C. A. Morris

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.

Breeding sheep in New Zealand that are less reliant on anthelmintics to maintain health and productivity

Abstract Breeding sheep that are less reliant on the use of anthelmintics to maintain acceptable health and productivity is one of several options that may assist farmers to manage the growing anthelmintic-resistance problem in New Zealand and meet consumer demands to minimise drug usage in livestock. Although it has been known for many years that genetic factors contribute to the ability of sheep to cope with roundworm challenge, attempts to selectively breed for such factors have occurred only recently. Two host traits, ‘resistance’ and ‘resilience’, are thought to be involved in limiting the deleterious effects of roundworms on the health and productivity of sheep, and the associated need for treatment with anthelmintics. Over the last decade, considerable advances have been made in our understanding of the feasibility and implications of breeding for these traits under practical conditions. The experimental breeding lines developed as part of this research are now proving to be a valuable resource for further work directed at identifying genes and/or genetic markers associated with host resistance and understanding the mechanisms of host immunity to nematode parasites in ruminants. This review provides an up-to-date summary of the results of research in this field, with particular reference to dual-purpose sheep in New Zealand, and describes how this information is being applied in practical breeding programmes.

Heritability of and genetic correlations among faecal egg counts and productivity traits in Romney sheep

Abstract A total of 2611 spring-born Romney ewe lambs, the progeny of 60 sires over 3 years, were studied on a Hawkes Bay farm to estimate the heritability of faecal egg count (FEC), and correlations between FEC and production traits. Weaning weight, an autumn weight, the weight gain between these 2 times, and yearling fleece weight were recorded in each of 3 years. A dag score was obtained in the final 2 years. An anthelmintic drench was administered to 1987-born lambs in mid January after which further treatment was withheld until April. In the 2 subsequent years, drench treatment was administered in the first week of December and further treatment withheld until the mean FEC in a small monitor group reached a target value of 1000-1500 eggs/g. Once the target value was reached, a faecal sample was obtained from all animals for an FEC, the dag score and autumn liveweight were taken, and routine drenching was then resumed. Variance components were estimated using a multivariate restricted maximum likelih...

Genetic and environmental factors affecting lamb survival at birth and through to weaning

Abstract Pedigree and early performance records from lambs on three New Zealand research stations, involving 51 station‐years of data (55 146 recorded lambs born), were analysed in order to study genetic and environmental factors affecting perinatal and preweaning survival. Mean birth weights at each site were very similar, being 4.26 kg at Woodlands, 4.22 kg at Tokanui, and 4.32 kg at Rotomahana Station. Total survival rates to weaning (preweaning survival) across sites averaged 79.0, 78.9, and 80.1%, respectively. Analyses of variance for perinatal survival and preweaning survival showed significant effects of contemporary group of lamb, age of dam, and birth rank‐sex combinations, whilst linear and curvilinear effects of birth weight were also significant. Optimal birth weights were 4.36 kg and 4.77 kg for maximal perinatal survival and maximal preweaning survival, respectively. Heavy singles and twins were at higher risk of not surviving, but light singles and twins were also at risk. At birth, survival was consistently lowest from lambs out of 2‐year‐old dams, whilst preweaning survival was lower amongst lambs from 2‐ and 5‐year‐old dams, and higher in lambs from 3‐ and 4‐year‐old dams. Estimates of total heritability (direct + maternal + direct‐maternal covariance) for perinatal survival as a transformed (logit) trait were 0.055 (Tokanui and Woodlands data), and 0.105 (Rotomahana data). Corresponding estimates for preweaning survival were 0.031 and 0.101, respectively. Maternal genetic variances for perinatal and preweaning survival as logit traits were 1.5–5 times the size of the lambs additive genetic variance. Our analyses confirm previous low genetic parameter estimates for lamb survival.

Some genetic factors affecting temperament in Bos taurus cattle

Abstract Temperament scores were recorded by two operators on a herd of Bos taurus beef cattle, including Angus and Hereford controls and various crossbred groups. The herd consisted of 765 cows, 653 calves at foot (average age 2 months), and 250 yearling heifers. Recording of temperament in the yards was carried out at weighing time in November 1982 using a 1–8 scale, and immediately afterwards when the herd was drafted for natural mating using a 1–6 scale, with higher scores indicating more difficulty experienced by stockmen in carrying out the routine weighing and drafting operations. In addition, a calving temperament score was recorded on 2121 cows calving in 1981–90 using a 0–5 scale. Both scores in the yards differed significantly among cow breed groups (P < 0.001). The range of means was 1.73 units (1.86 phenotypic standard deviations: σ) for the weighing score (Score 1) and 1.57 units (1.29σ) for the drafting score (Score 2). Corresponding data for yearling breed groups were 1.11σ for Score 1 (P ...

Genetic improvement of beef cattle in New Zealand: breeding objectives

Abstract A breeding objective was developed for general purpose beef cattle in New Zealand. Income was partitioned between 18-month steers, surplus heifers and cull cows. Expenses were calculated for all ages and classes of stock. Profit (dollars per herd per year) was derived from income minus expense. The breeding objective included net reproduction (calves weaned per cow joined), carcass weight and food intake. Selection criteria (indices of recorded characters) included birth weight (direct and maternal), weaning weight (direct and maternal), yearling weight, carcass weight, net reproduction of the dam and scrotal circumference. Economic values were calculated on an income and expense per year basis and with 0, 5 and 10% discounting. Correlations between objectives ranged from 0.95 to 1.0. In general, predicted selection responses for individual characters were greater on an income and expense per year basis than with discounting. Growth traits yielded greater responses than reproductive traits because the latter were expressed later in life and had smaller heritabilities. Removal of food intake from the objective tended to increase selection response for growth and food intake at the expense of reproduction. There was an 11% loss in efficiency by removing net reproduction from the index, but a 15% loss when scrotal circumference was removed, pointing to the potential usefulness of scrotal circumference to enhance selection for reproduction.

Genetic parameters for growth, puberty, and beef cow reproductive traits in a puberty selection experiment

Abstract A selection experiment to change reproductive traits in Angus cattle has been maintained for 14 years, with first calvings in 1985. Alongside an unselected control line, three lines were established, selected for increased age at puberty in heifers (AGE+ line), reduced age at puberty in heifers (AGE‐ line), or increased scrotal circumference (SC line). The last two lines were merged at the 1992 matings, with the revised objective of applying further selection in both sexes to reduce age at puberty in heifers. Dates at puberty in heifers from an average of 8 to 16 months of age and SC in bulls were recorded in all lines, along with the pregnancy rates (PR) and subsequent calving dates (CD) in heifers and all cow‐age groups. Heritabilities of single‐record SC, standardised age at first behavioural oestrus (SFO), and single‐record CD were 0.41 ± 0.04 (repeatability 0.70 ± 0.01), 0.27 ± 0.04, and 0.09 ± 0.04 (repeatability 0.19 ±0.03), respectively. Genetic correlations of SC with SFO and CD were ‐0.25 ± 0.09 and ‐0.23 ± 0.15, respectively; SFO with CD 0.57 ± 0.17; and PR with SFO and SC‐0.36 ±0.13 and 0.12 ± 0.11, respectively. The selection‐line difference in PR over seven years (AGE‐ mean minus AGE+ mean), excluding yearling heifer matings, was 4.7 ± 2.1% (P < 0.05). Mean CD in the AGE‐ line was 3 days earlier than in the AGE+ line (P < 0.09). These correlation and selection‐line results suggest that selecting for higher SC and earlier heifer puberty leads to earlier CD and higher PR.

Phenotypic Markers for Selection of Nematode-resistant Sheep

Nematode-resistance of an animal can be defined as an enhanced natural ability, relative to its peers, to both prevent establishment of larval nematodes and evict any that do establish. These parameters are not measurable in a practical sense and consequently nematode-resistance has usually been defined in terms of low faecal nematode egg counts (FEC). Studies in New Zealand and Australia have demonstrated that nematode-resistance, as measured by FEC, has a heritability of about 0.3 in Romney and Merino sheep. However as a selection trait FEC has practical limitations and its use may incur production penalties through withholding drench treatment for prolonged periods or from a need for artificial challenge. FEC is influenced by the level and composition of a natural nematode challenge and especially the expression of the immune response. Thus immunological parameters which reflect the underlying genetic resistance could potentially be used as phenotypic markers. Ideally, a useful phenotypic marker would be easy to sample and its assay would be inexpensive and able to be automated, in addition to being strongly correlated with nematode-resistance. Results from several New Zealand trials have indicated that antibody levels (particularly IgG1) to excretory/secretory antigens of L3 nematodes such as Trichostrongylus colubriformis may meet these criteria. Levels of antibody against L3 antigens are also independent of on-farm drenching strategies. Blood eosinophil count has also been considered for use as a selection parameter but a high degree of sample variability reduces its potential. Other immunological parameters associated with nematode-resistance which have potential as phenotypic markers include serum nematode-specific IgE and products of mucosal mast cells such as proteinases. It is likely that as the critical immune responses of sheep to nematodes become more clearly defined, new immunological parameters with potential for use as phenotypic markers will be found. The definition of these immune responses will also assist in the identification and characterization of genetic markers.

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.

Identification and characterisation of an aspartyl protease inhibitor homologue as a major allergen of Trichostrongylus colubriformis

Allergens were identified from the gastrointestinal nematode of sheep, Trichostrongylus colubriformis, by probing Western blots of infective larvae (third stage) somatic antigen with IgE purified from the serum of sheep grazed on worm contaminated pasture. A 31 kDa allergen was frequently recognised by sera from immune sheep, particularly those deriving from a line that has been genetically selected over 23 years for parasite resistance. Using a proteomic approach, the 31 kDa allergen was identified as an aspartyl protease inhibitor homologue. The entire coding sequence of T. colubriformis aspartyl protease inhibitor (Tco-api-1) was obtained and the mature protein expressed in Escherichia coli. Anti-Tco-API-1 antibodies revealed that a commonly observed 21 kDa T. colubriformis allergen species is a truncated form of Tco-API-1. Specific IgE responses to T. colubriformis aspartyl protease inhibitor were significantly correlated with the degree of resistance to nematode infection as measured by faecal egg count in sheep. Surprisingly, IgE responses to Tco-API-1 were not correlated with breech soiling (dag score), which is thought to be caused, in part, by allergic hypersensitivity to worms. Therefore, a specific IgE response to this allergen may be a suitable marker for identifying lambs at an early age that will develop strong immunity to gastrointestinal nematodes.