Effects of dietary energy and protein density on plasma concentrations of leptin and metabolic hormones in dairy heifers

The hormonal and metabolic signals that communicate the level of body energy reserves to the reproductive-mammary axis remain undefined in dairy cattle; consequently, our hypothesis was that leptin may fulfill this role. Our objectives were to determine the effects of diets differing in energy and protein density on dry matter intake (DMI), growth traits [body weight (BW), body condition score (BCS), back-fat (BF) thickness], and temporal changes in plasma concentrations of leptin, insulin, growth hormone (GH), insulin-like growth factor-1 (IGF-1), glucose, and nonesterified fatty acids (NEFA) in dairy heifers during the pre- and postpubertal periods. In period 1, heifers were randomly allotted (n = 10/diet) at 103 kg of BW to diets for a predicted average daily gain of 1.10 (high, H), 0.80 (medium, M), or 0.50 kg/d (low, L). Five heifers in each of the H and L groups were further studied during period 2, either at 12 mo of age (HA, LA) or at 330 kg of BW (HW, LW). The data provide evidence that 1) DMI (18%), BW (17%), and BF (5%) together explained 40% of the variation in plasma leptin concentrations (r² = 0.396); 2) unlike the acute postprandial increase in plasma insulin as a result of increased nutrient density (H 1.42 ± 0.09, M 1.02 ± 0.09, L 0.68 ± 0.11 ng/mL), plasma leptin concentrations did not respond acutely with a distinct postprandial profile; 3) although plasma leptin concentrations increased with age, leptin at puberty did not differ among treatment groups (H 5.63 ± 2.48, M 4.28 ± 0.55, L 4.12 ± 0.72 ng/mL) and there was no evidence of an abrupt transition in prepubertal plasma leptin concentrations; 4) plasma leptin concentrations may not be a critical trigger for puberty in rapidly growing heifers, but are apparently essential for puberty in heifers with normal or restricted growth rates; and 5) plasma concentrations of insulin (H 0.59 ± 0.07, M 0.43 ± 0.09, L 0.30 ± 0.09 ng/mL), IGF-1 (H 151.08 ± 16.47, L 82.51 ± 17.47 ng/mL), and glucose (H 81.35 ± 3.39, M 73.59 ± 2.34, L 68.25 ± 3.39 mg/dL) reflected nutrient density, whereas GH (H 1.82 ± 0.23, L 5.87 ± 0.45 ng/mL) and NEFA (H 209.54 ± 50.83, L 234.93 ± 48.97 μM) were inversely related to the plane of nutrition. Collectively, these data suggest that plasma concentrations of leptin may play a role in long-term regulation of energy reserves and puberty in growing Holstein heifers.     

The effect of oestrus behaviour on muscle glycogen concentration and dark-cutting in beef heifers

Preliminary observations at an abattoir showed an association between oestrus behaviour and dark-cutting in beef. Two follow-up experiments examined the relationship between oestrus behaviour and muscle glycogen content, carcass bruising and meat ultimate pH. In the first experiment heifers in oestrus were compared with controls in mid-cycle. Oestrus was associated with a loss of glycogen in M. longissimus dorsi. Also plasma creatine kinase activity increased, reflecting bruising or strenuous muscle activity. In the second experiment heifers were slaughtered during oestrus. On the basis of pre-slaughter behaviour they were assigned to active or inactive groups, which subsequently yielded 39% and zero dark-cutting carcasses, respectively. Loss of muscle glycogen was accounted for by the number of times an animal mounted (r = -0·85). Likewise, variation in meat ultimate pH was associated with mounting activity (P < 0·001). Carcass bruising was higher in the active group (P < 0·0.001) and the main cause of bruising was being mounted (r = 0·74). It was concluded that single penning of oestrus heifers to eliminate mounting activity would reduce the incidence of dark-cutting.     

The effect of dry period duration and dietary energy density on milk production, bioenergetic status, and postpartum ovarian function in Holstein-Friesian dairy cows

Following parturition, it is typical for dairy cows to enter a period of negative energy balance and body condition loss to support mammary milk synthesis; this is associated with compromised reproductive performance. Alternative management strategies during the prepartum (dry) and early postpartum periods may ameliorate this loss. Forty mature Holstein-Friesian cows were assigned to 1 of 2 dry period treatments [standard 8-wk dry period (SDP) or no planned dry period (NDP)] and 1 of 2 dietary energy density treatments [standard TMR (STMR) or high-quality TMR (HTMR)]. Milk yield during wk 1 to 12 postpartum was reduced in cows assigned to the NDP treatment. Energy balance and body condition score (BCS) during wk 1 to 4 postpartum were increased in cows assigned to the NDP treatment compared with the cows assigned to the SDP treatment, and BCS increased from wk 5 to 12 postpartum in the NDP cows compared with the SDP cows. During the first 12 wk postpartum, cows assigned to the HTMR diet had greater milk yield and reduced milk fat concentration compared with the cows assigned the STMR diet. The BCS was greater from wk 5 to 12 postpartum in HTMR cows compared with STMR cows. During the period from wk −3 to +3 relative to parturition, circulating concentrations of insulin, glucose, and IGF-I were greater in cows in the NDP treatment compared with cows in the SDP treatment. Cows assigned to the HTMR diet had greater circulating insulin and glucose concentrations compared with the STMR cows from wk −3 to +3 relative to parturition. The first postpartum ovulation occurred earlier for cows in the NDP treatment compared with cows in the SDP treatment (16.9 vs. 24.8 d postpartum. Cows assigned to the STMR diet tended to have a higher conception rate to first service compared with cows assigned to the HTMR diet. Energy balance and metabolic status can be improved by either eliminating the dry period or by feeding a higher energy diet, but effects on the reproductive axis appear to be different.     

The effect of dietary energy and vitamin E administration on performance and intramuscular collagen properties of lambs

The effect of different dietary energy levels, with or without injections of vitamin E, on growth, carcass traits and intramuscular collagen (IMC) characteristics of growing lambs was studied. Twenty-four Ile de France ram lambs were evaluated in a 2×2 factorial design involving different DL-α-tocopheryl acetate injections (C, control=0 and V=150IU/wk, i.m. for eight wk) and energy level (N, normal=7.61 and L, low=6.47MJ/kg DM). Growth and slaughter performance, and IMC characteristics were not influenced by diet. DL-α-tocopheryl acetate increased ADG during suckling, while it did not affect live weight, carcass weight and dressing percentage. Vitamin E injections reduced carcass shrinkage but also had a negative effect on pelvic limb percentage. The Longissimus muscle pH values were higher in V than in C lambs. DL-α-tocopheryl acetate reduced IMC maturity and muscle hydroxylysylpyridinoline crosslink concentration, more markedly in lambs fed low energy diets.     

Short communication: The effect of dry period duration and dietary energy density in early lactation on the rennet gelation properties of milk

This study was carried out to examine the effects of decreasing the dry period (DP) duration and altering the energy density of the diet during early lactation on the rheological characteristics of milk. Forty mature Holstein-Friesian cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to 1 of 2 dry period treatments and 1 of 2 nutritional treatments. The DP treatments were continuous milking (CM) or an 8-wk standard dry period (SDP), and the nutritional treatments were a standard energy diet (SE) or a high energy diet (HE). Actual DP lengths were 6.3 ± 1.7 d and 62.1 ± 1.9 d for cows on the CM and SDP treatments, respectively. Milk samples were collected at 2, 6, and 10 wk postpartum. The concentrations of fat, protein, and lactose were determined in each sample. The rennet gelation properties were measured at 31°C using dynamic low-amplitude strain oscillatory rheometry. The following parameters were obtained from the resultant elastic shear modulus (G′): gelation time, maximum curd firming rate, and gel strength. Reducing the DP duration from 62 to 6 d resulted in increases in milk protein concentration (31.8 vs. 34.7 g/kg), maximum curd firming rate (2.58 vs. 3.60 Pa/min), and gel strength (69.4 vs. 90.5 Pa). Increasing the dietary energy density decreased percentage milk fat (43.1 vs. 37.7 g/kg) but otherwise had no effect. Gel strength was correlated with maximum curd firming rate (r = 0.99), and both variables were correlated with milk protein concentration (r = 0.71 and r = 0.73, respectively). The results indicate that decreasing the duration of the DP increased milk protein concentration and improved the rennet gelation properties of milk, but that dietary energy density had little effect.     

Effects of prepartum diets varying in dietary energy density and monensin on early-lactation performance in dairy cows

Our objectives were to evaluate the effects of prepartum monensin supplementation and dry-period nutritional strategy on the postpartum productive performance of cows fed monensin during lactation. A total of 102 Holstein cows were enrolled in the experiment (32 primiparous and 70 multiparous). The study was a completely randomized design, with randomization restricted to balance for parity, body condition score, and expected calving date. A 2 × 2 factorial arrangement of prepartum treatments was used; the variables of interest were prepartum feeding strategy [controlled-energy diet throughout the dry period (CE) vs. controlled-energy diet from dry-off to 22 d before expected parturition, followed by a moderate-energy close-up diet from d 21 before expected parturition through parturition (CU)] and prepartum monensin supplementation [0 g/t (control, CON) or 24.2 g/t (MON); Rumensin; Elanco Animal Health, Greenfield, IN]. Lactation diets before and after the dry period contained monensin at 15.4 g/t. During the close-up period, cows fed CU had greater DM and NE_L intakes than cows fed CE. Calf BW at birth tended to be greater for cows fed CU than for those fed CE but was not affected by MON supplementation. Diet did not affect calving difficulty score, but cows supplemented with MON had an increased calving difficulty score. We found a tendency for a MON × parity interaction for colostral IgG concentration, such that multiparous MON cows tended to have lower IgG concentration than CON cows, but colostral IgG concentration for primiparous MON and CON cows did not differ. Postpartum milk yield did not differ between diets but tended to be greater for cows supplemented with MON. Milk fat and lactose content were greater for cows fed CU than for those fed CE, and lactose content and yield were increased for cows supplemented with MON. Solids-corrected and fat-corrected milk yields were increased by MON supplementation, but were not affected by diet. Overall means for postpartum DMI did not differ by diet or MON supplementation. The CU diet decreased the concentration of nonesterified fatty acids during the close-up period but increased it postpartum. Neither diet nor monensin affected β-hydroxybutyrate or liver composition. Overall, postpartum productive performance differed little between prepartum dietary strategies, but cows fed MON had greater energy-corrected milk production. In herds fed monensin during lactation, monensin should also be fed during the dry period.     

The effect of nutritional supplements on growth rate, stress responsiveness, muscle glycogen and meat tenderness in pastoral lambs

Nutritional supplements and a magnesium bolus and were used in lambs in a 2×2 factorial design to investigate the effect on growth, preslaughter stress measurements, muscle glycogen, and meat quality. In total, 64 Perendale lambs were used (32.7±0.53 kg, mean±SEM). Feed supplemented animals received 150 g feed pellets day⁻¹ in addition to pasture grazing, and this increased growth from 183 to 207 g day⁻¹. Mean delivery of Mg from the boluses was 0.17 g day⁻¹ for 28 days, with no effect on growth rates, or any other of the variables measured. Urinary noradrenaline, adrenaline and cortisol did not differ between groups in the immediate pre-slaughter period. The meat ultimate pH was not different between groups and had a mean range of 5.47–5.53. Muscle residual glycogen did not differ between groups and had a mean range of 42–43 mmol kg⁻¹. Finally there were no differences in shear force values at all ageing times. The final shear force value of 2.5 kg F after 72 h ageing at 15 °C was a low value representing tender meat. These studies indicate that if nutrition is adequate and stress levels are low, there are no differences in meat tenderness of pasture fed lambs compared with those having feed supplements to increase growth rate.     

Effect of precalving and postcalving dietary energy level on performance and blood metabolite concentrations of dairy cows throughout lactation

The effects of the level of energy intake (high E and low E) offered before and after calving on body condition score at calving, production performance, and energy status in the first 250 d of lactation were evaluated in a 2 × 2 factorial design experiment involving 80 Holstein-Friesian dairy animals (40 primiparous and 40 multiparous). From d 80 until d 21 precalving, primiparous animals were offered either high or low pasture allowances. Thereafter, these animals were housed and had ad libitum access to a high energy density diet (high E) or restricted access [6 kg of dry matter (DM) per d] to a low energy density diet (low E), respectively, until calving. From d 100 until d 42 precalving, multiparous animals were offered either ad libitum or restricted (10 kg of DM/d) access to a late lactation diet, and thereafter, had ad libitum access to a high E diet or restricted access (7 kg of DM complete diet/d) to a low E diet, respectively, until calving. The forage to concentrate (F:C) ratios (DM basis) of these high E and low E diets [d 42 (d 21 in primiparous animals) until calving] were 64:36 and 83:17, respectively. Cows offered high E and low E precalving diets were allocated to either a high E or low E postcalving diet [F:C ratio (DM basis) of 30:70 and 70:30, respectively] and remained on these diets until d 250 of lactation. Multiparous animals offered a high E diet precalving had a significantly higher body condition score at calving than those offered the low E diet precalving. This effect was not evident in primiparous animals. Precalving diet had no significant effect on plasma nonesterified fatty acid concentrations during the last 3 wk precalving in primi- or multiparous animals. Primiparous animals offered a high E diet precalving had significantly higher postcalving plasma concentrations of nonesterified fatty acid, suggesting greater mobilization of body reserves. Primi- and multiparous animals offered a high E diet postcalving had a significantly higher dry matter intake, milk yield, and energy status postcalving compared with animals offered a low E diet postcalving. Milk yields of primiparous animals offered high E and low E diets postcalving were 29.7 and 24.8 kg/d, respectively, and milk yield of multiparous animals offered high E and low E diets postcalving were 33.5 and 28.2 kg/d, respectively. It is concluded that altering body condition score during the dry period is difficult but that specific dietary regimens applied precalving can have a significant influence on postcalving production and energy-related parameters.     

Effects of transition diets varying in dietary energy density on lactation performance and ruminal parameters of dairy cows

Forty cows and twenty heifers were used to study the effects of dietary energy density during late gestation and early lactation on lactation performance and ruminal parameters. A 2 x 2 factorial arrangement of treatments was used. During prepartum (-28 d to calving), animals were fed a low energy density diet [DL; 1.58 Mcal of net energy for lactation (NE(L))/kg, 40% neutral detergent fiber (NDF) and 38% nonfiber carbohydrate (NFC)] or a high energy diet (DH; 1.70 Mcal NE(L)/kg, 32% NDF and 44% NFC). After calving, half of the cows from each prepartum treatment group were assigned to a low energy density diet (L; 1.57 Mcal NE(L)/kg, 30% NDF and 41% NFC) or a high energy density diet (H; 1.63 Mcal NE(L)/kg, 25% NDF and 47% NFC) until d 20 postpartum. After d 20, all cows were fed H until d 70. Animals fed DH had 19.8% greater dry matter intake (DMI; % of body weight) and 21.5% greater energy intake than animals fed DL prepartum and the response was greater for cows compared to heifers. Animals fed DH had lower ruminal pH compared to animals fed DL, but no major changes in volatile fatty acid concentrations were observed. Effects of dietary energy density during prepartum on postpartum production responses were dependent on parity. Primiparous cows fed DL had higher 3.5% fat-corrected milk yield and milk fat production and percentage during the first 10 wk of lactation than those fed DH. Prepartum diet did not affect lactation performance of multiparous cows. Cows fed H had higher DMI and energy intake for the first 20 d of lactation compared to cows fed L. Diets did not affect DMI after the third wk of lactation. Milk production increased faster for cows fed H compared to cows fed L. Animals fed DL-L sequence of treatments tended to have the lowest energy intake during the first 10 wk of lactation. Prepartum treatments did not affect ruminal fermentation characteristics postpartum. Cows fed H had lower ruminal pH and higher propionate concentrations than cows fed L. No prepartum x postpartum interactions were observed for ruminal fermentation parameters. The effects of DH on prepartum DMI did not carry over to the postpartum period or influence early postpartum production. Increasing concentrate content of the diet immediately postpartum instead of delaying the increase until d 21 postpartum is associated with a higher rate of increase.in milk production and higher DMI.     

Effects of pre- and postfresh transition diets varying in dietary energy density on metabolic status of periparturient dairy cows

Effects of dietary energy density during late gestation and early lactation on metabolic status of periparturient cows were studied. Four weeks before expected calving, animals were fed a low (DL; 1.58 Mcal of NE_L/kg) or high energy density diet (DH; 1.70 Mcal of NE_L/kg). After calving, half of the cows from each prepartum treatment were assigned to a low (L; 1.57 Mcal of NE_L/kg) or high energy density diet (H; 1.63 Mcal of NE_L/kg) until d 20 postpartum. After d 20, all animals were fed H until d 70. Animals fed DH had a more positive energy balance during the prepartum period. Animals fed DH had higher plasma concentrations of glucose and insulin and lower concentrations of plasma nonesterified fatty acid (NEFA) on d −7 relative to calving compared with animals fed DL. No differences in blood concentrations of metabolites, insulin and liver triglycerides (TG) content were observed on d 1. Liver TG content at d 1 and 21 were more related to magnitude of change in energy intake prepartum than to energy intake in the last week of gestation. Cows fed H had higher concentrations of plasma glucose and insulin, but similar plasma NEFA during the postpartum period compared with cows fed L. Plasma concentrations of β-hydroxybutyrate (BHBA) and liver TG content on d 21 were 46 and 30% lower, respectively, for cows fed H compared with cows fed L. Interactions between prepartum and postpartum treatments indicated that negative effects of delaying higher concentrate feeding until d 21 postpartum can be partially offset by increasing concentrate in the diet before calving. Cows fed L had a higher increase in white line hemorrhage scores between prepartum and 10 wk postpartum compared with cows fed H. Energy density of prepartum diets had a minor influence on metabolic status of cows postpartum. A more favorable metabolic profile occurs when increasing the concentrate content of the diet immediately postpartum compared with delaying the increase until d 21 postpartum.     

The effect of dietary antibiotics on protein and energy metabolism in rats: possible significance of the gut microflora.

The influence of the intestinal microbial activity on protein metabolism was tested in rats with three diets fed without and with antibiotics (Nebacitin). True protein digestibility, biological value, net protein utilisation, true amino acid digestibility and apparent digestible energy were measured. The intestinal microbial activity was on average reduced to one-fifth by antibiotics. On a diet low in crude fibre (2.5%) but high in crude protein (17.6%), this reduction had only a minor influence on the parameters for protein quality that were measured. However, true digestibilities of histidine and cystine were strongly reduced by the antibiotic treatment. The digestibility of energy was also significantly reduced (5%). For diets higher in crude fibre and lower in protein, the influence of the microbial activity was more pronounced. Digestibility of protein and energy were severely reduced by the dietary antibiotic treatment. In general, antibiotic supplementation decreased the parameters that were measured.     

Bovine Longissimus dorsi muscle glycogen and color response as affected by dietary regimen and post-mortem electrical stimulation in young bulls

Eighty bulls were assigned to one of two groups and fed a dietary regimen to defer or accelerate growth until slaughter. Bulls fed at an accelerated rate of growth (or high energy regimen) had higher post-mortem pH, and lower muscle glycogen stores, with darker lean color, and improved shear and palatability traits compared to deferred fed animals. Bulls fed at an accelerated rate of growth also had a higher degree of marbling and USDA quality grade. Electrical stimulation did not affect (P > 0·05) ultimate pH, but reduced (P < 0·05) glycogen values at 0 and 2 h post mortem. Electrical stimulation also improved muscle color, lowered cooking losses and improved the palatability of cooked longissimus dorsi steaks.     

粮食相对密度测定的影响因素

粮食相对密度测定的影响因素很多,通过比较发现,相对密度测定在室温下进行,称样量选择5 g,量筒精度选择0.1 mL,乙醇液浓度选择20%,可以得到较为准确的结果.     

环境湿度对植物蛋白膜的影响研究

研究了环境湿度对小麦蛋白膜、大豆蛋白膜以及小麦-大豆复合膜机械性能、通透性等的影响。结果表明,由于蛋白腹为亲水性膜,受环境湿度的影响,其水分含量、分子间作用力有所不同,从而导致蛋白膜的机械性能、透湿性和吸湿率也随之发生变化。膜的阻止水蒸汽渗透的能力下降,吸湿率降低,透氧率呈上升趋势。     

PSE肉和DFD肉中糖原含量变化分析

利用蒽酮比色法进行检测正常肉、PSE肉和DFD肉中糖原含量的变化。糖原标液水解率为95.8%～98.7%,平均值为97.46%,相对标准偏差为1.25%。在0h,正常肉、PSE肉和DFD肉中糖原的平均含量分别为0.7560、0.7456、0.5284mg/g,RSD为0.3689%～0.7566%。PSE肉中糖原含量2h后下降到0.0420mg/g,RSD为2.3890%。正常肉和DFD肉的糖原含量在72h后分别下降到0.0608mg/g和0.0794mg/g,RSD为2.1445%和4.5931%。     

茶对氟化物和呕吐毒素对大鼠肝糖原分解的保护作用

目的探究茶对氟与呕吐毒素染毒大鼠肝糖原含量降低的保护作用。方法将50只Wistar大鼠分为空白组、呕吐毒素染毒组、氟染毒组、联合染毒组和饮茶干预组,染毒5周后解剖大鼠,用蒽酮比色法试剂盒检测肝糖原含量。结果氟单独染毒、呕吐毒素与氟联合染毒后肝糖原含量显著性降低(P0.05),呕吐毒素与氟联合染毒后的肝糖原含量显著性低于呕吐毒素单独染毒(P0.05),饮茶干预后的肝糖原含量显著提高(P0.05)。结论呕吐毒素和氟化物对肝糖原有损伤作用,茶对其损伤有保护性作用。     

The effect of swimming lambs and subsequent resting periods on the ultimate pH of meat

The effect of washing lambs in a swim-through bath and subsequent resting periods in the stockyards on the ultimate pH of the M. longissimus dorsi (LD) was studied in 662 animals at a meat export works. There was a linear relationship between the number of times the animals were washed and mean ultimate pH of the LD but there was no statistical association between the duration of the resting period after washing and the ultimate pH. The mean ultimate pH of meat from Perendale lambs from one farm was significantly greater than that recorded from Romney lambs from another farm. It is suggested that such differences may be related to variations in behavioural response and catecholamine secretion in these groups of animals.     

Assessment of dietary fiber fermentation: effect of Lactobacillus reuteri and reproducibility of short-chain fatty acid concentrations

This investigation had two aims: (i) to determine the reproducibility of SCFA production of two fibers: wheat dextrin and inulin, in two separate in vitro batch fermentation systems, and (ii) to determine if the addition Lactobacillus reuteri, a probiotic bacterium, enhanced the fermentation of wheat dextrin, inulin, and psyllium using in vitro batch fermentation. Samples were removed at 0, 4, 8, 12, and 24 h. SCFAs were measured by GC. L. reuteri improved inulin's fermentation profile by reducing the total SCFA peak at 4 h and enhancing fermentation at 8 and 12 h. Wheat dextrin and psyllium were largely unaffected. Wheat dextrin's total SCFA and propionate production curves were steady and replicable, but concentration values varied between fermentations. Partially hydrolyzed guar gum (PHGG) and wheat dextrin had similar fermentation patterns from 0-8 h, but PHGG plateaued at 8 h for all measures. Psyllium produced peak SCFA concentrations at 8 h, similar to inulin. L. reuteri could be combined with inulin for enhancing fermentation, but it does not improve wheat dextrin or psyllium fermentation. Wheat dextrin will likely produce similar physiological within a group of individuals due to the reproducibility of fermentation.