|dc.description.abstract||Chromium (Cr) is an essential mineral element for humans and animals. Various forms of Cr have been used in farm animals in order to improve growth performance, insulin sensitivity, immune response, carcase traits and to reduce stress responsiveness. However, Cr is normally poorly absorbed and utilised even when supplemented in an organic form, perhaps in part because of the tendency to form large aggregates. Interestingly, the efficiency of uptake of 100 nm size particle by intestinal tissue was 15 to 250 fold higher compared to 1μm size particles. This thesis aims to develop a novel nano sized Cr tri-picolinate (nCrPic) and examined the effect of nCrPic on growth performance, body composition and physiological and metabolic response to dietary fat and heat stress in pigs and sheep.
Four experiments involving different particles size Cr, different dose nCrPic and cinnamon were fed to gilts over the growing-finishing phase and sheep to evaluate the effect of nCrPic and cinnamon on growth performance, carcase trait, and glucose metabolism.
In the first experiment, finisher gilts were allocated to eight treatment groups in a 2×4 factorial treatment structure. The respective factors were dietary fat (22 or 57 g/kg) and dietary Cr (0, 400 ppb normal size CrPic, 400 ppb 1μm CrPic (μCrPic) and 400 ppb nm CrPic (nCrPic)). Over the first 21 days, ADG was increased by dietary CrPic, although there was no difference between the different sized Cr. High dietary fat also increased ADG over this period. Dietary CrPic increased carcase weight and muscle depth with responses being greatest for nCrPic. Also, dietary CrPic decreased P2 back fat with the greatest response seen in pigs fed nCrPic and a high fat diet. Furthermore, dietary CrPic tended to decrease plasma insulin without changing plasma glucose indicating an improvement in insulin sensitivity. Moreover, work reported in this thesis further examined the changes occurring at the mRNA level in finisher gilts fed with nCrPic (0 or 400 ppb nCrPic) and fat (22 or 57 g/kg). Skeletal muscle and subcutaneous adipose tissue were collected 25 minutes post-slaughter. This experiment provided some strong evidence that dietary nCrPic can improve insulin sensitivity in pigs consuming a high fat diet. In particular, the expression of the insulin-signaling pathway genes PI3K and AKT were increased by dietary nCrPic. Furthermore, the expression of SOCS3 in skeletal muscle, which can aggravate insulin resistance, was reduced by nCrPic. Dietary nCrPic also increased UCP3 and IL-15 in skeletal muscle, both of which facilitate glucose metabolism. In subcutaneous adipose tissue, the expression of adiponectin was up-regulated by dietary nCrPic. These findings indicate the improvement in the insulin-signaling pathway by dietary nCrPic may be via decreased SOCS3 and increased UCP3 and IL-15 in skeletal muscle, as well as increased adiponectin in subcutaneous adipose tissue.
The second experiment was designed to examine the effects of nCrPic on growth performance, carcase traits in finisher gilts under commercial pig production facility. Finisher pigs were allocated to either control or nCrPics treatment during the mid-summer (January-February, 2011). The average maximum temperature during the experiment was 29.7 oC, with a total of 24 days where the daily maximum temperature was above 28 oC. The data reported in this chapter indicated that dietary nCrPic supplementation at 400 ppb can increase feed intake in finisher gilts during mid-summer suggesting that nCrPic can ameliorate some of the negative effects of heat stress in pigs, possibly via decrease of circulatory cortisol. These results provided an interesting insight into the anti- heat stress response of nCrPic in farm animals.
The third experiment investigated the effects of two different doses (400 ppb and 800 ppb nCrPic) in sheep. Additionally, the physiological responses to chronic heat stress were also examined. Animals were exposed to temperatures of either an average 22.3 °C ambient temperature for thermo-neutral control or peak at an average 40.4 °C for heated animals. The higher ambient temperature resulted in increased rectal and skin temperature, respiration rate, and reduced feed intake and weight gain. Dietary nCrPic ameliorated the increase in rectal temperature observed during heat load. Moreover, dietary nCrPic supplementation also increased feed intake and weight gain when animals were exposed to heat treatment. The metabolic and tissue responses to nCrPic are examined by subjecting these sheep to glucose, insulin and ACTH challenges to assess the metabolic responses to both heat and nCrPic. Tissue samples were also examined for the gene expression responses to heat and nCrPic. In response to the glucose tolerance test, basal plasma glucose was decreased by heat treatment and dietary nCrPic. Sheep fed nCrPic had a lower glucose response as assessed as area under the curve (AUC) and insulin AUC in response to glucose infusion. Animals under heat treatment had a lower NEFA AUC response to glucose infusion. Dietary nCrPic also down regulated the expression of JNK in skeletal muscle tissue. Together, the results from this experiment indicated that nCrPic can improve insulin sensitivity when animal under heat stress and the improvement of insulin sensitivity may be via decrease the expression of JNK in skeletal muscle tissue.
A large number of endocrine and inflammatory pathways have been shown to be dysregulated in obesity. These endocrine and inflammatory factors that reduce body fat deposition are usually associated with an improvement in insulin sensitivity. Data from the first experiment showed that dietary nCrPic can decrease body fat and improve insulin sensitivity. Furthermore, cinnamon has been reported to have similar effects to Cr. The fourth experiment reported in this thesis examined the impact of oral supplementation with nCrPic and cinnamon on body fat deposition and insulin resistance in a high fat fed pig model. Data from this experiment provided evidence that dietary nCrPic and cinnamon have effects on glucose and fat metabolism. In particular, dietary nCrPic and cinnamon can improve insulin sensitivity metabolically and via the insulin signaling gene AKT and GLUT4 mRNA expression. Some of these effects may be mediated, at least in part, by alterations in fatty acid oxidation as the evidence showed that UCP3 and CPT-1B mRNA expression in skeletal muscle were up-regulated by dietary nCrPic and cinnamon supplementation.
The results presented in this thesis conclude that heat stress is able to impact nutrient partitioning and metabolism. Dietary nCrPic supplementation can improve growth performance and carcase traits as well as amelioration of the negative effect of heat stress is possibly via improved insulin sensitivity. Both nCrPic and cinnamon activate insulin receptors by up-regulating insulin signaling gene expression such as PI3K, AKT, and GLUT4, and genes involved in fatty acid oxidation such as UCP3 and CPT-1B.||en_US