Puberty and early sexual development in Libyan fat-tailed ram lambs

Puberty and early sexual development were studied in 143 Libyan fat-tailed ram lambs, equally representing Brownhead and Blackhead strains of this breed. The two strains did not differ in any of the measured parameters in a consistent way, yet the Brownhead lambs tended to be slightly heavier and to have a slightly larger testis diameter than Blackheads. At the commencement of the observations when the lambs were 69 days old, 25.2% had fully descended testes at a significantly higher (P less than 0.01) mean (SD) body weight (24.1 +/- 4.1 kg) than those with partly descended (69.2%, 15.7 +/- 6.3 kg) or with non-descended testes (5.6%, 19.5 +/- 3.2 kg). Testes development followed a triphasic pattern with an initial and a final phase of slow growth and a middle phase of fast growth, commencing at a weight of 24.5 kg and an age of 85 days and lasting until the weight of 36-43 kg and age of 180-200 days in both strains. The separation of penile adhesions commenced at a mean body weight and age of 33.6 +/- 3.7 kg and 125.5 +/- 27.4 days respectively and was completed at a mean weight and age of 38.3 +/- 4.2 kg and 153.4 +/- 29.9 days. Only four lambs failed to show complete penile separation. Age had little influence on testis descent or on penile development. Puberty was assessed in 71 lambs using sperm recovery following electroejaculation as an end point. Most of these lambs (92.9%) reached puberty at a mean (SD) age of 171.5 (39.9) days, mean body weight of 39.9 (9.3) kg, mean testis diameter of 4.1 (0.4) cm and mean horn length of 21.4 (3.7) cm. Puberal lambs were significantly superior to non-puberal lambs (P less than 0.01) in all these counts except for age which was similar in both categories. Direct testicular observation showed a strong correlation between testis diameter, testis weight, body weight, sperm concentration/g testis weight and to testis histology. Age was poorly correlated to testis weight, histology or sperm concentration. It is concluded that the body weight is a major determinant of puberty in this breed. It is also considered that the two strains of the breed are remarkably similar in the studied aspects of puberty and sexual development.     

Effects of breed and intake level on growth and feed efficiency in ram lambs

Effects of breed and intake level on growth and feed efficiency in ram lambs were tested with 52 Rambouillet, 46 Dorset and 53 Finnish Landrace (Finn) rams. Rams were individually fed at 100, 85 or 70% of ad libitum or at maintenance. The experimental diet contained 79% digestible dry matter (DM), 3.28% N and 2.95 Mcal metabolizable energy/kg DM. Rams were serially slaughtered every 35 d for 175 d. The efficiency of deposition of body weight, protein, energy and trimmed cuts was determined by breed and intake level over constant time, weight, fat and maturity intervals. Ranking of the breeds for feed efficiency depended upon both the interval and the criterion of evaluation. Efficiency of protein and trimmed cut gain was positively related to mature size in the time and weight intervals, but all differences in efficiency were small in the fat or maturity intervals. Gross energetic efficiency did not differ greatly among breeds in any interval. Dorsets appeared to have a somewhat greater propensity to fatten than the other breeds and to be less able to retain N at a fixed N intake. In the constant time interval, maintenance requirements were estimated to be 115 kcal/kg.75, and the estimated partial efficiencies of energy deposition in fat and protein were .49 and .26, respectively.     

饲料工艺与饲料安全

饲料安全,通常是指饲料产品(包括饲料和饲料添加剂)中不含有对饲养动物的健康造成实际危害,而且不会在畜产品中残留,蓄积和转移的有毒、有害物质或因素;饲料产品以及利用饲料产品生产的畜产品,不会危害人体健康或对人类的生存环境产生负面影响。     

Relationship between performance,metabolic profile,and feed efficiency of lactating beef cows

Tropical Animal Health and Production - Twenty-seven Nellore cow-calf pairs were submitted for feed efficiency testing. The animals were weighed every 21 ± 5 days to...     

On the relationships between glucocorticoids and feed efficiency in beef cattle

Improvement in the utilization of feed in livestock is an important target of breeding and nutritional programs. Recent evidence indicates a potential association between feed efficiency and fecal cortisol metabolites, which could eventually be used as an indirect assessment of this trait. This evidence is more comprehensively evaluated in here with samples for plasma cortisol (PC; ng/ml) and fecal cortisol metabolites (FCM; ng/ml) collected more often during the entire finishing phase in beef steers. Individual daily feed intake of 112 steers fed a high-moisture corn-based and haylage diet was measured over 168 d. Body weight, blood and fecal samples were collected every 14 d and ultrasound measures of backfat thickness and longissimus muscle area were taken every 28 d. Four productive performance traits were calculated: daily dry matter intake (DMI), average daily gain (ADG), feed to gain ratio (F:G) and residual feed intake (RFI). At the end of the feedlot phase, steers were ranked according to RFI and samples were analyzed for PC and FCM from the 32 steers with greatest and 32 steers with lowest feed efficiency. In addition, a sub-group of 12 steers from each of these two groups with divergent feed efficiency were subjected to hourly blood sampling for 24 h. Less efficient steers had greater DMI, F:G and consumed 1.5 kg/d more DMI (P<0.05) than steers with improved feed efficiency. No differences (P>0.10) in PC over the 12 biweekly sampling periods between steers with divergent feed efficiency were observed. However, a trend toward significance between 19:00 and 02:00 h over the hourly sampling evaluation was noticed, with the sub-group of more feed efficient steers presenting higher levels of PC in this period of the day (P=0.08). On the other hand, FCM levels displayed a distinct pattern between RFI groups over the biweekly sampling period, with more efficient cattle presenting greater levels of these metabolites (P<0.05). This study reinforces the positive association between improved feed efficiency and FCM levels over the finishing phase; and the lack of association between feed efficiency and PC when single samples are collected every two weeks through a single jugular venipuncture performed after handling the cattle for sampling. Further studies to develop sampling protocols for assessing FCM as an indicator trait for feed efficiency are warranted, as well as, studies to understand the role of endogenous glucocorticoids in the performance of the bovine.     

Biochemical evaluation of mitochondrial respiratory chain enzymes in canine skeletal muscle

OBJECTIVE: To perform respiratory chain enzymatic activity assays on canine skeletal muscle biopsy specimens and establish reference range values of skeletal muscle enzyme activities for dogs. SAMPLE POPULATION: Biopsy specimens from the vastus lateralis muscle were obtained from 24 dogs (8 sexually intact males and 14 sexually intact females) ranging from 15 months to 6 years of age. PROCEDURE: Mean values of citrate synthase, cytochrome-c oxidase, succinate dehydrogenase, succinate dehydrogenase-cytochrome-c reductase, nicotinamide adenine dinucleotide (NADH) dehydrogenase, and NADH dehydrogenase-cytochrome-c reductase activities were established by use of 6 standard spectrophotometric assays for respiratory chain enzyme analysis. RESULTS: Compared with published data for skeletal muscle enzyme activities in humans, skeletal muscle enzyme activities in dogs were 2- to 4-fold higher. Additionally, citrate synthase activity, a marker for mitochondrial volume, was positively correlated with age in dogs, suggesting that mitochondrial volume increases with age, although no apparent change in respiratory chain enzymatic activity with an increase in age was found. CONCLUSIONS AND CLINICAL RELEVANCE: Reference range values for skeletal muscle enzyme activities of dogs are needed to accurately interpret results of respiratory chain enzymatic activity assays. During investigation of metabolic myopathies, if skeletal muscle biopsy specimens are evaluated for respiratory chain enzyme kinetics, they should be performed and evaluated in concert with skeletal muscle biopsy specimens from clinically normal animals of the same species.     

Relationship between LH and testicular development in progesterone-implanted prepubertal ram lambs

The relationship between systemic luteinizing hormone (LH) and testicular development was investigated in Finn and Suffolk ram lambs treated at 2 wk of age with sc progesterone implants for 0, 4, 8 or 12 wk. Serial samples of blood (30-min intervals for 3 h) were collected from five rams X breed-1 X treatment-1 at 6, 8, 10, 12, 14, 18 and 22 wk of age plus 1 and 2 wk after implant removal. Scrotal circumference was measured at 10, 14, 18 and 22 wk of age. A testicular biopsy was obtained at 14, 18 and 22 wk for microscopic evaluation of testicular development and spermatogenesis. Pulsatile LH releases occurred 60 to 180 min apart in control lambs between 6 and 22 wk of age; LH secretion was not affected by age except for a decrease (P less than .01) in mean LH at 22 wk. Transient increases in testosterone were found subsequent to LH pulses. Systemic testosterone increased (P less than .01) progressively with age, was higher (P less than .05) in Finn than in Suffolk rams at 18 and 22 wk and was correlated positively (P less than .01) within breeds with seminiferous tubule diameter at 14 wk and with scrotal circumference at 10 and 14 wk. Tubule diameter was larger (P less than .01) but testes size and weight were smaller (P less than .01) in Finn than in Suffolk rams. Progesterone implants decreased (P less than .01) LH secretion at 4, 6, 8, 10 and 12, but not at 14 wk of age; decreased systemic testosterone between 4 and 14 wk; decreased (P less than .01) seminiferous tubule diameter at 14 wk, which was related inversely to duration of progesterone treatment; and delayed puberty from 18 to 22 or more wk in rams implanted from 2 to 10 or 14 wk of age. Both control and treated rams with elongated spermatids at 18 vs 22 or more wk had increased LH secretion, higher systemic testosterone and larger tubule diameter and testes size at a younger age. These results suggest that rate of sexual maturation in ram lambs is related to level of postnatal LH stimulation and to the prepubertal age when increased LH stimulation occurs.     

The relationship between mitochondrial function and residual feed intake in Angus steers

The objective of this study was to examine the relationship between mitochondrial function and residual feed intake in Angus steers. Individual feed intakes were recorded for a contemporary group of 40 steers via the GrowSafe feed intake system. Intakes were then used to calculate residual feed intake (RFI), a measure of efficiency. Based on these calculations, 9 low (RFI = -0.83) and 8 high (RFI = 0.78) RFI animals were selected for further study. Blood samples were collected via jugular venipuncture 1 wk before slaughter for the determination of plasma glucose and insulin concentrations. Tissue samples were taken from the LM from both the high and low RFI animals and mitochondria were isolated for measurement of oxygen consumption and hydrogen peroxide production. Average daily gain and carcass composition were not different between the high and low RFI steers; however, ADFI by the high RFI animals was 1.54 kg/d greater (P < 0.001) than for the low RFI animals. Low RFI steers exhibited a greater (P < 0.05) rate of state 2 and 3 respiration, respiratory control ratio, and hydrogen peroxide production than high RFI steers when provided with glutamate or succinate as a respiratory substrate. The acceptor control and adenosine diphosphate:oxygen ratios were not different between the 2 groups for either substrate. When hydrogen peroxide production was expressed as a ratio to respiration rate there was no difference between groups, signifying that electron leak was similar for both groups. Plasma glucose concentration was greater (P < 0.05) in the high RFI steers than in the low RFI steers; however, plasma insulin concentration was not different (P = 0.22) between the 2 groups. The ratio between plasma glucose and insulin concentration was similar (P = 0.88) between the 2 groups indicating no difference in glucose metabolism. The increased plasma glucose concentration observed in the high RFI steers was presumed to be the result of a greater feed intake by these animals. It seems that mitochondrial function is not different between the high and low RFI groups but rather the rate of mitochondrial respiration is increased in low RFI steers compared with high RFI steers.     

饲料安全与畜产品安全关系及建议

饲料是畜禽的食品，饲料安全与畜产品安全密切相关，并近而关系到人类的健康。改革开放以来，我国畜牧业持续稳定发展，人们的膳食结构发生了根本转变，人们对肉、蛋、奶的需求逐渐增加。与此同时，我国畜产品安全问题也突出的表现出来。     

Genetic relationships between feed efficiency in growing males and beef cow performance

Most studies on feed efficiency in beef cattle have focused on performance in young animals despite the contribution of the cow herd to overall profitability of beef production systems. The objective of this study was to quantify, using a large data set, the genetic covariances between feed efficiency in growing animals measured in a performance-test station, and beef cow performance including fertility, survival, calving traits, BW, maternal weaning weight, cow price, and cull cow carcass characteristics in commercial herds. Feed efficiency data were available on 2,605 purebred bulls from 1 test station. Records on cow performance were available on up to 94,936 crossbred beef cows. Genetic covariances were estimated using animal and animal-dam linear mixed models. Results showed that selection for feed efficiency, defined as feed conversion ratio (FCR) or residual BW gain (RG), improved maternal weaning weight as evidenced by the respective genetic correlations of -0.61 and 0.57. Despite residual feed intake (RFI) being phenotypically independent of BW, a negative genetic correlation existed between RFI and cow BW (-0.23; although the SE of 0.31 was large). None of the feed efficiency traits were correlated with fertility, calving difficulty, or perinatal mortality. However, genetic correlations estimated between age at first calving and FCR (-0.55 ± 0.14), Kleiber ratio (0.33 ± 0.15), RFI (-0.29 ± 0.14), residual BW gain (0.36 ± 0.15), and relative growth rate (0.37 ± 0.15) all suggest that selection for improved efficiency may delay the age at first calving, and we speculate, using information from other studies, that this may be due to a delay in the onset of puberty. Results from this study, based on the estimated genetic correlations, suggest that selection for improved feed efficiency will have no deleterious effect on cow performance traits with the exception of delaying the age at first calving.     

Effect of feeding olive-pulp ensiled with additives on feedlot performance and carcass attributes of fat-tailed lambs

Feed cost has a significant effect on the economic efficiency of feedlot lambs; therefore, the use of low-cost non-conventional feedstuffs, such as olive pulp (OP), has the potential to decrease the production costs. Because optimum inclusion of OP-treated silages has not been determined in feedlot lambs, an experiment was conducted to determine the effect of inclusion of OP ensiled with additives in the diet on the feedlot performance and carcass attributes of feedlot lambs. Ram lambs of Mehraban and Ghezel breeds (n?=?50 lambs per breed) were randomly allotted to 10 groups and fed with one of the nine diets containing OP silage or a control diet. Silage treatments were: (1) OP silage without additives (OPS), (2) OP ensiled with 8 % beet molasses and 0.4 % formic acid (OP-MF), and (3) OP ensiled with 8 % beet molasses, 0.4 % formic acid and 0.5 % urea (OP-MFU). The control diet contained 50 % alfalfa hay and 50 % barley grain. Three levels from each silage were chosen to replace the barley grain (10, 20, or 30 % dry matter basis). The lambs were slaughtered after 92 days, and the average daily gain (ADG), feed conversion ratio (FCR), and carcass characteristics were determined. Feeding OPS to fat-tailed lambs, at an inclusion level of 30 %, decreased the carcass dressing percentage, mainly as a result of decreased brisket percentage, but the ADG and FCR values were not adversely affected. Ghezel lambs had higher ADG than Mehraban lambs, but the visceral fat weight percentage, flap weight percentage, and back fat depth were higher in Mehraban. The crude protein content in the longissimus dorsi (LD) muscle was higher in Ghezel, but the dry matter percentage was higher in Mehraban (P?<?0.05). Other attributes were not significantly affected by breed (P?>?0.05). Most carcass characteristics, including major cuts, were not affected by OPS feeding; therefore, feeding OPS (up to 30 %) can be economical for feedlot lambs. Most carcass characteristics, including major cuts, were not affected by OPS levels used in this experiment; therefore, inclusion of OPS (up to 30 %) in the diet may reduce the cost of raising feedlot lambs. This also could help alleviate the problem of storage of OP in oil factories.     

Dietary concentrate level affects the feed sorting behaviour of lambs

The objective of this study was to evaluate the effect of forage concentration on sorting, nutrient intake and feeding behaviour of growing lambs. Twelve weaned lambs were exposed, in a crossover design with 7‐day periods, to each of two treatment diets: (i) lower‐concentrate diet (LC; 40.0% concentrate) and (ii) a higher‐concentrate diet (HC; 60.0% concentrate). Alfalfa hay was used as forage source. Sorting was determined by subjecting fresh feed and ort samples to particle separation and expressing the actual intake of each particle fraction as a percentage of the predicted intake of that fraction. Lambs sorted against long particles (>19 mm) on both treatments. On the LC diet, lambs sorted for medium particles, whereas animals fed the HC diet did not sort for or against medium particles. Lambs sorted for fine particles (<1.18 mm) on both treatments (p < .05). The extent of sorting for the fine particles was greater on the LC diet compared with the HC diet (p < .05). Dry matter intake was increased by increasing the concentrate content of the diet. Intake per visit and eating rate increased, and total chewing time was decreased in lambs fed HC diet. In conclusion, lambs sorted most against the longest particles and for the fine particles. Furthermore, feed sorting behaviour is affected by the forage level, and lambs sorted more for the fine particles in the LC diet.