Effect of duration of dominance of the ovulatory follicle on onset of estrus and fertility in heifers.

In cattle, prolonged progestogen treatments following luteolysis result in persistent dominant follicles (DF) that are associated with precise onset of estrus but marked reductions in pregnancy rate (PR). The aim was to determine whether increasing duration of dominance of the ovulatory follicle in heifers affected 1) precision of onset of estrus and 2) the timing and nature of the decline in PR. In Exp. 1, duration of dominance of the ovulatory follicle was controlled by causing corpus luteum (CL) regression at emergence of the second follicle wave (mean duration of dominance of 2.1+/-.3 d, Dm2, n = 11) or first day of dominance of the second DF of the cycle; the latter was combined with insertion of a 3-mg norgestomet ear implant for 2 to 10 d to maintain the second DF for 4 (Dm4, n = 32), 6 (Dm6, n = 19), 8 (Dm8, n = 49), 10 (Dm10, n = 28), or 12 d (Dm12, n = 20). Heifers detected in estrus were inseminated approximately 12 h later with frozen-thawed semen. Durations of dominance of the ovulatory follicle of up to 8 d did not affect (P>.05) PR (Dm2 8/9, Dm4 19/28, Dm6 14/18, and Dm8 34/48 heifers pregnant), but PR in Dm10 heifers (12/23 heifers pregnant) was reduced (P = .05) compared with Dm2 heifers; PR in Dm12 heifers (2/17 pregnant) was less compared with all other treatments (P<.01). Fitting a logistic regression model to the pooled PR data to examine the trend in PR showed that extending the duration of dominance from 2 to 9 d and from 10 to 12 d resulted in a predicted decline in PR of 10 to 25% and a further decline of 35 to 75%, respectively. Onset of estrus was delayed in heifers assigned to Dm4 treatment relative to all other treatments (P<.001); it was less variable than that for heifers on Dm6, Dm8, and Dm10 treatments (P<.1). In Exp. 2, heifers received a PGF2alpha analogue and a norgestomet implant on d 12 of the cycle for 3 or 7 d to give approximate durations of dominance of the preovulatory follicle of 2 to 4 d (Dm2-4, n = 29) or 6 to 8 d (Dm6-8, n = 24), respectively. The PR did not differ (P>.05) between heifers on Dm2-4 (22/29) and Dm6-8 (15/24) treatments, but the interval to onset of estrus was delayed (P<.05) by 7 h in the Dm2-4 heifers. In conclusion, restricting the duration of dominance of the preovulatory follicle to < or =4 d at estrus, results in a precise onset of estrus and a high PR following a single AI at a detected estrus.     

In vivo depletion of CD8+ cells does not affect primary maedi visna virus infection in sheep

T-cells have been implicated both, in promoting and reducing viral replication during lentivirus infection. CD8+ lymphocytes are believed to be important in controlling viral load through direct killing of virus-infected cells and by secretion of inhibitory chemokines and cytokines. To evaluate the role of CD8+ T-cells in the induction and control of the primary phase of a lentivirus infection, we have used a non-T-cell tropic lentivirus, maedi-visna virus (MVV), to study the initial pathogenesis and subsequent immune responses in sheep depleted in vivo of CD8+ cells. Sheep were depleted of CD8+ cells in both blood and efferent lymph for up to 14 days. No difference in MVV replication was observed in either the draining efferent lymph or lymph node of these sheep. Surprisingly, these animals displayed a normal induction of pCTL whereas the virus-specific proliferative responses were reduced. This could reflect either that a proportion of functional CD8+ lymphocytes remained in these animals, as suggested by the appearance of pCTLs, or that CD8+ cells are not required for control of primary MVV infection.     

Rainbow trout Oncorhynchus mykiss (Walbaum) type IV ice‐structuring protein LS‐12 in the acute‐phase response to Flavobacterium psychrophilum infection

A previous proteomic study examining the plasma acute‐phase response of rainbow trout to sterile inflammation highlighted an unidentified 9.5‐kDa spot using 2D‐PAGE, which was dramatically increased. The 15 amino acid sequence obtained from this protein spot allowed rapid amplification of cDNA ends PCR to generate a 443‐bp nucleotide sequence that was 98.6% similar to type‐4 ice‐structuring protein LS‐12 from Atlantic salmon Salmo salar Linnaeus. Quantitative reverse translation PCR and an ELISA were used to measure gene expression and plasma concentrations of LS‐12 following experimental intraperitoneal injection of rainbow trout with either 10⁶ or 10⁸ colony‐forming units (CFU) of Flavobacterium psychrophilum. There was no significant change in the plasma concentration of LS‐12 up to 15 days post‐infection in any group. Hepatic LS‐12 gene expression was significantly reduced at 3 and 6 days (p < 0.001) post‐infection in fish injected with 10⁸ CFU of F. psychrophilum relative to control fish, while branchial or head kidney expression was unchanged. Infected fish had significantly increased hepatic gene expression of serum amyloid A, confirming an acute‐phase response. Under the conditions used, LS‐12 is not a positive acute‐phase protein in rainbow trout.     

Bluegill Picornavirus isolated from a mortality event involving Bluegill (Lepomis macrochirus) in the upper Mississippi River

A mortality event involving an estimated 1,000 adult bluegills (Lepomis macrochirus) was observed in an ice‐covered backwater lake of the upper Mississippi River near Alma, Wisconsin, in December of 2017. Macroscopic signs of disease included abdominal distension due to fluid accumulation within the internal organs as well as external and internal haemorrhaging. Histological evaluation revealed chronic peritonitis with peritoneal adhesions in all fish examined. Kidney, spleen and ascites fluid samples were collected from diseased bluegills and examined for the presence of pathogens. Bluegill picornavirus (BGPV) was isolated using tissue cell culture methods utilizing a recently developed, uncharacterized bluegill fry cell line (BF‐4), and the presence of this virus was confirmed through molecular identification. The current geographic range, known susceptible hosts as well as historical epizootics associated with BPGV is discussed. The ability of BGPV to cause significant mortality in wild fish further emphasizes the importance of monitoring both wild and hatchery populations for this pathogen.     

Fisher accessibility and habitat complexity influence the distribution of adult Cherax cainii (Decapoda: Parastacidae) in a water supply reservoir

相似文献   

Potential for nitrogen fertilization and Hessian fly-resistance to improve Morocco's dryland wheat yields

Hessian fly (Mayetiola destructor, Say) is a perennial scourge of cereal production in the Mediterranean region, particularly in North Africa. In Morocco, it accounts for considerable yield losses of wheat (Triticum spp.), especially in the semi-arid southwestern coastal provinces. Breeding for resistance is the only feasible approach to abate its effects. Nine major Hessian fly-resistance genes have been identified in bread wheat. Two bread wheat varieties have these characteristics; the first variety with complete resistance was ‘Saada’, released to farmers in 1989, whereas a tolerant variety ‘Massira’ was released in 1994. Another widespread limiting factor for all cereals in Morocco is lack of adequate nitrogen (N). With favorable farmer acceptance, Saada became the focus of on-farm N fertilizer trials throughout the low rainfall (250-450 mm year⁻¹) zone, where it consistently out-yielded the susceptible common bread wheat, Nesma, except when no Hessian fly infestation occurred. In most cases, 40 kg N ha⁻¹ was adequate for maximum yield. Substituting resistant cultivars for Hessian fly-susceptible cultivars and increased N use could have an immediate and positive effect on wheat production in Morocco, especially in areas where the insect is endemic. The future impact will be greater when Hessian fly resistance is also transferred to other bread wheat cultivars and to durum (T. durum) wheat, the major staple food in the Mediterranean region.     

Monitoring the temporal changes in herbicide-resistant Amaranthus tuberculatus: a landscape-scale probability-based estimation in Iowa

Background

A landscape-scale probability-based sampling of Iowa soybean [Glycine max (L.) Merr.] fields was conducted in 2013 and 2019; Amaranthus tuberculatus [Moq.] J.D. Sauer seed was collected from 97 random geospatial selected fields. The objectives were to evaluate the prevalence and distribution of herbicide-resistant A. tuberculatus (waterhemp) in soybean fields and evaluate temporal changes over 6 years. Amaranthus tuberculatus seedlings were evaluated for resistance to imazethapyr, atrazine, glyphosate, lactofen and mesotrione at 1× and 4× label rates.

Results

Resistance to imazethapyr, glyphosate, lactofen and mesotrione at the 1× rate increased significantly from 2013 to 2019 and was found in 99%, 97%, 16% and 15% of Iowa A. tuberculatus populations in 2019, respectively. Resistance to atrazine at the 4× rate increased over time; atrazine resistance was found in 68% of populations in 2019. Three-way multiple herbicide-resistant A. tuberculatus was the most frequent and increased significantly to 4× rates from 16% in 2013 to 43% of populations in 2019. All A. tuberculatus populations resistant to HPPD-inhibitor herbicides also were resistant to atrazine.

Conclusion

To the best of our knowledge, this is the first probability-based study that presented evolution of A. tuberculatus herbicide resistance over time. The results demonstrated that imazethapyr, atrazine and glyphosate resistance in Iowa A. tuberculatus populations was frequent whereas resistance to lactofen and mesotrione was less frequent. Most Iowa A. tuberculatus populations evolved resistance to multiple sites of action over time. The results of our study are widely applicable given the similarities in weed management practices throughout the Midwest United States. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Partitioning spatial,environmental, and community drivers of ecosystem functioning

Landscape Ecology - Community composition, environmental variation, and spatial structuring can influence ecosystem functioning, and ecosystem service delivery. While the role of space in...     

Genetics of resistance in lettuce to races 1 and 2 of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> from different host species

Race 1 resistance against Verticillium dahliae in lettuce was originally shown in the cultivar La Brillante to be conditioned by a single dominant gene (Verticillium resistance 1, Vr1). Multiple, morphologically diverse sources of germplasm have been identified as resistant to race 1. In this study, allelism tests indicated that resistance in these different lettuce cultivars is closely linked or allelic to the Vr1 gene. The Vr1 gene is defeated by race 2 isolates of V. dahliae. Only partial resistance to race 2 isolates is available in a few plant introductions (PIs). Greenhouse and field experiments conducted with these PIs demonstrated partial resistance to V. dahliae race 1 as well as race 2 isolates from lettuce. Cultivars resistant to race 1 and PIs with partial resistance to race 2 were challenged with several race 1 and 2 isolates originating from hosts other than lettuce. This indicated that cultivars resistant to race 1 and the breeding lines derived from them would also be resistant to race 1 isolates from other hosts; similarly, the partial resistance would be effective against race 1 and 2 isolates from hosts other than lettuce. Nevertheless, there were specific interactions that warrant further study. Although race 1 currently predominates in the major lettuce production area of the Salinas Valley, CA, breeding lettuce for resistance to V. dahliae should take both races into account.     

Recent development of national parks in Nicaragua

Nicaragua, a Central American country, has established two national parks recently and more reserves are in the planning stage. Saslaya National Park, 11,800 ha of virgin tropical rain forest and cloud forest, was established in 1971. Management of the park is as yet minimal, and few data have been collected. Masaya Volcano National Park, 4400 ha, contains an active volcano, a crater lagoon, and lava flows supporting successional stages to the dry deciduous forest. A Master Plan prepared for the area will soon be implemented. An inventory of other potential wildlands is being conducted, from which other reserves will be established. Obstacles to the management of a wildlands system include lack of a responsible government agency, principally, and also lack of trained manpower and funds.