Effect of long-term fluticasone treatment on immune function in horses with heaves

Background: Corticosteroids currently are the most effective pharmacological treatment available to control heaves in horses. Systemically administered corticosteroids have been shown to alter immune response in horses, humans, and other species. Aerosolized administration theoretically minimizes systemic adverse effects, but the effect of inhaled corticosteroids on immune function has not been evaluated in horses. Objectives: To evaluate the effects of prolonged administration of inhaled fluticasone on the immune system of heaves‐affected horses. Animals: Heaves‐affected horses were treated with inhaled fluticasone (n = 5) for 11 months or received environmental modifications only (n = 5). Methods: Prospective analysis. Clinical parameters and CBC, lymphocyte subpopulations and function, and circulating neutrophil gene expression were sequentially measured. Primary and anamnestic immune responses also were evaluated by measuring antigen‐specific antibodies in response to vaccination with bovine viral antigen and tetanus toxoid, respectively. Results: No clinical adverse effects were observed and no differences in immune function were detected between treated and untreated horses. Conclusions and Clinical Importance: The treatment of heaves‐affected horses with inhaled fluticasone at therapeutic dosages for 11 months has no significant detectable effect on innate and adaptive (both humoral and cell‐mediated) immune parameters studied. These results suggest that prolonged administration of fluticasone would not compromise the systemic immune response to pathogens nor vaccination in adult horses.     

Factors affecting pregnancy rate in Holstein-Friesian cattle mated during summer in a tropical upland environment

SUMMARY The relationships between some environmental factors and reproductive rates of dairy cattle during summer in a tropical upland area were studied using records for Holstein-Frieslan milking cows and non-lactating growing helfers maintained at the Kalri Research Station on the Atherton Tableland in north Queensland. The Station is situated in a tropical upland environment with warm, wet summers and dry, cool winters. Data were collected over a 12-year-period (1977 to 1988) for cows grazing nitrogen (N)-fertilised grass pastures and receiving either no supplement or about 3.5 kg molasses/cow/day. Cattle were mated over a 10-week period starting from mid-January to early February, with 32 to 36 cows and 5 to 42 heifers used in each year. There was considerable variation among years in the pregnancy rate after 3 Inseminations, with a low of 39% and a high of 94% pregnancy. This variation from year to year was reduced for cows grazing pastures receiving 300 kg N/ha/yr after molasses feeding commenced in 1984–85. Pregnancy rates after molasses Introduction were higher for cows grazing pastures receiving 300 compared with 100 kg N/ha/yr. Pregnancy rate in cows and heifers was reduced from 80 to 55% as mean daily maximum temperature increased from 26°C to 27.5°C. At mean maximum temperatures above 27°C for cows and 27.6°C for heifers pregnancy rates to 3 Inseminations were consistently below 60%. Much of the year to year variation in pregnancy rate was related to rainfall during the mating period. There was a positive association between pregnancy rate and rainfall up to 1000 mm, and this was associated with differences in growth rate of pasture. In years of very high rainfall, above 1500 mm, there was a depression in pregnancy rate, which may be related to the intense humidity in very wet years causing heat stress in cows and associated problems such as feet infections, or a deterioration in pasture quality. We conclude that much of the variation in pregnancy rate during summer may have been related to heat stress and the level of feed supply in the form of pasture and supplements.     

Cartilage matrix changes in the developing epiphysis: early events on the pathway to equine osteochondrosis?

REASONS FOR PERFORMING STUDY: The earliest osteochondrosis (OC) microscopic lesion reported in the literature was present in the femorotibial joint of a 2-day-old foal suggesting that OC lesions and factors initiating them may arise prior to birth. OBJECTIVE: To examine the developing equine epiphysis to detect histological changes that could be precursors to OC lesions. METHODS: Osteochondral samples from 21 equine fetuses and 13 foals were harvested from selected sites in the scapulohumeral, humeroradial, metacarpophalangeal, femoropatellar, femorotibial, tarsocrural and metatarsophalangeal joints. Sections were stained with safranin O and picrosiruis red to assess cartilage changes and structural arrangement of the collagen matrix. RESULTS: Extracellular matrix changes observed included perivascular areas of paleness of the proteoglycan matrix associated with hypocellularity and, sometimes, necrotic chondrocytes. These changes were most abundant in the youngest fetuses and in the femoropatellar/femorotibial (FP/FT) joints. Indentations of the ossification front were also observed in most specimens, but, most frequently, in scapulohumeral and FP/FT joints. A cartilage canal was almost always present in these indentations. The vascular density of the cartilage was higher in the youngest fetuses. In these fetuses, the most vascularised joints were the metacarpo- and metatarsophalangeal joints but their cartilage canals regressed quickly. After birth, the most vascularised cartilage was present in the FP/FT joint. Articular cartilage differentiated into 4 zones early in fetal life and the epiphyseal cartilage also had a distinct zonal cartilage structure. A striking difference was observed in the collagen structure at the junction of the proliferative and hypertrophic zones where OCD lesions occur. CONCLUSION: Matrix and ossification front changes were frequently observed and significantly associated with cartilage canals suggesting that they may be physiological changes associated with matrix remodelling and development. The collagen structure was variable through the growing epiphysis and a differential in biomechanical properties at focal sites may predispose them to injury.