Fluid and particulate retention times in sheep as influenced by intake level and forage morphological composition

Objectives of this study were 1) to measure small-particle and liquid mean retention time (MRT) of 12 grass hays similar in NDF (61.3 +/- 1.9% NDF) but differing in morphological composition and to relate passage rates to proportions of blade, sheath and stem and 2) to evaluate the influence of MRT of small and large blade and stem fractions and large sheath fractions, in addition to morphological composition, on intake and digestibility of the 12 hays. In each of two periods, 24 sheep (wethers) were offered one of 12 hays at three consecutive levels of feeding: (L1) ad libitum, allowing 15% refusal; (L2) restricted to 100% of hay consumed ad libitum by an individual wether during L1; and (L3) 1.8% of BW on a DM basis. Hays offered included two sorghum-sudan, four barley, four oat and two pearl millet. Marked particles were pulse-dosed in L2 and L3. Large and small particles of stem and leaf were extracted with neutral detergent and marked with Cr or rare earth metals. Marked large and small stem particle MRT generally were longer (P less than .05) than those of corresponding large and small blade particles. Large sheath particles generally had an intermediate (P less than .05) MRT between those of large stem and blade particles. Mean retention times of marked fractions were lower (P less than .05) in L2 than in L3. Small particle MRT in L2 was longer than MRT for liquid, though correlations were high (r = .74 to .86, P less than .01). Large particles were retained longer than small particles. Particle size, morphology, and percentage of stem in the forage influenced the mean retention time. Use of representative samples of all fractions fed to measure retention times may lead to a better understanding of ruminal function and to improvements in explanations of intake regulation, because marked fractions do not behave identically for all forages.     

Relationships between genetic, environmental and nutritional factors influencing osteoporosis in laying hens

1. The effects upon bone quality of feeding limestone in flour or particulate form and housing type (cage or aviary) in lines of hens divergently selected for high (H) or low (L) bone strength over 7 generations were investigated. 2. As in previous generations, highly significant phenotypic differences between lines were observed in all measured bone traits at peak egg production (25 weeks) and towards the end of production (56 weeks) in both cage and aviary systems. 3. At 25 weeks there were no significant effects on bone variables of feeding particulate limestone although a significant reduction in osteoclast number was observed at this age. By 56 weeks osteoclast numbers were further reduced in hens fed particulate limestone and beneficial effects on some bone variables were observed in this treatment group. 4. The genotypic and dietary improvements upon bone quality were independent and additive at both ages. There were very few interactive effects. 5. Hens with the freedom to move in an aviary environment during the laying period had improved bone status compared to caged siblings. Environmental and genotypic effects were additive. 6. There were no effects of line on egg production although H line hens had slightly higher egg production by 56 weeks. Egg numbers were unaffected by diet. Eggshell thickness and strength were unaffected by line but hens fed particulate limestone had thicker- and stronger-shelled eggs over the production period as a whole. 7. We conclude that; (a) genetic selection is extremely effective in improving bone strength and resistance to osteoporosis; (b) allowing hens freedom to exercise can also improve bone strength but may increase the risk of keel damage if they do not have genetically-improved bone status; (c) feeding hens a particulate form of limestone from 15 weeks onwards can also increase bone strength and eggshell quality; (d) genetics, environment and nutrition all have independent and additive effects on bone status in laying hens but the relative effectiveness of these factors is genetics > environment > nutrition.     

Seasonal changes in the interactions among leptin, ghrelin, and orexin in sheep

The adaptation of the physiology of an animal to changing conditions of light and food availability is evident at the behavioral and hormonal levels. Melatonin, leptin, ghrelin, and orexin, which exhibit rhythmic secretion profiles under ad libitum feeding conditions, are sensitive to changes in daylength, forming a tight web of interrelationships in the regulation of energy balance. The aim of this study was to determine the effects of central injections of leptin, ghrelin, and orexin on the reciprocal interactions among these hormones and the influence of photoperiod on these responses. Twenty-four ovariectomized and estradiol-implanted ewes were used in a replicated switchback design. The ewes were assigned randomly to 1 of 6 treatment groups, and the treatments were infused into their third ventricles 3 times at 0, 1, and 2 h, with 0 h being at dusk. The treatments were as follows: 1) control, Ringer-Locke buffer; 2) leptin, 0.5 μg/kg BW; 3) ghrelin, 2.5 μg/kg BW; 4) orexin B, 0.3 μg/kg BW; 5) leptin antagonist, 50 μg/kg BW, then ghrelin, 2.5 μg/kg BW; and 6) leptin antagonist, 50 μg/kg BW, then orexin B, 0.3 μg/kg BW. Blood samples (5 mL) were collected at 15-min intervals for 6 h. The administration of leptin increased (P < 0.05) plasma concentrations of melatonin during short-day (ShD) photoperiods and decreased (P < 0.05) them during long-day (LD) photoperiods, whereas ghrelin decreased (P < 0.05) melatonin concentrations during ShD photoperiod, and orexin had no effect (P > 0.1). Leptin attenuated (P < 0.05) ghrelin concentrations relative to the concentration in controls during ShD. The plasma concentrations of orexin were reduced (P < 0.05) after leptin infusions during LD and ShD photoperiods; however, ghrelin had the opposite effect (P < 0.05) on orexin concentration. Orexin increased (P < 0.05) ghrelin concentrations during LD. Ghrelin and orexin concentrations were increased (P < 0.05) after leptin antagonist infusions. Our data provide evidence that the secretion of leptin, ghrelin, and orexin are seasonally dependent, with relationships that are subject to photoperiodic regulation, and that leptin is an important factor that regulates ghrelin and orexin releases in sheep.     

Evaluation of genetic and metabolic predispositions and nutritional risk factors for pasture-associated laminitis in ponies

OBJECTIVE: To evaluate genetic and metabolic predispositions and nutritional risk factors for development of pasture-associated laminitis in ponies. DESIGN: Observational cohort study. ANIMALS: 160 ponies. PROCEDURES: A previous diagnosis of laminitis was used to differentiate 54 ponies (PL group) from 106 nonlaminitic ponies (NL group). Pedigree analysis was used to determine a mode of inheritance for ponies with a previous diagnosis of laminitis. In early March, ponies were weighed and scored for body condition and basal venous blood samples were obtained. Plasma was analyzed for glucose, insulin, triglycerides, nonesterified fatty acids, and cortisol concentrations. Basal proxies for insulin sensitivity (reciprocal of the square root of insulin [RISQI]) and insulin secretory response (modified insulin-to-glucose ratio [MIRG]) were calculated. Observations were repeated in May, when some ponies had signs of clinical laminitis. RESULTS: A previous diagnosis of laminitis was consistent with the expected inheritance of a dominant major gene or genes with reduced penetrance. A prelaminitic metabolic profile was defined on the basis of body condition, plasma triglyceride concentration, RISQI, and MIRG. Meeting > or = 3 of these criteria differentiated PL- from NL-group ponies with a total predictive power of 78%. Determination of prelaminitic metabolic syndrome in March predicted 11 of 13 cases of clinical laminitis observed in May when pasture starch concentration was high. CONCLUSIONS AND CLINICAL RELEVANCE: Prelaminitic metabolic syndrome in apparently healthy ponies is comparable to metabolic syndromes in humans and is the first such set of risk factors to be supported by data in equids. Prelaminitic metabolic syndrome identifies ponies requiring special management, such as avoiding high starch intake that exacerbates insulin resistance.     

Rain and windchill as factors in the occurrence of pneumonia in sheep

A computerised information retrieval system of abattoir pathology and meteorological data has been used to investigate the effect of prevailing weather conditions on the occurrence of pleurisy and pneumonia in the sheep population of Northern Ireland. Significant correlation coefficients were found between the percentage condemnations due to pleurisy and pneumonia in sheep and rainfall, windspeed, temperature and humidity. The most significant correlation was found with windspeed. The paper describes the calculation of a new meteorological variable, the rain/windchill factor. Very highly significant correlation coefficients were found between the percentage lung condemnations in sheep and the rain/windchill factor prevailing during the same month and both one and two months previously. The paper discusses the practical implications of these findings for sheep production and highlights the desirability of protecting sheep from adverse climatic conditions during the winter months.     

Phalangeal bone ash as an aid in diagnosing some nutritional causes of lameness in sheep

Normal bone ash levels were determined on first phalangeal bones from lambs dying of acute causes and from abattoir specimens. First phalanges were chosen because they represent a whole bone thereby ensuring constant and natural proportion which would be difficult if sampling only a portion of a bone. No practical difference in percentage ash, expressed in terms of green bone weight, was found between fore or hind feet of young male or female sheep. Consequently a single regression equation can adequately express the relationship between bone ash and bone length for sheep up to about 9 months of age. Lambs suffering from hypocuprotic osteoporosis or osteodystrophy consistent with hypovitaminosis D have phalangeal bone ash values which tend to lie outside the lower range expected for normal sheep with first phalanges of similar length. Consequently bone ash can be a useful aid in the diagnosis of certain nutritional causes of lameness in sheep.     

A study of nutritional myopathy in weaner sheep

The effectiveness of various treatments upon, and pathological and biochemical changes in, ovine weaner nutritional myopathy were observed. Clinical myopathy was already apparent in the sheep at the start of the study, and they were fed decreasing amounts of a ration containing low levels of selenium and alpha-tocopherol, and periodically deprived of water. In spite of this management there was a spontaneous remission of the clinical myopathy in the sheep, but a subclinical myopathy was identified in some of the sheep at the end of the trail. The conclusions were that the myopathy was not caused by a low dietary intake of selenium and/or alpha-tocopherol alone, that alpha-tocopherol was involved in the aetiology, that alpha-tocopherol was completely effective and selenium possibly partially effective in treating it, and that the condition may be a Type II muscle fibre disease. Data on plasma creatine phosphokinase and erythrocyte glutathione peroxidase activities, and terminal liver selenium and alpha-tocopherol concentrations are presented, and their roles in the diagnosis of ovine weaner nutritional myopathy discussed.