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Background: Meat goat production is a worldwide industry with products such as meat, milk, soap, and fiber being produced. There are approximately 2.6 million meat goats in the United States. For breeding female ruminants, early pregnancy loss is estimated to be 30% within the first month of gestation. Extracellular L-citrulline (a precursor to L-arginine) is not degraded by ruminal microbes due to the lack of uptake. L-Arginine and thus L-citrulline, have beneficial impacts on placentation and, subsequently, fetal-placental development and survival. This study aimed to determine the impact of feeding L-citrulline to meat goats during gestation to improve reproductive success. Meat goats were fed either a control (CON) or L-citrulline (CIT) supplemented diet from d 12 to 82 of gestation. Blood samples were collected and sera were subjected to high-performance liquid chromatography analyses to quantify the abundance of amino acids. Pregnancy rates were determined on d 30, 61, and 90 of gestation, and litter weight, individual birth weights, and 90 d adjusted weaning weights were collected., Results: The concentrations of citrulline, ornithine, and arginine were greater in CIT does compared to CON does, but there was no difference in pregnancy rates between CON and CIT does. Birth weight was greater for male kids born as singles when compared to females, but this phenotype was not observed for kids born as twins or triplets. Further, males born to CON does had greater 90 d adjusted weaning weights than females, but this was not observed in the CIT group. Female kids born to CON and CIT Boer goats had heavier 90 d adjusted weaning weights than those born to Spanish or F1 Boer-Spanish does., Conclusion: This study provides proof of concept that feeding dietary L-citrulline increases concentrations of citrulline and arginine in blood of gestating meat goats. However, further studies are needed to understand the cellular mechanisms impacted by feeding this supplement. Regardless, this study demonstrated that feeding L-citrulline has the potential to increase reproductive performance in gestating ruminants., Competing Interests: Declarations. Ethics approval and consent to participate: All experimental procedures followed the Guide for the Use of Agriculture Animals in Research and Teaching and were approved by the Institutional Animal Care and Use Committee at Prairieview A&M University. Consent for publication: Not applicable. Competing interests: The authors have no conflict of interest to declare., (© 2025. The Author(s).)

Adult humans generally experience a 0.5-1%/year loss in whole-body skeletal muscle mass and a reduction of muscle strength by 1.5-5%/year beginning at the age of 50 years. This results in sarcopenia (aging-related progressive losses of skeletal muscle mass and strength) that affects 10-16% of adults aged ≥ 60 years worldwide. Concentrations of some amino acids (AAs) such as branched-chain AAs, arginine, glutamine, glycine, and serine are reduced in the plasma of older than young adults likely due to insufficient protein intake, reduced protein digestibility, and increased AA catabolism by the portal-drained viscera. Acute, short-term, or long-term administration of some of these AAs or a mixture of proteinogenic AAs can enhance blood flow to skeletal muscle, activate the mechanistic target of rapamycin cell signaling pathway for the initiation of muscle protein synthesis, and modulate the metabolic activity of the muscle. In addition, some AA metabolites such as taurine, β-alanine, carnosine, and creatine have similar physiological effects on improving muscle mass and function in older adults. Long-term adequate intakes of protein and the AA metabolites can aid in mitigating sarcopenia in elderly adults. Appropriate combinations of animal- and plant-sourced foods are most desirable to maintain proper dietary AA balance.

As for other mammals, the digestive system of dogs (facultative carnivores) and cats (obligate carnivores) includes the mouth, teeth, tongue, pharynx, esophagus, stomach, small intestine, large intestine, and accessory digestive organs (salivary glands, pancreas, liver, and gallbladder). These carnivores have a relatively shorter digestive tract but longer canine teeth, a tighter digitation of molars, and a greater stomach volume than omnivorous mammals such as humans and pigs. Both dogs and cats have no detectable or a very low activity of salivary α-amylase but dogs, unlike cats, possess a relatively high activity of pancreatic α-amylase. Thus, cats select low-starch foods but dogs can consume high-starch diets. In contrast to many mammals, the vitamin B 12 (cobalamin)-binding intrinsic factor for the digestion and absorption of vitamin B 12 is produced in: (a) dogs primarily by pancreatic ductal cells and to a lesser extent the gastric mucosa; and (b) cats exclusively by the pancreatic tissue. Amino acids (glutamate, glutamine, and aspartate) are the main metabolic fuels in enterocytes of the foregut. The primary function of the small intestine is to digest and absorb dietary nutrients, and its secondary function is to regulate the entry of dietary nutrients into the blood circulation, separate the external from the internal milieu, and perform immune surveillance. The major function of the large intestine is to ferment undigested food (particularly fiber and protein) and to absorb water, short-chain fatty acids (serving as major metabolic fuels for epithelial cells of the large intestine), as well as vitamins. The fermentation products, water, sloughed cells, digestive secretions, and microbes form feces and then pass into the rectum for excretion via the anal canal. The microflora influences colonic absorption and cell metabolism, as well as feces quality. The digestive tract is essential for the health, survival, growth, and development of dogs and cats., (© 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

The hair and skin of domestic cats or dogs account for 2% and 12-24% of their body weight, respectively, depending on breed and age. These connective tissues contain protein as the major constituent and provide the first line of defense against external pathogens and toxins. Maintenance of the skin and hair in smooth and elastic states requires special nutritional support, particularly an adequate provision of amino acids (AAs). Keratin (rich in cysteine, serine and glycine) is the major protein both in the epidermis of the skin and in the hair. Filaggrin [rich in some AAs (e.g., serine, glutamate, glutamine, glycine, arginine, and histidine)] is another physiologically important protein in the epidermis of the skin. Collagen and elastin (rich in glycine and proline plus 4-hydroxyproline) are the predominant proteins in the dermis and hypodermis of the skin. Taurine and 4-hydroxyproline are abundant free AAs in the skin of dogs and cats, and 4-hydroxyproline is also an abundant free AA in their hair. The epidermis of the skin synthesizes melanin (the pigment in the skin and hair) from tyrosine and produces trans-urocanate from histidine. Qualitative requirements for proteinogenic AAs are similar between cats and dogs but not identical. Both animal species require the same AAs to nourish the hair and skin but the amounts differ. Other factors (e.g., breeds, coat color, and age) may affect the requirements of cats or dogs for nutrients. The development of a healthy coat, especially a black coat, as well as healthy skin critically depends on AAs [particularly arginine, glycine, histidine, proline, 4-hydroxyproline, and serine, sulfur AAs (methionine, cysteine, and taurine), phenylalanine, and tyrosine] and creatine. Although there are a myriad of studies on AA nutrition in cats and dogs, there is still much to learn about how each AA affects the growth, development and maintenance of the hair and skin. Animal-sourced foodstuffs (e.g., feather meal and poultry by-product meal) are excellent sources of the AAs that are crucial to maintain the normal structure and health of the skin and hair in dogs and cats., (© 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

The authors present a case of giant aneurysm of the posterior inferior cerebellar artery. It was successfully excised with reversal of neurological deficits.