Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 2. Organ growth, deoxyribonucleic acid, ribonucleic acid, and protein content

Association of feed efficiency with organ characteristics and fatty liver haemorrhagic syndrome in laying hens

Poor feed efficiency (FE) in hens impacts body weight (BW) and may reflect suboptimal health. Fatty Liver Haemorrhagic Syndrome (FLHS) is mostly observed in laying hens and affects egg production and hen performance. The aim of this study was to investigate the relationships of FE and BW with organ characteristics, liver composition and incidence of FLHS of 150 individually housed ISA Brown hens ranked on the basis of feed conversion ratio (FCR) attained from early lay. At 45 weeks, 10 birds per FE group (HFE-High feed efficient; MFE-medium feed efficient; LFE-low feed efficient) were randomly selected and euthanized. Hen BW was positively associated with feed intake and FCR. The HFE hens had a lower abdominal fat pad and liver weight compared to LFE hens. FLHS lesion score was higher (worse) in the LFE than HFE hen group and was moderately positively associated with BW and abdominal fat pad, but strongly positively associated with liver weight. Liver pathology of LFE hens showed hepatocytes with abnormal retention of lipids causing distended cytoplasmic vacuoles compared to the HFE hens. Hens which exhibited poorer FE in early lay had heavier abdominal fat pads, heavier, fatter livers and were more prone to FLHS.

Chickens from lines artificially selected for juvenile low and high body weight differ in glucose homeostasis and pancreas physiology

Artificial selection of White Plymouth Rock chickens for juvenile (day 56) body weight resulted in two divergent genetic lines: hypophagic low weight (LWS) chickens and hyperphagic obese high weight (HWS) chickens, with the latter more than 10-fold heavier than the former at selection age. A study was designed to investigate glucose regulation and pancreas physiology at selection age in LWS chickens and HWS chickens. Oral glucose tolerance and insulin sensitivity tests revealed differences in threshold sensitivity to insulin and glucose clearance rate between the lines. Results from real-time PCR showed greater pancreatic mRNA expression of four glucose regulatory genes (preproinsulin, PPI; preproglucagon, PPG; glucose transporter 2, GLUT2; and pancreatic duodenal homeobox 1, Pdx1) in LWS chickens, than HWS chickens. Histological analysis of the pancreas revealed that HWS chickens have larger pancreatic islets, less pancreatic islet mass, and more pancreatic inflammation than LWS chickens, all of which presumably contribute to impaired glucose metabolism.

Expression profiles of somatotropic axis genes in lines of chickens divergently selected for 56-day body weight

The objective of this study was to evaluate mRNA expression of somatotropic axis genes in chickens divergently selected for high (HWS) or low (LWS) body weight at 56 days of age. Gene expression was measured on days 16, 18, and 20 of incubation, day of hatch, and days 3, 7, 28, and 56 posthatch. Pituitary growth hormone mRNA raised from prehatch to posthatch, with a similar profile in both lines. Liver growth hormone receptor (GHR) mRNA was high during embryogenesis, declined to low levels at day 3 posthatch, and then increased to day 56. Expression of liver insulin-like growth factor 1 (IGF-1) mRNA increased sharply by day 28 in line HWS and day 56 in line LWS. Pectoralis major muscle GHR mRNA was greater in line LWS than HWS. Muscle IGF-1 mRNA declined during embryogenesis, increased posthatch, and declined after day 7. IGF-1 mRNA was 1,000-fold greater in embryonic muscle than embryonic liver. Muscle IGF-1 receptor mRNA was greater in line LWS than HWS posthatch. These results demonstrate that genetic selection for high or low body weight has altered the expression profiles of somatotropic axis genes in a line-, age-, and tissue-specific manner.

Effects of delayed feed intake on body, intestine, and muscle development in neonate broilers

The short-term effects of delayed feeding (DF) for 2 d posthatching were measured in neonate chicks and compared to early feeding (EF). Chicks from 10 independent families were used in this study to determine whether genetic background control of growth may be influenced by EF and DF. Early feeding maintained significant interfamily body weight variations from hatch to 4 d of age, whereas there were no significant differences from 1 d of age when feeding was delayed to 48 h posthatching. These results suggest that posthatching feeding delay may distort genetic selection by masking the expression of genetic potential and disturbing the estimation of chick breeder value. In DF chicks, overall body growth was delayed until the beginning of feeding and body weight at 6 d of age was 25% lower than EF chicks. Availability of feed after the fasting period was not sufficient to compensate for the retardation of weight gain in either body weight or in intestine and breast muscle weight. However, initiation of intestine growth in DF chicks occurred from 1 d of age despite the lack of feeding, whereas feed intake was essential to enhance muscle growth. The potential for protein synthesis was lower in DF than in EF chicks during the first 2 d posthatching (P < 0.001) and then reached similar values after feed intake. These results confirm that initiation of growth in neonate chicks is improved by earlier feeding after hatching. Awareness of changes in overall body weight caused by posthatching food deprivation, especially in the intestine and muscle might help in the development of new diets which could minimize retardation of body weight gain in chicks.

Expression of myostatin is not altered in lines of poultry exhibiting myofiber hyper- and hypoplasia

Decades of selective breeding have yielded lines of poultry with substantial myofiber hyperplasia, vet little is known about what genes have been altered during the course of selection. Myostatin is a strong negative regulator of muscle mass in mice and cattle and could have been one of many genetic factors contributing to increased myofiber deposition in growth-selected lines of poultry. To test this hypothesis, the sequence and expression patterns of myostatin were analyzed in growth-selected lines of chickens and quail. The sequence of broiler myostatin cDNA, amplified via reverse transcription (RT)-PCR from embryonic muscle RNA, contained no missense mutations in the coding sequence when compared to that of White Leghorn layers, although two silent single nucleotide polymorphisms (SNP) were found. Northern analysis of myostatin transcripts from embryonic pectoralis and quadriceps showed no significant differences in expression levels between broiler and layer muscle RNA. However, levels of myostatin transcripts were greatly reduced in muscles of posthatch chicks compared to embryonic muscle. Myostatin protein was also present in broiler and layer embryonic muscle at similar levels. No significant polymorphisms or differences in RNA expression levels were found in embryonic muscles of divergently selected lines of Japanese quail. These results indicate that intense artificial selection in these growth-selected lines of poultry has neither silenced the expression of myostatin nor created null alleles via mutation in the lines analyzed.

In ovo peptide YY administration improves growth and feed conversion ratios in week-old broiler chicks

The effects of in ovo Peptide YY (PYY) administration on growth and feed conversion ratios in a commercial broiler line were investigated. Six hundred Ross male x Cobb female eggs were administered either 0.9% saline (control) or 600 microg/kg egg weight PYY in ovo at Day 18 of incubation. On day of hatching, 210 birds from each treatment group were randomly placed by sex into pens. Body weights at placement were not different between treatment groups. Average chick body weight and adjusted pen feed conversion ratios were improved by PYY in ovo treatment at 7 d posthatch (165.7 vs. 170.2 g, P<0.02; and 1.55 vs. 1.49, P<0.04, respectively). No significant differences between treatments were noted for these parameters at 21 or 42 d of age. These results suggest that in ovo treatment of broiler chicken eggs with gastrointestinal hormones that increase intestinal nutrient absorption, such as PYY, may enhance chick performance.

Jejunal glucose uptake and oxygen consumption in turkey poults selected for rapid growth

Two lines of turkey poults, one selected for rapid growth at 16 wk of age (F line) and the other a randombred control line (RBC2) were used to investigate the effect of selection for rapid growth on jejunal O2 consumption and glucose transport as well as whole-body O2 consumption. All trials used unsexed poults and were designed as a randomized complete block with day and line as independent variables. In Trial 1, 120 turkey poults, fed a standard starter ration (25.5% CP), were used to examine the effect of selection on feed intake, body weight gain, and efficiency from hatching (Day 0) to 13 d of age. At Day 14, 36 of 60 birds from each line were killed to measure intestinal length and weight and jejunal O2 consumption after 18 h of feed deprivation. Compared with the RBC2 line, the F line had relatively shorter but heavier small intestinal segments when adjusted by 18 h feed-deprived body weight (FBW; P < 0.001). The F line consumed more O2 over the entire jejunum adjusted to FBW than RBC2 line (43.8 vs 34.6 nmol O2/min.g FBW; P < 0.001). Jejunal ouabain- and cycloheximide-sensitive O2 consumption were greater (P < 0.05) in the F line. In Trial 2, 16 14-d-old poults from each line were used to measure in vitro jejunal glucose transport rate. There was no difference in glucose transport of the jejunum (nanomoles per minute per gram of FBW) between the lines. In Trial 3, 20 poults from each line were used to measure whole-body O2 consumption at 7 to 10 d of age. The F and RBC2 lines had similar whole-body O2 consumption rate per gram of FBW. These data suggest that selection of turkeys for rapid growth at 16 wk of age did not increase efficiency of jejunal glucose uptake in 14-d-old turkey poults.

Long-term divergent selection for eight-week body weight in white Plymouth rock chickens

This paper provides an overview of results from a long-term (38 generations) selection experiment. Lines were developed from individual phenotypic selection for high or low body weight at 8 wk of age. Included are data for the selected lines, sublines in which selection was relaxed, crosses of the selected lines, and sublines in which the sex-linked dw gene was introduced. Periodically (and in some cases every generation) data were obtained for unselected traits. These unselected traits included feed consumption and intake behavior, reproduction, allomorphic relationships, and metabolic, immunological, endocrine, and molecular factors. These responses have been integrated into a resource allocation paradigm.

Growth related traits in body weight selected lines and their crosses reared under different nutritional regimens

1. Four populations--two that had undergone 37 generations of selection for high (HH) and low (LL) body weight, and reciprocal crosses between them (HL and LH) were fed two diets differing in protein and energy. Diet A, under which selection had been made, contained 200 g protein and 11.23 MJ/kg. Diet E contained 240 g protein and 13.16 MJ/kg. 2. Body weight and feed efficiency were measured weekly from hatch to 56 d of age at which time oesophagus, abdominal fat pad, heart, liver and lungs were removed and weighed. At 35 d of age chicks were inoculated with sheep erythrocytes (SRBC) and antibody titre was measured 6 d later. 3. Chicks fed diet E were heavier than those fed diet A. HH chicks were heavier than LL chicks with HL and LH chicks intermediate to the parental lines. LH chicks were heavier than HL ones reflecting large maternal effects. 4. Food efficiencies among stocks and diets were consistent with those for body weight, with HH > LH > HL > LL and E > A. Relative differences between diets were similar across ages and heterosis for food efficiency was about 15%. 5. Relative to body weight, oesophagus and liver weights were heavier in chickens fed diet A than fed diet E. The pattern reversed for abdominal fat pad. 6. Antibody to SRBC antigen was greater in the crosses than in line HH and in cross HL than line LL, with heterosis of 70%.