Livestock disease threats associated with intensification of pastoral dairy farming

This paper provides an overview of the changes in the pasture-based dairy systems of New Zealand and Australia that may influence the health of cattle.

There are relatively few available data that can be used to quantify the effects of increased intensification of milk production on the health of cattle. There is evidence that increased production increases the risk of mastitis and culling for udder health. Increased risks of mastitis with treatment with somatotropin support these findings; however, the risk of mastitis may decrease with increased milking frequency. Larger herds with greater stocking density should increase the risk for infectious disease, but evidence to support this contention is sparse.

Very intensive grazing patterns associated with higher grass yields achieved using better cultivars and greater use of fertilisers favour nematode parasites. There is some evidence of anthelmintic resistance in both nematodes and liver fluke. Veterinarians will need to be aware of the potential for these to reduce the productivity of cattle.

There have been benefits of improved nutrition on the efficiency of energy use for dairy production. Diseases such as bloat and ketosis appear to be of lower prevalence. It also appears that mineral nutrition of pasture-fed cattle is being better addressed, with gains in the control of milk fever, hypomagnesaemia and trace-element deficiencies. However, acidosis is a condition with a high point prevalence in pasture-based dairy systems where cows are fed supplements; one study in Australia found a point prevalence of approximately 11% of cows with acidosis. There is evidence from this study that the neutral detergent fibre (NDF) in pasture-based diets may need to be higher than 30% of the diet to maintain rumen stability. Laminitis and acidosis are different conditions with a similar pathogenesis, specifically highly fermentable diets. The prevalence of lameness was 28% in herds in Australia, suggesting that this condition must be a focus for preventive medical approaches, including the design of laneways, feedpads and dairies.     

Rescue of cardiac defects in id knockout embryos by injection of embryonic stem cells

We report that Id knockout mouse embryos display multiple cardiac defects, but mid-gestation lethality is rescued by the injection of 15 wild-type embryonic stem (ES) cells into mutant blastocysts. Myocardial markers altered in Id mutant cells are restored to normal throughout the chimeric myocardium. Intraperitoneal injection of ES cells into female mice before conception also partially rescues the cardiac phenotype with no incorporation of ES cells. Insulin-like growth factor 1, a long-range secreted factor, in combination with WNT5a, a locally secreted factor, likely account for complete reversion of the cardiac phenotype. Thus, ES cells have the potential to reverse congenital defects through Id-dependent local and long-range effects in a mammalian embryo.     

Observations on the pathology of canine microsporidiosis.

The available literature on canine microsporidiosis indicates that this disease, primarily of young dogs, is a distinct clinicopathological entity. It has been confused with canine distemper and rabies, and must be differentiated from toxoplasmosis. Information available on the spectrum of pathological change associated with this disease is incomplete but a distinct pattern emerges from a study of the reports. The aetiological agent appears to have a predilection for the central nervous system and kidneys, but other tissues and organs, and especially the liver, may also be infected. Vasculitis and perivasculitis, which may include fibrinoid necrosis, seem to be a basic lesion. Cellular inflammation ranges from polymorphonuclear leukocyte infiltration in areas of necrosis to focal granulomas. There may be no cellular reaction to compact groups of organisms. Histopathological and ultrastructural studies of this case augment our knowledge of the pathological changes seen with canine microsporidiosis.     

The effects of lactation on the fertility of dairy cows

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.     

An outbreak of contagious bovine pleuropneumonia in the Owambo Mangetti area of South West Africa/Namibia: microbiological, immunofluorescent, pathological and serological findings

An outbreak of contagious bovine pleuropneumonia (CBPP) in the Owambo Mangetti area of South West Africa/Namibia in 1982 led to the slaughter of 3,153 cattle. The lungs of 266 of these animals were scrutinized for gross lesions of CBPP and samples of lung tissue, sequestral contents or pleural fluid were submitted to the Veterinary Research Institute (VRI), Onderstepoort for microbiological, immunofluorescent and pathological examination. Immunofluorescence proved to be the most successful method of diagnosis producing 96% of positives, while mycoplasma isolations were only positive in 64% of the 55 specimens processed in parallel. This clearly demonstrated the value of the former technique in the accurate as well as rapid diagnosis of CBPP. The impression smear technique employed, using Eriochrome black counterstaining proved most satisfactory and easy to interpret. The isolation of M. mycoides was influenced by the transit times and temperature of the samples on arrival at the VRI. No pathogenic bacteria were found in routine aerobic bacterial cultures from 27 of the samples submitted. Complement fixing antibodies were present in the sera of 16 cattle and titres varied between 10 and 320. Animals in which antibodies were absent included those with early lung lesions and some with sequestra.     

Observations on naturally acquired hepatozoonosis of wild carnivores and dogs in the Republic of South Africa.

Hepatozoonosis was studied in hyaenas, lions, jackals, cheetahs and one leopard in the Kruger National Park and compared with the condition seen in dogs in the Republic of South Africa. Hepatozoon schizonts were found in the wild carnivores. The genesis of microschizonts was followed and is illustrated. The schizonts were sometimes very plentiful in the lung, myocardium and skeletal muscle, and were also encountered in the spleen, liver and lymph nodes. Gametocytes were present in leucocytes. The host response was usually very mild. sporogenous development in ticks was observed in Rhipicephalus simus females removed from an infected hyaena and R. sanguinelus adults fed on an infected jackal in the nymphal stage. Attempts to transmit Hepatozoon from a jackal to dogs by means of ticks gave inconclusive results.     

C, N, and noble gas isotopes in grain size separates of presolar diamonds from efremovka

Nanometer-size presolar diamonds from the Efremovka CV3 chondrite were physically separated into several grain size fractions by ultracentrifugation. The coarsest size fraction is the most enriched in carbon-12; the others have broadly similar carbon isotopic compositions. Measurement of noble gases shows that their concentration decreases with decreasing grain size. This effect is attributed to ion implantation. Such an episode could occur in the envelope of a supernova that produced the diamonds, or in interstellar space; in either case, ions with energies above a certain threshold pass completely through the smaller diamond grains without being captured. Concentrations of nitrogen show only minor variations with grain size, indicating a different mechanism of incorporation into the diamonds.