Pollott, G E; Karlsson, L J E; Eady, S; Greeff, J C
Fecal egg count (FEC) has been widely used as an indicator of host resistance to gastrointestinal parasites in sheep and has been shown to be a heritable trait. Two other possible indicators of parasites, dag score (DS; accumulated fecal material) and fecal consistency score (FCS), were investigated in this study, along with BW. All four traits were studied to see how heritability and genetic correlations varied with age from weaning (4 mo) to hogget age (approximately 400 d). More than 1,100 lambs, the offspring of 37 rams, were recorded eight times between weaning (3 to 5 mo of age) and hogget age (13 to 18 mo of age) on two farms. Sire models were fitted to the data from each trait at each recording and in a repeatability model involving the whole data set. Overall, the heritabilities were 0.28+/-0.072 (FEC), 0.11+/-0.036 (DS), 0.12+/-0.036 (FCS), and 0.23+/-0.070 (BW). By fitting random regression models to the time-series data, it was possible to see how these heritability values varied as the lambs aged, from weaning to hogget age. The heritability of FEC rose from 0.2 at weaning to 0.65 at 400 d. Dag score had a higher heritability (0.25) in the middle of the age range and a low value at weaning (<0.1) and hogget age (0.16). The heritability of FCS was low, with a value of 0.2 at weaning reducing to 0.05 as the animals aged. Body weight had zero heritability at weaning, which rose to greater than 0.6 at hogget age. Most traits had low genetic correlations between them, the only exception being that between FCS and DS (0.63). Most genetic correlations varied little over the age range with the exception of FEC and BW, which fell from 0 at weaning to -0.63 at hogget age. Whereas FCS and DS may be good indicators of scouring, they are very different from FEC as an indicator of host resistance to gastrointestinal parasites.
Greeff, J C; Safari, E; Fogarty, N M; Hopkins, D L; Brien, F D; Atkins, K D; Mortimer, S I; van der Werf, J H J
Genetic parameters for carcass and meat quality traits of about 18-month-old Merino rams (n = 5870), the progeny of 543 sires from three research resource flocks, were estimated. The estimates of heritability for hot carcass weight (HCW) and the various fat and muscle dimension measurements were moderate and ranged from 0.20 to 0.37. The brightness of meat (colour L*, 0.18 +/- 0.03 standard error) and meat pH (0.22 +/- 0.03) also had moderate estimates of heritability, although meat relative redness (colour a*, 0.10 +/- 0.03) and relative yellowness (colour b*, 0.10 +/- 0.03) were lower. Heritability estimates for live weights were moderate and ranged from 0.29 to 0.41 with significant permanent maternal environmental effects (0.13 to 0.10). The heritability estimates for the hogget wool traits were moderate to high and ranged from 0.27 to 0.60. The ultrasound measurements of fat depth (FATUS) and eye muscle depth (EMDUS) on live animals were highly genetically correlated with the corresponding carcass measurements (0.69 +/- 0.09 FATC and 0.77 +/- 0.07 EMD). Carcass tissue depth (FATGR) had moderate to low genetic correlations with carcass muscle measurements [0.18 +/- 0.10 EMD and 0.05 +/- 0.10 eye muscle area (EMA)], while those with FATC were negative. The genetic correlation between EMD and eye muscle width (EMW) was 0.41 +/- 0.08, while EMA was highly correlated with EMD (0.89 +/- 0.0) and EMW (0.78 +/- 0.04). The genetic correlations for muscle colour with muscle measurements were moderately negative, while those with fat measurements were close to zero. Meat pH was positively correlated with muscle measurements (0.14 to 0.17) and negatively correlated with fat measurements (-0.06 to -0.18). EMDUS also showed a similar pattern of correlations to EMD with meat quality indicator traits, although FATUS had positive correlations with these traits which were generally smaller than their standard error. The genetic correlations among the meat colour traits were
Kennedy, C; Buckley, D J; Kerry, J P
Longissmus dorsi loins were removed from Suffolk cross-breed lambs (4-9 months) and hoggets (15-20 months). The effect of package gas composition was investigated by packaging loins with gas mixtures containing 80:20:0, 60:20:20 and 60:40:0/O(2):CO(2):N(2) with a 2:1 headspace to meat volume ratio. The most effective gas mixture for prolonging shelf-life was used to study the effect of different headspace to meat volume ratios. Loins were packaged with a headspace to meat volume ratio of 2:1, 1.5:1 or 1:1. All modified atmosphere (MA) packs were held under refrigerated display conditions (4 °C, 616 lx) for 12 days. Loins were assessed for microbial, oxidative and colour stability and headspace composition every 3 days. The 80:20:0/O(2):CO(2):N(2) gas composition and the 2:1 headspace to meat volume ratio was the most effective packaging combination at maintaining and prolonging the attractive red colour of MA packaged lamb and hogget meat. 80:20:0/O(2):CO(2):N(2) resulted in significantly (p<0.01) higher Hunter a values in lamb. The 2:1 ratio gave higher visual assessment values in lamb and higher Hunter `a' values for hogget meat throughout the trial. The 2:1 ratio was the most effective at decreasing Pseudomonas and increasing the numbers of lactic acid bacteria in the total microbial load in both lamb and hogget meat. Lipid oxidation in lamb and hogget meat occurred at a slower comparative rate than discolouration or microbial growth and was not the major determinant of shelf-life. The 2:1 headspace to meat volume ratio was most effective at maintaining the initial gas mix in both lamb and hogget MA packs.
Smith, K C; Brown, P J; Barr, F J
Congenital abnormalities of the reproductive tract of male sheep were surveyed at three abattoirs in the south west of England during the period June 2000-January 2004. A total of 7307 rams were examined [6521 lambs (prepubescent) and hoggets (aged from their first autumn after birth until first shorn) and 786 adult rams mature rams that had been exposed to ewes]. A total of 156 congenital lesions were detected, 87 of which occurred in lambs. Testicular hypoplasia was the most common lesion occurring in 69 lambs as well as eight hoggets ('microtestes' were recognized in nine other animals in which the testis was disproportionately smaller than the epididymis). The second most common lesion found was notched scrotum occurring in 34 animals (27 young rams and seven adults). Some cases of notched scrotum were accompanied by hypospadias which was seen in a total of seven lambs and eight hoggets. Other lesions, detected in five or less animals (less than approximately 0.05% of the animals examined), included cryptorchidism and various abnormalities of the epididymis (segmental aplasia of the epididymis, blind efferent ducts and epididymal cyst) and congenital scrotal hernia. The overall prevalence of congenital lesions of 2.21% emphasizes the importance of undertaking breeding soundness examinations of young rams before they are put with the flock.
Thompson, G M; Jess, S; Gordon, A W; Murchie, A K
Sticky traps were mounted on heifers and sheep to assess Culicoides spp. (Diptera: Ceratopogonidae) host preference. Initially, four coloured 200-cm(2) sticky traps (white, clear, yellow and blue) were attached to the backs of each of ten Friesian heifers that were released into open pasture for 24 h, repeated on six occasions. More Obsoletus group Culicoides were caught on the white and clear traps than on the yellow and blue. Trap position on the right or left flank also affected midge catch, probably due to heifer orientation in the field. Next, six Friesian heifers and six Charollais hoggets each had one clear and one white sticky strap attached to their backs for one 24-h period per week, repeated for 24 weeks. Overall, Obsoletus group Culicoides comprised 91.8% (n = 5, 955) of the midge catch but there was no evidence of host preference, either discounting or including host live weight in the analyses. However, Pulicaris group Culicoides did demonstrate a significant host preference for sheep, providing that the analysis was adjusted for live weight. On heifers, the Pulicaris group comprised 7.5% of biting midges caught, whereas on hoggets, it comprised 12.7%.
Wang, Peng-Yu; Guanque, Zha-Xi; Qi, Quan-Qing; De, Mao; Zhang, Wen-Guang; Li, Jin-Quan
The maternal genetic effects on estimating genetic parameters for growth traits and wool traits of Qinghai fine-wool sheep were investigated.The genetic parameters for production traits of Qinghai fine-wool sheep were estimated by average information restricted maximum likelihood (AIREML) with different animal models, and the differences between different animal models were tested by likelihood ratio test. Fixed effects, direct genetic effects, and residual effects were included all models; and random effects were individual permanence environmental effects, maternal genetic effects, and maternal permanence environmental effects. The six models differ in the way of considering random effects: in model 1 individual permanence environmental effects, maternal genetic effects, and maternal permanence environmental effects were not contained; in model 2 maternal permanence environmental effects were included; in model 3 maternal genetic effects were included; in model 4 both maternal genetic effects and maternal permanence environmental effects were include; in model 5 both individual permanence environmental effects and maternal genetic effects were contained;in model 6 all random effects were contained. The direct heritabilities were 0.1896~0.3781, 0.2537~0.2890, 0.2244~0.3225, 0.2205~0.3983, 0.1218~0.1490, 0.0983~0.4802, and 0.1170~0.1311 for birth weight, weaning weight, yearling weight, hogget weight,greasy fleece weight, fiber diameter, and staple length,respectively. Compared with model 1, model 3 was-significant(P<0.01) for birth weight and weaning weight, other models were not significant (P>0.05)for Yearling weight, Hogget weight; and paralleled with model 6, both model 4 and model 5 were significant(P<0.01) for fiber diameter,model 4 was significant(P<0.05) for staple length, and other models were not significant(P>0.05) for greasy fleece weight by likelihood ratio test.The maternal effects were important determinants of estimated the genetic parameters for
Smith, K C; Long, S E; Parkinson, T J
A survey of abnormalities of the reproductive tract of female sheep was undertaken at two abattoirs in the south west of England over a period of 12 months. During the survey, 9970 reproductive tracts from cull ewes and 23,536 tracts from nulliparous sheep (prime lambs and hoggets) were examined. A total of 655 (6.57 per cent) ewes and 459 (1.95 per cent) nulliparous sheep had abnormalities of the reproductive tract. Of these, congenital abnormalities of the paramesonephric ducts accounted for 2.4 per cent of the ewes and 7.4 per cent of the nulliparous sheep, congenital abnormalities of the ovaries accounted for 2.6 per cent of the ewes and 7.4 per cent of the nulliparous sheep and cystic structures that were considered to have been of congenital origin accounted for 27.2 per cent of the ewes and 52.7 per cent of the nulliparous sheep. The most common lesion was paraovarian cysts (26.6 per cent of ewes and 39.0 per cent of nulliparous sheep), but few of these appeared to have affected the sheep's reproductive function. Several specific conditions were recorded, including some described for the first time in sheep. Uterus unicornis occurred in 20 sheep and other forms of segmental aplasia of parts of the paramesonephric ducts occurred in a further 13 animals. Uterus didelphys occurred in six sheep, and 11 animals were intersex. Intersex sheep had vestigial structures that were derived from the paramesonephric ducts, hypoplastic or masculinised gonads and some had masculinised external genitalia. Ovarian hypoplasia occurred in 34 sheep, and in a further 12 mainly nulliparous animals, the ovaries were fused. Sixty nulliparous animals and two ewes had hydatids of Morgagni.
Safari, E; Fogarty, N M; Gilmour, A R; Atkins, K D; Mortimer, S I; Swan, A A; Brien, F D; Greeff, J C; van der Werf, J H J
Data from seven research resource flocks across Australia were combined to provide accurate estimates of genetic correlations among production traits in Merino sheep. The flocks represented contemporary Australian Merino fine, medium and broad wool strains over the past 30 years. Over 110,000 records were available for analysis for each of the major wool traits, and 50,000 records for reproduction and growth traits with over 2700 sires and 25,000 dams. Individual models developed from the single trait analyses were extended to the various combinations of two-trait models to obtain genetic correlations among six wool traits [clean fleece weight (CFW), greasy fleece weight, fibre diameter (FD), yield, coefficient of variation of fibre diameter and standard deviation of fibre diameter], four growth traits [birth weight, weaning weight, yearling weight (YWT), and hogget weight] and four reproduction traits [fertility, litter size, lambs born per ewe joined, lambs weaned per ewe joined (LW/EJ)]. This study has provided for the first time a comprehensive matrix of genetic correlations among these 14 wool, growth and reproduction traits. The large size of the data set has also provided estimates with very low standard errors. A moderate positive genetic correlation was observed between CFW and FD (0.29 +/- 0.02). YWT was positively correlated with CFW (0.23 +/- 0.04), FD (0.17 +/- 0.04) and LWEJ (0.58 +/- 0.06), while LW/EJ was negatively correlated with CFW (-0.26 +/- 0.05) and positively correlated with FD (0.06 +/- 0.04) and LS (0.68 +/- 0.04). These genetic correlations, together with the estimates of heritability and other parameters provide the basis for more accurate prediction of outcomes in complex sheep-breeding programmes designed to improve several traits.
Morales, Juan Manuel
Background. A large proportion of natural grasslands around the world is exposed to overgrazing resulting in land degradation and biodiversity loss. Although there is an increasing effort in the promotion of sustainable livestock management, rangeland degradation still occurs because animals’ foraging behaviour is highly selective at different spatial scales. The assessment of the ecological mechanisms modulating the spatial distribution of grazing and how to control it has critical implications for long term conservation of resources and the sustainability of livestock production. Considering the relevance of social interactions on animals’ space use patterns, our aim was to explore the potential effects of including animals’ social context into management strategies using domestic sheep grazing in rangelands as case study. Methods. We used GPS data from 19 Merino sheep (approximately 10% of the flock) grazing on three different paddocks (with sizes from 80 to 1000 Ha) during a year, to estimate resource selection functions of sheep grazing in flocks of different levels of heterogeneity. We assessed the effects of sheep class (i.e., ewes, wethers, and hoggets), age, body condition and time since release on habitat selection patterns. Results. We found that social rank was reflected on sheep habitat use, where dominant individuals (i.e., reproductive females) used more intensively the most preferred areas and low-ranked (i.e., yearlings) used less preferred areas. Our results showed that when sheep grazed on more heterogeneous flocks, grazing patterns were more evenly distributed at all the paddocks considered in this study. On the other hand, when high-ranked individuals were removed from the flock, low-ranked sheep shifted their selection patterns by increasing the use of the most preferred areas and strongly avoided to use less preferred sites (i.e., a highly selective grazing behaviour). Discussion. Although homogenization and segregation of flocks by