Olav Reksen

Olav Reksen
Norwegian University of Life Sciences (NMBU) · Department of Production Animal Clinical Sience

DVM, PhD, Diplomate ECAR

About

73
Publications
18,760
Reads
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1,703
Citations
Citations since 2017
16 Research Items
751 Citations
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120
2017201820192020202120222023020406080100120
Additional affiliations
February 2014 - present
Norwegian University of Life Sciences (NMBU)
Position
  • Professor
Description
  • Teaching and clinical training in physiology and pathology of female in cattle and pigs, including both individual animals and herd level approaches.
November 1995 - November 2000
Norwegian University of Life Sciences (NMBU)
Position
  • PhD Student
October 1995 - present
Norwegian University of Life Sciences (NMBU)
Position
  • Professor
Description
  • Reproductive physiology and reproduction on a herd and flock basis. I have used field and laboratory data to model complex associations between environmental factors and reproductive efficiency both on the single animal and at herd level.

Publications

Publications (73)
Article
Full-text available
The use of technologies for measurements of health parameters of individual cows may ensure early detection of diseases and maximization of individual cow and herd potential. In the present study, dry-film Fourier transform infrared spectroscopy (FTIR) was evaluated for the purpose of detecting and quantifying milk components during cows’ lactation...
Article
The objective of the study was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) analysis of milk samples to predict body energy status and related traits (energy balance (EB), dry matter intake (DMI) and efficient energy intake (EEI)) in lactating dairy cows. The data included 2371 milk samples from 63 Norwegian Red dairy...
Chapter
Full-text available
Climate change affects food security and livelihood in Malawi, and the Food and Agricultural Organization emphasises the intensification of milk and meat production to reduce greenhouse gas emissions. Measures to increase the robustness of smallholder dairy production to better cope with the new challenges are urgently needed. A field experiment wa...
Chapter
Full-text available
Smallholder Zebu cattle farming is of prime importance for the livelihood of Malawians, and optimising cattle reproductive efficiency represents one way to increase food production. The objective of this study was to determine the reproductive performance and associated factors in a cohort of Malawi Zebu cows (n = 100) across 36 smallholder farms f...
Article
Full-text available
Fully automated on-line analysis equipment is available for analysis of somatic cell count (SCC) at every milking in automatic milking systems. In addition to results from on-line cell counters (OCC), an array of additional cow-level and quarter-level factors considered important for udder health are recorded in these systems. However, the amount o...
Article
Management of udder health is particularly focused on preventing new infections. Data from the DeLaval Online Cell Counter (DeLaval, Tumba, Sweden) may be used in forecasting to improve decision support for improved udder health management. It provides online cell counts (OCC) as a proxy for somatic cell counts from every milking at the cow level....
Preprint
Timely and accurate identification of cows with intramammary infections is essential for optimal udder health management. Various sensor systems have been developed to provide udder health information that can be used as a decision support tool for the farmer. Among these sensors, the DeLaval Online Cell Counter (DeLaval, Tumba, Sweden) provides so...
Article
Milking-time testing (MTT) is a method for evaluating the vacuum conditions in the teatcup during milking. The purpose is to evaluate the possible impact of the milking and milking equipment on udder health and milk quality. The method is commonly implemented by herd health advisory services, but results are interpreted empirically due to lack of s...
Article
Full-text available
A multiphase modeling approach that describes the transmission dynamics of intramammary infections (IMI) caused by Corynebacterium species in US dairy herd is presented in this paper. It is based on the stratification of the days of study (calendar days) in several strata and the modeling of the transmission of Corynebacterium spp. by using lactati...
Article
Full-text available
We present a novel deterministic modelling approach that describes the transmission dynamics of intramammary infections (IMI) caused by Corynebacterium spp. (Corynebacterium species) in a US dairy herd. Longitudinal, quantitative, dynamic models are likely to be valuable for predicting infections outbreak risk, quantify the effectiveness of respons...
Article
Full-text available
Background Having a poor teat-end condition is associated with increased mastitis risk, hence avoiding milking machine settings that have a negative effect on teat-end condition is important for successful dairy production. Milking-time testing (MTT) can be used in the evaluation of vacuum conditions during milking, but the method is less suited fo...
Article
Full-text available
Preweaning mortality in piglets is a welfare issue, as well as an ethical and economic concern in commercial pig farming. Studying the causes of preweaning mortality and their prevalence is necessary to reduce losses. Preweaning piglet mortality was investigated in a field study including 347 sows from 14 loose-housed Norwegian piglet-producing her...
Article
The development of reliable models for transmission of intramammary infections (IMI) is the subject of extensive research. Such models are useful to enhance the identification and understanding of factors that affect pathogen-specific IMI dynamics. Longitudinal transmission models are valuable for predicting infection outbreak risks, quantifying th...
Presentation
Full-text available
Presentation @2ND SEMINAR ON COAGULASE-NEGATIVE STAPHYLOCOCCI in Gent
Article
Full-text available
Colostrum provides newborn piglets with energy and passive immunity and is essential for survival of the piglets. The plasma concentration of immunoglobulin G (IgG) in piglets is dependent on several factors, most importantly the concentration of IgG in sow colostrum (colostrum IgG). The main aims of this study were to investigate the variation in...
Article
Full-text available
Colostrum provides newborn piglets with energy and passive immunity and is essential for survival of the piglets. The plasma concentration of immunoglobulin G (IgG) in piglets is dependent on several factors, most importantly the concentration of IgG in sow colostrum (colostrum IgG). The main aims of this study were to investigate the variation in...
Article
Full-text available
To investigate the feasibility of milk fatty acids as predictors of onset of luteal activity (OLA), 87 lactations taken from 73 healthy Norwegian Red cattle were surveyed over 2 winter housing seasons. The feasibility of using frozen milk samples for dry-film Fourier transform infrared (FTIR) determination of milk samples was also tested. Morning m...
Article
Full-text available
The piglet's fetal growth is highly dependant on its placenta, and the newborn piglet birth weight is highly associated with post partum death. However, there is little information available in the literature on the assessment of the placenta in relation to post partum death in piglets. The aim of this study was to evaluate the impact of the placen...
Article
Full-text available
The majority of herds in Norway participate in the national dairy herd recording system. For disease events, this involves transferring information registered on farm, using individual cow health cards (CHC), to the central cattle database (CCD). Before using data from such a database, validation with an aim of describing data quality should be per...
Article
Full-text available
A field trial was conducted on 2 US dairy herds to evaluate the transmission dynamics of coagulase-negative staphylococci (CNS) during the lactation period. Quarter milk cultures positive for CNS were classified as intramammary infection (IMI) or incidental isolation (transient colonization). The average proportion of quarters with CNS IMI was 0.11...
Article
Full-text available
Intrapartum death in multiparous gestations in sows is often caused by hypoxia. There is little information in the literature on the assessment of the placenta in relation to intrapartum death in piglets.The aim of this study was to evaluate the impact of the placental area and weight upon piglet birth characteristics and intrapartum death. Litters...
Article
Full-text available
Improving survival is a continuous objective in swine breeding. The aim of this study was to record 22 blood parameters and weight gain the first day of life in Landrace-Yorkshire-Duroc crossbred piglets and to find associations between these parameters and survival at weaning. All live piglets from 18 litters were weighed and blood sampled at birt...
Article
Full-text available
In order to investigate associations between individual calf parameters and/or herd management practices and dairy calf body weight (BW) attainment in smallholder farms in Tanzania, a prospective study was carried out at 121 farms in Mvomero and Njombe districts and included 156 crossbred dairy calves. Information on management factors and sources...
Article
Full-text available
Improving survival is a continuous objective in swine breeding. The aim of this study was to record 22 blood variables and BW gain on the first day of life in Landrace-Yorkshire-Duroc crossbred piglets and to find associations between these variables and survival at weaning. All live piglets from 18 litters were weighed and blood sampled at birth a...
Article
Full-text available
A study was undertaken to investigate Cryptosporidium infection in crossbreed dairy calves in two districts in Tanzania. A total of 943 fecal samples from 601 dairy calves were included in the study, with calves from both smallholder dairy farms and from large-scale and medium-scale dairy farms. The modified Ziehl-Neelsen (mZN) technique was used t...
Article
Full-text available
Genetics of different pig lines affects litter size, birth weight, and neonatal losses. Low birth weight has long been associated with neonatal losses, but piglet body mass index is reported to show stronger correlation with stillbirth. The aim of this study was to investigate differences in litter size, number of stillborn piglets, piglet BW gain,...
Article
Full-text available
A longitudinal observational study on calf health and growth was conducted in smallholder dairy farms in Mvomero and Njombe districts, Tanzania to investigate whether calf growth in these regions was predominantly affected by clinical diseases or other factors. The clinical health and growth of 156 calves from 121 farms were monitored for one year....
Article
Full-text available
An investigation of the shape of the lactation curve and the mastitis incidence was conducted to identify whether management interventions of the lactation curve constitute a potential for reducing incidence of mastitis at herd level. Lactation curves were estimated to describe the variation of daily milk yield during the 305-d lactation period in...
Article
Full-text available
This study was carried out to determine if an association exists between the shape of the lactation curve before it is influenced by the event of conception and the time from calving to conception in Norwegian dairy cattle. Lactation curves of Norwegian Red cows during 5 to 42 days in milk (DIM) were compared between cows conceiving between 43 and...
Article
Full-text available
Smallholder farmers' knowledge and practice of dairy calf management on 129 farms with calves less than 10 months of age in Southeastern and Southern Highland areas of Tanzania was assessed. The method of study included both a farm visit and completion of a questionnaire. Most of the farmers were female, with a primary level of education, and major...
Article
Full-text available
Reproduction is the single greatest factor limiting beef cattle production. Previous research on beef suckler luteal activity has largely focused on the mechanisms, and duration, of postpartum anoestrus. However, the temporal pattern of luteal activity after resumption of post-partum ovarian activity, and the impact of pattern type on days open (DO...
Article
Full-text available
The objectives of this study were to investigate whether there were differences between Norwegian Red cows in conventional and organic farming with respect to reproductive performance, udder health, and antibiotic resistance in udder pathogens. Twenty-five conventional and 24 organic herds from south-east and middle Norway participated in the study...
Article
Full-text available
Progesterone profiles in Norwegian Red cows were categorized, and associations between the occurrence of irregularities in the profiles and the commencement of luteal activity were investigated. The cows were managed in 3 feeding trials from 1994 to 2001 and from 2005 to 2008 at the Norwegian University of Life Sciences. The cows were followed from...
Article
Full-text available
A cross sectional study was conducted during October and November 2006 on 69 smallholder dairy farms with lactating cows in Mvomero and Njombe districts Tanzania, to determine the prevalence of mastitis and to assess the milk quality on the study farms. Clinical mastitis was investigated using clinical changes of udder and milk at animal level. Cow...
Article
Full-text available
Relationships among commencement of luteal activity (C-LA), milk yield, and energy balance (EB) were investigated in 3 selection lines of Norwegian Red cows at the Norwegian University of Life Sciences from 1994 through 2001. The cows were selected for low genetic merit for milk yield (LMP), high genetic merit for milk yield (HMP), and a combinatio...
Article
Full-text available
The study was conducted on smallholder dairy farmers in Tanzania. A number of forage species and feed supplements were collected and analysed. Panicum maximum and P. purpureum constituted the bulky forage in about 20 and 11 households, respectively. The crude protein (CP) content of P. maximum and P.purpureum ranged from 6.5 to 8.5% and 7.8 to 10.2...
Poster
The purpose of this study was to establish the accuracy of manual ovarian palpation in purebred beef cows compared to the ‘gold standard’ of milk progesterone levels measured by modified EIA (P4≥3ng/ml = luteal activity). The reproductive tracts of 87 Hereford cows (120 lactations) were manually examined per rectum by two experienced veterinary sur...
Article
Full-text available
The objectives of the study were to estimate pregnancy incidence and calving rate after first artificial insemination (AI) in Norwegian Red cows undergoing spontaneous estrus, to assess the relationship between pregnancy and management factors at herd or cow level, to evaluate differences between 60-d nonreturn rate (NRR60d) and pregnancy incidence...
Article
Full-text available
Associations between test-day composite milk somatic cell counts (CMSCC) and results from quarter milk cultures for various pathogens associated with mastitis, including Staphylococcus aureus, Streptococcus spp., coagulase-negative staphylococci (CNS), were investigated. S. aureus was dichotomized according to sparse (<or=1,500 colony forming units...
Article
Full-text available
Milk progesterone measurements were used to study post-partum ovarian activity and risk factors for ovarian dysfunction in Zebu cows reared under a traditional pastoral management system in three villages in Morogoro region, Tanzania. Milk samples for progesterone analysis were collected twice per week from a total of 98 lactations. The most preval...
Article
Full-text available
Associations between test-day milk yield and positive milk cultures for Staphylococcus aureus, Streptococcus spp., and other mastitis pathogens or a negative milk culture for mastitis pathogens were assessed in quarter milk samples from randomly sampled cows selected without regard to current or previous udder health status. Staphylococcus aureus w...
Poster
English, The reproductive performance of Hereford cattle using milk progesterone analysis
Article
Full-text available
The objective of the present field study was to compare the fertility results for boar semen diluted in X-cell stored up to 4-5 days before artificial insemination (AI) with semen diluted in Beltsville thawing solution (BTS) used for AI following 2-3 days of storage (where the first day being the collection day). A total number of 2601 double insem...
Article
Full-text available
The present study was based on data obtained from artificial inseminations (AIs) performed with cryopreserved semen from elite bulls used in the Norwegian breeding program. Semen was diluted to standardize the number of spermatozoa to 18 million per AI dose. The aim of the study was to investigate whether the net sperm concentration at semen collec...
Article
Full-text available
In quarter milk samples from 2,492 randomly sampled cows that were selected without regard to their current or previous udder health status, the relationships between the following outcome variables were studied: treatment of clinical mastitis; the joint event of either treatment or culling for mastitis; culling for all reasons; culling specificall...
Article
Full-text available
A prospective longitudinal study was carried out from September 2001 to June 2004 in three adjacent villages in a semi-arid area of Tanzania. The objectives of this study were to measure the intervals between calving and either resumption of cyclical activity or confirmation of pregnancy, to estimate calving intervals, and to investigate the effect...
Article
Full-text available
A nationwide random computerized assignment survey that included 3,538 sets of 4 quarter milk samples from 2,834 dairy cows was conducted during 2000. Every fifth cow from every 50th herd was randomly selected for sampling and culture during each quarter of the year. Milk culture results of pathogens known to be related to mastitis were recorded re...
Article
Full-text available
The objectives of this study were to assess changes in nutritional status/body condition score, percentage pregnancy and calving rate in Zebu cows and to establish the relationship between body condition score loss and postpartum interval to resumption of ovarian activity. A total of 198 cows and postpubertal heifers of the Tanzanian Shorthorn Zebu...
Article
Full-text available
The effects of four seasons of semen collection and of artificial insemination on conception in dairy cows were studied. The solstices and equinoxes (December, March, June and September) defined the beginning and/or end of each season. Semen was collected from 973 progeny-test bulls over 8 years at the two Norwegian AI stations at 60.8 degrees N an...
Article
Full-text available
The objective of this retrospective field study was to determine the effects of storing, for up to 62 h, heterospermic and homospermic semen in the short-term extender Beltsville thawing solution (BTS), on reproductive performance in Norwegian swine of four different breed combinations. The study was based on fertility records after single or doubl...
Article
Full-text available
The aim of the present study was to investigate if environmental doses of PCB 153 and PCB 126 could produce effects in a controlled animal model. Possible adverse effects on the hypothalamic-pitutitary-gonadal axis were examined by measuring gonadotrophins and gonadal steroid hormone concentrations in goat kids exposed during gestation and lactatio...
Article
Full-text available
Relationships among milk progesterone, concentrate allocation, energy balance (EB), milk yield and conception rate were studied in 146 lactations in 94 moderate yielding cows. All animals were of the dual purpose breed Norwegian cattle, and were monitored through their first and second lactations. The cows were assigned three different concentrate...