Potential of in-plant intramuscular fat predictions to enable sheep breeders to incorporate consumer preferences in breeding programmes.

The inclusion of eating quality traits in sheep genetic improvement programmes is desirable. Intramuscular fat (IMF) plays a key role in ensuring consumer satisfaction when eating lamb, but genetic progress for IMF is constrained by a lack of routine data collection. This study investigated the potential for IMF predictor traits to substitute for measured IMF in genetic improvement programmes. Carcass and predicted IMF (near-infrared estimated IMF and marbling score) data were available on 10,113 New Zealand lambs, 1678 of which also had measured chemical IMF on a slice of M. longissimus lumborum on which the predictions of IMF had been made. Genetic antagonisms were observed between carcass lean traits and IMF. The genetic correlation between the predictors and measured IMF approached one, indicating that predictors of IMF can be used in genetic improvement programmes. Through using selection indexes, simultaneous increases in IMF and the existing terminal selection index are possible, provided all traits are measured. This study highlights the importance and potential of predicted IMF to achieve genetic improvement in traits of importance to consumers.

Can we have our steak and eat it: The impact of breeding for lowered environmental impact on yield and meat quality in sheep.

Global agreements in place to reduce methane emissions in livestock are a potential threat to food security. Successful but independent breeding strategies for improved production and lower methane are in place. The unanswered questions are whether these strategies can be combined and how they impact one another, physically and economically. The New Zealand economy is largely dependent on pastoral agriculture from grazing ruminants. The sheep industry produces ∼20 million lamb carcasses for export each year primarily from grass. Methane emitted from the fermentation of forage by grazing ruminants accounts for one-third of all New Zealand's greenhouse gas emissions. Here, we use sheep selection lines bred for divergent methane production and large numbers of their relatives to determine the genetic and phenotypic correlations between enteric methane emissions, carcass yield, and meat quality. The primary objectives were to determine whether previously shown physiological differences between methane selection lines (differing by ∼12% in methane) result in a negative impact on meat production and quality by measuring close relatives. The results show no negative effects of breeding for lowered methane on meat and carcass quality. Gross methane emissions were highly correlated with liveweight and measures of carcass weight and negatively correlated with dressing-out percentage and fat yield (GR). Trends were similar but not significant for methane yield (g CH4/kg DMI). Preliminary evidence, to date, shows that breeding for low methane may result in animals with higher lean yields that are economically favorable even before carbon costs and environmental benefits are taken into account. These benefits were seen in animals measured for methane on fixed intakes and require validation on intakes that are allowed to vary.

Animal board invited review: genetic possibilities to reduce enteric methane emissions from ruminants.

Measuring and mitigating methane (CH4) emissions from livestock is of increasing importance for the environment and for policy making. Potentially, the most sustainable way of reducing enteric CH4 emission from ruminants is through the estimation of genomic breeding values to facilitate genetic selection. There is potential for adopting genetic selection and in the future genomic selection, for reduced CH4 emissions from ruminants. From this review it has been observed that both CH4 emissions and production (g/day) are a heritable and repeatable trait. CH4 emissions are strongly related to feed intake both in the short term (minutes to several hours) and over the medium term (days). When measured over the medium term, CH4 yield (MY, g CH4/kg dry matter intake) is a heritable and repeatable trait albeit with less genetic variation than for CH4 emissions. CH4 emissions of individual animals are moderately repeatable across diets, and across feeding levels, when measured in respiration chambers. Repeatability is lower when short term measurements are used, possibly due to variation in time and amount of feed ingested prior to the measurement. However, while repeated measurements add value; it is preferable the measures be separated by at least 3 to 14 days. This temporal separation of measurements needs to be investigated further. Given the above issue can be resolved, short term (over minutes to hours) measurements of CH4 emissions show promise, especially on systems where animals are fed ad libitum and frequency of meals is high. However, we believe that for short-term measurements to be useful for genetic evaluation, a number (between 3 and 20) of measurements will be required over an extended period of time (weeks to months). There are opportunities for using short-term measurements in standardised feeding situations such as breath 'sniffers' attached to milking parlours or total mixed ration feeding bins, to measure CH4. Genomic selection has the potential to reduce both CH4 emissions and MY, but measurements on thousands of individuals will be required. This includes the need for combined resources across countries in an international effort, emphasising the need to acknowledge the impact of animal and production systems on measurement of the CH4 trait during design of experiments.

Estimates of genetic parameters for breech strike and potential indirect indicators in sheep.

AIM: To determine flystrike incidence, and estimate genetic parameters and potential indicator traits to reduce breech strike susceptibility in Romney sheep in New Zealand. METHODS: Seventeen Romney-based flocks, on 11 farms from throughout New Zealand, were enrolled in a case-control study in 2009/10 and 2010/11. Farmers observed lambs with flystrike and recorded dag score, breech bareness score and flystrike location for each lamb. Flystrike location was classed as breech, body, belly, shoulders, head or feet. Paternity of lambs was determined from tissue samples collected from lambs and all potential sires on farms. Control lambs without flystrike were selected by matching birth year, flock and sex. Due to the majority of strike occurring in the breech, genetic parameters for breech strike were explored. Dag score and breech bareness were investigated as indirect indicators of breech strike. Heritabilities and genetic and phenotypic correlations were estimated for breech strike, dag score and breech bareness using an animal model. RESULTS: For the 2009/10 season, 484 cases of flystrike were recorded with mean incidence rate per farm of 1.76 (min 0.47, max 2.95)%. For the 2010/11 season, 352 cases were recorded with a mean incidence rate per farm of 2.54 (min 0.43, max 8.18)%. Over both years 694/792 (88%) cases of flystrike occurred on the breech. Heritability on the observed scale for breech strike was 0.32 (SE 0.10). Heritabilities for dag score and breech bareness were 0.23 (SE 0.09) and 0.35 (SE 0.11), respectively. Breech strike had a high positive genetic correlation with dag score (0.71) and a low negative genetic correlation with breech bareness (-0.17). Breech strike had a high phenotypic correlation with dag score (0.62) and negative phenotypic correlation with breech bareness (-0.06). CONCLUSIONS: The high genetic and phenotypic correlations between breech strike and dag score makes dag score a viable option for indirect selection for breech strike resistance in Romney sheep in New Zealand. The heritability, genetic and phenotypic correlations require validation in other dual-purpose breeds, before breeding values for breech strike can be implemented, for use throughout the New Zealand sheep industry.

Genetic parameters for predicted methane production and laser methane detector measurements.

Enteric ruminant methane is the most important greenhouse gas emitted from the pastoral agricultural systems. Genetic improvement of livestock provides a cumulative and permanent impact on performance, and using high-density SNP panels can increase the speed of improvement for most traits. In this study, a data set of 1,726 dairy cows, collected since 1990, was used to calculate a predicted methane emission (PME) trait from feed and energy intake and requirements based on milk yield, live weight, feed intake, and condition score data. Repeated measurements from laser methane detector (LMD) data were also available from 57 cows. The estimated heritabilities for PME, milk yield, DMI, live weight, condition score, and LMD data were 0.13, 0.25, 0.11, 0.92, 0.38, and 0.05, respectively. There was a high genetic correlation between DMI and PME. No SNP reached the Bonferroni significance threshold for the PME traits. One SNP was within the 3 best SNP for PME at wk 10, 20, 30, and 40. Genomic prediction accuracies between dependent variable and molecular breeding value ranged between 0.26 and 0.30. These results are encouraging; however, more work is required before a PME trait can be implemented in a breeding program.

Genetic relationships between dagginess, breech bareness, and wool traits in New Zealand dual-purpose sheep.

Genetic and phenotypic parameters were estimated for dagginess, breech, wool, and fiber traits from approximately 29,500 progeny born in 2009 and 2010 in New Zealand dual-purpose ram breeding sheep flocks. Dagginess is adherence of fecal matter to the wool, and this study investigates the genetic and phenotypic correlations between dagginess and breech and wool traits. Estimates for heritability were moderate (0.21 to 0.44) for the following traits: dag score at 3 and 8 mo (DAG3, DAG8), breech bareness, wool length, wool bulk (BULK), mean fiber diameter, mean fiber diameter SD, mean fiber diameter CV, curvature (CURV), weaning weight at 3 mo, and autumn BW. Heritability estimates for fleece weight at 12 mo and proportion of medullated fibers were high (0.49 and 0.53, respectively). Dag score at 3 mo and DAG8 had low genetic and phenotypic correlations with all traits. Breech bareness had positive genetic and phenotypic correlations with CURV and BULK and mostly negative genetic correlations with all other wool traits. In summary the quantity and attributes of wool were not primary causative factors in fecal accumulation, leaving fecal consistency and composition as the major factors.

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 parameters for production traits in New Zealand dual-purpose sheep, with an emphasis on dagginess.

Genetic and phenotypic parameters were estimated for production and disease traits (including dagginess) from about 2 million pedigree-recorded animals born between 1990 and 2008 in New Zealand dual-purpose ram breeding flocks. This is the most comprehensive study of genetic parameter estimates for the New Zealand sheep industry to date and includes estimates that have not previously been reported. Estimates of heritability were moderate for BW at 8 mo (LW8), fleece weight at 12 mo (FW12), dagginess score at 3 and 8 mo (DAG3, DAG8; 0.31 to 0.37), typical for weaning weight (WWT), fecal egg count in summer (FEC1) and autumn (FEC2), and analogous Nematodirus counts (NEM1, NEM2; 0.17 to 0.21), and low for number of lambs born to ewes (NLB; 0.09). The genetic correlations among production traits, WWT, LW8, and FW12, were positive and moderate to high. Correlations of DAG3 and DAG8 with production and disease traits were low and mostly negative. The NLB had low, but typically positive, correlations with other traits. Disease traits also had low, but positive, correlations with production traits (WWT, LW8, and FW12), and were highly correlated among themselves. In general, the heritability estimate for BW and dagginess were greater than what is currently used in the New Zealand genetic evaluation service (Sheep Improvement Limited), and the availability of accurate estimates for dagginess plus parasite resistance and their genetic correlations with production traits will enable more accurate breeding values to be estimated for New Zealand sheep.