Effect of β-carotene supplementation on vitamin A status, composition of growth, and gene expression of feedlot cattle
Abstract
The hypothesis for this thesis was that replacing pre-formed vitamin A (VA) (retinyl palmitate) with β-carotene (βC) in the diet of feedlot cattle will increase intramuscular fat deposition through changes in expression of VA related and lipogenic genes. To test this hypothesis, 140 Angus × Simmental crossbred calves were allotted by BW (351.3 ± 12.1 kg) and sex (19 steers, 9 heifers per treatment) to 5 treatments (6 pens per treatment) to evaluate the effects of VA form on performance and carcass characteristics. Treatments consisted of retinyl palmitate (RP) supplemented at the NRC VA requirement (2200 IU/kg), synthetic βC, all-trans isomer supplemented at 1× (SβC1x), 5× (SβC5x), or 10× (SβC10x) the NRC VA requirement, and natural βC (50/50 mix of all-trans and 9- cis-βC) supplemented at 5× the NRC VA requirement (NβC5x). Longissimus muscle (LM), liver, and small intestinal (SI) tissue were collected immediately after slaughter, snap frozen in liquid nitrogen, and stored at −80°C for subsequent analysis of mRNA expression by quantitative PCR. Steaks were collected 24 h after slaughter for analysis of fatty acid profile. SβC1x did not change plasma concentrations of RP, βC, or other carotenoids (P > 0.26) compared with RP. Increasing dietary βC increased (P < 0.04) plasma concentrations of RP as well as the all-trans, 9-cis, 13-cis, and 15-cis isomers of βC. Natural βC decreased (P < 0.04) plasma concentrations of RP, all-trans-βC, and 13- cis-βC, and increased (P < 0.01) α-carotene when compared with SβC5x. Concentrations of 15-cis- βC (P = 0.04), 13-cis- βC (P = 0.01), βC (P = 0.01), and 9-cis βC (P = 0.02) increased linearly in the liver as dietary SβC increased. Similarly in muscle, βC (P = 0.01) and 9-cis βC (P = 0.01) increased quadratically. Retinoic acid concentrations in liver tended to be greater in SβC5X compared to NβC5X (P = 0.09) and liver retinoic acid tended to respond quadratically to SβC supplementation. Form of VA did not impact BW or ADG (P > 0.35), however, SβC tended (P < 0.10) to have a quadratic effect on overall daily DMI, with a decrease from SβC1× to SβC5× and an increase from SβC5× to SβC10×. Marbling and fat thickness were not affected by form of VA (P > 0.35), however, increasing concentration of SβC tended (P < 0.10) to linearly increase LM area while NβC5x tended (P < 0.10) to decrease LM area compared with SβC5x. L* values of LM decreased linearly in response to SβC supplementation (P < 0.05) and b* values of subcutaneous fat responded quadratically to SβC supplementation (P < 0.05), with an increase from SβC1× to SβC5× and a decrease from SβC5× to SβC10×. β-carotene monooxygenase 1 (βCMO1) and β-carotene oxygenate 2 (βCO2), the enzymes responsible for symmetric and asymmetric cleavage of βC, respectively, were both expressed in the SI. Liver and LM tissues did not express βCMO1, but did express βCO2. Expression of βCO2 in muscle linearly decreased as SβC supplementation increased (P < .02), and was greater for SβC1x compared to VA (P < 0.04). Expression of aldehyde dehydrogenase (ALDH1), which converts retinaldehyde to retinoic acid in the small intestine tended to linearly decrease with increasing SβC supplementation (P <0.08) and tended to increase in SβC1X cattle compared to RP cattle (P < 0.10). No differences in ALDH1 were noted in liver and LM (P > 0.13). Expression of RARα in the small intestine tended to decrease linearly with increased SβC supplementation (P < 0.06). Furthermore, RARα expression in the muscle tended to decrease with increasing SβC supplementation (P < 0.10). Expression of RXRα in the small intestine and liver did not differ significantly based on VA treatment (P > 0.13). However, in LM with increasing SβC supplementation RXRα expression decreased (P < 0.05). Expression of PPARγ was not detected in the small intestine and expression of PPARγ in the liver did not differ due to dietary vitamin A. Conversely, expression of PPARγ in muscle decreased linearly as SβC concentration increased (P = 0.02). In addition, expression of PPARγ in muscle was increased in SβC1X compared to RP (P < 0.03). Saturated fatty acid (SFA) content of LM tended to decrease (P = 0.08) and polyunsaturated acids (PUFA) tended to linearly increase (P = 0.10) as dietary SβC concentration increased. As a result, PUFA/SFA ratios linearly increased from as dietary SβC increased (P < 0.05). Palmitic acid (C16:0) content of LM decreased linearly as dietary SβC increased (P < 0.01) and LM CLA content was greater in VA compared to SβC1x (P < 0.05). (Abstract shortened by UMI.)
Degree
M.S.
Advisors
Schoonmaker, Purdue University.
Subject Area
Animal sciences
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