 mm often resulting in incomplete concussion. MRI provided detailed insights into brain injuries, aligning well with gross pathological findings. This study highlights the importance of precise bolt placement and appropriate PCB configurations in ensuring humane outcomes, with MRI proving to be a valuable tool for assessing brain trauma in stunned animals. These findings enhance the understanding of effective stunning techniques and support improved welfare practices in livestock management.Item Reduced anthelmintic use on 13 New Zealand sheep farms: farmer motivations and practical implementation(Taylor and Francis Group on behalf of the New Zealand Veterinary Association, 2024-09-19) Ridler AL; Hytten K; Gray DI; Reid JIAIMS: To describe the personal drivers, sources of information and gastro-intestinal parasite control methods used by a group of New Zealand sheep farmers identified as low users of anthelmintic (AHC), and their perception of the efficacy and impacts of this approach. METHODS: A convenience sample of 13 sheep farmers farming with a policy of reduced AHC use (no pre-determined routine treatments of ewes >19 months old and/or lambs not routinely treated at pre-determined intervals from weaning through to late autumn) were identified. Semi-structured interviews were conducted regarding their farming philosophy, motivations for reducing AHC use, perceptions of the impacts of farming with reduced AHC use, and parasite control practices. Semi-quantitative data were analysed using descriptive statistics for demographic data and categorising participants' use of AHC and non-chemical control methods. Qualitative data regarding participants' motivations, approaches and rationale were analysed by systematic analysis of the transcripts and distillation of key concepts. RESULTS: Participants had been operating with reduced AHC use for 3 to ≥20 years. Key motivators for reducing AHC use were a diagnosis of anthelmintic resistance (AR) or concerns about AR developing. Parasite management information came from a wide range of sources. All respondents expressed overall positive views regarding the impacts of reduced AHC use but detailed information was not available.All identified that regular monitoring, based primarily on subjective animal and non-animal factors was important for their parasite control strategy. Most used faecal egg counts (FEC), often in an ad hoc manner. Five never treated adult ewes, two routinely treated ewes prior to lambing with short-acting AHC and the remainder occasionally treated a small number in low body condition. Four routinely treated some or all lambs at 28-30-day intervals from weaning to late autumn while the remainder based their treatment decisions for lambs on monitored information. All placed heavy emphasis on feeding sheep well, ensuring high post-grazing residuals, and cross-grazing. CONCLUSIONS: AR was a key motivator for participants to reduce AHC use, and a range of information sources and decision-making processes were used. Key parasite management practices were monitoring, primarily using subjective assessments, emphasis on feeding stock well and cross-grazing. CLINICAL RELEVANCE: The rising prevalence of AR will likely result in increasing the motivation for sheep farmers to reduce their AHC use. Veterinarians will play a key role in providing advice and assistance to facilitate changes in parasite management.Item Where do all the ewes go? Ewe culling and mortality in 34 sheep flocks in New Zealand.(Taylor and Francis Group, 2024-10-17) Ridler AL; Corner-Thomas RA; Mote S; Morgan S; Kenyon PR; Flay KJAims To describe rates of and reasons for culling and mortality of ewes between breeding and mid-lactation on New Zealand sheep farms; to investigate associations of these variables with farm demographic variables; and to describe rates of and reasons for culling of ewes at weaning. Methods Participants were a convenience sample of 34 farms from across New Zealand. Demographic data were initially collected for each farm via a questionnaire administered in-person to the flock owner or manager. During approximately 8 months from breeding to mid-lactation, ewe tally, culling and mortality data were collected and used to calculate various parameters related to flock performance and to investigate associations. During the main ewe-culling event at weaning, ewe-culling data were collected from 29/34 flocks participating in the study. Results There was considerable variation between flocks, but the between-flock mean replacement percentage was 29.2 (SD 5.0)%. Overall, a between-flock mean of 10.5 (SD 4.6)% of ewes presented for breeding were culled or dead/missing by mid-lactation and thus did not rear any lambs. Additionally, from 27 flocks that reported data on ewes’ success at rearing lambs, a between-flock mean of 3.9 (SD 2.5)% of ewes that remained alive at mid-lactation failed to rear any lambs, resulting in an overall between-flock mean loss of 23.1 (SD 6.3) potential lambs per 100 ewes. Two-thirds of ewe mortalities between breeding and mid-lactation occurred during the lambing period. Model results showed flocks with higher pregnancy scanning percentages had lower rates of culling and mortality between breeding and mid-lactation. However, apart from farm contour, from breeding to mid-lactation there were no associations for culling and mortality with farm size, flock size, number of ewes per labour unit, whether ewe hoggets (7–9 months of age) were presented for breeding, or duration of the breeding period. A between-flock mean of 16.5 (SD 8.3)% of ewes present at weaning were culled, and among mixed-age ewes, the most common reasons for culling at this time were age, incisor teeth defects and udder defects. Conclusions To reduce unnecessary ewe culling and mortality, attention should be focused on maximising conception rates, ensuring judicious culling decisions, optimising body condition score, and identifying farm-specific causes of death over the lambing period to facilitate targeted intervention strategies. Clinical relevance Identifying why and when ewes exit flocks, and comparing it with the data presented here, will facilitate the development of flock-specific interventions to reduce ewe culling and mortality.Item Isolation of Aerobic Bacterial Species Associated with Palpable Udder Defects in Non-Dairy Ewes.(MDPI (Basel, Switzerland), 2024-08-09) Zeleke MM; Kenyon PR; Flay KJ; Aberdein D; Pain SJ; Velathanthiri N; Ridler AL; Zecconi AThe objectives of these studies were to identify associations between udder half defects (hard or lump) and bacteria isolated from milk or mammary tissue swabs, to compare with samples from normal udder halves at different physiological time points and to compare bacterial species isolated via milk and swabs of mammary tissue from within the same udder halves. A total of 1054 samples were aseptically collected from each udder half of 199 non-dairy breed (Romney) ewes from three different studies (Study A, n = 77; Study B, n = 74; and Study C, n = 48). Conventional bacterial culture and MALDI-ToF mass spectrometry were used for bacterial identification. Of the 225 samples from which bacteria were isolated, Mannheimia haemolytica and Streptococcus uberis were the dominantly identified species from defective udder halves, whereas coagulase-negative staphylococcus (CNS) species, mostly Staphylococcus simulans and Staphylococcus chromogenes, were more frequently isolated from normal udder halves. The ongoing presence of bacterial species over time was variable, although less frequently identified species showed less stability over time. A very high agreement (91.5%) of bacterial species identified was observed between the mammary tissue swab and udder half milk samples during post-weaning. In summary, palpable udder half defects were associated with bacterial positivity, and the ongoing presence of the bacteria over time was dependent on the species involved. Hence, culling ewes with palpable udder half defects that had more stable bacterial species could contribute to reducing the recurrence of palpable defects or mastitis.Item Ewe culling in New Zealand: an interview study of 38 farmers(Taylor and Francis Group, 2023-11-19) Ridler AL; Kenyon PR; Greer AW; Logan CM; Morgan S; Corner-Thomas RARemoval of ewes from a flock before the end of their productive life, sometimes described as ewe wastage, can potentially lead to reduced flock productivity. While the main reasons for culling ewes are largely known, their relative importance to New Zealand farmers and farmers’ rational behind their culling decisions are not. Therefore, this study involved semi-structured interviews with 38 sheep farmers from throughout New Zealand to explore their ewe culling decisions. Farmers consistently culled mixed-age and two-tooth ewes who failed to become pregnant or who had a vaginal prolapse. For other culling reasons, farmers’ use of them and their rationale for doing so was diverse and varied between farmers based on ewe age-group, severity, season, perceived economic consequences and farmers’ personal preference. This diversity indicates that there is scope for some farmers to carefully evaluate some of their culling decisions.Item Deaths due to suspected hypothermia in sheep and alpacas on a Manawatū farm in New Zealand in mid-summer.(Taylor and Francis Group, 2024-01-01) Ridler AL; Gulliver EL; Castillo-Alcala FCASE HISTORY: In mid-summer (February), 42 of a flock of 68 ram hoggets (approximately 5 months of age) and two of a group of 14 alpacas on a farm in the Manawatū region of New Zealand were found recumbent or dead following a period of persistent rain, strong winds and relatively low temperatures. The hoggets and alpacas had been shorn 4 and 53 days previously, respectively, and were in adequate to good body condition with access to ad libitum pasture. Post-mortem and histological examinations were undertaken on four hoggets and two alpacas. CLINICAL FINDINGS: Apart from hypothermic body temperatures from four recumbent hoggets, nothing of significance was identified on clinical or gross pathological examination. Histological changes of vacuolar hepatopathy, renal tubular degeneration and pulmonary congestion were present in all animals examined. DIAGNOSIS: Based on the history and clinical and pathological findings, hypothermia was highly probable to have been the cause of the deaths. CLINICAL RELEVANCE: These cases emphasise the importance of shelter for recently shorn sheep and alpacas regardless of the season.Item Identification of risk factors for ewe mortality during the pregnancy and lambing period in extensively managed flocks(BioMed Central Ltd, 2023-12-06) Flay KJ; Chen AS; Yang DA; Kenyon PR; Ridler ALBACKGROUND: Ewe mortality during pregnancy and lambing is an issue for sheep producers globally, resulting in reduced productivity and profitability, compromised ewe welfare, and poor consumer perception. Despite these negative consequences, there was little investigation into factors associated with ewe death during this time. Therefore, this study aimed to assess associations between ewe body condition score (BCS), weight, reproductive parameters, and risk of mortality during pregnancy and lambing. METHODS: Four cohorts from three commercial New Zealand farms participated, with 13,142 ewe lambs enrolled and followed over time. Data were collected for five consecutive lambings. Visits aligned with key on-farm management times, specifically: prior to breeding, at pregnancy diagnosis (PD), prior to lambing (set-stocking), and, at weaning of their lambs. At each visit, ewes were weighed, BCS assessed and reproductive status was recorded when relevant (litter size at PD and lactation status after lambing). Ewes that died or were culled were recorded, and any ewes that were absent from consecutive visits were presumed dead. Logistic regressions were developed to assess the relationship between weight and BCS at each visit, PD result (single or multiple-bearing) and lactation status (wet or dry) in each year, and, risk of mortality during the pregnancy and lambing period in each year. RESULTS: In the PD to weaning period, mortality incidence ranged from 6.3 to 6.9% for two-tooth (18-months-old at breeding) to mixed-age (54-months-old at breeding) ewes. For ewe lambs (7 to 8-months-old at breeding), mortality was 7.3% from set-stocking to weaning. Heavier ewe lambs at PD were less likely to die during lambing (OR: 0.978, p = 0.013), as were those with greater set-stocking BCS. In subsequent years, BCS was a predictor of ewe death, with odds of mortality greatest for ewes < BCS 2.5. Additionally, for poorer BCS ewes, increasing weight reduced risk of mortality, but there was no impact of increasing weight in greater BCS ewes. CONCLUSIONS: This study identified risk factors associated with ewe mortality during the pregnancy and lambing period. Flock owners can use these to either cull at-risk ewes or proactively intervene to reduce likelihood of mortality, thereby improving flock productivity, profitability and welfare.Item Factors Associated with Ewe Death and Casting in an Extensively Farmed Sheep Flock in New Zealand(MDPI (Basel, Switzerland), 2021-12) Capdevila-Ospina K; Corner-Thomas RA; Flay KJ; Kenyon PR; Ridler AL; Garcia Ispierto IEwe deaths affect the productivity and profitability in sheep farming systems and have potential animal welfare and market perception implications. Internationally, there is scant data on the timing and causes of ewe deaths in extensive grazing systems. There is no published literature on the incidence and risk factors associated with casting (ewe in late gestation accidentally immobilised, often in dorsal recumbency). This study, undertaken using a cohort of 1789 ewes on a New Zealand farm, reports on the timing and risk factors associated with production parameters for ewe deaths through an almost two-year period, along with causes of death during both peripartum periods. Ewe deaths occurred throughout both years but were most frequent during the peripartum (pre-lambing to mid-lactation) period. Casting was the most commonly identified cause of death in both years, responsible for approximately a quarter to a third of potential annual mortality. Few risk factors for death or casting were identified. In conclusion, the peripartum period is a high-risk time period for ewe deaths (and, by extension, will also contribute to lamb perinatal mortality). In extensively grazed flocks where casting events occur, it is recommended that all ewes are monitored daily during the peripartum period.Item Assessment of Changes in Udder Half Defects over Time in Non-Dairy Ewes(MDPI (Basel, Switzerland), 2023-02-21) Zeleke MM; Flay KJ; Kenyon PR; Aberdein D; Pain SJ; Ridler AL; D’Alessandro AGA total of 1039 non-dairy breed (Romney) ewes were enrolled in two studies to assess the changes in udder half defect status (hard, lump, or normal) over time and to predict the risk of future udder half defect occurrence. In the first study (study A), udder halves of 991 ewes were assessed utilizing a standardized udder palpation method and scored four times a year, for two successive years (pre-mating, pre-lambing, docking, and weaning). The second study (study B) assessed the udder halves at pre-mating, and at six weekly intervals in the first six weeks of lactation in 46 ewes that had defective and normal udder halves. Udder half defect change over time was visualized via lasagna plots, and multinomial logistic regression was used to predict the risk or probability of udder half defect occurrence. In the first study, the highest occurrence of udder halves categorised as hard was observed at either pre-mating or docking. Udder halves categorised as lump had their highest occurrence at either docking or weaning. Udder halves detected with a defect (hard or lump) at pre-mating were more likely (RRR: 6.8 to 1444) to be defective (hard or lump) at future examinations (pre-lambing, docking, or weaning) within the same year or pre-mating the following year, compared to udder halves categorised as normal. In the second study, the change of udder half defect type over the first six weeks of lactation was variable. However, it was observed that the udder half defects, particularly udder halves categorised as hard, decreased during lactation. Failure to express milk in udder halves in early lactation was associated with a higher occurrence and persistency of udder half defects. In conclusion, the occurrence of diffuse hardness or lumps in an udder half changed over time, and the risk of future occurrence of a defect was higher in udder halves previously categorised as either hard or lump. Hence, it is recommended that farmers identify and cull ewes with udder halves categorised as hard and lump.