Effect of age at the onset of natural molting on carcass traits, muscle oxidative stability, and amino acid and fatty acid profiles in commercial laying hens

Guanidinoacetic acid in laying hen diets with varying dietary energy: Productivity, antioxidant status, yolk fatty acid profile, hepatic lipid metabolism, and gut health

This study aimed to investigate the effects of GAA supplementation in diets differing in ME levels on productive performance, egg quality, blood parameters, yolk fatty acid profiles, hepatic expression of genes related to lipid metabolism, gut morphology, and nutrient digestibility in laying hens during their post-peak production phase. Over a 12-week period (52-64 weeks of age), 288 laying hens were randomly assigned to 6 treatments. Each treatment consisted of 8 replicates, with 6 hens per replicate. The experimental treatments were assigned in a 2 × 3 factorial arrangement, comprising 2 levels of dietary ME (a recommended level and a low level, the latter characterized by a 100 kcal/kg reduction in ME) and 3 levels of GAA supplementation (0, 0.6, and 1.2 g/kg). The results showed significant interaction effects (P < 0.05) between GAA supplementation and dietary ME levels on laying rate, egg mass, feed conversion ratio, crude protein digestibility, and AMEn. In hens fed the low-ME diet, GAA supplementation, particularly at 1.2 g/kg, significantly improved laying performance. Moreover, at both 0.6 and 1.2 g/kg under low-ME conditions, GAA significantly enhanced crude protein digestibility and AMEn. The low-ME diet was associated with decreased expression of key lipogenic genes, including sterol regulatory element-binding transcription factor 1 (SREBF1), acetyl-coenzyme A carboxylase (ACC), and fatty acid synthase (FAS), alongside increased expression of genes involved in fatty acid oxidation, such as peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase 1 (CPT1). Regardless of ME content, GAA supplementation linearly improved eggshell strength, enhanced the polyunsaturated-to-saturated fatty acid ratio in the yolk, elevated serum levels of creatine and total antioxidant capacity, improved intestinal morphology, and increased radical scavenging activity in the yolk (P < 0.05). Furthermore, GAA supplementation linearly increased the relative mRNA expression of several metabolic genes, including SREBF1, ACC, PPARα, and ApoB (P < 0.05). In conclusion, GAA supplementation enhanced productive performance in low-ME diets and exerted positive effects on egg characteristics and lipid metabolism, regardless of dietary ME content.

How molting of laying hens influences body composition and blood parameters

The physiological and metabolic changes laying hens undergo during molt are poorly understood, but could aid in understanding why hens stop egg production during the first cycle of lay. We therefore induced a molt and studied how this influenced body composition, blood parameters and production performance. Additionally, four diets postmolt were fed in a 2 × 2 factorial design with two levels of metabolisable energy lay (ME Lay; low = 11.0 MJ and high = 11.9 MJ) and two apparent faecal digestible lysine levels (AFD; low = 0.58% and high = 0.72%). Data were subjected to mixed model analyses. A molt was successfully induced at 58 weeks of age, during which hens stopped consuming feed and producing eggs, and lost on average 21% BW. Most of this BW loss was due to body breast weight loss (-56 g, time effect P < 0.05) and ovary loss (-33.6 g, time effect P < 0.05) and to a lesser extent due to fat pad loss (-7.1 g, time effect P > 0.05). Early laying rate and egg mass production of hens fed the high AFD Lys diets postmolt were significantly higher compared to hens fed the low AFD Lys diet. Egg weights of hens fed high AFD Lys diets were lower. Both effects were only short-term in weeks 59-62 and indicated that high amino acid intake is important for early laying rate in the second cycle of lay, potentially related to feather growth and restoration of body protein. Hens fed low ME Lay diets increased average daily feed intake (ADFI) in weeks 62-65, compared to hens fed high ME Lay diets (P < 0.05). This resulted in higher ME Lay and AFD Lys intake (P < 0.05). Hens fed these low ME Lay diets had a higher egg mass production in weeks 62-65 (P < 0.05), due to higher egg weights (P < 0.05), without a difference in laying rate (P > 0.05). Average daily gain was also significantly higher, mostly due to higher breast percentage (P < 0.05). Hens fed low ME Lay diets probably needed a higher lipoprotein production in the liver to meet the egg production demand, indicated by higher plasma cholesterol (P = 0.07) and triglyceride (P < 0.05) levels, and heavier liver weights (P < 0.05). In conclusion, molting significantly influenced the body composition of laying hens, with reduced breast, liver and ovary weights. Lower postmolt ME Lay diets increased breast, liver and ovary weights and increased egg weights and egg mass production. High AFD Lys diets only showed a short-term positive effect on the laying rate.

Performance, Carcass Yield, Muscle Amino Acid Profile, and Levels of Brain Neurotransmitters in Aged Laying Hens Fed Diets Supplemented with Guanidinoacetic Acid

Guanidinoacetic acid (GA) is a natural precursor of creatine in the body and is usually used to improve the feed conversion and cellular energy metabolism of broiler chickens. The objective was to elucidate the effect of dietary supplementation of GA on carcass yield, muscle amino acid profile, and concentrations of brain neurotransmitters in laying hens. In total, 128 72-week-old ISA Brown laying hens were assigned to four equal groups (32 birds, eight replicates per group). The control group (T₁) was fed a basal diet with no supplements, while the other experimental groups were fed a basal diet supplemented with 0.5 (T₂), 1.0 (T₃), and 1.5 (T₄) g GA kg^-1 diet. The T₃ and T₄ groups showed higher hen-day egg production and carcass yield compared to the control group (p = 0.016 and 0.039, respectively). The serum creatine level increased linearly with the increased level of dietary GA (p = 0.007). Among the essential amino acids of breast muscle, a GA-supplemented diet linearly increased the levels of leucine, isoleucine, phenylalanine, methionine, and threonine in the breast (p = 0.003, 0.047, 0.001, 0.001, and 0.015, respectively) and thigh (p = 0.026, 0.001, 0.020, 0.009, and 0.028, respectively) muscles. GA supplementation linearly reduced the level of brain serotonin compared to the control group (p = 0.010). Furthermore, supplementation of GA in the diet of laying hens linearly increased the level of brain dopamine (p = 0.011), but reduced the level of brain Gamma-aminobutyric acid (p = 0.027). Meanwhile, the concentration of brain nitric oxide did not differ between the experimental groups (p = 0.080). In conclusion, the dietary supplementation of GA may improve the carcass yield and levels of essential amino acids in the breast muscles, as well as the brain neurotransmitters in aged laying hens.