Concentrate-fed Lambs Research Articles

Change in fat skatole and indole content in lambs switched from a concentrate-based diet indoors to alfalfa grazing for various durations before slaughter

Meat from lambs fattened on alfalfa is at risk of excessive pastoral flavours due to high levels of in-fat volatile indolic compounds (especially, skatole). Skatole has also been identified as a potential marker of interest for authenticating pasture-fed lamb meat. Here, we investigated the change in skatole and indole concentrations in kidney fat from lambs switched from an indoor-fed concentrate based diet to outdoor alfalfa grazing for various durations (0, 21, 42, 63 days) before slaughter. The study used a total of 219 lambs over 3 consecutive years. Kidney-fat skatole and indole concentrations increased from as early as 21 days on alfalfa, and then reached a plateau. Similarly, the proportion of lambs that had a kidney fat-skatole concentration above 0.15 μg/g liquid fat, a value that has been established as a sensory rejection threshold for pork, increased significantly from as early as 21 days on alfalfa and then reached a plateau. This value was reached or exceeded in a significant proportion of lambs fattened on alfalfa pastures (45.1%). However, skatole was not detected in kidney fat from 20 out of 164 alfalfa-fattened lambs (i.e., 12.2%) but was detected in 15 out of 55 concentrate-fed lambs (i.e., 27.3%). We thus conclude that while skatole content in kidney fat can inform on dietary changes made shortly before slaughter, it does not have the discrimination power needed to reliably authenticate pasture-fed lamb meat, let alone duration of finishing on pasture.

Feeding regimens affecting carcass and quality attributes of sheep and goat meat - A comprehensive review.

Sheep and goats can efficiently convert low quality forage into high-quality meat which contains specific nutrients and quality traits. Carcass traits and quality attributes of sheep and goat meat depend upon several factors and one of most effective strategies amongst these is feeding regimens. In this review, the major aspects of feeding regimens affecting growth rate, carcass traits and quality attributes of sheep and goat meat are thoroughly discussed, with a particular focus on physical-chemical composition, flavor profile, and fatty acid (FA) profile. Grazing lambs and kids receiving concentrate or under stall-feeding systems had greater average daily gain and carcass yield compared with animals reared on pasture only. However, growth rate was higher in lambs/kids grazing on pastures of improved quality. Moreover, the meat of grazing lambs receiving concentrate had more intense flavor, intramuscular fat (IMF) content, and unhealthy FA composition, but comparable color, tenderness, juiciness, and protein content compared to that of lambs grazed on grass only. In contrast, meat of concentrate-fed lambs had more intense color, greater tenderness and juiciness, IMF and protein contents, and lower flavor linked to meat. Additionally, the meat of kids grazed on concentrate supplementation had higher color coordinates, tenderness, IMF content and unhealthy FA composition, whereas juiciness and flavor protein content were similar. In contrast, kids with concentrate supplementation had superior color coordinates, juiciness, IMF content and unhealthy FA composition, but lower tenderness and flavor intensity compared to pasture-grazed kids. Thus, indoor-finished or supplemented grazing sheep/goats had higher growth rate and carcass quality, higher IMF content and unhealthy FA composition compared to animals grazed on grass only. Finally, supplementation with concentrate increased flavor intensity in lamb meat, and improved color and tenderness in kid meat, whereas indoor-fed sheep/goats had improved color and juiciness as well as reduced flavor compared to pasture-grazed animals.

Gene Expression and Fatty Acid Profiling in Longissimus thoracis Muscle, Subcutaneous Fat, and Liver of Light Lambs in Response to Concentrate or Alfalfa Grazing.

A better understanding of gene expression and metabolic pathways in response to a feeding system is critical for identifying key physiological processes and genes associated with polyunsaturated fatty acid (PUFA) content in lamb meat. The main objective of this study was to investigate transcriptional changes in L. thoracis (LT) muscle, liver, and subcutaneous fat (SF) of lambs that grazed alfalfa (ALF) and concentrate-fed (CON) slaughtered at 23 kg and using the Affymetrix Ovine Gene 1.1 ST whole-genome array. The study also evaluated the relationship between meat traits in LT muscle, including color, pigments and lipid oxidation during 7 days of display, α-tocopherol content, intramuscular fat (IMF) content and the fatty acid (FA) profile. Lambs that grazed on alfalfa had a greater α-tocopherol concentration in plasma than CON lambs (P < 0.05). The treatment did not affect the IMF content, meat color or pigments (P > 0.05). Grazing increased the α-tocopherol content (P < 0.001) and decreased lipid oxidation on day 7 of display (P < 0.05) in LT muscle. The ALF group contained a greater amount of conjugated linoleic acid (CLA), C18:3 n−3, C20:5 n−3, C22:5 n−3, and C22:6 n−3 than did the CON group (P < 0.05). We identified 41, 96 and four genes differentially expressed in LT muscle, liver, and subcutaneous fat, respectively. The most enriched biological processes in LT muscle were skeletal muscle tissue development, being the genes related to catabolic and lipid processes downregulated, except for CPT1B, which was upregulated in the ALF lambs. Animals grazing alfalfa had lower expression of desaturase enzymes in the liver (FADS1 and FADS2), which regulate unsaturation of fatty acids and are directly involved in the metabolism of n−3 PUFA series. The results found in the current study showed that ingesting diets richer in n−3 PUFA might have negative effects on the de novo synthesis of n−3 PUFA by downregulating the FADS1 and FADS2 expression. However, feeding diets poorer in n−3 PUFA can promote fatty acid desaturation, which makes these two genes attractive candidates for altering the content of PUFAs in meat.

Nitrogen stable isotope and carotenoid pigments signatures in the meat as tools to trace back the diet: Comparison between two sheep breeds

We compared the response of two dietary biomarkers (nitrogen stable isotope and carotenoid pigments signatures in lamb meat) in two sheep breeds when fed two dietary lucerne levels, and we deduct subsequent implications for diet authentication issues. Two breeds (Limousine and Romane) and two daily dietary lucerne levels (H: High, 500g;L: Low, 0g) were used for 60days pre-slaughter. Treatment H comprised 35 lambs of each breed, individually penned and fed. Treatment L comprised 8 lambs of each breed, fed in groups. The δ15N value of the muscle did not differ between breeds and gave a correct classification score of 92.9% comparing lambs from both feeding treatments. The absolute value of the mean integral of perirenal fat reflectance spectrum, which quantifies light absorption by carotenoid pigments present in perirenal fat, and plasma carotenoid content were similar in L Romane and L Limousine lambs, but were higher in H Romane lambs than in H Limousine lambs As the carotenoid pigments are highly involved in the discrimination process between pasture-fed lambs and concentrate-fed lambs using visible spectroscopy on the fat, further work is required to test the extent to which this between-breed variability may modulate the reliability of pasture-feeding authentication using visible spectroscopy of the fat over a range of breeds.

The effect of feeding system on slaughter-carcass characteristics, meat quality, and fatty acid composition of lambs

Abstract. In this study, we aimed to determine the slaughter-carcass characteristics, meat quality, and fatty acid composition in lambs raised under intensive and extensive conditions. The animal material consisted of 30 Norduz male lambs, with an average age of 171 days. The lambs were divided into two groups: concentrate-fed lambs (CO) and pasture-fed lambs (PS). The results showed that the CO lambs had heavier carcasses (p&lt; 0.001), a higher dressing percentage (p&lt; 0.001), and higher intramuscular fat (p&lt; 0.01) than the PS lambs. It was determined that the longissimus thoracis muscle of the CO lambs had a lower ultimate pH and higher L* and water-holding capacity than the PS lambs. In this study, intramuscular fat (longissimus thoracis, semimembranosus, triceps brachii), subcutaneous and tail fat samples were used to evaluate the effect of feeding system on fatty acid composition. The polyunsaturated fatty acid to saturated fatty acid ratio (PUFA ∕ SFA) of intramuscular fat was found to be significantly higher in the CO group than in the PS lambs, while similar subcutaneous and tail fat results were found in both groups. Moreover, the PS lambs had a lower n6 ∕ n3 ratio and higher percentage of omega-3 than the CO lambs in all tissues studied (p&lt; 0.05). Overall, the CO lambs have heavier and fattier carcasses with better meat quality traits than the PS lambs. However, the effects of feeding system have varying results based on the fatty acid composition of different types of fat deposits.

Comparison of visible and near infrared reflectance spectroscopy on fat to authenticate dietary history of lambs

Since consumers are showing increased interest in the origin and method of production of their food, it is important to be able to authenticate dietary history of animals by rapid and robust methods used in the ruminant products. Promising breakthroughs have been made in the use of spectroscopic methods on fat to discriminate pasture-fed and concentrate-fed lambs. However, questions remained on their discriminatory ability in more complex feeding conditions, such as concentrate-finishing after pasture-feeding. We compared the ability of visible reflectance spectroscopy (Vis RS, wavelength range: 400 to 700 nm) with that of visible-near-infrared reflectance spectroscopy (Vis-NIR RS, wavelength range: 400 to 2500 nm) to differentiate between carcasses of lambs reared with three feeding regimes, using partial least square discriminant analysis (PLS-DA) as a classification method. The sample set comprised perirenal fat of Romane male lambs fattened at pasture (P, n=69), stall-fattened indoors on commercial concentrate and straw (S, n=55) and finished indoors with concentrate and straw for 28 days after pasture-feeding (PS, n=65). The overall correct classification rate was better for Vis-NIR RS than for Vis RS (99.0% v. 95.1%, P<0.05). Vis-NIR RS allowed a correct classification rate of 98.6%, 100.0% and 98.5% for P, S and PS lambs, respectively, whereas Vis RS allowed a correct classification rate of 98.6%, 94.5% and 92.3% for P, S and PS lambs, respectively. This study suggests the likely implication of molecules absorbing light in the non-visible part of the Vis-NIR spectra (possibly fatty acids), together with carotenoid and haem pigments, in the discrimination of the three feeding regimes.

Rumen fermentation and histology in light lambs as affected by forage supply and lactation length

This study determined whether the rumen fermentation and histology traits may reflect the feeding strategy in light lambs (22–24kg). Thirty-two single Rasa Aragonesa lambs were assigned to one of four treatments in a 2×2 factorial design. The factors were the inclusion of forage in the diet (alfalfa grazing vs. concentrate-fed indoors) and lactation length (weaning at 13kg vs. suckling until slaughter). A multivariate canonical analysis discriminated individuals among feeding strategies. The main function differentiated weaned concentrate-fed lambs from the rest according to dorsal sac papillae height, ventral sac muscular layer thickness and the proportion of rumen valerate. The second function differentiated suckling concentrate-fed lambs from the rest according to plasma urea levels. Lactation length played an important role on rumen histology and protein utilization, especially in concentrate-fed lambs. Alfalfa grazing light lambs had similar rumen morphometric measures and fermentation characteristics, regardless of milk access.

Do alfalfa grazing and lactation length affect the digestive tract fill of light lambs?

This experiment tested the hypothesis that alfalfa-raised light lambs suckling their mothers until slaughter (22–24 kg) and having concentrate ad libitum may consume forage to achieve a similar performance to their weaned concentrate-fed counterparts. Thirty-two single Rasa Aragonesa lambs were assigned to one of four treatments in a 2 × 2 factorial design. The factors were the inclusion of forage in the diet (alfalfa grazing vs. concentrate-fed indoors) and lactation length (weaning at a target body-weight (BW) of 13 kg vs. suckling until slaughter). After slaughter, the digestive contents of each gastrointestinal compartment were weighed individually and the pH of the rumen and caecum contents was recorded. Samples of the reticulo-rumen, caecum and colon-rectum contents were collected for neutral-detergent fibre (NDF), acid-detergent fibre (ADF) and lignin analysis. The empty BW was not affected by forage inclusion or suckling ( P > 0.05). The fresh reticulo-rumen and whole digestive tract contents (liquids + solids) were greater in weaned alfalfa-fed than in suckling alfalfa-fed lambs ( P < 0.05), but they were similar in concentrate-fed lambs ( P > 0.05). On a dry matter (DM) basis, these digestive contents did not differ between alfalfa and concentrate-fed lambs ( P > 0.05), but they were greater in weaned than in suckling lambs ( P < 0.01). Weaned alfalfa-fed lambs had greater ruminal and caecal pH values than the rest of treatments ( P < 0.05). The reticulo-rumen NDF content was greater in weaned alfalfa-fed than in suckling alfalfa-fed lambs ( P < 0.05), while it was similar in concentrate-fed lambs ( P > 0.05). The lowest reticulo-rumen ADF and lignin contents were observed in both groups of concentrate-fed lambs ( P < 0.05). The caecum and colon-rectum NDF contents did not differ among treatments ( P > 0.05). The caecum and colon-rectum ADF contents were greater in alfalfa-fed than in concentrate-fed lambs ( P < 0.05). According to digesta composition, weaned lambs raised on alfalfa consumed more forage than suckling lambs on these swards. Lactation length rather than forage supply was a major effect on the digestive tract fill capacity of light lambs.

Metabolic fate of fatty acids involved in ruminal biohydrogenation in sheep fed concentrate or herbage with or without tannins1

A 2 x 2 factorial experiment was carried out to evaluate the effect of herbage or concentrate feeding and dietary tannin supplementation on fatty acid metabolism and composition in sheep ruminal fluid, plasma, and intramuscular fat. Twenty-eight male lambs were divided into 2 equal groups at 45 d of age and kept in individual pens. One group was given exclusively fresh herbage (vetch), and the other group was fed a concentrate-based diet. Within each treatment, one-half of the lambs received supplementation of quebracho powder, providing 4.0% of dietary DM as tannins. Before slaughter, blood samples were collected. The animals were slaughtered at 105 d of age, and ruminal contents and LM were collected. Blood plasma, ruminal fluid, and LM fatty acid composition was determined by gas chromatography. Tannin supplementation reduced (P < 0.05) the concentration of stearic acid (-49%) and increased the concentration of vaccenic acid (+97%) in ruminal fluid from concentrate-fed lambs. Within concentrate- and herbage-based diets, tannin supplementation reduced the accumulation of SFA in blood (P < 0.05) compared with lambs fed the tannin-free diets. When tannins were included in the concentrate, the LM contained 2-fold greater concentrations of rumenic acid compared with the LM of the lambs fed the tannin-free concentrate (0.96 vs. 0.46% of total extracted fatty acids, respectively; P < 0.05). The concentration of PUFA was greater (P < 0.05) and SFA (P < 0.01) less in the LM from lambs fed the tannin-containing diets as compared with the animals receiving the tannin-free diets. These results confirm, in vivo, that tannins reduce ruminal biohydrogenation, as previously reported in vitro. This implies that tannin supplementation could be a useful strategy to increase the rumenic acid and PUFA content and to reduce the SFA in ruminant meats. However, the correct dietary concentration of tannins should be carefully chosen to avoid negative effects on DMI and animal performance.

Effects of feeding system on carcass and non-carcass composition of Churra Tensina light lambs

Thirty-eight single male lambs (3.6 ± 0.08 kg live weight at birth) were used to study the influence of feeding system on carcass and non-carcass composition of Churra Tensina light lambs. Treatments: indoor (IND), lambs housed indoors consuming concentrate ad libitum until weaning at 53 days of age, and ewes grazing 8 h a day without their offspring and receiving a supplement of barley meal after grazing; grazing (GR), ewes and lambs grazed continuously without concentrate and lambs were unweaned. When lambs reached 22–24 kg live weight they were slaughtered. Carcass and non-carcass composition was recorded. GR lambs displayed higher carcass shrink ( P < 0.05) and lower dressing percentage ( P < 0.01) than concentrate-fed lambs. IND lambs had more body fat mainly due to the heavier kidney ( P < 0.001) and subcutaneous ( P < 0.001) fat depots. Total non-carcass weight was not affected by treatment ( P > 0.05), but red organ (heart, lung and trachea, thymus, liver, spleen, kidney, diaphragm, pancreas, gall bladder, bladder, and testicles and penis), digestive tract (stomach, small intestine and large intestine) and head, skin, and feet (HSF) weights differed between treatments ( P < 0.05). IND lambs had heavier red organs and HSF ( P < 0.05) although this difference disappeared when expressed as a percentage of empty body weight. Small intestine weight in grazing lambs was heavier ( P < 0.001) and, consequently, the total digestive tract differed similarly ( P < 0.01). Treatment influenced the weights ( P < 0.05) of all joints except leg ( P > 0.05), showing heavier joints for IND carcasses. The feeding system had a greater effect on subcutaneous fat ( P < 0.001) than on intermuscular fat ( P < 0.05) in most of the standardized joints. IND carcasses produced a greater proportion of muscle/bone in all joints, except neck, whereas GR produced a greater proportion of muscle/total fat due to the lower amount of fat recorded in this treatment. The percentage of fatty acids was not affected by treatment ( P > 0.05) although the percentage of C18:3 was greater and the ratio of C18:2/C18:3 was lower in grazing-fed lambs. The absence of any effect of treatment on the fatty acid percentages may be influenced by the short raising period and by the similar amount of intramuscular fat in both treatments. It is concluded that light lambs reared under grazing conditions can produce carcasses of acceptable quality, due to the lower percentage of subcutaneous fat, but with a similar intramuscular fat content.

Effect of grass vs. concentrate feeding on the fatty acid profile of different fat depots in lambs

The aim of this study was to produce high-quality meat from lambs under different feeding conditions, as measured by the accumulation of n-3 fatty acids and conjugated linoleic acids (CLA) in muscle and subcutaneous fat. In total, 13 male crossbred lambs (Black Head x Gotland), each at 24 kg live weight, were divided into two feeding groups. Lambs were kept either on pasture (pasture grazing, n = 6) or in the stable (concentrate feeding, n = 7). The linolenic acid (C18:3n-3) contained in the grass was absorbed and deposited into the different lipid classes of muscle and subcutaneous fat. The proportion of total n-3 fatty acids in the different lipids of grazing lambs was significantly (p = 0.05) higher compared to that in concentrate-fed lambs. The n-6/n-3 ratio (mean ± SEM) in muscle of grazing lambs was 1.2 ± 0.09 in contrast to 2.3 ± 0.09 (p = 0.05) of the animals kept in the stable. In subcutaneous fat, this ratio was 0.9 ± 0.2 in lambs kept on pasture versus 3.5 ± 0.2 (p = 0.05) after indoor keeping. The relative concentration of C18:1trans-11 in total muscle lipids, phospholipids, triacylglycerols and subcutaneous fat was significantly increased by grass feeding compared to concentrate feeding. Significant influences of feeding were shown for saturated fatty acids. In concentrate-fed lambs, a lower content of saturated fatty acids was detected. The proportion of CLAcis-9,trans-11 (1.9 ± 0.2% vs. 1.1 ± 0.1% in muscle, 2.5 ± 0.2% vs. 1.4 ± 0.2% in subcutaneous fat, 0.7 ± 0.04% vs. 0.4 ± 0.04% in phospholipids) in lambs was significantly (p = 0.05) higher after grazing than after concentrate feeding, respectively.

Characteristics of lambs fed concentrates or grazed on ryegrass to traditional or heavy slaughter weights. II. Wholesale cuts and tissue accretion1

Targhee x Hampshire lambs (average BW 24 +/- 1 kg) were used to determine the effect of finishing on concentrate or by grazing ryegrass forage on slaughter weights of 52 kg (N) or 77 kg (H) on tissue accretion and lamb wholesale cutout. When fed to similar slaughter weights, the wholesale cuts of concentrate-fed lambs were heavier (P < 0.05) than the same cuts from forage-fed lambs; however, when expressed as a percentage of side weight, carcasses of forage-fed lambs had a higher (P < 0.001) percentage of leg than concentrate-fed lambs. Increasing slaughter weight from 52 to 77 kg resulted in a 1-kg increase in loin weight for lambs finished on concentrate and a 0.60-kg increase for lambs finished on forage (diet x slaughter weight, P < 0.03); however, the increased loin weight for lambs finished on concentrate was due largely to increased fat deposition. For lambs slaughtered at 77 kg, those finished on forage had more lean mass in the leg, loin, rack, and shoulder than those finished on concentrate, but lean mass in these cuts did not differ between diets for lambs slaughtered at 52 kg (diet x slaughter weight, P < 0.01). At the normal slaughter weight (52 kg), concentrate-fed lambs had 50% more dissectible fat than forage-fed lambs, whereas at the heavy slaughter weight, a 79% greater amount of dissectible fat was observed for concentrate- vs. forage-fed lambs (diet x slaughter weight, P < 0.001). Lean and fat accretion rates were higher (P < 0.001) for concentrate-fed lambs than for forage-fed lambs. The lean-to-fat ratio of forage-fed lambs was higher (P < 0.001) than that of concentrate-fed lambs; however, forage finishing decreased accretion rates of all tissues compared with concentrate feeding, and these differences between forage and concentrate feeding were magnified at heavier slaughter weights.

Analysis of the volatile fraction of lamb fat tissue: influence of the type of feeding

The volatile compounds of subcutaneous fat tissue of lambs were analysed by dynamic headspace sampling-high resolution gas chromatography-mass spectrometry (DHS-HRGC-MS). The animals were produced in six European countries according to local traditional rearing conditions and they were classified into two groups according to the predominant type of feed consumed (pasture or concentrate). The analysis showed that the pasture-fed lambs clearly differed from the concentrate-fed lambs. Fat samples from the pasture-fed lambs desorbed greater quantities of compounds of green leaf tissue origin such as long-chain alkanes, C7 aldehydes and 2,3-octanedione. The fat samples from the concentrate-fed lambs desorbed greater quantities of short-branched and non-branched acids and methyl ketones. The present results suggest that 2,3-octanedione or long-chain alkanes, and 4-heptanone or 2-octanone in the lamb subcutaneous fat tissue are specific of feedings consisting predominantly of pasture and concentrate, respectively. These compounds could be used as markers of the feeding background of the animal.

Effect of dietary sodium bicarbonate supplementation on fermentation characteristics and ciliate protozoal population in rumen of lambs

Effects of sodium bicarbonate (NaHCO 3) inclusion on rumen fermentation characteristics and ciliate protozoal population in high concentrate-fed lambs were studied. Twenty-four weaner (90 days old) Malpura lambs divided into four equal groups (G1, G2, G3 and G4) were fed basal (25:75 roughage and concentrate) diet (G1) or basal diet supplemented with 0.75% (G2), 1.50% (G3) and 2.25% (G4) sodium bicarbonate for 90 days. Daily dry matter (DM) intake and digestibility of organic matter (OM), crude protein (CP), gross energy and plane of nutrition were similar in all the groups while cellulose digestibility was higher in G4 than in G2 and G1. Ruminal pH increased ( P<0.05) with increasing levels of dietary sodium bicarbonate. Concentrations of total volatile fatty acids (TVFA), total nitrogen and trichloroacetic acid-precipitable nitrogen (TCA-ppt.-N) were higher while ammonia nitrogen was lower in the rumen fluid of G4 and G3 than in G2 and G1. The number of total protozoa, Isotricha, Dasytricha, large and small spirotrichs were higher ( P<0.01) in the rumen of G4 and G3 than in G2 and G1. Total live weight gain and average daily gain were also higher in lambs supplemented with sodium bicarbonate. It is concluded that sodium bicarbonate inclusion at the rate of 1.50% of total ration increased cellulose digestibility, ciliate protozoal number, ruminal pH and total nitrogen concentration resulting in improved growth of lambs maintained on high concentrate diet.

Quality of Italian Istrian Milk lamb meat. Influence of carcass weight and feeding system

The Istrian Milk sheep is an endangered breed of the Pramenka group raised in the North-Adriatic Karst region. Carcass and meat characteristics of 46 suckling, 6- to 14- week-old intact male light lambs from two feeding systems were analysed. Thirty-two lambs were raised in a flock fed only with forage (hay supplied in stall during winter or fresh herbage directly grazed during the other seasons). The lambs had free access to the forage supplied to their dams (feeding system: milk and forage; MF). The other fourteen suckling ovine were grown on a farm with a feeding system incorporating a concentrated supply of the forage base. The lambs were stabled and creep fed on a concentrate (20% CP) at a daily rate of 100 g/head, in addition to the suckled milk (feeding system: milk and concentrate; MC). The carcasses were divided into three categories of weight, following the Community scale of light lambs classification: A (≤7 kg, n=17), B (7.1 - 10 kg, n=15) and C (10.1 - 13 kg, n=14). The frequency of 1st quality carcasses increased with carcass weight, reaching 100% in category C. On average, 72% of the carcasses were scored as 1st quality, without significant differences between feeding systems. The lightness of lamb meat from A carcasses was higher than that from the heaviest ones. Cooking losses showed a pattern opposite to that of pH (mean 5.44; SE 0.058), increasing where pH decreased (categories A and B and concentrate-fed lambs). Shear force values were significantly affected by factors linked to the feeding system; in fact, MC lambs provided more tender meat than MF ones (32.6 vs 46.6 N). As carcass weight increased, moisture concentration decreased steadily (from 77.8% to 75.5%), while lipid content increased progressively (from 1.58% to 3.14%). In agreement with these patterns, the contribution of individual fatty acids (FA) to muscle weight generally increased with carcass weight. A similar trend was observed for the relative concentration of saturated FA and monounsaturated FA, while that of polyunsaturated FA (PUFA) showed an opposite evolution. The feeding system modified the relationship between ω3 and ω6 PUFA series: with respect to MC meat, MF meat presented a higher content of linolenic acid and its long chain ω3 derivatives and a lower content of linoleic acid and its major product, arachidonic acid. As a consequence, MF lambs furnished meat with a ω3/ω6 ratio and an index of thrombogenicity more favourable for human health than those from MC lambs.

Alpha-tocopherol concentrations and case life of lamb muscle as influenced by concentrate or pasture finishing

Two experiments were conducted to evaluate alpha-tocopherol accumulation in muscle of lambs finished on pasture or concentrates. The objective for Exp. 1 was to compare accumulation of alpha-tocopherol in the longissimus muscle of pasture-fed lambs to that of lambs fed three concentrations (15, 150, and 300 IU/kg of DM) of supplemental vitamin E (all rac alpha-tocopheryl acetate) in all-concentrate diets. The objective in Exp. 2 was to investigate the effect of duration of supplemental vitamin E feeding on alpha-tocopherol content and color change during display case storage of lamb muscle. Treatments evaluated in Exp. 2 were: 15 IU of supplemental vitamin E/kg DM fed to finish; 15 IU/kg followed by 300 IU/kg of DM during the last 21 d; and 15 IU/kg DM until 7 d prior to finish, then 300 IU/kg DM. In Exp. 1, alpha-tocopherol concentration of rotational grazed alfalfa and perennial ryegrass averaged 137 and 169 mg/kg of DM. Vitamin E treatments for lambs fed concentrate diets did not affect ADG (P > 0.15), but ADG was greater (P < 0.01) for concentrate-fed lambs than for grazing lambs. For the concentrate-fed lambs, alpha-tocopherol in longissimus muscle increased quadratically (P < 0.05) as dietary concentrations of vitamin E increased. Predicted maximum alpha-tocopherol concentration in muscle occurred at about 400 IU/kg of diet DM. Longissimus muscle from lambs grazing alfalfa or ryegrass had similar (P > 0.50) alpha-tocopherol concentrations, and those concentrations were similar to values obtained when the concentrate diet supplemented with 150 IU of vitamin E/kg was fed. In Exp. 2, no differences (P > 0.10) in ADG were observed. Concentrations of longissimus alpha-tocopherol were highest when 300 IU supplemental vitamin E was fed for 21 d prior to slaughter. During a 6-d display period, semimembranosus steaks from lambs fed 300 IU of supplemental vitamin E/kg for either 7 or 21 d had higher a* and b* color readings than steaks from lambs fed 15 IU/kg of supplemental vitamin E. Increased consumption of vitamin E either via pasture or supplementation results in higher alpha-tocopherol concentrations in meat.

Mineral retentions and body composition of grazing lambs

ABSTRACTGrowth rates and chemical compositions were measured with ram lambs grazing pure stands of perennial ryegrass, timothy, cocksfoot and tall fescue. A group of lambs slaughtered at the start of the trial enabled estimates to be made of the live-weight gains over the summer and the composition of these gains. The composition of the grass was also measured in samples taken at weekly intervals and estimates were made of the nutrients consumed from the different grass plots.The quantities of ash, Ca, P and Mg in the empty bodies of the lambs were within the range of published values from similar studies. They support the contention that grass-fed lambs tend to have larger contents of ash, Ca and P in their empty bodies than concentrate-fed lambs of similar weight. Perennial ryegrass provided a superior diet in that lambs eating this grass grew more quickly, with leaner tissues and higher levels of ash, Ca and P in their empty-body gains. Lambs consuming tall fescue grew most slowly but their mineral contents were as large as the ryegrass-fed lambs when data were adjusted for differences in empty-body weight. Lambs fed on timothy or cocksfoot were the most poorly mineralized in spite of consuming considerably more Ca, P and Mg than the lambs on ryegrass. The data suggest that the efficiencies of absorption of Ca and P in ryegrass may be high, at about 0·64 for Ca and 0·71 for P.

THE GROWTH PERFORMANCE AND CARCASS COMPOSITION OF RAM AND EWE LAMBS FED ON PASTURE OR IN CONFINEMENT AND SLAUGHTERED AT SIMILAR FATNESS

Forty-nine crossbred ram lambs and 62 crossbred ewe lambs were allotted at weaning (average weight 30.6 kg) to pasture (P) or concentrate (C) feeding. The number of lambs per treatment was as follows: rams, 24 P fed and 25 C fed; ewes, 31 P fed and 31 C fed. The lambs were slaughtered after 56, 72, 100 and 121 days on feed. Offal components were weighed, and the alimentary tract was emptied of digesta. One side of each carcass was broken into four cuts (leg, loin, rib, shoulder) which were further separated into fat, muscle and bone. C-fed lambs were 4.0% heavier live than P-fed lambs (P &lt; 0.05) and ram lambs were 9.0% heavier live than ewe lambs (P &lt; 0.05) when evaluated at a constant depth of subcutaneous fat (4.5 mm). However, P-fed lambs required an extra 21 days (P &lt; 0.05) to reach the same fat depth as C-fed lambs. C-fed lambs had greater rib eye areas than P-fed lambs, but carcasses from all treatments had similar proportions of dissected muscle, bone and fat when evaluated at a constant proportion of subcutaneous fat. P-fed lambs had a greater proportion of their empty bodies as head and reticulo-rumen, and a lower proportion as liver and large intestine than C-fed lambs. Ram lambs had a greater proportion of their empty bodies as head, and a lower proportion as caul fat, mesenteric fat, omasum and small intestine than ewe lambs. Distribution of muscle and bone among each of the four meat cuts which were evaluated was similar for all carcasses. Sex and feeding system had only a minor effect on the distribution of the fat depots. In this study, lambs fed on pasture required 21 days longer on feed to reach the same external fatness as concentrate-fed lambs, but produced carcasses of similar composition at slightly lighter liveweights (45.3 vs. 47.1 kg). Ram and ewe lambs spent a similar time on feed to reach a similar finish, but rams were heavier live than ewes (48.2 vs. 44.2 kg). Key words: Lambs, carcass composition, offal, constant fatness