S. M. Hickey

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.

Heritability estimates of methane emissions from sheep

The objective of this study was to determine the genetic parameters of methane (CH4) emissions and their genetic correlations with key production traits. The trial measured the CH4 emissions, at 5-min intervals, from 1225 sheep placed in respiration chambers for 2 days, with repeat measurements 2 weeks later for another 2 days. They were fed in the chambers, based on live weight, a pelleted lucerne ration at 2.0 times estimated maintenance requirements. Methane outputs were calculated for g CH4/day and g CH4/kg dry matter intake (DMI) for each of the 4 days. Single trait models were used to obtain estimates of heritability and repeatability. Heritability of g CH4/day was 0.29 ± 0.05, and for g CH4/kg DMI 0.13 ± 0.03. Repeatability between measurements 14 days apart were 0.55 ± 0.02 and 0.26 ± 0.02, for the two traits. The genetic and phenotypic correlations of CH4 outputs with various production traits (weaning weight, live weight at 8 months of age, dag score, muscle depth and fleece weight at 12 months of age) measured in the first year of life, were estimated using bivariate models. With the exception of fleece weight, correlations were weak and not significantly different from zero for the g CH4/kg DMI trait. For fleece weight the phenotypic and genetic correlation estimates were −0.08 ± 0.03 and −0.32 ± 0.11 suggesting a low economically favourable relationship. These results indicate that there is genetic variation between animals for CH4 emission traits even after adjustment for feed intake and that these traits are repeatable. Current work includes the establishment of selection lines from these animals to investigate the physiological, microbial and anatomical changes, coupled with investigations into shorter and alternative CH4 emission measurement and breeding value estimation techniques; including genomic selection.

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.

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.

Genetics of resilience to nematode parasites in young Romney sheep)—use of weight gain under challenge to assess individual anthelmintic treatment requirements

Abstract The performance of 2997 male Romney lambs, sired by 102 rams and born in spring 1992 on four farms in southern North Island, was measured under a selective anthelmintic treatment regime to obtain genetic information on the resilience of grazing lambs to nematode challenge. The basis on which selective treatment decisions were made was modified from that of an earlier study (which used farmer assessment of body condition and dag score) in an endeavour to make the procedure more objective. On the first two drenching occasions after weaning, only those lambs whose liveweight gain was below an acceptable threshold, defined using data from flock mates, received anthelmintic treatment (selective drenching). A resilience score for each animal was derived from drench requirement data either as age at first drench (normalised to include animals never drenched) (NAD), or as a binary code denoting whether or not the animal had been drenched by the end of the selective drenching regime (BY2). Productivity, b...

Quantitative trait loci for organ weights and adipose fat composition in Jersey and Limousin back-cross cattle finished on pasture or feedlot

A QTL study of live animal and carcass traits in beef cattle was carried out in New Zealand and Australia. Back-cross calves (385 heifers and 398 steers) were generated, with Jersey and Limousin backgrounds. This paper reports on weights of eight organs (heart, liver, lungs, kidneys, spleen, gastro-intestinal tract, fat, and rumen contents) and 12 fat composition traits (fatty acid (FA) percentages, saturated and monounsaturated FA subtotals, and fat melting point). The New Zealand cattle were reared and finished on pasture, whilst Australian cattle were reared on grass and finished on grain for at least 180 days. For organ weights and fat composition traits, 10 and 12 significant QTL locations (P<0.05), respectively, were detected on a genome-wide basis, in combined-sire or within-sire analyses. Seven QTL significant for organ weights were found at the proximal end of chromosome 2. This chromosome carries a variant myostatin allele (F94L), segregating from the Limousin ancestry, and this is a positional candidate for the QTL. Ten significant QTL for fat composition were found on chromosomes 19 and 26. Fatty acid synthase and stearoyl-CoA desaturase (SCD1), respectively, are positional candidate genes for these QTL. Two FA QTL found to be common to sire groups in both populations were for percentages of C14:0 and C14:1 (relative to all FAs) on chromosome 26, near the SCD1 candidate gene.

Quantitative trait loci for live animal and carcass composition traits in Jersey and Limousin back-cross cattle finished on pasture or feedlot

A quantitative trait locus (QTL) study was carried out in two countries, recording live animal and carcass composition traits. Back-cross calves (385 heifers and 398 steers) were generated, with Jersey and Limousin breed backgrounds. The New Zealand cattle were reared on pasture to carcass weights averaging 229 kg, whilst the Australian cattle were reared on grass and finished on grain (for at least 180 days) to carcass weights averaging 335 kg. From 11 live animal traits and 31 carcass composition traits respectively, 5 and 22 QTL were detected in combined-sire analyses, which were significant (P < 0.05) on a genome-wise basis. Fourteen significant traits for carcass composition QTL were on chromosome 2 and these were traits associated with muscling and fatness. This chromosome carried a variant myostatin allele (F94L), segregating from the Limousin ancestry. Despite very different cattle management systems between the two countries, the two populations had a large number of QTL in common. Of the 18 traits which were common to both countries, and which had significant QTL at the genome-wise level, eight were significant in both countries.

Genetic studies of carotenoid concentration in the plasma and milk of New Zealand dairy cattle

Abstract Blood and milk samples were collected in 1992/93 from 2‐year‐old heifers in the Livestock Improvement Corporations Sire Proving Scheme, for analysis of carotenoid concentration (CC). The trial comprised heifers in 127 spring‐calving North Island dairy herds, where blood samples were taken from a total of 2744 heifers (Holstein‐Friesians (F), Jerseys (J), and their crosses) in early/mid lactation (spring), and from a sub‐group of the same animals in autumn. These heifers were the daughters of 157 young F and J sires, and 15 older sires. Whole‐lactation yields of milk, fat, and protein, and fat% and protein% were also obtained. Sire‐model restricted maximum likelihood (REML) analyses were carried out to estimate genetic and phenotypic parameters. Purebred F and J breed means for plasma CC in spring were 14.1 and 17.9 μg ml‐1 (P < 0.001), respectively, and for milk CC 5.24 and 7.50 μg g‐1 fat (P < 0.001), and corresponding heritabilities for the two traits were 0.46 ± 0.08 and 0.11 ± 0.10. The repeatability of plasma CC across seasons was 0.64 ± 0.02. The genetic correlation between spring plasma CC and milk CC g‐1 fat was 0.66 ± 0.22, whereas genetic correlation estimates for spring plasma and milk CC g‐1 fat with other traits were: with milk volume ‐0.01 ± 0.16 and 0.41 ± 0.35, with fat yield 0.06 ± 0.22 and 0.29 ± 0.54, and with fat% 0.03 ± 0.13 and ‐0.26 ± 0.29. It was concluded that plasma CC was a repeatable and heritable trait, whereas milk CC g‐1 fat was lowly inherited; plasma CC was essentially uncorrelated with the standard milk production traits; if bulls were selected for lower plasma CC, there would be reduced CC in both the plasma and milk of their daughters.

Sire effects on antibodies to nematode parasites in grazing dairy cows

Abstract A study was carried out on New Zealand dairy cows at pasture, to test for evidence of genetic differences in immunological response to nematode parasites. Nine widely used Holstein‐Friesian artificial insemination bulls, with daughters in many herds, were evaluated for nematode antibodies by sampling milk of their daughters in mid lactation in each of 20 North Island herds. One milk sample was taken from each cow (ranging from 4 to 11 years of age), during a routine herd test in the period from mid November 2000 to early February 2001. Assays were undertaken subsequently on pooled samples of skim milk (0.2 ml per cow; up to 20 cows per sire x herd) to assess antibodies to both the infective third larval (L3) and adult parasitic stages of Cooperia oncophora and Ostertagia ostertagi. Sire effects were significant for all four antibody types (P < 0.001). For O. ostertagi L3, there was a 1.20‐fold range in the mean antibody levels of the sire groups; corresponding proportional ranges for the other three antibody types were from 1.22 to 1.23. The correlations of sire means among the four antibody types were high, averaging 0.81 (range 0.65–0.99). These results show that significant sire effects on anti‐parasite antibody levels were present in mature lactating dairy cows at pasture in New Zealand, with repeatabilities of sire means across herds of 0.29–0.39, and that sire effects on antibody levels to two different nematode parasite species were highly correlated (for antibodies to either the L3 or the adult stages).

Genetic mapping of quantitative trait loci for meat quality and muscle metabolic traits in cattle

A whole-genome scan was carried out in New Zealand and Australia to detect quantitative trait loci (QTL) for live animal and carcass composition traits and meat quality attributes in cattle. Backcross calves (385 heifers and 398 steers) were generated, with Jersey and Limousin backgrounds. The New Zealand cattle were reared and finished on pasture, whilst Australian cattle were reared on grass and finished on grain for at least 180 days. This paper reports on meat quality traits (tenderness measured as shear force at 4-5 ages on two muscles as well as associated traits of meat colour, pH and cooking loss) and a number of metabolic traits. For meat quality traits, 18 significant QTL (P < 0.05), located in nine linkage groups, were detected on a genome-wise basis, in combined-sire (seven QTL) or within-sire analyses (11 QTL). For metabolic traits, 11 significant QTL (P < 0.05), located in eight linkage groups, were detected on a genome-wise basis, in combined-sire (five QTL) or within-sire analyses (six QTL). BTA2 and BTA3 had QTL for both metabolic traits and meat quality traits. Six significant QTL for meat quality and metabolic traits were found at the proximal end of chromosome 2. BTA2 and BTA29 were the most common chromosomes harbouring QTL for meat quality traits; QTL for improved tenderness were associated with Limousin-derived and Jersey-derived alleles on these two chromosomes, respectively.