The effects of feed intake and body fatness on progesterone metabolism in ovariectomized gilts

We studied the effects of feed intake and fatness on metabolic clearance rate (MCR) and half-life of progesterone in 40 ovariectomized gilts (10x4 littermates). One gilt from each litter was randomly allocated to each of four treatments in a randomized block design. Gilts were reared to be either lean (Ln), 113 kg BW and 10 mm backfat measured 65 mm from the midline at the level of the last rib (P2), or fat (F), 124 kg BW and 20 mm P2 backfat. They were ovariectomized and fitted with bilateral jugular catheters. Fat and Ln gilts were then fed either low (1.15 x maintenance energy, L), or high (2.30 x maintenance energy, H) feed intakes. Gilts received an i.m. injection of 130 mg of progesterone on two consecutive days (d1 and 2). From d 3, progesterone was infused at 5.4 mg/h (130 mg/d) for 60 h. Blood samples for progesterone analysis were taken during the last 24 h of infusion and for a further 72 h. Gilts were then slaughtered, and livers were sampled for microsomal studies. Fatness did not affect any aspect of progesterone metabolism measured. Postprandial MCR was greater in H than in L gilts, 103.0 vs. 76.1 mL x min(-1) x kg BW(-1) (P<.01), respectively. Feed intake did not affect the disappearance rate constant of progesterone (mean -.019), and the estimated half-life of progesterone was 36.5 h. High-intake gilts had larger proportional liver size (P<.001) than L gilts. Microsomal metabolism of progesterone and P450 enzyme concentration were similar across treatments. We conclude that increasing feed intake increases MCR of progesterone and could be used to manipulate progesterone concentration in sows.     

Effect of growth hormone-secreting tumors on body composition and feed intake in young female Wistar-Furth rats

Growth hormone (GH) was elevated in young growing, intact female Wistar-Furth rats bearing growth hormone (GH1) or growth hormone and prolactin (GH3) secreting tumors. Animals were injected with GH1 or GH3 cells at 1 wk of age. Total feed intake was measured for the 8-wk period from weaning until killed at 11 wk of age. Animals were fed a commercial chow diet throughout the trial. Body composition and composition of the liver and tibialis anterior muscle were determined. Tumor-bearing rats were about 65% heavier than control rats at 11 wk of age: most of the difference in body weight gain was obtained during the last 4 wk of the trial. Total feed intake during the 8 wk after weaning was increased in both GH1 and GH3 tumor-bearing rats when compared with controls. Overall feed efficiency (grams feed consumed/gram body weight gain) was improved in tumor-bearing animals when compared with controls. The GH1 tumor-bearing rats were slightly hyperphagic during wk 8, 9 and 10 (grams feed consumed/gram body weight) when compared with controls. The total amount of body dry matter, protein and ash was increased in tumor-bearing rats when compared with controls. There was no effect on total body fat. Tumor-bearing rats had increased liver weight and increased fat, protein, RNA, DNA and dry matter content when compared with controls. Tumor induction increased the weight, total RNA and total fat content of the tibialis anterior muscle when compared with controls. There was no effect on muscle protein content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of rumen-protected nutrients on feed intake,body weights,milk yield,and composition in Murrah buffaloes during early lactation

The effect of rumen-protected nutrients (bypass fat, BPF; bypass protein, BPP; or their combination, BPPF) was investigated in Murrah buffaloes during the early stage of lactation. Forty Murrah buffaloes (BW 531.92?±?10.85 kg) just after parturition were randomly distributed into four groups according to parity and milk production. Buffaloes individually fed ration from day 0 to 90 postpartum according to feeding group and nutrient requirement. Control and BPF fed groups received a concentrate mixture, CM1 with 25% rumen-protected protein (using barley, wheat bran, and mustard oil cake), BPP and BPPF groups received a second concentrate mixture, CM2 with 40% rumen-protected protein (using barley, de-oiled rice bran, and cottonseed cake). Bypass fat fed groups (BPF and BPPF) additionally were supplemented with 15 g BPF (Ca salt of long-chain fatty acids) per kg milk yield in their respective concentrate mixtures. Dry matter intake, body weights, body condition score, and total milk yield were similar between groups (P?>?0.05). Fat-corrected milk (FCM) production was improved (14.5%, P?>?0.05) in groups fed BPP and BPPF, while significant (19.45%, P?<?0.05) improvement was observed in BPF-fed group. Overall mean values of milk fat, solid not fat, protein, lactose, and total solids were found to be high (P?<?0.05) in treatment groups as compared with control values. It may be concluded that supplementation with BPP or BPF either alone or in combination positively influences the quality of milk produced in Murrah buffaloes during early lactation and BPF additionally had improvement on the quantitative trait of milk as well.

     

The influence of premating feed intake on the reproductive performance of gilts.

In an attempt to improve the reproductive performance of gilts mated at puberty, 70 Yorkshire x Landrace gilts were allocated at 120 d of age and 60 kg body weight to one of two treatments. Restricted gilts were fed 2.0 kg d-1 of a diet formulated to provide 18% crude protein and 14.5 MJ DE kg-1 from selection until mated at their first estrus (n = 35). Flushed gilts were fed 2.0 kg d-1 of the same diet from 120 to 150 d of age, but then had their feed intake increased to 3.5 kg d-1 until mated at their first estrus (n = 35). An additional group of gilts (control fed; n = 33) were fed 3.0 kg d-1 from selection until they were bred at their third estrus in order to investigate the influence of feed restriction on the onset of puberty. During gestation all gilts were fed 1.8 to 2.2 kg d-1 of a 16.8% crude protein diet having 13.7 MJ DE kg-1. Control fed gilts were younger (p less than 0.05) at puberty (150 d) than restricted (165 d) or flushed gilts (165 d). There was no difference in subsequent litter size between the restricted and flushed gilts (7.7 and 8.0, respectively). It is concluded that the institution of a flushing nutritional regime in the prepubertal period will not enhance piglet production from gilts mated at puberty.     

Consequences of different patterns of feed intake during the estrous cycle in gilts on subsequent fertility

The impact of different patterns of feed restriction between d 1 and 15 of the estrous cycle on subsequent reproductive performance of 23 trios of littermate gilts was tested. Some gilts were fed a high plane of nutrition (HH gilts) throughout the cycle, in contrast to HR gilts, which were restricted from d 8 to 15, and RH gilts, which were restricted from d 1 to 7. During feed restriction, weight gain in RH gilts (2.5 +/- .7 kg) was lower (P = .006) between d 1 and d 7 than in their HH and HR littermates (5.6 +/- .7 and 5.6 +/- .8 kg, respectively) and it was lower (P = .0001) in HR gilts (5.5 +/- .5 kg) between d 8 to d 15 than in their HH and RH counterparts (8.5 +/- .4 and 9.4 +/- .5 kg, respectively). There were no differences in backfat changes among groups. Embryonic survival in HR gilts at d 28 of gestation (68.3 +/- 4.8%) was lower (P < .05) than in HH and RH gilts (83.6 +/- 4.3 and 81.7 +/- 4.5%, respectively). Plasma progesterone concentrations in HR gilts were lower (P < .05) at 48 and 72 h after onset of standing estrus (.82 +/- .2 and 3.6 +/- .5 ng/mL, respectively) than in HH and RH gilts (1.44 +/- .2 and 1.24 +/- .2 ng/mL, 5.0 +/- .4 and 5.0 +/- .5 ng/mL, respectively at 48 and 72 h). No differences in ovulation rate were observed among treatments. Placental area was positively correlated to embryo size at d 28 (embryo size = .0003 x (area) + 18.35; r = .28, P = .03) but placental volume was negatively correlated to the number of embryos in utero (placental volume = -4.317 x (number) + 207.55, r = -.39, P = .002). These data demonstrate that the timing of feed restriction during follicular development has important consequences for subsequent embryo survival, possibly mediated by differences in progesterone concentrations in early pregnancy.     

Evidence of residual feed intake reranking in crossbred replacement heifers

The objective of the study was to examine whether residual feed intake (RFI) reranking exists between 2 consecutive periods in replacement heifers fed the same diet. The study collected feed intake and BW data from 190 crossbred heifers over a 3-yr period (61 in 2007, 68 in 2008, and 61 in 2009) during the winter-spring season. The heifers were fed a roughage-based diet (90% barley silage and 10% rolled barley grain) throughout the feeding trial, which was broken down into 2 feeding periods with ADG of 0.94 and 0.90 kg?d(-1) in the first and second periods, respectively. The RFI was calculated for the entire period using different models, which included ADG, mid-metabolic BW, body composition, and feeding activity. Gain:feed ratio and Kleiber ratio were also calculated. Rank correlations among the RFI calculated from different models were obtained, as well as rank correlations between the 2 feeding periods for the feed efficiency measures. Including body composition and feeding activity only improved the R(2) by 1 to 5%. The rank correlations among the different models were high (90 to 95%) for RFI calculated for the entire feeding period. However, the RFI calculated within the second feeding period had greater rank correlation than the RFI calculated from the entire feeding period. Compared with G:F and Kleiber ratio, RFI gave lesser reranking between periods 1 and 2. About 49% of the heifers maintained their RFI class, whereas 51% of the heifers had a different RFI class in period 2. Furthermore, 41% of the heifers changed their RFI in period 2 by <0.5 SD, whereas the rest of the heifers changed by ≥0.5 SD. These results indicate that reranking exists in heifers despite receiving the same diet in the 2 feeding periods and that the reranking may be more serious in heifers (28%) with extreme RFI performances in each period.     

Dietary nano-chromium tripicolinate increases feed intake and decreases plasma cortisol in finisher gilts during summer

Chromium (Cr) is an essential mineral element and has been used in pig diets to improve growth performance, insulin sensitivity, immune response and carcase traits and to reduce heat or other stress responses. The aims of thiss study were to determine the impact of nano-sized chromium tripicolinate (nCrPic) on growth performance, feed efficiency and carcase characteristics of finisher gilts during the summer period. A total of 60 finisher Large White x Landrace gilts were stratified on initial weight and then within strata randomly allocated into two treatment groups in three replicates during mid-summer for 28 days. All pigs were housed in individual pens and had ad libitum access to feed and water. Pigs were fed either a control finisher diet (wheat-based diet containing 13.8 MJ digestible energy (DE) per kilogram and 0.56 g available lysine/MJ DE) or a control diet containing 400 ppb Cr as nCrPic. Dietary nCrPic supplementation increased feed intake by 6 % over the entire study (P?=?0.05). In particular, dietary nCrPic increased average daily feed intake (ADFI) by 8 % (P?=?0.02) during the final 2 weeks of the study. Moreover, dietary nCrPic tended to improve average daily feed (ADFI) over the entire study (P?=?0.09). However, there were no significant effects of nCrPic on feed conversion ratio (FCR), final weight, hot standard carcase weight (HCWT), P2 depth or dressing percentage. Plasma cortisol was decreased by 25 % (P?=?0.06) by dietary nCrPic supplementation. However, there were no effects of nCrPic on plasma glucose, insulin and nonesterified fatty acids (NEFA), might because of the higher feed intake. In conclusion, this study demonstrates that dietary nCrPic supplementation at 400 ppb can increase feed intake in finisher gilts during mid-summer, suggesting that nCrPic can ameliorate some of the negative effects of heat stress in pigs, possibly via decreased of circulating cortisol.     

Residual feed intake, body composition, and fertility in yearling beef heifers

One hundred thirty-seven spring-born yearling beef heifers of British breed types were used to determine the relationships between residual feed intake (RFI) and growth rate, body composition, mature size, and fertility. Heifers were housed in a dry lot facility during the experimental period, and data were collected over a 2-yr period (yr 1, n = 67; yr 2, n = 70). Individual feed intake, BW, BCS, hip height, and ultrasonic measurements [subcutaneous rib fat (UBF), rump fat (URF), LM area (LMA), and intramuscular fat (IMF)] of body composition were recorded. Individual feed intakes (kg of TDN consumed/d) were used to calculate RFI combining both years of data. Heifers averaged 387.0 ± 19.4 d of age and 337.1 ± 29.9 kg of BW at initiation of the experiment. Mean ADG was 1.14 ± 0.21 kg/d during the trial. Based on RFI, with year of test and farm of origin included in the model as covariates, heifers were classified into groups: positive (POS; 0.74 kg of TDN/d) or negative (NEG; -0.73 kg TDN/d) for first analysis and high (HI), medium (MED), or low (LO; mean RFI = 1.06, -0.01, and -1.13 kg of TDN/d, respectively) subsequently. An initial phenotypic relationship (P < 0.05) between RFI and both UBF and URF (r = 0.19 and 0.17, respectively) was sustained (P < 0.01) with UBF (r = 0.27) and URF (r = 0.24) to trial conclusion. No other correlations with RFI were significant. Heifers classified as POS reached puberty earlier than those classified as NEG (414 ± 3.83 vs. 427 ± 4.67 d of age, P = 0.03), and possessed greater LMA per 100 kg of BW (LMACWT) at conclusion of the trial (P < 0.01). Medium heifers exhibited less URF (P < 0.05) compared with either HI or LO heifers at trial initiation. Low heifers possessed less LM area (cm(2)) per 100 kg of BW (P < 0.05) than HI but did not differ (P > 0.10) from MED heifers at either the beginning or the end of test. Additionally, a negative linear relationship was observed between RFI and age at puberty (P < 0.05). Each 1-unit increase in RFI corresponded to a decrease of 7.5 d in age at puberty, but did not affect pregnancy or conception rates (P > 0.10). Differences in body fat and rate of metabolism associated with RFI could delay reproductive maturity.     

Effects of increased dietary energy and protein during late gestation on mammary development in gilts

Thirty-two gilts were used to evaluate the effects of increased dietary energy and CP during late gestation on mammary development. On d 75 of gestation, gilts were assigned randomly in a 2 x 2 factorial arrangement to adequate (5.76 Mcal ME/d) or increased (10.5 Mcal ME/d) energy and adequate (216 g CP/d) or increased (330 g CP/d) protein. On d 105 of gestation, gilts were slaughtered and total mastectomies were performed. Mammary tissue was separated into mammary parenchymal and mammary extraparenchymal stromal tissue and analyzed for DNA, RNA, protein and lipid. No interactions between dietary energy and protein level were detected (P greater than .20). When adjusted for number of mammary glands and maternal BW (weight of the sow less the weight of the fetuses), mammary parenchymal weight was 27% greater (P less than .03) in gilts fed adequate energy than in gilts fed increased energy, but mammary extraparenchymal stroma weight was unaffected by dietary energy level. Total mammary parenchymal DNA was 30% greater in gilts fed adequate energy than in gilts fed increased energy (P less than .03). Total mammary parenchymal RNA (P less than .02) and total mammary parenchymal protein (P less than .02) also were greater in gilts fed adequate energy than in gilts fed increased energy. Dietary protein level did not affect mammary variables measured, except that increased dietary protein tended to reduce mammary extraparenchymal stromal weight (P less than .09). Increased dietary protein between d 75 and d 105 of gestation did not benefit mammary development, but increased dietary energy was detrimental to development of mammary secretory tissue.     

Effect of selection for growth on normal and reduced protein diets on weight gain, feed intake, feed efficiency and body composition in mice

Mice selected for weight gain from 3 to 9 weeks of age on a normal (N) protein diet containing 19.3% protein and a reduced (R) protein diet with 5.1% protein were reared on both diets in generations 7 and 9. The lines NH, NC, NL, RH, RC and RL (H, high; C, control; L, low) were tested for weight gain on diet N and R and for feed intake and feed efficiency on diet N in generation 7. In generation 9, the lines were tested for body composition traits (fat, protein and water percentage) at 3, 6, 9 and 12 weeks of age on both diets. A significant (p < 0.0001) genotype × environment interaction for growth rate was observed in generation 7. Weight gain at both the protein levels was best improved by selection at the protein level itself. Furthermore, the ranking of the lines on diet N was similar for weight gain, feed intake and feed efficiency. In generation 9 at 9 weeks of age, the ranking of the lines for fat percentage was equal to the ranking for weight gain in generation 7 on both test‐diets. The association between weight gain and protein or water percentage was less pronounced, particularly on diet R. These results suggest that the largest genetic improvement in growth rate is obtained when the protein content of the feed is the same in selection and production. However, when selection is carried out in one environment while the animals have to perform under conditions with varying nutrient protein contents, selection in an inferior environment may be advantageous.     

Lactation efficiency as a result of body composition dynamics and feed intake in sows

Through genetic selection and improvement of environment, litter size of sows increases. Increased energy requirement during lactation, increases the risk of excessive mobilization from body stores, with detrimental effects on reproductive performance. Feed intake capacity tends to decrease due to selection towards leaner pigs with a lower feed conversion ratio. However, to facilitate sows to wean large litters extra feed intake, or even better, a higher feed efficiency during lactation would be favourable. The objective of the present study was to describe the dynamics of body composition of sows and piglets during lactation, and to relate these traits to a newly introduced trait called “lactation efficiency”. Energy metabolism of lactating sows was described, based on on-farm observations of weight and backfat of sows before parturition and at weaning, weight of piglets at birth and at weaning and feed intake of sows during lactation. “Lactation efficiency” was defined as energy efficiency of sows, and calculated for individual sows at two different farms. The average lactation efficiency was 68% and 65% for both farms; meaning that 68 and 65% of the metabolisable energy through feed intake or mobilization from body stores, above maintenance of the sow (input), was used for piglet growth and piglet maintenance (output). The association between lactation efficiency and other reproductive traits was studied by estimating the correlations within farms. Sows with a higher lactation efficiency showed lower feed intake (r = − 0.27 and r = − 0.35 for both farms respectively) and smaller fat losses (r = − 0.34 and r = − 0.29, respectively). The energy output of efficient sows was slightly higher (r = 0.23 and r = 0.30). The more efficient sows were the better mothers, as mortality of their piglets was lower (r = − 0.12 and r = − 0.16), piglet growth rate was higher (r = 0.16 and r = 0.23), and at weaning their litters were less variable (r = − 0.08; only available at one farm). Results were remarkably similar for the two farms, despite different feeding strategies. Extra input, by means of feed intake or mobilization from body stores generated extra output by means of litter weight at weaning. This experiment demonstrated that an accurate recording of energy metabolism and relevant reproduction traits with little intervention is possible on commercial farms.     

Effect of supplementation on the feed intake and performance of confined and scavenging crossbred growing chickens in Burkina Faso

An experiment was conducted to evaluate the performance of crossbred growing chickens (Rhode Island Red × indigenous Burkina Faso hens) from 6 to 17 weeks of age, under five feeding/management regimes: (1) CMx(+), confined and given a mixed feed containing cracked maize and cowpea and a vitamin–mineral premix ad libitum; (2) CS(+), confined and offered ad libitum a choice of cracked maize and cowpea with the premix; (3) ScS(+), scavenging from 09:00 to 16:00 with the diet in treatment (2) available from 16:00 to 09:00; (4) ScS(−), treatment (3) but without the premix; and (5) ScO, scavenging only, with no supplements provided. Daily dry matter (DM) intake was highest for CS(+) (43.5 g), and lowest for CMx(+) (33.6 g) (p < 0.05), with intermediate intakes for ScS(+) and Sc(−) of 36.7 g and 36.2 g, respectively. The ratios of intakes of cowpea to maize were 50:50, 21:79, 27:73 and 22:78 for CMx(+), CS(+), ScS(+) and ScS(−), respectively (p < 0.05). Dietary concentrations of crude protein (CP) were 15.7%, 11.5%, 12.3% and 11.6% of DM for CMx(+), CS(+), ScS(+) and ScS(−), respectively. Average daily gains (ADG) were 8.15 g, 5.24 g, 6.03 g, 5.36 g and 4.45 g for CMx(+), CS(+), ScS(+), ScS(−) and ScO, respectively, and were significantly higher for CMx(+) (p < 0.05). Feed conversion ratio was highest for CS(+) and lowest for CMx(+). ADG of the males (6.44 g) was significantly (p < 0.05) higher than that of the females (5.86 g). Breast and thigh muscle weights were highest for ScS(+) (p < 0.05).     

Partial-genome evaluation of postweaning feed intake and efficiency of crossbred beef cattle

The effects of individual SNP and the variation explained by sets of SNP associated with DMI, metabolic midtest BW, BW gain, and feed efficiency, expressed as phenotypic and genetic residual feed intake, were estimated from BW and the individual feed intake of 1,159 steers on dry lot offered a 3.0 Mcal/kg ration for at least 119 d before slaughter. Parents of these F(1) × F(1) (F(1)(2)) steers were AI-sired F(1) progeny of Angus, Charolais, Gelbvieh, Hereford, Limousin, Red Angus, and Simmental bulls mated to US Meat Animal Research Center Angus, Hereford, and MARC III composite females. Steers were genotyped with the BovineSNP50 BeadChip assay (Illumina Inc., San Diego, CA). Effects of 44,163 SNP having minor allele frequencies >0.05 in the F(1)(2) generation were estimated with a mixed model that included genotype, breed composition, heterosis, age of dam, and slaughter date contemporary groups as fixed effects, and a random additive genetic effect with recorded pedigree relationships among animals. Variance in this population attributable to sets of SNP was estimated with models that partitioned the additive genetic effect into a polygenic component attributable to pedigree relationships and a genotypic component attributable to genotypic relationships. The sets of SNP evaluated were the full set of 44,163 SNP and subsets containing 6 to 40,000 SNP selected according to association with phenotype. Ninety SNP were strongly associated (P < 0.0001) with at least 1 efficiency or component trait; these 90 accounted for 28 to 46% of the total additive genetic variance of each trait. Trait-specific sets containing 96 SNP having the strongest associations with each trait explained 50 to 87% of additive variance for that trait. Expected accuracy of steer breeding values predicted with pedigree and genotypic relationships exceeded the accuracy of their sires predicted without genotypic information, although gains in accuracy were not sufficient to encourage that performance testing be replaced by genotyping and genomic evaluations.     

Effect of diet composition and feed intake level on diet digestibility and ruminal metabolism in growing lambs.

Lambs (29 +/- 2.5 kg) were fed three diets at various intakes to determine whether diet composition or level of intake was reflected in changes in diet digestibility or ruminal fluid characteristics. In Exp. 1, a 90% concentrated, pelleted diet or a whole shelled corn diet with a pelleted protein supplement was fed at three levels of intake: ad libitum and 92.5 and 85% of ad libitum (n = 15). Exp. 2 compared the 90% concentrate diet with diets in which the energy density was diluted to 55 or 72.5% concentrate by including alfalfa hay as a possible method of restricting energy intake (n = 6). Lambs were adapted to diets for 13 d; feces were collected for 6 d and ruminal fluid was collected 0, 3, and 6 h after feeding on the day following fecal collection. Restricting intake in Exp. 1 did not affect DM digestibility or digestibility of CP or starch. Digestibility of ADF was increased (P less than .10) by restricting intake. Ruminal fluid pH, ammonia concentration and VFA concentrations were affected little by either restricted intake level. Digestibility of DM was 4% higher (P less than .001) and starch 5% higher (P less than .001) for the whole shelled corn diet than for the pelleted, high-concentrate diet. Ruminal pH of lambs fed the whole shelled corn diet was higher and fluctuated less than the ruminal pH of lambs fed the high-concentrate, pelleted diet. In Exp. 2, diet digestibility was reduced (P less than .01) and ruminal pH was increased (P less than .002) by addition of hay. Restricted feeding of lambs did not seem to increase diet digestibility or alter ruminal conditions.     

Accuracy of genomic breeding values for residual feed intake in crossbred beef cattle

The benefit of using genomic breeding values (GEBV) in predicting ADG, DMI, and residual feed intake for an admixed population was investigated. Phenotypic data consisting of individual daily feed intake measurements for 721 beef cattle steers tested over 5 yr was available for analysis. The animals used were an admixed population of spring-born steers, progeny of a cross between 3 sire breeds and a composite dam line. Training and validation data sets were defined by randomly splitting the data into training and testing data sets based on sire family so that there was no overlap of sires in the 2 sets. The random split was replicated to obtain 5 separate data sets. Two methods (BayesB and random regression BLUP) were used to estimate marker effects and to define marker panels and ultimately the GEBV. The accuracy of prediction (the correlation between the phenotypes and GEBV) was compared between SNP panels. Accuracy for all traits was low, ranging from 0.223 to 0.479 for marker panels with 200 SNP, and 0.114 to 0.246 for marker panels with 37,959 SNP, depending on the genomic selection method used. This was less than accuracies observed for polygenic EBV accuracies, which ranged from 0.504 to 0.602. The results obtained from this study demonstrate that the utility of genetic markers for genomic prediction of residual feed intake in beef cattle may be suboptimal. Differences in accuracy were observed between sire breeds when the random regression BLUP method was used, which may imply that the correlations obtained by this method were confounded by the ability of the selected SNP to trace breed differences. This may also suggest that prediction equations derived from such an admixed population may be useful only in populations of similar composition. Given the sample size used in this study, there is a need for increased feed intake testing if substantially greater accuracies are to be achieved.     

杂交改良与饲料组成对羔羊育肥性能的影响

以杂交改良和饲料组成为试验因子,对育肥羔羊的增重速度、饲料效率和增重的饲料成本进行了试验研究.试验动物为70日龄断奶羔羊26头,分为3组,即对照组（小尾寒羊8头）、试验1组（小尾寒羊8头）和试验2组（道寒杂一代10头）.分别配置饲料配方,全混合日粮颗粒饲料充分饲喂,进行为期65天的强度育肥.试验表明：杂一代育肥羔羊提高增重速度14.05%,提高饲料转化率4.70%;杂交和优质饲料的共同作用使增重速度提高22.46%,饲料效率提高11.45%.使用一定比例苜蓿草粉作为日粮粗饲料的成本优势体现在100日龄以前,此后适当增加玉米秸秆粉降低日粮成本是可行的.     

Effect of dietary beta-carotene on the early embryonic development and uterine fluid composition of gilts

The role of beta-carotene in reproduction was investigated in gilts assigned to three dietary supplementations: VA (4000 IU vitamin A); VA + VA (4000 IU + 8300 IU); VA + BC (4000 IU + 100 mg beta-carotene) per kg diet for 14 weeks. Gilts were slaughtered at day 12 of gestation. In the VA + BC group, number of corpora lutea was lowest, but the number of embryos was greatest, resulting in a non-significant decreased prenatal mortality (p<0.07). The proportion of less developed spherical and tubular embryos compared with filamentous was greatest in the VA + BC group (p<0.01). No differences were observed for vitamin A and retinal binding protein (RBP) in the uterine fluid. When animals were grouped according to the development of blastocysts, vitamin A and RBP levels were higher in the VA + BC group with only filamentous embryos (p<0.01). This indicates that the supplementation of beta-carotene to gilts might affect embryonic losses possibly because of slower alterations in the uterine environment, resulting in a higher and less variable number of embryos, despite an apparently more heterogeneous development.