Document Type

Dissertation - Open Access

Award Date

2022

Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

First Advisor

Crystal Levesque

Keywords

amino acid, linear logistic model, pregnant sow, protein, reproduction, requirement

Abstract

The efficient use of protein in animal production is dependent on the protein supply and its constituent amino acids (AA) in relation to the animal's needs. Excess AA are deaminated, and the resulting nitrogen (N) is excreted, whereas suboptimal AA intake reduces animal performance. Both increased nutrient excretion and decreased animal performance reduce the overall efficiency of the production unit. In sows, AA requirements should be adequate for optimizing reproductive performance, as measured, for example, by the number of pigs produced per sow per year while limiting N excretion. There is a desire to feed pregnant sows AA levels that meet both physiological needs and environmental considerations. Current methods for estimating AA requirements, however, are geared toward reducing N excretion, rather than optimizing reproductive performance. Minimizing N excretion increases N utilization efficiency but decreases overall meat production efficiency if these dietary levels do not maximize pregnant sow reproductive performance. Thus, the overall objective of this dissertation is to increase our understanding on the dynamics of N excretion and retention across gestation and to determine dietary AA levels that optimize reproductive performance. To accomplish these objectives a series of in silico and in vivo studies were performed and are outlined in four research chapters (Chapter 2, 3, 4, and 5). In Chapter 2, a mechanistic model was developed to quantify and characterize the N and AA deposition in the different tissue pools that make up the pregnant sow as well as their interaction in terms of nutrient competition: placenta, allantoic fluid, amniotic fluid, fetus, uterus, mammary gland, and maternal body were considered. Growth curves for each tissue were developed, as well as curves describing retention of the 10 essential AA and N for each tissue. The growth and nutrient retention curves were developed as a function of the model's inputs: parity, body weight (BW) at breeding, litter size, average piglet birth weight, and number of available teats. All functions were combined in an algorithm that dynamically distributed the dietary N and AA to the different tissues based on the inputs of the model. The model characterized a trend in maternal N retention that could not be previously explained, although identified as time-dependent protein deposition (Pd), by the NRC (2012) gestating sow model. The trend in N retention described by the time-dependent protein pool appears to be due to a drop in daily N retention, particularly during early gestation, rather than increased N retention, as previously thought, implying that current energy and/or AA requirements for early pregnancy should be reviewed. In Chapter 3, a dose-response curve defined as the linear-logistic model was developed based on experimental data from pregnant gilts at d 50 of gestation to describe the response of N retention to graded levels of the AA lysine (Lys). The linear-logistic model describes two inflection points defined as: 1) N retention max (NRmax) and 2) N retention minimum (NRmin). Based on the hypothesis that Lys intakes corresponding to NRmax maximized maternal body growth and Lys intakes corresponding to NRmin maximized the reproductive performance of pregnant sows, a meta-analysis was performed. The standardized ileal digestible (SID) Lys requirements for sows throughout gestation were calculated using the linear-logistic model and observations from Chapter 2. The meta-analysis confirmed that SID Lys levels corresponding to NRmax and NRmin maximized maternal growth and reproductive performance, respectively. Because current AA requirements are more likely to represent NRmax, current AA requirements appear to optimize maternal lean tissue deposition rather than conceptus development. Optimal reproductive performance appears to occur at AA levels above current recommendations. In Chapter 4, a study was performed to test model outputs from Chapters 2 and 3 and investigate the effects of SID methionine (Met) intakes greater than current requirements on the metabolic status of gilts at breeding age. The metabolic status of the animals was evaluated using plasma AA concentration, with a particular emphasis on plasma taurine (Tau) which is a non-proteogenic AA that is biosynthesized from Met and regulates a variety of functions in the body. In addition, the dynamics of N retention at potential SID Met intakes that maximize Tau biosynthesis were investigated. The results of this study showed that SID Met intakes corresponding to 230% of current requirements maximized Tau biosynthesis and, thus, potentially Tau-related metabolic functions, and resulted in a decrease in whole-body N retention. Optimal metabolic status appears to occur at AA levels above current recommendations. In Chapter 5, a pilot study was performed to study the effects of SID Met intake levels corresponding to 230% of the requirement for gilts during the first 90 days of gestation on sow BW gain. A total of 39 sows were provided either a control or a high Met diet. Sows in the control group gained in average 1.67 kg more than those in the high Met group (P=0.070). The reduced BW gain in the high Met group may be explained by a decrease in the priority for maternal body deposition and an increase in reproductive function and metabolic status, as predicted in Chapter 3 and 4. However, due to a disease outbreak in the research herd, the effects of dietary SID Met on litter size could not be determined and the previous claim could not be fully supported. In summary, the developed mechanistic model enhanced understanding of the dynamics of N retention across gestation. Observations made in all four research chapters suggest that current AA requirements are underestimated when metabolic status and reproductive function are considered. In Chapter 3, 4 and 5 it is suggested that at optimal AA intake for metabolic and reproductive status there is a decrease in the efficiency of N utilization (i.e. increased N excretion). As a result, it is advised that AA requirements based on maximal N efficiency may be limiting sow performance. The linear-logistic model is proposed as an analytic tool for the estimation of dietary AA requirements that maximize reproductive performance and metabolic status. The SID Lys requirements estimated using the linear-logistic model and the SID Met requirements empirically estimated using plasma Tau measurements have the potential to improve pregnant sow reproductive performance.

Number of Pages

186

Publisher

South Dakota State University

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Rights Statement

In Copyright