نوع مقاله : مقاله پژوهشی
نویسندگان
گروه علوم دامی، دانشکدگان کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
This study investigated the effects of glucose precursors (propylene glycol and glycerol) combined with two protein sources corn gluten meal (a source of branched-chain amino acids) and meat meal on newly calved Holstein cows. The primary objective was to evaluate the individual and interactive effects of different glucose precursors and branched-chain amino acids on performance in early-lactation Holstein cows. A total of 42 multiparous Holstein cows, from 3 to 35 days postpartum, were utilized in a 2×3 factorial design with six treatment groups and seven replicates per treatment. The experimental diets consisted of a basal ration supplemented with 300 g of glucose precursors in three ratios of propylene glycol to glycerol (75:25, 50:50, and 25:75) as the first factor, and 600 g of protein source (corn gluten meal or meat meal) as the second factor. Daily feed intake and milk production were recorded, and milk, feed, and feces samples were collected at regular intervals.The results showed that the inclusion of glucose precursors, in combination with different amino acid sources, had no significant effect on daily dry matter intake, feed efficiency, or negative energy balance. While the interaction between treatments did not significantly affect daily milk yield, a significant difference was observed between glucose precursor treatments (p < 05/0). Milk yield was not influenced by the source of branched-chain amino acids but was affected by the type of glucose precursor, with higher levels of propylene glycol and lower levels of glycerol resulting in increased milk production. No significant differences were detected in fat-corrected milk (5/3%), milk fat content, or other milk components across the experimental treatments. The increased milk yield in cows fed propylene glycol may be attributed to its role in enhancing dietary energy density, promoting greater ruminal propionate production, and subsequently increasing glucose availability in cows experiencing negative energy balance. Nutrient digestibility and feed intake were unaffected by the treatments.
کلیدواژهها [English]
Extended Abstract
Introduction
One of the most widely used strategies for preventing and treating postpartum disorders caused by negative energy balance (NEB), such as ketosis, fatty liver, and other associated diseases, as well as enhancing milk production, is the supplementation of glucose precursors. These include oral administration or injection of glucose, or a combination of both. The application of glucose precursors is particularly important for maintaining liver health, which plays a crucial role in the successful transition to lactation. The primary objective of using glucose precursors is to sustain and improve hepatic gluconeogenesis, ensuring adequate glucose production and preventing triglyceride accumulation in the liver. Commonly used glucose precursors include propylene glycol and glycerol. These glucogenic (anti-ketogenic) compounds, when administered to livestock, are metabolized in the rumen into propionate, which is then transported to the liver for gluconeogenesis and glucose production. Another portion of these compounds escapes ruminal fermentation, is absorbed, and reaches the liver via the bloodstream, where it is ultimately converted to glucose.
Leucine, isoleucine, and valine are three branched-chain amino acids (BCAAs), which are among the ten essential amino acids (EAAs) required for protein synthesis in mammary tissues. These BCAAs are crucial for milk protein production and account for up to 50% of the total EAAs in milk.
Given that propylene glycol and glycerol help improve the negative energy balance and liver health in early lactation by partially fulfilling the glucose needs of cows, and considering that BCAAs are limiting factors for milk production during this period, the hypothesis of this study was that supplementing these nutrients in the diets of early-lactating cows could enhance body condition scores and milk production due to their individual and potential synergistic effects. The objective of this research was to evaluate the effects of propylene glycol and glycerol in combination with BCAA-rich protein sources on the performance of Holstein cows during early lactation.
Materials and Methods
This study was conducted at the Educational and Research Farm of the Animal Science Department, College of Agriculture and Natural Resources, University of Tehran, located in Karaj, Iran. A total of 42 multiparous Holstein cows in early lactation were randomly assigned to six treatments with seven replicates per treatment. The cows were housed individually with separate feeding and watering facilities from days 3 to 35 postpartum. The experimental diets consisted of a basal ration supplemented with 300 g of glucose precursors in three ratios of propylene glycol to glycerol (75:25, 50:50, and 25:75) as the first factor, and 600 g of a protein source (corn gluten meal or meat meal) as the second factor. Experimental diets were offered as a total mixed ration (TMR) twice daily at 8:00 AM and 4:00 PM. Daily feed intake and orts were recorded. The dry matter (DM), organic matter (OM), crude protein (CP), and ether extract (EE) contents of feed and fecal samples were analyzed according to AOAC (2000) methods. During days 30 to 33 of the experiment, feed and fecal samples were collected from each cow to determine DM, OM, CP, EE, and neutral detergent fiber (NDF) concentrations. Acid-insoluble ash was used as an internal marker to calculate the apparent digestibility of each nutrient. Cows were milked three times daily at 8:30 AM, 4:30 PM, and 12:30 AM, with milk yield recorded at each session.
Results and Discussion
The use of glucose precursors combined with a branched-chain amino acid (BCAA) source, such as corn gluten meal, did not significantly affect dry matter intake (DMI), feed efficiency, or energy balance in early-lactation Holstein cows. No significant differences were observed among treatments in the apparent digestibility of dry matter, organic matter, crude protein, or ether extract. Digestibility of neutral detergent fiber (NDF) also showed no significant differences between treatments but exhibited the lowest p-value, decreasing linearly as glycerol levels increased in the diets.
Daily milk yield was not significantly affected by the interaction between treatments. However, there was a significant main effect of glucose precursors on milk yield (p < 05/0). Specifically, milk production was not influenced by the BCAA source but was significantly affected by the varying proportions of glucose precursors. For instance, milk yield significantly differed between treatment P75 (75% propylene glycol and 25% glycerol) and treatment G75 (25% propylene glycol and 75% glycerol), while neither differed significantly from treatment 50/50 (50% propylene glycol and 50% glycerol). These results suggest a linear relationship between increasing levels of propylene glycol and decreasing levels of glycerol, leading to higher milk production.
No significant differences were observed among treatments for 5/3% fat-corrected milk or other milk components. Propylene glycol appears to enhance dietary energy concentration and increase propionate production in the rumen, subsequently supporting greater glucose synthesis via gluconeogenesis. This compensates for the energy and glucose deficits in early-lactation cows experiencing negative energy balance, leading to improved milk production. Nutrient digestibility and feed utilization were not significantly influenced by the different sources of glucose precursors.
This article contains all the data that were created or evaluated during the research.
The authors would like to sincerely thank the members of the Faculty of Animal Sciences, University of Tehran Research Council for the approval and support of this research.
The author declares no conflict of interest.
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