Associations between productivity and a range of immune traits were tested by multiple regression analysis on 128 Large White pigs (62 male, 66 female). Daily weight gain, daily feed intake, and efficiency (i.e. weight gain/feed intake), assessed from 14 to 24 weeks of age, were the productivity traits. Total and differential white blood cell count and leukocyte sub-sets positive for CD4, CD8, CD11R1, gamma delta T cells, B cell, and monocyte markers, all measured at 18 and 24 weeks, were the immune traits. At 24 weeks of age, higher percentages of monocytes were associated with a decrease in daily weight gain. Higher percentages of B cells were associated with a decrease in daily feed intake. Higher percentages of CD11R1 positive cells were associated with a decrease in daily weight gain and a decrease in efficiency. Relationships at the age of 18 weeks were similar, but slightly less significant. Associations between the numbers of monocytes, MIL-4 positive cells and B cells and certain performance traits were also observed at the age of 24 weeks. Overall, these results indicate an association between productivity and certain immune traits. We suggest that the observed associations between these immune traits and performance could be due to the impact of sub-clinical infections.
"Within pig PBML, CD16 is expressed on NK cells and monocytes [6,10,11] whilst, in pigs, CD14 is a marker of monocyte differentiation . Lastly, CD11R1+ cells may be sub-divided into CD8α+ and CD8α- subsets since these cell subsets differ according to cell size, complexity and phenotype  (Clapperton, unpublished observations). "
[Show abstract][Hide abstract] ABSTRACT: There is a need for genetic markers or biomarkers that can predict resistance towards a wide range of infectious diseases, especially within a health environment typical of commercial farms. Such markers also need to be heritable under these conditions and ideally correlate with commercial performance traits. In this study, we estimated the heritabilities of a wide range of immune traits, as potential biomarkers, and measured their relationship with performance within both specific pathogen-free (SPF) and non-SPF environments. Immune traits were measured in 674 SPF pigs and 606 non-SPF pigs, which were subsets of the populations for which we had performance measurements (average daily gain), viz. 1549 SPF pigs and 1093 non-SPF pigs. Immune traits measured included total and differential white blood cell counts, peripheral blood mononuclear leucocyte (PBML) subsets (CD4+ cells, total CD8α+ cells, classical CD8αβ+ cells, CD11R1+ cells (CD8α+ and CD8α-), B cells, monocytes and CD16+ cells) and acute phase proteins (alpha-1 acid glycoprotein (AGP), haptoglobin, C-reactive protein (CRP) and transthyretin). Nearly all traits tested were heritable regardless of health status, although the heritability estimate for average daily gain was lower under non-SPF conditions. There were also negative genetic correlations between performance and the following immune traits: CD11R1+ cells, monocytes and the acute phase protein AGP. The strength of the association between performance and AGP was not affected by health status. However, negative genetic correlations were only apparent between performance and monocytes under SPF conditions and between performance and CD11R1+ cells under non-SPF conditions. Although we cannot infer causality in these relationships, these results suggest a role for using some immune traits, particularly CD11R1+ cells or AGP concentrations, as predictors of pig performance under the lower health status conditions associated with commercial farms.
[Show abstract][Hide abstract] ABSTRACT: The reduction in feed intake and growth rate that occurs following weaning is of major economic consequence to the pig industry. Currently, a range of antimicrobial products can be used to minimise the impact of weaning on piglet health and subsequent performance. However, the use of these products in pig diets is subject to increasing restriction worldwide because of perceived risks to public health and to the environment. Thus, alternative methods are required to mitigate the growth check that almost invariably occurs after weaning in most production systems.
Piglets produced outdoors are claimed to experience less of a growth check at weaning and to be able to thrive in relatively unsophisticated weaner accommodation. However, these claims have not been substantiated under Western Australian conditions, nor a scientific basis for these claims established. Consequently, a series of experiments was designed to test the general hypothesis for this thesis – ‘the gut structure and function, and lifetime performance of the weaned pig are affected by its pre- and post-weaning rearing environments’.
Experiment 1 was conducted in two parts to quantify differences in the growth performance, health and gut structure of weaner pigs produced indoors or outdoors and reared in conventional or deep-litter pens. The weaner diet in the first part of the experiment contained 100 ppm of olaquindox and 3,000 ppm of zinc oxide (Exp1a). This experiment was repeated without using dietary antimicrobial products (Exp1b). Experiment 2 was conducted in conventional buildings to examine the effect of exposing piglets in lactation to similar substrates to those available to outdoor piglets used in Exp1a and Exp1b in the absence of other differences in the outdoor production milieu.
Pre-weaning environments in Exp1a (indoor production (IP) and outdoor production (OP)) appeared to have little effect on gut structure and overall growth rate but significantly affected carcass composition, whereas post-weaning environments (conventional (C) or deep-litter (DL)) affected both overall growth rate and carcass composition. Although feed disappearance was similar, OP pigs grew faster than IP pigs in the first 47 d after weaning in Exp1a but not in Exp1b. Lifetime growth rate (GR), P2 backfat, feed disappearance and feed conversion ratio (FCR) were not significantly affected by the production environment in Exp1a whereas OP pigs grew slower with higher P2 backfat and FCR in Exp1b. Interestingly, OP pigs had heavier carcass weights and higher dressing percentages than IP pigs in both parts of the experiment. The effects of post-weaning environment were more consistent as DL pigs grew faster, were fatter, and had higher carcass weights and dressing percentages than C pigs.
Villus height and crypt depth of IP and OP pigs were not different at 21 (weaning) or 28 d, but villus height decreased and crypt depth increased in the week after weaning. Pigs reared in C pens had greater faecal concentrations of volatile fatty acids than pigs in DL, indicating that the latter ingested sufficient straw to alter fermentation characteristics.
In Experiment 2, there were no differences in gut structure or pre-weaning and lifetime GR of pigs offered no creep feed (NC), a commercial creep feed (CF) or an ‘outdoor’ mix (OM) comprising of 1 part straw, 5 parts sow feed and 25 parts of soil taken from paddocks in which OP pigs used in Exp1a and Exp1b were farrowed. However, NC pigs grew slower in the week after weaning than the other two treatments. Backfat and feed disappearance were similar for all treatments but pigs on the OM treatment had higher carcass weights and dressing percentages than pigs on the NC and CF treatments. Villus height and crypt depth were not different between treatments and, although the piglets were weaned at 28 d, villus height decreased and crypt depth increased in the week after weaning to an extent similar to that experienced by piglets weaned at 21 d in Experiment 1.
Although all piglets received intramuscular injections of 200 mg iron (Fe) dextran when 1 to 2 days old, piglets offered the OM during lactation had higher serum iron and blood haemoglobin (Hb) levels than those offered NC or CF. Furthermore, half the piglets offered NC or CF had Hb levels indicative of chronic Fe deficiency anaemia. The average parity of sows used in this experiment was 6.3 litters, suggesting that piglets may have been born with low Fe stores, possibly because of low Fe stores in their dams due to sub-optimal mineral nutrition over successive parities.
In summary, the findings from these experiments partly supported the general hypothesis for this thesis. Under the conditions of these experiments, access to outdoor substrates in lactation had little effect on gut structure and lifetime growth rate but increased both carcass weight and dressing percentage, whereas rearing in DL pens increased feed intake, FCR, growth rate, P2 backfat, carcass weight and dressing percentage.
[Show abstract][Hide abstract] ABSTRACT: A panel of innate immune traits were compared between Meishan and Large White pigs. These pigs were of similar age and kept under the same environmental conditions to reduce non-genetically derived variation in immune traits. The animals were all apparently healthy and were not experimentally challenged with any pathogen during the study. The measures only required a small blood sample. Total white cell counts were similar between the pig breeds. However, the numbers of lymphocytes, neutrophils and monocytes differed significantly, with Meishans having higher neutrophil and monocyte counts and lower lymphocyte counts. Flow cytometric methods were used to determine quantitatively the characteristics and function of neutrophils and monocytes. Meishan neutrophils were smaller and less complex than Large White neutrophils, and phagocytosis of Escherichia coli and the ensuing oxidative burst was lower in Meishan neutrophils compared to Large White neutrophils. Monocyte phagocytosis of E. coli was significantly less than that of neutrophils in both breeds but the function of Meishan monocytes as measured by phagocytosis and tumour necrosis factor alpha (TNFalpha) release did not differ from that of Large White monocytes. Levels of acute phase proteins also differed between the breeds with a significantly higher proportion of Meishans having elevated serum amyloid A levels. However, Meishans had lower alpha(1)-acid glycoprotein levels than Large Whites and haptoglobin levels were similar. Such differences in innate immune traits may have implications in the resistance to infection by a broad range of pathogens and subsequent disease effects in these breeds. Further studies are warranted to investigate the genes underlying these traits.
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