Sheep of divergent genetic merit for wool growth do not differ in digesta kinetics while on restricted intakes

2014 ◽  
Vol 54 (9) ◽  
pp. 1243 ◽  
Author(s):  
I. De Barbieri ◽  
R. S. Hegarty ◽  
V. H. Oddy ◽  
M. C. Barnett ◽  
L. Li ◽  
...  
Keyword(s):  
Compartmental Model ◽  
Genetic Selection ◽  
Amino Nitrogen ◽  
Feeding Level ◽  
Wool Growth ◽  
Selection For ◽  
Fleece Weight ◽  
Estimated Breeding Values ◽  
Growth Differences ◽  
Weight Groups

Sheep selected for high wool growth were previously shown to exhibit higher microbial protein outflow from the rumen and higher uptake of amino nitrogen in portal blood than those selected for low wool growth. This suggests that genetic selection for wool growth may induce changes in foregut physiology. This study was undertaken to determine whether differences in digesta kinetics, especially mean retention mime (MRT), are associated with differences in fleece production between sheep with low or high estimated breeding values (EBVs) for fleece weight. Twenty mature Merino wethers with uniform EBVs for liveweight were allocated to two groups of 10 animals on the basis of high or low EBVs for yearling fleece weight. Five sheep with low-EBVs and five sheep with high-EBVs for fleece weight groups were allocated in a crossover design to low and high feeding-level treatments, which comprised a blended hay diet fed at maintenance or 1.5 times maintenance. All sheep were given single doses of chromium-mordanted fibre and cobalt-EDTA as inert, non-digestible markers. Digesta kinetics was determined by analysis of the faecal marker excretion patterns using a compartmental model. Higher feed intakes from animals fed 1.5 times maintenance were associated with higher rates of wool growth and higher masses of indigestible fibre in the gut, but reduced MRT of digesta. Although sheep with higher EBVs for fleece weight had higher wool growth rates, there was no indication that these wool growth differences were associated with differences in digesta kinetics. The lack of interaction between feeding level and genotype suggests that MRT did not contribute to genotype differences in wool growth in sheep fed restricted intakes. The differences in wool growth among commercial Merino sheep with divergent fleece weight EBVs achieved by multi-trait selection are not attributable to differences in digesta kinetics, at least when feed is not available ad libitum.

Efficiency of conversion of food to wool in selected and unselected Merino types

1972 ◽  
Vol 23 (1) ◽  
pp. 117 ◽  
Author(s):  
DG Saville ◽  
GE Robards
Keyword(s):  
Body Weight ◽  
Food Intake ◽  
Surface Area ◽  
Fibre Diameter ◽  
Response To Selection ◽  
Gross Efficiency ◽  
Wool Growth ◽  
Selection For ◽  
Fleece Weight ◽  
Growth Differences

Comparisons were made between Collinsville, Bungaree, and Peppin Merino ewes in efficiency of conversion of food to wool. The effect of selection for some characters on efficiency of conversion within the Peppin Merino was also investigated. The Collinsville ewes grew 14% more wool and had an 8% lower food intake at maintenance than did the Peppins. Differences in wool growth between the Peppin and Collinsville types fed ad lib. were mainly due to efficiency and body weight differences. Efficiency, intake, and body weight each had a similar influence on wool growth differences between Peppins and Bungarees. Peppin ewes selected for wool production, either alone or together with crimp frequency, had a higher gross efficiency than unselected sheep fed below maintenance (13 and 8%) or ad lib. (14 and 13%). The efficiency difference between selected and unselected sheep increased, then decreased, with increasing intake. The decrease in efficiency differences at higher intakes did not appear to influence the ranking of selected or unselected sheep. The response to selection for clean fleece weight was shown to develop a plateau after about one generation of selection. Selection had resulted in the elimination of a relationship between efficiency and wool growth. The present results indicate that further progress in fleece weight is unlikely to be made either by selecting for fleece weight with some control on fibre diameter or by selecting for increased surface area.

Indices of cellular development in muscles of lambs are influenced by sire estimated breeding values and pastoral nutritional system

2006 ◽  
Vol 57 (6) ◽  
pp. 651 ◽  
Author(s):  
P. L. Greenwood ◽  
G. E. Gardner ◽  
R. S. Hegarty
Keyword(s):  
Muscle Growth ◽  
Genetic Selection ◽  
Inverse Association ◽  
Semitendinosus Muscle ◽  
Eye Muscle ◽  
Weaning Weight ◽  
Breeding Values ◽  
Sire Group ◽  
Selection For ◽  
Estimated Breeding Values

This study examined influences of sire (n = 9) estimated breeding values (EBVs), sire-group (Muscle, Growth, and Control), and nutrition (low and high quality and availability pasture) from birth to slaughter at ~8 months of age on indices of muscle cellularity and transcriptional and translational capacity in 56 castrate lambs. Effects of nutritional systems to 8 months of age were greater, overall, than those due to EBVs or sire-group. Amount of DNA increased with increasing EBV for post-weaning eye muscle depth (PEMD or Muscle EBV) in longissimus but not in semimembranosus and semitendinosus muscles, while Muscle EBV also had an inverse association with concentration of DNA. Protein to DNA and RNA to DNA were related positively to Muscle EBV, the associations being strongest for the semitendinosus muscle. Post-weaning weight (PWWT or Growth) EBV correlated positively with the RNA to DNA ratio and, among high but not low nutrition lambs, was inversely related to concentration of muscle DNA, whereas post-weaning fat depth (PFAT or Fat) EBV was correlated positively with RNA concentration. Overall, the magnitude of effects of sire-group was less than for sire EBVs, presumably due to differing selection pressures for muscling, fatness, and growth. High nutrition lambs had more protein to DNA than low nutrition lambs in the longissimus and semitendinosus muscles, but not in the semimembranosus muscle. In low compared with high nutrition lambs, concentration of DNA was greater in the longissimus and semitendinosus muscles. Total amount of DNA was reduced by more in low compared with high nutrition in the longissimus and semimembranosus than in the semitendinosus, and amount of protein was reduced by more in low compared with high nutrition in the longissimus than in the other two muscles. We conclude that genetic selection for eye muscle depth in sheep has differing effects on cellular characteristics of the longissimus, semimembranosus, and semitendinosus muscles, and has greater effects on muscle cellular characteristics than genetic selection for post-weaning weight or fat depth.

Plasma insulin concentrations and amino acid turnover in Merino sheep with high or low fleece weight

2004 ◽  
Vol 55 (8) ◽  
pp. 833 ◽  
Author(s):  
N. R. Adams ◽  
S. M. Liu ◽  
J. R. Briegel ◽  
M. J. Thompson
Keyword(s):  
Amino Acids ◽  
Plasma Insulin ◽  
Plasma Concentrations ◽  
Amino Nitrogen ◽  
Whole Body ◽  
Metabolic Demand ◽  
Body Protein ◽  
Wool Growth ◽  
Staple Strength ◽  
Fleece Weight

Although sheep with a relatively high fleece weight have reduced fat deposition and a lower reproductive rate, research has failed to identify any specific metabolic demand that growing a fleece places on the physiology of the sheep. This paper reports two experiments in which the effect of fleece weight was examined in ewes infused intravenously with amino acids. The first experiment was carried out when the ewes were 107 days pregnant, and the second 2 years later in non-pregnant ewes from the same flock. The ewes were derived initially from groups that differed in staple strength, but there was no effect of staple strength group on the characteristics measured in either experiment. In Expt 2, ewes were also infused with a bolus of l-[ring-d5] phenylalanine, and the enrichment in plasma determined by GC/mass spectrometry over the next 24 h. In both experiments, fasting plasma insulin concentrations were lower (P < 0.05) in ewes with a high fleece weight, and this difference continued during infusion in Expt 2 (P < 0.05). In Expt 1, infusion of ewes with amino acids resulted in higher (P < 0.05) plasma concentrations of α-amino nitrogen (indicating amino acids) in the ewes with a higher fleece weight, and in Expt 2, ewes with a high fleece weight had a 19% higher rate of appearance of endogenous phenylalanine (P < 0.05). We conclude that sheep with high wool growth rates have higher whole-body protein turnover rate, which may be achieved in part by lower insulin concentrations. Lower insulin in turn provides a mechanism through which wool growth rate may influence energy availability to other tissues.

Effect of selection for wool growth on seasonal patterns of yield, fibre diameter, and colour in Romney lines

1995 ◽  
Vol 35 (1) ◽  
pp. 27 ◽  
Author(s):  
T Wuliji ◽  
IL Weatherall ◽  
RN Andrews ◽  
KG Dodds ◽  
PR Turner ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fibre Diameter ◽  
Seasonal Patterns ◽  
Control Line ◽  
Wool Growth ◽  
Growth Decline ◽  
Selection For ◽  
Staple Strength ◽  
Fleece Weight

Seasonal wool growth and associated wool characteristics were measured in a Romney line selected for high fleece weight and an unselected control line in 1990 and 1991. Both had a significant (P<0.01) decline in wool growth rate in winter compared with summer. The wool growth rate advantage (P<0.001) of the selected line over the control averaged 19 and 33% for ewes, and 24 and 36% for hoggets, in summer and winter, respectively. Staple strength, yield, and fibre diameter differences were closely associated with wool growth. Colour analysis showed no difference between lines in either brightness (Y) or yellowness (Y - Z). However, both the Y and Z values were lower in spring and summer, while Y - Z was highest in summer. The results suggest that selection for high fleece weight also improves major wool characteristics and reduces the relative winter wool growth decline in Romneys.

Fat depth, muscle depth, fat score and wool growth in Merino dams selected for high or low clean fleece weight and bodyweight

2010 ◽  
Vol 50 (6) ◽  
pp. 479 ◽  
Author(s):  
G. Refshauge ◽  
S. Hatcher ◽  
G. N. Hinch ◽  
D. L. Hopkins ◽  
S. Nielsen
Keyword(s):  
Body Composition ◽  
Stocking Rate ◽  
Body Fatness ◽  
Fat Reserves ◽  
Reduced Fat ◽  
Wool Growth ◽  
Selection For ◽  
Fleece Weight ◽  
Fat Score ◽  
The Impact

Concerns exist that selection for increased clean fleece weight (CFW) is expected to reduce body fatness. Such an effect is likely to impact on reproduction; however, all previous studies have examined non-reproductive yearlings or hoggets. The present study, using adult reproductive dams examined the impact of phenotype [based on high or low phenotypic CFW and bodyweight (BWT) performance], stocking rate (high or low) and litter size on body composition and wool traits. High CFW dams were heavier (P < 0.01) with lower fat depth (P < 0.01) and muscle depth (P < 0.05). The high CFW twin-weaning dams had a lower fat score from lamb marking to pre-joining (P < 0.05), but tended to replete fat reserves faster (P < 0.1) between weaning and pre-joining. At these times of repletion these animals grew longer wool staples (P < 0.05). High BWT ewes had reduced staple length (P < 0.01), and when adjusted for maternal liveweight also reduced fat depth (P < 0.001) and muscle depth (P < 0.05). We conclude that the CFW phenotype impacts on fat reserves but that management of dams in groups according to their CFW performance is not warranted.

Protein synthesis rates in skin components and skeletal muscle of sheep selected for divergent clean fleece weight in response to below- and above-maintenance nutrition

2007 ◽  
Vol 58 (11) ◽  
pp. 1031 ◽  
Author(s):  
L. Li ◽  
S. M. Liu ◽  
V. H. Oddy ◽  
J. V. Nolan
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Feed Intake ◽  
Synthesis Rate ◽  
Breeding Values ◽  
Fractional Synthesis Rate ◽  
Feeding Level ◽  
Fractional Synthesis ◽  
Fleece Weight ◽  
Estimated Breeding Values

Protein metabolism in skin and muscle was studied in Merino wethers selected for high (F+, n = 10) or low (F–, n = 10) estimated breeding values for clean fleece weight, but with similar estimated breeding values for liveweight and fibre diameter, raised to 20 months of age under the same conditions, and then offered two levels of nutrition (0.8 or 1.8 × maintenance) for 37 days. Over 37 days, F+ sheep had greater rate of wool production, liveweight gain, and had greater eye-muscle and fat depth than F– sheep (P < 0.05). Fractional synthesis rates of protein (%/day) in the epidermis, dermis, whole skin and muscle were affected by both feeding level (P < 0.05) and genotype (P < 0.05). The fractional synthesis rates of protein were greater (P < 0.05) in F+ sheep at both levels of intake. There was an interaction (P < 0.01) between genotype and feeding level for the protein fractional synthesis rate in muscle, where F+ sheep were more responsive to higher feed intake. Muscle of F– sheep responded to increased amino acid supply by reducing the rate of protein degradation without altering synthesis rate; whereas muscle of F+ sheep responded by increasing the rates of both protein synthesis and degradation. The overall muscle fractional synthesis rate (1.6%/day) was ~7-times lower than the skin fractional synthesis rate (10.8%/day) in these animals (P < 0.01). F+ sheep had a higher rate of protein synthesis in dermis and whole skin to support their higher wool protein accretion at both levels of feed intake. Muscle protein synthesis rate was greater in F+ sheep offered above-maintenance metabolisable energy (ME) intake than those given below-maintenance ME intake but was unaffected by ME intake in F– sheep. The results indicate that selection for wool growth not only affects production of wool and the wool follicle, but also affects the rate of protein turnover in components of the skin and skeletal muscle.

Protein metabolism in skin and muscle of sheep selected for or against staple strength

2000 ◽  
Vol 51 (5) ◽  
pp. 541 ◽  
Author(s):  
N. R. Adams ◽  
S. M. Liu ◽  
J. R. Briegel ◽  
J. C. Greeff
Keyword(s):  
Growth Rate ◽  
Protein Synthesis ◽  
Synthesis Rate ◽  
Deuterated Water ◽  
Feeding Level ◽  
Fractional Rate ◽  
Wool Growth ◽  
Fractional Synthesis ◽  
Selection For ◽  
Staple Strength

Two experiments were carried out to determine the mechanisms underlying the reduced effect of nutritional status on wool growth rate in Merino sheep that have been selected for high staple strength (SS). In Expt 1, each group of 6 young sheep of SS+ and SS– genotypes were fed at 0.4 or 1.1 times maintenance, and in Expt 2, groups of 8 sheep of each genotype were fed at 1.1 and 1.8 times maintenance. In both experiments, rates of protein synthesis in skin, muscle, gut, rumen, and liver were determined using a flooding dose of labelled phenylalanine. Feed intake and the digestibility of feed were not affected by genotype. Neither dissection of the carcasses at slaughter, nor deuterated water analysis in Expt 1, detected any differences between the genotypes in body composition. The feeding level affected the total daily amount of protein synthesised in all the organs examined, and the fractional rate of protein synthesis was affected by feeding level in all organs except the liver. The fractional synthesis rate of protein was less responsive to feeding level in the SS+ sheep in both skin and muscle (P < 0.05), but not in the liver, jejunum, or rumen. Total protein synthesis in muscle, and the estimated rate of protein degradation, were also less responsive to feeding level in the SS+ sheep (P < 0.05). We conclude that sheep genetically selected for high or low SS have altered local mechanisms in both skin and muscle that control the way they respond to nutrition. These findings provide a mechanism by which selection for wool growth rate also affects body metabolism.

The effect of selection for fleece weight upon urea metabolism and digestive function in Romney sheep

1989 ◽  
Vol 40 (5) ◽  
pp. 1065 ◽  
Author(s):  
BC Thompson ◽  
DW Dellow ◽  
TN Barry
Keyword(s):  
Creatinine Clearance ◽  
Clearance Rate ◽  
Genetic Selection ◽  
Plasma Urea ◽  
Voluntary Feed Intake ◽  
Outflow Rate ◽  
Urea Metabolism ◽  
Selection For ◽  
Fleece Weight ◽  
Plasma Urea Concentration

The effect of 30 years genetic selection for greasy fleece weight upon rumen metabolism, apparent digestibility and nitrogen metabolism was investigated in Romney sheep.Fleece weight (Fwt) animals had a 1 mM lower plasma urea concentration than control (C) animals when fed on both diets given, but there was no difference in plasma urea IRL, urinary urea excretion or urea recycling to the digestive tract between the Fwt and C sheep when fed either diet. Relative to the C shccp, the Fwt animals had a higher creatinine clearance rate when fed the meadow hay diet, and a higher urea clearance rate when fed both diets.When fed the meadow hay diet there were no differences between the Fwt and C animals in voluntary feed intake (VFI) or apparent DM digestibility. However, when fed on the lucerne chaff diet the Fwt animals had a higher VFI than the C animals and a lower apparent DM digestibility. These changes were associated with an increase in the rumen fractional outflow rate (FOR) of lignin in the Fwt sheep, and a higher molar proportion of acetate and a lower proportion of propionate in rumen fluid.The differences in urea and creatinine clearance rates suggest that selection for fleece production may have altered kidney function, with expression of this and rumen FOR being related to nutritional level. A factor contributing to the superior wool production of the Fwt sheep is suggested.

Skin characteristics and skin protein composition of Merinos differing in estimated breeding values for wool growth and fed at above and below maintenance

2006 ◽  
Vol 46 (7) ◽  
pp. 937 ◽  
Author(s):  
L. Li ◽  
I. Godwin ◽  
S. M. Liu ◽  
V. H. Oddy ◽  
J. V. Nolan
Keyword(s):  
Protein Content ◽  
Fibre Diameter ◽  
Fibre Length ◽  
Skin Thickness ◽  
Feeding Level ◽  
Secondary Follicle ◽  
Wool Growth ◽  
Skin Protein ◽  
Estimated Breeding Values ◽  
True Protein

Twenty castrated male sheep were selected from a commercial flock, 10 with high estimated breeding values (EBVs) (F+) and 10 with low EBVs for wool production (F–). Five of each EBV treatment were offered feed at 0.8M [0.8 times their metabolisable energy (ME) requirement for maintenance] and the other 5 were offered feed at 1.8M for 6 weeks. On the midside area of skin, the F+ group had a greater rate of clean wool growth (g/100cm2.day) and daily growth in fibre length (mm/day) than the F– group at both feeding levels (P<0.05). Fibre diameter (FD) was finer for F+ than F– sheep at both feeding levels (P<0.001). As the feeding level increased, FD increased (P<0.001), but the ratio of fibre length growth to mean FD remained constant. The secondary follicle density in F+ sheep decreased with an increase in the feeding level (P<0.01), whereas the secondary follicle density of F– sheep remained unchanged (P>0.05). The ratio of secondary to primary follicles (S/P) was 21% higher (P<0.01) in skin from F+ sheep than in skin from F– sheep, but this difference was not related to the feeding level. Skin thickness at the midside was thinner (P<0.05) when sheep were underfed, but F+ sheep had a thicker (P<0.05) skin than F– sheep. The trephine (diameter: 1.5 cm; area: 1.766  cm2)-sampled skin weight was heavier for F+ than for F– (0.339 v. 0.294 g, P<0.05) but did not differ (P>0.05) with the level of intake. The weight of the dermis layer was greater in F+ than F– sheep (0.231 v. 0.190 g per trephine, P<0.05) and F+ sheep also tended to be more responsive to feeding level than F– sheep (interaction: P = 0.06). True protein content per 100 g wet skin did not differ between F+ and F– sheep or between feeding levels, whereas the protein content per 100 cm2 skin was significantly (P<0.05) higher in F+ sheep. The concentration of collagen in skin protein (g/100 g) was lower in F+ sheep than F– sheep at both feeding levels (P<0.05). Of the amino acids evaluated, significant differences occurred between F+ and F– sheep for the methionine (Met) concentration in plasma (P<0.05) and in the free amino acid pool in the skin (P = 0.06). The distribution ratio of skin Met concentration to plasma Met concentration was significantly lower in the F+ sheep than F– sheep (0.77 v.1.18 kg skin/ L plasma). Results presented here indicate that skin characteristics such as skin thickness, follicle density, S/P ratio, skin weight, dermis weight, true protein or collagen content were a consequence of genetics and nutritional variation in wool growth rate, fibre length and fibre diameter. Selection for high EBVs for wool growth has resulted in animals which grow more wool at the 2 levels of feed intake provided, supported by their higher S/P ratios, higher skin and protein masses, more responsive dermides and higher efficiency of Met usage in skin tissue.

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