Breed effects and heterosis for weight traits and tick count in a cross between an indigenous fat-tailed and a commercial sheep breed.

Ticks can compromise productivity and welfare in free-ranging sheep. Chemical tick control may not be sustainable in the long term. Alternative control measures must be sought for an integrated control programme. Birth and weaning weights as well as log transformed overall tick count of indigenous fat-tailed Namaqua Afrikaner (NA), commercial Dorper and NA x Dorper cross lambs were studied under extensive conditions. Relative to NA lambs, Dorper lambs were 22.2% heavier at weaning (P < 0.05). Geometric means for total tick count on Dorper lambs exceeded those of their Namaqua Afrikaner contemporaries by more than twofold (P < 0.05). Relative to the pure-breed midparent value, the mean performance of NA x Dorper lambs was 7.9% more for birth weight, 11.2% more for weaning weight and 26.2% less for the back transformed means for total tick count (P < 0.05). Heterosis for total tick count was slightly greater at -29.3% when data were adjusted for the larger size of NA x Dorper lambs. Crossing commercial Dorper sheep with a hardy, indigenous breed therefore resulted in lower levels of tick infestation without compromising live weight in progeny so derived. Hardy, indigenous genetic resources like the NA should be conserved and used in further studies of ovine genetics of resistance to ticks in South Africa.

Genetic parameters for tick count and udder health in commercial and indigenous ewes in South Africa.

The genetics of tick infestation in sheep need study, as host resistance often forms part of integrated pest control programs. Repeated udder health scores, site-specific tick count, mating weight and reproduction records (N=879-1204) were recorded annually from 2010 to 2015 on ewes of the indigenous Namaqua Afrikaner (NA) fat-tailed breed, as well as the commercial Dorper and SA Mutton Merino (SAMM) breeds. Udders were scored subjectively on a 1-5 scale (1 - udder intact and 5 - udder damaged severely) and ticks were counted on three locations. The body sites counted were the head and thoracic limb (HTLTC), udder-pelvic limb (UPLTC) and perineum-breech-tail (PBTTC). These counts were also totaled for a total tick count (TTC). Reproduction traits were number of lambs weaned per ewe lambed and total weight of lamb weaned per ewe lambed. Udder health scores of NA ewes were lower than those of Dorpers, which in turn had lower scores than SAMM ewes. NA ewes had lower values for HTLTC, UPLTC and TTC than the commercial breeds, but higher values for PBTTC than Dorpers. Heritability estimates amounted to 0.26±0.04 for HTLTC, 0.53±0.04 for UPLTC, 0.07±0.06 for PBTTC, 0.44±0.06 for TTC and 0.61±0.03 for udder health score. Animal permanent environment also affected PBTTC (0.14±0.07). Significant genetic correlations were found between the HTLTC and UPLTC (0.47±0.10), UPLTC and udder health score (0.52±0.07), HTLTC and UPLTC (0.24±0.11) as well as UPLTC and PBTTC (-0.44±0.11). Heavier ewes had higher UPLTC (0.38±0.09), TTC (0.33±0.09) and impaired udder health (0.21±0.08). Udder health scores and tick counts at all sites were not related to reproduction traits. The indigenous NA breed outperformed the commercial breeds with lower values for HTLTC, UPLTC, TTC and a better udder health score. Mechanisms contributing to the better performance of the NA breed under pastoral conditions and the scope for selection for tick tolerance within breeds should be studied further.

A survey of the prevalence of blowfly strike and the control measures used in the Rûens area of the Western Cape Province of South Africa.

Blowfly strike and the methods used to combat blowfly strike were recorded on 33 properties in the Rûens area of South Africa during 2003/2004. Data were recorded on Merino and Dohne Merino hoggets (n = 4951) with at least 3 months' wool growth. The following data were captured: presence or absence of strike, site of the strike (body or breech), presence or absence of dermatophilosis as well as subjective scores for wool quality and wool colour. Control measures recorded include: chemical treatment (preventative and spot treatment), crutching, mulesing and the use of the Lucitrap system. Blowfly strike was not significantly influenced by gender or breed. Hoggets suffering from dermatophilosis were more likely to be struck, compared with contemporaries not suffering from the skin disorder (0.057 vs 0.027; P < 0.05). Merino hoggets generally had higher scores than their Dohne Merino contemporaries for wool quality (32.6 vs 27.4; P < 0.05) and wool colour (29.0 vs 27.2; P < 0.05). There was an indication that the Lucitrap system may have reduced flystrike, but the effect was not statistically significant (P = 0.19 for overall strikes and P = 0.12 for body strike). The Mules operation benefited overall flystrike (0.013 vs 0.110; P < 0.05); mainly through an effect on breech strike (0.010 vs 0.109; P < 0.05). The proportion of fly strikes increased with wool length, and declined with an increase in farm size in wool colour score. None of the ethically acceptable control measures assessed could substantially reduce blowfly strike on their own, and an integrated pest management programme was proposed.

A preliminary evaluation of a sheep blowfly trap in the Western Cape.

An insecticide-free sheep blowfly trapping system, utilising a synthetic lure, was evaluated at 4 localities in the Western Cape. Control sites, where no suppression was practised, were identified for each locality. The blowfly population was monitored for 48 hours monthly at each of the localities. Five to 7 suppression traps at the respective localities were identified for this purpose. Three to 10 traps were set monthly for monitoring in the control areas. Trapping resulted in the suppression (P < 0.01) of the Lucilia population at Caledon, where a large area of approximately 50 km2 was trapped. The suppression area of all the localities was < or =850 ha. At Elsenburg, blowfly numbers were low. There was a strong suggestion of a general reduction in the Lucilia numbers at this locality. Trapping failed to reduce Lucilia numbers at Tygerhoek and Langgewens. Lack of control over the influx of Lucilia from adjacent sheep-producing areas probably contributed to this result. The observed response at Elsenburg was probably due to its situation in a predominantly wine-growing area. Most of the blowflies recovered from the control traps during the month with the highest yield at the respective localities belonged to the genus Lucilia. The results obtained at Caledon and published reports suggest that large-scale trapping of Lucilia spp. may play a role in an integrated pest management system for blowflies.

Parenteral copper and selenium supplementation of sheep on legume-grass pastures: biochemical and production responses in lambs to maternal treatment.

Liver and kidney copper (Cu) and selenium (Se) concentrations were studied over a 7-month period after parenteral supplementation using Cu heptonate and barium (Ba) selenate in 44 8-month-old South African (SA) Mutton Merino wethers. Responses in plasma Cu and blood Se concentrations, as well as fecundity were also measured in a breeding flock of SA Mutton Merino ewes for 3 consecutive years. The effect of maternal supplementation with Cu and Se was assessed in terms of biochemical parameters and production responses in 654 lambs produced by these ewes. Parenteral treatments with Cu and Se raised liver and kidney concentrations (P < or = 0.05) for up to 7 months in wethers under conditions where liver Cu and Se respectively declined to concentrations below 30 mg/kg DM and 300 micrograms/kg dry matter (DM) in spring. Plasma Cu concentrations of breeding ewes which received Cu heptonate were increased (P < or = 0.05) by 18% relative to the control group in which concentrations declined to 91 micrograms/dl during late pregnancy. Blood Se concentrations of control ewes exceeded 200 ng/ml, and were unaffected by parenteral Se supplementation. Survival of progeny of Cu heptonate treated ewes tended (P < or = 0.10) to be improved by 13% (0.68 vs 0.60). This tendency was accompanied by generally higher (P < or = 0.10) plasma Cu concentrations of these lambs relative to control lambs at 10 - 20 and 45 - 55 d of age. Lambs of Cu supplemented ewes that died prior to weaning, had higher (P < or = 0.05) liver Cu concentrations than control group contemporaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Production responses of sheep supplemented with copper, cobalt and selenium on kikuyu ryegrass pastures.

The copper (Cu) and selenium (Se) status of SA Mutton Merino ewes grazing kikuyu-ryegrass pastures was investigated by analysing blood and liver samples. The response of ewes to oral supplementation with Cu, Cobalt (Co) and Se as single elements, or in 4 combinations were simultaneously assessed in a 2 x 2 x 2 factorial experiment. Pastures grazed were low in Cu (less than 5 mg Cu/kg DM) except for the summer months, while pasture Se concentrations remained at concentrations less than 0,03 mg Se/kg DM for almost the entire period. Plasma Cu concentrations remained in excess of 80 micrograms/dl until pasture Cu concentrations decreased below 5 mg/kg DM. Blood Se concentrations generally reflected liver Se concentrations. Supplementation of ewes with 5 g Cu oxide needles (Embamin Copper LA, Rhône Poulenc) markedly increased (P < or = 0,01) hepatic Cu and plasma Cu concentrations. The monthly drenching of ewes with 5 mg Se as sodium selenite elevated blood Se concentrations to normal levels in excess of 100 ng/ml while ewes not supplemented with Se had blood Se concentrations indicative of a deficiency (50-100 ng/ml). Supplementation of ewes with Cu and Se elevated (P < or = 0,05) concentrations of these trace elements in the plasma and blood of their progeny. Supplementation of ewes with Cu and Se resulted in respective improvements (P < or = 0,05) of 5,3 and 4,8% in live mass during lactation, compared to contemporaries which did not receive either Cu or Se.(ABSTRACT TRUNCATED AT 250 WORDS)