Data-driven investment and performance management in the livestock sector.

Evidence-based decision-making is now axiomatic in many sectors and has become increasingly important in prioritising development in low- and middle-income countries. In the livestock development sector, there has been a lack of data on health and production required to establish an evidence base. Thus, much strategic and policy decision-making has been based on the more subjective grounds of opinion, expert or otherwise. However, there is now a trend towards a more data-driven approach for such decisions. The Centre for Supporting Evidence-Based Interventions in Livestock was established in Edinburgh by the Bill and Melinda Gates Foundation in 2016, to collate and publish livestock health and production data, lead a community of practice to harmonise livestock-data-related methodologies, and develop and monitor performance indicators for livestock investments.

La prise de décision fondée sur des données probantes est désormais une évidence pour de nombreux secteurs, et elle devient de plus en plus importante dans la priorisation des initiatives de développement dans les pays à revenus faibles et intermédiaires. Dans le secteur du développement de l'élevage, peu de données sont disponibles concernant la santé et la production animales, or ces éléments sont nécessaires pour établir une base de données probantes. De nombreuses décisions politiques et stratégiques sont donc prises sur la base d'éléments plus subjectifs - opinions d'experts ou autres. On observe cependant une tendance en faveur d'une approche davantage ancrée dans les données pour ce type de décisions. Le Centre for Supporting Evidence-Based Interventions in Livestock [Centre de soutien aux interventions basées sur des données probantes dans le domaine de l'élevage] a été établi par la Fondation Bill et Melinda Gates en 2016 à édinbourg. Il a pour objectif de rassembler et de publier les données relatives à la production et à la santé du bétail, d'animer une communauté de pratiques en vue d'harmoniser les méthodologies relatives aux données sur le bétail et d'élaborer et de superviser les indicateurs de performance utilisés pour orienter les investissements dans le secteur de l'élevage.

La adopción de decisiones atendiendo a datos y criterios factuales, algo que ya es un axioma en muchos sectores, ha venido cobrando creciente importancia a la hora de fijar prioridades de desarrollo en los países de renta baja o de renta media. En el sector pecuario han faltado los datos de sanidad y de producción necesarios para establecer una sólida base factual. De ahí que buena parte de los procesos decisorios de carácter estratégico y normativo hayan discurrido por el terreno más subjetivo de las opiniones, ya provengan estas de expertos o de cualquier otro ámbito. Ahora, sin embargo, se tiende cada vez más a tratar de adoptar este tipo de decisiones a partir de una base más objetiva. En 2016, la Fundación Bill y Melinda Gates estableció en Edimburgo el Centre for Supporting Evidence-Based Interventions in Livestock [Centro de apoyo a las intervenciones basadas en datos factuales en ganadería], cuyos objetivos se cifran en reunir y publicar datos de sanidad y producción pecuarias, encabezar una dinámica de praxis colectiva para armonizar los métodos referidos a los datos de la ganadería y elaborar y seguir de cerca los indicadores de rendimiento utilizados para orientar las inversiones en el sector pecuario.

Neonatal immunisation against a novel gonadotrophin-releasing hormone construct delays the onset of gonadal growth and puberty in bull calves.

The aim of the present study was to investigate the effect of the neonatal immunisation of bull calves against a novel gonadotrophin-releasing hormone (GnRH) construct, comprised of GnRH coupled to the glycoprotein D subunit of the bovine herpes virus-1 (GnRH-BHV1 gD), on endocrine status, reproductive organ development and carcass quality. Eighteen bull calves received either GnRH construct (n=9) or saline (control; n=9) at 2, 6 and 13.5 weeks of age. Blood samples were taken to determine antibody titres against GnRH, FSH and testosterone (T) concentrations and LH pulse characteristics, with testicular circumference monitored monthly. Immunisation reduced LH pulse amplitude (P<0.05) and T concentrations (P<0.05), particularly at the peak in anti-GnRH titres after the second booster at 16 weeks of age (P<0.001), but not when titres fell. Despite antibody titres decreasing after 16 weeks, immunisation reduced testicular size between 16 to 57 weeks of age (P<0.05), provoking an 8-week delay in puberty onset, defined as testicular circumference ≥14 cm. In conclusion, neonatal immunisation induced a significant immune response against GnRH, provoking a temporary endocrine disturbance that had a long-term effect on testicular development, delaying the onset of puberty. These results support the hypothesis that a developmental window exists during testicular development, such that disturbance of the endocrine drive to the gonads during this period results in a longer-term impairment of gonadal function.

The consequences of introducing non-indigenous species: two case studies, the grey squirrel in Europe and the brushtail possum in New Zealand.

Two examples of the introduction of non-indigenous invasive species are reviewed: the grey squirrel in Europe (United Kingdom, Ireland and Italy) and the brushtail possum in New Zealand. Both have become very successful in their respective non-native habitats since their introductions in the mid-to-late 19th Century. Both species impact extensively on native biodiversity, environmental sustainability, forestry, and agriculture through a range of direct and indirect mechanisms. Management is currently mainly by lethal control, namely poisoning, trapping and shooting. Such methods of control are, however, increasingly contentious for both species, and alternative, non-lethal methods of population control, e.g. fertility control, are being developed. The case studies highlight many of the issues in invasive animal control; for example, prevention being better than control, lack of good understanding of impacts and the success of control measures on reducing impacts, interactive impacts on native biodiversity and ecosystems, the telling influence of public opinion on management options and, lastly, the need to better inform and educate the public.

Exploring the landscape of livestock 'Facts'.

The role of livestock in supporting human well-being is contentious, with different perceptions leading to polarised opinions. There is increasing concern about the health and environmental impacts of a high rate of consumption of livestock products in high-income countries. These concerns are heightened by an increase in consumption in middle-income countries. On the other hand, livestock support the livelihoods of many people, particularly in low income countries. The benefits of livestock for poor livestock keepers are multiple, including the important role livestock play in supporting crop production in mixed systems, in supplying nutrients and income, and in fulfilling cultural roles. In addition livestock can provide resilience against economic and climate shocks. In view of these apparent positive and negative impacts, the role of livestock in human wellbeing is highly contested, with arguments 'for' or 'against' sometimes distorted by vested interests or misinterpretation of evidence. The Livestock Fact Check project, undertaken by the Livestock Data for Decisions community of practice, has investigated several ideas concerning livestock commonly taken as 'fact'. By exploring the provenance of these 'facts' we highlight their importance and the risks of both misinterpreting them or using them out of context. Despite the diversity of the livestock sector resulting in equally diverse viewpoints, the project calls for participants in the livestock discourse to adopt a nuanced appreciation of global livestock systems. Judgement of livestock's role in global sustainable diets should be based on clear and well-interpreted information.

Reduced lung lesions in pigs challenged 25 weeks after the administration of a single dose of Mycoplasma hyopneumoniae vaccine at approximately 1 week of age.

Two independent studies assessed the duration of immunity of an inactivated adjuvanted Mycoplasma hyopneumoniae vaccine against mycoplasmal pneumonia in seronegative (study A, n=52) and seropositive (study B, n=52) pigs. The pigs were allocated randomly to treatment and were then injected with a single dose of either the vaccine or a placebo at approximately 1 week of age. Twenty-five weeks after treatment administration, the pigs were challenged with a virulent strain (LI 36, Strain 232) of M. hyopneumoniae and the extent of lung lesions consistent with mycoplasmal pneumonia was assessed 4 weeks later. In study A, the geometric mean lung lesion score (expressed as least squares mean percentages of lung lesions) was significantly (P=0.0001) lower in vaccinated (0.3%, n=20) than in control pigs (5.9%, n=24) seronegative to M. hyopneumoniae at enrolment; similarly, in study B, the extent of lung lesions was significantly reduced (P=0.0385) in seropositive vaccinated pigs (2.0%, n=22) compared to controls (4.5%, n=26). At the end of the investigation period, 4 weeks after challenge, mean antibody sample-to-positive (S/P) ratios were significantly higher both in seronegative (P=0.0012) and seropositive (P=0.0001) vaccinated pigs (mean values=0.77 and 0.81, respectively) than in controls (mean values=0.51 and 0.38, respectively).

Efficacy of a quadrivalent vaccine against respiratory diseases caused by BHV-1, PI3V, BVDV and BRSV in experimentally infected calves.

The efficacy of a quadrivalent vaccine against viral bovine respiratory diseases (BRD) was assessed in four experimental studies. Calves between 2 and 9 months of age were allocated to one of two treatment groups (n=9-15) and then received either the vaccine or sterile saline in two doses approximately 3 weeks apart. Three to 5 weeks after the second injection, animals were challenged experimentally with one of the viruses, bovine herpes-virus-1 (BHV-1), parainfluenza type-3 virus (PI(3)V), bovine viral-diarrhoea virus type 1 (BVDV), or bovine respiratory syncytial virus (BRSV) and were then monitored for at least 2 weeks. The administration of the vaccine was associated with enhanced antibody response to all four viruses post-challenge, with the reduction of the amount or duration (or both) of virus shedding in the BHV-1, PI(3)V, BVDV and BRSV studies and with an improvement of some clinical signs in the BHV-1 (nasal discharge, and rectal temperature) and the PI(3)V studies (abnormal respiration, and depression).

Recent research on the effects of excess dietary nitrogen on the fertility of dairy cows.

High concentrations of dietary nitrogen have been associated with reductions in the fertility of dairy cows, but the evidence is not conclusive and many studies have shown little or no effect. This paper reviews recent investigations of the effect of rapidly degradable sources of nitrogen on parameters of fertility, and concludes that high levels of dietary nitrogen do not routinely reduce fertility, even at intakes above those in normal dairy cow diets. It also concludes that cows may be able to adapt to high nitrogen diets so that diets that may reduce their fertility when introduced at critical periods, for example, when they are inseminated, do not reduce it when introduced at an earlier stage.

Timing of follicular phase events and the postovulatory progesterone rise following synchronisation of oestrus in cows.

In cows the timing of both ovulation and the subsequent postovulatory progesterone rise are critical to successful fertilisation and early embryo development. The aim of this study was to determine the degree of variability in the timing of ovulation relative to other follicular phase events and to determine how variations in the timing of follicular phase events contribute to the timing of the postovulatory progesterone rise. Plasma concentrations of progesterone, oestradiol and luteinising hormone (LH) and the timing of oestrus and ovulation were determined following induction of luteolysis were determined in 18 mature, non-lactating Holstein-Friesian cows. Four cows were excluded on the basis of abnormal reproductive function. In the remaining 14 cows oestrus occurred at 57.4+/-4.3h and the LH surge at 54.6+/-4.0h following luteolysis (progesterone <1ngmL(-1)) followed by a fall in circulating oestradiol concentration at 64.6+/-4.4h. Cows ovulated at 88.0+/-4.7h with the postovulatory progesterone rise (to >1ngmL(-1)) occurring 159+/-7.2h after luteolysis. There was considerable variation in the timing of ovulation following luteolysis (range 64-136h) onset of oestrus (range 24-40h) and onset of the LH surge (range 24-44h). Cows were then split on the basis of interval from progesterone fall to progesterone rise giving groups (n=7 per group) with intervals of 180.6+/-6.7 and 138.3+/-5.7h (P<0.001). Between groups, both the intervals from luteolysis to ovulation (98.3+/-6.9 vs 77.7+/-3.4h; P<0.05) and ovulation to progesterone rise (82.3+/-4.2 vs. 60.6+/-5.5h; P<0.01) were longer in late rise cows. There was no difference between groups in the interval from oestrus or LH surge to ovulation. In conclusion the results of this study further highlight the high variability that exists in the timing and interrelationships of follicular phase events in the modern dairy cow, reemphasising the challenges that exist in optimising mating strategies. However, the data do suggest that in cows with poor post ovulatory progesterone secretion, the key problem appears to be poor post ovulatory development rather than a delay in ovulation.

Veterinary clinical application of GnRH--questions of efficacy.

The efficacy of GnRH treatments are reviewed in relation to prevention of embryo mortality, control of follicle development in synchronization programmes using PG as luteolysin, induction of ovulation in post-partum anoestrus and in bovine cystic ovarian disease. It is suggested that in cattle that GnRH is effective in increasing pregnancy rates when given either at the time of insemination (first or repeat) or between days 11 and 14 after insemination. Evidence is also presented for positive effects on pregnancy rates in sheep, mares and sows. Use of GnRH as an integral part of synchronising regimens where it is given 7 days before PG and then again 48-60 h after PG appears to be effective in increasing the synchrony of ovulation in controlled breeding programmes. The main synchronizing effect seems to reside in the second GnRH injection whereas the importance of the first is in prolonging the luteal phase in those cows treated late in the cycle. The published work on the potential use of GnRH to induce ovulation in anovulatory cattle is reviewed. Neither bolus dose injections, pulsatile, continuous infusion, nor controlled release formulations of GnRH, have yet proved effective in inducing fertile ovulations in a predictable or consistent manner. It is suggested that this is due to the variability of follicular status when treatment is initiated. GnRH is commonly used in the treatment of bovine cystic ovarian disease. However, although stimulating ovulation/luteinisation of a new follicle and luteinisation of the cyst, fertility of treated cattle remains very poor and it is suggested that a better understanding of the disease is needed before more effective treatments can be developed.

NMR studies of interactions between inhibitors and porcine pancreatic phospholipase A2.

Two-dimensional NMR studies were performed on the complexes of porcine pancreatic phospholipase A2, bound to a micellar lipid-water interface of fully deuterated dodecylphosphocholine, with competitive inhibitors derived from the following general structure: [formula: see text] X and Y are alkyl chains with various 'reporter groups'. The interactions between the inhibitor and the enzyme were localized by comparison of 2-D nuclear Overhauser effect spectra using protonated and selectively deuterated inhibitors, and inhibitors with groups having easily identifiable chemical shifts. These experiments led us to the following conclusions for the phospholipase A2/inhibitor/micelle complex: i) the His48 C2 ring proton is in close proximity to both the amide proton and the methylene protons at the sn-1 position of the glycerol skeleton of the inhibitor, ii) the acyl chain of the inhibitor at the sn-2 position makes hydrophobic contacts near Phe5, Ile9, Phe22 and Phe106; iii) no interactions between the acyl chain at the sn-1 position and the protein could be identified. Comparison of our results on the enzyme/inhibitor/micelle ternary complex with the crystal structure of the enzyme-inhibitor complex shows that the mode of inhibitor binding is similar. However, in several cases we found indications that the hydrophobic chains of the inhibitors can have multiple conformations.

Effects of exogenous cortisol on the uptake of corticosteroid by the isolated perfused guinea-pig mammary gland.

Assay of corticosteroids in the plasma of guinea-pigs showed that concentrations were higher in lactating than in non-lactating and male animals. In five isolated perfused mammary gland experiments in which corticosteroids were at concentrations of 1,3--3,0 microgram/ml in the perfusate, equivalent to concentrations during lactation, the mean (+/- S.E.M.) uptake by the mammary gland was 900 +/- 210 ng g-1 h-1. In five experiments in which the concentrations of corticosteroid in the perfusate were 190--580 ng/ml, the uptake by the mammary gland was significantly lower (316 +/- 73 ng g-1 h-1; P less than 0.05). For the ten experiments there was a significant correlation between the concentration of corticosteroid in the perfusate and uptake by the mammary gland (P less than 0.05). No convincing evidence for a galactopoietic role of corticosteroids in the guinea-pig was obtained, although administration of cortisol signficantly stimulated the uptake of glutamine by the perfused gland.

Reaction products from platinum(IV) amine compounds and 5'-GMP are mainly bis(5'-GMP)platinum(II) amine adducts.

The reaction products obtained from mixtures of 5'-GMP and platinum(IV) compounds with formula Pt(IV)Cl4(LL) and Pt(IV)Cl2(OH)2(LL) (LL representing two monodentate or one bidentate amine ligand) have been characterized by proton NMR spectroscopy. The amines used are NH3, H2N-CH2-CH2-NH2 (ethylenediamine, en), H2N-CH2-C(CH3)2-CH2-NH2 (2,2-dimethyl-1,3-diaminopropane, dmdap), and HC(CH3)2-NH2 (isopropylamine, ipa). Conditions varied during the reaction are pH (values of 4, 7, and 10), effect of visible light, and addition of vitamin C as a reducing agent. In all cases, the major product appeared to be the bis(5'-GMP)(LL)Pt(II) compound. The pH effect is limited; i.e., at pH 4 the reactions proceed somewhat faster than at neutral pH, while at pH 10 slower reactions occur. The illumination with visible light also induces only slight differences in the yields of the products. On the other hand, when vitamin C is present, the reactions proceed quite rapidly, resulting in the same main product but in higher yields (up to 80%). The facts that apparently no Pt(IV) adducts with 5'-GMP can be observed under these conditions and that the major products are bis(5'-GMP)(LL)Pt(II) compounds clearly support the hypothesis that the antitumor activity of certain platinum(IV) compounds is based upon in vivo reduction to the corresponding platinum(II) compounds.

The accuracy of image registration for the brain and the nasopharynx using external anatomical landmarks.

We investigated the accuracy of 3D image registration using markers that are repeatedly applied to external anatomical landmarks on the head. The purpose of this study is to establish a lower limit of the errors that would occur in, for instance, MRI-SPECT matching, which in some situations can only be achieved using external landmarks. Marker matching was compared with (single-modality) volume matching for 20 MRI scans. The results were compared with a published expression for the target registration error (TRE) which gives the 3D distribution of the mismatch between both scans. It was found that the main error source is reapplying the external markers on the anatomical landmarks. The published expression describes the relative distribution of the TRE in space well, but tends to underestimate the actual registration error. This deviation is due to anisotropy in the error distribution of the marker position (errors in the direction perpendicular to the skin surface are in general much smaller than errors in other directions). A simulation of marker matching with anisotropy in the errors confirmed this finding. With four reapplied markers, the TRE is 6 mm or smaller in most regions of the head.

Experimental and practical approaches to the establishment and maintenance of pregnancy.

A series of three large field trials was carried out to assess the effect of buserelin on fertility in dairy cows. In the first, 10 micrograms buserelin was injected on the day of insemination. There were no significant effects on fertility parameters compared to untreated controls. In the second trial cows were injected on day 12 after insemination. Mean pregnancy rates to first insemination were 53.4 and 65.4% for control and treated cows respectively (P < 0.01). Mean pregnancy rates to repeat inseminations were 52.9 and 59.4% for control and treated cows (NS). Mean calving to conception intervals were 91.4 and 85.3 days (P < 0.01) and the incidence of barren cows was 10.2 and 5.3% (NS). Overall the economic benefit of buserelin injection on day 12 was calculated to be 27.43 pounds per cow treated excluding the cost of the treatment. In trial 3 cows were injected with buserelin either on day 8 or 10 after insemination. There were no significant effects on fertility parameters compared to untreated control cows. In a fourth trial ewes were injected with 4 micrograms buserelin on day 12 after service. There were indications that both pregnancy rate and lambing percentage could be increased by buserelin treatment. Daily blood samples were collected from 5 dairy cows during a control cycle and a cycle in which 10 microgram buserelin was injected on days 11 and 13. Cycle length was unaffected by treatment and the concentration and pattern of progesterone secretion did not differ between control and treated cycles. Plasma oestradiol concentrations were similar in the control and treated cycles before day 11. However from day 12 to 16, equivalent to the time of maternal recognition of pregnancy, the mean concentration of oestradiol was significantly reduced in the treated cycle. As oestradiol stimulates both the development of uterine oxytocin receptors and the secretion of PGF2 alpha we suggest that any improvement in pregnancy rate after buserelin is due to a weakened luteolytic mechanism, resulting from a lower plasma oestradiol concentration.

Duration of immunity of a quadrivalent vaccine against respiratory diseases caused by BHV-1, PI3V, BVDV, and BRSV in experimentally infected calves.

Several laboratory studies assessed the duration of immunity of a quadrivalent vaccine (Rispoval 4, Pfizer Animal Health) against bovine respiratory diseases (BRD) caused by bovine herpes-virus type-1 (BHV-1), parainfluenza type-3 virus (PI3V), bovine viral-diarrhoea virus type 1 (BVDV), or bovine respiratory syncytial virus (BRSV). Calves between 7 weeks and 6 months of age were allocated to treatment and then were injected with two doses of either the vaccine or the placebo 3 weeks apart. Six to 12 months after the second injection, animals were challenged with BHV-1 (n=16), PI3V (n=31), BVDV (n=16), or BRSV (n=20) and the course of viral infection was monitored by serological, haematological (in the BVDV study only), clinical, and virological means for > or =2 weeks. Infection induced mild clinical signs of respiratory disease and elevated rectal temperature in both vaccinated and control animals and was followed by a dramatic rise in neutralising antibodies in all treatment groups. Titres reached higher levels in vaccinated calves than in control calves after challenge with BHV-1, BVDV, or BRSV. On day 3 after PI3V challenge, virus shedding was reduced from 3.64 log10TCID50 in control animals to 2.59 log10TCID50 in vaccinated animals. On days 6 and 8 after BRSV challenge, there were fewer vaccinated animals (n=2/10 and 0/10, respectively) shedding the virus than control animals (n=8/10 and 3/10, respectively). Moreover, after challenge, the mean duration of virus shedding was reduced from 3.8 days in control animals to 1 day in vaccinated animals in the BVDV study and from 3.4 days in control animals to 1.2 days in vaccinated animals in the BRSV study. The duration of immunity of >or =6 months for PI3V, BHV-1 and BVDV, and 12 months for BRSV, after vaccination with Rispoval 4, was associated mainly with enhanced post-challenge antibody response to all four viruses and reduction of the amount or duration of virus shedding or both.

The effect of feeding diets high in quickly degradable nitrogen on follicular development and embryo growth in lactating Holstein dairy cows.

This study investigated the effect on follicular and embryo development of increasing quickly degradable nitrogen (QDN) intake in lactating Holstein dairy cows. Forty mature post-partum cows were fed one of two diets for a minimum of 10 weeks, starting 10 days before first insemination. The Control diet was a high production dairy ration. The High QDN diet comprised the Control ration plus 250 g urea/head/day. Both diets were formulated to ensure that the energy requirements of the cows were satisfied. The High QDN treatment resulted in a significant increase in milk urea, plasma urea and plasma ammonia concentrations. The highest plasma urea (8.2 mmol/l) and ammonia concentrations (120 micromol/l) were recorded within 7 days of the urea supplement being added to the diet. There was no effect of diet on plasma progesterone or glucose concentration. There was also no significant effect of treatment on follicular development or embryo growth. The results from this study suggest that the lactating cow can adapt to increased intakes of QDN if the increase starts at least 10 days before insemination.

Plasma gonadotrophin responses in beef cows two progesterone plus prostaglandin treatment.

Progesterone Releasing Intravaginal Devices (Prids) were inserted into six post-partum beef cows for nine days and 0.5 mg cloprostenol was injected i m on day eight. Blood samples were taken via jugular venous catheters at frequent intervals for seven days after Prid removal and assayed for LH, FSH and progesterone. The induced pre-ovulatory type LH and FSH surges occurred between 35 and 123h after Prid withdrawal in five of the cows. In four cows which underwent surges during the time of most intensive sampling, LH levels were significantly higher during the 30h period prior to the LH surge than during the 30h period after the surge. FSH values were low for the 30h period preceding and the 14h period following the time of maximum FSH/LH concentrations. 16 - 30h after the FSH and LH surges, FSH values were again significantly raised compared with the period immediately after the surge. Despite the success of this Prid/PG regime in inducing ovulation, the variability in time between progestagen withdrawal and the LH surge and ovulation is such that the use of fixed time artificial insemination may give poor results.

A meta-analysis of studies of the effect of GnRH 11-14 days after insemination on pregnancy rates in cattle.

A number of studies have used GnRH between 11 and 14 days after insemination to improve pregnancy rates in cows, however published results have not been consistent. We wished to investigate whether a consolidated estimate of the response could be quantified. Therefore we conducted a meta-analysis of the available data, 19 studies from 14 published papers, on the effect of GnRH analogs on pregnancy rate when given between Days 11 and 14 after first insemination. Odds ratios (the relative probability of pregnancy between treated and control cows) were compared for each study and found to vary significantly among studies, ranging from 0 to 22%. We showed by logistic regression analysis that response to GnRH treatment varied with cow type (beef or dairy), age (cow or heifer), estrus synchronization (synchronized or natural), pregnancy diagnosis (method and time) and effect of individual study. When all these variables were included only 6 of 14 publications could be analyzed, representing 2,541 instead of 10,945 cows. In this limited subgroup of data, a significant improvement in pregnancy rate was detected among treated cattle (odds ratio = 1.33; P<0.01).

The effect of the gonadotropin-releasing hormone analog, buserelin, on pregnancy rates in horse and pony mares.

We conducted a series of trials over a four-year period on a total of 2,346 mares, to determine the effect of a single dose of the GnRH analog buserelin (20 to 40 microg i.m. or s.c.) on pregnancy rates when given between 8 and 12 days after service. Although there were some statistically significant improvements in pregnancy rates in individual trials, meta-analysis of the data overall showed significant improvements at all times examined, i.e. 13 to 16, 19 to 23, 28 to 31 and 38 to 42 days after service. These results indicate that treatment of mares with 20 to 40 microg buserelin between Days 8 and 12 significantly increases pregnancy rates by approximately 10 percentage points.

Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows.

High protein diets, which lead to excess production of nonprotein nitrogen such as ammonia and urea, have been associated with reduced fertility in dairy cows. In this study we test the hypothesis that diets containing high levels of quickly degradable urea nitrogen (QDN) compromise embryo development. Lactating dairy cows were fed mixed silage and concentrates twice daily. At 60 days postpartum, a synchronized estrus was induced and the cows were subsequently superovulated and inseminated using a standard protocol. On Day 7 after insemination, the uteri were flushed and embryos retrieved. At the start of treatment, cows were randomly allocated into three nutritional groups: control (CONT, n = 8), long (L-) QDN (n = 8) and short (S-) QDN (n = 9). The L-QDN cows were fed a supplement of urea from 10 days before insemination, and the S-QDN cows were fed the supplement from insemination until embryo collection. Both L- and S-QDN diets produced significant increases in plasma ammonia and urea 3 h post-feeding. The S-QDN but not the L-QDN diet was associated with a significant reduction in embryo yield. Embryo quality was also significantly reduced in the S-QDN cows. This study indicates that there is no deleterious effect on the yield and quality of embryos recovered 7 days after breeding when QDN feeding is initiated during the previous midluteal phase. However, introduction of a similar diet 10 days later, at the time of insemination, was deleterious. We suggest that QDN is toxic to embryos but cows can adjust within 10 days.