F-strain Mycoplasma gallisepticum (FMG) may alter reproductive performance in layers through its effects on lipid metabolism. Therefore, the influences of 1.5% supplemental dietary poultry fat (PF) and FMG infection on the early performance of commercial egg-laying hens were determined. Birds were either sham- or FMG-inoculated at 12 wk, and experimental diets were initiated at 20 wk of age. Body weight at 12, 20, and 24 wk, total daily egg mass, feed consumption and feed conversion at 20 and 24 wk, weekly egg weight between 19 and 26 wk, weekly egg production (EP) between 18 and 26 wk, and weekly mortality between 12 and 26 wk of age were determined. Inoculation with FMG reduced EP at 18 and 19 wk of age. Between 20 and 26 wk, FMG reduced EP in birds fed control diets, conversely, PF eliminated differences in EP between sham- and FMG-inoculated birds. Furthermore, at wk 20 and 24, birds consumed less feed when fed PF-supplemented diets than when fed control diets if they were sham-inoculated, but the difference in feed consumption between diets was ameliorated if birds were previously inoculated with FMG. These data demonstrate that the effects of a 12-wk inoculation of FMG on EP and feed consumption through 26 wk of age in commercial egg-laying chickens can be modified by 1.5% supplemental dietary P F. More specifically, PF may alleviate reductions in early EP due to FMG.

In two trials, the effects of an F-strain Mycoplasma gallisepticum (FMG) inoculation at 12 wk of age on the blood characteristics of commercial Single Combed White Leghorn laying hens were investigated throughout lay. Variables measured in both trials were whole blood hematocrit, plasma protein (PP), and serum cholesterol, triglycerides (ST), and calcium. In both trials, hematocrit at 20 wk of age was significantly increased in birds inoculated with FMG. In trial 1, ST and PP were significantly increased at 22 wk of age by FMG, while ST and PP were significantly decreased in FMG-inoculated birds at wk 54 and 52, respectively. When combined with the establishment of an FMG infection, the initial weeks of egg production become particularly stressful to the bird. Increases in these independent blood parameters between 8 and 10 wk postchallenge are suggestive of compensatory responses in these birds to an FMG challenge. Postpeak decreases in both ST (54 wk) and PP (52 wk) in FMG-infected birds may be the result of a more chronic effect of FMG on lipid and protein synthesis in the liver. These data are the first to suggest that alterations in egg production in response to FMG-infection in commercial layers, as noted in a previous report, may be associated with changes in hematocrit. However, because ST and PP were not affected by FMG in both trials, the responses of these blood parameters to FMG-infection may be inconsistent among flocks.

In two experiments, the effects of dietary fat and breeder hen age on relative yolk sac weight (RYSW) and total serum cholesterol (CHOL), high (HDLC) and low (LDLC) density lipoprotein cholesterol, triglycerides (TRI), and glucose (GLU) were monitored in broiler embryos and chicks. In Experiment 1, embryos at 18 d of incubation and chicks at hatch were sampled from eggs laid by breeder hens at 26 (young), 36, and 48 wk of age. No dietary effects were noted in either experiment; however, chicks from young hens exhibited elevated serum CHOL, HDLC, LDLC, and lower GLU when compared with chicks from hens at either 36 or 48 wk of age. Additionally, embryos from young breeders displayed a lower RYSW at 18 d of incubation. Conversely, by hatch there was no difference in RYSW among offspring from different aged hens. In Experiment 2, newly hatched chicks were sampled from breeder hens at 36, 51, and 64 wk of age. Dietary effects were also not evident in this experiment; however, chicks from 51-wk-old breeders displayed the highest and lowest serum HDLC and TRI, respectively, compared to the other two age groups, whereas chicks from either 51- or 64-wk-old breeders exhibited higher levels of CHOL than those at 36 wk. Chicks from 64-wk-old breeders displayed an increase in LDLC when compared with the other two ages. These data suggest that serum concentrations of lipids and GLU, and RYSW in 18 d embryos and newly hatched chicks are influenced by hen age and not by added dietary fat.

The effects of thyroid suppression induced during the rearing period by providing various dietary thiouracil (TU) regimens on plasma thyroxine (T4) concentrations, growth, and subsequent egg production (EP) and eggshell quality were determined in Single Comb White Leghorn chickens. Thiouracil was provided in the feed at levels of 0, .1, and .2% from 0 to 6 wk of age in Experiment 1, and at levels of 0, .05, and .1% from 6 to 16 wk of age in Experiment 2. In both experiments, T4 concentrations were reduced during TU treatment. However, T4 later became elevated at 12 and 20 wk in both dosage level groups in Experiment 1. Additionally, BW and egg weights were suppressed by both TU treatments, and EP was reduced up to Week 23 in the .1% TU-treated birds and through Week 25 in the .2% TU-treated birds. No effects on EP were noted in Experiment 2, but feed consumption (FC) was reduced during Week 6 in birds fed .05% TU and during Weeks 6, 10, and 19 in birds fed .1% TU. Both liver and thyroid weights were increased in .1% TU-treated birds relative to controls at Week 16. Eggshell quality was affected only in Experiment 2, in which birds given .05% TU had a higher relative conductance, or maximum rate of water loss, at Week 38 than 0 and .1% TU dosage levels, and .1% TU-treated birds had a higher breaking strength than 0 and .05% TU-treated birds at Week 22.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this experiment was to investigate the effects of breeder flock age (30 vs. 39 weeks) and sex of the newly hatched chicks on lipoprotein composition and apolipoprotein AI (apoAI) and B (apoB) concentrations. Additionally, fast protein liquid chromatography (FPLC) was used to evaluate which lipoprotein fraction (VLDL vs. LDL vs. HDL) carried the bulk of cholesterol in newly hatched chicks. Other lipoproteins were separated by density gradient ultracentrifugation to determine their chemical composition. Serum apoAI and apoB were compared by density scanning of VLDL, IDL, LDL and HDL fractions from sequential ultracentrifugation spins. The lipoprotein profile and apolipoprotein concentrations were similar for all chicks, so samples were pooled across both sexes and age groups to strengthen the data. For the lipoproteins, VLDL had the highest level of triglycerides followed by IDL, whereas the LDL particles had the highest levels of cholesterol esters compared to all other fractions. After separating the lipoprotein particles by size (FPLC) it was determined that both LDL and HDL carried approximately equal levels of cholesterol. These data suggest that lipoproteins in newly hatched chicks are not effected by sex or flock age chosen. In addition, LDL and HDL cholesterol are carried equally in newly hatched chicks.