Variation in the Milk Macronutrient and Fatty Acid Composition of Captive Tree Shrews (Tupaia belangeri) during Different Lactation Periods
The tree shrew (Tupaia belangeri) is an increasingly valuable model animal for research purposes. However, the lactation biology of the tree shrew remains underexplored, hindering progress in their nutritional management during laboratory domestication. Milk samples from tree shrews in captivity at postnatal days 0, 2, 8, 14, 20, 26, and 32 were analyzed, through microanalysis for macronutrient determination and gas chromatography for fatty acid composition. At the midlactation stage, tree shrew milk averaged 44.75% dry matter, 26.35% fat, 11.93% protein, 1.63% sugars, 1.34% ash, and 1323.99 kJ/100 g energy. As lactation progressed, significant increases were observed in dry matter, sugar, and ash content. The fatty acid profile was predominated by C16:0, C14:0, C18:2n6, and C18:1n9. Levels of most saturated fatty acids increased steadily during lactation, while the majority of unsaturated fatty acids exhibited an opposite pattern. In brief, our results suggest that the macronutrient composition and fatty acid profile are influenced by the lactation stage. These findings may aid in formulating milk products that closely approximate the maternal milk of tree shrews, thereby enhancing breeding and domestication efforts for research purposes.
Experimental scheme and milking procedures. (A) To investigate the milk composition of tree shrews and its changes during lactation, milk samples on postnatal days 0 (P0), 2 (P2), 8, 14, 20, 26 and 32 were collected for chemical analysis. The P0 and P2 samples were from the captive dams that failed to nurse the young from the first or the third day after delivery, and the others were from the ones with normal maternal behaviors. At the same time, the offspring of dams with normal maternal behavior were also included in the experiment to evaluate the milk yield of dams and growth of the young during the early and mid-lactation. (B) Apparatus for milking tree shrews in the present study. a, Electric breast pump; b, filter of disposable infusion set; c, disposable infusion needle used as the pulse tubing; d, rubber stopper; e, centrifuge tube used as a collection container; f, part of disposable infusion needle used as milk tubing; g, enlarged, smooth incision at the end of pipe used as a teat cap. (C) Lactating mother being milked using the homemade milk apparatus for tree shrews. (D) Mother being suckled by her pup after being milked and waking up from anesthesia.
Changes in the (A) day matter, (B) lipids, (C) protein, (D) sugars, (E) ash, (F) energy, (G) energy from lipids, (H) energy from protein, and (I) energy from sugars in milk from captive tree shrews during lactation. Each point represented a single sample. Bars represent the mean ± SD. Means not sharing any lowercase letters are significantly different at the 5% level, while those not sharing any uppercase letters are significantly different at the 1% level. ANOVA with a Bonferroni test was used to analyze the normally distributed data with equal variances, whereas a Welch ANOVA with a Tamhane T2 test was for the normally distributed data with unequal variances. When the data were not in a normal distribution, the nonparametric Kruskal–Wallis test with a Dunn test was run.
Changes in the relative proportions of (A) C6:0, (B) C8:0, (C) C10:0, (D) C11:0, (E) C12:0, (F) C13:0, (G) C14:0, (H) C14:1n5, (I) C15:0, (J) C15:1n5, (K) C16:0, (L) C16:1n7, (M) C17:0, (N) C18:0, (O) C18:1n9c, (P) C18:2n6c, (Q) C18:3n3, (R) C18:3n6, (S) C20:1, and (T) C20:2n6 during lactation. Each point represented a single sample. Bars represent the mean ± SD. Means that do not share any lowercase letters are significantly different at the 5% level, while those that do not share any uppercase letters are significantly different at the 1% level. A Welch ANOVA with a Tamhane T2 test (for normally distributed data with heterogeneous variances) or a nonparametric Kruskal–Wallis test with a Dunn test (for nonnormally distributed data) was used.
Changes in the relative proportions of (A) C20:3n6, (B) C20:4n6, (C) C20:5n3, (D) C22:5n3c, (E) C22:6n3, (F) C23:0, (G) SFAs, (H) UFAs, (I) MUFAs, (J) PUFAs, (K) SFAs/PUFAs, (L) n3-FAs, (M) n6-FAs, (N) MCFAs, (O) LCFAs, (P) VLCFAs, and (Q) OCFAs during lactation. Each point represented a single sample. Bars represent the mean ± SD. Means with no lowercase or uppercase letters in common are significantly different at α = 5% or α = 1%. A Welch ANOVA with a Tamhane T2 test for normally distributed data that violated the assumption of homogeneity of variance or a nonparametric Kruskal–Wallis test with a Dunn test for the nonnormally distributed data was used. SFAs (saturated fatty acids) include C6:0, C8:0, C10:0, C11:0, C12:0, C13:0, C14:0, C15:0, C16:0, C17:0, C18:0, C20:0, C21:0, C22:0, C23:0, and C24:0. UFAs (unsaturated fatty acids) include MUFAs (monounsaturated fatty acids) and PUFAs (polyunsaturated fatty acids). MUFAs include C14:1n5, C15:1n5, C16:1n7, C17:1n7, C18:1n9t, C18:1n9c, C20:1, C22:1n9, and C24:1n9. PUFAs include C18:2n6t, C18:2n6c, C18:3n3, C18:3n6, C20:2, C20:3n3, C20:3n6, C20:4n6, C20:5n3, C22:2, C22:5n3c, and C22:6n3. n3-FAs (omega-3 fatty acids) include C18:3n3, C20:3n3, C20:5n3, C22:5n3c, and C22:6n3. n6-FAs (omega-6 fatty acids) include C18:2n6t, C18:2n6c, C18:3n6, C20:2n6, C20:3n6, and C20:4n6. MCFAs (medium-chain fatty acids) include 6 to 12 carbons. LCFAs (long-chain fatty acids) include 13 to 21 carbons. VLCFAs (very-long-chain fatty acids) include 22 or more carbons. OCFAs (odd–chain fatty acids) include 11, 13, 15, 17, and 23 carbons.
Correlations among fatty acids (A) and fatty acid groups (B) in milk from captive tree shrews at different lactation periods. The Spearman rank correlation test was used to evaluate the correlation between any 2 fatty acids or fatty acid groups.
Changes in (A) the milk yield of lactating tree shrews from postnatal days 2 to 26 and (B) the weight of tree shrew pups before they began consuming solid food. Lactating tree shrews, n = 18. Tree shrew pups, n = 58 (27 males and 31 females) at the start of the experiment, with 3 pups dying at 9, 12, or 16 d of age. Therefore, the litter size for these 18 litters of pups was 3.22 ± 0.65 during postnatal days 2 to 8, 3.17 ± 0.71 on postnatal days 12 and 14, and 3.06 ± 0.87 from postnatal day 16 onward. Bars represent the mean ± SD.
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