Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583
Performing Department
Animal Science
Non Technical Summary
Milk protein represents one of the most nutritional and valuable components of bovine milk. The concentration of milk protein in milk is also variable and is affected by the supply of both energy and amino acids in the feed a cow consumes. Practically the dairy cows often do not produce the amount of milk protein that is possible given their genetic potential. This is a problem because this represents an economic loss to the dairy producer. This research describes a series of studies that attempts to determine how the concentration of energy and amino acids in the diet may be manipulated to support the great amount of milk protein and to also determine the extent to which these nutrients interact with each other. To do this this research plans to conduct a series of feeding studies that will involve different diets and the measure of milk protein production and also by using state-of-the-art instrumentation will measure energy flow by and through the lactating dairy cow.
Animal Health Component
75%
Research Effort Categories
Basic
25%
Applied
75%
Developmental
(N/A)
Goals / Objectives
1. To establish the relationship between parity and amino acid supply on the production of milk protein. The pattern of utilization of nutrients especially energy entering the metabolic pool is a function of the overall physiological state of the animal and this is affected by stage of lactation and parity. The working hypothesis for experiments associated with this objective is that because they are growing, primiparous cows have additional needs for AA and when these requirements are met, with produce more milk protein when the supply of energy is increases. The approach used to test this working hypothesis will be to establish a series of studies in which the supply of energy and AA are manipulated. Utilization of energy will be studied and efficiency of energy utilization will be established using in direct calorimetry. The rationale underlying this objective is that further understanding of utilization of amino acids and energy by lactating dairy cows will lead to a more precise knowledge about how the U.S. dairy industry may best use nutrients contained in feedstuffs and this should result in reduce N excretion.2. To establish the relationship between the supply of energy and amino acids on the production of milk protein. Simply feeding more AA does not guarantee more AA will reach the mammary gland and support greater milk protein synthesis. This is because much of the protein supplied to a cow in is delaminated and used for energy, especially during early lactation when the cow is in a negative energy balance (Patton, 2009). Conversely, it is also likely that improving amino acid supply has, at least to some affect, a driving effect on utilization of metabolizable energy (Holter et al., 1972) and milk synthesis (through affecting lipid and/or glucose metabolism). These responses likely are intimately linked with body tissue mobilization support production, The working hypothesis for this research objective is that response of dairy cows to increasing the supply of AA is dependent energy balance. This may in part explain why cows in early lactation and in negative energy balance do not respond by producing more milk protein when the supply of AA is increased. This will be tested by using a series of in vivo experiments in which dairy cows will be fed diets that differ by the concentration of energy and the supply of AA. Whole animal energy and nitrogen balance will also be evaluated. The completion of the proposed studies will greatly improve our understanding of factors affecting AA utilization and this should also translate into more efficient use of rumen protected AA when included in dairy diets. This result is expected to have a significant impact on the field because it should improve the current understanding AA that may be made available for milk production.3) To establish the relationships between glucogenic and lipogenic substrates and the supply of AA and described their effects on milk yield and the production of milk protein. Dairy cattle in early lactation and in negative energy balance likely benefit more from glucogenic energy substrates than they do from lipogenic energy substrates (Van Knegsel et al., 2007). This is likely because animals in negative energy balance are likely metabolizing lipogenic fuels at capacity but increasing the supply of glucogenic fuels, especially to support mammary lactose synthesis (Van Knegsel, 2007). Most amino acids can be converted to glucose interestingly when animals are consuming insufficient amounts of energy, lysine may be converted to ketone bodies. Additionally alanine is the most imported precursor for gluconeogenesis when it is released from the muscle and small intestine (Newsholme and Leech, 1983) thus its role in metabolism when cows are mobilizing body tissue during early lactation is of interest (Shibano et al., 2005) . The working hypothesis for this research objective is that the metabolism of dairy cows to increasing the supply of Lys is dependent nature of the energy source. In cases where energy balance is negative cows may respond by increasing milk fat when consuming a lipogenic but not a glucogenic diet. However when supplemented with Lys, it is possible that the glucogenic diet will result in little change in milk fat but result in increases in milk protein. This will be tested by using a series of in vivo experiments in which dairy cows will be fed diets that differ by the the source of energy (either glucogenic or lipogenic) and the supply of Met and Lys. Milk production and whole animal energy and nitrogen balance will also be evaluated. The completion of the proposed studies will greatly improve our understanding of factors affecting AA utilization and this should also translate into more effect use of rumen protected AA when included in dairy diets. This result is expected to have a significant impact on the field because it should improve the current understanding AA that may be made available for milk production.
Project Methods
This research not only seeks to test the effects of formulation on digestibility of protein and energy, but unlike most methods testing the topic, also directly measures and quantifies whole animal nitrogen and energy utilization. All experimental procedures will be submitted for review and approval by the University of Nebraska Animal Care and Use Committee (IACUC). The University of Nebraska-Lincoln is uniquely capable of testing ration manipulations of both nitrogen and energy utilization. This is because we are among a small number of sites in the U.S. that possess and maintains an energy metabolism facility for dairy cows (Foth et al., 2015). Based on measures of methane, oxygen, and carbon dioxide, this headbox-style indirect calorimeter system allows us to estimate heat loss in lactating cows. The system is constructed with plexiglass sides allowing the animal to stay in visual contact with other animals, and is mounted on wheels to let the animal stay in the normal environment. Additionally, the temperature-controlled facility is equipped with the ability to measure the loss of energy and nitrogen in both the urine and feces through total collection.Experimental Plan and DesignsAnimals A series of experiments will be carried out to meet the proposed objectives. In each experiment 8 - 12 lactating dairy cows will be used in each experiment. All cows will be housed in a temperature-controlled barn at the Dairy Metabolism Facility at the Animal Science Complex at the University of Nebraska - Lincoln (Lincoln, NE) and milked at 0700 and 1800 hr in individual tie stalls equipped with rubber mats. At the conclusion of the last experimental period, all cows will be less than 90 days pregnant so energy calculations could be taken. This will be because energy to fetus is very minimal less than 90 days pregnant.The experimental design for each experiment will be a replicated 4 × 4 Latin square. Cows will be randomly assigned to 1 of the 4 dietary treatments (See Tables 1 and 2) which will depend upon the experimental objective of each individual study. Animals will be blocked into each square by milk production. Treatments alternated over 4 experimental periods and measurements will be collected on each animal consuming each treatment. The study will be conducted with a total of 4 experimental periods each being 35 days in duration. Each period included 28 days for ab libitum diet adaptation, targeting about 5% refusals during that time, followed by 7 days of collection with 4 days of 95% ad libitum feeding to reduce the amount of refusals. All dietary treatments will contain a mixture of forage grain and minerals/vitamins and will be combined as a TMR. The TMR will be mixed in a Calan Data Ranger (American Calan, Inc, Northwood, NH) and fed once daily at 0900 hr to the cows.Experimental Plans for Meeting Objectives 1 and 2. Experiments 1 and 2. A whole-animal energy balance study using animals and experiment designs described below. The treatments will be adequately replicated and be describe the response in milk protein to increasing AA supply and the supply of energy is also varied.The supply of Lys and Met will be manipulated by varying the proportion of ingredients high in either Lys or Met.The supply of energy will be manipulated by varying proportion of forage and grain included in the diet.Experimental Plans for Meeting Objectives 1 and 3. Experiments 3 and 4. A whole-animal energy balance study using animals and experiment designs described below. The treatments will be adequately replicated and be describe the response in milk protein to increasing AA supply and the supply of energy is also varied. The supply of Lys and Met will be manipulated by varying the proportion of ingredients high in either Lys or Met.The nature of energy will be manipulated by varying proportion corn grain and fat included in the diet.