Wether Lambs Research Articles

Comparison of different magnesium sources on lamb muscle quality

Wether lambs ( n=20) were used to compare the effect of dietary magnesium oxide (MgO), unweathered Magnesium Mica® (UMM) and weathered Magnesium Mica® (WMM) on muscle quality. Lambs were fed a corn-based, control diet (Ctrl), or the Ctrl supplemented with either MgO, UMM, or WMM for 95 days before harvest. Following a 24-h chill, carcasses were fabricated, and L*, a* and b* values were determined on the triceps brachii (TB), longissimus thoracis (LT), semimembranosus (SM), and semitendinosus (ST) muscles. Supplemental magnesium had no ( P > 0.10) effect on live and carcass weights, fat thickness, loin eye area, and USDA yield grade. Carcasses from lambs supplemented with MgO had higher ( P < 0.10) flank streaking scores and USDA quality grades than those from lambs fed diets containing UMM. Although magnesium-supplementation had no ( P > 0.10) effect on marbling scores, the LT from Ctrl-fed lambs had more ( P < 0.05) intramuscular lipid than lambs fed diets containing UMM or WMM. Lambs supplemented with UMM had greater ( P < 0.05) LT shear force values than lambs fed MgO or WMM. Magnesium-supplementation had no ( P > 0.10) effect on muscle color; however, supplementing finishing diets with UMM may result in less palatable lamb.

The effect of restricted feeding on growth hormone (GH) secretory patterns in genetically lean and fat wether lambs

AbstractThe aim of this work was to determine whether developmental changes in growth hormone (GH) secretory patterns and carcass composition were influenced by nutrition and genotype in sheep. Four-month-old wether lambs from lean (low backfat), fat (high backfat) and control selection lines were nutritionally restricted to maintain a 28 kg live weight or given food ad libitum for 24 weeks. Plasma concentrations of GH and insulin-like growth factor 1 (IGF-1) were measured at predetermined times and carcass composition of the animals determined at the end of the trial.From week 3 on, restrictions in dry matter (DM) intake were observed as the ad libitum treatment group had a significantly greater intake than the restricted treatment group (7·70 v. 5·80 kg DM per week, s.e.d. = 0·81). Differences in live weight between the feeding treatments were significant (P &lt; 0·05) at week 9. The restricted feeding regime was associated with significant reductions in plasma levels of IGF-1 but had no effect (P &gt; 0·05) on carcass weight-adjusted carcass fat proportion at the close of the trial. The effect of food restriction on GH secretory patterns was variable. Although there was initially a suppression in mean plasma GH, there was subsequently significantly higher mean plasma GH in the restricted feeding treatment. Periodogram analysis indicated that both the absolute levels of GH and the GH secretory pattern were altered by restricted feeding. In all animals, mean and basal GH concentrations, as well as the frequency and amplitude of pulses, declined from February to March and then increased from May to July (P &lt; 0·001).DM intake and live weight did not differ (P &gt; 0·05) between genotypes, however the fat genotype had greater carcass fatness than lean or control genotypes (P &lt; 0·01). There were no consistent differences between genotypes in plasma IGF-1 concentrations. In the ad libitum treatment, the lean and control genotypes had higher plasma GH levels than the f at genotype but the pattern of GH release did not vary. Under restricted feeding, both the pattern and the level of plasma GH varied between genotypes.It is concluded that the developmental change in GH secretory patterns is affected by nutrition but not in a consistent manner. Although restricted feeding resulted in higher mean plasma GH concentrations later in the trial, this did not result in a change in carcass composition. The biological cues which lead to increased fat deposition in older lambs need further study but plasma GH levels may not he an important mechanism in this process.

A comparison of the effects on voluntary intake by sheep of either dietary or intra-ruminal addition of silage juices

AbstractTwo silages were made from a regrowth of perennial ryegr ass following a 24-h wilt using either 2·5 l/t (LF) or 5·5 l/t (HF) of Add Safe (an aqueous solution of ammonium tetraformate, Trouw Nutrition, Cheshire, UK). Composition of silages LF and HF respectively were for dry matter (DM, g/kg) 205, 217; crude protein (g/kg DM) 106, 104; digestible organic matter (g/kg DM) 665, 692, pH 3·8, 3·9; lactic acid (g/kg DM) 103, 84; neutralizing value (meq/kg DM) 1051, 892; acetic acid (g/kg DM) 18·4, 14·0. Experiment A measured the intakes of the two silages using 12 Scottish Blackface wether lambs (mean live weight 25 kg) using a cross-over design with periods of 21 days. Intakes (g DM per day) were significantly greater (P &lt; 0·05) for silage HF (329) than for LF (268). Experiment B measured the voluntary intakes of dried silage residues following juice extraction using the same protocol as for experiment A, except that only six lambs were used. There were no significant differences in composition or intake (P &gt; 0·05) of the dried residues from the two silages. Experiment C used a 5 × 5 Latin-square design to measure the effects on voluntary intake of adding juices from the two silages to unmolassed sugar-beet nuts (SBN) pre-feeding or administered directly into the rumen in two discrete doses per day. Sheep on treatments LED and HFD received juices added to SBN (1·5 l/kg) and water added into the rumen in equal volume to the juice consumed with the previous day’s SBN. Treatments LFR and HFR received water added to the SBN (1·5 l/kg) and juice into the rumen in equal volume to the water consumed with the previous day’s SBN. The control treatment (W) was water added both to the SBN and into the rumen. Total mean daily intakes (g/day) were 1930,1954,1296, 2034 and 1703 (s.e.d. 179) for treatments LED, HFD, LFR, HFR and W respectively. Treatment LFR gave significantly lower mean daily intakes (P &lt; 0·05) than all other treatments. Values for pH, volatile fatty acids and ammonia in the rumen fluid were not significantly affected by treatment (P &gt; 0·05). Differences in voluntary intake for the two silages made from the same crop using different ensilage methods were attributed to differences in the silage liquid and volatile phases and not to the non-volatile solid phase. The effects of juice composition on intake were greater when added directly to the rumen than when added to the diet suggesting that effects on taste or smell were relatively unimportant.

In vivo and in vitro lipogenesis and aspects of metabolism in ovines: Effect of environmental temperature and dietary lipid supplementation

Twenty-four wether lambs were randomly allocated to six treatments to investigate the effect of temperature and dietary lipid supplements on fatty acid synthesis and metabolic activity in sheep. The treatments consisted of four groups exposed to either cold (0 °C) or warm temperature (+23 °C) and given ad libitum access to either a control barley-based diet or with lipid supplementation. Two other groups were placed on the dietary regimen at 0 °C, but pair-fed to intake of animals in the +23 °C environment. At 5 wk, fatty acid synthesis was measured by [1-14C]acetate incorporation into tissue lipids. Cold exposure and dietary lipid supplementation had no effect (P &gt; 0.05) on in vivo fatty acid synthesis rates in either longissimus dorsi or the liver. In both subcutaneous and mesenteric adipose tissue depots, the rate of acetate incorporation into tissue lipid was not significantly affected by cold exposure. In the perirenal fat depot, cold exposure increased (P &lt; 0.05) the rate of fatty acid synthesis, while lipid supplementation decreased (P &lt; 0.05) the rate in all tissue adipose depots. In vitro, mesenteric and perirenal adipose tissues from cold pair-fed animals had higher (P &lt; 0.05) rates of fatty acid synthesis compared to tissues from animals in the warm environment. However, there was no effect of dietary lipid supplementation in these two fat depots. Metabolic heat production, and energy and nitrogen excretion by animals were increased (P &lt; 0.05) by cold exposure while lipid supplementation had the opposite effect (P &lt; 0.05). The relationship between average daily gain and feed intake was linear at both warm and cold environments, but with higher (P &lt; 0.05) average daily gain at all levels of intake in the cold compared to the warm environment. Results indicate that both environment and diet regulate metabolic activity in sheep. However, there were differences in lipogenic response by tissues to the treatments. Key words: Environmental temperature, dietary lipid, fatty acid synthesis, metabolic rate, sheep

Metabolic and endocrine responses to cold and feed restriction in ruminants

Twenty-four wether lambs were assigned to different temperature and feeding levels to assess their metabolic and endocrine profiles and to test the hypothesis that energy conservation responses of sheep to feed restriction occur in warm but not cold environments. Lambs were kept in warm (W; 23 ± 2 °C) or cold (C; 0 ± 2 °C) environments and received either an ad libitum (A) or a restricted (1.35 × maintenance) (R) level of feed intake, thus creating four treatment groups (WA, WR, CA and CR). Average daily gain (ADG), feed intake, metabolic rates, rectal temperature, and plasma levels of insulin, thyroxine (T4), triiodothyronine (T3) and cortisol were recorded during three periods of 5 wk each. The ADG was lower (P &lt; 0.001) in feed-restricted groups. Cold exposure reduced the ADG along with feed efficiency in the first period (P &lt; 0.01). Metabolic rate was lowered by feed restriction (P &lt; 0.01) in periods 1 and 3, but was increased by cold exposure in ad libitum-fed sheep during period 1 (P &lt; 0.05). Both cold exposure and feed restriction lowered rectal temperature (P &lt; 0.001). Plasma insulin concentration was lowered by feed restriction (P &lt; 0.05) and was increased (P &lt; 0.05) by cold exposure during periods 2 and 3. Plasma T3 concentration was reduced (P &lt; 0.05) by feed restriction and was increased by cold exposure during periods 1 and 2. Plasma T4 level remained unaltered (P &gt; 0.05) while plasma cortisol concentration was increased by both cold exposure and feed restriction (P &lt; 0.01). The results indicate that lambs show metabolic and physiological responses to feed restriction, which conserve energy in a cold as well as a warm environment. Key words: Sheep, hormone, cold-exposure, feed-restriction.

Beta-adrenergic receptors in skeletal muscles of ruminants: Effects of temperature and feed intake

Adrenergic receptors mediate effects of catecholamines on physiological processes including protein and energy metabolism. We determined the effects of temperature and feed intake on beta-1 and beta-2 adrenergic receptors (β1 AR and β2 AR) in skeletal muscle of lambs to assess the potential to modify physiological responses through adrenergic receptors. Twenty-four wether lambs received either restricted (R) or ad libitum (A) levels of feed intake, and were exposed to either cold (C; 0 ± 2 °C) or warm (W; 23 ± 2 °C) temperatures, resulting in four experimental treatment groups (WA, WR, CA and CR). At the end of 4 mo the lambs were slaughtered and biceps femoris, semitendinosus and gastrocnemius muscles were harvested for isolation of plasma membrane. Binding of [3H]dihydroalprenolol to crude plasma membrane was used to determine the β AR densities and binding affinities (Kd). The densities of β1 AR were 28.02 ± 4.17, 40.68 ± 2.26, 28.99 ± 4.68 and 55.56 ± 6.05 fmol mg−1 protein for biceps femoris, 29.35 ± 1.49, 35.34 ± 2.59, 28.36 ± 2.94 and 37.89 ± 3.30 fmol mg−1 protein for gastrocnemius, and 22.66 ± 2.66, 31.21 ± 4.65, 21.84 ± 1.81 and 38.62 ± 3.67 fmol mg−1 protein for semitendinosus, for WA, WR, CA and CR, respectively. The Kd values for all groups ranged from 1.7 to 8.5 nM for β1 AR. Feed restriction increased (P &lt; 0.01) the density of β1 AR in both environments but there was no significant effect of temperature. β1 AR densities and binding affinities were significantly higher in biceps femoris than in gastrocnemius and semitendinosus muscles when feed intake was restricted. The densities of β2 AR ranged from 9.0 to 16.0 fmol mg−1 protein. There was no effect of treatments on the density or receptor binding affinity of β2 AR in muscles. It is concluded that feed restriction causes increased density of β1 AR in sheep and that feed restriction could potentially increase the metabolic responsiveness of skeletal muscle to elevated levels of catecholamines. Key words: Catecholamine receptors, skeletal muscle, temperature, feed

Effect of environmental temperature and dietary lipid supplement on activity and protein abundance of acetyl-CoA carboxylase and fatty acid synthase in skeletal muscle, liver and adipose tissues of sheep

To determine the effects of temperature and dietary lipid on the key enzymes regulating fatty acid synthesis, 24 wether lambs were exposed to three temperature treatments (+23 °C warm, 0 °C cold, or coldpairfed) and fed either a control barley-based diet or a lipid supplemented diet for a 5-wk period. After slaughter, tissue samples were collected and frozen for analysis for enzyme activity and enzyme protein abundance. Thermal environment or lipid supplementation did not affect (P &gt; 0.05) acetyl-CoA carboxylase (ACC) activity in longissimus dorsi (LD) muscle. In liver, cold exposure increased (P &lt; 0.05) while lipid supplementation depressed (P &lt; 0.05) ACC activity. In subcutaneous (SC) and mesenteric (MS) adipose tissue ACC activity was not affected (P &gt; 0.05) by cold exposure. Dietary lipid supplementation increased (P &lt; 0.05) ACC activity in both SC and MS but the increase in perirenal (PR) fat was not significant. Western-blot analysis with peroxidase-labelled streptavidin identified two isoforms of ACC (280 and 265 kDa) in LD muscle and the 280 kDa was the more abundant isoform. In liver and adipose tissues only one isoform (265 kDa) was identified but there was a poor relationship between enzyme protein abundance and activity. Neither environment nor diet affected fatty acid synthase (FAS) activity in LD or liver. Cold exposure reduced (P &lt; 0.05) FAS activity in SC tissue of ad libitum fed animals but increased FAS activity in MS tissue of pair-fed sheep and had no effect in PR fat. Dietary lipid supplementation reduced (P &lt; 0.05) FAS activity by 30% in all three fat depots. A single isoform of FAS with MW of 260 kDa was present in all tissues examined with cold exposure increasing FAS protein expression in all tissues. The results indicate that temperature and dietary lipid affect enzyme catalytic activity with differential responses in different tissues. Key words: Environmental temperature, lipid supplement, lipogenic enzymes, enzyme activity, protein abundance, sheep

Tenderization of wether lambs meat through pre-rigor infusion of calcium ions

A study involving 36 wether lamb carcasses was conducted in order to evaluate the effects of 0.3 M CaCl 2 injection on final tenderness in muscle Longissimus thoracis et lumborum. Injection of wether lamb carcasses with CaCl 2 accelerated the post mortem tenderization process. Both control and distilled water injected animals had similar Ca 2+-dependent proteases (μ-calpain and m-calpain) and their inhibitor (calpastatin) activities, whereas these were all significantly decreased in CaCl 2 injected animals. The effect of CaCl 2 injection on tenderness was recorded by measuring shear force values 2 and 6 days post mortem. Tenderness was significantly improved by CaCl 2 injection at both at 2 and 6 days post mortem. It was concluded that activation of μ-calpain and m-calpain was responsible for the observed post mortem proteolysis and tenderization.

Effect of β-adrenergic agonist L-644,969 on the impact of the thermal environment on in vitro fatty acid synthesis and lipogenic enzymes in sheep

The effect of temperature and β-adrenergic agonist (BAA) on in vitro rates of fatty acid synthesis and catalytic activity of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) was examined in wether lambs after 5 weeks at either 0 or 20°C. Feeding BAA increased ( P<0.05) rate of fatty acid synthesis by 38% in subcutaneous adipose (SC) tissue from cold-acclimated animals but the rate decreased ( P<0.05) by 27% in SC tissue from warm-acclimated animals. In mesenteric fat (MS), BAA increased ( P<0.05) fatty acid synthesis in the cold environment. In perirenal (PR) fat, rate of fatty acid synthesis was reduced ( P<0.05) by 20% by BAA in the warm but had no effect in the cold. Activity of ACC in longissimus muscle was depressed ( P<0.05) when BAA was fed in the warm environment. In adipose tissues BAA reduced ( P<0.05) ACC activity in the warm, but reduced activity in the cold was limited to SC tissue. In PR tissue FAS activity was reduced ( P<0.05) in the cold environment, while BAA increased FAS activity in the warm environment. Western blot analysis showed two isoforms of ACC with MW of 280 000 and 265 000 Da in longissimus muscle whereas only one isoform was recognized in each of Biceps femoris (280 000 Da) and adipose tissues (265 000 Da). Feeding BAA in the cold environment reduced ( P<0.05) ACC and FAS immunoprotein expression in both MS and PR adipose tissues. The studies indicate that the effect of BAA on fatty acid synthesis and lipogenic enzymes is influenced by acclimation temperature.

Influence of dietary intake and lasalocid on serum hormones and metabolites and visceral organ growth and morphology in wether lambs

Twenty-four black face, crossbred wether lambs (32.4 ± 6.1 kg) were assigned to one of four treatments arranged in a 2 × 2 factorial. Individually penned wethers were fed a pelleted total mixed diet at low intake (LI; 60% of ad libitum) or high intake (HI; 95% of ad libitum); diets contained either low lasalocid (LL; 0 mg per lamb daily) or high lasalocid (HL; 40 mg per lamb daily). Measurements of serum hormones and metabolites were taken during two 3-day collection periods following a 14-day adjustment to treatments. After 42–45 day on treatments, wethers were slaughtered and weight (wt) of liver and intestinal segments were recorded and tissues subsampled. Serum insulin and glucose concentrations were increased ( p < 0.10) in lambs on HI compared with those on LI. Total ruminal VFA concentration (millimolar) was increased ( p < 0.10) with greater for HI vs LI. Compared with LI, HI had greater ( p < 0.10) final BW, eviscerated BW (EBW), and total visceral wt; colon fresh, dry, and dry fat-free wt; cecum dry wt; liver fresh wt, dry wt and dry fat-free wt, liver RNA : DNA ratio, RNA content, and protein content; and duodenum RNA content. Liver DNA concentration was decreased ( p < 0.10) in HI vs LI. Neither labeling index nor morphology of intestinal segments were influenced ( p > 0.10) by intake or lasalocid. Lasalocid had little influence on metabolic hormones or growth and development of visceral organs. These data indicate that high intake increased serum insulin and glucose concentrations, liver wt and cell size.

Influence of undegraded intake protein on intake, digestion, serum hormones and metabolites, and nitrogen balance in sheep

In Exp. 1, 20 ewes of mixed breeding were fed grass hay : straw mixtures, assigned to one of four supplemental treatments and evaluated during six collection periods. Supplemental treatments were control (no supplement), and low, medium, and high levels (5.2%, 22.1%, and 41.3% of DM, respectively) of undegraded intake protein (UIP). Supplements were formulated to be similar in degraded intake protein (DIP; 21%). Digestibilities of DM, OM, and CP were increased ( P < 0.10) with protein supplementation and in medium and high compared with low UIP supplemented ewes. Digestibility of CP also was increased ( P < 0.10) in ewes on high compared with medium treatments. Serum insulin was not influenced ( P > 0.10) by UIP treatment, except in collection period four. In contrast, serum glucose and growth hormone were not influenced ( P > 0.10) by UIP treatment. In Exp. 2, four wether lambs fed the same treatments as in Exp. 1, were used in two 4 × 4 Latin squares trials. In trial 1 lambs received a grass hay diet (6.7% CP) and in trial 2 lambs were fed 40 : 60 blend (6.6% CP) of grass hay and spring wheat straw. In both trials, N intake, urinary N, N digestion, apparent N absorption, and N retention were increased ( P < 0.10) with protein supplementation. In addition, in trial 1, urinary N, N digestion, and apparent N absorption were increased ( P < 0.10) in medium and high compared with low UIP and also in high compared with medium UIP treatments. In trial 2 of Exp. 2, total feed intake (g/kg BW), digestibility of DM and OM, BW, and fecal N were increased ( P < 0.10) with protein supplementation. Organic matter digestion, BW, N intake, and N retention were increased by medium and high compared with low UIP. Fecal N, BW, N intake, and N retention were increased ( P < 0.10) in high compared with medium UIP. These data indicate that increasing levels of UIP supplementation increases DM, OM, and CP (N) digestibility, serum urea N concentration, and N retention in sheep fed low quality forage.

Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa.

Targhee x Hampshire lambs (average BW 23 +/- 1 kg) were used in two experiments to determine the effects of finishing on concentrate with an anabolic implant or forage grazing after concentrate feeding on growth, organ and viscera weights, and carcass tissue accretion. In Exp. 1 and 2 lambs were penned by sex and assigned for slaughter at initial (23 kg), intermediate (37 kg), or end BW (ewes, 47.7; wethers 50.4 kg). From 23 to 37 kg BW, lambs were fed all-concentrate diets in drylot (DL) or grazed on alfalfa (ALF). Experiment 1 was a 2 x 2 factorial with 28 lambs; factors were wether vs ewe lambs and unimplanted vs DL implanted with trenbolone acetate-estradiol benzoate. There were no differences in organ and viscera weights due to implant status. However, ADG (P < .03) and lean gain (P < .02) were greater for implanted than for unimplanted wethers (507 vs 357 g and 1,314 vs 656 g, respectively). Ewes did not respond to the implant. Fat accretion was not affected by implantation. Experiment 2 was a 2 x 3 factorial with 42 lambs; factors were wether vs ewe lambs and drylot during growing and finishing phases (DL-DL) vs drylot during growing and alfalfa grazing during finishing (DL-ALF) vs alfalfa grazing during growing and finishing phases (ALF-ALF). In Exp. 2, ADG of DL-DL lambs was greater (P < .01) than ADG of DL-ALF or ALF-ALF lambs. Lambs on ALF-ALF had smaller (P < .05) livers and rumen/reticulum weights but heavier (P < .04) kidney, omasum, small and large intestine, and cecum weights than those on DL. In Exp. 2, DL-ALF and ALF-ALF lambs had overall hindsaddle lean gain equal to those on DL-DL with less mesenteric fat and 100 g less separable fat. Finishing lambs on alfalfa reduced fat accretion without decreasing lean accretion, whereas trenbolone acetate implants for lambs fed concentrate increased BW gain and lean accretion without affecting fat accretion.

Effect of untreated and formaldehyde treated whole linseed on the performance and fatty acid composition of milk produced by Friesland ewes

Increasing the n-3 polyunsaturated fatty acid (PUFA) content of ruminant products is widely accepted as a potential means of reducing the incidence of cardio-vascular disease in man. However, after ingestion dietary PUFAs are extensively hydrogenated in the rumen. Whole linseed is particularly high in a-linolenic acid (C18:3 n-3) and the feeding of whole seeds with an intact seed coat has been reported to double the duodenal supply of C18:3 in wether lambs (Wachira et al. 1998). This supply may be further enhanced by treating the whole seed with formaldehyde (Gulati et al. 1997). The objective of the experiment was to investigate the effect of untreated and formadehyde treated whole linseed on the performance and fatty acid composition of milk produced by Friesland ewes.

Influence of the novel urease inhibitor N-(n-butyl) thiophosphoric triamide on ruminant nitrogen metabolism: II. Ruminal nitrogen metabolism, diet digestibility, and nitrogen balance in lambs.

Three lamb metabolism experiments were conducted to investigate the effects of chronic administration of the novel urease inhibitor N (n-butyl) thiophosphoric triamide (NBPT) on ruminal N metabolism, fermentation, and N balance. In Exp. 1, ruminally cannulated wethers (n = 28; 45.0 +/- .9 kg) were administered one of seven doses of NBPT (0 [control], .125, .25, .5, 1, 2, or 4 g of NBPT daily) and fed a common cracked corn/cottonseed hull-based diet twice daily containing 2% urea at 2.5% of initial BW for the duration of the 15-d experiment. Overall, NBPT decreased (linear P < .0001; quadratic P < .001) ruminal urease activity, resulting in linear increases (P < .0001) in ruminal urea and decreases in ruminal NH3 N concentrations. However, the detection of an NBPT x day interaction (d 2 vs 15; P < .01) indicated that this depression in urea degradation diminished as the experiment progressed. Increasing NBPT linearly decreased (P < .01) total VFA concentrations on d 2 of the experiment, but it had no effect (P > .10) on d 15. Increasing NBPT had no effect (P > .10) on DM or ADF digestibilities, but it linearly decreased (P < .01) N digestibility. Supplementing NBPT produced a linear increase (P < .05) in urinary N excretion and a linear decrease (P < .01) in N retention. In Exp. 2, ruminally cannulated wethers (n = 30; 46.8 +/- .6 kg) were fed one of two basal diets (2.0 vs 1.1% dietary urea) at 2.5% of initial BW and dosed with either 0 (control), .25, or 2 g of NBPT daily for the duration of the 15-d experiment. There were no NBPT x dietary urea interactions (P > .10) for Exp. 2. Increasing NBPT depressed (linear and quadratic P < .0001) ruminal urease activity, producing linear (P < .0001) increases in urea N and linear decreases in NH3 N in the rumen. As in Exp. 1, an NBPT x day interaction (P < .05) was noted for urea, NH3 N, and total VFA concentrations; the maximum response to NBPT occurred on d 2 but diminished by d 15 of the experiment. Administration of NBPT did not influence (P > .10) DM, ADF, or N digestibilities in Exp. 2. In Exp. 3, wether lambs (n = 30; 26.4 +/- .7 kg) were subjected to the same treatment regimen as in Exp. 2 for a 14-d N balance experiment. Although several NBPT x dietary urea interactions (P < .05) were noted, increasing NBPT did not affect (P > .10) N digestibility. Administration of NBPT quadratically increased (P < .10) urinary N excretion, producing a linear decrease (P < .05) in N retention. These results suggest that although NBPT is capable of inhibiting ruminal urease short-term, the ruminal microflora may be capable of adapting to chronic NBPT administration, thereby limiting its practical use in improving the utilization of dietary urea.

Effects of diet forage:concentrate ratio and metabolizable energy intake on visceral organ growth and in vitro oxidative capacity of gut tissues in sheep.

We used 28 crossbred wether lambs to determine the effects of dietary forage:concentrate ratio and metabolizable energy intake on visceral organ growth and oxidative capacity of gut tissues in lambs. Lambs were assigned randomly to a factorial arrangement of dietary treatments consisting of pelleted diets containing either 75% orchardgrass or 75% concentrate fed once daily at either .099 or .181 Mcal ME x (kg BW(.75))(-1) x d(-1). After a 52-d feeding period, lambs were slaughtered to obtain measurements of visceral organ mass and composition and oxidative capacity of isolated epithelial cells. Lamb performance, as measured by DMI, ADG, and efficiency of gain, was greater (P = .0001) for both diets at high ME intake. Likewise, lambs fed 75% concentrate gained faster and more (P < or = .01) efficiently than lambs fed 75% forage. Total digestive tract (TDT; includes rumen, reticulum, omasum, abomasum, and intestines) weight increased (P = .0001) with ME intake and was greater (P = .03) in lambs fed 75% forage than in those fed 75% concentrate. As a percentage of empty body weight (EBW), TDT weight increased with ME intake in lambs fed 75% forage, but it was unaffected by ME intake in lambs fed 75% concentrate (diet x intake, P = .03). Liver weight increased (P = .0001) with ME intake and was greater (P = .005) in lambs fed 75% concentrate vs 75% forage; however, liver weight as a percentage of EBW was increased (P = .0002) with ME intake but was unaffected by diet. Greater ME intake increased (P < or = .02) small intestinal (SI) epithelial and muscle mass of 15-cm sections, whereas jejunal epithelial mass was greater (P = .01) for lambs fed 75% forage vs 75% concentrate. Rumen epithelial concentrations of DNA and RNA increased (P < or = .02) with greater ME intake, whereas SI concentrations of DNA and RNA were largely unaffected by diet or ME intake. The activity of Na(+)-K(+)-ATPase increased in ileal epithelium (P < or = .02) with ME intake and concentrate in the diet, but activity in ruminal epithelium increased (P = .05) with concentrate. Total oxygen consumption by isolated ruminal and intestinal epithelial cells was unaffected by treatment. These data suggest that ME intake and level of dietary forage affect ruminal and intestinal growth via changes in cellular hyperplasia. Additionally, this study supports the concept that ME intake and diet composition alter gut energy expenditure, at least in part, through changes in mass rather than mass specific metabolism.

Effect of the callipyge gene on muscle growth, calpastatin activity, and tenderness of three muscles across the growth curve.

Changes in muscle growth, calpastatin activity, and tenderness of three muscles were assessed in 20 callipyge and 20 normal wether lambs slaughtered at live weights (LW) of 7, 20, 36, 52, and 69 kg. At 24 h postmortem, the longissimus (LM), semimembranosus (SM), and supraspinatus (SS) muscles were removed and weighed and samples were obtained for calpastatin activity (CA; 24 h) and Warner-Bratzler shear force (WBS; aged 6 d). For muscle weights and calpastatin activity, the weight group x muscle x phenotype interaction was significant (P < 0.05). Muscle weights were similar (P > 0.05) between phenotypes for all three muscles at 7 kg LW. At 20 kg LW, the LM and SM muscles from the callipyge lambs were heavier (P < 0.05) than those from normal lambs; however, the SS did not differ (P > 0.05) between phenotypes at 7, 20, or 52 kg. From 20 to 69 kg LW, the LM and SM weights were 42 and 49% heavier (P < 0.05) for callipyge than for normal lambs. Calpastatin activity of the callipyge LM was greater (P < 0.05) than that of normal LM at 36, 52, and 69 kg. In the callipyge LM, CA was similar (P > 0.05) at 20, 36, and 52 kg LW and did not differ (P > 0.05) from 7-kg or 69-kg values. Calpastatin activity declined (P < 0.05) across the growth curve for the SM and SS, but values were higher (P < 0.05) in the SM in callipyge than in normal lambs. Shear force values of the LM were lower (P < 0.05) for normal lambs at 36, 52, and 69 kg LW than for callipyge lambs. In the SM and SS, WBS values decreased (P < 0.05) across the growth curve, but values were higher (P < 0.05) for callipyge lambs in the SM only. These data indicate that the selective muscular hypertrophy of the callipyge phenotype develops during the postnatal growth period between 7 and 20 kg LW (19 and 100 d of age). Longissimus and semimembranosus muscles in the callipyge lambs were over 40% heavier from 20 to 69 kg LW; however, they also had higher levels of calpastatin activity and Warner-Bratzler shear force during this time period, indicating the need for postmortem tenderization treatments to improve palatability.

Effects of diet forage:concentrate ratio and metabolizable energy intake on isolated rumen epithelial cell metabolism in vitro.

Crossbred wether lambs were used to assess the effect of altered forage:concentrate ratio and metabolizable energy intake on metabolism of substrates by ruminal epithelium using an isolated cell system. Lambs (n = 28; 20.1 +/- 3 kg BW) were assigned randomly to a factorial arrangement of dietary treatments consisting of either 75% forage or 75% concentrate fed once daily at either .099 or .181 Mcal ME x(kg BW(.75))(-1) x d(-1) for 52 d. After a 52-d feeding period, isolated rumen epithelial cells (IREC) were incubated in the presence of an oxidizable substrate with a single 14C label (acetate, propionate, butyrate, glucose, glutamate, and glutamine) at concentrations ranging from .1 to 50 mM, and substrate oxidation to 14CO2 or metabolism to beta-hydroxybutyrate (beta-HBA), acetoacetate, pyruvate, and lactate was determined. For all substrates, oxidation to CO2 was concentration-dependent and saturable within the physiological range. Differences in substrate oxidation to CO2 by IREC at specific substrate concentrations did not affect Vmax (maximal rate of substrate oxidation, nmol oxidized to CO2 x 1 x 10(6) cells(-1) x 90 min(-1)) and K(ox) (concentration of substrate at which half Vmax oxidation rate is achieved, mmoles/L) estimates for the dietary treatments. Production of beta-HBA from butyrate by IREC from the lambs fed 75% forage was not affected by ME intake; however, production was elevated by high ME intake of the 75% concentrate diet (diet x intake interaction; P < .02). Acetoacetate production from butyrate by IREC from lambs fed at high ME intake was greater (P = .001) than from those fed at low ME intake. Lactate and pyruvate production from glucose, glutamate, and propionate were generally unaffected by dietary treatment; however, rate of glutamine metabolism to lactate and pyruvate by IREC was increased with increased ME intake. The observed changes in metabolite production rates across groups did not affect the predicted Vmax and K(ox) parameter estimates. The estimated K(ox) values corroborate that VFA are the primary oxidizable fuels used by ruminal epithelial cells while illustrating that other substrates such as glucose, glutamate, and glutamine would not be expected to be oxidized extensively in vivo due to the high K(ox) relative to substrate concentrations in vivo. In conclusion, the capacity of isolated ruminal epithelial cells to oxidize substrates was largely unaffected by ME intake or dietary forage:concentrate ratio of the diet.

The effects of urea supplementation on production and parasitological responses of sheep infected with Haemonchus contortus and Trichostrongylus colubriformis

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH 3–N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.

Estimated relative bioavailability of supplemental inorganic molybdenum sources and their effect on tissue molybdenum and copper concentrations in lambs

Forty crossbred wether lambs, 44 kg initial body weight, were used to study relative bioavailability of Mo in supplemental Mo sources and their effects on body Cu storage. The basal maize-soya-bean meal-cottonseed hulls diet contained 11.5 mg kg −1 Cu, 1.1 mg kg −1 Mo and 2.1 g kg −1 S (DM basis) and was supplemented with 0, 15, 30, or 45 mg kg −1 (as-fed basis) added Mo as reagent grade sodium molybdate as the standard, or 30 mg kg −1 added Mo as ammonium molybdate, molybdenum trioxide, or molybdenum metal. Diets were fed for 28 days and feces and urine were collected for the last 5 days and composited by lamb. At the end of the trial, serum, liver, kidney, muscle, and bile were collected and analyzed for Mo and Cu. Based on multiple regression slope ratios of tissue concentration or daily excretion (including that from bile) of Mo on added dietary Mo concentration, the average relative bioavailability values were 1.00, 1.04, 1.10 and 0.18 for sodium molybdate, ammonium molybdate, molybdenum trioxide, and molybdenum metal. Serum and muscle Mo concentrations had the best fits to a linear model. Kidney Cu, serum total Cu, serum TCA-insoluble Cu, and fecal Cu concentrations increased with increasing dietary intakes of Mo.

Glycogen metabolism and ultimate pH of muscle in Merino, first-cross, and second-cross wether lambs as affected by stress before slaughter

This experiment compared the metabolism of muscle glycogen and the ultimate pH (pHu) of muscle in Merino and crossbred lambs fed the same diet but subjected to different levels of stress pre-slaughter. Twenty- five Merino, 24 first-cross (Merino dam × Poll Dorset sire), and 23 second-cross (Border Leicester × Merino dam and Poll Dorset sire) wether lambs (6 months old, 30 kg liveweight) were maintained for 8 weeks on a complete pelleted diet based on lupin seed, straw, and barley grain (metabolisable energy, 10.8 MJ/kg; protein, 17.4% in dry matter), with a feed intake of 1.3 kg dry matter /day for each breed. At Week 6, muscle biopsies were taken from 15 lambs of each breed, and at Week 8, 5 animals from each breed were slaughtered at an experimental abattoir 10 min after removal from their pens (low pre-slaughter stress). The remaining lambs, separated into breeds, were transported for 2 h and slaughtered after 24 h lairage at a commercial abattoir. Muscle samples were taken at slaughter, and assayed with the biopsy samples for glycogen concentration (corrected for lactate concentration), myoglobin concentration, and citrate synthase activity. The pHu of muscle was measured 48 h post slaughter. Compared with commercially slaughtered lambs, the muscle tissues of lambs subjected to low pre-slaughter stress had higher glycogen concentrations post mortem, lower pHu, and no significant loss of glycogen between pen and slaughter. Breed had no effect on glycogen, pH, or the colour of muscle under low-stress slaughter conditions or when the muscle biopsy was taken. In contrast, breed had a significant influence under commercial slaughter conditions, the muscle of Merino lambs having the lowest glycogen concentration post portem, and the highest pHu and loss of glycogen between pen and slaughter. Irrespective of stress, second-cross lambs had higher myoglobin concentrations and citrate synthase activities than the Merino lambs, indicating greater pigmentation of muscle in the second-cross animals. We conclude that higher proportions of Merino genes are associated with a greater sensitivity to stress in lambs destined for slaughter.