1. Brown egg laying pullets were transferred from an 8‐h photoperiod to an 8‐, 10‐, 13‐ or 16‐h photoperiod at 6, 9, 12, 15, 18 or 20–3 weeks of age. Plasma luteinising hormone (LH) concentrations were measured at transfer and 7 and 14 d afterwards.
2. Significant increases in plasma LH occurred following light stimulations at 6, 9 and 12 weeks of age.
3. Changes in LH concentration 7 d after a light increase from 8 h to 8, 10, 13, 16 h were highly correlated with photoperiod length at 9 and 12 weeks of age.
4. Changes in LH were generally poorly correlated with age at sexual maturity, although the reduced influence on age at first egg of a light increase given close to sexual maturity was reflected in minimal LH responses at 18 and 20.3 weeks. 相似文献
Forage technology has been successfully introduced into smallholder cattle systems in Cambodia as an alternative feed source to the traditional rice straw and native pastures, improving animal nutrition and reducing labour requirements of feeding cattle. Previous research has highlighted the positive impacts of forage technology including improved growth rates of cattle and household time savings. However, further research is required to understand the drivers, challenges and opportunities of forage technology for smallholder cattle households in Cambodia to facilitate widespread adoption and identify areas for further improvement. A survey of forage-growing households (n = 40) in July–September 2016 examined forage technology adoption experiences, including reasons for forage establishment, use of inputs and labour requirements of forage plot maintenance and use of forages (feeding, fattening, sale of grass or seedlings and silage). Time savings was reported as the main driver of forage adoption with household members spending approximately 1 h per day maintaining forages and feeding it to cattle. Water availability was reported as the main challenge to this activity. A small number of households also reported lack of labour, lack of fencing, competition from natural grasses, cost of irrigation and lack of experience as challenges to forage growing. Cattle fattening and sale of cut forage grass and seedlings was not found to be a widespread activity by interviewed households, with 25 and 10% of households reporting use of forages for these activities, respectively. Currently, opportunities exist for these households to better utilise forages through expansion of forage plots and cattle activities, although assistance is required to support these households in addressing current constraints, particularly availability of water, if the sustainability of this feed technology for smallholder cattle household is to be established in Cambodia. 相似文献
Leptin may play a role in the endocrine-metabolic processes that guarantee the physiological course of lactation in dairy cattle. This study was aimed at determining the changes in plasma concentrations of leptin and some of the main hormones and metabolites involved in the lactogenetic process in high-yielding dairy cows throughout lactation; we also wanted to assess whether leptin secretion is subjected to seasonal influences. Blood samples were collected from 23 Italian Friesian dairy cows from the end of a lactation to the ninth month of the subsequent one; in addition, blood was sampled from 47 dairy cows in different phases of lactation during February and July. Plasma concentrations of leptin, growth hormone (GH), insulin, prolactin (PRL), glucose, non-esterified fatty acids (NEFA) and urea were quantified by either validated radioimmunoassay (RIA) or enzymatic colorimetric methods. At the beginning of lactation, GH concentrations significantly increased, while a significant reduction occurred in leptin and insulin. This endocrine condition, such as the significant increase in NEFA plasma concentrations, is indicative of a marked lipid mobilization. In the more advanced stages of lactation, when both energy and protein balances become positive, leptin plasma concentrations increased, whereas GH and NEFA concentrations declined. During the summer months, a significant increase in leptin plasma concentrations, irrespective of the phase of lactation, was observed. Collectively, our findings suggest that, in dairy cows, leptin may represent a 'metabolic signal' of animal's status of fattening and nutritional level; in addition, leptin seems to be influenced by photoperiod and environmental temperature. 相似文献
Phymastichus coffea LaSalle (Hymenoptera:Eulophidae) is an adult endoparasitoid of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera:Curculionidae:Scolytinae), which has been introduced in many coffee producing countries as a biological control agent. To determine the effectiveness of P. coffea against H. hampei and environmental safety for release in Hawaii, we investigated the host selection and parasitism response of adult females to 43 different species of Coleoptera, including 23 Scolytinae (six Hypothenemus species and 17 others), and four additional Curculionidae. Non-target testing included Hawaiian endemic, exotic and beneficial coleopteran species. Using a no-choice laboratory bioassay, we demonstrated that P. coffea was only able to parasitize the target host H. hampei and four other adventive species of Hypothenemus: H. obscurus, H. seriatus, H. birmanus and H. crudiae. Hypothenemus hampei had the highest parasitism rate and shortest parasitoid development time of the five parasitized Hypothenemus spp. Parasitism and parasitoid emergence decreased with decreasing phylogenetic relatedness of the Hypothenemus spp. to H. hampei, and the most distantly related species, H. eruditus, was not parasitized. These results suggest that the risk of harmful non-target impacts is low because there are no native species of Hypothenemus in Hawaii, and P. coffea could be safely introduced for classical biological control of H. hampei in Hawaii.
The relationship between the serological classification system for serogroup B and for serogroup H of Bacteroides nodosus and cross-protection between subgroups within these serogroups was examined. Protection against ovine footrot following vaccination was achieved against other subgroup strains provided sufficient cross-reactive antibody was induced by shared pilus antigens. Within serogroup B, better cross-protection against one subgroup was obtained with a pili vaccine than a whole cell vaccine which correlated with higher pilus antibody titres induced by the former. For serogroup H, a lack of cross-protection and serological reactivity between subgroups was demonstrated, which indicates that the prototype strain of subgroup H2 should be designated a new serogroup. 相似文献