W. S. Pitchford

Fatty acid synthase effects on bovine adipose fat and milk fat.

A quantitative trait locus (QTL) was identified by linkage analysis on bovine Chromosome 19 that affects the fatty acid, myristic acid (C14:0), in subcutaneous adipose tissue of pasture-fed beef cattle (99% level: experiment-wise significance). The QTL was also shown to have significant effects on ten fatty acids in the milk fat of pasture-fed dairy cattle. A positional candidate gene for this QTL was identified as fatty acid synthase (FASN), which is a multifunctional enzyme with a central role in the metabolism of lipids. Five single nucleotide polymorphisms (SNPs) were identified in the bovine FASN gene, and animals were genotyped for FASN SNPs in three different cattle resource populations. Linkage and association mapping results using these SNPs were consistent with FASN being the gene underlying the QTL. SNP substitution effects for C14:0 percentage were found to have an effect in the opposite direction in adipose fat to that in milk fat. It is concluded that SNPs in the bovine FASN gene are associated with variation in the fatty acid composition of adipose fat and milk fat.

A comparison of the fatty acid composition of triacylglycerols in adipose tissue from Limousin and Jersey cattle

The fatty acid composition of the triacylglycerol fraction of shoulder fat from Limousin and Jersey yearling heifers, yearling steers, and non-lactating cows was investigated. Significant breed differences in the degree of fatty acid saturation were apparent between Jersey and Limousin cows, but were not observed in the yearlings. Jersey cows had less saturated fatty acids than the Limousin. Jersey cows showed an increased percentage of monounsaturated fatty acids compared with the Jersey yearlings. In contrast, the level of monounsaturated fatty acids in the Limousin cows was the same as in the Limousin yearlings. The calculated indices of enzyme activities also differed between the breeds. Jersey cows had higher indices of Δ9-desaturase and elongase activities than Limousin. This was also reflected by differences in the ratios of total unsaturated and polyunsaturated to saturated fatty acids. Breed differences were also observed in the triacylglycerol fatty acid chain length. In this case, however, yearlings showed significant breed differences that were not detected in the cows. Limousin yearlings had more long chain fatty acids (C16 and C18) than the Jersey yearlings. Limousin yearlings also had a higher elongase activity index than their Jersey counterparts. Thus, breed and age affect the fatty acid composition in these cattle.

Joint modeling of additive and non-additive genetic line effects in single field trials

A statistical approach is presented for selection of best performing lines for commercial release and best parents for future breeding programs from standard agronomic trials. The method involves the partitioning of the genetic effect of a line into additive and non-additive effects using pedigree based inter-line relationships, in a similar manner to that used in animal breeding. A difference is the ability to estimate non-additive effects. Line performance can be assessed by an overall genetic line effect with greater accuracy than when ignoring pedigree information and the additive effects are predicted breeding values. A generalized definition of heritability is developed to account for the complex models presented.

Identification of risk factors for sub-optimal housing conditions in Australian piggeries: Part 2. Airborne pollutants.

The concentrations of total airborne bacteria, respirable endotoxins, ammonia, and respirable and inhalable particles were monitored in 160 piggery buildings in Australia between autumn 1997 and autumn 1999. The overall mean airborne bacteria, respirable endotoxins, ammonia (NH3), and inhalable and respirable particle concentrations measured were 1.17 x 10(5) cfu m(-3), 33.1 EU m(-3), 3.7 ppm, 1.74 mg m(-3), and 0.26 mg m(-3), respectively. The characteristics of the buildings and management systems used were documented at the time of sampling. A multifactorial general linear model (GLM) statistical procedure was used to analyze the effects of housing and management factors on the concentrations of the airborne pollutants. Both airborne bacteria and respirable endotoxin concentrations were affected by building classification (type), and respirable endotoxin concentrations were positively correlated with increasing humidity. The concentrations of airborne bacteria increased as the level of pen hygiene (cleanliness) decreased. The NH3 concentrations were primarily affected by level of pen hygiene, building volume, pig flow management, and season. Building classification, pig flow management, season, building volume, ventilation rates, and temperature affected inhalable particle concentrations. Respirable particle concentrations were primarily affected by building classification, pen hygiene, pig flow management, season, ventilation rates, temperature, and humidity. These findings suggest that environmental improvement strategies (such as improved cleaning, ventilation, and temperature control) are likely to reduce airborne pollutant concentrations in pig buildings and in the environment, thus improving the health and welfare of both pigs and farm staff.

Effects of the myostatin F94L substitution on beef traits

This study investigated the effects of a SNP in the myostatin gene (MSTN or growth differentiation factor 8, GDF8) on birth, growth, carcass, and beef quality traits in Australia (Aust.) and New Zealand (NZ). The SNP is a cytosine to adenine transversion in exon 1, causing an amino acid substitution of leucine for phenylalanine(94) (F94L). The experiment used crosses between the Jersey and Limousin breeds, with the design being a backcross using first-cross bulls of Jersey x Limousin or Limousin x Jersey breeding, mated to Jersey and Limousin cows. Progeny were genotyped for the myostatin SNP and phenotyped in Aust., with finishing on feedlot (366 calves, over 3 birth years) and in NZ with finishing on pasture (416 calves, over 2 birth years). The effect of the F94L allele (A allele) on birth and growth traits was not significant. The F94L allele in Limousin backcross calves was associated with an increase in meat weight (7.3 and 5.9% of the trait mean in Aust. and NZ, respectively, P < 0.001), and a reduction in fat depth (-13.9 and -18.7% of the trait means on live calves (600 d) and carcasses, respectively, Aust. only, P < 0.001), intramuscular fat content (-8.2% of the trait mean in Aust., P < 0.05; -7.1% in NZ, not significant), total carcass fat weight (-16.5 and -8.1% of the trait mean, Aust. and NZ; P < 0.001 and P < 0.05, respectively). Meat tenderness, pH, and cooking loss of the M. longissimus dorsi were not affected by the F94L variant. In the Jersey backcross calves, additive and dominance effects were confounded because the F94L allele was not segregating in the Jersey dams. The combined effects, however, were significant on LM area (4.4% in both Aust., P < 0.05, and NZ, P < 0.01), channel fat (-11.7%, NZ only, P < 0.01), rib fat depth (-11.2%, NZ only, P < 0.05), and carcass fat weight (-7.1%, NZ only, P < 0.05). The results provide strong evidence that this myostatin F94L variant provides an intermediate and more useful phenotype than the more severe double-muscling phenotype caused by knockout mutations in the myostatin gene.

Joint modeling of additive and non-additive (genetic line) effects in multi-environment trials.

A statistical approach for the analysis of multi-environment trials (METs) is presented, in which selection of best performing lines, best parents, and best combination of parents can be determined. The genetic effect of a line is partitioned into additive, dominance and residual non-additive effects. The dominance effects are estimated through the incorporation of the dominance relationship matrix, which is presented under varying levels of inbreeding. A computationally efficient way of fitting dominance effects is presented which partitions dominance effects into between family dominance and within family dominance line effects. The overall approach is applicable to inbred lines, hybrid lines and other general population structures where pedigree information is available.

Genetic improvement of feed efficiency of beef cattle: what lessons can be learnt from other species?

About half of the feed in beef production systems is used to maintain the breeding herd. Of the remaining 50%, about 20% is used by the breeding cow for pregnancy and lactation and 30% is used by the growing calf. There seems little opportunity to improve efficiency of production (lactation and growth) but reasonable opportunity to increase maintenance efficiency. The mean heritability of net feed efficiency from 35 estimates across 7 species/types was 0.25 ± 0.02. Unfortunately, the genetic correlation between net feed efficiency in young bulls and mature cows is likely to be significantly less than 1, thus responding slowly to selection. While it seems clear that improvements in maintenance efficiency can be made, they may come at a cost. In poultry and mice, increased net feed efficiency has been associated with increased fatness but in pigs and beef cattle there is some evidence of the reverse. While a number of studies have predicted that selection for efficiency may result in lower proportions of crucial, metabolically active visceral organ tissues, there are few studies to support this. Poultry and mouse studies both clearly show that increased net feed efficiency is associated with decreased heat production. This decrease is due to both decreased cost of digestion (heat loss) and decreased activity. In poultry, this decreased heat loss resulted in the more efficient line being more affected by high temperatures. Also, it is possible that at low temperatures, the differences in efficiency may not exist. At this stage it is not clear if the decreased activity is an adaptive advantage or disadvantage. In mice and possibly also pigs and poultry, increased net feed efficiency has been associated with a decreased reproductive rate measured as litter size or egg number. This should definitely be of concern when embarking on selection for improved net feed efficiency in the beef industry. It is recommended that since feed intake is both difficult and expensive to measure, a gene or marker test should be developed, and correlated effects on a range of production traits be carefully evaluated.

Identification of risk factors for sub-optimal housing conditions in Australian piggeries: Part 1. Study justification and design.

We undertook a literature search related to pig production facilities with two major aims: first, to review all the likely benefits that might be gained from air quality improvements; and second, to review previous research that had identified statistically significant factors affecting airborne pollutants and environmental parameters, so that these factors could be considered in a multifactorial analysis aimed at explaining variations in air pollutant concentrations. Ammonia, carbon dioxide, viable bacteria, endotoxins, and inhalable and respirable particles were identified as major airborne pollutants in the review. We found that high concentrations of airborne pollutants in livestock buildings could increase occupational health and safety risks, compromise the health, welfare, and production efficiency of animals, and affect the environment. Therefore, improving air quality could reduce environmental damage and improve animal and worker health. To achieve a reduction in pollutant concentrations, a better understanding of the factors influencing airborne pollutant concentrations in piggery buildings is required. Most of the work done previously has used simple correlation matrices to identify relationships between key factors and pollutant concentrations, without taking into consideration multifactorial effects simultaneously in a model. However, our review of this prior knowledge was the first important step toward developing a more inclusive statistical model. This review identified a number of candidate risk factors, which we then took into consideration during the development of multifactorial statistical models. We used a general linear model (GLM) to model measured internal concentrations, emissions, and environmental parameters in order to predict and potentially control the building environment.

Breed differences in the fatty acid composition of subcutaneous and intramuscular lipid of early and late maturing, grain-finished cattle

Fatty acid composition was measured in lipid extracted from adipose tissue and muscle collected at slaughter from 6 groups of crossbred cattle of about 2 years of age, grain-finished in a feedlot. The cattle ranged in biological type from late to early maturing. They were progeny of the following crosses: Charolais x (Simmental.Hereford), Simmental x (Simmental.Hereford), Charolais x (Jersey.Hereford), Hereford x Hereford, Hereford x (Jersey.Hereford), Jersey x Hereford. The fat content of muscle from the leanest late-maturing cross was 5.2% rising to 10.4% in the fattest early-maturing cross. There was no significant difference in the fatty acid composition of subcutaneous fat between the 6 crosses, but there was in the concentration of some of the fatty acids of intramuscular lipid. The latter was due on one hand to the increased deposition of neutral lipid in early-maturing animals and on the other to a higher proportion of polyunsaturated fatty acids in membrane phospholipid in late-maturing animals. The proportions of the monounsaturated fatty acids palmitoleic (C16:l) and oleic (C18:l) were higher in the early-maturing Jersey x Hereford crosses than in straight-bred Herefords or the other crosses, but only in the C16:l values was there a significant difference between breeds. There was also a significant difference between breeds in the sum of monounsaturates and the sum of polyunsaturates in intramuscular fat. The Jersey crosses had the highest level of monounsaturates and the lowest level of polyunsaturates. Intramuscular phospholipid was examined in the 2 breeds that were the most divergent in terms of intramuscular fat content, the Charolais x (Simmental.Hereford) and the Jersey x Hereford. The latter had significantly higher C16:l values and significantly lower C18:2 and polyunsaturate fatty acid values. The experiment demonstrated that breed differences occurred in fatty acid composition of muscle total lipid and phospholipid. The differences are of significance in human health and in identifying maturity breed-types of cattle.

GENETIC AND PHENOTYPIC RELATIONSHIPS BETWEEN FOOD INTAKE, GROWTH, EFFICIENCY AND BODY COMPOSITION OF MICE POST WEANING AND AT MATURITY

Genetic and phenotypic variation in post-weaning growth, food intake, efficiency and body composition of mice post weaning and at maturity, were examined to determine whether genetic variation in efficiency exists and to predict likely responses to selection for increased food efficiency in post-weaning animals. Genetic variation was found for average daily gain, mid-weight, daily food intake and proportion of body fat both post weaning and at maturity. Residual food intake calculated from phenotypic regression had a heritability of 0·27 (s.e. 0·06) post weaning and 0·24 (s.e. 0·08) at maturity, and was very similar to residual food intake calculated using genetic (co)variances, indicating genetic variation in efficiency exists in post-weaning and mature mice. Although the phenotypic correlation between residual food intake post weaning and at maturity was low (0·29), the genetic correlation was moderate (0·60). This suggests that selection for efficiency in young animals will lead to a correlated improvement in maintenance efficiency of mature animals. Genetic correlation estimates suggest that correlated responses in other traits would include a concomitant decrease in post-weaning food intake, a slight increase in weight at weaning, a slight increase in post-weaning fat proportion and little or no change in post-weaning growth. In mature animals there will be an associated decrease in daily food intake and a slight decrease in mature size and body fat proportion. The results suggest that residual food intake of young animals might be a suitable selection criteria for use in livestock species to improve efficiency in young animals and also in the breeding herd.