School of Agriculture, Food and Ecosystem Sciences

Onion-grass [Romulea rosea (L.) Eckl.] is a widespread perennial in pastures and turfs over most of Victoria and parts of the other southern states of Australia. Introduced from South Africa last century, its persistence, toughness of its leaves, uppalatability to stock, and association with animal disorders have caused some concern. The plant is thought to cause "romulosis", a severe infertility disease in ewes, and can be responsible for the formation of fibre balls (phytobezoars) in the digestive tracts of cattle and horses. Onion-grass corms, dormant over summer, shoot in autumn and send up thin, strap-like leaves. As growth proceeds, a single new corm replaces the old one for each plant. Flowering commences in August, and the seeds ripen in capsules which split open in late spring. The seeds are readily ingested by grazing animals and dispersed via the faeces, with often as many as 500 viable seeds being dispersed per sheep per day. Because germination is relatively slow, has a low optimum temperature (close to 11 C) and is inhibited by temperatures over 19 C, it is usually delayed until late autumn. The formation of contractile roots in both seedlings and plants arising from corms helps to draw the growing point well below the soil surface. With these characteristics, onion-grass is well adapted for survival. However it is not a vigorous plant, exerting little competitive effect on other pasture species, and is itself susceptible to competition from them if the pasture is uniformly defoliated. Neither is it an agressive spreader, and will not generally invade a vigorous sward. Where onion-grass is established, selective grazing favours its persistence, particularly at low stocking rates. The plant also thrives where grazing is excluded. While it is difficult to eradicate, some control may be achieved in the long term by periods of heavy grazing of pastures to which moderate rates of nitrogen and phosphorus have been applied. In some situations, mowing to a height of 2.5cm may also be of benefit. Herbicides have generally proved ineffective or uneconomic because of damage to useful pasture species, but glyphosate, using wick application, could be a valuable tool in the future. Cultivation can be effective, but the appropriate method and timing need further clarification.

1. The study concerned the significance of change of diet and feeding method on the clinical, pathological and growth responses of 3- to 4-week-old pigs when subjected either to challenge with an enterotoxigenic serotype of Escherichia coli or exposed to 'natural' infection with E.coli. It involved experiments with both hysterotomy-derived specific pathogen-free (SPF) piglets and conventionally reared animals. The dietary treatments involved comparisons between (i) wet versus dry feeding and (ii) skim milk versus soyabean (SB) meal as the major dietary protein source. 2. Under closely controlled SPF conditions, thirty-five 28-day-old piglets were used in five experiments. In the first four experiments, two groups were changed from a liquid cow's milk diet to a milk-based diet (termed the 'basal' diet), given either in wet or dry form. Within each group, half of the animals were orally challenged with enterotoxigenic E.coli (ETEC) bearing the K88 antigen and the remainder, serving as controls, were challenged with a non-pathogenic K12 E.coli strain. ETEC-infected piglets fed the dry, basal diet developed severe diarrhoea, depression and dehydration and at necropsy exhibited severe lesions in the small intestine associated with extensive bacterial adherence and marked reduction in intestinal lactase activity. Infected piglets fed the basal diet as a gruel had only mild diarrhoea, accompanied by limited bacterial adherence and minor mucosal and physiological changes. Control piglets, fed either dry or wet, remained clinically healthy and the morphology of the intestinal mucosa was normal. In the fifth experiment, two groups were changed from the liquid cow's milk diet to either a dry-fed basal diet or a dry-fed SB-based diet; each group consisted of both infected and control animals. Control piglets on both diets remained clinically normal with only minor mucosal changes; but the intestinal lactase activity of those fed the SB diet was depressed. Infected piglets fed the SB diet developed mild diarrhoea, depression and dehydration. Infected piglets fed the basal diet had no diarrhoea but were depressed. Bacterial colonization, mucosal and physiological changes were relatively more severe in the SB-fed animals than in those fed the basal diet. 3. Under conventional conditions, a total 0f one hundred and seventy-six piglets, from the Mt Derrimut herd, were used in three experiments. In each of these experiments, pigs were allocated among four dietary treatments: dry, basal; wet, basal; dry, SB; and wet, SB. In Expt 1, a total of twenty-four pigs were orally inoculated with K88 ETEC following their transfer at weaning to non-specialized pen accommodation (at the Attwood Institute for Veterinary Research). In Expts 2 and 3, (conducted at the Mt Derrimut Pig Centre), ninety-six and fifty-six pigs respectively were moved at weaning into specialized weaner accommodation that was routinely used for early weaning on a batch basis. No inoculations with ETEC were performed in these two experiments. In Expt 1, all pigs remained clinically normal except for one pig fed the SB diet dry. Post-mortem studies conducted on four selected pigs from each treatment group revealed very limited colonization by ETEC but without marked changes in gut morphology (although K88 ETEC were present in faecal materials). In Expts 2 and 3, natural infection with ETEC and manifestation of PWD (postweaning diarrhoea) occurred. As compared with the SB diet, the basal diet particularly when fed wet, resulted in a less severe diarrhoea. Morphological and physiological changes in the small intestine were less pronounced and bacterial adherence was less extensive. Whether the SB diet was fed wet or dry made little difference in these respects. In the first 14 days post-weaning pigs fed the basal diet, especially when this was fed wet, made faster and more efficient weight gains than those given the SB diet. The degree of infection was more widespread and severe in Expt 3 than in Expt 2. In Expt 3, the superiority of the milk-based diet compared to the SB diet was relatively greater during the first 14 days post-weaning. 4. The results indicated that both the type of diet and the form in which the diet was fed, significantly influenced the extent of colonization of the gut by ETEC, the severity of PWD and growth performance. The effects of feeding method were more apparent in the SPF piglets than in the conventional piglets. This was attributed to the greater influence of uncontrolled variables in the latter situation. 5. The greater variability of performance under the conventional rearing conditions and the marked difference in response to ETEC in Expt 1 compared with that in Expts 2 and 3 suggest that in addition to the dietary factors examined, other factors, such as the immune status of the animal, the level of 'background' pathogenic challenge and the physical environment were implicated in the pathogenesis of PWD.

School of Agriculture, Food and Ecosystem Sciences - Theses

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