THE INFLUENCE OF MILK REPLACER FAT SOURCE ON CALF METABOLOMICS

Giulia Berzoini Costa Leite

doi:10.7273/000007187

Given the high market value of bovine milk fat and whole milk (WM), alternative fat sources are often used in milk replacer (MR) formulations. However, these different fat sources contribute varying fatty acid (FA) profiles and triglyceride (TG) structures to the final product. Animal fat sources, such as lard and tallow, which are commonly used in North American MR formulations, tend to have higher levels of saturated fatty acids (SFA). In contrast, vegetable fat sources, such as palm, coconut, rapeseed, and soybean oils, typically contain a greater percentage of polyunsaturated fatty acids (PUFA) and are frequently incorporated into both European and North American MR formulations. Thus, the aim of this thesis was to assess calf plasma cholesterol during pre-weaning and serum metabolomics pre- and post-weaning in response to different high-fat (30% fat, dry matter (DM) basis) MR formulated using alternative fat sources to closely resemble the FA profile of WM. To evaluate calf plasma cholesterol during the pre-weaning period, 45 individually housed male Holstein calves (aged 2.3 ± 0.82 d; mean ± standard deviation) were blocked by arrival day and age and randomly assigned to one of three treatments: 1) an MR containing a fat blend with 65% rapeseed and 35% coconut fat (RC), 2) an MR containing 65% palm and 35% coconut fat (PC), and 3) an MR containing 65% lard and 35% dairy cream (LD). All MR were isoenergetic with 30% fat, 25% protein, and 36% lactose (DM basis). Calves were fed 6.0 L/d from d 1 to 5, 7.0 L/d from d 6 to 9, and 8.0 L/d from d 10 to 35 at 13.5% solids. Water and chopped straw were available ad libitum from arrival onwards. Milk, water, and straw intakes were recorded daily. Plasma was sampled and body weight (BW) was measured at arrival and weekly thereafter. Fecal scores were recorded daily. Growth and intakes did not differ among treatments. Plasma total cholesterol, high-density lipoprotein (HDL)-cholesterol, and low-density lipoprotein (LDL)-cholesterol concentrations were higher in calves fed RC than PC and LD, and higher in calves fed PC than LD. Thus, we conclude that including palm and rapeseed fats in the MR did not affect growth but increased plasma total cholesterol. To assess calf serum metabolomics during pre- and post-weaning, 30 male Holstein-Friesian calves (aged 3.1 ± 0.84 d; initial BW 46.6 ± 4.5 kg) were group-housed in 4 indoor pens with ad libitum access to the automatic MR feeders, water, chopped straw, and starter feed. Calves were blocked according to age and the date of arrival at the research facility. Each group pen included 3 blocks of 3 calves. Within each block, calves were randomly assigned to one of the MR diets, where blood of 2 treatment groups (LD and RC) was considered for metabolomics analysis in blood. From d 0 to d 42 calves had ad libitum access to MR. From d 43 to d 70, calves underwent a stepdown weaning process. Calves were fully weaned by d 71 but continued to be monitored until d 84. Blood was collected from the jugular vein on d 28 (wk 4) and d 84 (wk 12) to analyze lipid profiles in the serum. Targeted metabolomics of samples was performed by tandem mass spectrometry using the MxP® Quant 500 kit (Biocrates). Among the 350 serum metabolites analyzed, 105 were noted in higher concentrations and 42 in lower concentrations in the serum of calves fed the LD MR during the pre-weaning period. Metabolites were from lipid classes such as serum TG, phosphatidylcholines (PHO), cholesteryl esters (CE), lysophosphatidylcholines (lysoPHO), ceramides (Cer), diacylglycerides (DG), sphingomyelin (SM), and α-aminobutyric acid (AABA). These results possibly indicate shifts in enzymatic activity during digestion and lipid absorption in response to the degree of unsaturation, FA chain length, and FA positioning on the TG backbone. Most membrane lipid species, such as PHO, were greater in the serum of RC calves during pre-weaning, suggesting shifts in cell membrane structure and cellular signaling in response to dietary fat source. However, none of these variations were found on d 84, implying that the calf can adjust MR fat metabolism as the rumen develops and solid feeds are more frequently incorporated to the diet. Thus, it may be concluded that the effects of fat source in MR are transient and do not appear to have a long-term impact on calf growth and development.

THE INFLUENCE OF MILK REPLACER FAT SOURCE ON CALF METABOLOMICS

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