Using plant breeding and genetics to overcome the incidence of grass tetany

Plant breeders developing cultivars to minimize the hazards of grass tetany are concentrating largely on increasing herbage Mg concentrations in cool-season (C3) grasses. Significant genetic variation has been found for Mg, Ca and K concentrations within C3 grass species studied to date. For most C3 forage grass species, heritability estimates are highest for Mg, slightly lower for Ca and lowest for K concentrations. The largest genotype x environmental interactions are found for K values, whereas small environmental effects have been observed for Mg and Ca values. No C3 forage grass cultivar has been developed to date that would eliminate hypomagnesemia. Grass breeders need to develop more experimental C3 plant populations that have high Mg and Ca concentrations. These experimental synthetics with genetically altered mineral concentrations need to be fed to ruminants susceptible to grass tetany to determine whether grass tetany can be eliminated or reduced. Limited feeding trials using ruminants show that improved animal performance can be expected when feeding forage grasses bred for higher Mg concentrations.     

Use of animal breeds and breeding to overcome the incidence of grass tetany: a review

British breeds of cattle are not so effective as Zebu in extracting nutrients from low-quality roughages, and these breeds differ in their nutrient metabolism and animal physiology. Breeds of cattle may differ in their requirements for Mg. Brahman cows are less susceptible to death from disease and metabolic disorders than are British breeds of cattle, whereas cows with 50% or greater dairy breeding (Holstein and Jersey) are more susceptible than British or Brahman breeds when maintained in beef production herds. Brahman or Brahman crossbred cows are less susceptible than other breeds to metabolic disorders such as grass tetany. Magnesium absorption has been shown to be greater in Brahman than in Jersey, Holstein and Hereford cows. These differences in the efficiency of Mg absorption between different breeds of cows may be due to genetic variation in the absorptive mechanisms of Mg, in feeding behavior, in gastrointestinal tract motility, in gastrointestinal tract fill or to some combination.     

Factors predisposing dairy and beef cows to grass tetany

In a study of dairy and beef herds on 120 farms in south-western Victoria, losses attributed to grass tetany were shown to have been an important cause of economic loss during the cooler months of 1980. Thin dairy cows had a higher incidence of suspected grass tetany than dairy cows in moderate body condition, and both thin and fat beef cows had a higher incidence than beef cows in moderate body condition. A lower incidence was found among dairy cows when the available pasture or hay contained a high percentage of clover, when cows in moderate body condition had been grazed on pastures topdressed with low rates of potassium fertilisers, and when cows had been rotated onto fresh pasture at least daily rather than at 2 or 3 day intervals. The incidence among dairy cows was also associated with the length of available pasture, the correlation being positive for cows of moderate body condition, but negative for thin cows. Possible reasons for the associations are discussed. Only a small proportion of farmers adopted measures to prevent grass tetany, and those who did often applied them inefficiently. Practicable control measures are suggested on the basis of the survey results.     

Pathophysiology of grass tetany and other hypomagnesemias. Implications for clinical management.

Magnesium is an essential mineral with many physiologic and biochemical functions. Surprisingly, Mg homeostasis is not regulated by a hormonal feedback system, but simply depends on inflow (absorption) from the gastrointestinal tract and outflow (endogenous secretion, requirement for milk production, uptake by tissues). Any surplus (inflow greater than outflow) is excreted via urine. Conversely, if the outflow (mainly milk secretion and endogenous loss) exceeds inflow, hypomagnesemia occurs because of the lack of hormonal mechanisms of homeostasis. The major reason for insufficient inflow is a reduced absorption of Mg from the forestomachs. Recent studies from our laboratory and data from the literature permit the proposal of a putative transport model for the secondary active transport of Mg across the rumen epithelium. This model includes two uptake mechanisms across the luminal membrane (PD-dependent and PD-independent) and basolateral extrusion via a Na/Mg exchange. The well-known negative interaction between ruminal K concentration and Mg absorption can be explained on the basis of this model: an increase of ruminal K depolarizes the potential difference of the luminal membrane, PDa, and as the driving force for PD-dependent (or K-sensitive) Mg uptake. Because Na deficiency causes an increase of K concentration in saliva and ruminal fluid, Na deficiency should be considered a potentially important risk factor. The data obtained from in vitro and in vivo studies on the association of Mg transport, changes of ruminal K concentration, and PDa are extensive and confirm the model, if the ruminal Mg concentrations are below 2 to 3 mM. It is further proposed by the model that the PD-independent Mg uptake mechanism is primarily working at high ruminal Mg concentration (above 2 mM). Mg absorption becomes more and more independent of ruminal K with increasing Mg concentration, which can be considered as an explanation for the well-known prophylaxis of hypomagnesemia by increasing oral Mg intake. Fermentation products, NH4+ and SCFA, influence Mg absorption. The possible meaning regarding the pathogenesis of hypomagnesemia is not quite clear. A sudden increase of ruminal NH4+ should be avoided, because high NH4+ concentrations transiently reduce Mg absorption. The most prominent signs of hypomagnesemia are excitations and muscle cramps, which are closely correlated with the Mg concentration in the CSF. It is suggested that the clinical signs are caused by spontaneous activation of neurons in the CNS at low Mg concentrations, which leads to tetany. Prophylactic measures are discussed in context with the known effects on ruminal Mg absorption.     

Acquired urinary incontinence in bitches: its incidence and relationship to neutering practices

A five-year cohort study was conducted on bitches chosen by a sample of 233 randomly selected practising veterinary surgeons in the UK, to estimate the incidence of acquired urinary incontinence (AUI) in neutered and entire animals, and to investigate possible risk factors associated with neutering practices. Information was collected using questionnaires, and data on 809 bitches, of which 22 developed AUI, were obtained. The estimated incidence rates in neutered and entire animals were 0·0174 and 0·0022 per animal-year, respectively (95 per cent confidence intervals: 0·0110, 0·0275 and 0·0009, 0·0058, respectively). The relative risk, neutered vs entire, was 7·8 (95 per cent confidence interval: 2·6, 31·5). The attributable proportion_exposed and population attributable proportion were 87·1 per cent and 63·1 per cent (95 per cent confidence intervals: 61·9 per cent, 95·6 per cent, and 28·3 per cent, 88·5 per cent, respectively). An increased risk, significant at the conventional 5 per cent level, was not demonstrated in animals neutered before, vs after, first heat (relative risk: 3·9, 95 per cent confidence interval: 0·8, 10·4), although the result was significant at the 10 per cent level. Removal of the cervix was not shown to be a risk factor in neutered dogs.     

Questionnaire on the incidence and control of fleas in dogs and cats presented to German small animal practices

2590 small animal practitioners in Germany have been asked by a questionnaire from which 1694 (65.4%) replied. 1186 of these veterinarians (70%) often see ectoparasite infestation. Fleas are predominant and occur on cats (1016/60%), followed by dogs (424/25%), small mammals and birds (254/15%). Flea infestations on dogs and cats are observed throughout the year, but the prevalences are generally higher during the summer season. The results reveal that topically administered spot-on formulations is the most popular method used for flea control. The most common applied antiparasitic substances both in dogs and in cats were fipronil (535/31.6%; 690/40.7%), imidacloprid (290/17.1%; 417/24.6%) and selamectin (267/15.8%; 319/18.8%). Due to 771 (45.5%) of the answering veterinarians the animal owner himself, and according 694 (41%) respectively 229 (13.5%) of the replies the veterinarian or the veterinary technician applies the antiparasiticide onto the skin. 1457 veterinarians (86%) administer compounds against adult fleas and their developmental stages also in the animal's environment.     

如何克服宠物就诊后的恐惧心理

常有宠物主人反应,宠物就诊后,尤其回家后出现烦煤不安,莫名尖叫,喜阴暗角落,不理主人,甚至攻击主人.严重的会持续数天至数月,通过对症处理后才慢慢平息,恢复正常.那么,如何克服宠物就诊后的恐惧心理呢?