Small Ruminant Research, June 2017, Vol. 151, Issue Highlights

Production Systems and Sustainability
Reduced survival of lambs from maiden ewes exposed to mature ewes pre-lambing
S.M. Robertson, M.B. Allworth, M.A. Friend
Vol. 151, p11–15
 
The suboptimal survival of new-born lambs is a major source of reproductive inefficiency, is often lower in maiden (first-lambing) compared with multiparous ewes, and this may be associated with poor maternal behaviour due to inexperience. This study examined whether the survival of lambs from maiden ewes could be increased by exposing maiden ewes to multiparous lambing ewes in the month before lambing. Pregnant maiden Merino ewes (n = 446) which had been mated at 18 months of age were allocated to three replicates of two treatments.

During the month prior to the maidens lambing, control groups were grazed in paddocks each with 30 multiparous mature (5.5 and 6.5 years of age) Merino ewes which were due to lamb at the same time as the maiden ewes. The exposed treatment groups also grazed with 30 mature ewes, during which time the mature ewes lambed. All mature ewes and lambs were removed and the groups of maiden ewes grazed in separate 5.3 ha paddocks from 10 days before the maidens were due to lamb. The survival of lambs to marking age was lower (P = 0.035) from maidens exposed to mature lambing ewes (0.73) compared with those that grazed only with pregnant mature ewes (0.81). The number of lambs reared per ewe lambing was not lower (P = 0.274) from the exposed (0.92) compared with the control (0.98) ewes. This study showed that the survival of lambs from maiden ewes was reduced by exposing them to mature lambing ewes, and it is recommended to avoid grazing lambing mature ewes in the same paddock with maiden ewes in the month prior to the maiden lambing.
 
Keywords: Sheep, Behaviour, Reproduction, Mortality
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Effect of energy source and level, and sex on growth, performance, and carcass characteristics of lambs
J.R. Jaborek, H.N. Zerby, S.J. Moeller, F.L. Fluharty
Vol. 151, p117–123
 
The objective of the study was to compare ad libitum or restricted access of whole shelled corn (WSC) versus ad libitum alfalfa pellets, and sex of the lamb, on lamb growth and performance. Ewe (n = 48) and wether (n = 48) lambs were blocked by sex and stratified by initial weight to pen. The three diets offered were ad libitum access of a WSC diet, 85% access of ad libitum WSC diet, or an ad libitum access of an alfalfa pellet diet. There were four lambs per pen, and eight replicate pens per dietary treatment. Ewe and wether lambs were removed from the study when pens reached an average weight of 59.0 and 63.5 kg, respectively. Average daily gain (ADG) of lambs offered the ad libitum WSC diet was greater (P < 0.05) than lambs offered the restricted WSC and alfalfa pellet diets, which resulted in fewer (P < 0.01) days on feed for lambs offered ad libitum WSC. Lambs offered alfalfa pellets had a greater (P < 0.01) daily dry matter intake (DMI) than lambs offered the WSC diets. Wether lambs had greater (P < 0.01) daily DMI when compared with ewe lambs. Gain to feed ratio was greatest (P < 0.01) for lambs offered ad libitum access to WSC, followed by lambs offered restricted WSC, and lambs offered the alfalfa pellet diet. The cost of whole shelled corn was $0.15/kg, the cost of alfalfa pellets was $0.60/kg, and the cost of supplements was $0.51/kg on an as-fed basis. The resulting feed cost of gain was greatest (P < 0.01) for lambs offered alfalfa pellets, followed by lambs offered restricted WSC, and lastly lambs offered ad libitum WSC. Lambs offered the WSC diets produced a greater hot carcass weight (HCW; P < 0.01) and greater (P < 0.01) dressing percent when compared with lambs offered alfalfa pellets. Lambs consuming ad libitum WSC had a greater amount (P < 0.05) of kidney fat when compared with lambs consuming a restricted diet of WSC or ad libitum access to alfalfa pellets. Lambs consuming either of the WSC diets produced a greater (P < 0.05) amount of visceral fat when compared with lambs offered alfalfa pellets. Lambs offered alfalfa pellets had greater tissue weight of the reticulum (P < 0.05), omasum (P < 0.01), and total digestive tract (P < 0.05), consistent with the lower dressing percentage observed. Lambs offered WSC had greater (P < 0.05) backfat and body wall thicknesses, loin marbling scores, and yield grades (P < 0.01) when compared with lambs offered alfalfa pellets. Wether lambs had a greater (P < 0.05) final BW and HCW when compared with ewe lambs. Overall, lambs offered ad libitum WSC grew more efficiently at a lower cost of gain while producing carcasses with greater amounts of fat, whereas lambs offered alfalfa pellets had a lower dressing percentage and a greater total digestive tract weight.
 
Keywords:
Lambs, Feedlot, Corn, Alfalfa, Growth, Carcass
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Genetics and Breeding
Utilization of year-round data in the estimation of genetic parameters for internal parasite resistance traits in Dorper sheep
L. Ngere, J.M. Burke, A.D. Herring, J.O. Sanders, T.M. Craig, J.A. van Wyk, D.G. Riley
Vol. 151, p5–10
The objective of this study was to evaluate the effect on the estimates of heritability and permanent environmental effects as a proportion of phenotypic variance for FAMACHA score, fecal worm egg count and hematocrit value when year-round records are used. Records from 1008 Dorper sheep in a private South African flock comprised 17,711 FAMACHA scores, 6837 fecal worm egg counts (FEC; practically only Haemonchus contortus), and 4209 hematocrit (packed cell volume-PCV) values that were collected from 1997 to 2000. Animal models were used to conduct single-trait analyses. Data were analyzed in two sets: 1) warm season records only and 2) year-round records. Treatment (with anthelmintic) status was investigated as a 2-level fixed effect in both sets; additionally records of treated sheep were removed for another analysis of both data sets. In analyses of warm season records, estimates of heritability and permanent environmental variance as a proportion of phenotypic variance for FAMACHA score were 0.33 ± 0.03 and 0.04 ± 0.02, respectively, when treatment status was modeled, and 0.41 ± 0.02 and 0, respectively, when treated records were excluded from the analysis. Heritability estimates for PCV were 0.22 ± 0.06 (treatment status modeled) and 0.28 ± 0.07 (treated records excluded), while permanent environmental variance as a proportion of phenotypic variance was, respectively, 0.13 ± 0.05 and 0.09 ± 0.06. Fecal worm egg count heritability estimates were 0.10 ± 0.03 (treatment status modeled) and 0.13 ± 0.04 (untreated records only). Permanent environmental variance for FEC was 0.04 ± 0.03 when treated records were excluded and 0.05 ± 0.03 when treatment status was included in the analyses. In analyses of year-round records, estimates of heritability and permanent environmental variance as a proportion of phenotypic variance for FAMACHA score were 0.32 ± 0.03 and 0.03 ± 0.02, respectively (treatment status modeled) and 0.36 ± 0.03 and 0.02 ± 0.02 (treated records excluded). Packed cell volume heritability and permanent environmental variance were, respectively, 0.19 ± 0.05 and 0.18 ± 0.05 in the analyses of untreated records, and 0.18 ± 0.04 and 0.15 ± 0.04, when treatment status was modeled. Heritability estimates for FEC were the same (0.11) for untreated records only, and when treated records were included. Permanent environmental variance was 0.04 ± 0.02 (treated records included) and 0.03 ± 0.02 (treated records excluded) for FEC. Collection and inclusion of cool season (that is, outside of the regular worm proliferation season) records in analyses may not substantially change estimates of genetic parameters for these traits.
 
Keywords:
Genetic parameters, Haemonchus contortus, Season, Dorper sheep, Parasite resistance
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