Attainment of puberty in Romney ewe lambs was studied at Wye Sheep Research Unit of the Imperial College (University of London) in the U.K. 77% of females exposed to rams during the breeding season reached puberty. Ovulation effectively accompanied first behavioural oestrus. The evidence of silent ovulation before pubertal oestrus and after the last oestrus of the breeding season was established. Keywords : ewe lamb-puberty-ovulation-laparoscopy-progesterone RESUME Une etude sur l=avenement de la puberte chez les agnelles Romney a eu lieu a l=unite de recherche des ovins de l=Imprial College (Universite de Londres) a Wye au Royaume uni. 77% des agnelles ont atteint la puberte au cours de la saison de reproduction. L.oestrus pubertal etait effectivement suivi des ovulations. L.evidence des ovulations avant l.oestrus pubertal et apres le dernier oestrus de la saison de reproduction est confirmee. Mots cles : agnelle-puberte-ovulation-laparoscopie-progesterone Journal of the Cameroon Academy of Sciences Vol. 5(1) 2005: 29-35

Bovine Respiratory Disease (BRD) results from a complex, multifactorial interaction of stressors, animal susceptibility, and respiratory pathogens. The infectious agents associated with BRD are ubiquitous among cattle populations. Typically, one or a combination of stressors are necessary to initiate BRD. Prevention of BRD should, therefore, address management procedures to minimise stressors. Administration of vaccines against BRD agents may help reduce the incidence of BRD but is unlikely to eliminate the condition. The effectiveness of antimicrobials in the treatment of BRD depends primarily on early recognition and treatment. The use of antioxidant vitamins, minerals or other agents in the prevention and treatment of BRD warrants further research.

OBJECTIVES:To identify risk factors for culling of dairy cows from eight New South Wales dairy herds.DESIGN:A longitudinal population study of dairy cow culling in eight non-seasonally calving dairy herds in the Camden district of New South Wales. Cox's proportional hazards model was used to evaluate various risk factors for culling for a specific reason (sales, deaths, reproductive failure, disorders of the udder and low milk production).RESULTS:Age at first calving was not a significant risk factor for culling. Milk production in the first lactation greater than the population mean did not influence length of productive life overall, but was associated with a greater hazard of removal for disorders of the udder. Risk of culling for reproductive failure differed significantly between farms, and was not related to events in the previous lactation such as calving-to-first service interval or calving-to-conception interval. Shorter calving intervals were associated with increased risk of removal for low milk production and disorders of the udder.CONCLUSION:Longitudinal surveys to accurately identify reasons for removal from a wide range of herds, identification of herds with low culling rates (especially for reproductive failure and udder disorders), and the identification of practices associated with these culling rates would be worthwhile to the Australian dairy industry.

Australian Veterinary JournalVolume 76, Issue 9 p. 608-609 Free Access Food animal veterinary medicine: whereto and why? IJ LEAN, IJ LEAN Strategic Bovine Services, 7 Broughton Street, Camden, New South Wales 2570Search for more papers by this author IJ LEAN, IJ LEAN Strategic Bovine Services, 7 Broughton Street, Camden, New South Wales 2570Search for more papers by this author First published: 10 March 2008 https://doi.org/10.1111/j.1751-0813.1998.tb10239.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume76, Issue9September 1998Pages 608-609 ReferencesRelatedInformation

OBJECTIVES:To determine whether a multivariate model could be developed to describe farm factors affecting fertility of dairy herd and to examine the factors that determined better reproductive performance on dairy farms in New South Wales.PROCEDURE:We examined the results of a survey of breeding practices, mating policies, recording systems, timing of mating, heat detection, treatment of metritis and manager demographics of dairy farms using Principal components analysis, logistic regression and the sign test.RESULTS:Eight principal components for heat detection computed using Principal component analyses were included in the multivariate model to reflect primary and secondary heat detection signs used in the breeding decisions of managers. A final model identified three variables: optimum number of days to first service, number of people detecting heats, and age of manager which significantly influenced the risk of being in the high or low reproductive performance groups. A failure to breed at an appropriate time after calving and having more people responsible for heat detection was associated with herds with a prolonged intercalving interval. While the model provided a good fit for the data, it was not highly discriminatory. Examination of 83 management practices affecting fertility using the sign test (P = 0.01) indicated that managers of herds with good reproductive performance employed better management and breeding practices more often than managers of herds with poor reproductive performance.CONCLUSIONS:Mating cows sooner after calving and using fewer people to detect oestrus should reduce calving to conception intervals. Veterinarians investigating herd reproductive performance should consider the potential for a number of subtle failures of management to significantly impair fertility rather than limit investigations to a few factors.

Lactation has been negatively associated with fertility because pregnancy rates in maiden heifers exceed those obtained after first or subsequent calvings. The extent of this difference is less in pasture-fed dairy cows ( < 10%) than in American Holsteins ( > 20%) fed grain and conserved forages. The latter cows have pregnancy rates to first insemination and oestrus detection rates of only 40 to 45%. This suggests that the subsequent fertility of inherently fertile Holstein heifers may be severely compromised by high levels of milk production. International comparisons show that pasture-fed dairy cows may experience extended periods of anovulatory anoestrum but have normal fertility (60% pregnancy rate to first insemination) once cycling. The high-producing American Holstein may ovulate within 4 weeks postpartum but is more likely to continue ovulating without being detected in oestrus. Both situations are associated with negative energy balances (NEB) during early lactation. The severity and duration of this NEB may vary with body condition at calving, age or parity, ration formulation, production level and environmental factors. Relative daily milk yield is not an absolute indicator of NEB, because some lower producing cows within a herd have lower feed intakes and more severe energy deficits. NEB is not simple to measure; nonetheless, it is correlated with genetic improvement for milk yield. A positive energy balance, greater weight gain and higher body condition score have all been shown to be positively correlated with plasma progesterone concentrations in early lactation. No studies have investigated the possibility that the rapid increase in metabolic rate at this time may also alter steroid concentrations with consequent effects on oestrous behaviour and fertility. Studies to more precisely define the effects of increasing milk yields in early lactation, especially in Holsteins, may need to be completed in Australia and New Zealand. Oestrus detection rates and pregnancy rates for American Holsteins of less than 50% are accepted widely in the USA. Such low detection rates confound studies on fertility. The objective should be to increase these 2 rates to at least 80% and 60% respectively. This may involve the use of controlled breeding, especially if oestrous behaviour is less overt in high-producing Holstein cows.

Australasian dairy production is favored by excellent climates, temperate pastures and, in parts, access to low-cost commodities resulting in a lower cost of production.Poor production efficiency can result if quota systems are rigid, but some supply management is beneficial to producers, especially if market signals are ignored under production driven systems.The challenge facing the smaller farm worldwide is to expand or improve performance in the face of falling prices for milk.Farms that survive will perform better than their peers by managing rather than doing, by improving nutritional management of the herds, and by adapting to change.For Canada to gain a larger portion of the international market Canadian dairy products will need to be unique or of superior quality.